Low-power low-voltage CMOS A/D sigma-delta modulator for bio-potential signals driven by a single-phase scheme

Since the 1970´s, the analog switches in switched-capacitor (SC) circuits are operated by nonoverlapping bi-phase control signals (φ₁, φ₂). The nonoverlapping of these two phases is essential for successful SC operation since, a capacitor inside an SC circuit can discharge if two switches, driven by φ₁ and φ₂, are turned on simultaneously. Moreover, since 1983, two additional phases are generally used in many SC circuits, which consist of advanced versions of φ₁ and φ₂. These two additional phases overcome the problem of signal-dependent charge injection. This paper presents a low-power and low-voltage analog-to-digital (A/D) interface module for biomedical applications. This module provides an A/D conversion based on a mixed clock-boosting/switched-opamp (CB/SO) second-order sigma-delta (ΣΔ) modulator, capable of interfacing with several different types electrical signals existing in the human body, only by re-programming the output digital filter. The proposed ΣΔ architecture employs a novel single-phase scheme technique, which improves the dynamic performance and highly reduces the clocking circuitry complexity, substrate noise and area. Simulated results demonstrate that the signal integrity can be preserved by exploring the gap between the high conductance region of pMOS and nMOS switches at low power-supply voltages and the fast clock transitions that exist in advanced CMOS technologies. The mixed CB/SO architecture together with the overall distortion reduction resulting from using the proposed single-phase scheme, result that the dynamic range of the modulator is pushed closer to the theoretical limit of an ideal second-order ΣΔ modulator.