This paper presents the first experimental test results of the X-ray photon counting detectors based on our pixel readout ASIC . The chip integrates 64x128 array of pixels in the size of 150 m x 150 m and each pixel consists of four 12-bit energy windows. Two types of CdTe and one type CZT detectors have been bump bonded to the ASICs and have been tested.
The electronic characteristics of the readout chip were evaluated first by injecting charge through the calibration capacitor. The power consumption, the noise and the gain of the analog front-end were measured. The non-uniformity of the energy thresholds among pixels were measured and then were compensated by tuning the local DACs.
The detector performance were then characterized using both gamma radioactive sources and X-ray tubes. The energy responses of the detectors were measured using the characteristic X-ray of the target material. The global and local thresholds were then calibrated with these specific energies of photons. Polarization effects under different photon fluxes were also studied for different detector bias voltages. Preliminary imaging test was conducted. The detector response under uniform irradiation was investigated. The spatial uniformity of the detectors was analyzed and the flat field correction was then conducted to improve image quality. The test results show that most of the readout channels work well thus our photon counting detector can be used for imaging applications. Detailed test results will be discussed in this paper.