The modulation and demodulation of pulse trains, for example in Pulse Width Modulation circuits, is covered in subclass H03K.

The modulation and demodulation of sinusoidal signals, for example in AM and FM broadcasting, is covered in subclasses H03C and H03D.

The modulation by digital signals of the frequency, phase or amplitude of sinusoidal carrier, or carriers, is covered in subclass H04L. Quadrature (I-Q) modulation systems used for the transmission of digital information, e.g. QAM, the effect of which is to modulate a carrier in both amplitude and phase (often in discrete steps, which may be illustrated as a 'constellation' of points, each point representing a pair of carrier amplitude and phase values), are covered in subclass H04L.

Analogue quadrature modulation used in the NTSC and PAL colour television systems (where the I and Q signals representing colour difference values are substantially continuously variable), is covered in H04N.

In this subclass, where the claims of a patent document are not limited to a specific circuit element, the document is classified at least according to the elements described in the described embodiment.

Latching level shifters should be classified in the corresponding bistable circuit subgroups of this main group.

Multivibrators generating pulse signals other than finite-sloped or staircase signals should be classified in H03K 3/00.

H03K 4/026: Digital generators followed by a digital-to-analog converter to produce analogue output stepped signals.

Mostly pulse rate multiply by 2 circuits based on delaying and combining.

Also used for slew rate control circuits.

For instance circuits for staggering turn on signals.

Delay lines having propagation speed depending on input frequency.

Clamping circuits in general

The value of the threshold is generated by feedback AND the value is modified by switching.

i.e. the value of the threshold is generated by feedback.

The switching only relating to the switching instants.

Mostly used for pulse compression circuits using non-linear transmission lines having propagation speed depending on input amplitude, such as diode loaded transmission lines, to steepen one of the pulse edges and slow the other.

Mostly suppression of glitches in binary signals by delay and subsequent logic combination with the original signal.

Some documents (often also classified in H03K 5/156 or H03K 5/1565) relate to phase noise suppression in (interpolated) clock signals.

For glitches produced when switching from one clock signal to another G06F 1/08 takes precedence.

Additional aspects are classified as follows

Delay H03K 2005/00013

Phase H03K 2005/00286

Pulse H03K 2005/00293

Phase interpolation circuits H03K 2005/00052

Also classify in: H03K 2005/00058 (controlled by a digital setting)

Tapped arrangement

Pulse distributor with output stages driven more or less synchronously either in parallel in a tree-like structure OR sequentially with shift register like structure.

Providing simultaneous switching of two complementary signals.

In particular suitable for preventing simultaneous conduction in push pull stages.

Peak instant detectors only

Also contains ccts for suppressing jitter and phase noise in pulse signals.

Detecting presence of valid pulse signal, e.g monitoring amplitude and/or frequency of pulse signal.

Pulse comparators.

Slew rate correction in ramp or triangular waveform generators..

Continuous modulating signal meaning (quasi-)analog.

Only basic schemes for modulating one or more pulse characteristics are classsified here. See also application fields.

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Basic modulation concept such as comparing voltage to (quasi-)analog ramp signal.

Only for documents not showing the modulator or where the demodulator is clearly the main aspect.

General multiplexers (block diagrams)

More detailed structures are classified as follows:

bipolar transistor based mux circuits: H03K 17/62 and subgroups

field-effect transistor based mux circuits: H03K 17/693

diode based mux circuits: H03K 17/76

Acceleration means

Composite switches -> mainly IGBTs

Protection circuits for protecting the switch go in here, those protecting the load go in H02H 3/00 (remember to distribute it in classification). We will therefore in almost any case have to search in there as well.

Any document with a switch and a temperature detector is classified in H03K 2017/0806.

Caused by the switching, e.g. reducing switching noise

Soft switching aspects are also classified in H02H 9/001

Soft switching aspects are also classified in H02H 9/001

Any kind of state, i.e. not only the switching state but also e.g. if short-circuited, how many times overloaded so far etc. etc.

indicating -> display or generation of feedback signals to higher entity etc.

Merely power-on-reset circuits of any kind

Also Christmas tree type pre-programmable plugs

Keeping an absolute switching threshold or switching at a threshold different from the threshold of the switching element

Diode replacement Transistors can also be classified in H03K 17/06 or H03K 17/063.

Some detection methods which are not to be found elsewhere & details related to the operation of generic sensors.

This class contains different sensing priciples:

microwave

RF energy sensor

ultrasonic

infrasonic

acoustically activated

temperature activated

Power supply related documents are found here and in H03K 17/945 if for generic sensor. H03K 17/951 is for power supply for non-generic sensor, even if not magnetic.

Constructional details, housings for sensors, network of proximity sensors, programming of proximity switches

Temperature compensation, self-test, redundant sensors, security switches (using codes), passive and active responders, protection against noise and interference

For practical purposes also power supply details of non-magnetic touch sensors.

Also bistable magnetic elements (Barkhausen effect, Wiegand effect, Matteucci effect).

Hall effect sensors, magnetoresistance.

H03K 17/9537 takes precedence.

LC-resonant circuit in general (e.g. signal is interrogation pulse, usually generating damped or decaying oscillations)

LC-resonant circuit forming part of oscillator; the variable parameter is undetermined

LC-resonant circuit forming part of oscillator; the variable parameter is oscillation frequency

LC-resonant circuit forming part of oscillator; the variable parameter is oscillation amplitude

Charge transfer, phase comparison, frequency shift, resistance-capacitance timing circuits

Constructional details, detection principles, simulation of slider, key illumination details

Detection principle

Means for interpreting an external force as a variable resistance (e.g. strain gauges)

ONLY documents which disclose reflection on a permanent interface surface

Simulation of slider, in combination with display

With deformation of the light guide

An object (e.g. finger) provides path for current

Tactile feedback, illuminated, rotary, ...

Type of magnetic sensor: inductance, hall sensor, magnetoresistance

The movable part is an electrode forming part of the switch or the dielectric

Circuits having at least two inputs acting on one output inverting circuits or buffers.

When a circuit is used or adapted for switching a load, it is classified in H03K 17/00. When it is used/adapted for driving a logic circuit (e.g. output buffer), it goes to H03K 19/00.

The groups H03K 19/00369 take precedence over H03K 19/0005

H03K 19/003: Circuits for increasing the reliability, not for notifying the user that a failure took place

H03K 19/00323: Skew compensation

H03K 19/00346: Slope control, slew rate adaptation

H03K 19/007: Circuits in this class go, when they fail, to a safe state. They do not notify the user of a failure

H03K 19/01 covers accelerating switching in logic circuits and should not be confused with H03K 17/04 which covers accelerating the switching of a switch

H03K 19/177: Field Programmable Gate Arrays (FPGA).

Details of logic circuits having electric(digital) pulses as input signals and either counting incoming pulses or producing an output pulse stream based on the incoming pulse stream having a modified pulse repeating period.

Special logic at input for pulse treatment e.g. pulse shaping

Illustrative examples of subject matter classified in this group:

Figure taken from DE3842874

Special logic at register outputs e.g. for a counter value dependent reset.

Figure taken from JP57199337

Logic counter having multiple counting stages including a carry over bit between stages.

Figure taken from US5,946,369

Logic for representing the result to a user.

Figure taken from DE3031612

Logic for influencing the counter status.

Figure taken from EP0471390.

Monitoring whether an error occured during the counting process (not the process producing the pulses)

Figure taken from DE2550177

Logic for digital counting chains used in pulse counters or frequency dividers

Other elements as complementary IGFET's, electrically-ignited compounds e.g. pyrotechnical static relays

Detailed counting encoding scheme.

Details regarding the clock used for triggering the counting of incoming pulses

Counter with a "rippling" trigger pulse form stage to stage - asynchronous counters.

Variable counting base, non-integer or odd-number counters.

Static storage type counters - e.g. capacitive type

Figure taken from EP0916188

Figure taken from GB2008296.

A triggering pulse is generated in response to each input signal to be counted. The triggering pulse is applied to the device to change the voltage across the device. The voltage across the device is output as an indication of the number of received input signals. The device may be a resonant tunnelling diode with multiple peaks in its current versus voltage characteristic. The device may be a resonant tunnelling diode with multiple peaks in its current versus voltage characteristic.

Figure taken from US 5,033,069