DC offset compensation for zero if quadrature demodulator

Details DC offset compensation for zero if quadrature demodulator DC offset compensation for zero if quadrature demodulator

1998-06-30

2000-11-14

Vo, Don N.

Pulse or digital communications

Receivers

Interference or noise reduction

375278, 329320, H03D 104, H03D 106, H03K 501, H03K 604, H04B 110

Patent

active

061480479

ABSTRACT:
The present invention provides dc offset compensation circuit (800) for a zero IF FM quadrature demodulator in an AMPS cellular mobile telephone system. A frequency offset is introduced to remove modulation inherent dc components from supervisory audio tones and Manchester codes from a modulated signal. The local oscillator (608) is operated at a frequency that is slightly different, e.g. 5 kHz from a frequency which would mix down the intermediate frequency signal to zero. A dc offset is produced with a control loop to eliminate fixed dc components caused by leakage from a local oscillator (608). After a given time, the control loop may be frozen and the frequency offset of the local oscillator (608) can be removed.

REFERENCES:
patent: 4944025 (1990-07-01), Gehring et al.
patent: 5548244 (1996-08-01), Clewer
patent: 5628059 (1997-05-01), Kurisu
patent: 5701600 (1997-12-01), Wetters et al.
patent: 5724653 (1998-03-01), Baker et al.
patent: 6075409 (2000-06-01), Khlat

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