Research And Design Of CMOS Integrated Temperature Sensor

Temperature sensors are widely used in food storage,cold chain logistics,grid temperature detection,and electronic system temperature management.However,with the increasing demand of system integration,low-power consumption,and low cost,temperature sensors based on special materials are difficult to meet the requirements in various situations.In order to address the above problems,CMOS integrated temperature sensors are invented,and have been rapidly favored by industry and academia due to their low-power consumption,low cost and miniaturization.Generally,CMOS integrated temperature sensors are divided into two categories,namely voltage-domain and time-domain temperature sensors.The Voltage-domain temperature sensor uses a voltage signal varying with temperature to characterize the temperature information.It has the advantages of high precision and high accuracy.Since the analog-to-digital converter is an important part of this type of temperature sensor,it is difficult to design and has disadvantages such as high power consumption and large chip area.The time-domain temperature sensor is a temperature sensor based on frequency or delay time varying with the temperature.The temperature sensor uses a frequency-to-digital converter or a time-to-digital converter to digitize the temperature,so that the temperature sensor can be implemented in an all-digital way,which effectively reduces design difficulty,power consumption,and chip area.However,since the traditional time-domain temperature-sensing circuit is affected by non-ideal factors such as power supply voltage and nonlinearity,it has a large temperature measurement error.In order to solve the shortcomings of the voltage-domain and the time-domain temperature sensor,the temperature characteristics of CMOS process are deeply studied,and two temperature sensors are designed.Among them,the time-domain temperature sensor has good power supply voltage rejection and high conversion rate;the voltage-domain temperature sensor has a high measurement accuracy,small chip aera and low power consumption.The main researches include the temperature characteristics of CMOS process,the design method of the temperature-sensing circuit with low-power,low-noise,high-linearity and high-sensitivity,as well as the method of the high-resolution and high-precision quantization.The combination of theoretical analysis and circuit implementation is used to carry out the research,and the correctness of the theory and method is verified by chip test.Specifics include the following aspects:1).Study the temperature characteristics of CMOS process.In CMOS process,bipolar transistors,MOS transistors and resistors are the core devices to design temperature sensor.The temperature characteristics of bipolar transistors,MOS transistors and resistors in CMOS processes are studied.Quantitative analysis of temperature measurement errors caused by non-ideal factors of various devices,including mechanical stress,bias current,base resistance and base width,etc.Considering the spread of CMOS process,the calibration technology of the temperature sensor is studied in order to reduce the influence of process on temperature measurement accuracy.2).A high-speed,low-power and low-supply-sensitivity time-domain temperature sensor based on a ring oscillator is proposed.The chip converts the temperature information into a frequency that is complementary-to-absolute-temperature and then uses a frequency-to-digital converter to quantify it.The ring oscillator is powered by a voltage that is complementary-to-absolute-temperature to increase temperature sensitivity and conversion rate,thereby solving the problem that the temperature sensitivity of conventional time domain temperature sensors is limited by the temperature characteristics of the logic gate circuit.In view of the measurement error caused by the change of power supply voltage,an amplifier with a power gain of one is proposed.Considering the nonlinearity between frequency and temperature,a frequency-to-digital converter based on piecewise linear fitting is proposed to improve the accuracy of temperature measurement.The proposed sensor is implemented in a TSMC 180nm CMOS process,which occupies an active area of 0.048 mm².After a one-point calibration,the sensor achieves an inaccuracy of±1.5? from-45? to 85? under a supply voltage of 1.4V–2.4V showing a worst case supply sensitivity of 0.5?/V.The sensor maintains a high conversion rate of 45 kS/s with a fine resolution of 0.25?.Under a supply voltage of 1.8 V,the maximum energy consumption per conversion is only 7.8 nJ.According to experimental results,the proposed sensor is suitable for monitoring the hot-spots and the cold-spots in system on chip.3).A low-power,high-precision temperature sensor based on bipolar transistor is proposed.The core module includes a front-end temperature-sensing circuit based on bipolar transistor and ZOOM ADC.The ZOOM ADC quantifies the ratio of V_BE to?V_BE and then obtains the temperature measurement value in Celsius by a simple mathematical operation.The design goal is low power consumption,small chip area and high accuracy.First,the temperature error caused by non-ideal factors of the temperature-sensing circuit should be reduced to less than 0.01?.By combining autozeroing technique,system level chopping and bias circuit chopping,the error caused by the offset is reduced.A special bias circuit is used to make the sensor insensitive to current gain variation of the bipolar transistor and the supply voltage variation.Errors associated with mismatch are eliminated by dynamic element matching technique.So far,the process spread of the base-emitter voltage of the bipolar transistor and resistance are the significant source of error which can not be eliminated by the circuit technology.This error is eliminated by a one-point thermal calibration.At the same time,the ZOOM ADC,which combines SAR ADC and the incremental sigma delta ADC,is used to quantify the temperature-sensitive voltage.Thanks to the combination of SAR and incremental sigma delta architecture,the ADC offers the advantages of low-power consumption,high resolution and high accuracy.The conversion time is reduced by a factor of two due to an energy efficient sampling scheme.The circuit is implemented in a TSCM 65nm CMOS process with an active area of 0.16mm².After one-point calibration,the sensor achieves an inaccuracy of±0.4? from 40? to 125?.Under a supply voltage of 1.2V,the current consumption is 15?A and the conversion rate is 12 S/s.Under a supply voltage of 1.1V–1.3V,the sensor achieves a supply sensitivity of 1?/V.