Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Patent
1995-08-28
1996-12-10
Faile, Andrew
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
4551822, 4551922, 375344, H04B 126
Patent
active
055840680
ABSTRACT:
A direct conversion receiver for FSK modulated digital signals has two quadrature signal paths (I, Q) and an a.f.c. loop for controlling a local frequency generator. A control signal for the a.f.c. loop is produced by an offset frequency detector, and is in the form of a unipolar series of pulses having an average value which is proportional to the offset of the local frequency with respect to the carrier frequency of the signal being received. The offset frequency detector derives such control signal based on the difference between phase-shifted cross-products of the signals in the I and Q paths. This achieves fast a.f.c. loop response, improving the performance of the receiver, and permits a simpler loop filter for achieving the requisite signal averaging. The receiver also includes an out-of-range detector for detecting when the local frequency is outside a predetermined window with respect to the carrier frequency of the received signal, in which case the a.f.c. control signal is derived from the average level of data in the received signal rather than from the offset frequency detector.
REFERENCES:
patent: 4344178 (1982-08-01), Waters
patent: 4672636 (1987-06-01), Marshall et al.
patent: 4871975 (1989-10-01), Nawata et al.
patent: 4989220 (1991-01-01), Serrone
patent: 5179578 (1993-01-01), Ishizu
patent: 5365185 (1994-11-01), Bar-David
patent: 5438692 (1995-08-01), Mohindra
Faile Andrew
Marion Michael E.
Nguyen Lee
U.S. Philips Corporation
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