An A/D interface based on σ Δ modulator for thermal vacuum sensor ASICs

Abstract

A new σ Δ modulator architecture for thermal vacuum sensor ASICs is proposed. The micro-hotplate thermal vacuum sensor fabricated by surface-micromachining technology can detect the gas pressure from 1 to 105 Pa. The amplified differential output voltage signal of the sensor feeds to the σ Δ modulator to be converted into digital domain. The presented σ Δ modulator makes use of a feed-forward path to suppress the harmonic distortions and attain high linearity. Compared with other feed-forward architectures presented before, the circuit complexity, chip area and power dissipation of the proposed architecture are significantly decreased. The correlated double sampling technique is introduced in the 1st integrator to reduce the flicker noise. The measurement results demonstrate that the modulator achieves an SNDR of 79.7 dB and a DR of 80 dB over a bandwidth of 7.8 kHz at a sampling rate of 4 MHz. The circuit has been fabricated in a 0.5 μm 2P3M standard CMOS technology. It occupies an area of 5 mm2 and dissipates 9 mW from a single 3 V power supply. The performance of the modulator meets the requirements of the considered application.