A 0.5-V 95-dB rail-to-rail DDA for biosignal processing

Abstract

This paper presents a new low-voltage CMOS structure for differential difference amplifier (DDA) optimized for low frequency biosignal processing. The DDA input stage is based on a non-tailed bulk-driven (BD) differential pair offering rail-to-rail input common mode range (ICMR) under 0.5 V voltage supply. Unlike the conventional two differential pairs DDA structure, the proposed one employs one differential pair created by the multiple-input MOS transistor (MI-MOST) technique offering simple circuitry. Although the bulk-driven and the MI-MOST techniques reduce the amplifier's transconductance, the gain is boosted by increasing the output resistance using a self-cascode transistor and a partial positive feedback. As a result, a 95-dB voltage gain is achieved which is larger than achieved gain for most sub-0.5 V designs presented in the literature. The DDA has 12.66 kHz gain bandwidth product, and consumes 313nW of power. The input thermal noise is 0.88 µV/Hz1/2 and the average slew-rate is 14.7 V/ms at 20pF load capacitance. As an example of application, a band-pass filter (BPF) based on two DDAs with adjustable gain for electrocardiogram (ECG) signal processing is presented. The 0.18 µm CMOS technology from TSMC has been used and extensive simulation results in Cadence environment including process, voltage and temperature corners and Monte–Carlo analysis have been carried-out to demonstrate the robustness of the design.