Abstract: A programmable gain amplifier including first and second gain elements are connected by an impedance selector which allows programmability of the gain of both gain elements. The impedance selector is connected in series with the output of the first gain element. The impedance selector places an impedance in the feedback path of the first gain element or the input path of the second gain element. Errors introduced in the signal path due to the switches are attenuated by the open loop gain of the first gain element. The gain may be equally divided between both stages of the amplifier to allow for optimum band width. Optimum noise performance may be obtained by placing most of the gain in the first stage. An instrumentation amplifier may also be made which further includes a third gain element connected to the gain element with a second impedance selector in a manner similar to the connection of the first gain element to the second gain element.

Abstract: A signal conditioning circuit allows for adjustment of DC offset (zero) and gain (span) by use of a number of resistors and jumpers in an Op Amp circuit. By arranging both the zero and span resistors in a trinary weighted sequence (1/3/9), only 3 resistors and 3 jumpers will be needed for +/- 130% adjustment range in 26 steps of less than 10% each. The total requirement for both the zero and span adjustment in the conditioning circuit is 6 resistors and 6 jumpers, reducing component count, printed circuit space requirements and simplifying jumper settings.

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: A low-distortion radio-frequency amplifying apparatus is equipped with a distortion compensating circuit for generating a distortion signal which cancels a distortion generated during radio-frequency amplification. The apparatus detects a signal corresponding to an envelope power of the output or input of an amplifier, varies a distortion compensating characteristic according to the power value, and compensates a distortion over a wide dynamic range. The apparatus includes a detector for detecting an envelope detection signal of the amplifier, and a controller for compensating the distortion compensating characteristic according to the detected signal.

Abstract: A time variant signal switching circuit that includes circuitry (303 and 304) that detects prescribed zero crossings and restricts switch state changes of a switch complex (305) to those prescribed times the time variant signal is at zero. By restricting switch state changes to prescribed zero crossings voltage transients due to the switching action are avoided.

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

Abstract: A stored program amplifier compensation apparatus utilizing sensing elements to provide the operational states of an RF power amplifier to a controller processor unit which utilizes the operational data to provide a bias control signal to the RF power amplifier. Look-up tables which are stored in the controlled processor unit, contain a bias control signal for all the possible operational combinations.

Abstract: A linear amplifier includes a variable attenuator and a phase shifter for modifying the amplitude and phase of an input signal to compensate for amplitude and phase distortion caused by non-linear characteristics of a high-powered amplifier utilized in a microwave band communications system. An amplitude comparator and a phase comparator compare the amplitudes and phases of input and output signals of the linear amplifier circuit to develop control signals for controlling the operation of the variable attenuator and phase shifter. The elimination of digital signal processing circuitry allows increased speed of operation that is essential for use in the microwave bands.

Abstract: A variable-gain amplifier including a ladder attenuator to which the input signal is applied. The ladder nodes develop progressively attenuated (reduced level) signals corresponding to the input signal. Controllable-transconductance (g.sub.m) stages are connected respectively to the ladder nodes, and a composite of their outputs is directed to a fixed-gain output amplifier. The transconductances of the g.sub.m stages are controlled by an interpolator circuit which steers a control current to each of the g.sub.m stages in sequence in response to an analog control signal as it is varied between minimum and maximum attenuation values. The control current activates each g.sub.m stage in sequence, raising the transconductance of each from effectively zero to maximum and then back to zero, in an overlapping fashion, so as to smoothly lower the overall gain of the variable-gain amplifier as the control signal is swept through its control range.

Abstract: A new instrumentation amplifier design uses three operational amplifiers (op amps), each of which has a feedback circuit connected from its output to its inverting input. The first op amp has a unity gain feedback, and is connected through a gain setting resistor to the inverting input of the second op amp. The output of the third op amp is connected through a resistor to the inverting input for the second op amp, while the third op amp's non-inverting input is connected to one of the second op amp's inputs. Differential voltage input signals are applied to the non-inverting inputs of the first and second op amps, while a reference voltage is applied to the inverting input of the third op amp. The circuit is capable of operating with a single voltage supply (V+) by setting the negative voltage supply together with the reference voltage at ground potential. It has a simplified gain equation based upon the ratio between the feedback resistor for the second op amp and the gain setting resistor.

Abstract: A pulse amplifier has a driver stage and a following splitter/combiner stage for power division onto two output stages connected in parallel as well as a further splitter/combiner stage that combines the output signals of the output stages. The two splitter/combiner stages each comprise a respective further decoupled port each of which is respectively connected to a switch-over device. The further ports are connected to terminating impedances in a first switch position of the switch-over devices and are connected to one another via an additional signal path in a second switch position and the output stages can be respectively terminated with low impedances at their input sides and output sides via switch elements.

Abstract: The light reception signal circuit for photoelectric switch includes a photoelectric conversion circuit for receiving light from a light emitting part controlled for periodic emission. The photoelectric conversion circuit generates an electrical signal corresponding to the quantity of the received light. A programmable attenuator receives the output electrical signal, and attenuates it in even step in response to a digital control signal. A first comparator compares the output voltage with a predetermined upper bound threshold. The first comparator generates a clock signal when the output voltage exceeds the upper bound threshold. A peak holding circuit for receives an output voltage of the programmable attenuator, and holds the peak value of the output voltage on a time constant that is much longer than an emission period of the light emitting part.

Abstract: An analog-to-digital conversion circuit comprises a level detection circuit for detecting the level of an analog input, an amplifier for amplifying the analog input with its amplification degree increased when the detected level is smaller than a predetermined level and decreased when the detected level is larger than a predetermined level, an analog-to-digital converter for analog-to-digital converting the output the amplifier and an attenuator provided in a posterior stage of the analog-to-digital converter for attenuating the digital output of the analog-to-digital converter in association with the amplification degree of the amplifier to maintain a total gain between the analog input and the digital output substantially constant irrespective of the level of the input signal.

Abstract: In an amplifier stage comprising a pair of input current sources, connected in series between a pair of reference potential lines, a pair of output transistors connected between the pair of reference potential lines and defining an intermediate output terminal of the amplifier, a driving circuit comprising active elements and interposed between the input current source and the output transistors, and at least one saturation control circuit comprising at least one control transistor connected with its base to the driving circuit and with its collector and emitter between the output of the amplifier stage and the intermediate point between the input current sources, to detect distortion due to clipping, at least one distribution detection transistor is provided, connected to the control transistor so as to detect the current flowing through the latter, which current is related to the imbalance of the input current sources and therefore to the distortion generated in the stage.

Abstract: A speech amplifier circuit increases the maximum perceived loudness at the speaker (412) and reduces distortion at high volume levels without increasing the power consumed by the speech powder amplifier (410). When a low volume is selected by the volume control (414), the microcomputer (418) sets the step attenuator (406) at a correspondingly high attenuation level and the high-pass filter (408) is bypassed. As the volume control (414) is advanced and the speech power amplifier (410) is 12 dB into clipping, the microcomputer (418) activates the high-pass filter (408) and simultaneously steps the gain of the step attenuator (406) by 6 dB.

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 system for optimizing the RF input drive to a TWT amplifier over a frequency band of interest is disclosed. The system includes a microprocessor-based controller, an RF detector for detecting the TWT output, and a variable attenuator for adjusting the input drive to the TWT. The controller comprises an analog-to-digital converter for converting the video detector signals and providing digital RF level signals which are representative of the TWT output power level. Frequency data is also provided to the controller indicating the frequency of the RF exciter signals driving the TWT. The controller is, therefore, provided with frequency and RF level information, and is adapted to control the attenuator to adjust the TWT input drive for optimum TWT output. The system is operable in a calibration mode wherein the controller follows a calibration algorithm to determine the optimum attenuator setting, resulting in the maximum RF output, for each frequency of interest.

Abstract: A noise reduction system which is unaffected by bandwidth limitations of the transmission system with which the noise reduction system is employed. The noise reduction system is of a type including a compressor, the transmission system, which receives a compressed signal from the compressor, and an expander for expanding a signal outputted by the transmission system. In accordance with the invention, a low-pass filter having a pass band corresponding to the transmission band of the transmission system is provided in the stage prior to the compressor. In another embodiment, a low-pass filter is provided in a stage prior to a level detector within the compressor.

Abstract: An amplifying system and method produces a substantial reduction in the D.C. and even-order harmonics in an output signal by employing a first inverting amplifying stage cascaded with an attenuating stage which is cascaded with a second inverting amplifying stage. The electrical characteristics of each of the two inverting amplifying stages are substantially the same. The gain, in dB, exhibited by each of the amplifying stages is substantially equal to the attenuation loss, in dB, produced by the attenuator stage. Conventional components and fabrication techniques allow substantial attenuation of the D.C. and even-order harmonic components produced by the nonlinearities in the active devices of the amplifiers as compared to a single amplifier case producing the same gain A.

Abstract: An RF amplifier arrangement for providing output signals having a controlled frequency distribution and wherein the amplitude and phase of the input signals to an RF amplifier are controlled as a function of the amplitude and phase, respectively, of the output signals from the RF amplifier and also the amplitude of the input signals are adjusted so as to cause the power of the output signal to vary in accordance with a predetermined sequence, whereby such amplitude control of the input signals results in a modified frequency distribution in the energy of the output signals.

Abstract: An adaptive signal weighting system is disclosed for use in transmitting an electrical information signal of a predetermined bandwidth along a signal path. The system can be used to encode or decode the signal. The system comprises filter means disposed in the signal path for varying the gain impressed on the portion of the information signal within a first select spectral region within the preselected bandwidth. The gain is varied in response to and as a function of a first control signal. Means are provided means for generating the first control signal in response to and in accordance with the signal energy of the information signal substantially within at least a part of the first select spectral region.

Abstract: A variable impedance circuit employing an RIS field effect transistor which greatly reduces distortion at low and high frequencies is obtained by providing means for applying voltages to the RIS field effect transistor at values determined by the following equations: ##EQU1## where V.sub.BG is the backgate voltage, V.sub.D is the voltage applied to the drain, V.sub.S is the voltage applied to the source, V.sub.BO is the DC component of the voltage applied to the substrate, K is a constant, .alpha..sub.1 is a constant, .alpha..sub.2 is a constant, V.sub.GS is the voltage applied to the gate at the end nearest the source, V.sub.GD is voltage applied to the gate at the end nearest the drain and V.sub.GO is a control voltage.

Abstract: An electronic volume for effecting a control of an impedance circuit in audio devices or the like includes a variable impedance circuit disposed in a signal transmission path and adapted to vary the impedance in accordance with an electronic control signal. A hold/through gate switchable between a hold state and a through state and adapted to permit, when taking the through state, the input signal to pass therethrough in synchronization with a clock signal of a predetermined period and, when taking the hold state, to hold and deliver the input signal as a control signal to the variable impedance circuit, is connected to a control circuit adapted to vary the input signal supplied to the hold/through gate at a predetermined rate at each time of receipt of the hold/through gate, and a rate changing means is provided for changing the rate of variation of the input signal coming through the hold/through gate.

Abstract: A variable gain amplifier including common emitter input transistor, a plurality of common base switching transistor to form a cascode amplifier with said input transistor and a resistive network including a plurality of series resistors is disclosed. A plurality of predetermined gains are obtained by programming the resistors. The resistive network may be shared by two or more variable gain amplifiers to provide a selection amplifier.

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 device for measuring the level of a variable signal delivered by a sensor. It comprises a series of attenuators, receiving the signal from the sensor, a squaring and integrating chain for converting the value of the signal delivered by the attenuators into its root-mean-square value, and a recorder. The attenuations are calibrated in dB. The device comprises an AGC circuit, receiving the output signal from the squaring and integrating chain, for switching the attenuators and controlling the recorder. The output signal from the attenuators is maintained constant.

Abstract: To provide for essentially inertia-free amplitude adjustment of video signals, an electrical circuit is provided with a field effect transistor having variable source-drain resistance. The circuit includes two junction transistors which are connected to the gate electrode of the field effect transistor and either to the source electrode or the drain electrode. One such transistor is connected as an impedance converter, and the other in grounded base configuration. By means of a variable voltage applied to a resistor is connected to the gate electrode of the field effect transistor, source-drain resistance of the field effect transistor can be varied essentially linearly.

Abstract: A signal transmission system, particularly for television, comprising a nonlinearity precorrection device having a principal channel and a subsidiary channel. The subsidiary channel comprises a nonlinearity product generator with two amplification channels, a linear channel and a nonlinear channel which enable nonlinearity products having a suitable phase to be extracted by the difference of their output signals. The principal channel comprises a circuit formed from two linear channels in parallel whose output signals are added together in an adder. The output signals of the subsidiary channel and the principal channel are added. This precorrection device enables automatic correction of the nonlinearity products to be set up.

Abstract: An automatic gain control (AGC) circuit arrangement is disclosed as including an AGC loop responsive to an input signal and operative to maintain an output signal at a desired mean level represented by a reference signal applied in the loop and also subjected to amplitude modulation by an AF signal. The circuit arrangement includes modulators outside the loop for changing the level of the input signal by amounts corresponding respectively to changes in level represented by changes in the AF signal and by changes in the reference signal. Therefore, the level of the input signal as received by the AGC loop is at least approximately at the right value and its gain is held substantially constant even when the level of the required output signal for a given input signal changes. Therefore, variations of bandwidth resulting from gain variations are avoided.

Abstract: A digital gain control apparatus includes a digital control signal generator producing a plurality of serial-binary coded signals, a clock pulse signal and a strobe signal. A shift register is supplied with the plurality of serial-binary coded signals and the clock pulse signal from the digital control signal generator. A latch circuit is connected to the output of the shift register and is supplied with the strobe signal from the digital control signal generator to convert the plurality of serial-binary coded signals into a plurality of parallel-binary coded signals. A decoder is connected to the output of the latch circuit to produce a plurality of control signals from the plurality of parallel-binary coded signals. A function selector circuit and a volume adjusting circuit for the selected functions is also provided, each being controlled by the plurality of control signals. The shift register, latch circuit and volume adjusting circuit are formed in one chip-integrated circuit.

Abstract: In high speed high quality modems it is important to be able to preserve the gain value for the automatic gain control system during breaks in transmission to permit rapid resumption of normal operation. The a.g.c. circuit comprises a basic a.g.c. transistor amplifier whose emitter-collector conductance is varied by a control voltage derived from the envelope of the amplifier output voltage which is well known. The invention involves the use of a digital-to-analog converter which is controlled by a digital-updown counter. The counter is controlled by a window comparator which compares the rectified output voltage of the amplifier with a reference voltage level and upper and lower limits. If the output voltage exceeds either limit, the counter is enabled and the appropriate up or down indication is given. The counter is then clocked to change the drive to the d-to-a converter which thereby changes the conductance of the a.g.c. transistor. The state of the up down counter will be used to maintain the a.g.c.

Abstract: A signal control apparatus controls the gain of an amplifier in a proportional stepwise manner to produce in response to an input signal an output signal having a magnitude of relatively accurately controlled value. The amplifier gain is controlled in steps that are proportional to a parameter, such as the magnitude of the output signal itself, thereby providing an automatic gain control function. A method also is disclosed for effecting such signal control. Moreover, such apparatus and method are employed in a system and method for monitoring the occurrence of plural events in a cyclical process, such as the travel of a conveyor belt, the system, then, preferably being a conveyor belt rip detector system.

Abstract: A tone control circuit includes a variable gain amplifier circuit, a first mixer combining the variable gain amplifier output with a tone control circuit input and providing its output signal to the variable gain amplifier input, and a second mixer combining the outputs of the first mixer and variable gain amplifier. The mixers may be either adders or subtractors as long as the natural logarithm of the overall gain of the tone control circuit varies substantially linearly with changes in the feedback ratio of the variable gain amplifier.

Abstract: Circuit for automatic dynamic compression an/or expansion. The circuit has adjusting member (10) for varying the propagation constant in a useful signal path and a further similar adjusting member (30) for varying the propagation constant in a branch path which serves for deriving a control voltage which is applied to the control inputs (11,31) of the adjusting members (10,30) in the useful signal path and in the branch path. Further the circuit has a lowpass circuit (20 . . . 26) which is connected to the adjusting member (10) located in the useful signal path. The circuit can be changed over to a different compander characteristic when the adjusting member (10) located in the useful signal path is connected up as a controllable highpass (10,15). The limiting frequency is of the order of magnitude of the limiting frequency of the lowpass circuit (20 . . . 26).

Abstract: An automatic attenuation circuit comprises a variable loss attenuation circuit that drives circuitry for detecting the level of the output signal of the variable loss attenuation circuit. The level detector drives a periodically reset integrator, which in turn feeds a signal to a comparator, also responsive to a reference. A control circuit responsive to the output signal of the comparator controls the attenuation factor of the variable loss attenuation circuit. The control circuit, which may be a microcomputer, is so programmed that the attenuation factor of the variable loss attenuation circuit is stepwisely increased until the level of the output signal of the variable loss attenuation circuit becomes equal to or below a predetermined level.

Abstract: A syllabic compandor using a pilot in the signal frequency band, with a compression ratio between approximately 2 and 20, including a frequency and delay equalizer in the negative-feedback loss-control circuits of the compressor and expandor, to permit high compression and expansion ratios without positive feedback at any frequency or signal level, the expansion ratio materially less than the compression ratio in some cases, and sampling at more than the Nyquist frequency for the signal band to remove any unwanted periodic wave such as the pilot wave, lying in the signal frequency band, from the output, without altering phase and amplitude of other waves in the signal frequency band.

Abstract: A circuit which provides a control signal to dynamically adjust the level of clipping for an audio signal is described. The criterion for allowable clipping employed by the circuit is whether the clipper induced distortion is noticeable; the clipper induced distortion may be audible, however, remain unnoticeable. A frequency weighted correlation is performed on the audio signal to evaluate the waveform and establish an unnoticeable level of clipping.

Abstract: An adaptive equalizer for a telecommunication system, designed to process high-frequency signals in a band on the order of 50 MHz, comprises several weighting networks with input connections to respective taps of a delay line and with output connections to a summing amplifier, each weighting circuit having a control input to which a selected corrective voltage is applied. Each weighting network includes a bridge with two arms constituted by respective secondaries of an input transformer and two other arms in the form of indirectly variable resistance elements, specifically photoresistors photoelectrically coupled to a pair of light-emitting diodes, capacitively isolated for direct current from other parts of the bridge.

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 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 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: 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: An adaptive signal weighting filter for use in a compander performs a frequency response weighting function so that during the encoding process the spectral region of dominant signal energy of the program signal is preemphasized with respect to other spectral regions and during the decoding process the corresponding spectral regions of the encoded signal are deemphasized with respect to one another in a complementary manner.

Abstract: A multistage amplifier having an automatically programmable gain is disclosed in which the amplifier gain is incremented in binary steps to a desired level. Each amplifier stage is switchable between a first and second gain in a binary sequence such that the four digit output of a sixteen bit counter will increment the total amplifier gain in sixteen binary steps.A readback and decoding circuit for reading magnetic tape is also disclosed in which the signal amplitude of data read from the magnetic tape is compared to a reference voltage which corresponds to the data readback clipping level. Only amplified data which exceeds the predetermined clipping level is gated out of the circuit for processing.

Abstract: An improved gain control circuit for an amplifier having a plurality of parallel connected resistors each having a series switch to selectively switch the resistor into the control circuit to vary the gain incrementally as some continuous function of amplifier input voltage. In one embodiment, the parallel resistors are connected between the amplifier input and output. Alternatively, the parallel resistors may be connected as the amplifier input resistance. A peak follower circuit monitors the amplifier input and applies an output control voltage to a plurality of comparators each having a separate reference voltage. Each comparator generates an output signal when the control voltage exceeds its associated reference and this output is connected to one of the resistor switches to change the parallel resistance incrementally generating a corresponding incremental gain variation.

Abstract: A differential amplifier is connected to an amplifier for comparing an amplifier input signal with the signal fed back by the amplifier feedback circuit. The output of the differential amplifier is coupled to a full wave rectifier the output of which controls an attenuator connected between a source of electrical input signals and the amplifier. When the amplifier is operating in its linear range, the differential amplifier inputs are identical and it does not produce an output. Under this condition, the input signal is not attenuated. However, in the presence of amplifier clipping, the differential amplifier produces an output which, after full wave rectification, operates to increase the attenuation, and thus reduce the amplitude of the signal applied to the amplifier; clipping is limited.

Abstract: The compression portion of an instantaneous companding (compressing-expanding) system includes at least two and preferably four "bi-gain" amplifiers connected in cascade. Each bi-gain amplifier normally has a low-gain state and can be switched to a discrete high-gain state. A discrete reference voltage is provided to compare with the output of each amplifier. The amplifiers are initially switched to their low-gain states and the reference voltage corresponding to the first amplifier is selected. A comparator means makes a comparison between the system's output voltage and the selected reference voltage. The control means switches the first amplifier to its high-gain state or holds it in the low-gain state depending on the result of the comparison. By utilizing a different variable reference voltage and bi-gain amplifiers with two different amplification factors, the number of amplifiers and comparisons is significantly reduced.

Abstract: A noise reduction circuit for uncompressed and randomly compressed audio signals comprises a variable gain stage providing a gain which varies with the magnitude of a DC control signal fed to a control terminal thereby, an AC to DC converter for generating a DC signal proportional to the amplitude of the AC signal fed thereto and a filter for passing middle and upper frequencies and for eliminating or substantially reducing the low frequencies fed thereto and coupled between the audio signal input and the input to said AC to DC converter.

Abstract: An automatic level control circuit utilizes digital techniques in the gain control loop to maintain an output signal within a predetermined amplitude range. A comparator circuit, which has preselected limits or threshold levels that establish the predetermined amplitude range, produces a hysteresis property in its operation. The hysteresis provides a substantial improvement in noise immunity over conventional automatic gain control circuits. The output of the comparator is applied to digital circuitry which controls the variable gain of a linear amplifier. The digital circuitry also includes a preset circuit which sets the gain of the variable amplifier to the middle of its range, thereby reducing the average time required for an input signal to produce an output signal within the predetermined range.

Abstract: This is a seismic digital recording system for use where the seismic amplifiers are placed near the geophone locations and their outputs transmitted by common cable to the recording truck or recorded on magnetic tape at the geophone location. In such a digital recording system, it is impractical to use a high-speed, high gain-ranging amplifier of 15 or 16 bits range. In our design the gain-ranging amplifier is high-speed but employs fewer bits total range. The extra range is made up in a preamplifier which has a variable range of gain, which can be automatically set, but at slower speed. The invention involves a control system which is responsive to the output of an A/D converter which is connected to the output of the gain-ranging amplifier.