Development of a Simultaneous Photon Counting and Energy Integrating Readout ASIC for X-ray Imaging Applications

This paper presents the development of a photon counting and charge integrating readout ASIC for semiconductor detectors for X-ray imaging applications. The information of photon counts and energy integration can be obtained simultaneously from one detector. Photon counting will be used at low to medium rate to get rid of electronics noise and to improve the dose efficiency with optimum energy weights. While the energy integrating will be used at high rate when the photon counts start to be saturated and hence large dynamic range can be achieved. The integration of both photon counting and energy integrating channels is achieved by the introduction of the charge pump circuits.The readout ASIC consists of 128 signal processing channels and the periphery circuits. Each channel integrates photon counting mode energy integrating mode. The photon counting mode circuit consists of a charge sensitive preamplifier, a CR-RC shaper, two discriminators, two 15-bit photon-counters. The energy integrating mode circuit consists of the charge sensitive preamplifier shared with the counting channel, the charge pump circuit, the correlated double sampling circuit and a Wilkinson ADC. A local 24bit-register chain is also integrated into each pixel for calibration, gain and baseline tuning and selection of different working modes, which can be programmed through an SPI slow control interface. More design details and test results will be discussed in the paper.