Pixel ADC Design for Hybrid CMOS Image Sensors

This thesis presents the design of a pixel level analog-to-digital converter (ADC) circuit for hybrid CMOS image sensors. There are several methods to increase the dynamic range of the sensor through the readout algorithm. The multiple sampling method can increase the dynamic range (DR) without a loss of signal-to-noise ratio (SNR). The idea is to acquire several images during one frame. Based on the multiple sampling method, the method described in this thesis uses the special feature of the pinned photodiode to select the charge transfer time locally to change the total integration time in one frame based on the input light intensity. The comparator is reused during the different conversion phases to save power and area. Only one comparison is needed after each charge transfer, so compared with traditional multiple sampling method for DR enhancement this method can save a lot of power. In-pixel memory is used to store the converted data, and these data are read by column wise current sense amplifiers. The simulation results show that the charge transfer of the pinned photo diode is controlled locally and for a 7-bit dynamic range enhancement the additional power is only 2.2% compared with no DR enhancement.

Subject

Pixel ADC
smart pixel
dynamic range enhancement
multiple sampling

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Student theses

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master thesis

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