Digitally assisted low noise and fast signal processing charge sensitive amplifier for single photon counting systems

Single Photon Counting architectures used in X-ray pixel imaging systems have superior performance (essentially infinite dynamic range, noiseless imaging, possibility of photons´ counting only within a given energy window), however they offer only a limited photon count rate performance per single pixel. This paper presents a novel architecture of front-end readout electronics, which due to digitally assisted charge sensitive amplifier improves significantly count rate performance of these systems and allows to keep the low noise of the front-end electronics at the same time. The proposed architecture was amalyzed in 40 nm CMOS process. The simulations show that the single photon counting architecture operates correctly with frequency of input pulses f_in = 4 MHz and has Equivalent Noise Charge ENC = 70 el. rms only (for detector capacitance C_DET = 150 fF).