An ASIC for multi-energy x-ray counting

We have developed a new application specific integrated circuit (ASIC) for the readout of pixellated CdTe radiation sensors. The ASIC can be connected to 64 sensor pixels and can deliver up to 6-bin energy spectra. The ASIC is useful for new x-ray imaging applications with multi-bin energy resolved photon counting. The ASIC has 64 channels each containing a charge sensitive amplifier, up to 6 discriminators and 6 counters which increment when the amplitude exceeds a given threshold. The ASIC has been manufactured and tested with CdTe radiation sensors. The linear dynamic range is 4.3 fC corresponding to 122 keV in CdTe. At 50-ns shaping time the amplifier has an equivalent noise charge (ENC) of 105 e + 40 e/pF. The average ENC is 505 e rms when the ASIC is connected to CdTe pixels of 10-pF capacitance and 5-nA leakage current. This article describes the functionality of the ASIC and its performance with CdTe. We present x-ray shadow images from objects acquired with a CdTe linear array as well as energy spectra.