The Temperature Compensation Circuit Design Of The Silicon Bridge Piezoresistive Pressure Sensor

As an important kind of modern industrial sensors, pressure sensors play a crucial role in many areas of industrial automation, high precision measurement,medical etc.Along with the modern industrial developing towards miniaturization, integration and precision, accurate measurement is essential. Particularly, the silicon bridge piezoresistive pressure sensor with its good linearity, high sensitivity, small size, easy integration and many other advantages, has became the most widely used pressure sensor.But due to materials and processes of this sensor, the temperature drift inevitably occurs. Owing to the characteristic, in the unstable temperature environment, its application is limited. In order to expand the application scope of the silicon bridge piezoresistive pressure sensor and to improve its measurement accuracy, it’s necessary to research its temperature compensation. Analyzing the temperature drift of the silicon bridge piezoresistive pressure sensor, a temperature compensation circuit that can be realized by standard CMOS process is designed.From the structure and principles of the silicon bridge piezoresistive pressure sensor, based on the mechanism of temperature drift,zero temperature drift and sensitivity temperature drift are analyzed. According as the temperature characteristic equation of the sensor output sensitivity under5V supply voltage with a constant input pressure, the scheme of using a excitation voltage source with increasing output voltage linearly by increasing temperature to drive the sensor is designed.The temperature characteristic equation of the voltage source is presented, and the conditions to achieve temperature compensation are analyzed.On the basis of the temperature characteristic equation of the voltage source, the modules of compensation circuit are designed, including: the bandgap reference voltage source, PTAT voltage and the voltage buffer. The core circuit of the bandgap reference voltage source is Kujik structure,and it has been improved by adding cascade devices to improve power supply rejection ratio in this paper. Using a two folded cascade operational voltage amplifier in deep negative feedback state to "clamp voltage ". The PTAT voltage is obtained from the bandgap reference voltage source circuit, which is summed with the reference voltage can get the excitation voltage of the desired temperature characteristics. As the input resistance of the sensor is small, a voltage buffer following the excitation voltage is added. The voltage buffer is a two-stage operational voltage amplifier,and the output following the excitation voltage directly drives the sensor.A typical sensor is selected to be the object of temperature compensation,and the design of compensation circuit parameters is accomplished.In order to verify the effect of temperature compensation in the HSPICE, a SPICE model for the typical sensor is established. The entire circuit is simulated in TSMC0.35um CMOS process and the HSPICE simulation results show that at-20~100℃operating temperature range, the temperature coefficient of the output voltage from pre-compensation-2100ppm/℃reduced to24.9ppm/℃of the voltage range.Compared with the temperature compensation circuit of the same scheme, the more simplifid circuit structure is.achieved.In addition, the temperature compensation circuit is also used as the drive power of the sensor, can work normally under the power supply voltage of4.3~6V, with good performances.