Abstract: A multifunction amplifier uses a finite transconductance amplifier to provide an amplifier with a high impedance input and a desired output impedance. A pair of appropriate polarity binary signals are summed to form a ternary signal which may be filtered by a filter circuit upon command. The ternary signal, filtered or unfiltered, is input to one input of a differential transconductance amplifier while a feedback signal via a feedback path from an output node of the finite transconductance amplifier is input to the other input. The outputs of the differential transconductance amplifier are equally amplified by a pair of output current gain amplifiers. A unity gain bias level shifter is provided between one of the differential outputs and one of the pair of output amplifiers. The output amplifiers combine the amplified output currents at the output node.

Abstract: A low pass filter circuit for filtering out high frequency AC components from an electric signal including a DC component and possibly low frequency AC components is disclosed herein. This circuit includes a first order, low pass RC filter network, free of any active elements, for receiving a signal at an input and passing the entire DC component and any low frequency AC components present in the signal to an output. The circuit also includes circuitry utilizing at least some active components and a predetermined transfer function for filtering out high frequency components in the signal over a predetermined, relatively narrow roll-off frequency band. This latter circuitry cooperates with the RC network so that the operation of its active elements does not act on the DC component of the signal and therefore does not affect the amplitude of the DC component as it appears at the output.

Abstract: An analog two pole filter is provided which uses a single amplifier to implement a predetermined transfer function. The filter has a differential input and converts the two inputs to a single output utilizing the same amplifier which performs the filtering function. By coupling a capacitor across the differential input and utilizing the differential aspect of the input signals, the capacitor may be implemented with half the capacitance otherwise required to implement the predetermined transfer function, thereby minimizing circuit area.

Abstract: A phase shift circuit comprises a variable phase shifter responsive to an externally supplied voltage to change the amount of phase shift, and a phase detector operative to detect a phase difference between input and output signals of the variable phase shifter and supply a voltage complying with the phase difference to the variable phase shifter. When the center frequency of the variable phase shifter is changed by reason of production errors and temperature variations to deviate the phase shift amount from a desired value, the phase detector controls the center frequency such that the phase shift amount can be fixed to the desirably predetermined value.

Abstract: An input signal is divided equally by a divider and the equally divided outputs are applied to first and second amplifying means, respectively. A filter means, which rejects the fundamental wave component of the input signal but passes therethrough its harmonic component, is connected between the first and second amplifying means. The outputs of the first and second amplifying means are respectively connected to first and second select circuits which select the fundamental wave components of the input signal. The outputs from the first and second circuits are combined in phase with each other, by a combiner, into a composite signal.

Abstract: The drain-source conductance of a wide variety of FETs can be made to conform to a predetermined function of a control signal. The control signal is multiplied by a factor and an offset is added or subtracted therefrom to derive a modified control signal. The modified control signal is then applied to the gate of a FET. The factor and the offset are such that the drain-source conductance of the transistor is substantially the predetermined function of the control signal. When a desired attenuator characteristic defined with respect to a FET is to be provided using a FET having characteristics different from those of the reference FET, the control signal to the FET used can be similarly modified so that the desired attenuator characteristics are obtained.

Abstract: In an amplifier for a high frequency signal used to amplify a signal having a high frequency in a television tuner, a receiver for satellite broadcasting, and the like, at least two stages of dc-coupled grounded-emitter type amplifiers (Q.sub.1, Q.sub.2) are configured in an integrated circuit, a resistor (R.sub.13) is connected between an emitter of the grounded-emitter amplifier (Q.sub.2) in the second stage and the grounding, a terminal for connecting an external device is disposed to be connected via a bonding wire to the emitter of the grounded-emitter amplifier (Q.sub.2) in the second stage, and a filter circuit (11) including an inductance of the bonding wire and developing a low impedance for a particular frequency is disposed between the terminal and the external grounding.

Abstract: A towable broadband submarine antenna system for deployment in the ocean ing operation comprises an antenna element including a metallic termination tip and a length of single conductor buoyant cable. A broadband amplifier connects to the antenna element and provides separate paths for the VLF/LF and the HF/VHF signals with amplification provided only to the HF/VHF signals. The signal from the broadband amplifier is further transmitted on a coaxial cable.

Abstract: A compensating amplifier for an automobile antenna which is relatively short and free from interference from high frequency band television signals. The amplifier includes an inductive element in a primary serial tuning circuit of a multiple tuning circuit of an antenna which is connected in parallel to a condenser, and the parallel resonant frequency of a parallel circuit which is formed by the inductive element and the condenser is set at approximately the same resonant frequency as the resonant frequency of the antenna.

Abstract: A field effect transistor microwave circuit device includes first and second field effect transistors having common source connections with a pair of coupled transmission lines connecting the drain of a first transistor to the source of the second transistor and the source of the first transistor to the gate of the second transistor. The cross coupled transmission lines function as a balun between the transistors. The device is formed in III-V semiconductor and has an increased operating range in microwave frequencies. In alternative embodiments, the balun is connected to the circuit output thereby permitting the cascading of a plurality of FET devices. The balun can be integrated into the device structure or connected as a discrete element in a hybrid circuit arrangement.

Abstract: An integrable, high frequency superlinear amplifier and its fabrication method is disclosed which is related to the basic amplifier fabrication field having negative feedback and signal conversion. The three stage amplifier design involves a first and second stage which have a narrow bandwidth response and a third amplifier stage with a larger or wider bandwidth response. The bandwidth of the wide bandwidth stage is such that when the gain curve for the two narrow bandwidth stages passes through the -6dB point at a first frequency then the peak point of the wide bandwidth stage is located at a second frequency higher than the first frequency. The wide bandwidth stage utilizes a single capacitor so that the resulting curve of the three stages has an approximately flat portion below the zero gain point. The impedance of the network is adjusted to a desired value through a feedback configuration.

Abstract: A circuit arrangement for coupling alternating voltage signals having frequencies within the audio frequency range between a low noise audio frequency source and a zero ohm amplifier, wherein the audio frequency source has a known source impedance. The circuit arrangement includes an output connected to the zero ohm amplifier and a highly resistant input for receiving the alternating voltage signals from the audio frequency source. The input is more resistant by at least one power of ten than the source impedance of the audio frequency source and the arrangement has a voltage amplification factor which is so low that no overshooting of the output signal will happen at the maximum occcurring voltage of the signals received at its input. The output of the arrangement is configured as a short-circuit resistant alternating current source which furnishes a maximum effective current of at least 10 mA.

Abstract: An active low-pass filter especially suitable for inclusion in an integrated circuit and capable of operating at frequencies up to at least f.sub.T /.beta. of transistors within the filter. A bootstrap circuit is coupled to the emitter follower to reduce the capacitive effect of the emitter follower on the passed signal and to guarantee precision pass band gain match among the filters. A plurality of active filters may be connected across the signal path to provide a selection of bandwidths. A filter is switched into and out of the signal path by selectively enabling and disabling its current source.

Abstract: A differential charge amplifier design for a hydrophone pre-amplifier inces a calibration circuit for in situ measurement of the hydrophone/pre-amplifier gain. The hydrophone signal is input to a pair of amplifier stages which form a balanced differential input charge amplifier. The signal from the input charge amplifier is amplified by a second pre-amplifier stage and then passed to a balanced output cable driver. The calibration circuit is enabled by an external signal to inject a calibration signal into the input charge amplifier front end.

Abstract: A high-density analog integrated circuit having built-in resistor elements formed simultaneously with the formation of the base of transistor is disclosed in which a high-resistance element is formed of an ion-implanted resistor, a low-resistance element is formed of a base-diffused resistor, and a pair of high-resistance elements are connected in such a manner that a difference between a signal current flowing through one of the high-resistance elements and another signal current flowing through the other high-resistance element is outputted, and in which an ion-implanted resistor having a high resistance and a thin film capacitor having a small capacitance make up a built-in time constant circuit, which makes it possible to integrate on one semiconductor chip circuits such as a filter circuit for video signal and an input bias circuit.

Abstract: An active filter circuit having emitter coupled first and second transmittors and emitter coupled third and fourth transistors, wherein the base and collector electrodes of the third transistor are connected to the base electrode of the first transistor, and the base and collector electrodes of the fourth transistor are connected to the base electrode of the second transistor with a reactance circuit connected to a collector electrode of the second transistor and an output terminal connected by the collector electrode of the second transistor such that the filter circuit has a small number of components and operates over a broad band.

Abstract: A CMOS integrated filter includes a passive network of resistive and capacitive paired elements and a first differential amplifier, for implementing a second order low pass filter function. A second amplifier is connected in voltage following configuration at an input of the first amplifier. A filter output is provided by an output of the second amplifier.

Abstract: A low noise, high gain differential amplifier suitable for EEG amplification is constructed in a shielded metal enclosure, preferably on a ground plane circuit board. The amplifier is battery powered to eliminate all possibility of noise from the power system. The amplifier utilizes a pair of operational amplifiers to provide high input impedance for each of two input signals. A differential amplifier generates an internal signal which is filtered and amplified by a pair of bandpass amplifiers and overlapping low pass and high pass amplifiers.

Abstract: A second order all pass network for wide-band signals, and comprising second and third voltage-current converting circuits with their respective positive input terminals supplied with input signals from an input terminal of the network and their negative input terminals supplied with output signals from an output terminal of the network. A first voltage-current converting circuit has its positive input terminal supplied with a positive output of the second voltage-current converting circuit and a negative input terminal supplied with the output signals. A first capacitor is connected between the input and output terminals, and a second capacitor is connected between ground and the positive output of the second voltage-current coverting circuit.

Abstract: A RC coupling filter, especially an input filter for receivers of centralized ripple control systems, with at least two similar active RC four terminal networks with at least one amplifier each, each four terminal network having an input and every two adjacent RC four terminal networks being interconnected by means of exactly one coupling admittance connected between the inputs of the adjacent RC four terminal network, wherein, if the signal to be filtered is introduced into the input of the first RC four terminal network, a feeding admittance is connected at one end to the input of the first RC four terminal network, the signal to be filtered being introduced into the other end of the feeding admittance.

Abstract: A bandpass filter is presented which allows variation of bandwidth while passband gain remains constant. The presented bandpass filter relies on feedforward (as opposed to feedback) to compensate for losses within the bandpass filter. Two feedforward circuits are shown, one a current source and the other a voltage source in series with a resistance.

Abstract: A variable emphasis circuit comprises an operational amplifier for receiving an input signal, a modified integrator for receiving a first signal provided from the operational amplifier, and a dividing circuit for dividing the first signal to k times and 1-k times according to a control voltage. The 1-k times the first signal and a second signal provided from the modified integrator are fed back to the operational amplifier, and an output signal is formed from the second signal and the k times the first signal.

Abstract: A capacitor is disclosed having two capacitor elements of MIS structure, the capacitor elements being connected in a zigzag manner to realize a balanced parallel connection for the capacitor elements. A circuit having a pair of balanced impedance branches, the branches being bridged by the balanced parallel capacitor disclosed above, resultantly sustains the impedance branches balanced regardless of the amount of the parasitic capacity involved.

Abstract: A tuning system employs a specific resonant circuit which includes two electrodes confronting each other through a dielectric interposed therebetween. Each of the two electrodes has at least one bent portion to present a lumped-constant inductance and has a desired equivalent electrical length. The two electrodes respectively have common terminals located out of mutually confronting positions so that voltage signals induced by mutual inductance between the electrodes will be opposite in phase so as to thereby produce a parasitic distributed-constant capacitance. The two electrodes form a two-terminal circuit network having a first terminal disposed at a desired position on one of the two electrodes and the common terminals as a second terminal. The first terminal of the resonant circuit is connected to a feedback amplifier, an amplifier, or a mixer so as to form a tuning oscillator, a tuning amplifier or a mixer.

Abstract: A limiter amplifier having a pair of transistors connected in a common emitter, balanced push-pull amplifier type of circuit arrangement is disclosed. The transistors are interconnected by a series tuning capacitor at their emitters. A separate constant current source is connected to each of the emitters of the transistor pair. By selecting the value of the tuning capacitor to resonate with the inherent inductive component of the emitter source impedances in a particular frequency band, the limiter amplifier acts as a differential amplifier in the particular frequency band. The ac coupling of the emitters gives the limiter amplifier a bandpass filter type feature as well as high gain and low phase variation over large dynamic ranges of input signal amplitude. Impedance matching/buffer circuitry and isolation circuitry are also disclosed which permit the cascading of limiter amplifier gain stages.

Abstract: An adjustable active filter includes a transconductance amplifier (60) and a current source (40, 42) which may be adjusted in value. The resonant frequency of the active filter may be adjusted upwards by increasing the bias current of the transconductance amplifier using a frequency trim up network (48). The resonant frequency may be adjusted downward by decreasing the bias current using a frequency trim down network (44). The trim is preferably accomplished by shorting out zener diodes (120, 122, 124, 126, 150, 152) which control the bias current of the transconductance amplifier.

Abstract: A constant amplitude, variable-bandwidth filter is provided having a variable resistor and a high-Q passive filter cascaded between a pair of amplifiers. The input amplifier having a low output impedance and the output amplifier having a low input impedance. As the resistance of the variable resistor is varied, the Q of the system varies and thus its bandwidth. The gain of the system also varies as the variable resistor is varied. To compensate for the gain variation, a current, equivalent to the value of the output voltage of the input amplifier divided by the value of the equivalent series resistance of the high-Q passive filter, is inserted at the node where the variable resistor and the high-Q passive filter are coupled one to the other. This results in a constant current at resonance being conducted by the high-Q passive filter, independent of the selected overall bandwidth of the filter.

Abstract: The subject of the invention is a high frequency bandpass amplifier with adjustable impedance, in particular for a high frequency quartz resonator. It includes a transistor T connected in common base the emitter of which is connected to ground by a resistive divider bridge (R.sub.2, R.sub.1) the mid-point of which forms the input of the amplifier. The collector of the transistor (T) is connected to ground by a parallel circuit (LC) having one inductive side (L) and one capacitive side (C), a mid-point of the inductive side (L) or of the capacitive side (C) forming an output (s.sub.1 or s.sub.2) of the amplifier (A). The base of the transistor is biased and connected to ground via a capacitor (C.sub.3) ensuring common base operation in the pass-band of the amplifier. The invention also relates to an oscillator of transmission type including such an amplifier and a resonator (1) connected between the input (e) and one output (s.sub.1 or s.sub.2) of the amplifier (A).

Abstract: A two-stage band-pass amplifier filter circuit which uses a bi-quad amplifier in each stage, the bi-quad amplifier being connected between an AC feedback amplifier in the signal transmission path and ground. The bi-quad amplifiers each provide a variable impedance and effectively operate as series-resonant circuits such that, during closed loop operation, the overall amplifier-filter circuit has a high gain at or near resonance and a very low gain off-resonance and has a phase shift of 0.degree. at resonance and .+-.90.degree. substantially off-resonance. The bi-quad amplifiers are connected to the feedback resistance of the signal path amplifier via a coupling resistance, the signal path amplifier feedback resistance being greater than the coupling resistance, normally by a factor as high as 20 to 1, so that the bi-quad amplifier is thereby prevented from overloading during operation.

Abstract: Disclosed is a wide band high output amplifier in which a field effect transistor is used as an output element, in which a constant resistance circuit is inserted between the drain terminal of the field effect transistor and a load capacitance such that the impedance characteristic is a constant resistive value and provides a peaking function across the load capacitance so as to improve the high frequency characteristic of the amplifier without increasing the imput impedance of the field effect transistor.

Abstract: With narrow-band amplifiers whose output line is located close to the input line, an unwanted feedback may be produced which results in self-excitation of the circuit or at least in a reduction of the bandwidth. According to the invention, a supply line is arranged between the two lines, which supply line is completed with a capacitor to provide a resonant circuit which resonates at the signal frequency of the narrow-band amplifier. As result thereof, energy is withdrawn from the feedback path, causing the feedback to be reduced.

Abstract: A notch filter is provided having a low-pass section and a summing section which are capable of being integrated on a single semiconductor chip. The summing section provides an output signal which is the sum of a first component signal proportional to an output signal of the low-pass section and a second component signal proportional to current flowing in a capacitor in the low-pass section such that the high-frequency response of the low pass section is compensated to provide an output signal characteristic of a notch filter.

Abstract: A filter circuit which operates as a substantially optimum integrating circuit comprises input and output terminals and a differential amplifier, the amplifier having an inverting input connected to the output via a series circuit including a first capacitor and a first resistor. The amplifier output is coupled via a series circuit of a second resistor and a second capacitor to a terminal carrying a reference voltage. The non-inverting input to the amplifier has a DC connection to the reference voltage terminal. One input to the filter circuit connects to the reference voltage terminal, the other filter circuit input being in circuit with the inverting input to the amplifier. The junction between the second resistor and the second capacitor connects to the filter circuit output terminal. The RC time constant of the first capacitor and the first resistor is substantially equal to the RC time constant of the second capacitor and the second resistor.

Abstract: An active R bandpass filter network (10) is formed by four operational amplifier stages interconnected by discrete resistances. One pair of stages (12, 14) synthesizes an equivalent input impedance of an inductance (L.sub.eq) in parallel with a discrete resistance (R.sub.0) while the second pair of stages (16, 18) synthesizes an equivalent input impedance of a capacitance (C.sub.eq) serially coupled to another discrete resistance (R.sub.i) coupled in parallel with the first two stages. The equivalent input impedances aggregately define a tuned resonant bandpass filter in the roll-off regions of the operational amplifiers.

Abstract: An "all-pass" filter circuit for use, for example, as a delay section in an integrated circuit, and which should therefore be as simple and as little susceptible to production spreads as possible, comprises first and second long-tailed pairs of transistors (1, 2 and 3, 4 respectively) provided with input emitter followers (26, 28, 30, 32). The pairs are interconnected to form a gyrator having first and second ports (24 and 25 respectively). The first port is loaded by a first capacitor (17) shunted by a damping resistor (22) and the second port is loaded by a second capacitor (18). An input terminal (20) is coupled to the first port via one transistor (1) of the first pair and the relevant emitter follower (26), and the first port is coupled to an output terminal (21) via both transistors (3, 4) of the second pair and the relevant emitter follower (30).

Abstract: A notch filter system for eliminating a specific "stop" frequency from an AC electrical input signal, such as 60 Hz "hum" from an audio program signal. An L/C tuned circuit that is tuned to the stop frequency is used to develop a modified input signal that is in phase with the input signal only at the stop frequency. The two signals are amplitude-balanced and fed to the respective inputs of a balanced differential amplifier which is responsive to both input signal phase and amplitude differences so as to cancel the signals at the stop frequency where they have the same phase and amplitude but not at frequencies above and below the stop frequency where they differ in phase and amplitude.

Abstract: Comb filter having a comb like band pass characteristic curve by using an ultrasonic delay line (9) is improved to reduce its size. An input signal is given through an impedance element 13 to a single terminal 10a of an improved delay line 9, wherein the single terminal serves as the input terminal and at the same time as the output terminal. Signals at both ends of the impedance element 13 are given to a mixing circuit 15 for summing or subtracting thereby. In the improved delay line 9, the ultrasonic wave radiated from the input terminal travels twice the conventional delay line and comes back to the original terminal, and thereby a sufficient propagation distance is obtainable in a small delay line.

Abstract: A differential amplifier which incorporates at its preceding stage resistances and condensers combined with each other and serving as a low-pass filter, thereby omitting a conventional low-pass filter separate from a differential amplifier provided at a weight detection circuit for a load cell weighing scale or other detection circuit.

Abstract: A multi-purpose filter includes a first integration circuit including a first differential amplifier having first input terminals and a first output, a first capacitor connected with the first output, and a first output circuit; a second integration circuit connected in series with the first integration circuit and including a second differential amplifier having second input terminals and a second output, a second capacitor connected with the second output, and a second output circuit; a feedback circuit connected between the first and second output circuits and the first input terminals; and a plurality of capacitor terminals connected with both ends of the first and second capacitors such that different filter characteristics are obtained by selecting different ones of the first input terminals, the second input terminals and the plurality of capacitor terminals as an input and an output of the filter.

Abstract: This application discloses a virtual ground pre-amplifier for application with magnetic phono cartridges such as moving coil, moving magnet, moving iron, or similar types. The preamplifier according to the present invention comprises a forward path (an amplifier), and a reverse path (shunt feedback). By presenting a relatively low load impedance to the phono cartridge, the preamplifier effectively damps mechanical resonances of the stylus-cartridge system, and thus serves as a "stylus stabilizer."Also disclosed are techniques for equalizing the overall response of the stylus-cartridge-preamp system so as to provide a predetermined (e.g., flat) frequency response. This predetermined frequency response can be achieved by utilizing any of several circuit arrangements which serve to compensate for the intrinsic inductance and dc resistance of the magnetic phono cartridge.

Abstract: A wideband intermediate frequency (IF) amplifier including a GaAs FET input portion and a bipolar transistor output portion is disclosed. The high gain of the GaAs FET over higher frequencies is complemented by the high gain of the bipolar transistors at lower frequencies to provide high amplifier gain over a large bandwidth. The GaAs FET and bipolar portions are coupled by means of an equalizer circuit matching the two portions together only at the higher frequencies of the IF band to provide an inexpensive, high performance IF amplifier particularly adapted for use in a direct broadcast satellite receiver operating in the super high frequency (SHF) band.

Abstract: A plurality of passive filters in combination with a corresponding plurality of operational amplifiers form an individual series of quasi low-pass, bandpass, and quasi high-pass filters which when their outputs are summed in an operational amplifier summer, constitute a "semi-active" notch filter having a low frequency phase shift of substantially zero, and a notch frequency which can be adjusted independently of the low frequency phase shift. The existence of the notch is also independent of the properties and limitations of the operational amplifiers used.

Abstract: A signal processor for use in association with a frequency analyzer, can operate in the frequency translation mode or the filter mode.The signal processor comprises a first low pass filter, the signal from which is fed to two first parallel programmable gain amplifiers controlled by a first digital function controller. The signals then pass via two, second low pass filters to two second programmable gain amplifiers controlled by a second digital function controller. The signals from the second amplifiers are then added by an adder and filtered by a third low pass filter.The first controller is controlled by a frequency signal equal to the frequency in the middle of the bandwidth being translated and the first filter is controlled by a frequency which is a multiple of the control frequency to the first controller.

Abstract: The IF section of a television receiver includes an amplifier having an input terminal for receiving an IF signal and an output terminal at which an amplified version of the IF signal is developed and a SAW filter having two input terminals, one of which is connected to AC signal ground, for receiving the amplified IF signal and an output terminal for providing a modified IF signal having a bandpass characteristic determined by the SAW filter. An impedance transformation network is coupled between the output terminal of the amplifier and the input terminal of the SAW filter for increasing the effective load impedance of the amplifier and for decreasing the output impedance of the drive arrangement. The former aspect of the impedance transformation network allows a transistor with lower current supplying capabilities to be employed. The latter aspect of the impedance transformation network tends to reduce undesired voltages developed in response to reflections between the transducers of the SAW filter.

Abstract: A lowpass filter circuit having an electronically controllable cutoff frequency and utilizing a feedback current mirror circuit as a variable impedance element. The filter circuit employs low noise, low distortion output circuitry and includes means for electronically controlling resonance.

Abstract: A bandpass filter circuit includes first and second resistors connected in series between input and output terminals thereof, an amplifier having a gain of three and its output connected to the output terminal, and an RC circuit network connected between the connection point of the first and second resistors and the input of the amplifier and having bandpass characteristics. The RC circuit network comprises a series combination of a third resistor and a first capacitor connected between the connection point of the first and second resistors and the input of the amplifier, and a parallel combination of a fourth resistor and a second capacitor connected between the input of the amplifier and a common terminal of the filter circuit. The third and fourth resistors have an equal resistance value and the first and second capacitors have an equal capacitance value.

Abstract: A capacitor-resistor-capacitor (CRC) element for active filter realization, which is fully integrable and compatible with MOS technology, is described. The incorporation of the CRC element in a semiconductor integrated circuit active filter also is described. The structure of the CRC filter element is closely analogous to a depletion mode MOS field effect device, except that the channel zone 26 is doped to a level which substantially precludes conductivity modulation at the usual operating voltages. However, the doping level is such as to enable the use of the channel zone as a semiconductor resistance element. Thus, the N-channel CRC element realized in the NMOS technology comprises a first capacitance composed of the gate 27, gate dielectric 38, and resistive channel 26, paralleled by the resistive channel 26 itself constituting a resistor, and then the underlying PN junction capacitance between the N-type resistive channel 26 and the underlying P-type semiconductor body portion 21.

Abstract: In differential amplifier circuits of the type having first and second transistors, the emitter of each transistor is connected to a different current source and the emitters are coupled by a ceramic filter tuned to 455 KHz. In one embodiment, wherein the transistors have symmetrical resistive loads, an inductor is connected across the filter to tune out capacitance across the terminals of the filter. In another embodiment, the circuit includes an unbalanced and complex load. In yet another embodiment, the circuit has active load circuitry and an inductor is connected across the filter to tune out capacitance across the terminal of the filter.

Abstract: A unidirectional current with i-f variations superimposed thereon is applied to the interconnected emitters of a pair of transistors, the collectors of which are coupled to a succeeding stage by a narrow-band filter and by a wide-band filter respectively. The unidirectional current with i-f variations is amplified by a selected one of the transistors and filtered accordingly, depending upon which of two polarities of potential is applied between the bases of the transistors.

Abstract: An audio processing system for maximizing the efficiency of transferring audio frequency signals. Signals to be processed are supplied to a bandpass input filter, then to a primary active frequency control. Its output drives a primary voltage compressor selectively limiting audio dynamics to a predetermined window, the latter being controllably preset and driven with different audio bands of amplitude determined by the primary frequency control to maximum compression levels indicated by a visual indicator. The output of the primary compressor is presented to a secondary active frequency control driving a secondary dynamic compressor with different audio bands. A second visual indicator indicates maximum compression levels of the latter. An automatic gain control (AGC) tied to the secondary compressor supplies feedback to the primary voltage compressor via AGC circuitry to control primary compression as a function of average, overall dynamic compression of the system.