CCD manufacturers employ several techniques that use multi-phase clocks to shift the charges from place to place in an array. Suffice it to say that the shift register acts like a bucket brigade that moves charges from place to place, each in its own packet like a line of people passing along buckets of water. Usually the clock, driver, timing, and logic circuits that control a CCD array exist as separate devices. Two Registers Double the Speed To speed the charge-shifting process, CCD manufacturers may provide two shift registers, one on each side of a linear array. As a result, the CCD puts out the video information twice as fast as a single shift-register device.
External circuitry can recombine the two voltages to furnish a single video output.
Or a frame grabber could digitize the two signals and combine the results to reform a vector of pixel intensities. A full-frame CCD moves the charge packets down each column into a shift register along the bottom edge of a device. The shift register delivers the charges to an amplifier for conversion to a voltage. In an area-array CCD, which captures an entire image at a time, retrieving the charges from the array of sensors proves a bit more difficult. In a full-frame array, the control circuits move the charges in unison down each column from one MOS capacitor to the next.