Patent ID: 6667663
Filing Date: 2003-12-23
Classification: H03L

Abstract:
A PLL circuit having a gain control function, said PLL circuit comprising:a first phase comparator for outputting a first phase difference signal indicating a phase difference between a first input signal and a second input signal; a first loop filter for smoothing a signal based on said first phase difference signal and outputting a first control voltage; a VCO (voltage-controlled oscillator circuit) for oscillating at a frequency based on said first control voltage and thereby outputting a first clock; a dummy VCO having characteristics identical with those of said VCO for oscillating at a frequency based on a second control voltage and thereby outputting a second clock; a VCO gain detecting circuit for detecting a gain of said VCO on the basis of a frequency difference between said first clock and said second clock and a voltage difference between said first control voltage and said second control voltage; and a gain control circuit for effecting control so as to make a loop gain constant on the basis of the gain of said VCO detected by said VCO gain detecting circuit; wherein said second input signal is a signal based on said first clock.