High Dynamic Range Image Sensor Architectures

摘要

Digital photographers continuously demand more performance from their equipment. Digital camera performance is defined by a set of parameters including dynamic range, noise, frame rate, resolution, and color. Amongst these parameters dynamic range is becoming increasingly more important. This is true because the human eye typically has a wider dynamic range than a digital camera. At the heart of all digital cameras is either a CCD or a CMOS image sensor (CIS). The dynamic range of the sensor typically limits the dynamic range of the camera.rnIn this paper we review five CIS architectures designed to improve dynamic range. We start by reviewing standard CIS architectures and then present a simple sensor model. Using this model we show how signal to noise ratio (SNR) can be used to evaluate different wide dynamic range (WDR) sensor architectures. Then we sequentially review five different wide dynamic range techniques. The first WDR architecture is dual column amplifier and ADC CIS, and the second WDR architecture is logarithmic pixel CIS. The third WDR architecture is multiple sampled pixel level ADC CIS. The fourth WDR architecture is pixel level sigma delta ADC with residue readout, and the fifth and final WDR architecture is time to saturation with residue readout CIS. For each of these techniques we present the pixel level circuitry and its advantages and disadvantages. Furthermore, all of these techniques are analyzed based on dynamic range, SNR, and implementation complexity. We discuss how implementation complexity affects signal processing in a digital camera, and other parameters in the sensor such as quantum efficiency and read noise. We conclude with a few summary comments.