Noise optimised charge-sensitive CMOS amplifier for capacitive radiation detectors

A low-voltage, low-noise, charge-sensitive preamplifier (CSA) for particle tracking using a silicon strip detector was designed. The preamplifier was optimised in terms of the total output noise performance using a noise minimisation technique based on the MOSFET noise small signal equivalent circuit and readout front-end noise optimisation criteria valid in the strong inversion region. The preamplifier was designed and fabricated in a 0.35 m CMOS process by Austria Mikro Systeme for a specific silicon strip detector of 2 pF capacitance for X-ray spectroscopy. The circuit exhibits satisfactory performance compatible to the specific low-energy radiation detection application. Particularly, the CSA provides an equivalent noise charge of 254 e⁺13.5+e^-/pF, consumes 165 muW and achieves an output conversion gain equal to 2.81 mV/fC and a linearity <0.57 . Analysis is supported by extensive measurement results confirming the circuit characteristics and their flexibility to be used in a variety of readout applications.