Abstract: The device is adapted to sample and amplify with an optimum gain multiplexed analog signals. It comprises a chain of three interconnected amplifiers, the first of which has a gain of unity, the respective gains of the two others being selected in dependence on their output voltage as compared to a reference voltage. It also comprises three memorizing capacitors each of which is adapted to memorize the output voltage of a corresponding amplifier, and switches, actuated in accordance with the gain selection for each amplifier, to make the necessary connections for operating the chain of amplifiers with the selected gain.

Abstract: A feedback amplifier is configured as a contrast compressor for video signals including a reference blanking level. A feedback resistance is divided into two resistors coupled at a juncture. Contrast compression is accomplished by a diode coupled to the juncture and to a voltage source which may be adjusted to vary the point of onset of compression. The diode current perturbs the operating point of the amplifier, thereby producing a condition in which the blanking level at the output is other than zero volts. This is undesirable as it may affect following circuits adversely or require further setup. A clamp is coupled to the inverting input terminal for offsetting the perturbation of the amplifier operating point caused by the diode current.

Abstract: A circuit for generating a direct control voltage dependent on an alternating voltage, particularly for the generation of a direct control voltage in a system for dynamic compression and expansion, including a storage capacitor for providing the control voltage, at least one electronically controllable charging circuit and at least one electronically controllable discharging circuit connected to the storage capacitor, a comparator for comparing an alternating voltage input signal with a reference value, first and second control circuit paths for connecting the output of the comparator to the control inputs of the charging circuit and the discharging circuit respectively, a time-delay circuit connected in one of the control circuit paths, and an inverter connected in one of the control circuit paths so that the output signals from the two control circuit paths are inverted with respect to one another.

Abstract: A transistor amplifier utilizing AC, for an orchestral instrument, having a non-inverting input, with a predetermined range of linear amplification, a feedback means including a first path independent of transistors for controlling the input within said predetermined range, a supplementary path parallel with said first path and including a zener diode having a breakthrough point at the upper limit of said range, and a plurality of auxiliary paths having breakthrough points higher than that of the supplemental path, and each including a resistor and a zener diode, and arranged with the resistors in parallel and the zener diodes in series, forming a cascade arrangement, and the auxiliary path together being in parallel with the first path.

Abstract: In a circuit for automatic dynamic compression or expansion the control voltage generator generates a control voltage which is linear against the logarithm of the input amplitude. This characteristic is achieved by a transfer member consisting of several transistors which are subject to different reference voltages and the series resistances of which are staggered.

Abstract: Circuit arrangement for the compensation of leakage currents in control elements used for wide band amplifiers, said control elements including two transistors whose bases and collectors are respectively directly connected to one another, whose emitters form the resistor connections and in whose bases a control current is fed. A further identical control element is provided into which such a current is fed that a control current with the value required for the control process flows over its control branch; the control branch of this control element being connected to the control branch of the control element lying in the wide band amplifier for the purpose of feeding in the same control current.

Abstract: An active variable equalizer is arranged to provide a Bode type variable equalizer characteristic without requiring an inductor. The equalization shape remains unchanged as the amount of equalization is varied. This equalizer uses a tandem arrangement of additive feedforward and negative feedback to achieve the mentioned equalization shape.A circuit interconnects with input and output terminals for combining input and output signals into an intermediate signal having a magnitude equal to a weighted sum of the input and output signals. A frequency dependent circuit responds to the intermediate signal for producing a frequency dependent signal that is combined with the input signal to generate the output signal.

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 noise reduction system having an encoder which compresses the dynamic range of an analog audio signal, a transmission medium coupled to the encoder, and a decoder coupled to the transmission medium for expanding and thereby restoring the dynamic range of the compressed analog audio signal. The encoder includes a voltage controlled amplifier (VCA) receiving the audio signal, a high-pass filter also coupled to the analog audio signal, a circuit for obtaining a difference between the outputs of the VCA and the high-pass filter, weighting and level sensing circuits coupled to the encoder output for sensing the level of the compressed analog audio signal, and a limiter circuit coupled to the output of the weighting and level sensing circuits and producing a control voltage applied to the VCA control input in such a manner that the ratio of the gain of the VCA and the gain of the high-pass filter at the pass band thereof does not become less than one.

Abstract: An active variable equalizer is arranged to provide a Bode type variable equalizer characteristic without requiring an inductor. The equalization shape remains unchanged as the amount of equalization is varied. This equalizer uses a tandem arrangement of additive feedforward and negative feedback to achieve the mentioned equalization shape.

Abstract: A circuit arrangement for automatic dynamic compression and/or expansion having an auxiliary circuit provided in the useful signal path or in the negative feedback path of an amplifier. The auxiliary circuit has a first and a second connection point. On the one hand there are arranged between the first and the second connection point a first damping or amplifying member, an electronically controllable damping member and a second damping or amplifying member connected in series. On the other hand means for limiting the voltage or current are arranged between the first and second connection point.

Abstract: A variable gain alternating voltage amplifier having a d.c. negative feedback loop for setting the operating point of the amplifier wherein a change in gain of the amplifier is effected by a variable resistance feedback loop which is connected in parallel with the d.c. negative feedback loop and includes the series connection of a controllable resistor and a capacitor.

Abstract: A gain and impedance switching circuit for an amplifier includes an AF amplifier having an input impedance connected between the input terminal thereof and a reference point and a feedback circuit connected between the feedback and output terminals of the amplifier, a first series circuit consisting of a first impedance and a first ON/OFF switch and connected between the input terminal of the AF amplifier and a reference point (such as ground) and a second series circuit consisting of a second impedance and a second ON/OFF switch connected between the feedback terminal of the AF amplifier and the reference point, the first and second ON/OFF switches being ganged with each other so as to change the input impedance and the gain of the AF amplifier simultaneously.

Abstract: A programmable amplifier includes an operational amplifier receiving an analog input signal of a given polarity and voltage range and a read only memory (ROM) control which actuates six switches in a resistor configuration connected to the amplifier in such a manner as to provide a selection of two gain factors and direct or inverted polarity output in response to combinations of digital signals on two input lines to the ROM.

Abstract: Electrical circuitry for varying the relative distinctiveness between the lead and rhythm audio signals produced by an electrical guitar, or the like, according to the strength with which the musician picks the guitar strings. The rhythm signal is compressed in response to how hard the player strums or picks the guitar, while the lead signal is expanded as a direct function of rhythm signal compression. An electrical signal is generated from the rhythm signal for controlling the extent of compression and expansion of the audio signals.

Abstract: A miniature guitar amplifier, having at least one very small (13/4 inch) speaker driven by complementary transistors connected in an emitter-follower push-pull arrangement, is made to sound very much like a large guitar amplifier having one or more large (12 inch) speakers by providing negative feedback to an operational amplifier that drives the power transistors. The operational amplifier has a differential input stage to provide a noninverting input terminal for the signal from a guitar pickup and an inverting input terminal for the feedback signal.

Abstract: Disclosed is an analog tuning circuit, suitable for multiplexing, having a field-effect transistor connected to the output of an operational amplifier with the drain connected in a feedback loop to the inverting input of the amplifier.

Abstract: A circuit for optional dynamic compression or expansion, with one amplifier located in the useful signal path and controllable in amplification, and an auxiliary branch including one amplifier controllable in amplification and a control voltage generator, to the input of which a useful signal path is connected and the output voltage of which serves to control the controllable amplification in the useful signal path and in the auxiliary branch, and wherein as adjusting members for controlling the amplification of the controllable amplifiers there serve field effect transistors to the control electrodes of which respective direct control voltages are applied. In parallel with the source-sink path of one field effect transistor serving as adjusting member for an amplifier located in the useful signal path there is connected a voltage divider the tapping of which is connected via a separating amplifier to the control electrode of the field effect transistor.

Abstract: Left and right stereo power amplifiers receive power from the 12-volt D.C. automobile supply bypassed by a single capacitor for both amplifiers and energize left and right loudspeakers in series with the junction of the series-connected speakers coupled to ground through a capacitor that allows the left and right speakers to be independently driven by the left and right power amplifiers, respectively, by spectral components above the crossover frequency determined by the speaker impedance and the capacitor impedance. Each power amplifier is driven by an equalizing circuit including a photocell illuminated by an LED that is driven by a feedback signal from the power amplifier.

Abstract: A high fidelity hearing aid is disclosed for providing high quality sound and is primarily directed to those users whose hearing loss is such that they need some amplification for low level signals, but do not need amplification for high level signals.

Abstract: The present invention concerns the transmission of information, and consists in a continuous regulator responsive to the amplitude of a pilot tone included in the signal whose level is to be regulated, including a variable-gain quadripole through which said signal is passed, an automatic gain control loop including a circuit controlling the gain of the quadripole, and an auxiliary feedback loop through which the control circuit also controls the automatic gain control loop. The regulator is applicable with advantage to transmission systems.

Abstract: An automatic gain control circuit is provided with a constant potential circuit point, an amplifier circuit of which the input terminal is connected to the constant potential circuit via a resistor, and a feedback circuit which is connected between the output terminal of the amplifier circuit and the constant potential circuit point and the gain is controlled in accordance with the input voltage. The feedback circuit includes a first transistor whose base is connected to the output terminal of the amplifier circuit, the emitter is connected to a DC power source terminal and a second transistor which has a base connected to the collector of the first transistor and an emitter-collector path connected across the resistor.

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: A variable resistance device utilizes a control signal variable resistor and a first fixed resistor connected in series as a voltage divider as well as a second fixed resistor and an operational amplifier having an input connected between the first fixed resistor and one side of the variable resistor and an output connected through the second fixed resistor to the other side of the variable resistor, as a substantially linear variable resistance device where the variable resistance is obtained across the voltage divider.

Abstract: The gain of an operational amplifier is switched between +K dB and -K dB by switching circuit positions of the input and feedback impedances. The gain is changed in 0.1 dB steps by changing either the input or feedback impedance by a ratio of 1.0116 for each step. The gain is changed in 1.0 dB steps by changing the other of the feedback or input impedance by a ratio of 1.122 for each step. A novel two-pole switching arrangement employs the foregoing techniques to permit unambiguous gain polarity changes.

Abstract: A current mirror amplifier (CMA) has master and slave mirroring transistors of bipolar type, input and output terminals to which the collector electrodes of the master and slave mirroring transistors respectively connect, and a common terminal to which the emitter electrodes of the mirroring transistors connect. The master mirroring transistor is provided with collector-to-base feedback for applying base potential to it which conditions its collector-to-emitter path to conduct input current applied between the common and input terminals of the CMA. The current gain of the CMA as between its input and output terminals is determined by the ratio of the transconductance of the slave mirroring transistor to that of the master mirroring transistor, whenever the base potential of the master mirroring transistor is applied to the base electrode of the slave mirroring via a transmission gate rendered transmissive responsive to a first level control potential being applied thereto.

Abstract: A noise blanker circuit usable in a radio receiver is disclosed. Noise pulses in demodulated received signals are detected by a noise detector amplifier. These detected noise pulses are then processed by a control means which develops control signals that selectively control a blanking gate which is followed by a holding capacitor. The gate and holding capacitor combine to blank out noise in the demodulated signals in response to the production of the control signals. The control means includes an amplifier with an AC negative feedback loop that includes a varactor diode. A rectifier diode is used to develop a DC voltage proportional to the occurrence rate of noise pulses and this DC voltage biases the varactor diode such that noise blanking only occurs when the noise present on the received signal is below a predetermined rate of occurrence.

Abstract: A switchable gain amplifier for use in an FM broadcasting system wherein the gain of a modulating signal is automatically switched to a selected level in accordance with the use or non-use of plural input channels.

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.

Abstract: An amplifier whose transmission factor is to be controlled as a function of a control voltage and including an amplifier member having a negating input, connected to have its impedance varied by the control voltage and an electronically controllable variable impedance having one side connected to the amplifier member output, a second impedance connected between the other side of the first impedance and ground, and a switch assembly for switching the connections within the amplifier between two operating states providing mutually complementary control characteristics, the amplifier member output providing the amplifier output in one operating state and being connected to the negating input in the other operating state, and the point of connection between the impedances being connected to the negating input in the one operating state and providing the amplifier output in the other operating state.

Abstract: A voltage controlled variable gain circuit comprising: first, second, third and fourth same polarity transistors for dividing the output current of a first operational amplifier by dc gain control voltage and being connected with the output terminal of the first operational amplifier to which an input signal is applied; means for driving in inverse phase the respective pairs of a first and third transistors, and a second and fourth transistors; a first feedback circuit including a second operational amplifier with an inverting input terminal connected with the output terminal of the first transistor, a first resistor element and a first PN junction element connected in series between the input and output terminals of the second operational amplifier, and a second resistor element and a second PN junction element connected in series between the output of the second operational amplifier and the input terminal of the first operational amplifier, so as to negatively feedback the output current of the first trans

Abstract: A digitally controllable amplifier unit and musical instrument amplifier incorporating such a unit. Digital control of the transfer function of a high-gain virtual-earth amplifier is effected by switching input and feedback impedances by means of transistor switches. Digital storage means are used to control the transistor switches.

Abstract: A current mirror amplifier (CMA) with controlled current gain, the current gain being changed, for example, responsive to the output condition of a comparator in which the CMA is used in a differential signal combining circuit. In such a comparator application the switched gain of the CMA imparts hysteresis to the comparator characteristics.

Abstract: The input stage of an amplifier circuit formed from first and second semiconductor differential amplifiers comprising a pair of transistors having emitter electrodes connected to each other, respectively. The respective collector electrodes of one pair of transistors in each of the first and second semiconductor differential amplifiers is connected to the respective collector electrodes of the other pair of transistors, the base electrode of one transistor of each pair of transistors respectively being connected to an input terminal of the amplifier circuit and the base electrode of the other transistor of each pair of transistors respectively being connected to first and second negative feedback circuits connected to the output stage of the amplification circuit. First and second electrical switches are respectively connected to the common emitter electrodes of each pair of transistors. One of the first and second electrical switches is controlled to be closed selectively.

Abstract: An improved circuit for producing a signal indicative of an input signal floor level is disclosed for use in determining the noise level of an audio signal in a receiver voting system. An input audio signal which contains noise is amplified by variable gain amplifier circuitry consisting of a constant gain amplifier and a variable attenuator. Detector circuitry then develops a signal which is indicative of the noise level, this signal substantially corresponding to the minimum peak magnitude of the amplified input audio signal. During pauses between audio tones in the input audio signal, this minimum signal magnitude coincides the residual background noise level of the input audio signal. Control circuitry couples the noise level indicative signal to the variable attenuator and constitutes a negative feedback loop for inversely and nonlinearly varying the amplification of the input signal in response to the magnitude of the noise indicative signal.