Research And Design Of High-Resolution CMOS Temperature Sensors

With the development of Internet of Things(IoT),wireless body local area network and other technologies,IoT equipment has an increasingly strong demand for low power consumption and small size.Frequency reference is an indispensable part of the terminal system of the IoT,while traditional quartz crystal oscillator is one of bottlenecks limiting its continuous miniaturization.Film Bulk Acoustic Resonator(FBAR)has the advantages of high resonant frequency,high quality factor,small size and easy compatibility with CMOS process,providing support for low power consumption and small size of Internet of Things terminals.However,the resonant frequency of FBAR has a large deviation with the change of ambient temperature,which cannot meet the stability requirements of frequency reference in wireless communication system,so temperature compensation is needed to meet the stability requirements of frequency reference in IoT terminals.This paper studies and designs a high-resolution CMOS temperature sensor.The main work and innovations are as follows:(1)a Wien-Bridge(WB)temperature sensing front-end is designed.The circuit is composed of silicified poly resistor and MIM capacitor,which converts temperature to output phase shift,effectively improving the temperature measurement resolution and accuracy,and reducing the influence of process deviation and power supply voltage.(2)a continuous time phase domain DeltaSigma modulator is designed.used as the phase shift readout circuit,The second-order feedforward structure is adopted to reduce the difficulty of circuit design and the power consumption of the system.The system-level chopper technology is adopted to reduce the influence of non-ideal factors such as Offset Voltage and 1/f noise of the operational amplifier in the modulator.Then in-band signal-to-noise ratio and temperature resolution are improved.(3)A high linearity operational transconductance amplifier is proposed and designed,which eliminates the third harmonic(HD3)of the output current by using the exponential I-V characteristic of the sub-threshold region transistor and the tail resistance of a specific resistance value,thus achieving a high signal-tonoise distortion ratio.The temperature sensor chip is fabricated in a 0.18-μm standard CMOS technology.The simulated results show that the temperature error is less than ±0.5℃in the temperature range of-40℃～85℃,and the temperature resolution is 9.3mK when the conversion time is 10.24 ms.The measured results show that the temperature resolution is 14.9mK when the conversion time is 10.24 ms.