JPS6424542A - Timing synchronizing circuit for modem - Google Patents

Abstract

PURPOSE:To vary a reception timing phase to a transmission timing phase within a training period by deciding the direction and quantity of a shift in the reception timing phase and shifting the phase. CONSTITUTION:A signal with a transmission timing waveform is sampled at a frequency 6N (N: positive integer) times as large as a modulation speed according to the reception timing phase to discriminate whether the reception timing phase leads or lags from 1st and (4N)th comparison in one rotation of the reception timing and whether the shift quantity of the reception timing is larger or smaller than 90 deg. from the comparison result between the absolute values of (2N)th and (3N)th sampled values. Then when the shift quantity is <=90 deg., the reception timing phase is shifted in the opposite direction from the shift until 1st and (4N)th sampled values become equal to each other and when >90 deg., the reception timing phase is shifted in the same direction with the shift until the 1st and (4N)th sampled values become equal to each other. Consequently, the reception timing phase can be shifted by invariably <=90 deg. to the transmission timing phase.