Design of Common-Mode Feedback for High-Gain Charge Amplifier

We describe a common-mode feedback circuit (CMFB) for a charge detector. The amplifier is implemented in a 180-nm complementary metal-oxide-semiconductor (CMOS) process. The amplifier combines a folded differential topology, active reset, and small feedback capacitors. This allows for low noise, high-gain, high-dynamic-range, and robust operations. The design and analysis of the CMFB for the proposed high-gain charge amplifier is discussed. Simulation results show that the CMFB loop has a phase margin of 62.1 degrees and a gain margin of 25 dB. Measurement results show the amplifier chip exhibits a stable common mode voltage.