Precision temperature sensors in CMOS technology

Abstract This thesis describes the analysis and design of precision temperature sensors in CMOS technology. It focuses on so-called ?smart? temperature sensors, which provide a digital output signal that can be readily interpreted by a computer. Over the temperature range from ?55°C to 125°C, the inaccuracy obtained in previous work using such sensors was about +/-2°C. In this work, that inaccuracy is reduced to +/-0.1°, so that the performance of CMOS temperature sensors becomes comparable to that of conventional analog sensors, such as platinum resistors and thermistors. The production costs of CMOS smart sensors, however, are much lower, because a standard IC process is used, and the sensors need to be calibrated at only one temperature.The sensors described in this thesis are based on bipolar transistors, which are available as parasitic devices in standard CMOS technology. The relevant physical properties of these devices are described. It is shown in detail how the temperature characteristics of these transistors can be used to obtain an accurate digital temperature reading. The required analog-to-digital conversion is performed by a sigma-delta converter. The system-level and circuit-level implementation of such a converter are described. A separate chapter is devoted to low-cost calibration techniques. The thesis ends with a detailed description of three realized prototypes. The final prototype achieves the above-mentioned accuracy of +/-0.1°C, which is the highest performance reported to date.