A BJT-Based Temperature-to-Digital Converter With a 0.25 C 3 $\sigma$ -Inaccuracy From-40 C to 180 C Using Heater-Assisted Voltage Calibration

This article presents a BJT-based temperature-to-digital-converter (TDC) that achieves 0.25 C 3 $\sigma $ -inaccuracy from -40 C to 180 C after a heater-assisted voltage calibration (HA-VCAL). Its switched-capacitor (SC) ADC employs two sampling capacitors and, thus, the minimum number of critical sampling switches, which minimizes the effects of switch leakage at high temperatures and improves accuracy. The TDC is also equipped with an on-chip heater, with which the sensing BJTs can be rapidly (0.5 s) heated to about 110 C. This, in turn, enables VCAL at two different temperatures without the need for a temperature-controlled environment. Realized in a 0.16- $\mu \text {m}$ standard CMOS, the TDC, including the on-chip heater, occupies 0.15 mm(2) and operates from 1.8 V.