An Active-RC Complex Filter with Mixed Signal Tuning System for Low-IF Receiver

An active-RC complex filter synthesized from leapfrog low-pass prototype is proposed in this paper, which is less sensitive to components values variation comparing with the common used cascade-pole method. Furthermore, a mixed-signal tuning system was implemented to make the RC time constant stable, and can be turned off after the completion of tuning. The filter was implemented in 0.18mum CMOS process. It is centered at 4MHz with 2MHz of bandwidth. It has the voltage gain of about -2dB, the image rejection ratio of about 28dB, the output 1-dB compression voltage of 0.39V, the in-band integral output noise of 32muVrms, and the power consumption of 6.1mW. The filter can be used in the low-IF GPS receiver