This is the residual class for electrical devices, circuits or systems having an output not directly proportional to its input and comprising at least one component which can provide gain or can route electrical current and which device, circuit or system does not form a complete system such as is classified specifically elsewhere or a subcombination of utility only in such elsewhere classified system.
(1) Note. The scope of patents classified herein can be determined only by determining the scope of other related classes which are listed below under SEARCH CLASS. Also, consult search notes and definitions of these classes.
(2) Note. Typical active components are solid-state components, vacuum tubes, and gas filled tubes. However, also included would be components broadly claimed to have active properties, but which are not specifically limited to a particular embodiment such as a vacuum tube.
MAIN SUBDIVISIONS OF THIS CLASS
A. Specific Signal Discriminating (e.g., Comparing Or Selecting) Without Subsequent Control
Included here are circuits for the comparison, selection, or distinguishing of specific characteristics of either an input signal or signals without continuous regulation of such characteristic.
B. Signal Converting, Shaping, Or Generating
Included here are circuits wherein: (a) an inherent input signal parameter such as phase, frequency, amplitude or current is modified, maintained at some value, or changed to an entirely different parameter; (b) an input signal having a particular waveform modified into an output signal having a partially or a completely different waveform; or (c) an output signal of specified waveform is produced.
C. Specific Input To Output Function
Included here are circuits wherein an output signal is proportional to a mathematical expression involving an input signal or signals.
(1) Note. Characteristically, the input signals are continuous and slowly varying.
(2) Note. Circuitry performing Boolean Algebra functions, per se, are excluded from this class. See References to Other Classes, below.
(3) Note. The input signals of this subclass do not contain information (data). For data processing see References to Other Classes, below.
D. Gating (i.e., Switching Input To Output)
Included here are electron tube or solid-state gating circuits which distribute unmodified input signals to selected outputs.
E. External Effect
Included here are circuits, not elsewhere classified responsive to or compensating for an ambient nonelectrical condition such as heat or magnetism.
F. With Particular Control
Included here are circuits where current or power to a broadly recited device is controlled in response to a control signal. The control signal may be derived from an external source or from a feedback structure responsive to the condition of the load.
(1) Note. Where a specific load device is recited, classification will be in the particular class providing for the specific load device.
G. Specific Identifiable Device, Circuit, Or System
Included here are circuits having a particular structure, arrangement, or construction not classifiable elsewhere.
H. Miscellaneous
Included here are systems or circuits not provided for elsewhere.

LINES WITH OTHER CLASSES AND WITHIN THIS CLASS
ACTIVE FILTERS
The filters proper for this class include at least one active device utilized in producing the transfer function defining the frequencies that will be passed.
A filter in combination with a specific load will be classified in the class providing for the load. See References to Other Classes, below for filtering of data within an electrical digital calculating computer or analog computer.
The filters within the Specific Identifiable Device, Circuit, Or System area (see above) are active filters that suppress an unwanted input signal. See Noise Filters below for additional noise filter areas within Class 327.
NOISE FILTERS
Limiting, clipping, or clamping circuits which achieve transient or signal noise reduction by filtering or otherwise are classified in this class.
Compensation for a noise signal which is a by-product of switching thereof is found in this class.
Miscellaneous unwanted signal suppression is classified in this class.
See Subclass References to the Current Class below for these art areas.
PHASE LOCK LOOP
A nonlinear phase lock loop circuit, per se, is classified in Class 327. A phase lock loop circuit in combination with a special art device, is classified with the special art device. For example, a phase lock loop claimed in combination with an oscillator is classified in Class 331, subclasses 172+, a phase lock loop in combination with a telecommunication system is classified in Class 455, and a phase lock loop in combination with a pulse or digital communication system is classified in Class 375, subclasses 111+.
See Subclass References to the Current Class below for a phase lock loop to synchronize one signal with another for the creation of a replica signal.
DIGITAL LOGIC
Digital logic, per se, is classified in Class 326 and this includes, for example, multiple connections of AND, OR, or NOT gates. However, combinations of multiple AND or OR gates, etc., which perform a particular function proper to some other class are classified in that other class. For example, an AND gate claimed to be used as a comparator, for example, will be classified in Class 327, whereas a claimed AND gate, per se, would be classified in Class 326.
MULTIVIBRATOR
Patents reciting a free running astable multivibrator, per se, are classified elsewhere. For example, see References to Other Classes for a relaxation oscillator multivibrator.
Multivibrators having one or more stable states are classified in Class 327. See Subclass References to the current Class.
Generally, detailed flip-flops, per se, are in this class, subclasses 185+; however, multifunctional or programmable logic having a flip-flop is in Class 326, subclasses 37+ and redundant logic having a flip-flop is in Class 326, subclass 12.
INTEGRATED STRUCTURE
An integrated circuit chip, per se, is classified in Class 257.
Lead frames, per se, are classified in Class 257 since these are only used to connect an integrated circuit chip externally.
An integrated circuit chip in combination with a single lead, a battery or bias without any additional circuit configuration, is classified in Class 257.
An integrated circuit chip in combination with an external circuit proper for Class 327 will be classified in Class 327
since Class 327 is higher than Class 257 in the overall class hierarchy.
Circuit interconnections (e.g., point to point, lead interconnections, diode and transistor interconnections, etc.) within the confines of the integrated circuit chip itself are classified in Class 257, whereas circuit interconnections outside the environment of an integrated circuit chip are not.
If an integrated circuit is recited with other than a nominal recitation of a utility, the patent will be classified in the utility class.
CHARGE COUPLED DEVICES
CCD's recited as part of the circuitry within an integrated circuit chip are classified in Class 257.
CCD's recited with other than a nominal recitation of utility are classified in the utility class. See References to Other Classes, below.
POWER SUPPLIES
Power supplies in combination with another art device, classifiable elsewhere, will be found with the other art device. Tubes or solid-state device power supplies for a nonlinear device, circuit, or system, not elsewhere classified, will remain in this class (327).
A power supply in combination with a load, (i.e., a single power supply and a single load) without any claim to a substrate circuit is classified elsewhere. See References to Other Classes, below.
The power supply patents of this class, subclasses 530+ require a nonlinear device, circuit, or system as a load or control for the power supply. A claim to a power supply circuit in combination with a substrate containing a nonlinear device, circuit, or system is classified in Class 327.
SYSTEMS WITH SPECIFIC SOURCE OF INPUT ENERGY ONLY IDENTIFIED BY CHARACTERISTIC
This class does not provide for the subject matter included herein in combination with a specific type of electromagnetic wave energy since the broad recitation of the specific source would be classifiable with the art containing that particular source of energy. However, this class will take the systems and networks of the class in combination with a source of wave energy wherein the energy is expressed only as being composed of a band of frequencies or a source of pulses, etc., or wherein the source is recited by name only as a wave energy generator (such as an oscillator, pulse generator, etc.). Where the specific details of the source are recited
such systems are classified with the art which provides for systems utilizing such specific source.
MECHANICAL STRUCTURE
Claims to a specific mechanical structure in combination with generic circuitry are classified with the mechanical structure. However, claims to broad mechanical structure in combination with specific circuitry is classified in this class unless provided for in a mechanical or electrical class and provided the circuitry is nonlinear.
MEMORY CIRCUIT
A generic nonlinear circuit claimed with a memory inside the circuit is classified in this class (327), whereas a claim to generic circuitry in combination with a memory external to the circuit would be classified with the memory class.
MONITORING, TEST OR CALIBRATING
The following areas reciting monitoring, testing or calibrating take precedence over Class 327:
Class 73, subclasses 1.01+ for instrument proving or calibrating; and subclass 865.9 for testing of apparatus.
Class 324, subclass 601 for calibration, and subclasses 74+ for testing and calibrating of electric meters.
Class 342, subclasses 165+ for testing or calibrating a radar system.
Class 348, subclasses 180+ for television monitoring or testing.
Class 358, subclass 406 for facsimile measuring or testing.
Class 364, subclasses 571.01+ for testing and measuring which includes a computation.
Class 374, subclasses 1+ for thermal measuring and testing.
Class 455, subclass 115 for measuring, testing or monitoring of a transmitter and subclass 226 for measuring, testing, or monitoring of a receiver. Only monitoring, testing, or calibrating, not elsewhere classified, and related to nonlinear devices, circuits and systems are classified in Class 327. The following are examples of those found in Class 327: subclasses 20, 262, 292, 378, 509, and 538.
Class 600, subclass 486 for testing means inserted in the human body.
FUNCTION
Only those nonlinear circuits or systems whose function is
not specifically provided for elsewhere would be classified in this class (327) subclasses 334+.
SWITCHING
See References to Other Classes, below for examples of other areas for switching;
CIRCUITS WITH ELECTRON OR OTHER CHARGED PARTICLE BEAM TUBE
Only those nonlinear circuits utilizing electron or other charged particle beams that are not classifiable in other areas would be classified in Class 327.
Examples of electron or other charged particle beam tube circuits classified elsewhere are the cyclotron and CRT circuits of Class 313.
MODULATION OR COMMUNICATION
Nonlinear circuits used in combination with a modulated signal are classified in the classes containing the communication of information via a modulated signal.
ELECTRICAL CONTROL OF MACHINES
Electrical control with a broad machine is classified with the machine, if a class exists for the machine. Only those electrical control patents, not provided for in the machine classes, would be classified in Class 327, provided the circuit is nonlinear.
NEURON CIRCUITS OR NETWORKS
Patents reciting neuron simulator circuitry, per se, and neural networks are classified elsewhere. See References to Other Classes below.
FUSIBLE LINK AND INTENTIONAL DESTRUCT CIRCUIT
Miscellaneous circuits of this type are classified in this class (327) subclass 525.
OSCILLATORS
Free running oscillators (including the asynchronous type) are classified elsewhere. See References to Other Classes below.
PERSONNEL OR DEVICE PROTECTIVE CIRCUITS
Circuits used to protect personnel from harm, or protect devices from failure (e.g., overload, power surge) are excluded from this class. See References to Other Classes below.
SYSTEMS WITH SPECIFIC LOADS IN THE OUTPUT CIRCUIT
This class does not provide for the subject matter in combination with a specific load device even though the load device is recited by name only (as a motor, loud-speaker, etc.). Such systems are classified in general with the particular art device constituting the load.
AMPLIFIERS
This class does not include electronic circuits, per se, wherein a variable electric current or voltage input signal is applied to an electrical amplifying device to control a source of electrical energy applied to the same device, and from which is derived an output signal of substantially the same waveform as the input signal and substantially linearly related thereto.
LINEAR DEVICE, CIRCUITS OR SYSTEMS
This class excludes linear resistors, reactive apparatus and insulators, per se. Although the claimed solid-state device may be active or passive and have some insulative or reactive properties, it cannot be classified in this class if the device is generally thought of as being only an insulator or reactive apparatus such as a capacitor, inductor, transformer, motor, etc.
COUNTERS
See References to Other Classes for electrical pulse counters, pulse dividers, or shift registers.
PASSIVE FILTERS
See References to Other Classes for filters utilizing lumped or distributed parameter passive elements.
SPECIAL ART DEVICES
Special art devices are to be classified with the specified device.
GAS TUBE
Circuitry utilizing gas tubes not elsewhere provided for are included here. See, Subclass References To The Current Class, below, for an example.

SEE OR SEARCH THIS CLASS, SUBCLASS:
147 156+ provide for a phase lock loop to synchronize one signal with another for the creation of a replica signal.
185 for multivibrators having one or more stable states.
310 for limiting, clipping, or clamping circuits which achieve transient or signal noise reduction by filtering or
otherwise. (see "Noise Filters" above)
379 for compensation for a noise signal which is a by-product of switching thereof. (see "Noise Filters" above)
551 for miscellaneous unwanted signal suppression. (see "Noise Filters" above).
601 for circuitry utilizing gas tubes (see "Gas Tube" above)

REFERENCES TO OTHER CLASSES

SEE OR SEARCH CLASS:
73, Measuring and Testing, appropriate subclasses for systems and apparatus for making a measurement or test not provided for in other classes, particularly 1.01 for instrument proving or calibrating, and subclass 865.9 for testing of apparatus.
84, Music, 600 for electrical musical tone generation using transistors or space discharge devices.
136, Batteries: Thermoelectric and Photoelectric appropriate subclasses.
148, Metal Treatment, 33 for barrier layer stock material.
174, Electricity: Conductors and Insulators, appropriate subclasses for the physical structure of conductors.
178, Telegraphy, appropriate subclasses for telegraph apparatus and systems, particularly subclass 43 for space induction systems, and subclasses 66.1+ for alternating or pulsating current telegraph systems.
191, Electricity: Transmission to Vehicles, appropriate subclasses.
200, Electricity: Circuit Makers and Breakers, appropriate subclasses for electric switches and circuit breakers and for electrical and mechanical switches.
204, Chemistry: Electrical and Wave Energy, appropriate subclasses for apparatus for producing chemical changes through the agency of electrical wave energy.
219, Electric Heating, subclasses 600-780 for induction, electro-static or electro-magnetic heating systems and subclass 114 for welding circuits with space discharge tube control.
246, Railway Switches and Signals, appropriate subclass for electric circuits utilized in railway switches and signals.
250, Radiant Energy, appropriate subclasses for the detection
of nuclear or electromagnetic radiant energy, the testing of material by nuclear or electromagnetic radiant energy, the irradiation of material by nuclear or electromagnetic radiant energy, electron energy analysis, the deflection or focussing of an ion or electron beam, and the generation of control of nuclear or electromagnetic radiant energy.
252, Compositions, 62.3 for barrier layer compositions and subclasses 500+ for other semiconductor compositions.
257, Active Solid-State Devices (e.g., Transistors, Solid-State Diodes), appropriate subclasses for particular nonlinear solid-state devices, per se, also for an integrated circuit chip, per se, and for lead frames, per se, since these are only used to connect an integrated circuit chip externally. An integrated circuit chip in combination with a single lead, a battery or bias without any additional circuit configuration is classified in Class 257.
290, Prime-Mover Dynamo Plants, appropriate subclass for electric circuits utilized in prime mover dynamo plants.
307, Electrical Transmission or Interconnection Systems, appropriate subclasses for circuits providing electrical transmission or interconnection such as those having plural energy sources or plural loads and class appropriate switching systems, wave form determinative networks, and circuits responsive to external effects such as temperature or magnetism.
307, Electrical Transmission or Interconnection Systems, 326 for circuits used to protect personnel from harm, or protect devices from failure (e.g., overload, power surge). (see "Personnel Or Device Protective Circuits" above)
310, Electrical Generator or Motor Structure, appropriate subclasses for the physical structure of electric generators and motors and electromagnetic clutches and for the circuits that relate to electromagnetic clutches, and particularly 314 for piezoelectric devices in combination with tube structure where the significant structure claimed is that of the crystal, and the tube structure or circuitry is only incidentally claimed.
313, Electric Lamp and Discharge Devices, appropriate subclasses for the physical structure of electronic lamp and discharge devices, per se.
314, Electric Lamp and Discharge Devices: Consumable Electrodes, appropriate subclasses for electric lamp and discharge devices of the arc discharge type which may be combined with an electron space discharge tube.
315, Electric Lamp and Discharge Devices: Systems, appropriate subclasses for circuits in combination with charged particle beam tubes, cathode-ray tubes or electric lamp and space discharge devices, particularly 8.51 for
pulse storage systems utilizing cathode-ray tubes, and subclasses 84.51+ for pulse storing systems comprised exclusively of gaseous discharge tubes.
318, Electricity: Motive Power Systems, 677 for electric motor position servomechanisms utilizing electron space discharge apparatus; subclasses 126+ for energizing of winding circuit control responsive to condition, pulsed energy etc.; subclass 132 which relates to space discharge or unidirectionally conductive devices in a winding control circuit; subclass 138 for a space discharge device commutated motor; and subclasses 505+, 732, 752, 756, and 786 for motor control systems utilizing space discharge devices.
320, Electricity: Battery or Capacitor Charging or Discharging, appropriate subclass for a battery or capacitor charging or discharging application that employs a space-discharge device.
322, Electricity: Single Generator Systems, 72 for electron space discharge tube systems for controlling a single generator.
323, Electricity: Power Supply or Regulation Systems, appropriate subclasses for circuits utilized in power voltage magnitude and phase control systems.
323, Electricity: Power Supply Or Regulation Systems, for a power supply in combination with a load, (i.e., a single power supply and a single load) without any claim to a substrate circuit (See "Power Supplies" above)
324, Electricity: Measuring and Testing, appropriate subclasses for circuits utilized in electrical measuring, testing, and sensing systems.
326, Electronic Digital Logic Circuitry, appropriate subclasses for combinational or sequential logic, per se.
326, Electronic Digital Logic Circuitry, for circuitry for performing Boolean Algebra functions, per se. (see Class Definition, "Specific Input To Output Function" above)
326, Electronic Digital Logic Circuitry, for a logical function (see "Charge Coupled Devices" above)
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, for delay (see "Charge Coupled Devices" above)
329, Demodulators, appropriate subclasses for circuits extracting information from a carrier.
330, Amplifiers, appropriate subclasses for electron space discharge tube apparatus combined with circuitry to form an amplifier system and 250 for semiconductor amplifiers.
331, Oscillators, appropriate subclasses for electron space discharge tube or solid-state apparatus combined with tuned circuit apparatus forming an oscillatory system of the self-sustaining type, an asynchronous oscillator, per se, or in combination with other circuitry or an oscillator combined with a phase lock loop without any intelligence claimed; 8 for transistorized automatic frequency control for oscillators; and subclasses 108+ for solid-state oscillators.
331, Oscillators, subclass 144 for a relaxation oscillator multivibrators.
331, Oscillators, for free running oscillators (including the asynchronous type). (see "Oscillators," above)
332, Modulators, appropriate subclasses for circuitry which superimposes information on a carrier.
333, Wave Transmission Lines and Networks, subclass 19 for passive element wave differentiating or integrating systems, subclasses 24+ for passive filters, and subclass 20 for wave shaping networks of the passive element type; subclasses 167+, 186+, and 202+ for filters utilizing lumped or distributed parameter passive elements.
334, Tuners, appropriate subclasses for tuning circuitry.
335, Electricity: Magnetically Operated Switches, Magnets, and Electromagnets, appropriate subclasses for magnetically operated switches and circuit breakers.
336, Inductor Devices, appropriate subclasses for passive inductive devices.
337, Electricity: Electrothermally or Thermally Actuated Switches, appropriate subclasses for thermal switches, per se.
340, Communications: Electrical, subclass 146.2 for digital comparator systems, subclass 825.97 for electron beam type selective or remote control systems, subclass 825.57 for pulse responsive selective systems, subclass 825.67 for pulse responsive counting chains which may employ an electron space discharge device, and subclasses 870.01+ for telemetering systems. (also see "Charge Coupled Devices" above)
348, Television (see "Charge Coupled Devices" above)
341, Coded Data Generation or Conversion, 50 for code converters and subclasses 20+, 186, and 191 for a pulse transmitter or generator having a space discharge device.
342, Communications: Directive Radio Wave Systems and Devices (e.g., radar, Radio Navigation), appropriate subclasses for systems for object detection and utilizing pulse radio wave forms and subclass 165 for testing or
calibrating a radar system.
343, Communications: Radio Wave Antennas, appropriate subclasses for antennas, per se.
348, Television, 180 for television monitoring or testing.
352, Optics: Motion Pictures, 1 for sound accompanied motion pictures including active electronic devices.
356, Optics: Measuring and Testing, 3 for systems using light for distance finding and subclasses 26+ for light systems for the determination of velocity.
358, Facsimile and Static Presentation Processing, subclass 406 for facsimile measuring or testing.
359, Optics: Systems (Including Communication) and Elements, appropriate subclasses for optical components.
360, Dynamic Magnetic Information Storage or Retrieval, appropriate subclasses.
361, Electricity: Electrical Systems and Devices, 1 for safety and protection of systems and devices, subclasses 100+ for current fault sensor with semiconductor circuit interrupter, subclasses 139+ for control circuits for electromagnetic devices, and subclasses 196+ for control circuits for electromagnetic devices with time delay including a semiconductor device.
361, Electricity: Electrical Systems and Devices, 1 for circuits used to protect personnel from harm, or protect devices from failure (e.g., overload, power surge). (see "Personnel Or Device Protective Circuits" above)
363, Electric Power Conversion Systems, appropriate subclasses for circuits utilized in electric conversion systems where a single electrical source is connected to a single electrical load and particularly subclass 94, 99, 111+, 151, and 166 for systems whereby a current or voltage of one characteristic is converted to a current or voltage of another characteristic and utilizing electron space discharge devices.
365, Static Information Storage and Retrieval, 73 for recirculation of information in a storage read/write system, subclass 78 for plural shift register memory devices, subclasses 80+ for magnetic shift register, per se, subclasses 129+ for storage systems using a particular storage element, subclasses 189.01+ for read/write circuits peculiar to a storage and retrieval system, and subclasses 230.01+ for addressing circuits peculiar to a storage and retrieval system. (also see "Charge Coupled Devices" above)
367, Communications, Electrical: Acoustic Wave Systems and Devices, appropriate subclasses.
369, Dynamic Information Storage or Retrieval, appropriate subclasses.
370, Multiplex Communications, appropriate subclasses for multiplexing systems.
373, Industrial Electric Heating Furnaces, subclass 70, 102+, 135+, and 147 for electric furnaces having significant electrical circuits.
374, Thermal Measuring and Testing, 1 for thermal calibration.
375, Pulse or Digital Communications, 106 for digital communication synchronization.
377, Electrical Pulse Counters, Pulse Dividers, or Shift Registers: Circuits and Systems, appropriate subclasses for electrical pulse counters, dividers, and shift registers and particularly 57 for charge coupled devices used as a counter, pulse divider, or shift register. (also see "Charge Coupled Devices" above)
378, X-Ray or Gamma Ray Systems or Devices, 91 for circuits combined withX-ray devices.
379, Telephonic Communications, appropriate subclasses, for telephone systems.
380, Cryptography, appropriate subclasses for cryptos:graphic circuitry.
381, Electrical Audio Signal Processing Systems and Devices, 94.1 for noise suppressing audio circuitry and subclass 111 for circuitry combined with a specific type of microphone or loudspeaker.
382, Image Analysis, appropriate subclasses.
388, Electricity: Motor Control Systems, art collection 913 for motor control systems including space discharge devices.
396, Photography, appropriate subclasses for apparatus producing pictures on light sensitive material which may utilize electronic devices. (also see "Charge Coupled Devices" above)
427, Coating Processes, 58 for coating processes wherein an electrical product is produced.
428, Stock Material or Miscellaneous Articles, subclass 620 for semiconductor stock material.
438, Semiconductor Device Manufacturing: Process, for methods of making semiconductor electrical devices; see the search notes thereunder.
445, Electric Lamp or Space Discharge Component or Device Manufacturing, appropriate subclasses for circuits utilized in the manufacture or repair of electric lamp or electric space discharge devices.
455, Telecommunications, appropriate subclasses for telecommunication systems and subsystems.
600, Surgery, 300 for diagnostic apparatus utilizing transistors or tubes.
702, Data Processing: Measuring, Calibrating, or Testing, appropriate subclasses for testing and measuring which includes significant data processing.
706, Data Processing: Intelligent Processing Systems and Methods, 15 for neural circuits and networks. (see "Neuron Circuits Or Networks" above)
708, Electrical Computers: Arithmetic Processing and Calculating, 300 for digital filters unique to digital computing, subclass 540 for the performance of arithmetic operations by a CRT, subclass 819 for analog filters which are unique to analog computing, and subclass 849 for analog function generation which utilizes a CRT. (See "Active Filters", above.)
714, Error Detection/Correction and Fault Detection/Recovery, appropriate subclasses.

SPECIFIC SIGNAL DISCRIMINATING (E.G., COMPARING, SELECTING, ETC.) WITHOUT SUBSEQUENT CONTROL:
This subclass is indented under the class definition. Subject matter wherein an output signal is derived from one or more input signals by comparing, selecting, or distinguishing a particular input signal parameter and which parameter is not continuously thereafter regulated.

SEE OR SEARCH THIS CLASS, SUBCLASS:
100 for signal converting, shaping, or generating which may include control of the type of signal parameters found herein.

SEE OR SEARCH CLASS:
250, Radiant Energy, subclass 250 for wave meters, subclasses 281+ for systems adapted for ionic separation or analysis and comprising phase or frequency determining
devices.
318, Electricity: Motive Power Systems, subclass 683 for electric motor position servomechanisms involving phase comparison devices.
322, Electricity: Single Generator Systems, subclass 32 for automatic frequency control for generator systems.
323, Electricity: Power Supply or Regulation Systems, 212 for automatic phase control systems restricted to power circuits.
324, Electricity: Measuring and Testing, 76.39 for frequency measuring or testing of electricity and subclasses 76.77+ for phase comparison systems for measuring or testing electricity and involving plural inputs.
329, Demodulators, appropriate subclasses for demodulators of signals which have been modulated by an intelligence signal.
340, Communications: Electrical, subclass 146.2 for digital comparator systems, subclasses 315, 825.06+, and 870.18+ for electrical circuits whereby an indication or signal is transmitted to a distant point and which signal is indicative of an electrical condition which may comprise phase or frequency difference.
361, Electricity: Electrical Systems and Devices, 236 for speed-controlled systems involving phase or frequency determining devices.
375, Pulse or Digital Communications, 106 for synchronization in digital communications.
455, Telecommunications, 130 for a telecommunication receiver.
714, Error Detection/Correction and Fault Detection/Recovery, appropriate subclasses for error detection or correction of information content of a digital signal.

By phase:
This subclass is indented under subclass 1. Subject matter wherein the discriminated input signal parameter is that fractional part of a periodic waveform which has elapsed relative to a fixed origin.
(1) Note. If the time for one signal period is represented as 360 degrees along a time axis, the phase position is called the phase angle.

SEE OR SEARCH THIS CLASS, SUBCLASS:
39 for frequency comparison circuits.
231 for phase correction or control.
261 for output waveform production delay.

SEE OR SEARCH CLASS:
303, Fluid-Pressure and Analogous Brake System, 91 for speed-controlled vehicle systems.
329, Demodulators, 345 for phase angle demodulation in which a intelligence signal is extracted.
331, Oscillators, 1 for systems for stabilizing the frequency of an oscillator utilizing phase or frequency comparison devices, and subclasses 37+ for systems wherein two or more frequencies are combined to produce a beat frequency.
332, Modulators, 144 for systems wherein the phase of a carrier wave is modulated by an arbitrarily varying quantity.
455, Telecommunications, 214, for frequency or phase modulation with particular discrimination or detection.

Comparison between plural inputs (e.g., phase angle indication, lead-lag discriminator, etc.):
This subclass is indented under subclass 2. Subject matter wherein the output signal is indicative of the phase positioning or phase differences among two or more input signals.
(1) Note. Detectors producing an output which is a result of demodulation of a carrier having previously been modulated by an intelligence waveform which varies arbitrarily will not be classified here. See SEARCH CLASS below.

SEE OR SEARCH THIS CLASS, SUBCLASS:
40 for comparison between plural input frequencies.

SEE OR SEARCH CLASS:
329, Demodulators, 345 for circuits producing an output which is a result of demodulation of a carrier having previously been phase modulated by an intelligence waveform.
363, Electric Power Conversion Systems, appropriate
subclasses for phase conversion circuits with phase angle sensing.
455, Telecommunications, 130 for mixers or converters utilized in a superheterodyne receiver (commonly referred to as a first detector).

With transducer:
This subclass is indented under subclass 3. Subject matter wherein a device is included that converts energy forms other than electrical into electrical energy.
(1) Note. The other energy forms may be mechanical, thermal, hydraulic, or chemical, etc.

With input derived from feedback:
This subclass is indented under subclass 3. Subject matter wherein a portion of the output signal is returned to one of the plural inputs.

With electron space discharge:
This subclass is indented under subclass 3. Subject matter including a vacuum tube device or a gaseous medium within a gas tight envelope in which electron conduction takes place through the vacuum or gas.

With reference signal:
This subclass is indented under subclass 3. Subject matter wherein a signal of fixed phase acts as a constant for comparison to a variable input.
(1) Note. The reference signal is usually an input signal or produced from an input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
42 for frequency comparison between a fixed reference
frequency and a variable input.

With varying frequency:
This subclass is indented under subclass 7. Subject matter wherein the reference signal varies over a range of different frequencies or the reference signal is compared to different frequency signals.

With sampling:
This subclass is indented under subclass 7. Subject matter wherein a reference signal is derived by representation of an input signal at intermittently timed intervals.

SEE OR SEARCH THIS CLASS, SUBCLASS:
91 for details of sampling or holding in general.

Uniform pulse waveform:
This subclass is indented under subclass 7. Subject matter wherein the reference signal is a series of pulses evenly spaced.

SEE OR SEARCH THIS CLASS, SUBCLASS:
42 for a frequency comparison between a fixed reference frequency and a variable input.

With transformer:
This subclass is indented under subclass 7. Subject matter wherein an electromagnetic induction device transfers electrical energy from one circuit to another adjacent circuit at a constant frequency.
(1) Note. A transformer changes voltage in direct proportion to the ratio of the number of turns of its primary and secondary windings.

SEE OR SEARCH CLASS:
336, Inductor Devices, appropriate subclasses for transformer details.

With logic or bistable circuit:
Subject matter under 3 wherein the phase comparison (a) includes a device performing Boolean functions such as AND, OR, or exclusive-OR or (b) utilizes a device having two stable states.
(1) Note. The combination of logic with specific phase comparison circuitry or function, not elsewhere classified is classified here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for particular stable state circuits including bistable.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, 93 for clocking or synchronizing of one or more logic stages and appropriate subclasses for general digital logic circuitry not classified elsewhere.
331, Oscillators, subclass 1 for automatic frequency control synchronization with logic elements.

By shape:
This subclass is indented under subclass 1. Subject matter wherein input signal discriminating is based upon a predetermined geometric configuration.

SEE OR SEARCH THIS CLASS, SUBCLASS:
134 for sawtooth or triangular wave producing systems with slope or duration control.
172 for pulse signal shaping with duration or width control.

SEE OR SEARCH CLASS:
348, Television, 525 for sync separating systems which may depend upon differences in the slope or shape of the input
pulses.
455, Telecommunications, 296 for static or noise elimination in radio receivers which may depend upon the slope or shape of the pulse present in the input signal applied to the receiver.

Slope:
This subclass is indented under subclass 13. Subject matter wherein the predetermined geometric configuration is signal rate of change.
(1) Note. The rate of change may be determined by digital means (such as counters) or analog means (such as slope detection using a charging capacitor).

SEE OR SEARCH THIS CLASS, SUBCLASS:
134 for sawtooth or triangular waveform generation with slope control.
170 for slope control of a pulse or clock waveform.
261 for output waveform production delay.
335 for the miscellaneous determination of the derivative of an input signal.

With direction (i.e., positive or negative):
This subclass is indented under subclass 14. Subject matter wherein the output signal indicates an upward or downward inclination of the input.

Having feedback:
This subclass is indented under subclass 13. Subject matter wherein a portion of the output signal is returned to an input.

With reference signal:
This subclass is indented under subclass 13. Subject matter wherein a signal of predetermined shape acts as a constant for comparison to a variable input.

By presence or absence pulse detection:
This subclass is indented under subclass 1. Subject matter wherein an output signal is indicative of an unexpected occurrence or lack of occurrence of a pulse in either a clocking signal or a predetermined sequence of pulses.

Arbitration:
This subclass is indented under subclass 18. Subject matter wherein a particular pulse among plural pulses input during a particular time interval is selected based upon a predetermined priority arrangement.

SEE OR SEARCH THIS CLASS, SUBCLASS:
3 for phase discrimination.

Monitoring (e.g., failure detection, etc.):
This subclass is indented under subclass 18. Subject matter wherein the detection of an undesired absent or present pulse produces an output signal which indicates a failure.

SEE OR SEARCH THIS CLASS, SUBCLASS:
292 for clock fault compensation.

With variable frequency source:
This subclass is indented under subclass 18. Subject matter wherein the absent or present pulse is detected from a varying frequency input signal.

By pulse noncoincidence:
This subclass is indented under subclass 1. Subject matter wherein an output signal is produced when two or more input pulses are not received simultaneously.

By pulse coincidence:
This subclass is indented under subclass 1. Subject matter wherein an output signal is produced when two or more input pulse signals occur simultaneously.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, 104 for circuits performing fundamental Boolean Algebra functions, especially the "AND" function.

Edge sensing:
This subclass is indented under subclass 23. Subject matter wherein a beginning or trailing end of a pulse is determined to occur simultaneously with a corresponding beginning or trailing end of another pulse.

With uniform spacing:
This subclass is indented under subclass 23. Subject matter wherein an output signal is produced when two or more input pulse signals having the same time interval between consecutive pulses occur simultaneously.

SEE OR SEARCH THIS CLASS, SUBCLASS:
31 for detecting a pulse width or spacing in general.

With pulse width detecting:
This subclass is indented under subclass 23. Subject matter wherein pulse width discriminating is achieved via a pulse coincidence operation.

SEE OR SEARCH THIS CLASS, SUBCLASS:
31 for detecting pulse width or spacing in general.

SEE OR SEARCH CLASS:
329, Demodulators, subclass 312 for a pulse width demodulator.

With reference:
This subclass is indented under subclass 23. Subject matter wherein an input pulse signal is compared with a predetermined standard signal.

By polarity:
This subclass is indented under subclass 1. Subject matter wherein the input signal parameter is its positive or negative orientation with respect to a fixed origin.

Selection of a particular polarity:
This subclass is indented under subclass 28. Subject matter wherein only a predetermined polarity of an input signal is chosen.

Opposite polarity:
This subclass is indented under subclass 28. Subject matter wherein an output signal results from comparing pulses which have or are expected to have differing polarities.

By pulse width or spacing:
This subclass is indented under subclass 1. Subject matter wherein the input signal parameter is (a) a time interval between a leading edge and a trailing edge of a single pulse or (b) a time interval between a trailing edge and a leading edge of two consecutive pulses.

SEE OR SEARCH THIS CLASS, SUBCLASS:
172 for pulse signal shaping with duration or width control.

SEE OR SEARCH CLASS:
340, Communication: Electrical, subclass 825.63 for pulse width selective actuation and subclass 825.64 for pulse spacing selective actuation.

With shock-excited circuit:
This subclass is indented under subclass 31. Subject matter including a resonant circuit which oscillates at its natural frequency upon application of an electrical impulse.

SEE OR SEARCH THIS CLASS, SUBCLASS:
596 for miscellaneous circuitry containing shock excited resonant components.

SEE OR SEARCH CLASS:
331, Oscillators, appropriate subclasses for free running generators utilizing shock excited resonant circuits.
334, Tuners, appropriate subclasses for tuned networks for use in wave energy apparatus and comprising inductance and capacitance elements in circuit arrangement to form a resonant circuit and in which structure is provided for adjusting one or both of these elements for changing the mean resonant frequency of the circuit.

With sampling:
This subclass is indented under subclass 31. Subject matter including a circuit providing periodic representations of an input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
9 for phase discriminating with sampling.
91 for detailed sampling or holding circuits, per se.

Narrow pulse elimination or suppression:
This subclass is indented under subclass 31. Subject matter wherein the output signal does not include portions of the input signal having a pulse width shorter than a predetermined time interval.
(1) Note. Narrow or short pulse (spurious) duration in a system may be noise, which is unwanted disturbances superimposed upon a useful signal and which tends to obscure its information content.

SEE OR SEARCH THIS CLASS, SUBCLASS:
172 for rectangular or pulse waveform continuous width control.
178 for rectangular or pulse waveform amplitude control which may include some noise reduction.
310 for transient or signal noise reduction by limiting, clipping, or clamping.
379 for noise overriding in gating or switching.
551 for miscellaneous unwanted signal elimination.

Separating by duration or gap (e.g., duty cycle, etc.):
This subclass is indented under subclass 31. Subject matter wherein (a) an input pulse signal is divided between long and short pulses contained therein or (b) a space is inserted between the trailing edge of a pulse and the leading edge of the next pulse or (c) a spacing between pulses is detected.

SEE OR SEARCH THIS CLASS, SUBCLASS:
134 for duration control of a triangular or sawtooth wave.
172 for rectangular wave or pulse width control.

SEE OR SEARCH CLASS:
329, Demodulators, subclass 312 for a pulse width
demodulator.

Selection of a particular pulse width:
This subclass is indented under subclass 31. Subject matter wherein a predetermined pulse width is chosen from a series of input pulse signals.

SEE OR SEARCH CLASS:
329, Demodulators, subclass 312 for a pulse width demodulator.

Comparison by threshold or reference:
This subclass is indented under subclass 31. Subject matter wherein the output signal is indicative of the pulse width difference between an input pulse signal and a set value or predetermined standard.

With plural paths:
This subclass is indented under subclass 31. Subject matter wherein an input signal passes through more than one route or channel between an input terminal and an output terminal.

By frequency:
This subclass is indented under subclass 1. Subject matter wherein the discriminated signal parameter relates to the number of times a signal repeats its basic waveform within a unit of time.

SEE OR SEARCH THIS CLASS, SUBCLASS:
2 for discriminating by phase.
47 for circuits where the output is present only at a predetermined frequency of the input.
113 for miscellaneous frequency or repetition rate control.
114 for pulse generating which includes frequency or repetition rate control.
231 for phase correction or control.
261 for output waveform production delay.
552 for unwanted signal suppression by an active filter.

SEE OR SEARCH CLASS:
303, Fluid-Pressure and Analogous Brake System, 91 for speed-controlled fluid-pressure brake systems.
324, Electricity: Measuring and Testing, 76.19 for a frequency spectrum analyzer and subclasses 76.39+ for measuring and testing of the frequency of cyclic current or voltage.
329, Demodulators, 315 for frequency demodulation in which an intelligence signal is extracted.
331, Oscillators, 1 for systems for stabilizing the frequency of an oscillator utilizing phase or frequency comparison devices and subclasses 37+ for systems wherein two or more frequencies are combined to produce a beat frequency.
332, Modulators, 117 for systems wherein the frequency of a carrier wave is modulated by an arbitrarily varying quantity.
455, Telecommunications, subclass 214 for frequency or phase modulation with particular discrimination or detection.
702, Data Processing: Measuring, Calibrating, or Testing, 75 for frequency measurement system.

Comparison between plural inputs:
This subclass is indented under subclass 39. Subject matter wherein the output signal is a function of the differences among two or more input signal frequencies.
(1) Note. Systems wherein the claimed subject matter includes apparatus which responds only when a noninformation bearing input signal is in synchronism with a control signal locally generated (synchronous detectors) and which are not claimed as an integral part of a more comprehensive system will be classified herein. Detectors producing an output which is a result of demodulation of a carrier having previously been modulated by an intelligence waveform which
varies arbitrarily will not be classified here. See SEARCH CLASS, below.

SEE OR SEARCH THIS CLASS, SUBCLASS:
3 for phase comparison between plural input signals.

SEE OR SEARCH CLASS:
329, Demodulators, appropriate subclasses for a circuit having an output which is a result of demodulation of a carrier having previously been frequency modulated by an intelligence waveform.
455, Telecommunications, 130, for mixers or converters utilized in a superheterodyne receiver (commonly referred to as a first detector), and subclasses 313+ for combining frequencies in a receiver to produce a beat frequency.

With synchronous detection:
This subclass is indented under subclass 40. Subject matter wherein the output signal provides an indication of the maintenance of precise matching between two or more input signal frequencies.

SEE OR SEARCH THIS CLASS, SUBCLASS:
141 for synchronizing control.

SEE OR SEARCH CLASS:
331, Oscillators, 1 for controlling frequency synchronization in oscillator circuits (e.g., phase lock loop circuits, etc.).
348, Television, 638 and 726+ for television receivers that may include synchronous detectors.

Fixed frequency reference signal:
This subclass is indented under subclass 40. Subject matter wherein a signal of constant frequency acts as a standard for comparison to a variable input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
7 for a fixed phase signal compared to a variable input.

With logic or bistable circuit:
This subclass is indented under subclass 40. Subject matter wherein the frequency comparison of plural signals (a) includes a device performing Boolean functions such as AND, OR, or exclusive-OR or (b) utilizes a device having two stable states.
(1) Note. The combination of logic with specific frequency comparison circuitry or function, not elsewhere classified is classified here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for particular stable state circuits including bistable.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, 93 for clocking or synchronizing of one or more logic stages and appropriate subclasses for general digital logic circuitry not classified elsewhere.
331, Oscillators, subclass 1 for automatic frequency control synchronization with logic elements.

With predetermined frequency selection:
This subclass is indented under subclass 39. Subject matter wherein the output signal consists of a chosen input signal having a specific frequency characteristic.

SEE OR SEARCH THIS CLASS, SUBCLASS:
552 for unwanted signal suppression by an active filter.

SEE OR SEARCH CLASS:
329, Demodulators, appropriate subclasses for circuits which select signals from modulated wave signals.

Including sampling or reference frequency:
This subclass is indented under subclass 44. Subject matter
wherein (a) the predetermined signal frequency selected is derived by representation of another known signal frequency at intermittent time intervals or (b) wherein a signal of fixed frequency is utilized in the frequency selection.

SEE OR SEARCH THIS CLASS, SUBCLASS:
7 for phase angle sensing circuits using a reference signal.
42 for a fixed frequency reference signal used in plural signal frequency comparison.

Including plural frequency detection:
This subclass is indented under subclass 44. Subject matter wherein more than one signal frequency is detected by a single circuit or system.

Frequency detection:
This subclass is indented under subclass 39. Subject matter wherein an output signal is present or changes only at a predetermined input frequency.

SEE OR SEARCH THIS CLASS, SUBCLASS:
102 for the conversion of input frequency to output current or voltage.
113 for frequency or repetition rate control.
552 for unwanted signal elimination by an active filter.

SEE OR SEARCH CLASS:
379, Telephonic Communications, subclass 346 for a repeater with voice frequency discriminator.
708, Electrical Computers: Arithmetic Processing and Calculating, 311 for frequency detection/filtering using an electrical digital calculating computer.

With counting:
This subclass is indented under subclass 47. Subject matter wherein the output signal is incremented or decremented at a predetermined interval thereby forming a variable duty cycle according to the changes in the input frequency signal.
(1) Note. A counter is a device capable of changing between a sequence of distinguishable states upon each receipt of an input signal.

SEE OR SEARCH CLASS:
377, Electrical Pulse Counters, Pulse Dividers, or Shift Registers: Circuits and Systems, for counters, per se.

With logic or bistable circuit:
This subclass is indented under subclass 47. Subject matter wherein the frequency detection (a) includes a device performing Boolean functions such as AND, OR, or exclusive-OR or (b) utilizes a device having two stable states.
(1) Note. The combination of logic with specific frequency detection circuitry or function, not elsewhere classified, is classified here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for particular stable state circuits including bistable.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, 93 for clocking or synchronizing of one or more logic stages and appropriate subclasses for general digital logic circuitry not classified elsewhere.

By amplitude:
This subclass is indented under subclass 1. Subject matter wherein the discriminated input signal parameter is the magnitude of an electrical energy waveform measured with respect to a fixed origin.

SEE OR SEARCH THIS CLASS, SUBCLASS:
178 for rectangular or pulse waveform amplitude control.
306 for amplitude control in general.

SEE OR SEARCH CLASS:
324, Electricity: Measuring and Testing, 76 for the measuring or testing of electricity, per se.
329, Demodulators, 347 for amplitude demodulators.

With sensing amplifier:
This subclass is indented under subclass 50. Subject matter wherein low-level voltages (e.g., CCD charges, capacitive stored signal levels, etc.) are detected and increased in magnitude from one level to another.
(1) Note. The voltage amplitude or storage charge levels detected in this subclass include the type of levels found in storage memory cells of an array; however, the static storage and retrieval of information coupled with the functions of "write", "read-out", "erase", etc., wherein voltage amplitude is sensed, is classified elsewhere. See the Search Note below.
(2) Note. Differential comparator type sensing amplifiers including regenerative sensing arrangements (e.g., bistable flip-flops) are classified in this subclass.

SEE OR SEARCH THIS CLASS, SUBCLASS:
28 for discrimination by polarity.

SEE OR SEARCH CLASS:
365, Static Information Storage and Retrieval, 189.01 for networks including the inserting, extracting, or handling of information signals using the functions of "write", "read-out", "erase", etc., subclasses 185.01+ for floating gate memory storage (e.g., flash memory); subclasses 189.01+ for the static storage and retrieval of information coupled with the functions of "write", "read-out", "erase", etc., wherein voltage amplitude is sensed.

Differential amplifier:
This subclass is indented under subclass 51. Subject matter including a device responsive to the offset between two input voltages or currents and nonresponsive to voltages or currents which are identical in the two inputs.

Current mirror:
This subclass is indented under subclass 52. Subject matter wherein the sensing amplifier circuit utilizes collector current matching of two transistors when connected base to base and emitter to emitter.

Having feedback:
This subclass is indented under subclass 52. Subject matter wherein a portion of the output signal is returned to an input.

SEE OR SEARCH THIS CLASS, SUBCLASS:
57 for a miscellaneous sense amplifier with a latching type element.

Cross-coupled:
This subclass is indented under subclass 54. Subject matter wherein there are two elements or stages which are mutually interconnected (i.e., the output of one is connected to the input of the other and vice versa).

With reference signal:
This subclass is indented under subclass 52. Subject matter wherein a signal of fixed voltage potential acts as a constant for comparison to a variable input.
(1) Note. The reference signal is usually an input signal or produced from an input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
77 for amplitude comparison between an input signal and a fixed reference, in general.

With latching type element (e.g., flip-flop, etc.):
This subclass is indented under subclass 51. Subject matter wherein the sense amplifier includes a device providing signal retention.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for stable state circuits including bistable.

Maximum or minimum amplitude:
This subclass is indented under subclass 50. Subject matter wherein an output signal is caused by either a greatest absolute magnitude or a least absolute magnitude of an input signal during a time period of interest.
(1) Note. This subclass does not include comparison to a fixed reference or threshold.

Employing input compared to output:
This subclass is indented under subclass 58. Subject matter wherein a portion of an output signal is evaluated relative to an input signal.

Employing input compared to reference derived therefrom:
This subclass is indented under subclass 58. Subject matter wherein a signal from an external source is evaluated relative to a voltage or current obtained by processing signals from the same source.
(1) Note. For this subclass either the processing or means therefor should be claimed.

SEE OR SEARCH THIS CLASS, SUBCLASS:
72 for generic amplitude comparing between an input and a reference derived therefrom.

By diode-capacitor network:
This subclass is indented under subclass 58. Subject matter wherein maximum or minimum amplitude discriminating is achieved by an electrical energy storage element combined with an element providing unidirectional current flow.

Maximum and minimum amplitude:
This subclass is indented under subclass 58. Subject matter wherein an output signal is caused by both the greatest absolute magnitude and least absolute magnitude of an input signal during a time period of interest.

Comparison between plural varying inputs:
This subclass is indented under subclass 50. Subject matter wherein fluctuating input signals from two or more sources external to a system are evaluated relative to one another.

SEE OR SEARCH THIS CLASS, SUBCLASS:
72 for evaluation of an input signal relative to a reference derived therefrom.
74 for a system wherein a signal from an external source is evaluated relative to plural fixed reference levels.
77 for the evaluation of a signal relative to a single fixed reference level.
78 for detection of a crossover point between an input signal and a reference level.

With logic or bistable circuit:
This subclass is indented under subclass 63. Subject matter wherein the comparison by amplitude (a) includes a device performing Boolean functions such as AND, OR, or exclusive-OR or (b) utilizes a device having two stable states.
(1) Note. The combination of logic with specific amplitude comparison circuitry or function, not elsewhere classified is
classified here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for particular stable state circuits including bistable.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, 93 for clocking or synchronizing of one or more logic stages and appropriate subclasses for general digital logic circuitry not classified elsewhere.

Differential input:
This subclass is indented under subclass 63. Subject matter wherein the differences between the plural varying input signals are initially amplified prior to further processing.

Current mirror:
This subclass is indented under subclass 65. Subject matter wherein the comparison between plural varying inputs utilizes collector current matching of two transistors when connected base to base and emitter to emitter.

Having feedback:
This subclass is indented under subclass 65. Subject matter wherein a portion of the output signal is returned to an input.

Input provides varying reference signal:
This subclass is indented under subclass 63. Subject matter wherein at least one of the fluctuating inputs provides a changing signal to be used only as an evaluation standard.

SEE OR SEARCH THIS CLASS, SUBCLASS:
72 for amplitude discriminating where a reference signal is internally derived from one of the inputs.

With plural paths:
This subclass is indented under subclass 63. Subject matter wherein an input signal passes through more than one route or channel between an input terminal and an output terminal.

With single output:
This subclass is indented under subclass 69. Subject matter wherein the plural paths have a common output.

SEE OR SEARCH THIS CLASS, SUBCLASS:
407 for plural channel input, single channel output gating systems.

SEE OR SEARCH CLASS:
370, Multiplex Communications, appropriate subclasses for similar subject matter used with multiplexing.

Three or more inputs:
This subclass is indented under subclass 63. Subject matter wherein the number of external signal sources is greater than two.

Input signal compared to reference derived therefrom:
This subclass is indented under subclass 50. Subject matter wherein a signal from an external source is evaluated relative to a voltage or current obtained by processing signals from the same source.
(1) Note. For classification herein, either the processing or means therefor should be recited.

SEE OR SEARCH THIS CLASS, SUBCLASS:
68 for amplitude discriminating between plural varying inputs where at least one of the input signals is a varying reference.
74 for an input signal compared to plural fixed references.
205 for stable state circuits utilizing hysteresis.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuits, 22 for input noise margin enhancement.

Reference derived by feedback:
This subclass is indented under subclass 72. Subject matter wherein the processing includes extracting a signal from an output terminal of the circuit and applying a portion of the extracted signal to an input terminal.

Input signal compared to plural fixed references:
This subclass is indented under subclass 50. Subject matter wherein input signal amplitude is evaluated relative to two or more unvarying voltage or current levels.

SEE OR SEARCH THIS CLASS, SUBCLASS:
63 for amplitude comparison between plural varying inputs.
72 for an input signal compared to a reference derived therefrom.
77 for an input signal compared to a single fixed reference.
205 for a stable state circuit utilizing hysteresis.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuits, subclass 22 for input noise margin enhancement.

Three or more:
This subclass is indented under subclass 74. Subject matter wherein there are more than two unvarying reference levels.

With logic or bistable circuit:
This subclass is indented under subclass 74. Subject matter wherein the comparison by amplitude between the input signal and plural fixed references (a) includes a device performing Boolean functions such as AND, OR, or exclusive-OR or (b) utilizes a device having two stable states.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for particular stable state circuits including bistable.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, for general digital logic circuitry not classified elsewhere and particularly 93 for clocking or synchronizing of one or more logic stages.

Input signal compared to single fixed reference:
This subclass is indented under subclass 50. Subject matter wherein the input signal is evaluated relative to a standard which is at a constant level of amplitude.

SEE OR SEARCH THIS CLASS, SUBCLASS:
74 for an input signal compared to multiple fixed references.

Reference level crossover detecting:
This subclass is indented under subclass 77. Subject matter wherein an output signal is produced when an input signal actually transits the reference amplitude of a comparison standard.
(1) Note. The approach of the input signal to the reference level may be from either a positive or a negative direction.

SEE OR SEARCH THIS CLASS, SUBCLASS:
63 for evaluation of plural sources of varying input signals relative to each other.
74 for evaluation of an input signal relative to plural fixed thresholds.

Zero crossover:
This subclass is indented under subclass 78. Subject matter wherein the reference level which is transited is zero volts.

SEE OR SEARCH THIS CLASS, SUBCLASS:
451 for AC supply zero point switching utilizing a four or more layer device such as a thyristor.

Reference determined by threshold of single circuit element:
This subclass is indented under subclass 77. Subject matter wherein the amplitude of the comparison standard is established by one electrical component.

With transistor:
This subclass is indented under subclass 80. Subject matter wherein the single electrical component is a three terminal semiconductor device composed of n or p type material.

SEE OR SEARCH CLASS:
257, Active Solid-State Devices (e.g., Transistors, Solid-State Diodes), appropriate subclasses for transistor structure details.

Plural sources of input signal:
This subclass is indented under subclass 77. Subject matter wherein multiple input signals are to be evaluated relative to a standard.

SEE OR SEARCH THIS CLASS, SUBCLASS:
63 for an amplitude evaluation system having plural varying input signals which are to be evaluated against each other.
72 for a comparator system which evaluates an input signal against a reference derived from the same signal.

Temperature compensation:
This subclass is indented under subclass 77. Subject matter wherein an increase or decrease in thermal sensitivity of a system is cancelled or reduced by the effects of a counterbalancing element in the system.
(1) Note. A counterbalancing element may be, for example, a resistor, capacitor, or inductor.

SEE OR SEARCH THIS CLASS, SUBCLASS:
513 for miscellaneous temperature compensation.

With bridge circuit:
This subclass is indented under subclass 77. Subject matter including four or more devices with their input and output terminals connected in a closed loop to form a four arm network.
(1) Note. Another arm, called the diagonal arm, may be connected between an input terminal and an output terminal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
587 for a two electrode solid-state device bridge circuit.
588 for miscellaneous bridge circuits.

Inverting input or output:
This subclass is indented under subclass 77. Subject matter wherein an input signal or an output signal is reversed in sign.

With transformer:
This subclass is indented under subclass 77. Subject matter wherein an electromagnetic induction device transfers electrical energy between adjacent circuit portions at a constant frequency.
(1) Note. A transformer changes voltage in direct proportion to the ratio of the number of turns of its primary and secondary windings.

SEE OR SEARCH CLASS:
336, Inductor Devices, appropriate subclasses for transformer details.

Having feedback:
This subclass is indented under subclass 77. Subject matter wherein a portion of the output signal is returned to an input.

With source as reference:
This subclass is indented under subclass 77. Subject matter wherein a device which supplies signal power at a constant voltage or current level is used as a standard for comparison.

SEE OR SEARCH THIS CLASS, SUBCLASS:
100 for signal generating.
540 for stabilized bias circuits with voltage regulating.

With differential amplifier:
This subclass is indented under subclass 77. Subject matter including a device responsive to the offset between two input voltages or currents and nonresponsive to voltages or currents which are identical in the two inputs.

Comparison between two characteristics of an input signal:
This subclass is indented under subclass 50. Subject matter wherein the output signal is representative of the amplitude difference between two consecutive or selected points of the input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
91 for details of a sample or hold circuit.

Including details of sampling or holding:
This subclass is indented under subclass 50. Subject matter wherein a representation of an input signal magnitude at a particular point in time is produced or an established input signal magnitude value is maintained.

SEE OR SEARCH THIS CLASS, SUBCLASS:
124 for signal generation by periodic switching.
365 for gating of signals, in general.

With bridge circuit:
This subclass is indented under subclass 91. Subject matter including four or more devices with their input and output terminals connected in a closed loop to form a four arm network.
(1) Note. Another arm, called the diagonal arm, may connect an input terminal and an output terminal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
587 for a two electrode solid-state device bridge circuit.
588 for miscellaneous bridge circuits.

With reference source:
This subclass is indented under subclass 91. Subject matter including a device which supplies signal power to a sample or hold circuit at a constant voltage or current level.

SEE OR SEARCH THIS CLASS, SUBCLASS:
100 for signal converting, shaping, or generating.
530 for miscellaneous bias voltage supply circuits and particularly subclasses 538+ for a stabilized bias voltage supply circuit.

Sample and hold:
This subclass is indented under subclass 91. Subject matter wherein a representation of an input signal magnitude at a particular point in time is produced and subsequently maintained for a time in a storage element.

SEE OR SEARCH CLASS:
341, Coded Data Generation or Conversion, 122 for sample and hold circuits having code generation or conversion.

Having feedback:
This subclass is indented under subclass 94. Subject matter wherein a portion of the output signal is returned to an input.

With differential amplifier:
This subclass is indented under subclass 94. Subject matter including a device responsive to the offset between two input voltages or currents and nonresponsive to voltages or currents which are identical in the two inputs.

With logic or bistable circuit:
This subclass is indented under subclass 50. Subject matter wherein the comparison by amplitude (a) includes a device performing Boolean functions such as AND, OR, or exclusive-OR, or (b) utilizes a device having two stable states.
(1) Note. The combination of logic with specific amplitude comparison circuitry or function, not elsewhere classified is classified here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for particular stable state circuits including bistable.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, 93 for clocking or synchronizing of one or more logic stages and appropriate subclasses for general digital logic circuitry not classified elsewhere.

By separating composite signal:
This subclass is indented under subclass 1. Subject matter wherein the output signal is a selected component of a multicomponent input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
35 for pulse separating by width or spacing.
551 for miscellaneous signal suppression which may include an active filter.

SEE OR SEARCH CLASS:
307, Electrical Transmission or Interconnection Systems, subclass 105 for harmonic filters or neutralizing systems, in general.
324, Electricity: Measuring and Testing, 332 for geophysical exploration systems utilizing radiant energy with separate detector means whereby signal components are selected or suppressed and subclasses 76.12+ for measuring systems which analyze complex electric waves.
330, Amplifiers, appropriate subclasses for frequency selective linear amplifiers.
331, Oscillators, subclass 76 and 77 for oscillator systems combined with harmonic selecting means or wave filter, respectively, in the output circuit.
333, Wave Transmission Lines and Networks, appropriate subclasses for passive type wave selecting systems, particularly 167 for wave filters, per se.
340, Communications: Electrical, 825.71 for selective systems which are frequency responsive.
348, Television, subclass 506 for burst separation circuitry, subclasses 525+ for separating the synchronizing components from a composite signal wave, and subclasses 638+ for color signal deriving circuitry.
704, Data Processing: Speech Signal Processing, Linguistics, Language Translation, and Audio Compression/Decompression, subclass 200 for systems for analyzing complex speech waves (e.g., where the fundamental pitch frequency of the human voice is determined).

Having selection between plural continuous waveforms:
This subclass is indented under subclass 1. Systems wherein the output signal is one of a plurality of simultaneously applied input signal waveforms selected in accordance with a predetermined characteristic, the nonselected waveforms being attenuated or otherwise suppressed in such a manner that only the desired signal waveform appears at the output.

SEE OR SEARCH THIS CLASS, SUBCLASS:
98 for systems which select a signal component from a composite wave.
407 for distribution systems wherein plural channels are input and the output consists of a signal from a selected channel.

SEE OR SEARCH CLASS:
324, Electricity: Measuring and Testing, 76.12 for analysis systems of a complex wave.
331, Oscillators, subclass 76 for systems comprising an oscillator combined with a harmonic selection network and subclass 77 for oscillators with a wave selecting output filter.
333, Wave Transmission Lines and Networks, 167 for wave filters comprised of passive elements.
340, Communications: Electrical, 825.71 for remote control or selective signaling systems which are frequency responsive.
348, Television, 525 for separating the synchronizing components from a composite signal wave.

SIGNAL CONVERTING, SHAPING, OR GENERATING:
This subclass is indented under the class definition. Subject matter wherein (a) an inherent input signal parameter such as phase, frequency, amplitude, or current is modified, maintained at some value, or changed to an entirely different parameter, (b) an input signal having a particular waveform is modified into an output signal having a partially or completely different waveform, or (c) an output signal of specified waveform is produced.
(1) Note. An example of the second type above would be sine wave to triangular wave modification.
(2) Note. This subclass and indented subclasses do not include single energy systems for conversion wherein a single electrical source circuit is coupled to a single electrical load circuit and which involves current, phase or frequency conversion, and wherein the energy in the load is supplied solely by the source. Such systems in general are classified in Class 363, Electric Power Conversion Systems, appropriate subclasses. See References to Other Classes in Class 363 for other classes providing for conversion systems.
(3) Note. Excluded from this subclass and indented subclasses are free running signal generators which are classified, for example, in Class 331.
(4) Note. Bias circuits of the pulsing type which establish device operating points are classified below with the bias circuits.

SEE OR SEARCH THIS CLASS, SUBCLASS:
334 for circuits whose output is proportional to a mathematical function of the input.
544 for bias circuits of the pulsating type.
596 for miscellaneous circuits including a free running oscillatory type circuit.

SEE OR SEARCH CLASS:
128, Surgery, subclass 2.06 for electrocardiographs involving timing and subclasses 303.13+ for instruments for application of electricity to the human body involving timing.
236, Automatic Temperature and Humidity Regulation, subclass 46 for regulation systems involving timing.
237, Heating Systems, 2 for systems for automatic control of a heating system.
307, Electrical Transmission or Interconnection Systems, 401 for nonlinear reactor systems (e.g., saturable) and subclasses 106+ for a class appropriate wave shape determinative or pulse producing system. See also appropriate subclasses for plural source or load voltage magnitude and phase control.
315, Electric Lamp and Discharge Devices: Systems, 364 for cathode ray deflecting circuits involving timing and subclasses 209+ for systems involving a periodic switch in the supply circuit of a gaseous discharge tube.
318, Electricity: Motive Power Systems, subclass 445 for systems of automatically starting and/or stopping a motor with timing, subclasses 606+ for electric motor position servomechanisms with phase or frequency control, and subclass 683 for particular phase detectors used in such a servomechanism.
320, Electricity: Battery or Capacitor Charging or Discharging, 166 for charging or discharging a capacitor, per se.
322, Electricity: Single Generator Systems, 17, especially indented subclass 18 for systems involving time delay means in the control of a generator or driving.
323, Electricity: Power Supply or Regulation Systems, 212 for power supply phase control comprising an electron tube and wherein, in general, the tube does not act as an active element.
324, Electricity: Measuring and Testing, 83 for phase indicators, subclasses 78+, particularly subclass 82 for measuring or testing the frequency of cyclic current or voltage by phase comparison, and subclasses 160+ for systems for measuring time or speed.
330, Amplifiers, subclass 107 for amplifiers with phase shifting means in a feedback path.
331, Oscillators, 37 for systems including an oscillator or oscillators generating at least two different frequencies with a signal combining device (e.g., mixer, modulator, etc.) having a signal input circuit and a signal output circuit where the oscillator or oscillators are connected to the signal input circuit of the combining device and the device output comprises the sum or difference frequency of the outputs of the oscillator or oscillators.
332, Modulators, appropriate subclasses for systems including
beating a source of carrier frequency with a signal wave which varies arbitrarily in a continuous manner in accordance with some intelligence.
333, Wave Transmission Lines and Networks, subclass 18, 23, and 138+ for delay networks comprising passive elements and subclasses 138+. See (1) Note, above.
340, Communications: Electrical, subclass 870.24 for telemetering systems receiving information by pulse trains with length or spacing varied with respect to time.
341, Coded Data Generation or Conversion, 50 for systems converting an input consisting of a coded arrangement representing a particular group of values to an output consisting of another coded arrangement.
348, Television, 469 for systems generating or formatting a television signal.
361, Electricity: Electrical Systems and Devices, 195 for time delay networks which control a relay load switching operation.
363, Electric Power Conversion Systems, appropriate subclasses for single energy conversion systems wherein a single electrical source circuit is coupled to a single electrical load circuit. See (2) Note, above.
455, Telecommunications, 313 for mixer or converters in radio receiver circuits. See (3) Note, above.

Converting input current or voltage to output frequency:
This subclass is indented under subclass 100. Subject matter wherein a repetition rate of an output signal is directly related to the magnitude of an input signal current or voltage.

SEE OR SEARCH THIS CLASS, SUBCLASS:
113 for miscellaneous frequency or repetition rate conversion or control.

SEE OR SEARCH CLASS:
332, Modulators, 117 for a frequency modulator.

Converting input frequency to output current or voltage:
This subclass is indented under subclass 100. Subject matter wherein the magnitude of output signal current or voltage is directly related to the repetition rate of the input signal.
(1) Note. Included here are devices wherein an input signal of varying frequency is changed into a direct current output voltage which is a function of the input frequency.
(2) Note. Since period is inversely related to frequency, input period conversion to output current or voltage is also included here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
39 for frequency discrimination and particularly subclasses 47+ for frequency detection.

SEE OR SEARCH CLASS:
329, Demodulators, 315 for a frequency demodulator.

Converting input voltage to output current or vice versa:
This subclass is indented under subclass 100. Subject matter wherein electrical potential is changed to an equivalent electrical charge flow or vice versa.

SEE OR SEARCH CLASS:
363, Electric Power Conversion Systems, subclass 73 for power conversion systems between a constant current and a constant voltage or vice versa wherein a single source is connected to a single load.

Converting, per se, of an AC input to corresponding DC at an unloaded output:
This subclass is indented under subclass 100. Subject matter wherein an alternating current input signal wave is converted to an unloaded output wave consisting of a unidirectional representation of the half cycles of an input wave.
(1) Note. The conversion systems in this subclass do not include claimed subject matter such as would define demodulators, detectors, or rectifier systems classified elsewhere with specific art devices.

SEE OR SEARCH THIS CLASS, SUBCLASS:
28 for polarity selection or discrimination.
39 for selection or discrimination by repetition rate (i.e., frequency).
335 for a differentiating network.
336 for an integrating network.
348 for the determination of the RMS function of an input signal.

SEE OR SEARCH CLASS:
178, Telegraphy, appropriate subclasses for pulse producing (e.g., by rectification of AC signals, etc.) in combination with telegraph systems. In Class 178, the pulses are usually representative of a telegraph code. 118 relate to telegraph receivers which may include signal rectifiers.
246, Railway Switches and Signals, appropriate subclasses for railway signaling systems which may include signal rectifying or other conversion systems as subcombinations thereof.
307, Electrical Transmission or Interconnection Systems, subclass 6 for systems having series connected converters of different voltages, subclass 45 for plural supply circuits with intervening converter, subclass 58 for load current dividing circuits utilizing plural converters, subclass 82 for plural converter systems, subclasses 401+ for nonlinear reactor systems, and subclass 107 for wave form or wave shape determining systems with wave rectification.
320, Electricity: Battery or Capacitor Charging or Discharging, appropriate subclass for charging or discharging a capacitor or battery where a rectifier is employed, particularly Digest 31.
324, Electricity: Measuring and Testing, subclass 89 for phase comparison meters and subclass 119 for meters in general with rectifying.
329, Demodulators, for demodulating systems using rectification designed to change a signal modulated wave so as to produce in the output circuit a pulsating direct current representative of the signal.
330, Amplifiers, appropriate subclasses for amplifiers, especially subclass 10 for modulator-demodulator type amplifiers.
343, Communications: Radio Wave Antennas, appropriate subclasses for signaling systems including radar and directive radio systems which may include demodulating type conversion systems as subcombinations thereof.
363, Electric Power Conversion Systems, 13 for rectification and derectification involving a single source coupled to a single load in a power conversion system. See the class definition and search notes as to lines with other classes and further fields of search for rectifying systems.
375, Pulse or Digital Communications, appropriate subclasses and particularly 37 for pulse communication systems using alternating or pulsating currents.
379, Telephonic Communications, appropriate subclasses for pulse producing systems with signal rectifying or other converting for use in telephone call transmitter systems.

Synthesizer:
This subclass is indented under subclass 100. Subject matter wherein an output waveform is derived which at any instant is proportional to the combined values of the corresponding instantaneous values of a plurality of input signal waveforms.

SEE OR SEARCH THIS CLASS, SUBCLASS:
3 for circuits where the output is a function of the phase difference between plural input signal wave forms.
40 for circuits where the output is a function of the frequency difference between plural input signal wave forms.
129 for miscellaneous sine wave generation.
355 for circuits where the output signal is a function of a plurality of input signals.
361 for mathematical summing of two or more input signals.

SEE OR SEARCH CLASS:
84, Music, 600 for generation of electrical musical tones utilizing synthesizing techniques.
324, Electricity: Measuring and Testing, subclass 77 for systems for analyzing complex electric waves and subclass 140 for measuring and testing circuits which combine plural inputs.
331, Oscillators, 37 for oscillatory circuits whose output comprises a beat frequency and subclasses 46+ for plural oscillator systems.
332, Modulators, appropriate subclasses for plural wave modulating circuits.
333, Wave Transmission Lines and Networks, appropriate subclasses, especially subclass 20 for passive wave shaping networks.
455, Telecommunications, 313 for plural wave combining heterodyning systems utilized in radio receivers wherein the output is a beat frequency.

Having stored waveform data (e.g., in ROM, etc.):
This subclass is indented under subclass 105. Subject matter wherein information about a desired output waveform is placed into a memory device.

SEE OR SEARCH CLASS:
365, Static Information Storage and Retrieval, appropriate subclasses for read-only memory (ROM) circuits in general.

Having digital device (e.g., logic gate, flip-flop, etc.):
This subclass is indented under subclass 105. Subject matter wherein a device which operates on binary signals is included.

SEE OR SEARCH THIS CLASS, SUBCLASS:
185 for miscellaneous flip-flop circuits.

SEE OR SEARCH CLASS:
326, Electronic Digital Logic Circuitry, appropriate subclasses for logic gates, per se.

Current driver:
This subclass is indented under subclass 100. Subject matter wherein an input signal is modified into a similar output signal having an enhanced current supplying ability.
(1) Note. Current driving of the type associated with electronic digital logic circuitry is classified in Class 326.

SEE OR SEARCH THIS CLASS, SUBCLASS:
139 for sawtooth signal waveform production without output current drive enhancement and having an inductive load.

SEE OR SEARCH CLASS:
307, Electrical Transmission or Interconnection Systems, 401 and particularly subclass 412 for similar subject matter where a nonlinear reactive element (e.g., magnetic core) is claimed as forming part of the operative combination of the invention.
326, Electronic Digital Logic Circuitry, 82 for logic current driving.
365, Static Information Storage and Retrieval, appropriate subclasses for magnetic storage of signals on magnetic cores.

Having semiconductive load:
This subclass is indented under subclass 108. Subject matter wherein the output drive current is provided to a broadly recited semiconductive device.

SEE OR SEARCH CLASS:
257, Active Solid-State Devices (e.g., Transistors, Solid-State Diodes), appropriate subclasses for detailed semiconductor structure.

Having inductive load (e.g., coil, etc.):
This subclass is indented under subclass 108. Subject matter wherein the output drive current is provided to a broadly recited element which has the property of opposing current flow therethrough due to a resultant magnetic field.

SEE OR SEARCH THIS CLASS, SUBCLASS:
139 for a circuit providing a sawtooth or triangular waveform, as generated, to an inductive load.
190 for a stable state circuit utilizing a transformer or saturable core device.

SEE OR SEARCH CLASS:
336, Inductor Devices, appropriate subclasses for generic inductive devices.