A Phase-Domain Readout for Thermal-Diffusivity Based Temperature Sensors

Abstract

This thesis describes the implementation of a phase-domain readout system for a thermal-diffusivity (TD) based temperature sensor. Such sensors measure the phase shift of an electro-thermal filter (ETF), which exhibits a near-linear dependency on absolute temperature. The phase shift is measured by a phase-domain delta-sigma modulator (PD-DSM). Although ETFs can be very accurate, their readout circuitry often constrains overall performance. A notable concern is their offset, which is usually much larger than the ETF’s output signal and may cause the PD-DSM to clip. In this work, this issue is addressed by a hybrid offset-reduction strategy. The PD-DSM itself is designed to achieve a temperature inaccuracy of 0.04°C.
The design was fabricated using TSMC 180nm CMOS technology. Due to a design error, the PD-DSM did not achieve the targeted accuracy. Nonetheless, the hybrid offset cancellation scheme works as intended, demonstrating efficacy by effectively mitigating residual offset to sub-µV levels across temperature ranges extending up to 180°C.