This book describes the analysis and design of precision temperature sensors in CMOS IC technology. It focusses on so-called smart temperature sensors, which provide a digital output signal that can be readily interpreted by a computer. The sensors described in this book are based on bipolar transistors, which are available as parasitic devices in standard CMOS technology. The relevant physical properties of these devices are described. A sigma-delta converter plays a key role in the conversion to a digital output. Both the system-level design of such a converter, and the circuit-level implementation using both continuous-time and switched-capacitor techniques are described. Special attention is paid to the application of precision interfacing techniques. Precision Temperature Sensors in CMOS Technology ends with a detailed description of three realized prototypes. The final prototype achieves an inaccuracy of only ±0.1ºC (3Sigma) over the temperature range of 55ºC to 125ºC, which is the highest performance reported to date.