Abstract: In an FM detector circuit, a phase-shifting circuit is constituted by integrating circuits each consisting of a transconductance amplifier and capacitor. The phase-shifting circuit being arranged to cause limiter signal to be phase-shifted by 90 degrees at center frequency. A multiplying circuit is provided which is arranged to be provided with said limiter signal and output of said phase-shifting circuit, thereby effecting phase-detection of said limiter signal. Further, an error amplifier is provided which is supplied with a smoothed version of detection output derived from said multiplying circuit. The arrangement is made such that output of the error amplifier is applied to the transconductance amplifiers constituting said phase-shifting circuit.

Abstract: A polar leapfrog filter includes at least one polar network. The polar network comprises a differentiator constituted by an operational amplifier having input and output terminals, and a first integrator formed by a first capacitor for providing negative feedback to the operational amplifier and a first variable transconductance amplifier; and a second integrator formed by a second capacitor for providing negative feedback to the first integrator, and a second variable transconductance amplifier. A differentiator is provided at each of the input and output portions of the filter, and a third differentiator is provided immediately preceding the output side differentiator. In the case where two or more said polar networks are incorporated, an additional differentiator is provided between the polar networks. The sum of the number of the circuits constituting the differentiators and the number of the polar networks is selected to be even and equal to the order of the filter.

Abstract: A polar leapfrog filter includes at least one polar network. The polar network comprises a differentiator constituted by an operational amplifier having input and output terminals, and a first integrator formed by a first capacitor for providing negative feedback to the operational amplifier and a first variable transconductance amplifier; and a second integrator formed by a second capacitor for providing negative feedback to the first integrator, and a second variable transconductance amplifier. In the case where two or more said polar networks are incorporated, an integrator is provided between adjacent ones of the polar networks. The total number of all the circuits is selected to be odd and equal to the order of the filter. The adjacent ones of the circuits are connected in such a manner that leapfrog type negative feedback is effected.

Abstract: A polar leapfrog filter includes at least one polar network. The polar network comprises a differentiator constituted by an operational amplifier having input and output terminals, and a first integrator formed by a first capacitor for providing negative feedback to the operational amplifier and a first variable transconductance amplifier; and a second integrator formed by a second capacitor for providing negative feedback to the first integrator, and a second variable transconductance amplifier. An integrator is provided at each of the input and output stages, and a third integrator is provided immediately preceding the output side integrator. In the case where two or more said polar networks are incorporated, an additional integrator is provided between the polar networks. The total number of all the circuits is selected to be even and equal to the order of the filter.

Abstract: An all-pass filter includes an adder which comprises a variable conductance amplifier and a capacitor connected to the output terminal thereof. The adder is being arranged to add the output of a band pass filter and an input signal together.

Abstract: A variable time-constant differentiator comprises an operational amplifier t which a signal is inputted through a capacitor; and a variable transconductance amplifier connected between an input terminal to which a signal is applied and an 5 output terminal.

Abstract: A polar leapfrog filter includes at least one polar network. The polar network comprises a differentiator constituted by an operational amplifier having input and output terminals, and a first integrator formed by a first capacitor for providing negative feedback to the operational amplifier and a first variable transconductance amplifier; and a second integrator formed by a second capacitor for providing negative feedback to the first integrator, and a second variable transconductance amplifier. A differentiator is provided at each of the input and output stages of the filter. In the case where two or more said polar networks are incorporated, an additional differentiator is provided between the polar networks. The total number of all the circuit units constituting the filter is selected to provide odd order and equal order for the filter. The circuit units are connected in such a manner that leapfrog type negative feedback is effected.

Abstract: An active filter circuit comprises a differentiator constituted by an operational amplifier having an input terminal and output terminal, and a first integrator constituted by a first capacitor and a first variable conductance amplifier for providing negative feedback to the operational amplifier and a first variable conductance amplifier; and a second integrator constituted by a second capacitor and a second variable conductance amplifier for providing negative feedback to the first integrator. The active filter circuit is arranged such that a damping pole is set up at a predetermined frequency by adjusting operating currents of the first and second variable conductance amplifiers.