A Highly Tunable Ultra-Low Cut-Off Frequency gm-c Filter with Bandwidth Stabilization Technique

Abstract

In this paper, an efficient technique for stabilizing the bandwidth of low-bandwidth biomedical gm-c filters is proposed. Using this technique, the bandwidth of the filter becomes much less dependent on the circuit elements’ variations due to temperature or process, and thus the filter can be tuned more effectively and accurately. First, with circuit analysis, the reason for the dependency of the bandwidth on the circuit components is extracted. Then, an efficient circuit is proposed to reduce this dependency. The proposed 4th order gm-c filter has a symmetrical structure, and designed in TSMC 180 nm CMOS technology with bandwidth of 50 mHZ to 20 Hz, power consumption of 0.73 µW. Finally, using mathematical relationships and circuit simulations, the effectiveness of the proposed filter is proven.