Abstract: An automatic gain control circuit having a plurality of receiving systems is structured to unify the receiving systems for performing level detection into one system and feedback data for controlling the gains of variable gain amplifiers 11a and 11b is subjected to correction of dispersion of the temperature characteristics between the variable gain amplifiers 11a and 11b of the receiving systems by operating a thermistor 31 so that a portion of an automatic gain control loop is made to be common without use of automatic gain control loops by the number corresponding to the number of the receiving systems.

Abstract: An automatic gain control circuit comprising a variable gain amplifier having first and second differential gain control terminals, the first gain control terminal being connected to a constant reference voltage, a peak detector connected to the output of the variable gain amplifier and an integrator connected between the output of the peak detector and the second differential gain control terminal. The circuit further includes an integrating capacitor coupled to a ground terminal and a second capacitor connected between the first and second differential gain control terminals.

Abstract: To reduce power consumption by increasing amplifying efficiency in a low power mode, there is provided a radio communication apparatus in which each of field effect transistors of a radio frequency power module in a multi-stage configuration is controlled by an APC circuit based on a power level instruction signal, and in which a correction circuit is incorporated between the gate of a final stage transistor and the APC circuit to apply a linear gate voltage to the final stage transistor when a High level signal based on the power level instruction signal is applied and to provide a maximum gate voltage of the final stage transistor which is equal to or lower than the gate voltages of other transistors and whose rate of increase relative to the output voltage of the APC circuit gradually reduces when a Low level signal based on the power instruction signal is applied.

Abstract: A variable gain circuit amplifies an input signal with a gain which depends on a control voltage. The gain circuit has a first amplifier with a gain that is proportional to the control voltage in a relatively low region of the control voltage and a second amplifier with a gain that is proportional to the control voltage in a relatively high region of the control voltage. The second amplifier also includes a gain circuit which maintains the gain of the second amplifier constant in a relatively low range of the control voltage. The second amplifier is connected to the first amplifier via a pair of coupling capacitors. The variable gain circuit may be used in a transmitter of a CDMA telephone.

Abstract: A precision GaAs low-voltage DC amplifier includes a level shift circuit, an amplifier and a first and a second bias control circuit. The level shift circuit shifts an input signal to generate a level shifted input signal, whose bias level is controlled by a first bias control voltage. The amplifier amplifies the level shifted input signal to generate an output signal. The bias level of the output signal is controlled by a second bias control voltage. The first bias control circuit insures that the first bias control voltage varies as necessary with temperature to hold constant the bias level of the level shifted input signal. The second bias control circuit insures that the second bias control voltage varies as necessary with temperature to hold constant the bias level of the output signal.

Abstract: In a communications system, a power amplifier is dynamically biased in response to a control signal indicative of the required transmission power. In delivering relatively high transmission power, the DC operating point of an amplifying element in the power amplifier is placed far from the cutoff and saturation regions of the output characteristics of the amplifying element. As a result, the corresponding input signal at a high drive level to the power amplifier is virtually undistorted thereby and, at the same time, a high power efficiency is achieved. In delivering relatively low transmission power, although the DC operating point is placed relatively close to the cutoff region of the output characteristics of the amplifying element, because of the corresponding input signal which is at a low drive level, the power amplifier minimally distorts the input signal. However, a high power efficiency is maintained because the input DC power to the power amplifier is reduced as well as the transmission power.

Abstract: According to the method and apparatus of the present disclosure, dual drain control uses a variable voltage supply on the drains of a first stage (302) and a second stage (304) to control the output power. In particular, dual drain control having a 1:1 ratio is employed at lower power levels, with single drain control at higher power levels. Such drain control could be employed by directly varying (1008, 1010) the voltage on the drains of the power amplifier, such as with signals from a microprocessor, or by a specific circuit (203) to generate the drain voltages based upon a control voltage.

Abstract: A single bias block for a single or multiple low voltage RF circuits including one or more amplifiers and one or more single or double balanced mixers with compensation for temperature and integrated circuit process parameters. The power supply may be a lower voltage without sacrificing the dynamic range of the amplifier and/or mixer by applying full power supply voltage to the load with the bias applied to the base circuit through an operational amplifier and/or buffer circuit. For the mixer, a lower noise figure may also be realized by moving the gain control impedance from the emitter to the collector circuit. The circuits may be discrete components or part of an integrated circuit. Methods are disclosed for reducing the power supply voltage without affecting the dynamic range of an amplifier, for temperature and process parameter compensation, and for controlling the gain of a mixer without affecting input or output impedance.

Abstract: A method and apparatus provides control of the gain of an input amplifier (306) in a radio receiver (300), such as in a radiotelephone handset (104). The radio receiver (300) includes an automatic gain control circuit (318). The automatic gain control circuit (318) includes a timer circuit (370) which provides asynchronous, digital automatic gain control circuit to perform a coarse gain adjustment. The automatic gain control circuit (318) further includes an integrator (366) which provides analog automatic gain control for providing remaining needed gain regulation. The automatic gain control circuit (318) provides substantial reduction in input signal acquisition time for the radio receiver (300).

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: An attenuator circuit having three cascaded attenuator stages which become active, one at a time, as an input signal strength increases. In the highest gain state, the three attenuator stages are active. As the input signal increases, the attenuator stages become inactive sequentially starting with the last stage.

Abstract: The apparatus includes an amplifier (204) having an input and an output, the amplifier output coupled to an input of a Doherty amplifier (208). The Doherty amplifier (208) includes a control input and a Doherty output. The apparatus further includes a detector (224) having an input coupled to the output of the Doherty amplifier (208). The detector provides a detected signal at its output, to a controller (228), the controller responding to the detected signal by producing a first (230) and second control output (231). The first control output is coupled to a switching regulator (232) input, the switching regulator having an output coupled to the control input of the Doherty amplifier. The second control output is coupled to a control input of a variable attenuator (202), the output of the variable attenuator coupled to the input of the amplifier (204).

Abstract: A system (100 or 200) includes a first AGC stage (102) having a programming input and a gain input. A second AGC stage (104 or 210 and 234) is coupled in a common path with the first AGC stage, the second AGC stage having a programming input and a gain input. The first and second AGC stages are programmed by respective programming signals to produce independent gain characteristics responsive to a common gain signal at their respective gain inputs.

Abstract: A variable gain amplifying device for an AGC (Automatic Gain Control) circuit included in a receiver and having a broad dynamic range is disclosed. The device has a more linear gain-to-control voltage characteristic than the conventional device. Because the device broadens the range of control voltage without aggravating the deviation of the gain, its gain-to-control voltage characteristic is more stable than the characteristic of the conventional device.

Abstract: The present invention includes a variable gain amplifier to output two differential signals which are level shifted and compared through two comparators to drive a charge pump which produces either a discharge current or a charge current to provide feedback control to the variable gain amplifier.

Abstract: A dual band filter network for a radio communication apparatus is provided. The network has an antenna (212) for receiving and transmitting signals from a first frequency band and a second frequency band. The network has a first duplex pair (202) including a first transmit filter (204) including a first passband and stopband. The first duplex pair (202) also includes a second receive filter (206). The first filter (204) presents a consistent phase in the second passband due to the wide frequency separation between the first filter (204) and the second filter (206). The network has a second duplex pair (202') with similar characteristics as the first duplex pair (202). The network also has a switching circuitry (210) controlled by a switch control voltage (214) for selecting the appropriate filter circuitry. The network can be provided in a small sized, low cost package that also offers improved insertion loss performance.

Abstract: A method for amplifying an RF input signal using a power amplifier (105, 107 or 205, 207) comprises the steps of dividing or quadrature splitting (103) the RF input signal into an in-phase signal and a quadrature phase signal. A carrier amplifier bias input (111, 211) signal is varied relative to the magnitude of the RF input signal. A peaking amplifier bias input (113, 213) signal is varied relative to the magnitude of the RF input signal. The in-phase signal is amplified using a carrier amplifier (105, 205) to produce a first amplified signal. The quadrature phase signal is amplified using a peaking amplifier (107, 207) to produce a second amplified signal. The first amplified signal and the second amplified signal are combined (115, 117), in phase, to produce an output signal.

Abstract: An integrated circuit includes a gain control terminal that provides for a choice of discrete gain values for circuitry on the IC. Typically, the gain control terminal is connected to a high voltage source (V.sub.DD), or a low voltage source (V.sub.SS), or optionally left unconnected. In addition, the integrated circuit provides a gain set terminal for connection to an external impedance, typically a resistor, and also includes gain set circuitry for determining the value of the resistor as falling within one range out of several possible ranges. Based upon the range thus determined, the gain set circuitry selects the discrete gain values that are available for choice by the gain control terminal. In this manner, a large range of gain values are available for use even though only a few need to be selected in actual operation of the IC. This technique minimizes external package terminals for the IC, and allows for gain setting by low tolerance resistors.

Abstract: A power control circuit having a saturation preventing control loop including a variable gain amplifier, an RF power amplifier, a directional coupler, a detecting circuit, a comparator, a switch, and an adder. When the signal level of an output signal of the comparator is low, the switch is turned on. When the signal level of the output signal of the comparator is high, the switch is turned off. A system power control loop includes a system power control terminal, the adder, and the variable gain amplifier. Since the saturation preventing control loop is provided with the switch, the saturation preventing control loop operates only when the signal level of the amplified signal is larger than a reference value. The system power control loop can properly operate according to a system power control signal supplied from the system power control terminal.

Abstract: A transmitter (107) includes amplifying circuitry (203) and control circuitry (215, 217, 219) for biasing the amplifying circuitry (203) so that it operates closer to saturation with increased efficiency. The gate voltage signal (213), which provides a gate bias, is coupled to the amplifying circuitry (203) and is dynamically varied by the processor circuitry (219) in response to the value of the amplifier control voltage (211) coupled to the amplifying circuitry (203). The amplifier control voltage (211), which has a value for maintaining the output power of the amplifying circuitry (203) at a constant, is produced by the integrating circuitry (217) in response to a comparison of the detected power output signal (216) produced by the detecting circuitry (215) and the power output control signal (218) produced by the processor circuitry (219).

Abstract: Transconductance amplifiers having high speed, a wide output voltage swing, good linearity and expandability are disclosed. All active devices are n-channel MOSFET devices with the output current of the amplifiers being provided by devices with their sources tied to ground. Connection of one of the MOSFET transconductance amplifiers to a MOSFET load device and appropriate control of the MOSFET resistance devices in the transconductance amplifier and the load circuit provides a variable gain amplifier having a good estimation of an exponential response to the gain control signal, thus being suitable for use in closed loop automatic gain control circuits.

Abstract: An automatic transimpedance control amplifier is disclosed. The amplifier incorporates an automatic gain control circuit which simultaneously and automatically adjust the value of transimpedance and the voltage gain at each gain stage of the amplifier according to the input current. The amplifier has wide bandwidth, high sensitivity, and more importantly, wide dynamic range.

Abstract: An amplifier for reducing an overshoot when an AC current is applied during class "C" amplification includes a transistor used to amplify an AC signal and a device that, just before an AC signal is applied to the transistor, sends a DC current to the transistor. As a result, when the AC signal is applied to the transistor, the junction temperature of the transistor is elevated to substantially the same level as operating junction temperature of the transistor.

Abstract: A dual mode transmitter with bias control is described wherein an RF signal from a system modulator is fed to a gain control circuit, which can be either a voltage controlled amplifier or attenuator. The ultimate transmitter output power level depends on the attenuation/gain of the gain control circuit. The output signal from the gain control circuit is fed to a driver amplifier which amplifies the signal and feeds it to a power amplifier circuit, which may be comprised of several stages of bipolar transistors or GaAs FETs. The modulated signal to be transmitted is then fed from the power amplifier circuit through a coupler to an antenna terminal. The coupler is connected to an RF detector and is used for RF level monitoring. The Rf level signal from the RF detector is applied to a comparator circuit. An improved combination is provided by incorporating a bias control circuit. A Vpwr signal is applied as one input to the bias control circuit and a mode signal is applied as the other input.

Abstract: A hybrid analog/digital automatic gain control gain recovery system includes a variable gain amplifier (VGA) for receiving a variable amplitude input signal; a first AGC loop includes an analog to digital converter (DAC) for receiving the analog input signal and converting it to a digital signal; a digital gain error detection circuit for detecting variations of the digital signal in a first range and generating a digital error correction signal; and a digital to analog converter (DAC) for converting the digital error correction signal to a first analog correction signal; a second analog AGC loop includes an analog gain error detection circuit, responsive to variations in the output of the VGA in a second range greater than the first range for generating a second analog correction signal; and an integrator circuit responsive to the first and second analog correction signals for providing to the VGA a control signal to adjust the gain of the VGA to accommodate variations in the input signal amplitude.

Abstract: A control circuit for a transmission output is used in a TDMA system radio transmitter or the like and can control a transmission output burst wave stably with high accuracy over a wide range. There is provided a closed loop system in which part of the transmission output is taken out and detected to be compared with a reference voltage to control a power amplifier and an open loop system for controlling a drive amplifier connected to an input of the power amplifier, so that a wide range operation of the transmission output and multi-stage control are attained by combining controls of both the loops.

Abstract: A burst control circuit for use in a TDMA communications system comprises a power amplifier having two separate control terminals. A level control signal which is the difference between a reference signal and the level of the output burst signal of the amplifier, feedback-controls the level of the output burst signal through a first control terminal, and a waveform control signal having a predetermined waveform, controls the waveform of the output burst signal through a second control terminal. When the level of the reference signal is decreased, the amplitude of the waveform control signal is decreased as a function of the level of the reference signal.

Abstract: A detector for detecting changes in the output level of an amplifier included in, for example, a mobile communication signal. A first detecting circuit produces a detected voltage having linearity against low output levels of the amplifier. A second detecting circuit produces a detected voltage which is linear against high output levels of the amplifier. The detected voltages from the first and second detecting circuits are mixed by a mixer in a predetermined ratio. Even when the output level of the amplifier changes over a broad dynamic range, the detector detects the changes with accuracy.

Abstract: An RF power amplifier includes an RF power amplifying section having a variable amplification gain. A phase shifter connected to the RF power amplifying section serves to shift a phase of an output signal of the RF power amplifying section. The phase shifter has an input terminal subjected to the output signal of the RF power amplifying section and an output terminal subjected to a signal which results from shifting the phase of the output signal of the RF power amplifying section. A control-signal generating section serves to generate a control signal on the basis of the signals at the input terminal and the output terminal of the phase shifter. The control signal depends on a power of the output signal of the RF power amplifying section. The amplification gain of the RF power amplifying section is controlled in response to the control signal.

Abstract: The bias level of an amplifier is controlled by an active bias circuit. The active bias circuit establishes a predetermined amplifier bias level (such as class A mode) as a function of input signal level and load impedance. The load impedance value may be manually entered or determined automatically by a disclosed impedance measuring system. Power supply circuitry is responsive to the value of load impedance to vary the bias voltage applied to the amplifier's output devices.

Abstract: An amplifier device has a gain programmable between 2.sup.n and 2.sup.n-1 in steps of 2.sup.p where p<n and n is the number of gain control bits. The device comprises a plurality of stages having two gain values selectable by a control bit and at least two identical stages having a different control bit. Each stage has a maximum gain less than 2.sup.n-1.

Abstract: A power control circuit used for both analog/digital dual mode is disclosed which comprises a switching circuit (17) for applying the feedback signal to the gain control terminal (40) of the power amplifier (2) and applying a fixed bias voltage to the attenuation control terminal (30) of the attenuator (10) so that the amplifier operates as a C class amplifier in the case of analog mode, and for applying the feedback signal to the attenuation control terminal (30) of the variable attenuator (10) and applying the predetermined bias voltage to the gain control terminal (40) of the power amplifier (2) so that the amplifier operates as an A class amplifier in the case of digital mode. In the present invention, as a single amplifier operates for both analog mode and digital mode, the configuration is simplified and assembled cheaply.

Abstract: An amplifier circuit for providing precise linear control over the output of a nonlinear amplifier, including a nonlinear gain controllable amplifier and an output control circuit. The output control circuit is connected to sample the signal output by the nonlinear amplifier. The amplifier output signal may be a continuous or a discontinuous signal. The output control circuit also receives a baseband signal. The sampled amplifier output signal and the baseband signal are alternatively transmitted to a detector. The detector produces a signal representative of the power level of either the sampled amplifier output signal or the baseband signal. The signals produced by the detector are stored separately in a pair of sample-and-hold circuits. A difference amplifier determines the difference between the stored signals and transmits this difference signal to the gain control input of the amplifier. The output signal from the amplifier is thereby adjusted to linearly track the baseband signal.

Abstract: In a laser scanning system, an automatic gain control (AGC) circuit for dynamically adjusting the gain of a receiver that is used to receive light reflected from a bar code. The AGC provides a fast adjustment to receiver gain so that the receiver can provide a decodable signal quickly. To accomplish the fast adjustment, the AGC circuit, in addition to sensing the final output of the receiver, includes an additional feedback path from an amplifier in the receiver that is located before the final amplification stage. The additional feedback has a negligible attack time, and adjusts receiver gain quickly, thereby minimizing the time required to reach steady state.

Abstract: An amplifier circuit includes an amplifier and a biasing circuit. A control circuit generates an amplifier output level control voltage which is coupled to the biasing circuit for controlling the operating point of the amplifier in response to the level of control voltage.

Abstract: A control circuit for a radio frequency (rf) amplifier having multiple selectable power output levels in response to a plurality of input control signals is presented. The rf amplifier includes a variable gain input which is responsive to the control circuit. The control circuit includes an attenuator coupled to the output of the rf amplifier for providing an attenuated rf signal and an detector coupled to the output of the attenuator for generating a DC output signal which is substantially linearly related to the magnitude of the rf signal output by the rf amplifier. The control circuit also includes a means coupled to the input control signals for selecting one of a plurality of amplification factors. An amplifier is used to amplify the DC output signal generated by the detector using the selected amplification factors. The amplified output is coupled to the variable gain input of the rf amplifier.

Abstract: A power amplifying apparatus according to the present invention can provide a stable electric power output with wide range by controlling both of the output amplifier for amplifying the electric power and the pre-amplifier disposed at the front of the output amplifier. Furthermore, in order to avoid the disadvantage that a transmission spectrum is expanded because of no supply of a stable voltage to be supplied to the electric power amplifier, thereby producing a cross-talk, a stabilizing power source circuit is provided to stabilize the voltage between the power amplifier and the power source for supplying the voltage.

Abstract: A burst control circuit for use in a TDMA communications system comprises a power amplifier having two separate control terminals. The circuits also comprises an ALC circuit for producing and supplying a level control signal to the first control terminal of the power amplifier to perform negative feedback operation and to keep the level of an output burst signal constant. The burst control circuit further comprises a waveform control circuit which generates in response to a burst timing signal a waveform control signal having gently sloped leading and trailing edges and supplies the waveform control signal to the second control terminal of the power amplifier to control the waveform of the output burst signal.

Abstract: The junction temperature rise of a power MOSFET serially connected to a lamp whose resistance nonlinearly increases during turn-on is moderated by the use of control circuitry which initially sets up a relatively low essentially constant current flow through the lamp and transistor and then automatically after the lamp resistance reaches a preselected level, the lamp is allowed to draw significantly more current. The size and therefore cost of the power MOSFET is reduced significantly because the magnitude of the current spike generated by turning on the lamp is significantly reduced the use of the novel control circuitry.

Abstract: Circuitry changes the magnitude of power supply voltages to correspond to the desired level of a variable output power. This maximizes the electrical power efficiency of amplifiers. The circuitry also provides for automatic control of the amplitude of the amplifier output signal.

Abstract: An audio amplifier whose operating point and supply voltage can be change in response to a level of an input signal. The audio amplifier includes a delay circuit for delaying an input signal, an amplifier circuit having an amplification device for amplifying an output signal of the delay circuit, the amplifier circuit having a variable operating point, a power supply circuit capable of changing a supply voltage to the amplifier circuit, and a control circuit for detecting a level of the input signal to output a control signal corresponding to the detecting level, and changing the operating point and supply voltage of the amplifier circuit, in response to a level change of the input signal.

Abstract: A circuit arrangement has a pre-amplifier that has its input connected to an opto-electric transducer and whose gain is controllable by a final control element formed by a field effect transistor. In order to achieve an especially great range of dynamics, the pre-amplifier contains the drain-source path of a field effect transistor that is connected in parallel to a resistor in a feedback branch. This field effect transistor is activated or inhibited by a regulator. In this way, the range of control of a controllable amplifier arrangement following the pre-amplifier is doubly utilized. The circuit arrangement can be advantageously used in optical transmission equipment of PCM technology.

Abstract: The present invention is a method and apparatus for implementing a two stage AGC circuit. In the preferred embodiment, the present invention is used as part of a receive channel in a modem. The first stage of the AGC is a "coarse" AGC and is used to track large signal transients of an input signal. The coarse AGC locks on to transient signals without excessive settling time. In operation, the coarse AGC acquires a new signal by using a nonlinear clipped feedback loop technique supported by a linearized feedback loop. The coarse AGC stage uses an error signal derived from the noncoherent power fluctuations of the incoming signal. The second stage of the AGC circuit is a "fine" AGC using a decision-directed coherent amplitude error signal and a quick linear feedback loop to correct for finer signal level fluctuations. The fine AGC has a high pass characteristic which decouples its response from that of the equalizer for stability reasons.

Abstract: A circuit which attenuates an RF signal in response to a voltage level of a control signal is disclosed. A first PIN diode resides in series with an RF signal path, and a second PIN diode shunts the RF signal path to ground. A first differential amplifier responsive to the control signal drives the first PIN diode, and a second differential amplifier responsive to the control signal drives the second PIN diode. Gain and maximum current output for each of the amplifiers are independently controlled. Additionally, separate reference voltage sources may apply to one input of each of the differential amplifiers.

Abstract: An improved power amplifier is disclosed which is particularly useful with very high frequency (VHF) transceivers. The power amplifier includes a control loop configured to sense the input radio frequency signal and use that signal as a reference for comparison with the radio frequency output from the amplifier to control amplifier power output. The loop forces the amplifier's output radio frequency envelope to follow the input radio frequency envelope and thus produce a constant gain loop. A limiter in the loop forces the loop to produce a constant power output when the input signal exceeds a level set by the limiter.

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 automatic level control system is described for use with a voice processor which generates an AGC control signal to vary the gain applied to an audio input signal. The system includes a dynamically adjusting peak detector for detecting noise peaks and voice peaks while ignoring voice lulls which occur after a voice peak. Detected peaks are processed by an improved voice/noise sensor which develops a first output signal when voice is detected and a second output signal in the absence of detected voice. These output signals are received by a gain control circuit which is adapted to prevent the AGC control signal from increasing system gain for an indefinite interval in response to the second signal, and to permit normal variation in the AGC control signal in response to the first signal.

Abstract: A compressor limiter is provided for the processing of audio signals. Fundamentally, the invention includes an amplifier receiving audio input signals and including a photoresistive element in the feedback circuit thereof. The output of the amplifier is provided to a dual stage control voltage generating circuit. The first stage generates a current through a light emitting diode corresponding to the amplitude of the output signal from the amplifier. The light emitting diode sets a threshold for suppression of the output audio signal such that, as light is emitted from the diode, it effects the photoresistor in the feedback circuit of the amplifier, thus adjusting the gain. The other branch of the control voltage generating circuitry comprises a peak detector which is operative for controlling the light emitted from the diode when successive audio signals exceeding the threshold are received in rapid succession.

Abstract: This invention relates to automatic gain control (agc) circuitry and more particularly to circuitry for supplying respective automatic gain control signals to an amplifier that repeatedly receives a given sequence of signals. Each one of the signals in each sequence is sampled and compared with a reference voltage in a respective feedback loop. The respective agc loops are coupled to the amplifier in a predetermined sequence to control the gain of the amplifier in a desired manner. The steps in this predetermined sequence are initiated by an external trigger and by the receipt of the signals to be controlled.

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.