Abstract: An amplifier for measuring the charge stored on a source capacitor 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 a capacitive network. The capacitive network connects the signal input and the output of the opamp, and provides a capacitance of CT between the signal input and the output of the opamp wherein CT<Cpd. The capacitive network is constructed from a plurality of component capacitors. Preferably 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.