Design Of A High Accuracy Temperature Sensor

As one of the most widely used sensors nowadays,temperature sensors are indispensable in industrial manufacturing,agricultural production,scientific research and even national defense.Compared with traditional temperature sensors,temperature sensors based on CMOS are easier to be integrated,smaller,dissipating lower power and can be connected to digital system.However,with the effect of non-ideal factors such as process deviation,the measuring range of CMOS temperature sensors is smaller and the accuracy is worse.The temperature designed in this paper is based on the characteristics:The base-emitter voltage differenceΔV_BE of two bipolar transistors which are biased in two different density current is proportional to absolute temperature.With the quantization ofΔV_BE by analog to digital converter,the real temperature can be got.In this paper,the temperature,process characteristics and various non-ideal factors of bipolar transistors parasitic in CMOS process are analyzed.The various error factors are allocated by mathematical method.The temperature sensor is composed of temperature sensing circuit based on longitudinal parasitic bipolar transistor and ADC with low speed and high precision.Independent current bias is used to eliminate the error caused by the limited current gain of the bipolar transistor.Chopper technique is used to eliminate the influence of the misalignment voltage and flicker noise of the operational amplifier.Second order curvature compensation technique is used to eliminate the process deviation of the transistor,and dynamic matching method is used to eliminate the influence of non-ideal factors such as the mismatching of the current mirrors and the transistors.The SAR ADC with low power consumption,small area and high precision is adopted.The DAC module adopts segmented capacitive charge scaling,capacitor arrays are arranged in a concentric manner,which greatly reduces the chip area and power consumption.The comparator adopts the form of cascaded three-stage preamplifier and latch,which improves the speed and resolution of the comparator.Simulation results show that the ADC meets the design requirements of low power consumption and high precision.The temperature sensor designed in this paper is realized in the 0.18μm process.The overall layout area is 620μm×420μm,while the power supply voltage is 1.8V and the power consumption is 1.3mW.Simulation results show that the effective number of bit（ENOB）of the SAR ADC under 10k Hz sampling frequency is 10.8.The temperature measurement error between the range of-20℃and 80℃is less than 0.5℃in tt process corner before trimming,while the error is more than 1℃in ss and ff process corner.However,the measurement error is less than 0.5℃in all three process corners after trimming,which meets the design requirements.