Abstract: There are described herein methods and systems for estimating a system parameter in a closed loop scheme using a sensor model associated with a sensor performing a measurement of the system parameter. Past and current measurements of the parameter are used to provide an initial estimate of the system parameter and sensor dynamics are used to refine the estimated parameter.

Abstract: A power transfer electrical system includes an electrical signal source that generates a current at an output. An electrical load is electrically connected to the output of the electrical signal source. An output of a controllable voltage source is also electrically connected to the electrical load. The controllable voltage source generates a voltage that is proportional to the current generated by the electrical signal source. An input of a controller is electrically connected to the output of the electrical signal source and an output of the controller is electrically connected to a control input of the controllable voltage source. The controller generates a signal that controls the voltage generated by the controllable voltage source so that a desirable amount of power is transferred from the electrical signal source to the controllable voltage source.

Abstract: A digital input circuit includes a series connection of a current limiter and a switch having a switch control input coupled between a signal input and ground, and a logic level shifter coupled to the signal input and having a switch control output coupled to the switch control input and a signal output, where a maximum amplitude at the signal input is greater than a maximum amplitude at the signal output. A digital input method includes coupling an input signal to ground with a current limiter by closing an electronic switch, providing an output signal responsive to the input signal, where a maximum amplitude of the input signal is greater than a maximum amplitude of the output signal, by latching the output signal while the input signal is above a threshold voltage and opening the electronic switch after the output signal is latched.

Abstract: An amplifier assembly includes an input signal determiner that determines a first input signal and a second input signal based on an initial signal having an amplitude and an initial frequency. Amplifiers amplify the first and second input signal to form first and second output signals having a phase offset with respect to one another. The first and second amplified output signals are fed to a common coupling element that forms a useful signal and a loss signal, such that a total power of the useful signal and loss signal is independent of the phase offset, the power of the useful signal has a maximum corresponding to a predetermined value of the phase offset, and the partial power of the useful signal decreases with a deviation of the phase offset from the predetermined value.

Abstract: A system for controlling a power supplied to a load from a radio frequency amplifier system includes a radio frequency signal generator adapted for generating a radio frequency signal, an amplifier to which the radio frequency signal is supplied and that amplifies the radio frequency signal into a radio frequency power signal, a power coupler connected to the amplifying member for coupling the radio frequency power signals, where the power coupler includes a summing connection adapted for connection to the load and a compensating connection adapted for connection to a dissipative element. A first control value generating member is adapted for receiving a signal proportional to a power output from the power coupler at the summing connection and is adapted for generating a first control signal for controlling the amplifier or a current supply that supplies current to the amplifier.

Abstract: A transmission power control apparatus for a wireless communication apparatus which reduces a power value of a signal input to a power amplifier to the maximum allowable input power value of the power amplifier or below is provided in which the transmission power control apparatus includes: a part for setting a transmission power upper limit value of a call according to a circuit type of the call; and a part for reducing transmission power for the call to the transmission power upper limit value or below.

Abstract: A method and apparatus for compensating a base current of a bipolar junction transistor by replicating operating conditions of the BJT in a compensating circuit. An output current of the compensating circuit is fractionally related to the base current and thus can be supplied to an operational circuit comprising the BJT to compensate the base current. In a preferred embodiment, the BJT is operated between BVCEO and BVCBO and the base current to be compensated flows from the BJT.

Abstract: A circuit for regulating the gain of a variable differential gain amplifier. In one embodiment, a fully differential amplifier amplifies the outputs of the variable gain amplifier. The outputs of the fully differential amplifier are applied to a three input comparator so that if either of the outputs are greater than a reference voltage, a control signal is generated which is used to regulate the gain of the variable gain amplifier. In other embodiments, an analog OR function is used as an input to a conventional two input comparator in place of the three input comparator. In another embodiment, outputs of the variable gain amplifier are passed through switches to a scaling circuit which either voltage divides or amplifies and combines the outputs before application to a comparator. In each case, known asymmetries can be compensated for by independent gain control of each of the outputs of the variable gain differential amplifier.

Abstract: A dual band transmitter (1) including: a lower band power amplifier (2) and a higher band power amplifier (3), a lower band transmit path (4) between the output of the lower band power amplifier (2) and a combining means (8); and a higher band transmit path (5); between the output of the higher band power amplifier (3) and the combining means (8). A surface mounted device includes a stub (6) having a first (61) and a second (62) end, the first end of the stub (6) being connected to the higher band transmit path (5) and the second end of the stub (6) being coupled to a switch. The second (62) end of the stub (6) is substantially closed or opened, in dependence upon the state of the switch, so that, in use, spurious harmonics are prevented from being generated in, and transmitted from, the transmitter (1).

Abstract: A predistortion-based amplifier which compensates for distortions generated by the amplifier when a modulated wave signal is amplified thereby in accordance with a predistortion scheme, based on envelope information of the modulated wave information. An envelope information detector for detecting information related to the envelope of the modulated signal to be amplified comprises, between an input terminal A1 and an output terminal A2, matching circuits 11, 14, diode circuits 12, 15, 16 for rectifying the modulated wave signal, a stub circuit 13 for removing a carrier component of the signal output from the diode circuits, and a signal converter circuit 17 for converting an envelope signal output from the stub circuit from a current signal to a voltage signal.

Abstract: A circuit for regulating the gain of a variable differential gain amplifier. In one embodiment, a fully differential amplifier amplifies the outputs of the variable gain amplifier. The outputs of the fully differential amplifier are applied to a three input comparator so that if either of the outputs are greater than a reference voltage, a control signal is generated which is used to regulate the gain of the variable gain amplifier. In other embodiments, an analog OR function is used as an input to a conventional two input comparator in place of the three input comparator. In another embodiment, outputs of the variable gain amplifier are passed through switches to a scaling circuit which either voltage divides or amplifies and combines the outputs before application to a comparator. In each case, known asymmetries can be compensated for by independent gain control of each of the outputs of the variable gain differential amplifier.

Abstract: A comparator (5) compares a detected voltage obtained by detecting an output power of a nonlinear amplifier (2) with a reference voltage to generate a control voltage for the nonlinear amplifier (2). The control voltage is converted into such a control voltage as to cancel the nonlinearity of the nonlinear amplifier (2) by a nonlinearity compensating circuit (7) and is supplied to the nonlinear amplifier (2). The nonlinear compensating circuit (7) is comprised of a diode (71) and a resistor (72).

Abstract: A circuit having a double half-wave rectifier connected to the outputs of a differential amplifier in order to produce two quantities dependent on the amplitudes of the half-waves of the output signal of the amplifier. Two comparators each having an input are connected to an output of the rectifier and a reference input in order to produce respective output signals when the amplitudes of the respective half-waves are greater than the levels applied to the reference inputs. The circuit also has processing means for generating a signal for regulating the gain of the amplifier in dependence on the durations of the output signals of the two comparators. The circuit may advantageously be used when the signal to be amplified is not symmetrical.

Abstract: An electronic device is set forth that allows external control of a controllable electronic function of the device. The device includes a function circuit for implementing an electronic function in response to a signal at a function control signal input. The function circuit receives DC power from a power supply that is connected between two battery terminals. The DC power from the power supply circuit is supplied at a predetermined DC voltage level. A control circuit is included in the device and is responsive to a signal superimposed on the predetermined DC voltage level of the power supply at the two battery terminals for generating a function control signal to the function control signal input of the function circuit. In accordance with one embodiment of the present invention, the invention is implemented in the context of a hearing aid.

Abstract: An audio amplifier clipping avoidance apparatus (140) identifies signal segments of an audio signal that can have an amplitude peak greater than a particular amplifier clip avoidance threshold (530). A scaling factor is determined for each signal segment based on the particular threshold (540). Signal segments are scaled with corresponding scaling factors to produce a modified audio signal having no signal segments with an amplitude peak greater than the particular threshold (560).

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 highly sensitive optical receiver where one terminal of the photodiode of the receiver is connected to a negatively biased amplifier while the other terminal of photodetector is connected to a positively biased amplifier, where such connections automatically bias the photodiode and use the current from both terminals (anode and cathode) of the photodiode. This invention also provides an optical receiver which has a DC cancellation circuit to eliminate the biasing voltages in the final output signal.

Abstract: A data independent AGC control circuit for telecommunication applications is provided and includes an AGC amplifier, a fixed gain amplifier, a capacitor, and first, second, and third control circuits. The AGC amplifier has a data input, a control input, and a data output. The capacitor is coupled to the control input, and the charge on the capacitor effectively controls the gain of the AGC amplifier. The first control circuit is coupled to the data output of the fixed gain amplifier and to the capacitor and increases the stored charge on the capacitor when the data output exceeds a desired peak voltage level. The second control circuit is similarly coupled between the data output of the fixed gain amplifier and the capacitor, and decreases the stored charge on the capacitor when the data output exceeds a threshold voltage (typically 1/2 the desired peak voltage level).

Abstract: A receiver comprises an AGC circuit including a low noise amplifier for amplifying a reception input signal and an AGC amplifier, a level detection circuit for producing a strength indication signal indicative of an input field strength, and a demodulator. The receiver has a function of controlling a gain to keep an amplitude of a demodulator input signal at a constant level. A bias control circuit controls on and off of a bias voltage source to allow and inhibit supply of a bias voltage to the low noise amplifier when the strength indication signal has a signal level lower than and not lower than a first threshold level, respectively. When the signal level is thereafter decreased to a second threshold level lower than the first threshold level, the bias control circuit turns on the bias voltage source to supply the bias voltage. A level output circuit serves to keep the strength indication signal at a predetermined high level when the bias voltage source is turned off.

Abstract: A method and apparatus for controlling an amplifier power output, in particular, a transmitter RF Amplifier includes a control circuit connected to the RF Amplifier. The control circuit derives a control signal from a shaper circuit and this control signal is applied, together with a feedback signal representative of the flow of dc current through one of the stages of the amplifier, to a comparator to generate an error signal. The error signal is applied to a common amplifier base bias line. Preferably, all of the stages of the error amplifier are in a saturated state so that the effect of the error signal on the bias line causes the amplification envelope of the transistors in the amplifier to follow the error signal, thus generating a pulsed output signal having an envelope shape corresponding to the control signal.

Abstract: Disclosed is a control circuit which provides a control signal to a control terminal of a voltage controlled amplifier (VCA), such as a SSM-2018 VCA manufactured by Analog Devices, such that a signal input to the VCA is amplified between full gain and full attenuation. The VCA is characterized by a predetermined control attenuation relationship which determines the gain of the input signal. The control circuit includes: a DC voltage source, preferably a linear potentiometer, which provides a voltage in a fixed range; an operational amplifier for rescaling the fixed range of voltages to a second range; a pair of curve-shaping circuits which adjust the second range; a scaling circuit, including an amplifier circuit, a voltage divider and a zener diode, which adapts the signal from the DC voltage source to a range of voltages calculated from the control attenuation relationship.

Abstract: Disclosed is a control circuit which provides a control signal to a control terminal of a voltage controlled amplifier (VCA), such as a SSM-2018 VCA manufactured by Analog Devices, such that a signal input to the VCA is amplified between +12 dB gain and full attenuation. The VCA is characterized by a predetermined control attenuation relationship which determines the gain of the input signal. The control circuit includes: a DC voltage source, preferably a linear potentiometer, which provides a voltage in a fixed range; an operational amplifier for rescaling the fixed range of voltages to a second range; a pair of curve-shaping circuits which adjust the second range; and a circuit, including an amplifier circuit, a voltage divider and a zener diode, which adds a DC offset and adapts the signal from the DC voltage source to a range of voltages calculated from the control attenuation relationship.

Abstract: A power controller for a class C radio frequency power amplifier that exhibits an output power threshold, including a detector circuit (299) that detects a output power level to provide a level signal when the radio frequency power amplifier has achieved the output power threshold, and a comparator apparatus (245) that combines a reference signal and the level signal to provide a control signal that is arranged to establish the output power level, and a generator function (247) that provides the comparator apparatus a substitute level signal until the amplifier has achieved the output power threshold.

Abstract: An amplifying system for variably amplifying electrical input signals, depending on magnitudes of those signals, with the variation in amplification being selectable as is substantially the maximum output signal value.

Abstract: The apparatus first measures the peak power of a multichannel signal, or representation thereof. The peak power is compared with one or more peak power threshold values. If the measured peak power exceeds a threshold value, the multichannel signal is attenuated prior to being processed by the linear power amplifier.

Abstract: A control device for a power amplifier controls the power amplifier upon a rise in output power based on a power variation pattern stored in storage means to suppress a power overshoot which occurs upon a rise in output power.

Abstract: An output level control circuit for radio-frequency transmitter which intermittently transmits radio-frequency carrier waves such as seen in the TDMA radio communication system and the digital cellular mobile telephone system. The variable gain amplifier unit of this transmitter amplifies the transmitting signal to a predetermined output power level in response to a control signal, the output power level is detected by a detecting diode which receives the application of a temperature-compensated bias voltage, and the sum of the detected output and the bias voltage becomes the detection output to the control loop.

Abstract: For use in amplifying an input signal having an input electric power in response to an amplification control signal to produce an output signal having an amplified electric power and a desired waveform, a power amplifying circuit comprises a reference signal generator (22) for generating a reference signal with a predetermined waveform which defines the desired waveform. A multiplier (23) multiplies the reference signal and a power control signal produced by a power control signal generator (21) to produce a level control signal. A comparator (17) compares the level control signal and a detection signal produced by a detector (14) to produce an error signal. A driver (18) drives a power amplifier (11) based on the error signal.

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: The power amplifier in accordance with the invention is responsive to a power level control signal so as to amplify radio frequency signals to define any one of a plurality of amplifier output power envelopes. The power amplifier comprises means for generating a predetermined time varying signal which represents a predetermined one of the plurality of amplifier output power envelopes, means for modifying the time varying signal in response to the power level control signal for definition of a selected output power envelope and control means for controlling the amplifier output power in response to the modified time varying signal to amplify the radio frequency signal according to the selected one of said plurality of output power envelopes. The time varying signal may be a sequence of values stored in memory.

Abstract: A closed loop amplifier circuit (100) having an on state (202) and an off state (204) is disclosed. The amplifier circuit (100) includes an Automatic Gain Control (AGC) circuit (116). The AGC circuit (116) controls the rate of change in the output power (120) of the amplifier circuit (100) when it changes from the off state (204) to the on state (202) or vice versa. The amplifier circuit (100) also includes a programming circuit (114) that is coupled to the AGC circuit (116). The programming circuit (114) is used to program a desired rate of change into the AGC circuit (116).

Abstract: Circuitry is disclosed for staggering the onset of gain reduction in a series of cascaded gain stages as a function of received signal strength. The staggering is effected by controlling the area ratio between corresponding components in two or more AGC control circuits whose topologies are otherwise identical. The technique is particularly well suited for use in radio receivers fabricated in integrated circuit form.

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: An apparatus for adjusting the amplitude of an electronic signal to a predetermined level in a MOS integrated circuit device. A variable amplifier comprising a plurality of operational amplifier stages whose gain is controlled by capacitor ratios is utilized to amplify an input signal. The output of the variable amplifier is coupled to a comparator comprising a single operational amplifier to compare the output with a reference signal level corresponding to the desired output level of the circuit. The comparator generates an instruction signal to a flip-flop circuit and an up/down counter to provide digital control to the amplifier gain stages. The digital bits of the counter, depending on whether high or low, selectively switch the appropriate capacitors into operation to vary the gain of each operational amplifier stage.

Abstract: A preclipping control technique is utilized to prevent the occurrence of clipping distortions evidenced in the output of an amplifier. Reference means provides an upper voltage level slightly lower than the upper saturation or clipping level of the amplifier output signal, and also provides a lower voltage level slightly higher than the lower saturation or clipping level of the amplifier output signal. A comparator is connected to the output of the amplifier and compares the output signal with the reference levels. Under normal conditions, when the output signal is located within the range lying between the upper and lower reference levels, the amplifier input signal is not attenuated. However, when the output signal goes out of the range, this will activate an attenuator connected between a signal source and the amplifier to introduce a controlled attenuation in the amplifier input signal; clipping is prevented.

Abstract: An AGC circuit for amplifying burst signals has output power which does not vary, regardless of variations in the burst time. This automatic gain control (AGC) circuit has an amplifier for receiving a burst signal input and providing an amplified burst output. The level of amplification is controlled in response to a control signal applied to the amplifier. A negative feedback circuit includes an envelope detector for receiving the burst output and a circuit for providing a comparison signal in response to a comparison between the voltage leads of the detected envelope signal and a reference voltage. The comparison signal is converted into a binary signal which is counted down to provide the amplifier control signal.

Abstract: Circuitry for optimizing the signal-to-noise ratio of a light receiving circuit having an avalanche photo diode to receive the light and an amplifier connected thereto to provide an output signal, the level of the output signal being kept constant despite variations in the light input level by controlling the multiplication factor of the avalanche photo diode and the gain of the amplifier. For this purpose, when the light input level is low, the multiplication factor control voltage for the avalanche photo diode is controlled through a loop which includes a differential amplifier, a diode, and a high voltage generator circuit.

Abstract: A system for detecting an abnormal condition of a high frequency output signal in its power level, comprising: a variable gain power amplifier which receives a high frequency input signal and produces an amplified high frequency output signal; a negative feedback control loop connected to the power amplifier, for automatically setting the power level of the amplified high frequency output signal to a desired one of a plurality of predetermined power levels, the negative feedback control loop being so arranged as to produce a DC signal which is constant in its magnitude so far as the power level of the high frequency output signal is maintained at its set value whichever one is selected from the plurality of predetermined power levels, the gain of the power amplifier being controlled on the basis of the DC signal; and a comparator which compares the DC signal with a reference signal to judge as to whether the high frequency output signal is abnormal or not in its power level.

Abstract: A dynamic range expander which substantially limits the amount of positive expansion without affecting the amount of negative expansion is disclosed. In one arrangement, gain reduction in the amplitude of the output signal is increased when the amplitude of the input signal decreases toward or becomes less than the noise level present in the input signal. The dynamic range expander includes a detector (24) for sensing the amplitude of the input signal and providing a variable DC signal related to the amplitude of the input signal, a control signal generator (30) and an amplifier (34) for amplifying the input signal by a gain variable responsively to the output of the control signal generator. The control signal generator includes a time averager (50) and a summer (40) for providing a second variable DC signal related to the sum of the detector output and the time averaged detector output.

Abstract: A unity gain, closed loop, feedback amplifier is described which accurately defines the changeover point in an AGC system to provide a first output which varies in response to an AGC input signal and is indicative of the level thereof up to a predetermined threshold value and thereafter remains constant and then to provide a second output which is indicative of the applied AGC input signal becoming more positive than the threshold level. The amplifier changeover circuit comprises a first circuit loop and a second circuit loop coupled with a comparator amplifier which is adapted to receive the AGC input signal. With the AGC input signal being less than the threshold level the first circuit loop is responsive to increases in the input signal to provide an output signal which is indicative of the level thereof.

Abstract: A fast slew rate automatic gain control circuit (10) includes a variable gain amplifier (14) which is responsive to a gain control signal and an amplitude detector (18) which produces an amplitude signal corresponding to the amplitude of the received signal transmitted through amplifier (14). The amplitude signal is provided to the input node of a loop filter (24) and to the inputs of threshold detectors (30, 32). Positive and negative slew threshold circuits (34, 38) provide threshold signals respectively for the threshold detector circuits (30, 32). When the amplitude signal is within the range of the threshold signals the loop filter produces the gain control as the function of the amplitude signal. When the amplitude signal is less than the positive slew threshold signal the threshold detector (32) produces a drive signal which is provided to the loop filter (24) and causes the generation of the gain control signal to have an accelerated positive slew rate which increases the gain.

Abstract: An improved system for compressing or expanding the dynamic range of an electrical input signal of the type which includes a variable gain device for controlling the gain of the input signal and a circuit for generating a control signal for the variable gain device including a rectifier for producing responsively to the input signal a DC signal which substantially follows dynamic variations of the input signal. The improvement resides in the provision in the control signal generating circuit of a network of at least three signal paths having a common input terminal connected to receive the DC signal and a common output terminal connected to the variable gain device for coupling a control signal thereto, which signal paths have differing time constants and are automatically selectable as a function of the rate and amount of change in amplitude of the DC signal.

Abstract: An A.G.C. circuit is disclosed having two modulators connected in series to modulate an input signal and an amplifier for amplifying the output of the second modulator and applying it to an output terminal. A detector detects the output of the amplifier and an integrator compares the detected level with a reference so as to produce a control signal dependent on the error. The control signal is applied to the first modulator through an impedance path having an impedance which decreases with increasing frequency, and is applied to the same modulator through an impedance path having an impedance which increases with increasing frequency. In this way, the first modulator performs modulation primarily dependent on the A.C. component of the control signal and a second modulator performs modulation primarily dependent on its D.C. components of the control signal.

Abstract: A delayed AGC circuit in which an AGC detection output is divided into two portions, one of them is applied through buffer means to an IF amplification stage to thereby control the gain thereof, and the other portion is applied to a tuner through a threshold circuit to thereby control the gain thereof. A variable resistor or potentiometer for AGC delay adjustment and a high-frequency bypass device are connected at a point in the AGC signal path from the output of the buffer means to the IF amplification stage.

Abstract: A circuit for limiting the output power of a power amplifier to a preselected value in order to prevent the amplifier from either clipping the input signal or applying potentially damaging signal levels to a loudspeaker connected to the output of the amplifier. The limiting and clipping circuit includes a voltage controlled attenuator through which the input signal passes before entering the amplifier. The amplifier output is compared to an output reference by a control circuit which supplies an attenuation command to the attenuator whenever the output level reaches the reference level. The value of the output reference can be easily adjusted from a fairly low percentage of the amplifier power capacity to the amplifier's maximum power capacity in which condition the circuit prevents amplifier clipping. The circuit is relatively quick to attenuate input signals responsive to excessive output levels, but is relatively slow to reduce the attenuation when the output level is subsequently lowered.

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 audio signal amplitude detector for applying stereo audio signals above a predetermined amplitude to at least one pair of speakers. The audio signal for each channel is amplified and compared with two reference voltages. When the amplified audio signal is below a lower one of the reference voltages, the signal is blocked to the connected speaker amplifier. As the amplitude of the audio signal increases between the first and second reference voltages, an increasing portion of the audio signal is applied to the connected speaker amplifier until a maximum signal is applied when the amplitude is above the second reference voltage.

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: A system for compressing an electrical input signal so that the output signal is related to the input signal in accordance with a predetermined continuous gain function exhibiting (1) fixed gain where the input signal is below a predetermined set threshold level; (2) infinite compression limiting the output to some predetermined level so that as the input increases beyond a certain input level infinite compression is provided; and (3) a soft threshold between unity gain and infinite compression. The system includes a threshold level adjustment which automatically provides a gain adjustment so that the maximum output level (preferably on an RMS basis) remains unchanged with changes in the threshold level.

Abstract: The output voltage of a variable control circuit, such as a variable gain amplifier, (20, FIG. 1), is controlled by a circuit interconnected in the feedback circuit of the amplifier. The circuit determines whether the output voltage falls within a predetermined range by comparing (201, FIG. 2) the output voltage with a reference voltage. If the output voltage falls within the predetermined range, a capacitor (207) is charged. Interconnected with a control input lead (72) of the variable gain amplifier (20), the charge on the capacitor controls the output voltage produced by the variable gain amplifier.