A Time-Domain Temperature Sensor using Nwell Diodes on 820µm^2 in 7nm FinFET

Abstract

We present a novel concept for thermal sensing, which provides a duty-cycle modulated output signal for high resolution measurement. The circuit is self-contained and features distinct simplicity, containing only a few switches, capacitors and an auto-zero comparator. The active Nwell-Substrate diode is utilized as a robust sensing device in advanced FinFET nodes. Two sampling capacitors operate as a charge-pump and discharge periodically across the diode. The sampled voltages represent PTAT and CTAT signals, which are balanced by means of adjusting the diode current through pulse timings. This control pulses are generated in a feedback loop by the comparator and a counter, while the temperature is extracted from their duty-cycle. Our prototype in 7nm FinFET consumes only 820µm2 active area, due to low matching requirements. From simulated data, the sensor operates down to Vdd = 0.90V and achieves an untrimmed accuracy of ±2.8°C from -10°C to 120°C. It dissipates ~11µW including an internal clock generator, with a conversion time between 2.5µs and 600µs.