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

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 mu V/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 mu m 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.