CPC Definition - Subclass H03F

Last Updated Version: 2024.01
AMPLIFIERS
Definition statement

This place covers:

  • Linear amplification, there being linear relationship between the amplitudes of input and output, and the output having substantially the same waveform as the input;
  • Dielectric amplifiers, magnetic amplifiers, and parametric amplifiers when used as oscillators or frequency-changers;
  • Constructions of active elements of dielectric amplifiers and parametric amplifiers if no provision exists elsewhere.
Relationships with other classification places

The structural association with elements coupled with amplifiers can be classified either in H03F or in the subclass covering the element (or in both the subclasses), depending on which aspect is more relevant.

In particular H03F units represented as "black boxes" in a specific application (e.g. a servo loop control circuit for a motor) are in general not classified in H03F, unless a specific technical effect which is relevant for H03F is achieved (e.g. linearity of amplification).

Components covered by specific subclasses (e.g. resistors, inductors, transmission lines, etc.):

  • if relevant for their structural association with the amplifier are classified in H03F;
  • if relevant only per se are not classified in H03F, but in the specific subclass.
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Measuring; Testing

G01R

Optical parametric amplifiers

G02F

Circuit arrangements with secondary emission tubes

H01J 43/30

Semiconductors or other solid state devices

H01L

Waveguides, resonators

H01P

Masers; Lasers

H01S

Emergency protection circuit arrangements

H02H

Dynamo-electric amplifiers

H02K

AC/DC, DC/DC, AC/AC power converters

H02M

Generation of oscillations

H03B

Modulation

H03C

Demodulation

H03D

Control of amplification

H03G

Coupling arrangements independent of the nature of the amplifiers, voltage dividers

H03H

Amplifiers capable only of dealing with pulses

H03K

Control of generators of electronic oscillations or pulses, e.g. phase locked loops

H03L

A/D and D/A converters, sigma delta modulators

H03M

Repeater circuits in transmission lines

H04B 3/36, H04B 3/58

Application of speech amplifiers in telephonic communication

H04M 1/60, H04M 3/40

Nanotube transistors

H10K 99/00

Special rules of classification

As general remark, it must be noted that multiple classification symbols may be given. The philosophy is to classify documents in several sub-groups as the case may be, i.e. the classifier should not stop the classification task once that the first suitable symbol is found, but he should continue to assign symbols until all the aspects have been properly classified.

The subclass has a very large number of related technical areas, e.g.:

  • "application" fields such as transmitters, receivers, voltage regulators, multimedia devices, etc.

Indexing Code orthogonal classification

In addition to one or more classification symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to orthogonal classification (H03F 2200/03 - H03F 2200/555), i.e. covering aspects which are spanning over one or more groups, should be allocated for the following ranges:

Vacuum tube amplifiers classification

The following IPC groups, which are mostly related to discharge tube amplifiers or general type amplifiers, are used to classify circuit topologies based also on vacuum tubes, valve amplifiers, due to historical reasons (see vacuum tube amplifier in the "Glossary of terms" section below):

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

Class A

media0.png Amplifying devices operating in class A conduct in their linear range over the whole of the input cycle.

Class B

media1.png Amplifying devices operating in class B conduct in their linear range half of the time and are turned off for the other half

Class AB

media2.png Amplifying devices operating in class AB conduct in their linear range for more than half of the time

Class C

media3.png Amplifying devices operating in class C conduct in their linear range for less than half of the time

Class D

media4.png In the basic class-D amplifier the input signal is converted into a sequence of pulse width modulated (PWM) pulses via a comparator (C). Said PWM sequence is amplified via switching amplifying devices and filtered in order to produce an amplified replica of said input signal at the output.

Class E

media5.png The basic topology of class-E amplifier includes a transistor T, operated as a switch, a shunt capacitor (C1) which includes the intrinsic transistor output capacitance, RF choke inductor (L1), a load resistor R, a series resonance circuit (Co, Lo), and an excess inductance XL. The reactive elements shape the current and voltage waveforms across the transistor as shown. Thus as current flows, there is essentially no voltage across the device and a highly efficient switching power amplifier is achieved.

Class F

media6.png In realizing a class F amplifier, the active device operates primarily as a switch and the output network, generally, is designed to yield short circuit impedances at even harmonics of the fundamental frequency and to yield open circuit impedances at odd harmonics of the fundamental frequency.

Class G

media7.png The Class G amplifiers (which use "rail switching" to decrease power consumption and increase efficiency) provide several power rails at different voltages (HV, LV) and switch between them as the signal output approaches each level. Thus, the amplifier increases efficiency by reducing the wasted power at the output transistors.

Class H

media8.png Class-H amplifiers take the idea of class G one step further creating an infinitely variable supply rail. This is done by modulating the supply rails (VCC, VEE) so that the rails are only a few volts larger than the output signal at any given time. The output stage operates at its maximum efficiency all the time. Switched-mode power supplies can be used to create the tracking rails.

Class S

media9.png Class S amplifiers are used essentially for RF transmitters or as tracking power supply building blocks. The basic architecture consists of a modulator, e.g., of delta-sigma type, a fast broadband switch-mode amplifier, and an advanced filter at the output. The big advantage of the concept is that it can potentially be driven with a digital input without A/D conversion at the input.

Totem pole

media10.png Amplifier with two or more amplifying elements having their DC paths in series with the load, the control electrode of each element being excited by at least part of the input signal.

Distributed amplifier

media11.png The input/output terminals of the amplifying elements are connected in series through respective distributed elements.

Doherty Amplifier

media12.png Amplifier using a main and one or several auxiliary peaking amplifiers wherein the load is connected to the main amplifier using an impedance inverter.

Push Pull

media13.png The amplifying devices are each used for amplifying the opposite halves of the input signal.

Single Ended Push Pull

media14.png Push pull amplifier wherein the output terminals of the amplifying elements are tied together as a single ended output without additional balun elements.

Differential amplifier

media15.png the basic differential amplifier amplifies the difference between two voltages; the output voltage is determined according to the following equation: media16.png wherein Ac is the common mode gain and Ad is the differential mode gain.

Common mode rejection ratio

the common-mode rejection ratio (CMRR) indicates the ability of the amplifier to accurately cancel voltages that are common to both inputs. The common-mode rejection ratio is defined as: media17.png

Vacuum tube amplifier

media18.png Until the invention of the transistor in 1947, all practical amplifiers were made using Vacuum tubes, which rely on thermionic emission of electrons from a hot filament (cathode), that then travel through a vacuum toward a collecting electrode (anode). The simplest vacuum tube was invented by John Ambrose Fleming while working for the Marconi Company in London in 1904 and named the diode, as it had two electrodes. The diode conducted electricity in one direction only and was used as a radio detector and a rectifier. In 1906 Lee De Forest added a third electrode (grid) and invented the first electronic amplifying device, the triode, which he named the Audion. This additional control grid modulates the current that flows between cathode and anode.

Common emitter/source /cathode

media19.png Amplifying device wherein the emitter/source/cathode terminal is connected to RF ground/earth and the input (control) terminal is the base/gate/grid.

Common base/gate /grid

media20.png Amplifying device wherein the base/gate/grid terminal is connected to RF ground/earth and the input (control) terminal is the emitter/source/cathode.

Cascade coupling

media21.png Two or more amplifying devices wherein the output terminal of the first device is connected to the input (control) terminal of the second device in order to form a chain of amplifying elements.

Cascode coupling

media22.png A cascade coupling of a common emitter/source/cathode amplifying device followed by a common base/gate/grid amplifying device.

Common collector/drain/anode, i.e. Emitter/source /cathode follower

media23.png Amplifying device wherein the input (control) terminal is the base/gate/grid, and the output terminal is the emitter/source/cathode. The output voltage "follows" the input voltage, because the voltage gain almost equals one.

Emitter/Source degeneration

media24.png Amplifying device in common emitter/source/cathode configuration wherein an additional element (degeneration element) is connecting the emitter/source/cathode terminal with the RF ground/earth.

Darlington amplifier

media25.png Bipolar transistors are in Darlington configuration when they have the collector terminals tied together and the emitter of the first transistor is connected to the base of the second transistor so that the current gain of the composite transistor is increased.

Bridge type

media26.png Two amplifying devices are in bridge type when the output signal of one device is in opposition of phase with the output signal of the other device. A load is connected between the two amplifying device outputs, bridging the output terminals. This can double the voltage swing at the load as compared with the same amplifying device used alone without bridging.

Esaki diode

media27.png Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave frequency region, by using quantum mechanical effects. When forward-biased, an odd effect occurs called "quantum mechanical tunnelling" which gives rise to a region where an increase in forward voltage is accompanied by a decrease in forward current (negative resistance region)

Chopper amplifier

media28.png A basic chopper amplifier is formed by adding so-called choppers S1 and S2 before and after an input stage A1. The choppers consist of switches with two positions. In the first position, the inputs I1 and I2 are connected to the outputs O1 and O2, respectively. In the second position, the inputs I1 and I2 are connected to the outputs O2 and O1, respectively. The choppers S1 and S2 are synchronized to repeatedly switch between the first and the second positions at the rate of a clock signal f1. This configuration is commonly used to reduce the offset (e.g. Vos1) and the flicker noise.

Differential amplifier long tail pair

media29.png The basis configuration of a long-tailed pair (LTP) differential amplifier consists of two amplifying transistors, which are connected so that the BJT emitters (or FET sources, or valve cathodes) are connected together. The common electrodes are then connected to a circuit, forming the "long tail" of the name, the long tail providing a current source, i.e. having a very high equivalent impedance in parallel, so that high common mode rejection ratio is achieved.

Differential amplifier PI type

media30.png The basic configuration of a PI type differential amplifier consists of two amplifying transistors, which are connected so that the BJT emitters (or FET sources, or valve cathodes) are connected together via a resistor. The resistor terminals are then respectively connected to a shunting current source, forming the "PI" of the name, so that high common mode rejection ratio is achieved.

Pseudo differential amplifier

media31.png The basic configuration of a pseudo differential amplifier consists of two amplifying transistors, wherein the BJT emitters (or FET sources, or valve cathodes) are not connected together but directly coupled to the ground. Thus, since the difference between I1 and I2 is output in proportion to the difference between gate signals Va, Vb, the configuration acts as a differential transconductance amplifier.

Reflex amplifier

media32.png In a basic reflex amplifier an AC input signal is amplified and then rectified and, using the same circuit elements, the fed back resultant rectified DC signal is again amplified. The reflex circuit thus achieves two stages of amplification, plus rectification, in a single stage.

Travelling Wave Tube Amplifier (TWTA)

media33.png A travelling wave tube (TWT) integrated with a regulated power supply and protection circuits is referred to as a travelling wave-tube amplifier (TWTA). The basic configuration of a TWT is an elongated vacuum tube with an electron gun (a heated cathode that emits electrons) at one end. A magnetic containment field around the tube focuses the electrons into a beam, which then passes down the middle of an RF circuit (wire helix or coupled cavity) that stretches from the RF input to the RF output, the electron beam finally striking a collector at the other end. A directional coupler, which can be either a waveguide or an electromagnetic coil, fed with the low-powered radio signal that is to be amplified, is positioned near the emitter, and induces a current into the helix. The RF circuit acts as a delay line, in which the RF signal travels at near the same speed along the tube as the electron beam. The electromagnetic field due to the RF signal in the RF circuit interacts with the electron beam, causing bunching of the electrons (an effect called velocity modulation), and the electromagnetic field due to the beam current then induces more current back into the RF circuit (i.e. the current builds up and thus is amplified as it passes down). A second directional coupler, positioned near the collector, receives an amplified version of the input signal from the far end of the RF circuit.

Klystron

media34.png A klystron amplifies RF signals by converting the kinetic energy in a DC electron beam into radio frequency power. A beam of electrons is produced by a thermionic cathode (a heated pellet of low work function material), and accelerated by high-voltage electrodes (typically in the tens of kilovolts). This beam is then passed through an input cavity. RF energy is fed into the input cavity at, or near, its natural frequency to produce a voltage which acts on the electron beam. The electric field causes the electrons to bunch: electrons that pass through during an opposing electric field are accelerated and later electrons are slowed, causing the previously continuous electron beam to form bunches at the input frequency. To reinforce the bunching, a klystron may contain additional "buncher" cavities. The RF current carried by the beam will produce an RF magnetic field, and this will in turn excite a voltage across the gap of subsequent resonant cavities. In the output cavity, the developed RF energy is coupled out. The spent electron beam, with reduced energy, is captured in a collector.

Envelope Elimination and Restoration (EER)

media35.png The Envelope elimination and restoration technique was first proposed in 1952 by L.R. Kahn as a way to linearise nonlinear amplifiers. In Kahn's approach, an RF input signal is processed by two parallel paths. In one path, the envelope of the RF input signal is "eliminated" using a limiting amplifier that removes any amplitude modulation and which provides a phase modulated signal. In the other path, the RF input signal envelope is detected, amplified, and applied to the PA as an amplitude modulating power supply voltage. The EER technique allows the phase modulated signal to be amplified with high efficiency using a saturated power amplifier, which has an amplitude modulating power supply voltage, in order to restore the RF signal envelope at the output of said amplifier and to obtain linear amplification of the RF input signal.

Envelope Tracking (ET)

media36.png In the Envelope Tracking configuration, the power amplifier is fed with a fully-modulated RF signal (RFin) at the input and supplied with a modulated drain bias (Vout) in accordance with the envelope of the modulated signal (Venv). As a result, the power amplifier at all times is kept near saturation where the efficiency is highest.

Charge amplifier

media37.png A charge amplifier is a current integrator driven by an electrical source with capacitive nature such as a piezoelectric sensor. Contrary to what its name may suggest, a charge amplifier does not amplify the electric charge present at its input (it can amplify only the exciting input voltage). The charge amplifier just transfers the input charge to another reference capacitor and produces an output voltage equal to the voltage across the reference capacitor. Thus the output voltage is proportional to the charge of the reference capacitor and, respectively, to the input charge; hence the circuit acts as a charge-to-voltage converter. Charge amplifiers are usually constructed using op-amps with a feedback capacitor.

Synonyms and Keywords

In patent documents, the following abbreviations are often used:

RF

Radio Frequency

HF

High Frequency, Hoch-Frequenz (German). Haute Fréquence (French)

NF (German)

Nieder-Frequenz (German)

NF

Noise Figure

LF

Low Frequency

BF (French)

Basse Fréquence (French)

LNA

Low Noise Amplifier

MMIC

Microwave Monolithic Integrated Circuit

IC

Integrated Circuit

OP-AMP

Operational Amplifier

FET

Field Effect Transistor

TEC (French)

Transistor à Effet de Champ (French)

AC

Alternate Current

DC

Direct Current

DAT

Distributed Active Transformer

SEPP

Single Ended Push Pull

BALUN

Balanced/Unbalanced or Unbalanced/Balanced

EMI

Electromagnetic Interference

ESD

Electro Static Discharge

TD

Time Domain

PD

Predistorter

BiFET

Bipolar and Field Effect Transistor

CMMR

Common-Mode Rejection Ratio

CCCS

Current Controlled Current Source

CCVS

Current Controlled Voltage Source

VCVS

Voltage Controlled Voltage Source

VCCS

Voltage Controlled Current Source

TIA

Trans-Impedance Amplifier

OTA

Operational Transconductance Amplifier

TWT

Travelling Wave Tube

PA

Power Amplifier

DPA

Doherty Power Amplifier

MMPA

Multi-Mode Power Amplifier

TWTA

Travelling Wave Tube Amplifier

LTP

Long Tailed Pair

EER

Envelope Elimination and Restoration

ET

Envelope Tracking

BTL

Bridged Tied Load

Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
Definition statement

This place covers:

Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements, wherein said details are addressing a specific technical effect for the amplification:

Raise the efficiency

Reduce detrimental influences of internal impedances of the amplifying elements

Reduce influence of noise generated by amplifying elements

Reduce influence of variations of temperature or supply voltage or other physical parameters

Reduce non-linear distortion (except when using negative feedback)

Negative feedback with or without positive feedback

Positive feedback without negative feedback

Bandwidth extension

Protection

Modification of input or output impedances

The technical effect is specified according to the IPC definitions for the individual subgroups of H03F 1/00 which follow hereinafter.

Special rules of classification

A document may be temporarily allocated in the main group H03F 1/00 only for EPO internal circulation, e.g. to receive it from neighbouring field classifiers via the classification code.

Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
Definition statement

This place covers:

Modifications of amplifiers to raise the efficiency, wherein said modification comprises the following techniques:

dynamic bias control based on the input/output signal

supply control based on the input/output signal

selection of one or more amplifiers from a plurality of amplifier

reduction of the number of DC current paths

use of particular circuit topologies, e.g. Doherty amplifier, LINC Amplifier

use of discharge tube amplifiers acting also as modulators.

References
Limiting references

This place does not cover:

Transmitter circuits with power amplifiers having gain or transmission power control, with means for improving efficiency

H04B 2001/0416, H04B 2001/045

Informative references

Attention is drawn to the following places, which may be of interest for search:

Amplitude modulation by converting angle modulation to amplitude modulation

H03C 1/50

Gain control details, gain control by varying the supply voltage, gain control dependent on the supply voltage

H03G 1/00, H03G 3/004, H03G 3/007

Transmission power control

H04W 52/04

Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements (wide-band amplifiers with inter-stage coupling networks incorporating these impedances H03F 1/42)
Definition statement

This place covers:

Modification of amplifiers to achieve frequency stabilisation or signal isolation among amplifying stages, wherein said modification comprises the following techniques:

use of particular circuit topologies, e.g. transimpendance amplifier, cascode amplifier

use of amplifying elements with multiple electrode connections

use of attenuating means

use of neutralising means, e.g. Miller effect compensation circuitry, pole/zero cancellations in the transfer function

use of distributed coupling

References
Limiting references

This place does not cover:

Wide-band amplifiers with inter-stage coupling networks incorporating these impedances

H03F 1/42

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Informative references

Attention is drawn to the following places, which may be of interest for search:

Distributed amplifiers using coupling networks with distributed constants

H03F 3/605

Eliminating transit-time effects in vacuum tubes

H01J 21/34

Gain control in emitter coupled or cascode amplifiers

H03G 1/0023

Modifications of control circuit to reduce distortion caused by control

H03G 1/04

Muting circuits

H03G 3/26, H03G 3/34

Amplitude limiters

H03G 11/00

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

Current steering cascode

cascode amplifier formed by at least two common gate transistors which are both coupled to the drain terminal of the input common source transistor, in order to steer the current at that terminal among different paths.

Synonyms and Keywords

In patent documents, the following words/expressions are often used with the meaning indicated:

"cascade"

"cascode".

Modifications of amplifiers to reduce influence of noise generated by amplifying elements
References
Limiting references

This place does not cover:

Modifications of amplifiers to reduce influence of variations of supply voltage in case of switching on or off of a power supply, i.e. popping noise reduction

H03F 1/305

Constructional modification of discharge tubes amplifiers

H01J 23/11

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Chopper amplifiers

H03F 3/38

Transmitter circuits with means for limiting noise

H04B 1/0475

Modifications of amplifiers to reduce influence of variations of temperature or supply voltage {or other physical parameters (in differential amplifiers H03F 3/45479)}
Definition statement

This place covers:

Modifications of amplifiers to reduce influence of variations of temperature or supply voltage, or other physical parameters, wherein said modifications comprise:

bias stabilisation circuits

drifting protection circuits

using a switching device and eventually digital means

case of switching on or off a power supply

case of push-pull configuration

References
Limiting references

This place does not cover:

Differential amplifiers characterised by the way of common mode signal rejection

H03F 3/45479

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Push-pull amplifiers

H03F 3/26

Single-ended push-pull (SEPP)

H03F 3/30

Informative references

Attention is drawn to the following places, which may be of interest for search:

Voltage, current regulators

G05F 1/10, G05F 3/02

Muting circuits

H03G 3/26, H03G 3/34

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

Popping noise

audible noise which is present when switching on or off the power supply

Synonyms and Keywords

In patent documents the following expressions are often used as synonyms:

Popping noise

pop effect, plop noise, clic

Modifications of amplifiers to reduce non-linear distortion (by negative feedback H03F 1/34)
Definition statement

This place covers:

Modifications of amplifiers to reduce non-linear distortion, wherein said modifications comprise:

using feedforward circuits

using predistortion circuits, which are implemented with feedback, or via multiple paths, or in audio amplifiers, or with nonlinear elements, or acting on cartesian and polar parameters

case of differential amplifiers

case of single ended push pull amplifiers

References
Limiting references

This place does not cover:

Modifications of amplifiers to reduce non-linear distortion by negative feedback

H03F 1/34

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Analog transmitter circuits with power amplifiers with linearisation using predistortion and using feed-forward

H04B 2001/0425, H04B 2001/0441

Analog transmitter circuits with means for limiting distortions

H04B 1/0483, H04B 1/0475

Digital transmitters using predistortion

H04L 27/367

Special rules of classification

Indexing Code orthogonal classification

In addition to one or more classification symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to orthogonal classification (H03F 2201/3203 - H03F 2201/3236), i.e. covering aspects which are spanning over one or more EC subgroups, should be allocated for the following sub-groups range: H03F 1/32 - H03F 1/3241.

Negative-feedback-circuit arrangements with or without positive feedback (H03F 1/02 - H03F 1/30, H03F 1/38 - H03F 1/50, H03F 3/50 take precedence {; for rejection of common mode signals H03F 3/45479})
Definition statement

This place covers:

Negative-feedback-circuit arrangements with or without positive feedback, wherein said arrangements comprises:

adaptations for reducing the non-linear distortion

hybrid or directional couplers

transformers.

References
Limiting references

This place does not cover:

Differential amplifiers for the rejection of common mode signals

H03F 3/45479

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Analog transmitter circuits with means for limiting distortions

H04B 1/0483, H04B 1/0475

Positive-feedback circuit arrangements without negative feedback
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Generation of oscillation

H03B

Modifications of amplifiers to extend the bandwidth
Definition statement

This place covers:

Modifications of amplifiers to extend the bandwidth, wherein the modifications comprise:

periodic amplifiers

aperiodic amplifiers, i.e. wherein aperiodic means that there is no resonant circuit present.

References
Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Pulse shaping by amplifying

H03K 5/02

Analog transmitter circuits with means for limiting distortions

H04B 1/0483, H04B 1/0475

Optical receivers with bandwidth control

H04B 10/6932

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

Inductive peaking

an inductor is placed in the amplifying circuit to extend the bandwidth of amplification.

Circuit arrangements for protecting such amplifiers {(monitoring arrangements G01R 31/28; increasing reliability in communication systems, e.g. using redundancy H04B 1/74)}
Definition statement

This place covers:

Circuit arrangements for protecting such amplifiers, wherein the arrangements comprises:

using redundant amplifying elements

using protective devices, e.g. diodes.

References
Limiting references

This place does not cover:

Protection from temperature drifting

H03F 1/30

Vacuum tube testing

G01R 31/25

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Monitoring arrangements

G01R 31/28

Analog transmitter details for increasing reliability

H04B 1/74

Informative references

Attention is drawn to the following places, which may be of interest for search:

Emergency protective circuit arrangements

H02H 7/20

Over voltage protection in integrated circuits

H02H 9/046

Frequency-division multiplex system with monitoring arrangements

H04J 1/16, H04J 1/16

Modifications of input or output impedances, not otherwise provided for
Definition statement

This place covers:

Modifications of input or output impedances, not otherwise provided for, wherein said modifications may comprise:

matching and tuning circuits which are specifically designed for RF amplifiers

circuit adaptations in class E,F,E/F amplifiers.

References
Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

High frequency amplifiers

H03F 3/189

Switching amplifiers in general

H03F 3/217

Class E amplifiers

H03F 3/2176

Amplifiers in which coupling networks have distributed constants

H03F 3/60

Informative references

Attention is drawn to the following places, which may be of interest for search:

Matching with passive networks

H03H 7/38

Matching with active networks

H03H 11/28

Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
Definition statement

This place covers:

Electronic amplifiers based on tubes or semiconductors.

Amplifiers are classified according to topology (e.g., push-pull, emitter follower, differential) and/or according to use (e.g., LF, HF) and/or according to the amplifying element (e.g., tubes, tunnel diodes) and/or according to special functionality (e.g., multi-channel amplifiers, gated amplifiers).

Amplifiers with both tubes and semiconductors are classified in H03F 5/00.

Amplifiers based on other amplification principles such as magnetic, dielectric, mechanical/acoustic, superconductivity, etc., are classified in subgroups H03F 7/00-H03F 99/00.

Special rules of classification

A document may be temporarily allocated in the main group H03F 3/00 only for EPO internal circulation, e.g. to receive it from neighbouring field classifiers via the classification code.

{using switched capacitors, e.g. dynamic amplifiers; using switched capacitors as resistors in differential amplifiers (H03F 3/45 takes precedence)}
Definition statement

This place covers:

Amplifiers with switched capacitors used as synthesized resistors.

References
Limiting references

This place does not cover:

Amplifiers with charge pump- or other switched capacitor based power supplies

H03F 1/02

Modulator/demodulator (chopper) amplifiers

H03F 3/38

Chopper/auto-zero amplifiers for offset/noise reduction in differential amplifiers

H03F 3/45

Informative references

Attention is drawn to the following places, which may be of interest for search:

Switched capacitor filters

H03H 19/004

controlled by light
Definition statement

This place covers:

Amplifiers controlled by light, that is, for optically generated or transferred signals, e.g., transimpedance amplifiers for fiber optic links, optical isolation amplifiers.

References
Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Optical receivers

H04B 10/67

{with FET's (H03F 3/085 takes precedence)}
Definition statement

This place covers:

Amplifiers controlled by light, wherein the amplifier comprises FETs, e.g., JFET or CMOS transimpedance amplifiers for fiber optic links.

{using opto-couplers between stages}
Definition statement

This place covers:

Amplifiers controlled by light, wherein the amplifier comprises optically coupled stages, e.g., optical isolating amplifiers.

{with IC amplifier blocks (H03F 3/085 takes precedence)}
Definition statement

This place covers:

Amplifiers controlled by light, wherein the amplifier has functional units such as op-amps, i.e., not showing transistor level circuit details.

with diodes {(parametric amplifiers H03F 7/00)}
Definition statement

This place covers:

Amplifiers using diodes as an amplifying element, e.g., negative resistance diodes such as Gunn, IMPATT, Esaki (tunnel) diodes.

References
Limiting references

This place does not cover:

Switching amplifiers with freewheeling diodes

H03F 3/217

with Esaki diodes
Definition statement

This place covers:

Amplifiers using Esaki (tunnel) diodes as an amplifying element.

with amplifying devices having more than three electrodes or more than two PN junctions
Definition statement

This place covers:

Amplifiers with semiconductor amplifying devices having more than three electrodes, e.g., dual-gate MOSFETs, back-gate controlled MOSFETs, multi-emitter/collector BJTs. Note: by semiconductor amplifying devices is understood transistors; opamps and the like are not included, even if they have more than three terminals. Cascode amplifiers using dual-gate MOSFETs are classified in H03F 1/223.

with field-effect devices
Definition statement

This place covers:

Amplifiers with semiconductor field-effect amplifying devices, e.g., MOSFETs, JFETs, MESFETs.

{with junction-FET's}
Definition statement

This place covers:

Amplifiers with semiconductor junction field-effect amplifying devices, e.g., JFETs, MESFETs (but not MOSFETs).

Low-frequency amplifiers, e.g. audio preamplifiers
Definition statement

This place covers:

Low frequency amplifiers, in most cases which are suitable for amplification of audio signals.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Switching amplifiers

H03F 3/217

Gain control in low frequency amplifiers

H03G 3/3005, H03G 7/002, H03G 7/007, H03G 3/3089

Circuits for loudspeakers, microphones

H04R 3/00

High-frequency amplifiers, e.g. radio frequency amplifiers
Definition statement

This place covers:

High frequency amplifiers, e.g. radio frequency amplifiers, as detailed circuits or integrated circuit blocks.

References
Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Amplifiers in which coupling networks have distributed constant

H03F 3/60

IF amplifier circuits specially adapted for B&W TV

H04N 5/4446

Informative references

Attention is drawn to the following places, which may be of interest for search:

Switching amplifiers

H03F 3/217

High frequency adaptations of semiconductors

H01L 23/66

Gain control in high frequency amplifiers, bandpass amplifiers

H03G 3/3036, H03G 3/3052

Synonyms and Keywords

In patent documents, the following abbreviations are often used:

HBT

Heterojunction Bipolar Transistor

HEMT

High Electron Mobility Transistor

Power amplifiers, e.g. Class B amplifiers, Class C amplifiers (H03F 3/26 - H03F 3/30 take precedence)
Definition statement

This place covers:

Power amplifiers in general. e.g. class B amplifiers, Class C amplifiers, Class D amplifiers, Class E amplifiers, Class F amplifiers, Class G amplifiers, Class H amplifiers, Class S amplifiers, or combination of power amplifiers, or integrated circuits wherein the circuit topology is based on lumped elements.

References
Limiting references

This place does not cover:

Push pull amplifiers

H03F 3/26

Single ended push pull amplifiers

H03F 3/30

Combination of amplifiers in which coupling networks have distributed constant

H03F 3/602

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Multi-channel amplifiers

H03F 3/68

Analog transmitters

H04B 1/02

Digital transmitters

H04L 27/04

Special rules of classification

Documents which are addressing a power amplifier in general are usually not classified in this subgroup, but are allocated to the corresponding subgroups:

Indexing Code deep-indexing classification

In addition to one or more classification symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to deep-indexing classification (H03F 2203/21103 - H03F 2203/21196), i.e. covering embodiment aspects, should be allocated for the following sub-group: H03F 3/211

Class D power amplifiers; Switching amplifiers
Definition statement

This place covers:

Amplifiers using switches as amplifying elements, e.g., class D audio amplifiers, class E, class F, class S RF amplifiers, as well as control circuitry such as PCM-PWM conversion etc.

References
Limiting references

This place does not cover:

Amplifiers with switched-mode (e.g., tracking) power supplies

H03F 1/02

Chopper/auto-zero amplifiers

H03F 3/38; H03F 3/45

Gated amplifiers

H03F 3/72

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

MRI gradient amplifiers

G01R 33/3852

DC-AC converters

H02M 3/00

Deaf-aid sets

H04R 25/00

Stereophonic systems

H04S

Special rules of classification

Multiple classification symbols may be given, e.g., a stereo full-bridge class D audio power amplifier with protection means and anti pop-noise means would be classified in H03F 3/68, H03F 3/2173, H03F 1/52, H03F 1/305, and possibly also somewhere in H04S. A class D MRI gradient amplifier would be classified in both G01R 33/3852 and H03F 3/217. An RF amplifier with a class D amplifier used as a tracking power supply (aka class S) would be classified in the relevant H03F 1/02 sub-group, as well as in H03F 3/217 (provided that the class D amplifier is shown in some detail), and possibly also in H03F 3/189, for example.

{with field-effect devices (H03F 3/2173 - H03F 3/2178 take precedence)}
Definition statement

This place covers:

Switching amplifiers using FET switches as amplifying elements.

{of the bridge type}
Definition statement

This place covers:

Switching amplifiers with half- or full-bridges.

{using analogue-digital or digital-analogue conversion (H03F 3/2173 takes precedence)}
Definition statement

This place covers:

Switching amplifiers for digital input signals, or having explicit ADCs or DACs.

{Class E amplifiers}
Definition statement

This place covers:

Class E RF amplifiers.

References
Limiting references

This place does not cover:

Class F RF amplifiers (see the "Glossary of terms" section above). These are classified in other relevant H03F 3/217 subgroups.

{using more than one switch or switching amplifier in parallel or in series (H03F 3/2173, H03F 3/2175 take precedence)}
Definition statement

This place covers:

Switching amplifiers with one or more switches (e.g., segmented transistors in RF amplifiers) or output stages (such as in staggered phase class D amplifiers) in parallel or in series, cooperating to produce a common output signal.

References
Limiting references

This place does not cover:

Combinations of a switching amplifier and a linear amplifier to produce a single output signal (but a H03F 3/217 sub-group should still be given, by virtue of the switching amplifier).

H03F 3/211

Multi-channel amplifiers

H03F 3/68

with tubes only (H03F 3/24 takes precedence)
Definition statement

This place covers:

Power amplifiers with tubes (thermionic valves only).

References
Limiting references

This place does not cover:

Tube power amplifiers for radio transmitters

H03F 3/24

Tube push-pull amplifiers (two tubes connected to either side of a transformer primary with a center tap connected to a supply voltage and driven out of phase).

H03F 3/28

Tube single-ended push-pull amplifiers (tubes connected in series across two supply rails and the output signal taken at the node common to the tubes)

H03F 3/30

Push-pull amplifiers; Phase-splitters therefor (duplicated single-ended push-pull arrangements or phase-splitters therefor H03F 3/30)
Definition statement

This place covers:

Push-pull amplifiers (see the push-pull configuration in the "Glossary of terms" section above) and phase-splitters therefor, i.e. the phase splitter circuitry which is suitable for driving them.

References
Limiting references

This place does not cover:

Duplicated single-ended push-pull arrangements or phase-splitters therefor

H03F 3/30

Single-ended sense amplifiers

G11C 7/067

Single-ended push-pull {[SEPP]} amplifiers {(single-ended sense amplifiers G11C 7/067)}; Phase-splitters therefor
Definition statement

This place covers:

Single-ended push-pull amplifiers (see the SEPP configuration in the "Glossary of terms" section above) and phase-splitters therefor, i.e. the phase splitter circuitry which is suitable for driving them.

References
Limiting references

This place does not cover:

Switching amplifiers

H03F 3/217

Single-ended sense amplifiers

G11C 7/067

Special rules of classification

It must be noted that the expression "common drain output", which is present in the definition of subgroup H03F 3/301, relates to a common drain configuration for the output transistors (see the "Glossary of terms" section above), therefore it relates to the source terminals of the output transistors being tied together to form the output terminal.

Similar consideration applies for the expression "common source output", which is present in the definition of subgroup H03F 3/3022, and which relates to a common source configuration of the output transistors (see the "Glossary of terms" section above), i.e. the drain terminals of the output transistors being tied together to form the output terminal.

Furthermore, in the following subgroups the expression "symmetrical driving of the end stage" is present:

From a circuital topology point of view, it relates to the presence of symmetry in the driving stage circuitry of the SEPP, i.e. if the driving signal path for one of the output transistor has the same/corresponding/complementary elements of the driving signal path of the other output transistor.

As clarifying example the following circuit topology is shown.

media38.png

Example of SEPP with symmetrical driving of the end stage (drawing extracted from US2002109548).

Mostly of the times the presence of symmetry can be easily detected on the circuit topology by considering a virtual axis (see the dotted line "Symmetry axis" in the drawing above) passing through the output terminal to determine two sub-circuits which are located above and below said axis, respectively, and by examining the similarities/corresponding elements among the two sub-circuits.

If no symmetry is detected then the SEPP circuit is of the type having "asymmetrical driving of the end stage" and it has to be classified in one of the following subgroups:

Furthermore, it must be noted that, when two SEPPs are configured as class B or AB bridges, they are classified in H03F 3/3081 and when they are implemented with FETs they are classified in H03F 3/3061. Switching amplifiers in bridge configuration are classified in H03F 3/2173.

Indexing Code orthogonal classification

In addition to one or more EC symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to orthogonal classification (H03F 2203/30003 - H03F 2203/30156), i.e. covering aspects which are spanning over one or more EC subgroups, should be allocated for this subgroup.

DC amplifiers in which all stages are DC-coupled (H03F 3/45 takes precedence)
Definition statement

This place covers:

DC amplifiers which are formed by IC blocks, semiconductors or tubes, in which all the amplifying stages are DC coupled, e.g. without using capacitive or switching elements, which are not specific for RF amplifiers or audio amplifiers and which have circuit topologies that are not related to other H03F classification symbols.

References
Limiting references

This place does not cover:

Differential amplifiers

H03F 3/45

References out of a residual place

Examples of places in relation to which this place is residual:

Low frequency amplifiers

H03F 3/181

High frequency amplifiers

H03F 3/189

Power amplifiers

H03F 3/20

Informative references

Attention is drawn to the following places, which may be of interest for search:

DC current or voltage control circuits

G05F 3/02

DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers {(switched capacitor amplifiers H03F 3/005)}
Definition statement

This place covers:

DC amplifiers wherein only the AC signal is passed through the amplifying units, the DC signal is decoupled via switching elements, e.g. see the Chopper amplifier configuration in the "Glossary of terms" section above.

References
Limiting references

This place does not cover:

Switched capacitor amplifiers

H03F 3/005

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Switching amplifiers

H03F 3/217

Differential amplifiers

H03F 3/45

Arrangements for measuring bio-electric currents or voltages

A61B 5/24

Arrangements for measuring currents or voltages or for indicating presence or sign thereof by using conversion of dc into ac

G01R 19/18

Informative references

Attention is drawn to the following places, which may be of interest for search:

Modifications of amplifiers to reduce influence of noise generated by amplifying elements

H03F 1/26

Modulation

H03C

Demodulation

H03D

Switched capacitor networks

H03H 19/004

Amplitude modulation of pulses in general

H03K 7/02

Amplitude demodulation of pulses in general

H03K 9/02

Amplifiers with two or more amplifying elements having their dc paths in series with the load, the control electrode of each element being excited by at least part of the input signal, e.g. so-called totem-pole amplifiers
Definition statement

This place covers:

In most cases totem-pole amplifiers, see the "Glossary of terms" section above, which are implemented via semiconductor elements or tubes.

Differential amplifiers (differential sense amplifiers G11C 7/062)
Definition statement

This place covers:

Differential amplifiers in general and characterised by the technology used, the circuit topologies, and the way that the common mode signals are rejected.

References
Limiting references

This place does not cover:

Measuring currents or voltages from sources with high internal resistance by means of measuring circuits with high input impedance, e.g. OP-amplifiers

G01R 19/0023

Operational amplifiers for addition or subtraction in analog calculators

G06G 7/14

Differential sense amplifiers

G11C 7/062

Logic comparators

H03K 5/24

Optical receivers with offset control of the differential preamplifier

H04B 10/6933

Differential drivers

H04L 25/0272

Informative references

Attention is drawn to the following places, which may be of interest for search:

Gain control in emitter coupled or cascode amplifiers

H03G 1/0023

Tuned filters, switched capacitor networks

H03H 7/12, H03H 19/004

Special rules of classification

Pseudo differential amplifiers (see the "Glossary of terms" section above) are usually classified in H03F 3/4508, H03F 3/45179, H03F 3/45278, H03F 3/45376.

Furthermore, it is common practice at EPO, when classifying semiconductor differential amplifiers, to consider first the technology of the amplifying transistors and the circuit topology information, in order to classify under one of the subgroups belonging to H03F 3/45076.

About circuit topology, the expression "Complementary long tailed pairs having parallel inputs and being supplied in parallel" is present in the following subgroups:

As clarifying example the following circuit topology is shown:

media39.png

Example of differential amplifier with complementary long tailed pairs having parallel inputs and being supplied in parallel: the first transistor pair (711,712) and the second transistor pair (721,722) constitute two complementary transistor pairs, which, together with the corresponding current sources (710,720) constitute long tail pairs (see the "Glossary of terms" section above), and wherein said pairs have parallel inputs (see the common input terminals (VinN, VinP) and are supplied in parallel (see the common supplies VDD, VSS), (drawing extracted from US2005040889).

Similar consideration applies to the expression "Complementary PI types having parallel inputs and being supplied in parallel", wherein the complementary transistor pairs are forming differential amplifiers of the PI type, (see the "Glossary of terms" section above), and which are classified in the following subgroups:

About the expression "Complementary long tailed pairs having parallel inputs and being supplied in series", which is present in the following subgroups:

As clarifying example the following circuit topology is shown:

media40.png

Example of differential amplifier with complementary long tailed pairs having parallel inputs and being supplied in series: the first transistor pair (Q221,Q222) and the second transistor pair (Q223, Q224) constitute two complementary transistor pairs, which, together with the corresponding current sources (234,236) constitute long tail pairs (see the "Glossary of terms" section above), and wherein said pairs have parallel inputs (see the common input terminals (VIN-, VIN+) and are supplied in series (see the series connecting path from VD to GND, which is formed by element 234, the first transistor pair (Q221,Q222), the second transistor pair (Q223, Q224), element 236), (drawing extracted from FR2814554).

Similar consideration applies to the expression "Complementary PI types having parallel inputs and being supplied in series", wherein the complementary transistor pairs are forming differential amplifiers of the PI type, (see the "Glossary of terms" section above), and which are classified in the following subgroups:

Once that the technology and the circuit topology related to the differential amplifier are classified, a possible classification under one of the subgroups belonging to H03F 3/45479 has to be considered. It must be noted that the expression "common mode signal rejection", which is present in the definition of subgroup H03F 3/45479, has to be interpreted with a broader meaning than the one used in common practice (see the "Glossary of terms" section above). In practice common mode rejection has to be meant as operating point/DC level control/offset reduction, and said control can be implemented at sub-circuit level.

Hence all the subgroups of H03F 3/45479 are addressing all the possible implementations of said common mode rejection within the sub-circuits that are forming the differential amplifier architecture (for a detailed definition of said sub-circuits see the following section).

Indexing Code orthogonal classification

In addition to one or more EC symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to orthogonal classification (H03F 2203/45002 - H03F 2203/45732), i.e. covering aspects which are spanning over one or more EC subgroups, should be allocated for this subgroup.

Said aspects are mainly based on the following sub-circuits, which can be determined in a long tailed pair, PI type, and, although with limitations, in special types of differential amplifiers, e.g. pseudo-differential amplifier:

AAC = Active Amplifying Circuit, i.e. the elements comprising the amplifying transistors.

CSC = Common Source Circuit, i.e. the elements forming the long tailed circuit or the PI circuit.

IC = Input Circuit, i.e. the elements coupled to the input terminals of the amplifying transistors.

LC = Loading Circuit, i.e. the elements coupled to the output terminals of the amplifying transistors.

CMCL = Common Mode Controlling Loop, i.e. the elements which are controlling the common mode(s) of the differential amplifier.

FBC = Feed-Back Circuit, i.e. the elements which are introducing feedback signal(s) for the differential amplifier.

Here is an example of some of said sub-circuits above for a long tailed differential pair.

media41.png

drawing derived from US2006055463

Reflex amplifiers {(reflection amplifiers H03F 3/608)}
Definition statement

This place covers:

Reflex amplifiers, see the "Glossary of terms" section above, which are implemented via semiconductor elements or tubes.

References
Limiting references

This place does not cover:

Reflection amplifiers

H03F 3/608

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Receivers comprising at least one semiconductor device having three or more electrodes

H04B 1/24

Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
Definition statement

This place covers:

Amplifiers in cathode follower, source follower, emitter follower configuration (see the "Glossary of terms" section above).

References
Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Delay circuits

H03K 5/13

Special rules of classification

Indexing Code deep-indexing classification

In addition to one or more classification symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to deep-indexing classification (H03F 2203/5003 - H03F 2203/5045), i.e. covering embodiment aspects, should be allocated for this subgroup.

Amplifiers using transit-time effect in tubes or semiconductor devices (parametric amplifiers H03F 7/00; solid state travelling-wave devices H10N 70/10)
Definition statement

This place covers:

Amplifiers using transit-time effects, mostly Klystrons or Travelling Wave Tubes (TWT) see the "Glossary of terms" section above.

References
Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Solid state travelling-wave devices

H10N 70/10

Informative references

Attention is drawn to the following places, which may be of interest for search:

Parametric amplifiers

H03F 7/00

Travelling wave tubes in general

H01J 25/34

Resonators of the waveguide type

H01P 7/00

Amplifiers in which coupling networks have distributed constants, e.g. with waveguide resonators (H03F 3/54 takes precedence)
Definition statement

This place covers:

Amplifiers having distributed coupling networks, e.g. transmission lines, the so called microwave amplifiers.

References
Limiting references

This place does not cover:

Amplifiers using transit-time effect, e.g. TWTA

H03F 3/54

Parametric amplifiers

H03F 7/00

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Class E amplifiers

H03F 3/2176

Reflex amplifiers

H03F 3/46

Multi-channel amplifiers

H03F 3/68

Aerials or aerial systems providing at least two radiating patterns, beam-forming means

H01Q 25/00, H01Q 3/40

Informative references

Attention is drawn to the following places, which may be of interest for search:

Modification of amplifiers by use of distributed coupling, i.e. distributed lumped elements

H03F 1/18

Amplifiers having more than three electrodes with field-effect devices

H03F 3/16

High frequency amplifiers

H03F 3/189

High frequency adaptations of semiconductors

H01L 23/66

Coupling devices of the waveguide type

H01P 5/00

Two-way amplifiers
Definition statement

This place covers:

Two-way amplifiers, which are implemented via semiconductor elements or tubes and which are typically employed to amplify the signal levels of forward and reverse signals.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Multiport networks

H03H 7/48

Hybrid arrangements for transceivers

H04B 1/58

Intermediate station arrangements for frequency-division multiplex systems

H04J 1/10, H04J 1/10

Amplifiers simultaneously generating oscillations of one frequency and amplifying signals of another frequency
Definition statement

This place covers:

Amplifying-mixing devices for achieving a special technical effect, e.g. interference reduction.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Modifications of amplifiers to reduce non-linear distortion

H03F 1/32

Transference of modulation from one carrier to another

H03D 7/00

Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics {(power amplifiers using a combination of several semiconductor amplifiers H03F 3/211; combinations of amplifiers using coupling networks with distributed constants H03F 3/602)}
Definition statement

This place covers:

Stereo amplifiers or multi-channel amplifiers in the low frequency range.

Multi-band amplifiers in the high frequency range, wherein multiple outputs are present.

References
Limiting references

This place does not cover:

Aerials, beam-forming means

H01Q 25/00, H01Q 3/40

Circuits for stereophonic arrangements

H04R 5/04

Informative references

Attention is drawn to the following places, which may be of interest for search:

Low frequency amplifiers

H03F 3/181

Power amplifiers using a combination of several semiconductor amplifiers

H03F 3/211

Switching amplifiers

H03F 3/217

Combinations of amplifiers using coupling networks with distributed constants

H03F 3/602

Charge amplifiers
Definition statement

This place covers:

Charge amplifiers, see the "Glossary of terms" section above.

References
Limiting references

This place does not cover:

Charge pumps for DC/DC power converters

H02M 3/07

Charge pumps for automatic control of frequency or phase circuits

H03L 7/0891

Application-oriented references

Examples of places where the subject matter of this place is covered when specially adapted, used for a particular purpose, or incorporated in a larger system:

Measuring acceleration by piezoelectric pick-up

G01P 15/09

Integrators using operational amplifier and capacitor and resistor in the feedback loop

G06G 7/186

Sense amplifiers

G11C 7/06

Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
Definition statement

This place covers:

Amplifiers which are enabled or disabled by means of a control signal, e.g. via a controlled switch.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Gain control in amplifiers

H03G 3/00

Electronic switching or gating

H03K 17/00

Special rules of classification

Indexing Code deep-indexing classification

In addition to one or more classification symbols relating to the invention information, where appropriate, one or more Indexing Code symbols relating to deep-indexing classification (H03F 2203/7203 - H03F 2203/7239), i.e. covering embodiment aspects, should be allocated for this subgroup.

Parametric amplifiers
Definition statement

This place covers:

Parametric amplifiers, i.e. wherein a component parameter such as capacitance or inductance is varied to achieve amplification.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Amplifiers using superconductivity effects

H03F 19/00

Devices or arrangements for the parametric generation or amplification of light, infrared or ultraviolet waves

G02F 1/39

using variable-inductance element; using variable-permeability element
Definition statement

This place covers:

Parametric amplifiers where inductance/permeability is varied to achieve amplification.

using variable-capacitance element; using variable-permittivity element
Definition statement

This place covers:

Parametric amplifiers where capacitance/permittivity is varied to achieve amplification.

Magnetic amplifiers
Definition statement

This place covers:

Amplifiers using saturable reactors as amplifying elements (aka mag-amps).

current-controlled, i.e. the load current flowing in both directions through a main coil
Definition statement

This place covers:

Magnetic amplifiers where an AC load current flows in a main coil, controlled by the current in a control coil.

voltage-controlled, i.e. the load current flowing in only one direction through a main coil, e.g. Logan circuits (H03F 9/06 takes precedence)
Definition statement

This place covers:

Magnetic amplifiers where a load current flows in one direction in a main coil, and typically in the other direction in another main coil, controlled by the current in a control coil, e.g., a control coil in a center leg of a transformer controlling two main coils in two outer legs.

Control by voltage time integral, i.e. the load current flowing in only one direction through a main coil, whereby the main coil winding also can be used as a control winding, e.g. Ramey circuits
Definition statement

This place covers:

Magnetic amplifiers where the load current is auto-commutated by the main coil, the core being periodically reset by a control coil.

Dielectric amplifiers
Definition statement

This place covers:

Amplifiers using non-linear (hysteretic) dielectric elements to achieve amplification.

Amplifiers using amplifying element consisting of two mechanically- or acoustically-coupled transducers, e.g. telephone-microphone amplifier
Definition statement

This place covers:

Amplifiers with intermediate mechanical or acoustic energy transfer .

Amplifiers using galvano-magnetic effects not involving mechanical movement, e.g. using Hall effect
Definition statement

This place covers:

Amplifiers relying on galvano-magnetic effects, i.e., which arise when a conductor or semiconductor placed in a magnetic field carries current, such as the Hall-effect.

Amplifiers using electroluminescent element or photocell
Definition statement

This place covers:

Amplifiers relying on intermediate transformation into light to achieve amplification.

References
Limiting references

This place does not cover:

Amplifiers controlled by light, e.g., for fiber optic links

H03F 3/08

Amplifiers with optical coupling between stages

H03F 3/085

Subject matter not provided for in other groups of this subclass
Definition statement

This place covers:

Amplifiers not covered elsewhere, e.g. relying on radioactivity or using esoteric semiconductor structures.