Abstract: A signal level converting circuit for bidirectional transfer of logic signals between a first and second external logic circuit is disclosed. This signal level converting circuit is provided with a control circuit that generates control signals whose logic values can be arbitrarily set, and at least one bidirectional logic signal level converter. Each logic signal level converter is provided with first and second converting circuits. The first converting circuit is placed by the control signal of a first logic level into a high-impedance state that blocks the transmission of the logic signals between the two external logic circuits, and is placed by the control signal of a second logic level into a low-impedance state that allows transmission of logic signals, together with converting the logic signal level from a first signal level to a second signal level.

Abstract: A frequency discriminator is provided which comprises a phase shifter for shifting a phase of an IF signal, a multiplier for analogically multiplying the IF signal and an output signal of the phase shifter and outputting the resultant signal thus obtained as a differential current, a circuit for forming a differential current of a differential output current of the multiplier, an inverter circuit to be driven by the differential current thus formed, and a low-pass filter for integrating an output signal of the inverter circuit. As the circuit for forming the differential current thereof, a current mirror circuit is preferably used. Thus, a quadrature-type frequency discriminator can be realized on a C-MOS integrated circuit.