Abstract: An analog x-ray photon counting detector is provided. The detector may include a direct conversion medium such as CZT, a charge sensitive preamplifier receiving an electronic pulse form the direct conversion medium, pulse-shaping electronics for conditioning the amplified signal, and one or more time-over-threshold triggers set to differing trigger levels. The time-over-threshold data is the related back to photon energy through a calibration curve, where each trigger level is associated with one calibration curve. The calibration data may be contained in a nonlinear lookup table. Each photocurrent pulse may be analyzed according to one or more time-over-threshold measurements. Thus, the energy values computed from each-time-over threshold measurement may be averaged.