A DC-offset-compensated, CT/DT hybrid filter with process-insensitive cutoff and low in-band group-delay variation for WLAN receivers

A continuous-time/discrete-time (CT/DT) hybrid channel-selection filter (CSF) with a built-in pole-controllable dc-offset canceller (DOC) for WLAN receivers is proposed. Optimized in a 90-nm CMOS process, a 4^th-order CT/DT Hourglass architecture plus one frequency-extended real pole approximates the shape of a generic 5^th-order pure CT (active-RC) Butterworth structure, while achieving a stable cutoff frequency (i.e., ±10%) without calibration and small in-band group delay variation (i.e., 34 ns). The entire CSF consumes 10.3 mW at 1.2 V. The IIP3 is +15 dBm and the 0.2-mW DOC reduces more than 50% of the dc-offset, while providing a pole controllable feature to flexibly suit the different reception modes of WLAN systems.