A Low-Power Sigma-Delta Modulator for Healthcare and Medical Diagnostic Applications
Andrea Boni, Luca Giuffredi, Giorgio Pietrini, Marco Ronchi, Michele Caselli
Abstract
This paper presents a switched-capacitor Sigma-Delta modulator designed in 90-nm CMOS technology, operating at 1.2-V supply voltage. The modulator targets healthcare and medical diagnostic applications where the readout of small-bandwidth signals is required. The design of the proposed A/D converter was optimized to achieve the minimum power consumption and area. A remarkable performance improvement is obtained through the integration of a low-noise amplifier with modified Miller compensation and rail-to-rail output stage. The manuscript also presents a set of design equations, from the small-signal analysis of the amplifier, for an easy design of the modulator in different technology nodes. The Sigma-Delta converter achieves a measured 96-dB dynamic range, over a 250-Hz signal bandwidth, with an oversampling ratio of 500. The power consumption is <inline-formula> <tex-math notation="LaTeX">$30~\mu \text{W}$ </tex-math></inline-formula>, with a silicon area of 0.39 mm<sup>2</sup>.