A 0.45nW, 0.5V, 59-dB DR, Gm-C Low-pass Filter for Portable ECG Recording

This paper presents the design of a sub-threshold CMOS G,„-C low-pass filter in a portable ECG detection system. The proposed filter is formed by cascading 6 stages of identical l^'-order low-pass sections. With a minimum number of active components in the l^'-order section, the noise contribution of the circuit can be kept low while minimizing the size of transistors and capacitors. The filter cut-off frequency is designed to be adjustable over the range from lOOHz to 250Hz by changing the bias cun-ent. Circuit simulations, using AMS' 0.18|tm CMOS technology and operating from a 0.5V supply voltage, show that, for a cut-off frequency of 150Hz, the filter draws 0.9nA of cun-ent. An input referred noise of 88|aVnns is obtained while for 1% total haiTnonic distortion, the voltage swing can be as high as 0.23Vpp.