A charge-sensitive amplifier associated with APD or PMT for 511 keV, photon-pair detection

For positron emission tomography scanners requiring 511 keV two-photon detection, we present a charge-sensitive amplifier (CSA) to be associated with an avalanche photodiode (APD) or photo-multiplier tube (PMT). It is a two-stage structure. The input stage consists of a folded-cascode fully differential circuit and a common-mode feedback (CMFB) circuit. Feedforward technique is implemented to enhance frequency performance. The output stage employs complementary source followers. The amplifier has been designed in a 0.35-μm BiCMOS process with analysis and optimization of noise and speed performances. Testing of fabricated prototypes has given results in good agreement with post-layout simulated ones. The evaluated characteristics of the circuit are: 26 ns peaking time for pulsed stimulus, 2000 electron equivalent input noise charge (ENC) for a detector capacitance up to 80 pF and 136 mW power consumption from a 3.5-V supply.