Title:
DC OFFSET COMPENSATION FOR ZERO IF QUADRATURE DEMODULATOR
Document Type and Number:
WIPO Patent Application WO1999057912
Kind Code:
A3
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.
Inventors:
MOHINDRA RISHI
Application Number:
PCT/IB1999/000750
Publication Date:
January 20, 2000
Filing Date:
April 26, 1999
Export Citation:
Assignee:
KONINKL PHILIPS ELECTRONICS NV (NL)
PHILIPS SVENSKA AB (SE)
PHILIPS SVENSKA AB (SE)
International Classes:
H03D3/00; H04L27/14; H04L27/22; (IPC1-7): H04L27/14; H04L27/22; H04L27/38
Domestic Patent References:
| WO1998024209A1 | 1998-06-04 |
Foreign References:
| EP0676880A2 | 1995-10-11 | |||
| US5012208A | 1991-04-30 | |||
| US5396196A | 1995-03-07 |
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