A 120-MHz active-RC filter with an agile frequency tuning scheme in 0.18-μm CMOS

A wideband active-RC low-pass filter realized for high data rate wireless receivers is reported in this paper. This filter adopts the 5
^th
-order elliptic topology and achieves a bandwidth of 120 MHz and a stopband attenuation of more than 45 dB. The wide-bandwidth operational amplifiers employed in the filter adopt the feedforward compensation technique to extend the unity-gain bandwidth to 4.1 GHz. An agile tuning scheme is also proposed to automatically adjust the filter cutoff frequency. It uses the successive approximation register counter in the digital tuning loop to compensate for the RC variations while achieves short calibration time. The filter is fabricated in the TSMC 0.18-mum CMOS process and dissipates 38 mW under 1.5-V supply voltage. The measured IIP3 is 21 dBm and the tuning time is 8 mus.