A Fully Differential Charge-Sensitive Amplifier for Dust-Particle Detectors

This paper presents the design and measurements of a fully differential charge sensitive amplifier operating in the frequency range from 7 Hz to 300 kHz. In comparison to the typically employed single input transistor topology, the shown differential approach greatly simplifies the suppression of common mode noise. The theory of the fully differential charge sensitive amplifier and analytical rules for the correct sizing of the feedback resistor and the input transistor are derived. Finally a double-cascode-amplifier is presented, achieving an equivalent noise charge of 114 elementary charges rms in the 7 Hz to 300 kHz frequency band at 5.4 pF differential detector capacitance. The amplifier is realized in a 0.35 μm standard CMOS technology and consumes 26.4 mW at 3.3 V supply voltage.