Carrier recovery circuit for offset QPSK demodulators

Details Carrier recovery circuit for offset QPSK demodulators Carrier recovery circuit for offset QPSK demodulators

1988-12-23

1989-10-03

Laroche, Eugene R.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

331 12, 375 81, 375 82, 375 87, H04L 2722

Patent

active

048719757

ABSTRACT:
A carrier recovery circuit comprises a voltage-controlled oscillator with a .pi./2 phase shifter coupled to it for generating carriers of quadrature phase relationship. First and second phase comparators respectively detect phase differences between an offset QPSK modulated signal and the carriers of the quadrature phase relationship. Signal from the first phase comparator is delayed by a 1/2 symbol duration and applied to one input of a quadri-phase detector having stable phase angles at .pi./4, (3/4).pi., (5/4).pi. and (7/4).pi. radian and signal from the second phase comparator is applied to the other input of the quadri-phase detector. A bit timing recovery field (1010 . . . 1010) of the second channel is detected from the output of the second phase comparator. Signal from the quadri-phase detector is applied to a loop filter and thence to the voltage-controlled oscillator during the time when a bit timing recovery field (BTR) of the second channel is not still detected. To stabilize the operation of the carrier recovery loop of the circuit, the output of the second phase comparator from which that BTR is detected is briefly applied to the loop filter in response to the detection of a BTR of the second channel, instead of the signal from the quadri-phase detector.

REFERENCES:
patent: 4704582 (1987-11-01), Dixon et al.

Affiliated with

Also associated with

Rating

Carrier recovery circuit for offset QPSK demodulators does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Carrier recovery circuit for offset QPSK demodulators, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carrier recovery circuit for offset QPSK demodulators will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-666705