A CMOS channel-select filter for a direct-conversion wireless receiver

Abstract
A highly selective and linear switched-capacitor channel-select filter is fabricated in 1µm CMOS for a direct-conversion wireless receiver operating in the 902-928 MHz ISM band. The filter selects a 230 kHz wide channel, and attenuates by at least 50 dB from 320 kHz to 57 MHz. The input IP3 is +30 dBm, the input-referred noise in the passband is 70 nV/!Hz, and the circuit takes 4.6 mA from a 3.3 V supply. Direct subsampling of the 915 MHz RF input signal by the filter front-end is also demonstrated with only a small degradation in linearity. The input noise is halved in a redesign while keeping the current drain unchanged.

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