A low noise and high dynamic charge sensitive amplifier-shaper associated with Silicon Strip Detector for compton camera in hadrontherapy

Abstract

An 8-channel Front End Electronics (FEE) circuit has been designed and fabricated in 0.35 11m CMOS process from Austria Micro System to be coupled with the Silicon Strip Detector (SSD) of the Compton Camera for quality control of hadrontherapy. Each channel includes a Charge Sensitive Amplifier (CSA) followed by two parallel CR-RC shapers. Slow and fast shapers, with 1 IlS and 15 ns shaping time, are used to measure the energy and to time stamp all events respectively. The two sides of the SSD are read thanks to a configurable system for holes and electrons. The CSA presents an open loop gain of 67 dB and 90 degrees phase margin assuring a high stability. The circuit has been successfully tested. The test results are in good agreement with analytic and simulation calculations. Here, we describe the principles and present measured performances of the prototype. A high linearity over the range of 3E3 to 3E6 electrons is reached with a conversion gain of 3.6 mV/fC. The circuit achieves an ENC (Equivalent Noise Charge) of 412 electrons rms. 75% of the total noise is generated by the small value of the feedback resistor chosen to avoid pile up phenomenon due to the lE5 hits/s occupancy rate. A cross-talk of 2 % was measured, 99% of which is due to the power supply disturbances. The power supply dissipation is 21 mW/channel for 3.3 V supply voltage. The area of this design is 2871x1881 μm2 including pads.