Phase demodulator for psk-modulated signals

Abstract

A phase demodulator for directly demodulating carrier PSK signals, PSK-modulated with digital signals, without using any analog circuit. Where the invention is applied to a demodulator of the different detection type, the baud timing signal is converted into a synchronous band timing signal, synchronized with the first leading edge of the PSK signals converted into '1' or '0' in logical level. Meanwhile, the ring oscillator generates signals of a frequency substantially equal to the carrier frequency of the PSK signals, and generates outputs at N taps. the outputs obtained at the N taps have a 2.pi./N phase difference between every pair of mutually adjoining taps, and are latched with the synchronous baud timing signal in each baud period. The point at which the logical level of mutually adjoining latch outputs varies from '1' to '0' is the phase information of said digital signals. The corresponding phase information is encoded to constitute the demodulated output. In a demodulator of the synchronous detection type, meanwhile, the latch outputs are used as said phase information like in the case of the differential detection type. The reference phase of the PSK signals is fixed by subtracting from this phase information the offset phase, which is the output of the synchronous phase fixing circuit.