A Capacitive Readout Circuit for a Disposable Low-Cost Pressure and Flow Sensor with 200 Pa or 170 nl/s Resolution

The aim of this research is the development of a readout circuit for a low-cost capacitive pressure and flow sensor for medical as well as life science applications. The measuring cells of this sensor, which are in contact with the fluid, is disposable in order to avoid cross-contamination. Compared to previous work [1], the charge output of both measuring cells is directly evaluated differentially and a readout circuit based on chopping is implemented. This greatly improves the stability and eases a subsequent implementation as application specific integrated circuit (ASIC). Measurement results with a prototype PCB implementation show a full scale of more than 100 kPa or 50 μl/s and a RMS noise of the readout circuit lower than 320 μV over the measurement bandwidth of 500 Hz corresponding to a resolution better than 200 Pa or 170 nl/s.