Capacitive Wheatstone Bridge

A Capacitive Wheatstone bridge can be used as a sensor signal conditioning circuit that converts its impedance, at a specific frequency, to a voltage. The circuit below produces a change in differential voltage as a function of the capacitance change. An Alternate Current (AC) voltage source must drive the bridge; its frequency needs to be stable and accurate. R1 can be a digital potentiomenter that is controlled to zero-out the differential voltage, or it can be a regular resistor. R3 provides a means to bias the instrumentation amplifier correctly, and to keep the node between the capacitors from drifting over time. It needs to be much larger than C2's impedance (1/j𝜔C2).



  • Excellent common mode noise
  • Ratiometric output (with Analog-to-Digital Converter (ADC) using VDD as its reference voltage)
  • Detection of open or short sensor failure


  • Need AC stimulus
  • Power dissipation

Sensor Examples:

  • Remote capacitive sensors
    • Humidity sensor
    • Touch sensor
    • Tank level sensor
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