AMIC: An expandable front-end for gamma-ray detectors with light distribution analysis capabilities

A novel CMOS integrated front-end architecture is presented which enables a direct expansion of its number of inputs. This front-end is designed to be used with detectors based on continuous scintillation crystals plus position sensitive photomultiplier. Its structure aims at carrying out an analog computation which extracts fundamental information of the detected event. This fact allows us to avoid an individual acquisition of every input channel so that a large increase of inputs is feasible. In order to accomplish the processing task, a current buffer delivers a copy of each input signal to several computation blocks. Those processing units implement current mode analog filtering operations with a digitally programmable eight bits precision coefficient for each front-end input. Output currents are summed and sent to the output stage where a buffered current output is provided. A voltage signal is also available by means of a rail-to-rail transresistance amplifier. The final goal is to obtain several moments of the light distribution on the detector surface. Each one provides useful information, such as energy, position, depth of interaction (from the light distribution width), skewness (deformation due to border effect) etc. Since the computation is purely additive, the current outputs can be used as inputs to other equal devices thus creating a fully expandable architecture.