FREQUENCY CONTROL CIRCUIT AND CDR CIRCUIT

摘要

PROBLEM TO BE SOLVED: To eliminate the need for components requiring external connection terminals for adjustment and components requiring external connection components.

SOLUTION: A CDR circuit includes: a frequency control circuit; a first VCO 2 which generates a reproduction clock whose oscillation frequency is controlled according to control voltage and whose oscillation phase is controlled by input data; an FF 1 which performs data identification of the input data by the reproduction clock; and a second VCO 3 whose oscillation frequency is controlled according to control voltage. The frequency control circuit is constituted of: a frequency comparator 4 which compares a frequency of an output signal of the second VCO 3 with a frequency of a reference clock and outputs a signal according to detected frequency difference; an up/down counter 5 which makes a digital value to be output go up and down according to an output signal of the frequency comparator 4; and a D/A converter 6 which converts output of the up/down counter 5 into an analog signal and outputs the converted signal as the control voltage of the VCOs 2, 3.

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