INTRODUCTION TO THE PIEZO RESISTIVE SENSOR BRIDGE TEMPERATURE COMPENSATION TOOL
A very common type of pressure sensor consists of diaphram with piezoresistive strain gauges resistors diffused into it, fused to a silicon or glass backplate. This support tool helps the designer determine the appropriate values for the thermistor and fixed resistors used to implement this circuit. The network obtained will bias the voltage applied to a piezoresistive bridge compensating the output voltage of this bridge.
The tool gives the user the option to choose either a voltage source or current source. Next, the user should define the temperature range (between -55 °C and 150 °C). The limits defined here are very important as a narrow temperature range will automatically lead to a better fitting solution
The user has the option to choose what type of mechanical execution is needed for the NTC thermistor (leaded or SMD 0402, 0603, or 0805 case). The user will enter the value of the power supply and piezoresistive element, its temperature coefficient of resistance (TCR), and finally, the loss of sensitivity of the bridge output voltage as a function of the temperature coefficient of sensitivity (TCS). Five points within the temperature range will be used in order to identify the best fitting values for the thermistor and fixed resistors.
What is the TCR of a Piezo-resistive Sensor?
What is the TCS of a Piezo-resistive Sensor?
The part number of the thermistor will be defined after optimization, the optimal value will be displayed together with fixed resistor values (selected from E12, E48, and E96 series). The user will have option to define thermistor R25 tolerance depending on the required fitting level.
Click here for schematic cross-section of the basic elements of a silicon piezoresistor.
Click here for schematic cross-section of how resistors can be in compression or in extension on the same substrate.
Click here for sample schematic diagram of a four arm Wheatstone Bridge and a compensation network.
