Recording and reproducing apparatus using a modulator/demodulator for Offset Quadrature Differential Phase-Shift Keying

摘要

In an offset quadrature differential PSK modulator, input digital data is first converted by a serial-parallel converter into a first signal Xk and a second signal Yk (in which k is an integer) corresponding to even and odd bits of the digital data respectively with code change points thereof having a mutual deviation of one half data period and, after conversion by differential coders into data Pk = Xk +/ &cir& Pk-1 and Qk = Yk +/ &cir& Qk-1 (in which +/ &cir& means exclusive ORed), such converted data are fed to a quadrature modulator which balanced-modulates two quadrature carriers having a pi /2 phase difference from each other by the data Pk and Qk. The output signal of the offset quadrature differential PSK modulator is sent to a transmission channel or memory means. And in an offset quadrature differential PSK demodulator, the signal received from the transmission channel or memory means is fed to a coherent detector, which then phase-detects the signal by two quadrature carriers having a pi /2 phase difference from each other, and first and second detection outputs obtained therefrom are decoded by differential decoders and subsequently are fed to a parallel-serial converter, where the former digital data corresponding respectively to the even and odd bits are restored.