FREQUENCY CORRECTION CIRCUIT

PURPOSE: A frequency correcting circuit is provided which controls a capacitance value of the frequency correcting circuit and a clock generating digital codes to increase the number of step form waves for generation of correction codes to prevent overlapping correction codes and missing correction codes for RC variation from +50% to -50%. CONSTITUTION: A frequency correcting circuit includes an automatic correction code generator(31') for generating a correction code corresponding to the variation of RC deciding time constant, and a filter(32') controlled to uniformly maintain the time constant according to the correction code generated by the automatic correction code generator. The automatic correction codes generator and integrator, a counter and a decoder. The integrator serves as a continuous time integrator for a predetermined period of time after an initial reset section, and serves as a switched-capacitor integrator for generating a step form wave voltage whose amplitude and maintenance time is set to obtain at least one step form wave after the lapse of the predetermined period of time. The counter counts the number of steps of the step form wave voltage output from the integrator. The decoder compares the output of the counter with the number of steps of a previously stored step form wave voltage to decode the output of the counter to generate actual correction codes.