Image Processing Reference
In-Depth Information
Signal out
HSR
Column amplifier
Noise canceller
Column
control
Pixel array
MPX VSR
Noise canceller
Column amplifier
HSR
Signal out
FIGURE 5.78
Block diagram of OPF CMOS image sensor. (Reprinted with permission from Mori, M., Hirose, Y., Segawa, M.,
Miyanaga, I., Miyagawa, R., Ueda, T., Nara, H. et al.,
2013 Symposium on VLSI Technology
, 2-4, pp. 22-24, Kyoto,
2013.) Copyright [2013] by the Japan Society of Applied Physics.
The overall chip performances of three kinds of pixel pitch, 3.0, 1.75, and 0.9 μm, are
shown in Table 5.2. For a 3.0 μm pixel, the saturation charge is 77,000 electrons with a
V
dd
of 5.0 V. The dynamic range of the smallest pixel size of 0.9 μm pitch is 68 dB, with a satura-
tion charge of 6,500 electrons. The incident angle with sensitivity reduction of 20% is over
60 (±3 0)°.
5.4 Electronic Shutter
The basis of the electronic shutter was briefly described in Section 4.3. While it is an impor-
tant technique to control the amount and length of exposure, there is a big difference
between charge transfer-type CCD sensors and XY-address-type MOS and CMOS sen-
sors. Although the exposure timing of all pixels are the same in CCDs, it shifts in series at
each row in MOS and CMOS sensors, while exposure time length is the same, as explained
by Figure 5.34.
5.4.1 Electronic Shutter of CCD Sensors
In electronic shutter operation in IT-CCDs with a VOD structure, all signal charges inte-
grated in all PDs are discharged to the
n
-type silicon substrate at the start, as shown in
Figure 5.23. This operation is called global reset. After discharge completion, signal charge
integration, that is, the exposure period, starts at the same time for all pixels. Then, at the
end of exposure period, signal charges integrated at all pixels are read out to VCCDs at
the same time. Thus, in electronic shutter operation, start timing of exposure is delayed
