A Study on Ultra-low Power Leakage-Based Temperature Sensor

Abstract

The performance of critical building blocks for ultra-low-power (ULP) applications often causes strong temperature dependencies. Since the temperature sensitivities need to be compensated, an on-chip temperature sensor is becoming one of the essential blocks in ULP system-on-chips (SoC). This thesis presents temperature sensors with a leakage-based bandgap-Vth reference. The first temperature sensor combines a leakage-based bandgap-Vth reference and an asynchronous SAR ADC. By sampling leakage-based biases directly by the SAR ADC, the sensor consumes 490pW at 20ºC with a conversion time of 200ms and stably works with a 1-point calibration showing a peak-to-peak error of ±2.35ºC, a resolution of 0.59ºC in a range of -10-to-100ºC. The second temperature sensor uses a scaled reference voltage obtained by switched capacitor circuits and an on-chip leakage-based oscillator for internal clock generation. The SAR ADC operates with a scaled supply voltage by 1/2 generated by the switched capacitor. The sensor consumes 487pW with a conversion time of 128.6ms at 20ºC. Peak-to-peak error is -3.43/2.77ºC and ±1.63ºC after 1-point and 2-point calibration, respectively. In a temperature range of -30 to 100ºC, the sensor shows resolution of 0.37ºC that is about 60% improved, compared with the first sensor. The designed sensors are fabricated in 180nm CMOS process.