Fully differential fifth-order dual-notch low-pass filter for portable EEG system

Abstract

This paper presents a new fully differential fifth-order dual-notch low-pass filter based on multiple-input multiple-output operational transconductance amplifiers (MIMO OTA). This work shows that MIMO OTA-based fifth-order dual-notch filter can reduce the number of used OTAs, resulting in simplified realization and low-power consumption. The multiple-input OTA is obtained by using the multiple-input dynamic threshold MOS (DTMOS) technique without additional differential pairs. A simple common-mode feedback technique has been used; thus, fully differential OTA can be easily obtained. The proposed dual-notch low-pass filter can be applied to electroencephalogram (EEG) detection system to reject the 50 Hz powerline interference and the third harmonic 150 Hz. The proposed filter has been simulated using Cadence environment with 0.18 µm TSMC CMOS process. The power supply of 0.5 V is used and the total power consumption of the MIMO OTA is 17.5 nW. The proposed filter provides 49.7 dB dynamic range for 1% total harmonic distortion (THD) for a sine input signal of 250 mVpp at 10 Hz. At 50 Hz and 150 Hz the notch depths of attenuation are respectively −37.2 dB and −47.4 dB. The pre-layout simulation results are in good agreement with the theory.