Image Processing Reference
In-Depth Information
TABLE 5.2
Chip Performances of Developed Sensors with Different Pixel Sizes
Pixel Size
3.0 μm
1.75 μm
0.9 μm
V
dd
(V)
5.0
2.8
Number of pixels
999(H) × 630(V)
1690(H) × 1090(V)
1880(H) × 1600(V)
Saturation charge (e
-
)
77,000
60,000
6,500
Sensitivity (e
-
/lux/s)
35,500
12,500
3,200
Readout noise (e
-
)
2.9
2.7
2.5
Dynamic range (dB)
88
87
68
Image lag Below detection level
Source:
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.
to control the exposure period length by discharging all charges in each PD, and readout
timing is kept the same as that of normal exposure mode. The shutter mode with simulta-
neous exposure timings of all pixels is called global shutter.
5.4.2 Electronic Shutter of MOS and CMOS Sensors
Since reset operations at each PD are done in readout operation in normal exposure mode
without an electronic shutter in MOS and CMOS sensors, exposure periods of each row
repeat with no interruption, as shown in Figure 5.79a.
As MOS and CMOS sensors are XY-address type, the row select pulse generated by the
vertical access circuit such as shift register or decoder is applied to the row select transistor
to make it on-state. The readout timing is ruled by the vertical access circuit. In electronic
shutter mode, reset operation must be done during the exposure period before the read-
out timing to set the exposure period, as shown Figure 5.79b. Therefore, a different clock
pulse is needed for reset operation from that needed for the sequence of readout opera-
tion. Therefore, two series of row accessing signals are necessary. Many CMOS sensors
have two vertical access circuits: one is for readout and another is for reset, as shown in
Figure 5.80.
Exposure period of first row
Exposure period of first row
First row
First row
ird row
Second row
Second row
ird row
Final row
Final row
Exposure period of final row
Exposure period of final row
Time
Time
Readout timing of
first
row
Readout timing of first
row
Reset timing of first row
Reset timing of first row
(a)
(b)
FIGURE 5.79
Exposure period of each row in MOS and CMOS sensors: (a) normal exposure mode; (b) electronic shutter mode.
