Design And Study Of High Resolution Temperature Sensor

In this paper, a fully integrated CMOS temperature sensor with digital output is designed and studied. Comparing to its traditional counterparts with thermal resistors, this type of temperature sensor has merits of high-precision, low-power consumption, mini-area, easy-integration. Besides, with the help of SPI, its digital output can be employed in many other systems.After the temperature dependence of the junction diode being introduced, this thesis make use of the differential base-emitter voltage (△Vbe) of two bipolar transistors under different current density to measure the temperature. This physical variable is proportional to absolute temperature (PTAT) with high linearity and little correlative to process. It is then transferred to the∑△modulator to generate digital outputs, which is further filtered and extracted to remove the quantized noise. In the end, a high precision digital output which represents the temperature is sent out by the SPI block. In this paper, several non-ideal factors which can affect the transfer precision are introduced, together with some solutions. The dynamic matching technique is applied to improve the current mirrors’and capacitors’matching degree. The offset of OPAs and the charge injection of the switches are alleviated by the chopping technique and CMOS switches. During the slow-speed of temperature change, twice transitions in a second of the modulation are enough to meet the speed. Therefore, under the oversampling rate of12500, a14bits∑△ADC is applied to complete the transition. In the end,10effective bits is sent out to remove the noise and process error.In this paper, all the design is simulated by Cadence under3.3V power supply. The test results show that the overall power consumption is less than0.7mW and the precision is±0.5℃during-5-55℃temperature range.