Nanowatt High Order Analog Fully-Differential Bandpass Filter with Passive Switched-Capacitor Circuits

Abstract

This paper presents a kind of high order analog fully-differential bandpass filter based on passive switched-capacitor circuits. It can be widely used in many systems, such as voice feature extraction in voice activity detection and keyword spotter. By raising the thought of combining zero generation stages and pole generation stages rather than building stages separately in traditional ways, power consumption can be quite decreased. The power consumption of our filter bank composed of eight filters is 77.98nW in 180-nm CMOS. To analyze the bandpass filter theoretically, we use two methods both in z-domain and with its equivalent circuit. Besides, some effective improvements of switches and clocks are adopted for better performance, showing the result of $\boldsymbol{10.85}\mu \mathrm{V}_{\text{rms}}$ output-referred noise and 71.ldB dynamic range at 5% THD, having the advantages over other bandpass filters with similar functions.