Application-specific integrated circuit

Abstract

Improving the performance of positron-emission tomography (PET) systems for small animal imaging requires the use of high-speed detectors, such as a Lutetium Oxyorthosilicate (LSO) crystal coupled to avalanche photodiodes (APDs). We have developed an application-specific integrated circuit (ASIC) for reading out the multiple channels of an LSO-APD detector module for use in a small animal PET system. In this work, we characterize the performance of the ASIC, referred to as the AE172 chip. The AE172 can accommodate both positive and negative input signals, with a programmable conversion gain that ranges from 2.8 mV/fC to 21 mV/fC. The ASIC channels exhibit a linear response and an equivalent noise charge (ENC) of ~2000 electrons, RMS. The timing jitter depends on the amplitude of the input signal; and is less than 1 ns for test signals greater than 100,000 electrons. Connecting the ASIC to a linear APD detector reduces the relative readout noise to 26 electrons referenced to the input of the APD, which is operated at a gain of ~200. An LSO-APD- ASIC detector achieves an energy resolution of 13% for the 511 keV annihilation photons from a 22 Na source, and a coincident timing resolution of ~13 ns.