Clock recovery circuit in .pi./4 shift quadriphase PSK demodulat

Details Clock recovery circuit in .pi./4 shift quadriphase PSK demodulat Clock recovery circuit in .pi./4 shift quadriphase PSK demodulat

1994-02-25

1995-09-05

Pascal, Robert J.

Demodulators

Phase shift keying or quadrature amplitude demodulator

329307, 375329, 375327, 375331, 375354, H04L 2722

Patent

active

054482011

ABSTRACT:
A clock recovery circuit having a feedback system in a .pi./4 shift QPSK demodulator, comprising a signal state transition detector for detecting state transitions between consecutive symbols of the demodulated baseband signal which is formed from the detected baseband signal by .pi./4 reverse shifting. According to degree of the detected symbol state transition, the 1/2-symbol delayed baseband signal is shifted by the amount of .pi./8 in phase. According to direction of the detected symbol state transition, the .pi./8 phase shifted baseband signal is converted into an error signal in use for the feedback system. An oscillator generates a clock signal of a frequency controlled by the error signal such that the error signal is reduced in the feedback system.

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Otani, Susumu et al., "Development of Variable-Rate Digital Modem for Digital Satellite Communication Systems", I.E.E.E., 1988, pp. 0148-0152.

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