Capacitive and Resistive Sensing Based on Compensated Relaxation Oscillator

Relaxation oscillator based capacitance and resistance measurements are investigated with a compensation technique. Output oscillation frequency of op-amp based relaxation oscillator changes over a range of capacitance variation. The range of capacitance variation considered for measurement is between 57.1 and 206.4 pF. The output oscillation frequency deviates from the theoretical value due to non-idealities of op amp. A compensation technique has been proposed to reduce the oscillation frequency error observed in output waveform. The performance of the op-amp is evaluated again post compensation. The experimental results are compared with an integrator based relaxation oscillator and comparator configuration. Further, the concept of utilizing the compensated relaxation oscillator for resistance measurement has been experimented. The compensated relaxation oscillator provide the improved performance in oscillation frequency of the waveform. Thus, the compensated relaxation oscillator could be employed for both resistive and capacitive sensing for two different measurements such as temperature and moisture measurements.