H - Electricity – 03 – D
Patent
H - Electricity
03
D
H03D 7/18 (2006.01) H03D 7/16 (2006.01)
Patent
CA 2069104
2069104 9118445 PCTABS00008 A frequency converter for a transmitter of a microwave radio communications system comprises an image reject mixer (10) for mixing an IF signal with an LO or carrier frequency signal to produce an RF signal, and a nulling circuit for providing d.c. offsets to the image reject mixer to reduce carier leak to the RF signal. The nulling circuit includes a source (32) of phase quadrature chopper signals which are cross modulated (34) with the LO signal to produce a modulated signal, and a single-ended mixer (38) for mixing the modulated signal with part of the RF signal. The output of the single-ended mixer is low pass filtered (40) and the resulting filtered signal is cross demodulated (36) with the chopper signals to produce phase quadrature correction signals, which are integrated (44) to produce the d.c. offsets for the image reject mixer. The arrangement avoids the need for, and expense of, a subsequent carrier frequency filter.
Harman Stephen George
Haley R. John
Nortel Networks Limited
LandOfFree
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