Design of CMOS Temperature Sensors

• Main Authors: Ming-Chan Weng, 翁明鏟
• Other Authors: Jiin-Chuan Wu
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/52734077603755335871

博士 === 國立交通大學 === 電子工程系 === 91 === Three CMOS temperature sensors with digital output are presented. In order to achieve the requirements of low cost, low power and high accuracy of the temperature sensors, design and implementation issues are comprehensively investigated in this thesis. An on-chip temperature sensor uses the base-emitter voltage of the parasitic substrate bipolar transistor to measure its die temperature. A remote temperature sensor utilizes a diode-connected external bipolar transistor to measure the remote temperature. The same design principles are applied to both sensors. An improved chopping technique is used to cancel the offset of the op-amp with no loss in the accuracy, so that a precise bandgap reference voltage is obtained without resistance trimming. The proposed level scaler, which operates signals in voltage domain, has better linearity and accuracy. A first order SD ADC is used to produce the digital output. No trimming is needed to obtain good temperature linearity, so that only one-temperature calibration is needed which greatly reduces testing cost. On-chip and remote temperature sensors are realized in a 0.6 μm CMOS technology with active area of 0.55 mm2 and 0.65 mm2, respectively. After calibration, the error is ±1 °C for the on-chip temperature sensor over the temperature range of -20 to 130 °C, and ±2 °C for the remote temperature sensor over the range of 0 to 120 °C. The supply currents of the on-chip and remote temperature sensors are 3.5 μA and 38 μA at 8 samples/s, respectively. The third developed smart temperature sensor is aimed at the application of thermal management in a computer system. The proposed medium-current sampling and auto-range technique are used to reduce the dynamic range requirement of the ADC and increase the accuracy. A 9-bit SAR ADC converts the temperature signal into digital output. Fabricated in a 0.6 μm CMOS process, the smart temperature sensor occupies an area of 5.2 mm2. The measured accuracy is ±0.825 °C and ±1.5 °C in the respective temperature range from 60 °C to 100 °C and 0 °C to 120 °C without any trimming. It can work with supply voltage from 3 V to 5.5 V, and has a very small line regulation of 0.1 °C/V.