A capacitance measurement system with milliwatt power and attofarad resolution

A capacitive measurement system with attofarad resolution is presented. The electronics setup consists of a capacitive sensor interface with period-modulated output and a microcontroller board with 70 MHz clock to read out the output period. The electronic interface which is based on a capacitance-to-voltage converter and a relaxation oscillator has been designed and implemented in 0.7 µm standard CMOS technology. The measured data is transferred to a computer via RS232 port and analyzed in a Labview program. The resolution of about 1.5 aF is achieved for a range of 1 pF and a measurement time of 1 s. The highest resolution which can be achieved is about 0.5 aF for a measurement time of about 10 s.