Conventional photon counting always uses photo multiplication. However, the photo multiplication suffers from the excess noise due to the fluctuation of multiplication factor. In this study, we propose a method of photon count imaging with an extremely small capacitor and a high-precision adaptive quantization technique. The following equation is a model of photon counting in the proposed method, and the viewgraph shows the noise reduction effect of the adaptive quantization as a function of the amplitude of the noise due to readout circuits. If the quantization step(D) is just same as the integer multiple of the conversion gain of the sensor, and the readout noise amplitude is less than one-tenth of the quantization step, the noiseless detection, or photon counting is possible.
|sn : r.m.s. noise of readout circuits.
|Noise reduction effect as a function of readout noise amplitude.