A 85/215/430 KHz 3rd-Order Active-RC Low-Pass Filter with a Fast Automatic Frequency Tuning for a Zero-IF Receiver

In this paper, a 3
^rd
order active-RC Low-Pass Filter (LPF) is proposed for a zero-IF receiver. The LPF enables 85/215/430 KHz passband selection and 3 dB per step gain adjustment from 0 to 45 dB. In order to deal with the deviation of the filter cut-off frequency caused by process variation, an automatic frequency tuning circuit is applied to the filter, which can cover the RC value variation of ±40%. The low-pass filter circuit is implemented in 55 nm CMOS process. The measurement results show that when the cut-off frequency is 85/215/430 KHz, the rejection at 485/615/830 KHz is 48/32/24 dB respectively. The passband ripple is 1.2/0.3/2.5 dB respectively. The filter consumes 2.5 mA from 2 V supply. The area of the filter circuit is 350 um × 750 um.