FlexToT - Current mode ASIC for readout of common cathode SiPM arrays

A front end application specific integrated circuit (ASIC) for the readout of common cathode Silicon Photo-Multipliers arrays is presented with the following features: wide dynamic range, high speed, multi channel, low input impedance current amplifier, low power (≈10mW per channel), common cathode connection, directly coupled input with common mode voltage control and separated timing and charge signal output.A 16 channel prototype with 16 independent outputs for energy and pile-up detection and a single fast timing output is described. The low jitter current mode processing together with a configurable differential current mode logic (CML) output provides a timing signal suitable for Time of Flight (TOF) applications, such as TOF-PET (Positron Emission Tomography). Each channel delivers a digital output of a Time Over Threshold (TOT) type with a pulse width proportional to peak current (charge) input. The current mode input stage features a novel double feedback; a low speed feedback loop keeps input node voltage constant while a higher speed feedback loop keeps input impedance low. Dedicated circuitry allows SiPM high over-voltage operation, thus maximizing Photon Detection Efficiency (PDE) and timing resolution. Design was submitted in June 2012 in Austria Microsystems (AMS) 0.35 μm HBT BiCMOS technology and is under test.