Development of a high count rate readout system based on a fast, linear transimpedance amplifier for x-ray imaging

A new 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 linear array of CdTe sensors, a custom-made PCI card and two application specific integrated circuits (ASICs), a front-end readout chip and a digital counting chip. The operation of the readout ASIC is optimised for input capacitance of 2pF per strip, which includes both the detector and the interconnection capacitance. The dynamic range of the system is extended from 30 keV up to 250 keV. As the readout chip includes also a polarity select circuit, the system is suitable for applications with both types of detectors, that are electrons or holes collecting devices. Due to the adopted readout architecture the counting rate achieved is extremely high up to 3 MHz. In the expense of that, the measured noise was around 1200 electrons for the 2pF detector capacitance. The real-time imaging system would be used in a luggage inspection system. In this paper the architecture and the performance of the two ASICS of the system are presented.