Signal Conditioning of Capacitive Pressure Sensors

• Conversion of the relative capacitance change to the voltage or other electrical signal
• Different circuits can be used to convert a capacitance change into
  a voltage, frequency, or pulse width modulation

Typical example of a circuit based on impedance bridge is shown in following figure:

• A square wave generator E_inp drives the network at frequency f and the output voltage is:

• Excitation frequency should be reasonably high so that sensor impedance is as low as possible
• Frequency should also be low enough for easy circuit design.
• Impedance bridge based circuits of this type and its derivatives as well as other AC bridges
  have been successfully used in industry.
• Disadvantages:
  • Limitation of the full-scale output range due to non-linearity
  • Reduction of the sensitivity and resolution due to stray capacitances.