QAM Demodulator carrier recovery loop using n-m LSB's

Details QAM Demodulator carrier recovery loop using n-m LSB's QAM Demodulator carrier recovery loop using n-m LSB's

1984-06-22

1986-02-18

LaRoche, Eugene R.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

329109, 329124, 375 39, 375120, 455214, H03D 318, H03K 902, H04L 512, H04L 2302

Patent

active

045715505

ABSTRACT:
A quadrature amplitude modulation (QAM) demodulator system derives a local oscillator signal which has the frequency and phase of the suppressed carrier of the QAM signal, so as to permit proper demodulation. In-phase and quadrature channels of the demodulator system each have an analog-to-digital converter with n output bits, where n is greater than m, the number of bits required for the data output for each channel. The n-m less significant bits are used to derive a signal indicating the error in phase alignment between the local oscillator signal and the QAM signal. In a phase locked loop, this error signal drives a voltage-controlled oscillator to phase lock with the suppressed carrier of the QAM signal. To acquire frequency and phase lock, a digital-to-analog converter in the loop is clocked each time the phase alignment of the VCO signal and QAM signal is close.

REFERENCES:
patent: 3638125 (1972-01-01), Goell
patent: 3789316 (1974-01-01), Goetz et al.
patent: 4054838 (1977-10-01), Tretter
patent: 4105975 (1978-08-01), Sanders et al.
patent: 4188589 (1980-02-01), Brown et al.
patent: 4458356 (1984-07-01), Toy
patent: 4464770 (1984-08-01), Maurer et al.

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