CCD Sensor
The CCD (Charged-coupled device), a
functional semiconductor device, was
developed in 1970 by Dr. Boyle at the Bell Research Laboratory, U.S.A.
, taking full advantage of this
microprocessor technology, to allow implementation of high-density
devices. In the field of linear sensors, devices of 128
to 10,400 pixels have already been commercially manufactured for wide
range of barcode scanning devices.
As shown in the picture belo
w,
it consists of a MOS capacitor with
an electrode attached on top of the silicon dioxide on the semiconductor
substrate surface. When voltage is applied between the electrode
and the substrate, a depletion layer is formed in the region near the
interface of the silicon dioxide and semiconductor interface, causing
this region to become a low-energy-level potential well for the minority
carrier. If a signal charge generated by light radiation is injected
into this potential well, these signals are temporarily stored as analog
quantities.
An explanation of the operating
principle of the CCD scanner
analog shift register is as follows. The first case is an
introductory explanation of three-phase driving. As shown in the
picture below, multiple MOS capacitor units are arranged in close
proximity and signal charge is transferred from one MOS capacitor to the
next. In other words, when the signal charge stored under
Electrode
1
at time t1 applies positive voltage to Electrode
2,
a portion of the signal charge shifts beneath Electrode
2
(time :
2).
Furthermore, decreasing the positive voltage of Electrode1
(time: t2) shifts the entire signal charge beneath Electrode
2
(time : t4). When this operation is performed repeatedly, charge
is transferred.
