| 摘要 |
The direct conversion receiver is designed for demodulating signals in a TDMA system, in which the carrier frequency may vary from time slot to time slot. The received RF signal is demodulated by mixing with a local oscillator (LO) in a quadrature mixer (MIX). Due to carrier leakage, and imperfections in the mixers (CO1,CO2), the demodulated signal may have a DC offset, which must then be compensated by baseband processing (OCC). Because of the varying carrier frequency, and of the varying gain of the front end amplifier (LNA), the amount of DC offset will vary from time slot to time slot. In order to account for this, a correction loop is provided with a memory (MEM), for storing correction parameters for each carrier frequency and gain setting. This correction is updated slowly over many time slots, so that the error variance will be small. In order to correct offsets before this slow loop has converged correctly, a wide bandwidth loop is also provided, functioning within individual time slots. <IMAGE>
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