A broad-band tunable CMOS channel-select filter for a low-IF wireless receiver

This paper presents a broad-band bandpass filter (BPF) designed as a channel-select filter for wireless applications. It is implemented as a low-pass filter (LPF) in series with a high-pass filter (HPF) for lower power consumption compared to true BPF. Semiscaling of the filter nodes is superior in the wireless receiver over traditional full scaling. The HPF is built with low-pass feedback of an amplifier. The bandwidth is selectable from 625 kHz, 2.5 MHz, or 10 MHz. The filter stopband loss is more than 50 dB extending beyond 100 MHz, and passband ripple less than 2.5 dB. Fabricated in a 0.6-/spl mu/m CMOS process, it provides a minimum input noise of 16 nV//spl radic/Hz noise with 22.5-dBm out-of-band IIP3, while draining an average 14 mA from 3.3 V.