A 4.1-mW 10-MHz Fourth-Order Source-Follower-Based Continuous-Time Filter With 79-dB DR

In this paper, a "composite" source-follower is presented. Using a positive-feedback, the structure synthesizes complex poles with a single branch. This allows to realize a single-branch biquadratic cell. Moreover, due to the intrinsic feedback present in any source-follower, the proposed cell performs larger linearity for smaller V_ov(=V_GS-V_TH). This is the opposite of other active filters and allows saving the power otherwise used to increase linearity. A fourth-order prototype satisfy typical WLAN 802.11.a/b/g baseband filter specifications has been realized in a 0.18 mum CMOS at 1.8-V supply. It achieves a 17.5-dBm IIP3 and a -40 dB HD3 for a 600-mV_{pp_diff} input signal amplitude. A 24-muV_rms noise gives a DR=79 dB, with 2.25-mA current consumption