Phase locked loop providing three-level control signal to VCO

DETAILED DESCRIPTION It is an object of the present invention to provide a PLL circuit which is quickly responsive and highly stable and is capable of solving the problems of the conventional PLL circuits in respect to a high speed of respectivity and a high degree of stability.
It is another object of the invention to provide a PLL circuit which dispenses with any loop filter.
It is a further object of the invention to provide a PLL circuit which is capable of obtaining the same loop gain for all the bands.
It is still further object of the invention to provide a PLL circuit which has no transient response.
To achieve these objects, a phase-locked loop circuit embodying an aspect of this invention comprises a controllable oscillator; a phase detecting circuit to produce a control signal for controlling the oscillation frequency of the oscillator according to a phase difference between the output of the oscillator and an incoming signal; and a designating circuit for designating a specific period of time during which the oscillator is substantially controlled by the control signal.
These and further objects and features of the invention will become apparent from the following detailed description of the embodiments thereof taken in connection with the accompanying drawings.