LOW FPN HIGH GAIN CAPACITIVE TRANSIMPEDANCE AMPLIFIER FOR USE WITH CAPACITIVE SENSORS

摘要

An amplifier (20) for measuring the charge stored on a source capacitor (23) having a capacitance Cpd. The amplifier includes an opamp having a signal input, reference input and output; the first terminal of the source capacitor is connected to the signal input. The amplifier includes a reset switch for shorting the signal input and the output of the opamp, and provides a capacitance CT between the signal input and the output of the opamp where CT =Cpd. The capacitive network is constructed from a plurality of component capacitors. Perferably each component capacitor has a capacitance greater than or equal to Cpd. In one embodiment of the invention, the capacitive network includes first, second, and third component capacitors, each capacitor having first and second terminals. The first terminal of the first capacitor is connectecd to the outpout of the opamp; the second terminal of the first capacitor, the first terminal of the second capacitor, and the first terminal of the third capacitor are connected together at a first common node, the second terminal of the third capacitor is connected to he signal input of the opamp, and the second terminal of the second capacitor is connected the the second terminal of the parasitic capacitor. The capacitive network also includes a first network switch for connecting the first common node to the outpout of the opamp.