A 1.2V 83dB DR single-ended input SC sigma modulator including a large-swing analog buffer for portable ECG applications

Abstract

This study proposes a subsystem consisting of an analog buffer and a single-ended input to a fully differential sigma modulator to obtain low-power consumption for portable electrocardiogram applications. With the proposed subsystem, the need for an inverting amplifier is avoided, and low-power consumption is achieved. The sigma modulator with a second order, 1bit, and cascade of integrators feedforward structure consumes a low power, in which an inverting and a non-inverting path implement a single-ended input to fully-differential signals. A double sampling technique is proposed for a digital-to-analog converter feedback circuit to reduce the effect of the reference voltage, reduce the amplifier requirements, and obtain low-power consumption. Input-bias and output-bias transistors working in the weak-inversion region are implemented to obtain an extremely large swing for the analog buffer. At a supply voltage of 1.2V, signal bandwidth of 250Hz, and sampling frequency of 128kHz, the measurement results show that the modulator with a buffer achieves a 77dB peak signal-to-noise-distortion ratio, an effective-number-of-bits of 12.5 bits, an 83dB dynamic range, and a figure-of-merit of 156dB. The total chip size is approximately 0.28mm(2) with a standard 0.13 mu m Complementary Metal-Oxide-Silicon (CMOS) process. Copyright (c) 2016 John Wiley & Sons, Ltd.