Abstract: A filter circuit (2) is automatically tuned so that the positions of the poles and zeros of its frequency response characteristic are maintained in substantially fixed ratios to an input frequency (f.sub.r). The arrangement comprises a frequency discriminator (1) having its output (5) coupled to a controllable element (8) of a resonant circuit included therein, so that the resonant frequency of the resonant circuit is maintained equal to the input frequency. The output 5 also controls a counterpart (13) to element (8), which counterpart is included in an auxiliary circuit (3). The filter circuit is tuned by controlling an element (10) included therein, which element also has a counterpart element (14) included in the auxiliary circuit, both of these elements (10,14) being controlled by the auxiliary circuit output signal.

Abstract: A sinewave oscillator and a quadrature phase shift network fabricated as an integrated circuit for a Barber radio receiver comprising, in order that the network and oscillator be simply adjustable to provide an accurate 90.degree. shift and a sinewave of accurate frequency and high spectral purity, a first capacitance means (C1, C2; C4, C5) coupled to the input of a gyrator (G1; G2) comprising first and second amplifiers (10, 12; 22, 24) connected in feedback configuration with a capacitance (C3; C6) connected to the output of the first amplifier. The oscillator network may be adjusted by current control of transconductance of the amplifiers, and the amplifiers include input signal limiting means to limit the input signal to a linear operating region. An output load resistance (R) may be simulated using a further amplifier connected in feedback configuration.

Abstract: A reciprocal impedance conversion network is disclosed. Such conversion network preferably is used in a reciprocal negative impedance repeater for the nonloaded cable facilities of a telephone system. Two independent voltage sources for generating reciprocal negative impedance are connected between a first port and a second port. The first port is operably connected to the first voltage source such that a series negative impedance appears at that port. This port is specifically connected to the switching equipment of the telephone system. The second port is operably connected to the second voltage source such that a shunt negative impedance appears at that port. The second port is specifically connected to the nonloaded cable facilities of the telephone system. The invention further provides a frequency dependent gain circuit which is useful for equalizing the losses along the nonloaded cable facilities.

Abstract: A gyrator circuit usable in a resonant filter circuit comprises a first and a second transconductance amplifier circuit, A and B, respectively, having opposite conductances, which amplifiers are arranged in parallel between a first terminal a and a second terminal b and comprise a first capacitance C.sub.1 arranged between said first terminal a and an earth terminal m, which gyrator circuit simulates an inductance L.sub.g arranged between said second terminal b and said earth terminal m and comprises means for controlling the quality factor Q of said inductance, characterized in that the first transconductance amplifier circuit A comprises two series-connected inverting amplifier stages P.sub.1 and P.sub.2, in that the second transconductance amplifier circuit B comprises an inverting amplifier stage P.sub.3, and in that the means for controlling the quality factor Q comprise a first means P.sub.5 for influencing the output conductance q.sub.2 of the gyrator and a second means P.sub.

Abstract: An oscillator is disclosed comprising a pair of gm stages wherein the output of the second gm stage is coupled to the inverting input of the first stage and the output of the latter is coupled to the non-inverting input of the former; first and second capacitors coupled respectively between the outputs of the two gm stages and ground and feedback circuitry coupled between the output of the first gm stage and the non-inverting input of thereof while the inverting input of the second gm stage being coupled to ground. Because the first gm stage is operated as a negative gm, this stage simulates an inductor using the first capacitor that is coupled to the output of the stage.

Abstract: A magnetically tuned resonant circuit having a resonant frequency which is substantially invariant with external applied static and dynamic stresses is provided. The magnetically tuned resonant circuit includes a housing which provides a magnetic flux return loop. A central post of the magnetically tuned resonant circuit includes a pair of pole pieces, upper and lower portions of the housing, a magnet and an RF structure. The RF structure including a pair of coupling loops and a YIG sphere disposed between the coupling loops is disposed between the pair of pole pieces. In a first embodiment, the elastic compliance of the center post portion of the magnetically tuned resonant circuit is increased by a predetermined amount by providing a nonmagnetic collar around a first one of the pole pieces disposed between said pole piece and the RF structure.

Abstract: A modem or other data handling apparatus for connection to a transmission line includes an inductance simulation circuit for providing a low d.c. resistance to allow circulation of a line holding current, whilst presenting a high a.c. shunt impedance to the audio data tones on the line. The simulation circuit comprises two tranistors connected as a high gain amplifier across an input resistor in the modem/line coupling circuit amplifier via a capacitor and the amplifier applies tone signals across the input resistor to augment the tones thereacross. The conductive transistors also act as a low resistance connected across the input resistor for the passage of the line holding current. The simulation circuit acts, in effect, as an inductance, without the use of inductive components.

Abstract: A gyrator is comprised of a first voltage-current converter for converting the first voltage applied to a first terminal into electric current, a first light-emitting diode for converting the output current of the first voltage-current converter into a corresponding photosignal, a first phototransistor optically connected to the first light-emitting diode, the transistor converting the photosignal from the first light-emitting diode into a corresponding current, the transistor further supplying the converted current to a load capacitor connected to a second terminal, a second voltage-current converter for converting voltage, which is caused at the second terminal by the load capacitor, into a corresponding electric current, second light-emitting diode for converting the output current of the second voltage-current converter into a corresponding photosignal, second phototransistor optically connected to the second light-emitting diode, and for converting the photosignal from the second light-emitting diode int

Abstract: A low frequency sinusoidal oscillator, comprises a circuit which contains operational amplifiers, resistors and capacitors and has no inductor. The circuit, however, operates as an inductor. The circuit is arranged to resonate at a frequency which may be chosen by acting on only one component which preferably is a resistive component.

Abstract: In order to facilitate its construction as in integrated circuit, the inductive elements of two resonant circuits in a band-pass filter are each constituted by a first port of a respective gyrator circuit (22, 23 and 24, 25 respectively) the second port of which is loaded by a capacitor (3 and 6 respectively). The first ports, across which are connected capacitors (1 and 3 respectively), are connected by a signal path one to the other, as are the second ports, in such manner that a loop is formed comprising the two gyrator circuits and the two signal paths, enabling bilateral coupling of the two gyrator circuits to be obtained by coupling otherwise unused outputs (24+ and 22+) to otherwise unused inputs (22- and 24- respectively) of two-input two-output voltage-controlled current sources (22, 24) which form part of each gyrator circuit.

Abstract: Compensation for an effect produced by variations in the base-widths of integrated circuit transistors occurring from batch to batch is obtained by including in each integrated circuit a resistor the resistance of which has an inverse relationship to the transistor base widths and generating a phase shift in the signal path through the transistors, which phase shift depends on the value of the resistance in such manner that a relative phase advance is obtained with increasing values of the base widths. A control signal which depends on the value of a "base-under-emitter" resistor is produced at the output of a control signal generator circuit and is applied to an n-type island in which a "shallow-p" resistor is formed, thereby controlling the reverse bias of the island-resistor junction and hence the capacitance between the resistor and ground.

Abstract: An electronically adjustable capacitor (varactor), an active element such as a Field Effect Transistor arranged to exhibit negative resistance, and an inductor are arranged as a frequency tunable resonator suitable for use at microwave frequencies. The negative resistance of the active element may be adjusted to compensate for the resistance of the other resonator components such that the resonator exhibits very high Q and therefore high selectivity and low loss. The resonator may be used as a filter element in a tunable filter. Alternatively the negative resistance of the active element may be adjusted such that the resonator exhibits net negative resistance and may be incorporated in a tunable reflection type amplifier.

Abstract: In a filter circuit a reactance is simulated by a voltage amplifier the input of which is connected across a reactive element and the output of which is connected in series with that element, thereby enabling, for example, the series arrangement of a pair of inductances to be simulated by a single capacitively-loaded gyrator (15, 16, 7) and a voltage amplifier (15, 8). The circuit shown simulates a series-resonant circuit fed via a series inductor and is suitable for use as a sound trap in a television receiver. A current proportional to the voltage across the unloaded port (8) of the gyrator (15, 16) generates a corresponding voltage across a load resistor (12) and this voltage is injected effectively in series with any voltage present across a pair of input terminals (1, 2) by means of a differential voltage amplifier (13).

Abstract: The subject gyrator circuit is realized by a single amplifier and six resistors, which resistors are selected to satisfy a single equation. This permits great flexibility in setting the Z.sub.12 and Z.sub.21 impedance values without affecting the stability of the basic circuit.

Abstract: A network simulating an ungrounded inductor includes an active gyrator circuit which employs an operational amplifier, said gyrator being a two port device having an ungrounded port, and a grounded port. The ungrounded port is terminated in a capacitor C so as to provide an input impedance, Zin, looking into the grounded port, which simulates an inductor: Zin=e1/i1=j.omega.R.sup.2 C, where .omega.=2.pi.f, e1 the voltage across the port and i1 is the current into the port. A current i2 is developed in the gyrator circuit, from the operational amplifier output, and appears as an extraneous current at the grounded terminal of the grounded port. An active network including a second operational amplifier is connected to the active gyrator circuit and is arranged to provide a current i3 which is equal in value to but opposite in sign from said i2 current. The current i3 is combined with the i1 and i2 currents at the grounded terminal.

Abstract: An equalizer network that exhibits stability and may be cascaded with a transmission channel is disclosed. The network includes only two operational amplifiers, resistors and capacitors and provides a bump shaped amplitude characteristic at resonance frequency. The equalizer may be modified to exhibit selectively a `bump` or `dip` at resonance, and may be so constructed that trimming operations and the independent selection of parameters is facilitated.

Abstract: Quadrature transposition stage has two signal channels, each containing a filter. A gyrator circuit is coupled between the filters. The result is that the two filters have exactly the same transfer function which reduces signal distortion in such circuits as an FSK demodulator.