Research And Design Of A High-precision Temperature Sensor Based On Sigma-delta Modulator

Since the concept of "Sensing China" is advocated in 2009,the Internet of Things is listed as one of the five newly initiated strategic industries,attracting huge attention of the whole society.As the bottom stage of Internet of Things,sensor is now playing an increasingly important role in the development of Internet of Things.Sensor has the function of transforming natural non-electrical signal into electrical one in the form of analog signal with an amplitude of merely several mV.Hence,an amplifier is needed to read out the small signal and converts it into digital signal for further processing.Since the signal produced by sensor is almost close to DC level with a frequency of only several Hz,offset noise,1/f noise and drift noise can easily blend into signal band,which leads to the degrading of resolution.Therefore,the ADC applied in sensor should be able to not only filter out the in-band noise,but also have the advantages of high resolution,high linearity and low offset.This thesis describes the theory and design of a CMOS temperature sensor with resolution.The main topic of the work is to realize temperature sensing and thus convert it to digital codes in a Sigma-Delta ADC.The paper focus on the analysis of non-linear in the circuitry and introduces some optimization to improve the accuracyThe linearity,resolution and power consumption of the temperature sensor is mostly decided by the temperature sensing circuit and Sigma-Delta ADC.There are several non-linear contributes to the total error of temperature sensor.The paper make the temperature sensing BIT work in the proper condition to ensure the linearity.Use SCD technology to reduce the offset and 1/f noise,thus improving the resolution.Adopt the second order Sigma-Delta ADC to reduce the power consumption and ensure the resolution at the same time.The whole circuit is based on the Global foundries 0.18?m CMOS technology with a supply voltage of 1.8V and sampling frequency of 25 kHz.The chip can convert 15 times per second,with ±0.5? accuracy from-40? to 80?.Simulation results show that Sigma-Delta ADC has the resolution of 15 bit,meeting the requirement of the temperature sensor.The power dissipation of the chip is merely 0.15mW and the core size is 880?m×620?m.