Abstract: A distortion limiter for limiting the amount of distortion of an inverting amplifier is disclosed. A comparator produces a pulse when a signal level at an inverting input of the inverting amplifier exceeds a reference voltage level. The pulse charges a capacitor. When the charge on the capacitor is sufficient to raise the gate voltage of a junction field-effect transistor (FET) above cutoff, the FET shunts the input signal to reduce its level. The distortion characteristics can be controlled by using a voltage divider to adjust the voltage across the FET. A bias voltage at the gate of the FET, keeps the FET turned off when the inverting amplifier is not clipping.

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: The gain of a recursive integrator is controlled so as to be adaptive to the quality of a received signal by comparing the magnitude of its emphasized information component with a reference voltage and controlling the gain of the integrator's feedback delay path in accordance with the difference between the peak value of the emphasized information component and the reference voltage. As a result, when the signal to noise ratio of the input signal is high, the gain can be reduced, so that the recursive loop will adapt quickly to changes in a multipath profile.

Abstract: A detector for use in an automatic gain control amplifier and operated to generate a gain control voltage in response to an amplitude of the output signal of an amplifier circuit includes five transistors connected in a detector circuit. The first transistor receives a bias voltage at its base and the second transistor receives a true signal of an input signal along with the bias voltage at its base. The third transistor receives a complementary signal of the input signal along with the bias voltage at its base. A first current source is connected in common to the emitters of the first to third transistors. A control voltage is supplied between the bases of the fourth and fifth transistors. A second current source supplies an operating current to the fourth and fifth transistors. A first load is connected in common to the collectors of the first and the fourth transistors. A second load is connected in common to the collectors of the second, third and fifth transistors.

Abstract: An ECL logic circuit having differential inputs and differential outputs and programmable propagation delay time is provided. The differential inputs are coupled to a first differential amplifier as is done on a conventional differential ECL circuit. A second feedback differential amplifier is coupled to the collectors of the first differential amplifier. Current in the first differential amplifier is normally constant, whereas current in the feedback differential amplifier can be programmably adjusted. By adjusting the current in the feedback differential amplifier the feedback differential amplifier loads the logic circuit forcing a voltage swing which is up to double that normally provided by the first differential amplifier, therefore increasing the time required for either output to change from a logic LOW to a logic HIGH. This delay results in a variable propagation delay which is controlled by adjusting current flow in the feedback differential amplifier.

Abstract: A gain control circuit for an amplifier having a stepwise variable gain is disclosed, which includes a peak detector detecting and holding a peak value of an output voltage of the amplifier, a reference voltage generator generating first and second reference voltages having values different from each other, a comparator circuit comparing the peak value with the first and second reference voltages, and a control circuit responding to a comparison output derived from the comparator circuit and controlling the gain of the amplifier one step by one step such that the peak value becomes to intervene between the first and second reference voltages. When the peak value exists between the first and second reference voltages, the control circuit holds the gain of the amplifier at the current value, so that the amplitude of the output voltage is controlled to be substantially constant.

Abstract: An Automatic Gain Control (AGC) circuit which compensates receiving sensitivity on the part of subscribers depending on the line status of a central office line (C.O.L.) in a private branch exchange (PBX), by means of using an analog system, utterly.

Abstract: An integrated compression amplifier that can be constructed in CMOS technology and whose threshold voltages are programmable. The compression amplifiers can be built into a multi-channel AGC device, so that the circuit can be co-integrated on a "switched capacitor" filter chip in CMOS technology. The compression amplifier circuit essentially involve a feedback amplifier whose gain is controlled by the output amplitude. To this end, an amplifier SC having variable gain constructed as a "switched capacitor" amplifier, a rectifier unit GR' as well as a low-pass filtr TP' are in a feedback branch and a two quadrant multiplier ZM1 is connected between the input and output Ue', Ua' of the compression amplifier. The output of the lo-pass filter TP' is thereby fed back onto the control input of the two quadrant multiplier ZM'.

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: An improved compansion system that more effectively increases the dynamic range of other circuit elements. The system includes both a compression circuit to limit the input signal amplitude for a circuit element, such as a filter, and an expansion circuit to receive and modify the output of the circuit element. The expansion circuit restores a substantially linear input-output amplitude relationship and may prevent substantial overloading in the circuit element, thereby increasing the dynamic range of the circuit element.

Abstract: To increase the dynamic ratio of an amplifier, it is preceded by a switchable attenuator which is switched on when the output voltage of the amplifier exceeds a threshold, this output voltage being added to a shifting voltage.

Abstract: A current-saving CMOS signal input buffer is provided, having at least two CMOS output transistors (each having an input) connected in complementary fashion with a common output taken therebetween, complementary current mirrors coupled to the output transistor inputs, an input signal capacitively coupled to at least one of the output transistor inputs, a reference impedance coupled between the complementary current mirrors, and isolation impedances coupled between the complementary current mirrors and the output transistor inputs.

Abstract: A noise reduction system compresses an input signal at a constant ratio in response to a control signal derived from the compressed signal. Added to the derived control signal is a counterfeit control signal which causes the compressor to mistrack when the compressed signal falls below a preselected threshold level. Thus, low level compressor output signals are increasingly deemphasized. A constant counterfeit control signal produces a logarithmic decrease in compressor output signal levels below the threshold point. The resulting compressed signal is used in two ways to enhance system noise reduction. First, the compressed signal is expanded at a constant ratio over all signal levels so that low level mistracked signals are further deemphasized and the system noise floor is lowered.

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: 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 automatic gain control (AGC) amplifier circuit uses a control loop comprising a digital counter (70) which controls a multiplying digital-to-analog converter (10) arranged as an attenuator of the input v to the AGC. The counter (70) is arranged to count up or down depending upon the output signal of the AGC circuit. In addition, a latency can be introduced into the control loop so that in case of most signal envelope variations, the counter is frozen to prevent output fluctuations.

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: 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: There is disclosed a delay compensated automatic gain control which allows improved automatic gain control in analog and digitally implemented systems. The AGC system and technique includes a primary high speed control loop implemented after the intermediate frequency filtering and a secondary loop which controls the radio frequency gain prior to the intermediate frequency filter without affecting the overall response of the automatic gain control system. The resulting action of the two loops provides an automatic gain control for the radio frequency and intermediate frequency stages in both analog and digitally implemented systems without sacrificing speed of response or stability of the systems.

Abstract: An automatic gain control circuit suitable for use in a modem receiver for receiving a modulated carrier representing data, includes a variable gain amplifier adapted to receive an input signal and coupled to an output amplifier providing the gain controlled output and also coupled to a level detector which provides a high level output signal whenever the input thereto exceeds a reference level, such output signal causing an attack operation wherein a control current generator provides an exponentially decreasing control current for an operational transconductance amplifier included in the variable gain amplifier. When the level detector output is high for more than a predetermined time a noise hit protection circuit is effective to inhibit the attack operation for a further predetermined period of time, thereby alleviating the adverse effect of a noise pulse.

Abstract: The amplitude modulation detection device, which is provided with an AM (amplitude modulation) responsive to first and second input signals for maintaining a constant D.C. level output signal, the first signal being the AM signal, and the second signal produced by feedback loop which includes a D.C. voltage comparator connected to the detector for comparing the D.C. output level of the detector with a reference signal level.

Abstract: A wide dynamic range automatic gain ranging amplifier system includes an amplifier which receives an analog input signal and amplifies the received analog input signal in accordance with gain control signals to provide an amplified signal. A network connected to the amplifier also receives the analog input signal and provides the gain control signals corresponding to a desired gain for the amplifier in accordance with the received input signal and also provides gain status signals representative of the gain associated with the amplified signal.

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: An input signal level control device for a receiver particularly adapted for use in a mobile FM receiver in which the received electric field strength changes abruptly and greatly. An attenuating device such as a switching diode is coupled to an input of a high frequency amplifier to which the input received signal is fed. The attenuating device switches on when the received electric field strength reaches the first predetermined value. As the electric field strength continues to increase and reaches a second value greater than the first, a control circuit controls the gain of the high frequency amplifier in accordance with the electric field strength.

Abstract: In an automatic gain control circuit specifically adapted to control the gain of an amplifier for operating a noise cancelling circuit, a detector is provided for detecting a detector input signal, such as detected noise pulses. The detector includes a differential amplifier comprising a transistor pair connected to a constant current source. According to the detector input signal level, the constant current is switched between the transistor pair. The normally off transistor of the pair is connected to a third transistor, through which a substantially invariant current flows to relatively slowly charge a capacitor in a time constant circuit when the input signal level exceeds a reference level given by the difference between a pair of bias voltages for the transistor pair. The voltage accumulated across the capacitor serves as an automatic gain control signal, which rapidly disappears when the input signal level decreases below the reference level.

Abstract: For use in combination with a gain controllable amplifier for amplifying an input signal to produce an amplified signal with the gain controlled by a gain control signal, an automatic gain control circuit comprises a first section for shifting the level of the amplified signal by a first reference level and a second section for carrying out envelope detection of the amplified signal to produce an envelope detected signal of which the level is shifted by a second reference level different from the first reference level. A comparator compares the level-shifted signal with the envelope-detected signal to produce a pulse signal when the level of the latter signal traverses that of the former. The pulse signal is supplied to a smoothing circuit to produce a smoothed signal serving as the gain 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 detector suitable for use in a recording amplifier of a cassette recorder for limiting the signal which is applied to the write head at a specific average amplitude. The detector comprises a pre-amplifier T1 to T4 having an input (15) and an output (17); a comparator (T6) having a first input (base) coupled to the output of the pre-amplifier, and a second input (emitter) for detecting whether a detection voltage at the second input is exceeded by the voltage on the first input of the comparator circuit; a reference voltage source (V.sub.ref); first means (4) for maintaining the d.c. level at the output of the pre-amplifier (T1 to T4) at the level of the reference voltage source (V.sub.ref); and second means (T10, T11) for raising the detection level of the comparator circuit by the reference voltage.

Abstract: An automatic level control circuit including a current controlled attenuator wherein the amount of attenuation is controlled by a control current, an amplifier for amplifying an output signal of the attenuator, a current rectifier for forming a DC current source in accordance with the amplitude of the output signal voltage from the amplifier, and a current shunt for absorbing an output current fed from the rectifier. The control current is produced as a difference between the current from the rectifier and the current absorbed by the shunt. When the current fed from the rectifier is larger than that absorbed by the shunt, the automatic level control circuit operates in a manner that, when its input signal is at low level, the circuit gain is large and, as the input signal level rises, the circuit gain drops.

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 input signal is coupled via a capacitor to a base of a transistor which constitutes a differential amplifier with another transistor. The base of the transistors are respectively fed with first and second predetermined voltages via a pair of transistors so that the differential amplifier produces an output signal proportional to the difference between the peak value of the input signal and a predetermined value only when the peak to peak value of the input signal exceeds a predetermined voltage.

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 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.

Abstract: A circuit is provided for protecting an amplifier from signal overload upon the application of strong signals at the input to the amplifier. A unidirectionally conducting semiconductor device and a capacitor are serially coupled between the input to the amplifier and ground. Means for maintaining a constant voltage is coupled to the junction of the semiconductor device and the capacitor. Upon the application of a strong signal at the input to the amplifier, the semiconductor device conducts current to the junction of the constant voltage means and the capacitor, causing the voltage across the capacitor to increase. The constant voltage means senses this voltage increase, and responds by opposing the voltage increase so as to maintain a substantially constant voltage across the capacitor. The constant voltage at the junction of the semiconductor device and the capacitor maintains the semiconductor device in a low impedance state, thereby attenuating the strong signal at the input to the amplifier.

Abstract: The effective sensor width of a path following vehicle guidance system is enlarged by having a first gain control amplifier for amplifying the sum of the path sensor signals, a second gain control amplifier for amplifying the difference of the path sensor signals and a third amplifier, in tandem with the second amplifier for amplifying the output of the second amplifier once the second amplifier's output has peaked out. All three amplifiers are gain-controlled by the same negative feedback signal. The outputs of the first and third amplifiers are synchronously detected to provide an error signal for an electromechanical steering servo for the vehicle.

Abstract: In a multi-stage amplifier with delayed AGC-control gain control in one stage is effected by means of controllable current distribution between control transistors. The take-over point of the delayed AGC for a previous stage is determined from the ratio between the direct currents of said control transistors.

Abstract: An AC input signal and a DC supply voltage are applied to a tapped coil having end points from which differential input signals are coupled to a differential variolosser that controls the gain of cascaded differential amplifiers. The two output terminals of the cascaded amplifiers are electrically connected together through a pair of equal valued resistors to provide a DC reference voltage at the junction of the two resistors, where the AC signals cancel. The reference voltage is coupled to one side of a high-gain differential control amplifier and to both sides of a differential half-wave rectifier circuit. One side of the rectifier is also connected to one output of the cascaded amplifiers for detecting an amplified signal there. The detected signal is integrated and coupled to the other side of the control amplifier to produce the control signal which regulates the drive current to and loss presented by the variolosser, and thus the level of the input signals to the cascaded amplifiers.

Abstract: In a radio receiver IF amplifier, a high gain AGC circuit produces a constant signal output regardless of input signal levels in excess of a threshold value. A summing amplifier responds to the AGC voltage and the IF amplifier current to develop a d - c potential directly proportional to the signal input to the amplifier both above and below the AGC threshold. This voltage is useful in the squelch and signal strength meter circuits.

Abstract: A signal level stabilizer includes two amplifier stages, each stage having a respective feed-back loop to control its gain. The gains of the amplifiers are varied in response to variations in the level of the input signal to give a substantially constant output signal. At low levels of the input signal the gain of one of the amplifiers only is varied in response to variations of the input signal and at high levels of the input signal the gain of the other amplifier is varied. The amplifiers may be part of a repeater in an optical communications linkage and one of the amplifiers may then be a photodiode and the other a power amplifier.

Abstract: A sensitivity control circuit is described for use with a sound movie camera having an automatic sound level control circuit. In one embodiment, the automatic sound level control circuit includes a pair of cascaded amplifiers whose overall gain is controlled by the conduction of an active control element. The active control element has an input terminal which receives a control signal representative of the amplitude of the signal output of the cascaded amplifiers. To desensitize the automatic sound level control circuit to background noise, a voltage source and a variable impedance element are serially coupled to the control terminal of the active control element to provide a control current for selectably varying the conduction of the active control element. The gain of the cascaded amplifiers is thereby selectively controlled and the sensitivity of the automatic sound level control circuit is reduced.