3.1.2 Shutter

The electronic shutter that freezes the frame for read-out adds more complexity, but can be based on the standard MOS fabrication steps. In effect, at the end of image capture, the charge at each pixel is first switched into another ‘blind’ MOS capacitor that sits in the read-out line for each row, as the middle of the three buckets per pixel. You should have already guessed that the switch is yet another MOS device. Once switched into the read-out line, the row data are isolated from the photocapacitors and read-out march can begin. A further disadvantage of CCDs is that a large area of silicon surface is given over to data transfer functions at the expense of data capture: for every photocapacitor, one blind switch and three blind charge-transfer MOS structures have to be incorporated.