JPS6449459A - Timing synchronization circuit for modem - Google Patents

Abstract

PURPOSE:To take the timing synchronization of a modem, by providing a means to calculate a fine correction travel quantity and perform fine correction in a direction of deviation other than respective means for sampling, the polarity inspection of a sampled value, the discrimination of phase deviation at a sampling point, the calculation of the maximum deviation range, the specification of an error range, and the calculation and the correction of a phase shift quantity. CONSTITUTION:An A/D converter 10 samples the signal of transmission waveform of an amplifier 9 setting a reception timing phase as reference by a frequency of N times the modulation speed of a counter 21, and a control circuit 20 investigates the polarity of the sampled value at the sampling point obtained by a converter 19 from the output of a filter part 18 while the reception timing phase changes by 2pi, and discriminates the deviation of a reception timing in an inter-sample unit, and calculates respective maximum discrimination error range at the even and odd numbers of N by the maximum number of the sampling point with the same polarity decided by N and 2pi/N, and computes a coarse correction phase shift quantity by specifying a deviation discrimination error range. By detecting the micro deviation direction of the reception timing phase after initial correction, a phase difference can be calculated and corrected. The phase shift quantity on which coarse and fine correction is applied can be obtained only by the inspection of polarity and arithmetic operation without referring to a memory, and the synchronization of the reception and transmission timing phases can be obtained rapidly and with high accuracy.