Design Of Temperature Sensing Integrated Circuits In CMOS Technology

Body temperature is a vital physiological signal of the human body and it is also important for diseases diagnosis.Temperature sensors are irreplaceable in the medical field and they are the earliest developed and most widely used sensors.Compared with the traditional discrete temperature sensor,the integrated temperature sensors are compatible with the CMOS technology,and the temperature sensing circuit and the signal processing circuit can be integrated together,with the advantages of low cost,small volume,high sensitivity and better inaccuracy.This thesis is mainly about two CMOS temperature sensors with their interface circuits.One is the temperature sensor used in retinal prosthesis and the other is the thermometer for human body temperature sensing.The temperature sensor for the retinal prosthesis needs to achieve a resolution of 0.5?.Its design is based on the X-FAB 0.35?m CMOS process.The temperature-dependent voltage is generated by the temperature sensing circuit and amplified by a fully differential operational amplifier to increase sensitivity,and then converted to a digital signal by a 10-bit SAR ADC.The chip has been designed and taped out and chip testing results show that this temperature sensor can achieve a sensitivity of 0.125?in the range of 20-50?.The average power consumption is only 2.205?W in the duty cycle mode.Compared to the temperature sensor in the retinal prosthesis,the thermometer needs to achieve higher sensitivity and better inaccuracy.It is the key point of thermometer.First of all,literature surveys have been done on the architecture of the thermometer system.It uses parasitic bipolar transistors in CMOS technology to generate temperature-dependent currents,and then the induced currents will be converted into a square wave whose duty cycle positively changed with temperature,and finally the temperature message will be converted into a digital signal by counters.After that this thesis analyses and designs the sub-modules of thermometer,and introduces chopper to eliminate the offset voltage caused by the operational amplifier,dynamic element matching to reduce the error caused by components'mismatch,?compensation technique to decrease the inaccuracy caused by finite current gain.At last,this chip's layout is done and streamed out under the X-FAB 0.18?m process.The simulation results show that the average power consumption of the chip is 58?W at 1.8V power supply,and the area of the chip is 0.14mm~2,the inaccuracy is±0.02?in the range of 37-39?,0.15/-0.11?in the range of 35-37?and 39-45?,the sensitivity is 0.011?.The thermometer finally reaches the performance requirements.