Design of a tunable fully differential GHz range Gm-C lowpass filter in 0.18 /spl mu/ m CMOS for DS-CDMA UWB transceivers

Design of a fully differential sixth order GHz range gm-C lowpass filter for DS-CDMA UWB (ultra wideband) transceivers is presented. The filter is composed of three identical cascaded biquad sections. The core of the filter is isolated from the source resistance by a folded cascode input stage. An outer negative feedback loop is used to lower the source resistance seen by the core of the filter and extend the bandwidth to a GHz range. Schemes for near orthogonal tuning of bandwidth and passband gain are described and verified. Peaking in the passband is maintained low to avoid distortion and reduced linearity. The proposed lowpass filter is designed in TSMC 0.18 mum CMOS process. Post layout simulations show that the filter bandwidth is tunable over 600 MHz from 800 MHz to 1.4 GHz and the passband gain is tunable over 6 dB, while the passband peaking is maintained below 2 dB. The filter consumes 24.2 mW under supply voltage of 1.8 V