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: http://xmm.vilspa.esa.es/user/socpub/ccd_review/node2.html
Дата изменения: Fri Aug 30 15:54:59 1996 Дата индексирования: Tue Oct 2 11:51:43 2012 Кодировка: Поисковые слова: dust |
Figure 1 shows a simplified representation of a frame transfer CCD. An array of vertical electrodes is formed over the silicon surface and horizontal charge transfer columns are defined by implanted channel stop regions in the wafer surface. These orthogonally aligned elements are produced by conventional MOS fabrication procedures. Application of suitable bias voltages to the electrodes produces a matrix of potential wells which define the CCD picture elements.
The array operates as follows: when an image is focussed onto the CCD, photons which penetrate the electrode structure generate electron-hole pairs in the underlying silicon substrate, and the signal charges are stored in the potential wells beneath the electrode structure (gates). After an appropriate image accumulation time, clock pulses are applied to the electrodes to shift the potential wells and their associated charges across the device. Rows of data are moved one-by-one in parallel to the output register with each parallel clock pulse cycle. Each row placed in the output register is then moved pixel-by-pixel to the output node. At the end of each pixel clock cycle, the charge measured at the node is uniquely identified with a pixel address. For incident light in the visible band, the charge magnitude is proportional to the illumination level at the pixel.
The electrodes are generally arranged in two groups, one group is fabricated over the left half of the array, and a second group over the right half. If the entire array is photosensitive, the two groups may be wired in parallel using identical clock signals. When operated in this way as a single array the CCD is said to be in a full-frame mode of operation. Alternatively, the right (store) half may be shielded from light, and used to store successive image data frames previously collected in the left (image) section. This mode of operation is generally used for TV imaging and is called the framestore mode of operation. This eliminates the requirement for a mechanical shutter to shield the array during readout, since the data transfer from image to store section is accomplished in a fraction of the time (msecs) taken to read out the data in the array.