M08627;34/39
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Vertical timing: High speed/pulse width control/asynchronous shutter/normal scan/No fast dump
HD
Vinit
Ex pos ure time(nH)
ｎ
Ｆ Ｄ Ｖ
(
Hor izontal
synchronous signa l)
１
９
６
０
３
Internal
signal
(Internal
operation)
End of expos ure(SG)
２
４
３
５
Effective image(1960)
）
２ ０ ５４
１
ｎ＋ ２
STRB
１
ｎ
８
Image
output
Image signal
( Dig ita l)
０ ．１ ３
0 .15
０．３
Period where it is regarded invalid to newly input trigger signal
* Unless otherwise specified, the time unit of the numbers in the vertical timing chart is H(= 3156 PCLK =1920 x 1/32.50MHz
= 97.11
µ
S)
(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
1 2
Because of the above reason, consideration must be given to the fact that the exposure time becomes indefinite for the
period of 1H shutter speed 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 speed 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) Synchronize the external trigger signal with the use of the LDV signal of the camera to keep the Vinit phase
relationship constant.
••• Control can be made in the absence of the infinite time of 1H by stabilizing the generation phase of Vinit against the
internal HD.
(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.
