Digital still cameras are becoming a widely used alternative for conventional silver-halide cameras. This paper presents first the concept of frame-transfer CCD imagers designed for consumer digital cameras. Next, the different modes of operation are explained in detail and compared with alternative approaches. Finally, extensive evaluation results on four different imagers using this new concept are presented. It will be demonstrated that the flexible modes of operation, the high dynamic range, and excellent optical properties of FT-CCDs make them very suited for this type of electronic imaging.

Sensitivity improvements in a 3.2M-pixel CCD image sensor developed for digital still camera applications are presented. The introduction of gap-less microlenses increases the sensitivity with 25-30% while the high angular response is maintained. With the binning possibility at the image-storage transition, the sensitivity in monitor mode can be increased. Finally the sensor output amplifier now combines low noise and excellent linearity with a much higher conversion factor. This improvement is obtained by reduced paracitic capacitances around the Floating Diffusion area. CCDS FOR DIGITAL STILL CAMERASThe pixel race in the field of digital still cameras (DSC) still continues [1,2]. To maintain acceptable consumer price levels, the image diagonal of the CCDs should not exceed 2/3" (11").Thus pixel sizes have to decrease to meet the demands of increasing resolution. Shrinking pixels also implies a reduction of sensitivity. A 3.2M-pixel FT-CCD imager is presented in which three important contributions for maintaining a high CCD sensitivity with decreasing pixel size are combined: new type of microlenses optimised for frame-transfer CCD pixels, charge binning in monitor mode while maintaining color reproduction, and an improved output amplifier combining a high conversion factor and low noise with excellent linearity.

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A 1/1.8" 3M-pixel frame-transfer CCD (FT-CCD) with on-chip horizontal sub-sampling allows an additional preview mode where the image extraction rate is doubled (up to 60 images/s) while keeping the 25MHz classic readout frequency. Highsensitivity video clips, fast auto-focus, and auto-exposure is achieved on digital still cameras.