Abstract: Circuits for continuously varying the gain control for a low noise amplifier (LNA) of a wireless receiver are described. The gain, input third order intercept point (IIP3) and noise figure (NF) of an LNA are continuously varied according to the received power levels, causing the receiver to utilize less current at different power levels. At high gain levels the IIP3and NF are at a minimum, while at low gain levels the IIP3and the NF are at a maximum. By continuously varying the gain of an LNA throughout the operational range, the present invention achieves wider dynamic range and higher power efficiency. According to one aspect, the present invention includes a power coupler and a power detector which are utilized to produce a rectified voltage which is proportional to the input power or output power of an LNA. The rectified voltage is utilized by a control circuit which produces a signal which controls the gain, IIP3and NF of the LNA.

Abstract: A variable gain amplifier comprises a main amplifier circuit whose gain is controllable and which amplifies a difference signal between an input signal and a feedback signal, a feedback amplifier circuit whose gain is controllable and which amplifies an output signal of the main amplifier circuit, and a gain control circuit which complementarily control the gain of the main amplifier circuit and the gain of the feedback amplifier circuit.

Abstract: In an automatic level controlling circuit, an output from a full-wave rectifying circuit 12 is supplied to a first and a second time constant circuit. The first time constant circuit includes a first amplifier 22 and a capacitor 15. The second time constant circuit includes a second amplifier 23 and the capacitor 15. The first amplifier 22 operates when the output V1 from the full-wave rectifying circuit 12 is larger than a DC level VDC. In this configuration, the attack times when an input signal is switched from no signal into a middle level signal and when the input signal is switched from the middle signal into a high level signal can be set at optimum values, respectively.

Abstract: A limiter circuit is provided for limiting the output from a comparing circuit so that the attenuating characteristic curve of an amplifying circuit 11 relative to a detected voltage Vo has an inflection point. Namely, since the limiter circuit serves to limit a difference voltage between the outputs from differential transistors, it reduces the sensitivity of the attenuating characteristic within a region from a high level signal to a middle level signal. Thus, the detected voltage Vo increases for acquiring the same attenuating amount so that the recovery time can be prolonged. Further, another limiter circuit is provided for fixing a detected voltage Vo at a prescribed DC voltage when the input signal exceeding a cover range for automatic level control is supplied to the input terminal. The limiter circuit operates to fix the output signal at a DC voltage VL when the input signal exceeds the cover range and enters the range where the level of the output signal starts to rise.

Abstract: Voltage-induced hum modulation in an amplifier can be caused when shunt capacitors begin to saturate and enter their non-linear region of operation. Bypass coils within the amplifier are magnetically coupled to the shunt capacitors and exacerbate hum modulation by coupling additional energy to the shunt capacitors. By introducing a resistance (R) in series with the shunt capacitors (C), energy that would normally be stored in the shunt capacitors (C) is dissipated. As a result, the shunt capacitors (C) remain in their linear region of operation more often and present a more stable impedance. The resistor (R) is especially beneficial at reducing hum modulation at the resonant frequency of the shunt capacitors (C), when the transfer of energy from the bypass coils (L) is at a maximum.

Abstract: To make variable time constant of an AGC loop of an AGC circuit, there is provided an AGC circuit including a control circuit for controlling a level of an input signal and outputting an output signal, a rectifying circuit for rectifying the output signal from the control circuit and outputting a voltage V DET having a level in correspondence with a level of the output signal and a voltage to current converting circuit for converting the output voltage V DET from the rectifying circuit into a current. The voltage to current converting circuit is constituted to provide a differential amplifier supplied with the output voltage V DET from the rectifying circuit. A current I DET outputted by the differential amplifier is converted into AGC voltage V AGC by being supplied to a capacitor. By the AGC voltage V AGC, AGC is carried out by controlling the level of the input signal at the control circuit.

Abstract: Method for automatically controlling a controlled variable. In a feedback control process, a control loop is used to compare the controlled variable with a command variable that determines the setpoint of the controlled variable and minimizes a deviation between setpoint and actual value of the controlled variable with the help of a manipulated variable that acts on the controlled variable. A disadvantage of this process is the transient behavior of the control loop due to temperature influences and degradation phenomena. The method according to the invention is intended to prevent a change in the transient behavior of the control loop. In accordance with the invention, the loop gain (A) of the control loop (1) is regulated to a value at which the actual value of the controlled variable (x) overshoots the setpoint value (s) by a predetermined tolerance value (m) as the result of a pulse-shaped change in the command variable (w).

Abstract: A power supply circuit for a power amplifier of a mobile radio communication terminal, the power amplifier being suitable for delivering transmitter power that can present variations that are relatively fast and variations that are relatively slow, the power supply circuit essentially comprising:an active three-pole power device for controlling said power amplifier, the device receiving both a control voltage that is a function of said relatively fast variation and an active three-pole device power supply voltage, and delivering to said power amplifier a given power supply current at a given voltage referred to as the power supply voltage for said power amplifier; andmeans for generating the power supply voltage for said active three-pole device, and suitable for delivering to said active three-pole device a power supply voltage that is variable in such a manner that for a given value of said transmission power that is subject to relatively slow variations, the voltage drop across the terminals of said active

Abstract: In an output signal level control circuit, a level adjusting section receives an input signal to adjust the input signal in level in response to a level control signal. A branching circuit branches a portion of the input signal adjusted in level by the level adjusting section to produce a branched signal. A detecting section includes the first and second detecting sections and generates a detection resultant signal based on a first detection result of the branched signal by the first detecting section and a second detection result of the branch signal by the second detecting section. The first and second detecting sections are operable at a same time. A control signal generating unit generates the level control signal based on the detection resultant signal to output to the level adjusting section.

Abstract: A method for acquiring rapid automatic gain control (AGC) response in a narrow band receiver teaches opening the AGC loop (100), setting the gain control signal (106) amplitude of the AGC amplifier stage (104) to a known value, altering the gain control signal (106) amplitude over time, and monitoring the narrow band receiver for an output signal (112). Upon output signal (112) detection, halting alteration of the gain control signal (106) amplitude, closing the AGC loop (100) and commencing normal operation. A particular facet of this approach suggests detecting the output (112) with a varying gain detector (116,132) after the loop (100) is closed and before normal operations are commenced.

Abstract: A power control loop for a radio frequency transmitter includes a power control amplifier, an output and a detector that is coupled to the output for providing an output power signal indicative of output power from the power control loop. A controller generates at least first and second reference signals. A differential amplifier provides a control output that is indicative of a difference between the output power signal and a reference signal. A dual rate filter couples the control output to the power control amplifier so as to vary its gain. The dual rate filter exhibits a fast-reacting filter mode when the controller changes the reference signals to the differential amplifier and a slow-reacting filter mode when the controller applies the first reference signal to the differential amplifier. The fast filter mode enables rapid feedback of the control output to the power control amplifier.

Abstract: An automatic gain control (AGC) and D.C. offset correction method and apparatus for controlling signal power of a received RF signal within a dual mode quadrature receiver is disclosed herein. In a preferred implementation the automatic gain control apparatus may be adjusted to provide a desired control response to various fading characteristics of a received FM, FSK, GMSK, QPSK, or BPSK signal. The AGC apparatus includes an adjustable gain amplifier having an input port for receiving an input signal, a control port for receiving a gain control signal, and an output port for providing an output signal. A quadrature downconverter coupled to the output port serves to translate the frequency of the output signal to a baseband frequency, thereby producing baseband signals. In a preferred implementation the downconverter is operative to map the carrier frequency of the output signal to a baseband frequency offset by a predetermined margin from D.C.

Abstract: An automatic gain control (AGC) apparatus for a digital receiver is disclosed herein. The AGC apparatus includes an adjustable gain amplifier having an input port for receiving an input signal, a control port for receiving a gain control signal, and an output port for providing an output signal. The AGC apparatus further includes a measurement circuit for generating a received power signal based on the power of the output signal. A saturating integrator compares the received power signal to a reference signal and generates an gain control signal in response to a result of the comparison. The saturating integrator includes a decision circuit for enabling integration based on values of the received power signal, the reference signal, and the gain control signal. In a preferred implementation the utilization of an input limiter in conjunction with an analog to digital converter enables accommodation of an increased input signal dynamic range.

Abstract: A frequency discriminate leveler ("FDL") which controls its attack rate depending on the audio frequency to more perfectly preserve the natural sound of the audio program while very effectively controlling the long term average program level. The FDL has a function to attack more slowly for low frequency signals than for high frequency signals. The FDL includes a gain controller, an FDL control generator and a leveling detector. The gain controller coupled to an input signal and an output signal. The input signal is the unleveled audio program which can vary widely in average level. The output signal is the leveled signal which contains a more constant average level. The FDL control generator generates a suitable control output to cause the gain controller to increase or decrease gain. The FDL control generator is coupled to the leveling detector for the purpose of receiving the output of the leveling detector, and generating a control output to control the gain of the gain controller.

Abstract: An RF power amplifier is provided having means for defining rise and fall envelopes of the RF power, i.e. the key and de-key characteristics. A power amplifier (10), detector (13) and regulator (15 ) form a power control feedback loop. A further regulator (21) is provided having a first input coupled to the output of the power control loop regulator and an output coupled to the input of the power control loop regulator, thereby providing negative feedback to the power control loop regulator. Means are provided, coupled to a second input of the further regulator for providing a rising and falling control signal (Vramp) for control of the power amplifier.

Abstract: A method and apparatus incorporating a single self-compensating diode power detector in the feedback loop of a pulsed amplifier for exploiting the discontinuous nature of the pulsed amplifier to extract any thermally induced error voltage by a single power detector between the transmission bursts and use it to correct the power detector voltage during the bursts to obtain a true power indicative voltage, independent of temperature variation.

Abstract: An automatic gain controller includes a signal detector receiving an output signal from an amplifier for converting the signal into a DC current changing according to the output signal; first and second time-constant controllers receiving the DC current for removing an AC component to produce first and second pure DC components with different, predetermined time-response characteristics; a voltage subtracter receiving and subtracting the first and second pure DC components to produce a resultant voltage; a voltage comparator for comparing the resultant voltage with a predetermined reference voltage; a switch responsive to the voltage comparator for controlling transmission of the first pure DC component; a voltage sink for discharging the first pure DC component when the switch is closed; and a control voltage amplifier receiving the first pure DC component when the switch is open for producing an output signal to control the gain of the receiving amplifier.

Abstract: An information signal output apparatus is adapted, when controlling the amplitude of an input information signal to be a predetermined level, to control the speed of response of the amplitude control in accordance with the status of the input information signal. The apparatus is thereby able to output an input information signal without deteriorating the signal.

Abstract: Controlling transient responses in power amplifiers may be accomplished in the following manner. Upon detecting an output power adjustment request, a reference level is accessed from memory, wherein the reference level is based on a previous output condition that is substantially equal to the requested output condition. From the reference level, a first response time is calculated and supplied to a control circuit of the power amplifier such that the power amplifier operates at a first gain level. When the first response time elapses, the power amplifier operates at a second gain level, where the first gain level is greater than the second gain level.

Abstract: The normally slow rise time of a Class C bipolar transistor grounded base RF power amplifier is greatly enhanced by circuitry external to the amplifier transistor. Current is injected into the base of the transistor for the duration of the rise time, biasing it into Class A operation during this period. Then, after the base current injection, operation reverts to Class C to retain amplifier power efficiency. Finally, the normally slow fall time of the bipolar Class C RF power amplifier is greatly enhanced by reverse-biasing the base-to-emitter junction during the fall time. During this fall time the amplifier is forced into its cutoff region by the applied reverse bias, as stored charge is pulled out of the base-emitter region of the transistor. In this manner, the power efficiency advantage of Class C power amplifiers may be retained, while adding the benefits of sharper output rise and fall times that would not otherwise be achieved.

Abstract: An amplifier arrangement suitable for use in a receiver for use in a telecommunications system is described. The arrangement includes an amplifier and an FET switch arrangement arranged to alter the time constant of the amplifier in dependence upon the incident signal frequency. A balance switch arrangement is arranged such that switching transients of the switch arrangement are cancelled out in the amplifier arrangement.

Abstract: A controlled power amplifier system (211) wherein a sample (225) of the output power level of an on/off switched power amplifier (215) is compared with a reference signal (227) to produce a power level control signal (275) that controls the output power level of the power amplifier (215). When the power amplifier (215) is switched off, the control signal (275) is maintained at the level it had just prior to the transition from an on to an off state. The switching is performed offset from the ends of each switched power amplifier pulse envelope to allow the pulse amplitude to be leveled in the center of the pulse and yet allow the pulse rise and fall times of the pulse envelope to follow the power amplifier input.

Abstract: The present invention concerns apparatus having a voltage controlled amplifier wherein the gain of the amplifier is determined in response to the level of a control signal at an input terminal. A first rate of change is used for a change of gain from a low signal level to a higher signal level, and a second rate of change is used for a change from a high signal level to a lower signal level with the second rate being faster than the first rate.

Abstract: A voltage limiting circuit is disclosed for preventing distortion in amplified audio signals. Clipping of the output of a power amplifier is detected and a clipping signal is integrated in a two-step process for limiting a bass frequency gain and limiting a wideband frequency gain which are applied in series. Separate limiting thresholds cause the bass gain to be limited first. Wideband gain is reduced at higher levels of clipping but is more quickly restored when clipping stops. Voltage limiting feedback is provided using inexpensive RC integrator circuits.

Abstract: A gain of a variable gain amplifier circuit is controlled by applying a signal of a predetermined voltage level to the variable gain amplifier circuit during an idle period of an ultrasonic receiving signal, deriving an output from the variable gain amplifier circuit, comparing it with a voltage level obtained as an aimed value by a gain regulator or other control circuit of an ultrasonic signal amplifier circuit including the variable gain amplifier circuit and producing a gain control signal according to a difference resulting from the comparison to control the gain to the aimed value until the difference becomes zero. The gain of the variable gain amplifier circuit set in the idle period is maintained during a measurement period of a subsequent receiving signal so that the latter is amplified with the maintained gain. Thus, a stepwise and selective gain setting corresponding to the aimed value can be obtained by controlling the gain of the variable gain amplifier according to the aimed value.

Abstract: A gain control circuit (10) of an amplifier (3) for listening via a loudspeaker (4) in an apparatus, more specifically a telephone set, which includes a microphone (1), in order to suppress the Larsen effect. The gain control circuit comprises first control means (100) which control a first gain reduction of the amplifier (3) when the amplitude of the microphone signal (S) exceeds a first predetermined threshold determined by a first reference voltage VR1, in dependence on a first time constant (RD1+RD2.C). The gain control circuit also includes second control means (200) which start operating only after the said first time constant, and provide a supplementary reduction of the gain depending on a second time constant (RD2.C) which is shorter than the first time constant, as long as the amplitude of the microphone signal (S) exceeds a second threshold, which is lower than the first threshold, determined by a second reference voltage VR2.

Abstract: The present invention is directed to an automatic power control circuit for a signal power amplifier which maintains the output power to one of a plurality of output power levels. The output power level is controlled by an externally-generally level control signal which is used by a square wave signal generating circuitry for controlling the duty cycle of the generated square wave. The square wave is integrated by a filter network to produce a reference voltage level. The output voltage level of the RF amplifier is compared with the reference voltage level, and the difference between the two signals is used to control a drive circuit for generating the proper control voltage for controlling the RF amplifier so that the desired output power level is maintained.

Abstract: The invention relates to an automatic gain control circuit, preferably in magnetic recording and/or reproducing equipment, having a first input (1) and a second input (3). The impedance at output (5) of the automatic gain control circuit, when activated, is reduced to control the levels of the signals applied to the first input (1) and the second input (3), which impedance reduction in the case of actuation in response to signals applied to the first input is effected with a smaller time constant than in the case of actuation in response to signals applied to the second input. An audio signal without high frequency pre-emphasis is applied to the first input (1) and the same signal with high-frequency pre-emphasis is applied to the second input.

Abstract: A circuit for automatically controlling the operation of a variable gain control circuit in an audio signal processing system by verifying whether gain change is desirable and then gating the operation of the gain control circuit is disclosed. A pair of operational amplifiers along with a set of four diodes produce two equal absolute value signals representing a full wave rectified version of the audio input signal. A first filter circuit processes one of the absolute value signals to produce a third signal corresponding to average signal amplitude. A second filter circuit processes the other absolute value signal to produce a fourth signal corresponding to an average of peak values. A comparator compares the third and fourth signals and produces an output signal which is used as the control signal for controlling the variable gain control circuit.

Abstract: A gain control circuit, which has particular utility in a compressor or expander of a noise reduction circuit, is comprised of first and second detectors for detecting the output signal from a variable gain amplifier and providing respective detector outputs for charging first and second capacitors, respectively. Such first and second capacitors have discharge paths in which first and second resistors are respectively interposed, and the charge on the first capacitor is employed as a control signal for determining the gain of the variable gain amplifier. Further, the first resistor is connected between the first and second capacitors so that the discharge current through the first resistor is dependent on the difference between the charge voltages on the first and second capacitors, whereby a relatively long recovery time can be obtained without adversely affecting the attack time even when the input signal to the variable gain amplifier is of low level.

Abstract: An AGC amplifier having a fast response for recovery and reacquisition of gain control in microseconds after a signal break including a first and second amplifiers interconnected by a delay line equalizer. An integrator control loop is responsive to the output of the second amplifier and is connected to the control means provided on the first amplifier and includes a feedback loop having a peak detector, an ideal integrator connected to the output of the peak detector and directly controlling the first amplifier using an ideal integrator capacitor loop during control operation and having a switch removable reset loop for operating as a fixed high gain amplifier in the absence of signal. The latter is determined by a comparator operating to receive a second peak detector signal not in the control loop.

Abstract: A signal conditioning system is disclosed for modifying the dynamic range of an electrical input signal. The system comprises gain control means for controlling the gain of the input signal as a function of a gain control signal, and control signal generating means for generating the gain control signal. In accordance with one aspect of the present invention the control signal generating means comprises (1) means for generating a first signal as a function of the amplitude of the input signal, and (2) means responsive to the first signal for generating the gain control signal as a function of only those portions of one polarity of the time derivative of the first signal. In accordance with another aspect of the present invention means are provided for substantially lengthening and/or linearizing the release behavior of the control signal waveform applied as the control signal input signal to the gain control means.

Abstract: A resistance-capacitance filter smoothes the control voltage of an audio signal expander. An analog gate couples the greater, in a given sense, of the smoothed control voltage and a further voltage to the control terminal of a variable gain device in the audio signal path, the further voltage being equal to the filter input voltage less a constant equal to Vbe. A time constant modifier circuit reduces the filter time constant when the filter input voltage differs in either sense from the smoothed control voltage by a fraction, less than unity, of Vbe. The resultant, relatively "narrow" dead zones of the adaptive filter enable operation of the expander with relatively low signal voltage levels thereby enabling a corresponding reduction in supply voltage requirements and providing further advantages such as reduced power dissipation, reduced heat build-up and improved reliability.

Abstract: A transmitter power control circuit which provides normal power control functions, and provides a high speed loop response when abrupt changes in output power are required. The circuit utilizes an electronic switch to provide adaptive filtering to permit narrow bandwidth filtering during normal steady state operation of the transmitter and wide bandwidth filtering during desired abrupt changes in transmitter power output. This allows rapid changes in transmitter output power when desired, while substantially eliminating undesired noise during normal operation.

Abstract: The invention relates to a circuit arrangement in a compander system for generating a direct control voltage which is dependent on an alternating voltage with the circuit arrangement including a time constant switch. The conductance determining the time constant in a charging current circuit is constantly varied in the transfer range in dependence on the voltage of a charging capacitor when a time constant switch takes place from one fixed value to a second fixed value.

Abstract: A gain control circuit, which has particular utility in a compressor or expander of a noise reduction circuit, is comprised of first and second detectors for detecting the output signal from a variable gain amplifier and providing respective detector outputs for charging first and second capacitors, respectively. Such first and second capacitors have discharge paths in which first and second resistors are respectively interposed, and the charge on the first capacitor is employed as a control signal for determining the gain of the variable gain amplifier. Further, the first resistor is connected between the first and second capacitors so that the discharge current through the first resistor is dependent on the difference between the charge voltages on the first and second capacitors, whereby a relatively long recovery time can be obtained without adversely affecting the attack time even when the input signal to the variable gain amplifier is of low level.

Abstract: In a signal expander, the envelope of an input signal to be expanded is detected and applied as a control signal to the gain control input of a variable gain device which expands the input signal. The control signal is applied to the variable gain device via an adaptive filter having improved ripple reduction and transient performance characteristics to minimize audibility of gain changes. The adaptive filter includes a low pass filter for producing a smoothed control signal essentially free of ripple and an analog gate for coupling the greater of the smoothed signal or a further signal to the variable gain device, the further signal being equal to the detector output signal less a constant. Compression of an input signal is provided by applying the input signal to the non-inverting input terminal of an amplifier and coupling the (compressed) output signal of the amplifier to its inverting input terminal via the expander.

Abstract: An automatic gain control circuit comprising a gain-controlled amplifier for receiving a variable amplitude, pulse-type input signal to produce a substantially constant amplitude, pulse-type output signal which is applied to a feedback circuit for comparison with a predetermined reference voltage to generate a control voltage to set the gain of the amplifier. A voltage limiter included in the feedback circuit clips the pulse peaks of the output signal whenever the peaks exceed a predetermined amplitude so that the gain of the amplifier is reduced in a prescribed manner to preclude output signal dropout. A peak detector and a filter included in the feedback circuit are capable of operating in fast and slow modes. When operating in the fast mode, the peak detector responds essentially to each pulse peak of the output signal and the filter has a wide bandwidth so that the automatic gain control circuit operates with a prescribed fast time response.

Abstract: A non-linear filter which reduces high signal-to-noise ratio due to sharp and erratic variations in an input signal by charging a storage capacitor through a long time constant charging circuit so that the stored signal level lags an increasing input. A parallel path with a much lower time constant rapidly discharges the capacitor upon input decreases, so that the stored signal matches the more accurate lower input signal level. A practical application is for car space measurements in railroad yard storage tracks to substantially reduce erratic distance measurements due to poor shunting under moving cars. The distance measurement signal is applied through an integrator network to a first of four FET operational amplifiers, whose input and feedback networks have selected time constants to substantially filter out background noise due to the track signal frequency.

Abstract: An automatic gain control circuit includes a VCA, an AGC detector and an AGC time constant circuit which form an AGC loop. The AGC circuit further includes a level detector and a time constant designator. When the level detector detects an excess level of a signal derived from the VCA, the designator changes the time constant of the time constant circuit.

Abstract: A wide-band transistorized amplifier including between two line couplers a cascade of stages of amplification and a negative feed-back quadripole connecting the output from the last stage of the cascade to the input to the first, and including a stage of correction by forward gain control, which is arranged in parallel across one of the stages of the cascade, which is connected to one of the couplers, characterized by the fact that the stage (10, 12) of the cascade, across which the correction stage is arranged in parallel, introduces a phase reversal, and that the correction stage includes a CE transistor (20, 20', 20") the base of which is connected on the one hand through an inductive phase-shift impedance (19, 19', 19") to the input to the said stage (10, 12) of the cascade, and on the other hand through a resistor (23, 23', 23") to the output from the said stage of the cascade, and the collector of which is connected through the putting in parallel of a resistor (21, 21', 21") and a capacitor (22, 22', 2

Abstract: In a circuit which matches the speaker input signal in a car radio to the then-present noise level, an additional RC circuit is interconnected between the speaker input terminal and the input of the volume control element. Sudden increases in the speaker input voltage following a modulation pause which cause a high increase in the gain of the volume control circuit will counteract this gain, thereby preventing the excessive increase in speaker sound output following such a modulation pause which took place in the known circuits. Zener diodes to limit the voltage at the volume control elements in dependence upon the battery output voltage and to a value such that the output stage driving the speaker will not be overdriven are also provided.

Abstract: Signals carried over a multiplexed transmission medium between first and second stations suffer transmission losses such that the signal one station generates has a substantially greater magnitude than the signal it receives from the other station. A differential amplifier is utilized to extract and amplify the weaker signal thereby establishing signal balance. Following the differential amplifier is an automatic gain control stage which includes novel sample and hold and activity checker circuitry. The activity checker responds to the frequency of input signals to either allow variable gain control action or, when the frequency is representative of noise, to hold the gain control at its instantaneous value prior to the onset of noise.

Abstract: A regulation device for controlling the level of a signal having a controllable amplification, the signal fluctuating in amplitude, includes a signal control device, first and second threshold stages postcoupled to the signal control device having first and second thresholds, respectively, which thresholds define a predetermined signal range, and an element chargeable and dischargeable to first and second potentials, respectively, postcoupled to the threshold device, and connected by feedback to the signal control device for controlling its amplification within the predetermined range.

Abstract: An improved signal expansion system and technique is disclosed. The system comprises a detector for sensing an input signal and for producing responsively thereto a D.C. control signal having an amplitude as a function of the input signal, and a gain control amplifier for amplifying the input signal, the amplifier including means for controlling the gain of the amplifier as a function of the amplitude of the control signal. The improvement comprises means for varying the amplitude of the D.C. signal at least in part as a function of the time derivative of that amplitude.

Abstract: Apparatus for controlling the gains of a pair of gain-matched amplifiers includes means for applying to each amplifier a pilot tone in the form of an exponentially-decaying periodic signal. The apparatus also includes three control loops, one for comparing the output of one amplifier with a reference signal to derive an error signal used to control the amplifier gains when the pilot tone is absent, and a second for controlling the gains when the pilot tone is present. The third loop subtracts the outputs of the two amplifiers and uses the resulting error signal in conjunction with one or other of the signals from the other two loops to control the gain of one of the two amplifiers.

Abstract: A circuit determines whether the signal transmitted by a variable-gain amplifier comprises information or not. If it comprises information, its level is regulated, by comparison with a first reference signal, in order to give a predetermined correct listening level at the output of the receiver. If it does not comprise any, its level is regulated, by comparison with a second reference signal, in order to give at the output of the receiver the listening level corresponding to the hearing threshold.

Abstract: The invention relates to a circuit arrangement for adjusting the volume of an automobile radio receiver in dependence on road noise, comprising a microphone which picks up the noise and emits an electric signal which is conducted by way of an amplifier, a rectifier and a time-controlled circuit, to a control-adjustment member contained in the low frequency channel of the receiver.

Abstract: An apparatus for effecting automatic gain control comprises an attenuator employing pin junction diodes, a high-frequency amplifier employing a bipolar type automatic gain controlling transistor or a MOS-FET which is always supplied with automatic gain control signals, and switching means for selectively applying automatic gain control signals to the attenuator, thereby permitting increase of the gain control variable without deteriorating the noise factor and the cross modulation characteristic of the signal.

Abstract: A sound motion picture camera with sound recording equipment rendering it possible to record sound accompaniments by way of a magnetic track on the picture film and provided with an automatic gain control circuit operating with attack and recovery times automatically controlled in accordance with variation of the dynamic range of the sound accompaniment.