A COUNTING PIXEL READOUT CHIP FOR IMAGING APPLICATIONS

A pixel readout chip for imaging applications has been designed and te sted. It consists of an array of 12 x 63 pixels with an active pixel c ell area of 50 mu m x 350 mu m Every pixel contains a low-noise charge sensitive amplifier, a CMOS comparator including individually adjusta ble thresholds, and a 15 bit counter realized using a linear feedback shift register, During data accumulation, every pixel independently co unts the number of signal hits above threshold. After accumulation all counters in a column are sequentially read out, all columns in parall el. Thresholds can be set globally with the possibility of an individu al threshold adjust in every cell. The chip can be operated with thres hold settings in every cell well below equivalent noise charges (ENC) of 1000 electrons. The dead time of a pixel after being hit is similar to 500 ns. The chip is alive for data accumulation in > 99.9% of the total data acquisition time. For photon counting in biomedical or mate rial science applications, a suitable sensor with high Z material can be bump bonded to the counting chip. (C) 1998 Elsevier Science B.V. Al l rights reserved.