Abstract: A circuit having an effective output capacitance the value of which can be varied over a predetermined range of values includes first and second differential amplifiers. The differential inputs of the second differential amplifier are connected to the differential outputs of the first differential amplifier, the latter of which receives a variable control signal. The second differential amplifier includes a pair of transistors the emitters of which are AC coupled to ground. A capacitor is coupled between the base and collector of one of the pair of transistors, the collector of which is coupled to the output of the circuit. A diode is AC coupled between the base and ground of the one transistor whereby the impedance thereof is varied in direct relationship to the conduction of the one transistor in response to the control signal thereby causing the value of the output capacitance of the circuit to be varied.

Abstract: A switched-capacitor high pass filter is disclosed and in which a switched capacitor approximation of an inductor is inserted in the direct coefficient loop to prevent instability. The value of the inductor is selected to compensate for the filter termination phase error.

Abstract: A variable reactance circuit which can produce equivalent reactance varying from negative given values to positive given values in accordance with fundamental reactance elements such as capacitor, coil, etc. The present invention has a big advantage of being capable of easily producing the positive, negative equivalent reactance given times as much as the basic reactance element with the use of a circuit which can be integrated.

Abstract: A circuit having an inductive characteristic for the realization of filters in integrated circuits is constructed solely from switched capacitors and an operational amplifier. The circuit is provided between a first and a second terminal with a first capacitor in series with at least one switch. The switch is capable either of connecting the first capacitor between said two terminals or of isolating said capacitor from the first terminal. The circuit further comprises an operational amplifier having a feedback path between its output and its input via a second capacitor, and additional switches for transferring charges from the input of the circuit to the first capacitor and then from the first capacitor to the second capacitor, then again from the second capacitor to the first capacitor. Under these conditions, the circuit exhibits the characteristics of an inductance.

Abstract: An oscillator having sufficient accuracy and precision for use in aircraft microwave-landing systems is constructed without the use of an external inductor. A resonant tank circuit comprising both capacitance and inductance is attained by the use of inductance found internally in the base-emitter junction of a transistor suitably biased for operation at the frequencies of a microwave landing system. A transistor having greater-than-unity gain in the oscillation-frequency range is selected for which the angle of the reflection coefficient of the base-emitter junction is positive in the oscillation-frequency range.

Abstract: The combination of an amplifier with a capacitor connected between an input and output terminal is coupled to a data bus to effectively reduce the effective capacitance on the bus and thus enhance the response time of information sent through the data bus.

Abstract: An electronic hybrid voice frequency repeater having a pair of term sets interconnected by a four-wire circuit for separating the two directions of signal transmission and amplifying each direction separately. Each term set couples the repeater's four-wire circuit to a two-wire line and has a differential current driver for driving the two-wire line and a differential amplifier connected in a feedback loop for sensing the differential signal voltage across the two-wire line, to drive the current driver and to feed an incoming differential signal on the two-wire line to the repeater's four-wire circuit while nulling signals arriving at the term set from the four-wire circuit to prevent them from returning to the four-wire circuit. Other features disclosed include a low frequency clamping circuit, an adjustable-gain amplifier, and an equalizer for non-loaded cable.

Abstract: A two-terminal-pair circuit which simulates an inductance includes input and output terminal pairs and a first ohmic resistor. The voltage-carrying terminal of the input terminal pair is connected to one terminal of the first ohmic resistor. The circuit includes a bridge circuit having bridge branches and two opposite bridge diagonal terminals, two capacitors each connecting a respective one of the two bridge diagonal terminals to a respective one of the terminals of the first ohmic resistor, and a difference amplifier having two inputs each connected to a respective one of the two bridge diagonal terminals. The output of the difference amplifier is connected to the base of a transistor whose collector-emitter path is connected in one of the bridge branches in series with an effective resistor or with a parallel circuit comprising a capacitive reactance and an effective resistor.

Abstract: A circuit for simulating the parallel combination of a floating inductor and capacitor in the bilinear and LDI domains has a pair of nodes receiving an input voltage and connected to input terminals of associated first and second voltage followers. A first capacitor C1 is alternately or periodically connected across the output terminals of the voltage followers for sampling the input voltage, and connected between the output of the second voltage follower and the input terminal of an integrator including a second capacitor C2 which integrates and stores the charge voltage on C1. A third capacitor is periodically connected to the nodes for sampling the input voltage, and connected between the output terminals of the first voltage follower and the integrator for subsequently also sampling and storing the integrated voltage on C2. The sum of the input voltage and the integrated voltage that is stored by C3 is discharged to the new input voltage when C3 is again connected across the nodes.

Abstract: An active filter provides precision filtering of an output signal over a wide range of signal input frequencies. Overall the active filter comprises a simulated L/C resonating loop which includes: a first operational amplifier in a loop with an operational transconductance amplifier simulating a capacitance; and a second operational amplifier in a second loop with a second operational transconductance amplifier simulating an inductance. The apparent capacitance of the first loop and the apparent inductance of the second loop can be regulated by applying a control current to each of the operational transconductance amplifiers. In a preferred embodiment the control current is derived as an antilogarithm of a linear voltage where the linear voltage corresponds to the logarithm of the filter resonant frequency. The filter output provides a constant percentage band width signal independent of the tuned frequency. The amplitude gain at resonance similarly is independent of the tuned frequency.

Abstract: A switched-capacitor filter circuit having at least one simulated inductor and having an operational amplifier with a capacitor interconnected between its output and inverting input and a non-inverting input connected to a reference potential has a switch leading from the inverting input of the amplifier to a first circuit node from which a first capacitor is connected to the reference potential and also from which a second switch leads to a second circuit node from which another capacitor is connected to the reference potential, and has a third switch leading from the second circuit node to the inverting input of the amplifier and a fourth switch connected between the output of the amplifier and the second circuit node and a fifth switch connected to an input terminal. Each of the switches is controlled by one of a series of sequential non-overlapping clock pulse voltages with the first and fifth switches being simultaneously closed followed by sequential closing of the second, third and fourth switches.

Abstract: An easily integratable switched-capacitor filter circuit which can be employed to simulate a parallel resonance circuit has an operational amplifier having an inverting input connected to a first circuit node through a first switch, a capacitor interconnected between the first circuit node and a reference potential, a third switch interconnected between the first circuit node and a second circuit node, a capacitor interconnected between the second circuit node and the reference potential, a third switch interconnected between the second circuit node and the output of the operational amplifier, a fourth switch interconnected between the output of the operational amplifier and the first circuit node, and a fifth switch interconnected between the first circuit node and a non-grounded input terminal.

Abstract: This simulation circuit is a one-port network having a pair of nodes connected to inputs of first and second voltage followers that have associated switched capacitors alternately connected across them for being discharged and connected to an integrator for being charged to the output voltage on the latter. A third switched capacitor is alternately connected in series with the voltage follower outputs for sensing the input voltage applied to the nodes, and connected to the integrator where the input voltage is integrated and transferred to the first and second switched capacitors. A floating inductance L=T.sup.2 C4/C1C3 is simulated across the nodes, where T is the reciprocal of the switching frequency, C1, C2 and C3 are the capacitances of associated switched capacitors, C1=C2, C4 is the capacitance in the integrator, and the circuit is characterized by the LDI transformation.

Abstract: In an audio amplifier circuit in which the base of a bipolar transistor of a first-stage amplifier circuit is direct-coupled to an input terminal which is connected to a signal source such as a phono pickup cartridge, a parallel circuit of a resistor and an inductor is connected between the base of the bipolar transistor and ground. An equivalent inductance circuit for embodying a pure inductance is disclosed.

Abstract: A frequency selection circuit which is equivalent to an LCR series resonant circuit, though not provided with inductance and which can adjust resonant frequency, selectivity or quality factor Q and circuit impedance at resonance independently of one another, merely by adjusting resistance. The circuit comprises an operational amplifier connected to receive an input signal at its noninverting input, a band rejection filter connected to an output of the operational amplifier, a positive feedback resistor connected between an output of the band rejection filter and the noninverting input of the operational amplifier, and a voltage divider connected between the output of the band rejection filter and the output of the operational amplifier and connected at its output to an inverting input of the operational amplifier. The band rejection filter comprises a series combination of a first resistor and a first capacitor and a parallel combination of a second resistor and a second capacitor.

Abstract: A band-pass filter consists of a number of circuits resistively coupled together to form a ladder network between an input and an output. Each circuit includes a positive impedance converter terminated so as to provide an impedance inversely proportional to the square of the complex frequency, preferably a capacitatively-terminated positive impedance converter is used wherein the impedance conversion ratio is proportional to the complex frequency. The input and output of the filter are resistively terminated such that all reactive elements of the filter are contained within the said circuits. Preferably the capacitors all have the same capacitance value.

Abstract: A radio receiver comprises an antenna circuit represented by an equivalent circuit consisting of an antenna electromotive force, an antenna capacitance in series with said electromotive force and a cable capacitance in parallel with them, a negative capacitance circuit connected to the antenna circuit for at least partially cancelling the antenna capacitance and the cable capacitance and a tuning circuit for receiving the output of the antenna circuit. The negative capacitance circuit, composed of a capacitor, transistors and the like, improves the S/N ratio.

Abstract: An active filter employing a plurality of integrators which may be fabricated as a metal-oxide-semiconductor (MOS) integrated circuit is described. S-plane zeros are obtained without additional active devices when compared to prior art filters without such zeros. The zeros result from resistive coupling between the integrators. Resistance ratios and capacitance ratios primarily determine the filter's characteristics rather than the absolute value of these elements. This permits the filter to be readily fabricated with existing MOS technology.

Abstract: A circuit network with a pair of operational amplifiers and impedance elements, to show equivalent impedance, between two network terminals, of a value either well reduced or enlarged from the impedance of the impedance elements. The network may thus function as idealized diode when the impedance elements are diodes, or may be of large equivalent capacitance or inductance, as the impedance elements are capacitors or inductors.

Abstract: A construction of an active filter having the same characteristics as a predetermined passive filter is described in which the capacitors of the passive filters are replaced by a topologically equivalent first network of resistors and the inductors of the passive network are replaced by a topologically equivalent second network of resistors, the two networks of the resistors being interconnected in a manner corresponding to the connections in the passive filter and connected to points corresponding to interconnection points of the passive filter by means of negative impedance converters, the converters connected to the first network having conversion ratios effective to convert resistance into negative capacitance and the converters connected to the second network having conversion ratios effective to convert resistance into negative inductance. The input and output to the active filter may be through similar negative impedance converters or may be directly to points in one or other resistive networks.