Abstract: An automatic frequency control (AFC) circuit is disclosed which comprises an oscillating circuit for generating repetitive pulses, a generator for generating comparison signals having a slope portion in response to the repetitive pulses, and a phase comparison circuit which compares the comparison signals, and synchronous (sync) signals and based on the comparison supplies control signals to the oscillating circuit. The AF circuit further comprises a limiting circuit connected between the comparison signal generator and the phase comparison circuit which limits the maximum and minimum levels of the comparison signals to predetermined levels, and thereby predeterminedly limits the control range of the AFC circuit.

Abstract: A constant current generating circuit is provided which comprises first, second, third and fourth transistors of one conductivity type, each having base, emitter and collector electrodes, and a voltage supply source having first and second voltage terminals.