Non-idealities of temperature sensors using substrate pnp transistors

This paper describes the nonidealities of temperature sensors based on substrate pnp transistors and shows how their influence can be minimized The effects of series resistance, current-gain variation, high-level injection and the Early effect on the accuracy of the PTAT voltage are discussed. The results of measurements made on substrate pnp transistors in a standard 0.5 μm CMOS process are presented to show the effects of these nonidealities. It is shown that the modeling of the PTAT voltage can be improved by taking the temperature dependency of the effective emission coefficient into account using the reverse Early effect. With this refinement, the temperature can be extracted from the measurement data with an absolute accuracy of ±0.1°C in the range of -50°C to 130°C.