Delta-Sigma Modulator based Compact Sensor Signal Acquisition Front-end System

TL;DR

This paper presents a compact, integrated delta-sigma modulator-based front-end system for sensor signal acquisition, combining amplification, filtering, and digitization in a low-power CMOS implementation for high-precision sensing applications.

Contribution

It introduces a novel DDA-based architecture with noise reduction techniques, enabling high-precision, low-power sensor signal acquisition within a single delta-sigma modulator block.

Findings

Achieved 80 dB SNR and 109 dBFS dynamic range in simulation.

Implemented in 0.18μm CMOS with 100μW power consumption.

Measured SNR was about 9 dB lower than simulation.

Abstract

The proposed delta-sigma modulator ($\Delta\Sigma$M) based signal acquisition architecture uses a differential difference amplifier (DDA) customized for dual purpose roles, namely as instrumentation amplifier and as integrator of $\Delta\Sigma$M. The DDA also provides balanced high input impedance for signal from sensors. Further, programmable input amplification is obtained by adjustment of $\Delta\Sigma$M feedback voltage. Implementation of other functionalities, such as filtering and digitization have also been incorporated. At circuit level, a difference of transconductance of DDA input pairs has been proposed to reduce the effect of input resistor thermal noise of front-end R-C integrator of the $\Delta\Sigma$M. Besides, chopping has been used for minimizing effect of Flicker noise. The resulting architecture is an aggregation of functions of entire signal acquisition system within the single block of $\Delta\Sigma$M, and is useful for a multitude of dc-to-medium frequency sensing and similar applications that require high precision at reduced size and power. An implementation of this in 0.18-$\mu$m CMOS process has been presented, yielding a simulated peak signal-to-noise ratio of 80 dB and dynamic range of 109dBFS in an input signal band of 1 kHz while consuming 100 $\mu$W of power; with the measured signal-to-noise ratio being lower by about 9 dB.