Low-Power Amplifier for Readout Interface of Semiconductor Scintillator

We present the design of a readout system, comprising a charge sensitive amplifier and a pulse shaper, that directly interfaces a semiconductor scintillator. The designed amplifier quantifies optical response of a large-area epitaxial photodiode that registers luminescence produced by a scintillating semiconductor wafer when excited by ionizing radiation. The epitaxial photodiode is characterized by a capacitance of 50 pF and a dark current of 10 pA. The presented optimization procedure for the biasing and sizing the input transistor of the CSA directly relates the region of operation of the input transistor with the constraints on power, area and event rate of the readout system. Experimental results of the amplifier implemented in 0.5 μm CMOS technology, verify gain of 71 mV/fC, with the measured linearity of 1.3%. For the parameters of the photodiode, the measured equivalent noise charge (ENC) is 950 electrons with the measured time constant of the pulse shaper of 90 μs and the power consumption of 210 μW. The measured slope of the ENC dependence on the input capacitance is 18 e^-/pF.