An integrated LMS adaptive filter of TX leakage for CDMA receiver front ends

The theory and practical implementation of an adaptive filter of the TX leakage in CDMA receivers are described. The filter uses a continuous-time signa-data LMS algorithm. It was designed as part of a 0.25 /spl mu/m CMOS cellular-band receiver. It achieved the maximum rejection of the TX leakage of 28-30 dB, which was limited by the reference signal leakage to the LNA output. The LNA NF and gain degraded by 1.3 dB and 1.7 dB respectively after adding the filter.