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Vertical timing: High speed/pulse width control/asynchronous shutter
12
1080
End of Exposure
（ ＳＧ ）
CCD output signal
（VOUT_A,B）
ＯＢ
1
20
Effective lines
Start of Exposure
（ ＳＵ Ｂ）
Exposure period
Horizontal sync signal号
（ ＨＣ ）
Exposure period(nH)
Digital output
(Tap1,2)
ＦＤ Ｖ
ＬＤ Ｖ
1080
1080
1
2
1080
1079
Effective pixels
Exposure period（ｎＨ）
20
12
ＯＢ
3
33
ＤＵＡ Ｌ
12
1080
CCD output signal
（VOUT_A）
ＯＢ
1
20
Effective lines
20
12
ＯＢ
ＳＩＮ ＧＬＥ
Ｄ ＵＡ Ｌ
Digital output
(Tap1)
1080
1080
1
2
1080
1079
Effective pixels
Exposure period（ｎＨ）
33
Ｓ ＩＮ ＧＬＥ
Ｖ ｉｎ ｉｔ
Vertical sync signal
（ ＶＤ）
Ｓ ＴＲＢ
QUAD/DUAL: 29 μ秒
SINGLE
: 54 μ秒
ＢＵ ＳＹ
(Note) Strictly speaking, even if the same pulse width of Vinit is applied, the shutter speed differs for the period
corresponding to 1H width when the asynchronous shutter operation is executed in the pulse width control mode
(indefinite for 1H width).
Although an equal pulse width (value between 2Hs and 3Hs) is applied both for (A) and (B) in the figure below, the
phase relationship with the internal horizontal synchronous timing makes their shutter speeds different from each
other: (A) shutter speed = 2Hs and (B) shutter speed = 3Hs.
Vinit (A)
Vinit (B)
HD
(Internal horizontal
synchronous signal)
Example of 1H difference with same Vinit signal
(Shutter time:2Hs)
(Shutter time:3Hs)
1
2
3
2
1
1
Because of the above reason, consideration must be given to the fact that the exposure time becomes indefinite for the
period of 1H shutter exposure time when a Vinit signal that is not in synchronization with the internal horizontal
synchronous signal (HD) is input from the user side. Some of the countermeasures to be taken are as follows:
(1) Use only with the shutter speeds that do not have serious impact even if the shutter speed is indefinite for a period of
1H.
••• No practical problem may be caused when the shutter speed is fairly long, say 100H width or longer because the
impact of 1H difference in exposure time over the signal level is relatively small.
(2) Maintain the phase relationship of Vinit with the external trigger signal being synchronized with LDV signal of the
camera.
••• The exposure time can be controlled without generation of indefinite time of 1H by keeping Vint generating phase
against internal HD signal constant.
(Note) Since n does not have an upper limit, the exposure time can be prolonged to be more than one frame time. The
maximum exposure time to be employed, however, should be determined after implementing experiments based on
the conditions of the actual operation because a longer exposure time is accompanied by the degradation of S/N ratio
due to the accumulation of CCD thermal noises.
