Design Of Temperature Sensor Base On SAR-ADC

Compared with conventional temperature sensor, the integrated CMOS smart temperature sensor is used for the environment temperature measurement and the thermal protection of chip with the integrated singal processing. It has some advantages, such as high sensitivity, small volume, low power, small self-heat temperature rise, low cost, direct digital output and so on. However, due to the process varation and parasitic parameter limiting, the integrated CMOS smart temperature sensor also has disadvantage in measuring temperature range and achieving higher precision.Based on the analysis and design of temperature sensing circuit and SAR ADC, a high precision CMOS temperature sensor is proposed and realized. The proposed temperature sensing circuit is composed of △VBE of the parasitic PNP transistor in CMOS process and swith capacitor amplifier. A variety of precision techniques, such as the dynamic matching and chopping technique, are adoped. The SAR ADC uses conventional structure, the sampling and hold circuit adopts under-side plate sampling, the DAC uses combination structre with high 7bit capacitor DAC and low 5 bit resistor DAC, the comparator uses high speed type with three pre-amplifier following a latch, and adoptes output cancel offset technique.The proposed CMOS temperature sensor has been fabricated with Global Froundry 0.13unm 1P6M CMOS technology. Its area is 500um*600um, analog supply voltage is 3.3V, digital supply voltage is 1.2V and total power dissipation is less than 2.5mW. The test result shows that the 12 bit SAR ADC has ENOB of 10 bit at 1MHz sps and the error of temperature sensor is within ± 1 ℃ in temperature range of -40 ℃～125℃ with 0.25 ℃ sensitivity.