Abstract: The present invention provides an analog switching circuit including an input transistor, a base of which receives an input signal. A switching transistor has its emitter connected in common with the emitter of the input transistor and a constant current source is connected between the common emitter and ground. A control transistor effects ON and OFF control of the switching transistor in accordance with a control signal, and an output transistor extracts an output signal from the common emitter of the input transistor and switching transistor. An input clamping circuit composed of two or more Zener diodes connected in series with each other and in the reverse direction with respect to each other, is connected between the base of the switching transistor and the base bias point of the input transistor so that the base voltage of the switching transistor is increased, thereby avoiding reverse bias of the input transistor upon receiving a large amplitude input signal.

Abstract: A frequency discriminating circuit for readily discriminating between two signals having closely adjacent frequencies in which the effects of drift of circuit elements are eliminated. A frequency mixer receives the signals to be discriminated which have closely adjacent frequencies f.sub.1 and f.sub.2 and a reference signal with a frequency of f.sub.m. A first low-pass filter coupled to an output of the mixer produces an output signal containing only frequency difference components .vertline.f.sub.1 -f.sub.m .vertline. and .vertline.f.sub.2 -f.sub.m .vertline. between the signal to be discriminated and the reference signal. The output of the first low-pass filter is passed through a second low-pass filter. A phase comparator receives the output signals from the first and second low-pass filters and discriminates the input signals in accordance with a phase difference between the output signals from the first and second low-pass filters.

Abstract: An analog switch having a first feedback amplifier supplied with a signal superposed with a bias voltage and a second feedback amplifier supplied with the bias voltage. Each amplifier has a differential amplifier formed of two symmetrically connected transistors and having an output connected to both a common output terminal and its input through an impedance transforming transistor. The differential amplifier is biased by a constant current source formed of a transistor and a diode. In the presence of a control signal, the first amplifier is closed through the normal operation of its constant current source while the second amplifier is opened by disabling its constant current source. In the absence of the control signal, the first and second amplifiers are opened and closed, respectively.