A high-accuracy, high-speed interface circuit for differential-capacitance transducer

摘要

A novel high-accuracy and high-speed interface circuit based on lock-in detector is presented for differential-capacitance transducer. In the interface, the feedback capacitance rather than feedback resistance is used in the current detector to reduce the noise due to large resistance. Capacitor-array circuit proposed makes possible to cover a wide range of capacitance changes by choosing feedback capacitor close to the measurand, which results in transfer coefficient of the current sensing circuit about -1. A precision full-wave rectifier based on phase-sensitive-detector (PSD) incorporated in demodulator eliminates the effect due to threshold voltage of diode to improve the accuracy and suppress noise. A second-order low-pass filter is incorporated in demodulator, which allows high-speed and high-accuracy interface for differential-capacitance transducers. Moreover, the circuit is immune to parasitic capacitance, resistances and exciting source. It is capable of detecting the capacitance change as small as 0.005% of the total capacitance up to 16 pF with the speed higher than 5 ksps. A capacitance diaphragm pressure transducer and a standard pressure source (RUSCA 2465 piston gauge) are connected to the circuit to confirm the analysis. (c) 2005 Elsevier B.V. All rights reserved.