Research of Continuous Delta-Sigma Analog-to-Digital Converter for Bio-Electricity Signal Acquisition

Abstract

In this paper, a continuous delta-sigma analog-to-digital converter with a low power, single-ring, third-order mixed integrator for bio-electricity signal acquisition is proposed. For the trade-off between low power consumption and high resolution, the Active-RC integrator is used in the first-order of the third-order feedforward modulator and the Gm-C integrator with improved linearity is adopted for the second and third order integrators. Because of the infinite resistance provided by the Gm-C integrator, the first-order integrator can replace the traditional second-order operational transconductance amplifier (OTA) with a single-stage OTA operating in the weak invert region to achieve low power consumption and ensure the output swing of the first-order integrator. The structure of cascade-of-integrators with feedforward (CIFF) can scale the output voltage values of three integrators and reduce the requirement of linearity of the Gm-C integrator, to reduce the design difficulty of the Gm-C integrator. In addition, the linearity of the second and third-order Gm-C integrator is improved by using the auxiliary difference pair OTA with source-level negative feedback. Therefore, the matching between the circuit structure and the model coefficients is improved significantly.