Measurements of Matching and High Count Rate Performance of Multichannel ASIC for Digital X-Ray Imaging Systems

We present the measurements of matching and high count rate performance of a 64 channel readout ASIC called DEDIX for high count rate position-sensitive measurements using semiconductor detectors. The ASIC is designed in 0.35 mum CMOS process and its total area is 3900 times 5000 mum². The DEDIX has a binary readout architecture. Each channel is built of a charge sensitive amplifier (CSA) with a pole-zero cancellation circuit, a shaper, two independent discriminators and two independent 20-bit counters. The size of the input device in CSA has been optimized for a detector capacitance in the range of 1-3 pF per strip. An equivalent noise charge of 110 el rms has been achieved for a total detector capacitance of 1 pF at the shaper peaking time of 160 ns. Internal correction DAC implemented in each channel independently ensures a low spread of discriminator effective threshold, namely 0.4 mV at one sigma level. The mean gain in the multichannel ASIC is 54 muV/el, with a good uniformity from channel-to-channel (sd/mean ap 0.8%). Low noise performance and high rate capability have been demonstrated by the measurement up to and above 1 MHz average rate of input signals.