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This paper presents a power-efficient capacitive-sensor interface solution for high-speed and high-resolution subnanometer displacement measurement systems. The proposed solution utilizes a zoom-in capacitance-to-voltage converter stage to remove the offset posed by the large nominal sensor capacitance, which would otherwise dominate the dynamic range. The realized zoom-in factor is 100. The designed circuit uses a correlated-double-sampling technique to cancel both the amplifier offset and the reset noise. First, a printed-circuit-board solution was realized to verify the principle of operation and its limitations. Then, an integrated circuit was designed, fabricated, and tested. Measurement results show that the achievable capacitance resolution is better than 30 aF, from a sensor with a nominal capacitance of 10 pF, which translates into a dynamic range of 18 b. The measurement latency is only 5 μs. This performance is achieved with only 2.4-mW power consumption.
Instrumentation and Measurement, IEEE Transactions on (Volume:61 , Issue: 5 )
Date of Publication: May 2012