A 0.4 V 520 nW 990 μm² Fully Integrated Frequency-Domain Smart Temperature Sensor in 65 nm CMOS

This work presents an ultra-low voltage fully integrated frequency-domain smart temperature sensor. Two temperature sensitive ring oscillators (TSROs) are used to build a temperature-to-frequencyratio generator capable of operating at 0.4 V supply voltage. One is operated in near-threshold region, while the other is operated in sub-threshold region. The ratio of their output frequencies is then a monotonic function of temperature that is reasonably insensitive to process variation. With one-point calibration, a –1.81 °C∼ + 1.52 °C inaccuracy over a 0 °C∼ 100 °C temperature operation range has been measured for 12 test chips. At a conversion rate of 45 k samples/s, the proposed temperature sensor consumes an average power of 520 nW and achieves 0.49 °C/LSB at 11-bit output resolution. It occupies only 990 μm² in a TSMC 65-nm general purpose bulk CMOS process.