Research On CMOS Bandgap Temperature Sensor

During the process of industry, agriculture and scientific research, temperature is an important parameter to measure and control. Hence, temperature sensor is one of the most extensive applications among all kinds of sensors. Compared with other traditional temperature sensors, integrated temperature sensors have the advantages of good sensitivity, linearity, low power consumption, etc. Integrated temperature sensors made in bipolar (or BICMOS) technology are used extensively. However, CMOS is the most extensively used technology since it has the advantage of simple process, small device area, high integration density and low power. The fabrication of temperature sensors in standard high performance digital CMOS process is also desirable especially for the following applications: 1) in microsystems to compensate for temperature cross sensitivity of other sensors; 2) VLSI chips to control the dissipation; 3) in strongly automated production plants; and 4) in automated consumer products like cars and domestic appliances. In foreign countries, the design and production of CMOS temperature sensor has reached a higher level, but in China the research of the integrated CMOS temperature sensor and its production is just underway. There is no demestic product of CMOS temperature sensor in the market. In this thesis, the products and research papers of CMOS temperature sensor are analyzed and compared. Then, CMOS substrate bipolar transistors fabricated on the silicon substrate are chosen to measure the temperature. The temperature sensor in this thesis is based on the difference of two base-emitter voltages, biased at different current densities. That configuration is referred as bandgap. In the sensor circuit design, two bipolar transistors are connected in series to improve temperature sensitivity and reduce the relative influence of offset of operational amplifier (OP). A current mirror and a resistor are added to eliminate the influence of temperature coefficient of single resistor on temperature sensitivity and improve the linearity of temperature sensor. Then, voltage transfer circuit, which includes an OP and two resistors, and proportional amplifying circuit using an OP are designed to reach the requirement of voltage swing and temperature sensitivity of multi-sensor system. Circuit design tool of Hspice is employed to analyse the sensor circuit from—40 to +60℃. The simulation result indicates that the temperature sensitivity reaches about 10mV/℃and the range of output voltage is located in 0~3V which is one of the design requirement. The layout of the sensor circuit is developed by TannerTM Ledit layout edit software. To take cost and capability for handling in 5V power into accout, a 2μm P-well CMOS process is chosen to fabricate the temperature sensor circuit. The layout is designed strictly following the design rules. The extracted layout parameters files which are essential to get the post simulation netlist are also given out. The LVS check is completed by post simulation.The whole circuit is processed in 2μm P-well standard CMOS process. An overall testing on the circuit is completed, and the methods and results of testing are presented. The testing result of voltage transfer circuit and proportional amplifying circuit is in consistence with the simulation result. Finally the testing curve and the measured data are given.Since the validity and feasibility of CMOS bandgap temperature sensor design introduced by this thesis is confirmed to a certain extent, the design and fabrication of the circuits produced much experience for temperature sensor design in multi-sensor system of our lab.