A high-counting-rate readout system for X-ray applications

A data acquisition system for processing signals produced by direct photon conversion sensors, primarily for applications in digital X-ray imaging, has been developed. The system comprises a custom-made PCI card, a front-end readout ASIC, and a digital counting ASIC. The operation of the readout ASIC is optimized for input capacitance of 2 pF per strip, which includes both the detector and the interconnection capacitance. The dynamic range of the system is extended from 30 up to 250 keV. Since the readout chip also includes a polarity select circuit, the system is suitable for applications with electron or hole collecting detectors. Due to the adopted readout architecture the counting rate achieved is extremely high, up to 3 MHz, while the measured noise was around 1200 electrons for 2 pF detector capacitance. The real-time imaging system is under evaluation in combination with CdTe detectors as front-end of a luggage inspection system. In this paper, the architecture and the performance of the two ASICs of the system are presented.