Digital synchronizing circuit

Abstract

CMI code has many features, but the interference on a transmission line resulted from radiant noise is an unavoidable problem. In the invention, WALSH 1 code is employed to solve the problem. Clock pulses having a frequency twice that of code on a transmission line in the WALSH 1 code are extracted. The extracted clock pulses consists of zero phase clock pulses and pi phase clock pulses, wherein the zero phase clock pulses are accurately extracted. An embodiment comprises an clock extraction circuit for extracting extracted clock pulses of 2f.sub.0 from a receive pulse train of frequency f.sub.0, a latch circuit for latching the receive pulse train with the extracted clock pulses, a frame synchronizing circuit for obtaining frame pulses synchronized with the extracted clock pulses from the latched output pulses, a zero phase separation circuit for obtaining zero phase clock pulses from the extracted clock pulses and the frame pulses, and a regenerative discrimination circuit for obtaining a regenerated pulse train from the zero phase clock pulses and the latched output pulses. The regenerated pulse train has the same pattern as that of the original code from which the receive pulse train is converted by the WALSH 1 code.