Phase-error detecting circuit for QDPSK demodulator

Details Phase-error detecting circuit for QDPSK demodulator Phase-error detecting circuit for QDPSK demodulator

1992-09-17

1994-04-26

Mis, David

Demodulators

Phase shift keying or quadrature amplitude demodulator

Input signal combined with local oscillator or carrier...

329305, 375 81, 375 85, 375120, H03D 300, H04L 2722

Patent

active

053070216

ABSTRACT:
A phase-error detecting circuit for detecting a phase error of an output signal of the VCO in a QDPSK demodulating circuit in accordance with the Costas loop method is disclosed. The phase-error detecting circuit comprises a first circuit which generates a first product (P.times.Q) of a first demodulated signal (P) and a second demodulated signal (Q) of a QPSK signal. A second circuit generates the difference of the squares (P.sup.2 -Q.sup.2) of the first and second demodulated signals. A third circuit receives both the first product (P.multidot.Q) generated by the first circuit and the difference (P.sup.2 -Q.sup.2) generated by the second circuit and generates the product of the first product (P.multidot.Q) and the difference (P.sup.2 -Q.sup.2). The first circuit includes a first quadratic multiplier for generating the first product. The second circuit includes second and third quadratic multipliers, a phase-reversing mechanism for reversing the phase of the signal (Q), and an adding mechanism. The second quadratic multiplier generates the square of the first signal (P.sup.2). The third quadratic multiplier multiplies the second signal and the phase-reversed second signal generating (-Q.sup.2 ). The adding mechanism adds (P.sup.2) and (-Q.sup.2).

REFERENCES:
patent: 4592075 (1986-05-01), Tsukamoto
patent: 4856027 (1989-08-01), Nakamura et al.
"Principle of Operation of IC .mu.PC1478C adapted for QDPSK Demodulation in a Receiver for Satellite Broadcasting", Catalogue No. MA-102B, Dec. 1989, pp. 917 through 924, issued by NEC Corp. (no month/yr).

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