A low power CMOS temperature sensor

Abstract

Temperature sensing in an important new paradigm in Complementary Metal Oxide Semiconductor (CMOS) system design. Traditionally temperature sens- ing has been achieved via resistive platinum sensors which are bulky and incom- patible with CMOS processes. As a result, there been an increasing research focus over the last decade on developing on chip temperature sensing which comes at the cost of low accuracy, however the main advantage is the complete integration with the CMOS process flow. In this thesis we explore a low power temperature sensor, based on a Voltage to Time Converter (VTC) architecture. By eliminating power hungry analog to digital converters, extremely low power consumption can be achieved. We use a bipolar junction based bandgap as a front end for sensing temperature, then digitize the temperature information by employing a VTC cell. An on chip oscillator also cancels any non-linearity in the reference current thus making the system immune to any process variations from the temperature sensing frontend. We also explore a pulse width modulated based gas readout circuit for re- sistive gas detectors. Due to the extremely high changes in resistance over the gas sensing range, an ADC is an unsuitable architecture for these applications. The proposed PWM readout maintains excellent linearity over several decades of resistance change and is thus a suitable candidate for this application.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology