Photon count imaging using an extremely small capacitor and a high-precision low-noise quantizer

This paper presents a method of low light imaging using an extremely small capacitor for charge detection in a CMOS image sensor and a high-precision low-noise analog-to-digital converter. A condition for photon counting is that the charge-to-voltage conversion gain is much higher than the root mean square (rms) random noise of the readout circuits. The other condition is that the quantization step of the A/D converter is chosen to be the same as the conversion gain or the amplified conversion gain if the pixel output is further amplified. Simulation results show that if the rms random noise is reduced to one-sixth of the conversion gain, the 10 times digital integration without the noise increase is possible. This means that even if a very small charge detection capacitor and a relative small power supply voltage are used, a sufficient dynamic range can be achieved by the digital integration without noise increase.