Abstract: In an automatic gain control loop circuit supplied with two channel signals alternately input thereto, a first capacitor filter and stores the first signal output from the level detector circuit, and a second capacitor filters and stores the second signal output from the level detector circuit. The second signal is output only during the signal period of a second channel included in the two channels. An adder adds the second signal stored in the second capacitor to the first signal stored in the first capacitor. A switch selects the first signal stored in the first capacitor during the signal period of the first channel, and selects an output from the adder during the signal period of the second channel. The selected signal is fed back to the gain control input terminal of the variable-gain amplifier circuit. With there features, a flicker is prevented from occurring when the two channel signals are switched.

Abstract: In an amplifier apparatus of the type including an RF power transistor output stage, the control circuitry of the invention provides an automatic gain control mode of operation for its power transistor of a first response time and a power limiting mode of operation for its transistor of a second, faster response time, and with the power limiting mode of operation being switched into effect in response to the sensing of the collector current flow of the power transistor beyond a prescribed value.

Abstract: An AGC circuit varies a bandwidth of an input unit and accuracy of linearity of the AGC output. A first input unit converts a first input current into a first voltage. A second input unit, identical to the first input unit, converts a second input current into a second voltage. A variable constant current source generates first and second constant currents. The first constant current flows from the first input unit to the variable constant current source. The second constant current flows from the second input unit to the variable constant current source. The first and second constant currents are varied by a control signal supplied by an external signal source so that the bandwidths of the first and second input units are varied. The AGC output of the AGC circuit is calculated based on the first voltage and the second voltage.

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: A charge pump that receives complimentary metal-oxide semiconductor (CMOS) input signals, has high noise immunity, low static error and works at low power supply voltages. The charge pump includes a current switch for receiving a control signal from a control circuit and for generating a charge signal, a loop filter having a first and second node, and a common-mode loop for sensing the charge signal from the current switch and for providing a voltage level adjustment signal to the first node of the loop filter in response thereto. The common-mode loop includes a sensing circuit for sensing the voltage level at the first and second node, an averaging circuit for producing an averaged voltage signal, a comparing circuit for comparing the averaged voltage signal to a reference signal to produce a feedback control output signal, and a feedback current source for adjusting the voltage level at the first node of the loop in response to the feedback control output signal.

Abstract: The image sensor according to the present invention comprises a light emitting diode which irradiates light onto a document image, a phototransistor which receives the reflected light and executes photoelectric conversion, an amplifier which amplifies an analog signal from the phototransistor, a time constant circuit into which an analog signal from the amplifier is inputted and which delays the analog signal by a specified period of time, an amplifier into which the analog signal outputted from the amplifier and the analog signal delayed in the time constant circuit are inputted and which differentially amplifies the analog signals, and a knot gate into which the analog signals outputted from the amplifier are inputted and which outputs a digital signal of "0" or "1" according to whether a value for the analog signal is positive or negative.

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 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 amplifier for a radio transceiver overcomes the problem of gain being dependent on ambient temperature. Transmission power is matched to strength of a received signal by providing matched dual gate FET amplifier stages in both the transmitter and receiver portions of the transceiver. Changes in gain due to temperature are compensated for by detecting changes in the FET drain current by measuring the source voltage of the amplifier. The FET source voltage is compared to a reference voltage, and the output signal resulting from the comparison is provided as a control signal to one of the FET gates.

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: A high frequency power amplifier amplifies periodic signals in the form of HF bursts. The power output of the amplifier is adjusted by a control loop which produces a control signal in response to a comparison made between a set-point value (BV) and the actual power output (Put) of the amplifier and applies the signal to the power amplifier. The control loop includes a differential amplifier. A correction circuit measures the output voltage of the differential amplifier over a time period (t.sub.1 to t.sub.2) prior to each HF burst and stores in a memory (C) a magnitude proportional to this output voltage. During the following HF burst, this magnitude is used to introduce into the control loop a correction magnitude (Ukorr) for correction of offset voltages (Uoff) occurring in the control loop.

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 is compensated for variations in element values. A trim signal is generated based on element values of filter elements of a filter in the amplifier. An RC product in the amplifier is controlled based on the trim signal. The RC product corresponds to a product of a dynamic resistance value of a dynamic resistance element in the filter in the amplifier, and a capacitance value of capacitive elements in the filter. The RC product also determines a pole position of the amplifier. Gain in the amplifier is controlled based on the trim signal so that a desired gain is maintained.

Abstract: An input signal representing speech is preamplified, filtered, and fed foward in parallel to Automatic Gain Control (AGC) circuitry and to a gain controllable amplifier. The AGC detects the peak absolute value of the input signal, charing a capacitor in accordance with such detections. The capacitor is discharged at a faster rate (variable down to 1 msec) when a greater charge value is stored but at a slower rate (variable up to 4 seconds) when a lower charge value is stored. The gain controllable amplifier is controlled for gain inversely to the charge value stored on the capacitor. The AGC captures greater than 60 dB of allowable input signal range, compressing such input signal into a (controllable) limited amplitude dynamic range.

Abstract: A switched capacitor integrator is used within the feedback loop of an automatic gain control (AGC) circuit to provide a very long time constant (5 minutes or more) when the amplitude of the gain-controlled signal is within predetermined limits. The time constant is automatically and quickly changed to a much shorter value when the gain-controlled signal is outside the predetermined limits, thereby allowing the AGC circuit to rapidly bring the gain-controlled signal amplitude within the desired range between the predetermined limits. Time constants of orders of magnitude longer than those readily realized with prior art methods of long time-constant filtering are 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: Automatic gain control apparatus comprises a digitally adjustable amplifier, two threshold detectors with adjustable hysteresis, a latch and a control stage with an up/down counter. The latch stores only the logic states of the two threshold detectors. The digital output of the up/down counter is changed in value at the frequency of a first or second clock signal. The output of the up/down counter controls the gain of the amplifier.

Abstract: A closed loop automatic gain control (AGC) circuit with high dynamic range capabilities having an amplifier circuit for receiving an input signal, which is susceptible to variations in signal power, and a control signal. The amplifier circuit is responsive to the control signal for amplifying the input signal at a gain level corresponding to the control signal so as to provide a corresponding output signal. A measurement circuit is coupled to the amplifier means for measuring logarithmic signal power of the amplified input signal and providing a corresponding linear measurement signal. An integration circuit is included for receiving the measurement signal, and a reference signal which corresponds to a desired signal power of the output signal. The integration circuit integrates with respect to time the difference between the measurement signal and the reference signal, and generates the control signal which corresponds to the result of the integration.

Abstract: A power amplifying apparatus for amplifying an input signal to drive a load, includes an amplifier for amplifying the input signal so as to generate an output signal for driving the load and a current/voltage converter for current/voltage converting the output signal generated by the amplifier and feeding back the converted voltage to the amplifier. The converted voltage is used to control the amplitude of the output signal which flows into the load. The power amplifying apparatus further includes a circuit for determining a current-to-voltage conversion ratio of the current/voltage converter. The amplitude of the converted voltage converted by the current/voltage converter may be varied in accordance with the current-to-voltage converting ratio determined by the determining circuit.

Abstract: An automatic gain control circuit comprising an input terminal means for receiving first and second signals, an amplifier for receiving and amplifying first and second signals and outputting a first output signal when receives the first signal and outputting a second output signal when receives the second signals, input means for receiving an operation control signal and responsive to the operation control signal for separately inputting the first and second signals to the amplifier with a predetermined interval of time, control signal generating means responsive to the second output signal of the amplifier for generating a control signal, selection means connected to the input means for supplying the second output signal of the amplifier to the control signal generating means when the second signal is fed to the amplifier and sending out the first output signals to an external circuit when the first signal is fed to the amplifier and gain control means connected to the amplifier and the control signal genera

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: An automatic gain control device for use in an optical memory device has a circuit for producing an amplification control signal which is fed back to a gain control amplifier through a sample-hold circuit. A pulse train detection circuit is provided for detecting the pulse train indicating that the data stored are a on the optical memory device is being playedback. When the pulse train is detected, the sample-hold circuit is made inactive so that the amplification control signal is directly fed back to the gain control amplifier, and when the pulse train ends, the sample-hold circuit is made active to hold the amplification control signal obtained at the end of the pulse train and to produce the amplification control signal held in the sample-hold circuit.

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: The gain of a video intermediate frequency signal processing circuit (11) is varied in accordance with the charge voltage of a capacitor (C.sub.1). The capacitor (C.sub.1) is charged with a relatively small current when the peak of a video detection signal does not reach a reference voltage (V.sub.A) and discharged with a relatively large current when reaches. A current source (29) for rapid charge is activated when the peak of the video detection signal does not reach the reference voltage (V.sub.A) over a predetermined period longer than one horizontal synchronous period, to rapidly charge the capacitor (C.sub.1). Thus, a speed in increase of the gain of the video intermediate frequency signal processing circuit is quickened, to hasten the restoration of an amplitude of the video detection signal.

Abstract: An automatic volume control apparatus for use in a mobile audio apparatus in which a detection output from a noise detection section is compared with a control output applied to a volume control section, and a capacitor inserted between a control signal input terminal of the volume control section and a reference voltage point is charged/discharged by a current source section with a constant current on the basis of the output of the comparator to thereby make it possible to make the change of volume constant or linear relative to the change of noise level. Also, a control signal for a volume controller is obtained by subtracting a quantity of logarithmic change of an audio signal detection signal obtained from an audio signal detection section relative to a reference value from a value obtained by amplifying, with an amplification factor in a range of 1.5 to 2.

Abstract: An intermediate-frequency automatic gain control circuit generates an IFAGC voltage for controlling the gain of an IF amplifier, in accordance with the level of the output signal of the IF amplifier. An RFAGC voltage provides a voltage for controlling the gain of an RF amplifier of a tuner, in accordance with the IFAGC voltage level. The output voltage of the RFAGC circuit is supplied to a time-constant circuit made up of a series circuit including first and second resistors and a first capacitor, and a second capacitor connected in parallel with the series circuit. The time-constant circuit is connected to a time-constant control circuit made up of first and second diodes connected in parallel with the second resistor. When the output voltage level of the RFAGC circuit increases or decreases above or below the diode voltage, the first or second diode is conductive, to decrease the time constant of the time constant circuit.

Abstract: An automatic sound volume device which adjusts the volume of an audio signal in a vehicle to compensate for vehicle noise. A time constant circuit smooths the level output of a microphone to smooth the volume variations. However, the time constant is long for increases in noise but short for decreases in noise.

Abstract: A borehole televiewer circuit for compensating for out-of-roundness of a borehole. The circuit comprises an automatic gain control circuit having time constants that allow detection of borehole anomalies while having a fast enough rise time to adjust for the effects of out-of-roundness.

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 radio frequency receiver wherein received signals are directed to a mixer through a pair of signal channels, the bandwidth of one of the pair of signal channels being a selected narrow portion of the bandwidth of the other one of the pair of signal channels. With such arrangement a received signal within a wide band of frequencies is passed to the mixer through both channels to become homodyned to a fixed intermediate frequency signal. Noise received by the wide bandwidth receiver while also passed through the both channels is mixed with only a narrow portion of itself, and hence the amount of noise at the fixed intermediate frequency is reduced with the result that the sensitivity of the receiver is correspondingly increased. An instantaneous frequency measuring unit is also fed by the selected narrow portion of the wide bandwidth signal channel to determine the frequency of the received signal with improved sensitivity.

Abstract: An AGC voltage generating circuit for an AM radio comprises a product detector adapted to receive an IF signal modulated by an AF signal and synchronously detect the AF signal, a low pass filter adapted to derive from the product detector a filtered voltage indicating the average IF signal strength, and a reference voltage generating circuit ratiometrically related to the low pass filter through a common DC power supply and effective to generate high, medium and low reference voltages ratiometrically related to each other with the high and low reference voltages defining a voltage window about the medium reference voltage. Comparator apparatus is effective to compare the filtered voltage from the low pass filter with the high, medium and low reference voltages from the reference voltage generating circuit. Current source apparatus is responsive to the comparator apparatus to control the voltage on a capacitor to maintain the filtered voltage equal to the medium reference voltage.

Abstract: The remote control system having symmetrical signaling circuits for radio communications is coupled to a single wire line/audio channel and permits two or more units, base stations and/or remote consoles, to be coupled to the single wire line. Each signaling circuit comprises a wire line coupler for coupling to the wire line, an audio input line and an audio output line. An automatic gain control circuit is coupled between the wire coupler and the audio output line and a filter and line driver are coupled between the audio input line and the wire coupler. A control unit including a microprocessor, a tone encoder, a tone decoder, a timer, a clock, and a memory is coupled by output lines to the automatic gain control circuit for controlling the modes of operation thereof which include a slow decay mode, a fast decay mode, an adapt mode and a hold gain mode. The output from the gain control circuit is also routed through a band pass filter and a limiter to the control unit.

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: The invented device provides automatic gain control (AGC) of incoming sigs over a large dynamic range of input levels with a constant rise time. The constant rise AGC device includes a primary AGC loop for receiving the incoming or input signal and splitting the input signal to input and output components of the primary AGC loop. The input signal to the input component is processed within the primary AGC loop to control the gain of the input signal at the output component of the primary AGC loop. The primary AGC loop has a slow detector. A secondary AGC loop is provided within the primary AGC loop, and this secondary AGC loop includes the aforementioned input component and has its output connected to the slow detector. The secondary AGC loop has a fast detector for preventing self-imposed saturation.

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 electronic amplifier composed of an electronically controllable amplifier element having a control input for receiving a voltage the value of which determines the gain of the element, with one such value being a predetermined basic gain value of the amplifier element, a control voltage generating circuit for generating a control voltage whose value determines the voltage at the control input of the amplifier element, the element and circuit being constructed for causing the gain of the amplifier element to be unity for one voltage value at its control input and to be different than unity for other voltage values, a nonlinear filter unit connected between the control voltage generating circuit and the amplifier element control input for supplying to the control input a voltage determined by the control voltage, the filter unit including an integrating branch and a differentiating branch having a rectifier device for causing the differentiating branch to be effective only during periods when the control volt

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 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: The present invention relates to a linear, class A FET amplifier circuit capable of providing linear amplifier of input signals with a time-varying envelope function. An envelope detector (12) is responsive to an input signal (v.sub.i (t)) for extracting the envelope signal (V.sub.i (t)) therefrom. A gate controller (16) subsequently adds the envelope signal to a predetermined gate bias voltage (E.sub.G) and applies the sum (E.sub.G (t)) as the "d-c" gate input to the FET amplifier (14). Therefore, the gate bias voltage is dynamically controlled by the envelope of the input signal, resulting in a significant improvement in the power-added efficiency (.eta..sub.added) over prior art class A FET amplifiers.

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: A time-constant circuit suitable for being fabricated into an integrated circuit comprising a resistive element with its one end connected to a first input terminal, an impedance converting circuit with its input connected to another end of said resistive element and its output connected to an output terminal, a variable gain differential amplifier with its one input connected to the output of said impedance converting circuit and its another input connected to a second input terminal, an adder circuit for adding an output from said amplifier and an input signal appearing on said second input terminal, and a capacitive element connected between the junction of said resistive element and said impedance converting circuit and the output of said adder circuit. A plurality of the time-constant circuits are combined to construct a filter circuit.

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: 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: In a system such as an ultrasonic scanner in which a signal must be variably amplified with time in response to a time gain control (TGC) signal, automatic noise rejection is provided by periodically comparing amplified noise with a threshold value above which noise interferes with signal analysis. TGC signal control of a variable amplifier is permitted so long as the amplified noise is less than the threshold value. A maximum control voltage, V.sub.n, is applied to the variable amplifier when the amplified noise exceeds the threshold level.

Abstract: An automatic gain control circuit is disclosed which is direct coupled to phase opposed outputs of an IF amplifier and provides a DC control voltage for controlling the gain of the amplifier. The AGC circuit includes a peak-to-peak threshold detector and an integrating capacitor. The quiescent voltage across the capacitor is accurately established by a voltage divider network and a feedback network. Separate current sources are provided to establish dual time constants in the circuit so that distortion is minimized while accommodating a stop on station feature.

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.