An Inaccuracy Thermal Sensor with a New Digital Calibration Algorithm in 12nm CMOS

This paper presents an inaccuracy thermal sensor with a new digital calibration algorithm in 12 nm CMOS process. The conventional temperature-to-digital converter calibration relies on the reproducibility of VBE, which slightly depends on the process variation and becomes a challenge in designing an accurate thermal sensor. This work develops a new digital calibration algorithm that treats environmental temperature as an absolute reference to overcome process variation. It calibrates the BJT $|\mathrm{V}_{\mathrm{B}\mathrm{E}}|$ error using $|\mathrm{V}_{\mathrm{B}\mathrm{E}}|$ differences between two devices. The thermal sensor consists of a bipolar core, a bandgap reference (BGR), and a 10-bit successive-approximation-register (SAR) analog-to-digital converter (ADC) is fabricated in 12nm CMOS process. Thanks to the proposed digital calibration algorithm, the measurement results demonstrate -$2.09^{\circ}\mathrm{C}\sim 1.50^{\circ}\mathrm{C}$ inaccuracy over a temperature range of $0^{\circ}\mathrm{C}$ to $80^{\circ}\mathrm{C}$ without any device trimming.