Modulation/ Demodulation System for Capacitive Sensors

A modulation/demodulation system which is suitable for capacitive sensor signal processing is proposed. A capacitive sensor has very weak output signal (O. Brand and G.K. Fedder, 2005), which requires preamplification prior to any further processing. The unavoidable 1/f noises (P.R. Gray and R.G. Meyer, 1993) of the MOSFETs in the electronic circuit often eat away the signal from the sensor, which make the signal not readable. To overcome this problem, a modulation/demodulation system is proposed to modulate the 1/f noise to a higher frequency and then been low-pass filtered. The result shows that the circuit suffers an equivalent input noise of 468 nV/rt Hz and has a THD of 0.6% with 5 mW power consumption