Image Processing Reference
In-Depth Information
Photodiode (sensor part)
Pixel
Sensor array
Readout electrode
Image area
Storage area
HCCD
Output amplifier
(FDA)
FIGURE 5.29
Device configuration of FIT-CCD.
transfer frequency of IT-CCDs is around 10 KHz, the transfer frequency of FIT-CCDs is
around 1 MHz or more, that is, one hundredth or less the smear level of IT-CCDs while
obtaining the same pixel structure. Thus, an image sensor with a very low smear level was
developed and was employed as a standard sensor type for broadcasting cameras for a
long time.
5.2 MOS Sensors
MOS image sensors are XY-address-type sensors.
18,19
They were mass-produced for con-
sumer-use video cameras by Hitachi for the first time as solid state image sensors in 1981.
20
5.2.1 Principle of MOS Sensors
In the case of CCDs, addressing is done by signal charges transfer through the VCCD and
HCCD to the output part. In contrast, in MOS image sensors this is realized by selecting
vertical and horizontal MOSFET switches. Consequently, charges flow through a metal
signal line to the output part as signal current, as shown in Figure 5.30a with only one
pixel.
21
Vertical selection (row selection) and horizontal selection (column selection) are done
by the output pulses of vertical and horizontal shift registers, respectively. When signal
charges are read out, first by switching on the vertical MOSFET switch, charges move to
the vertical signal line because of the very large capacitor ratio of vertical signal line to PD.
Second, horizontal selection pulse is applied to the switch MOSFET to connect the vertical
signal line to video voltage through the horizontal signal line. Since signal current is in
