Phase comparison circuit and PLL circuits and oscillator driving device using the PLL circuit using the phase comparator circuit

摘要

PROBLEM TO BE SOLVED: To overcome the problem of a conventional PLL such that it has been unable to increase accuracy of oscillation frequency in VCO particularly because an error in an amplitude direction is easily caused in a signal before being integrated and smoothed with a lowpass filter.;SOLUTION: A switching circuit A4 is switched to output an upper limit voltage V1 from a buffer means A5 when a signal EX1 is larger than a threshold Va, and to output a lower limit voltage V2 from a buffer means A6 when being smaller. A phase difference signal SP1 can be generated as a composite signal of the output of the buffer means A5 and A6, thereby suppressing the amplitude fluctuation of the signal SP1. Accordingly, an integrating and smoothing means 15 can generate a control signal Sr with a small error. Since the accuracy of oscillation frequency in the VCO is increased, stability of the PLL can be improved.;COPYRIGHT: (C)2002,JPO