Readout for a 64/spl times/64 pixel matrix with 15-bit single photon counting

A single photon counting pixel detector readout chip (PCC) has been derived from previous work in the CERN RD19 collaboration for particle physics tracking devices, recently developed for high energy physics experiments. The readout chip is a 64/spl times/64 matrix of identical 170 /spl mu/m/spl times/170 /spl mu/m cells. It is to be bump-bonded to an equally segmented 1 cm/sup 2/ matrix of semiconductor sensors, e.g. Si or GaAs. Each readout cell comprises a preamplifier, a discriminator and a 15-bit counter. The input noise is 170 e/sup -/ rms. At the lowest nominal threshold of 1 400 e/sup -/ (5.1 keV in Si) the cells exhibit a threshold distribution with a spread before adjustment of 350 e/sup -/ rms. Each cell has a 5-bit register which allows masking, test-enable and 3-bit individual threshold adjust. After adjustment the threshold spread is reduced to 80 e/sup -/ rms. Absolute calibration of the electrically measured equivalent charge can be done once the readout chip is bump-bonded to a detector.