Gm-C biquad filter for low signal sensor applications

摘要

This paper presents a circuit topology for a Gm-C biquad filter, suitable for low frequency signals with low amplitude. The low cutoff frequencies are obtained reducing the transconductance Gm through a current division technique. Moreover, all the active devices are operating in weak inversion mode lowering the requirements for the level of the voltage power supply. A second and fourth order filter configuration, based on a Tow-Thomas biquad, is designed and simulated. The filter operates in weak inversion with a supply of 0.9V, achieves a cutoff frequency of 52Hz, and power consumption around 2.8μW. The integrated noise is 24.4μVrms, the dynamic range is 43dB, and the filter shows -40dB THD for 5mV input peak amplitude.