FEATURES & FUNCTIONALITY
Neo
SECTION 2
Page 33
2.3.4 - Rolling & Global Shutter mechanisms
The Neo camera offers 2 types of read out modes, i.e.
Rolling Shutter
and
Global Shutter
.
In Rolling Shutter mode, charge transfer happens on a per row basis whilst in global shutter charge transfer
happens for the whole sensor or globally. To read out a pixel in Rolling Shutter mode, the following occurs
within the analogue circuitry:
1. The read out node is reset
2. The node level (reference level) is measured
3. Charge is transferred from photodiode to node
4. The node level (signal level) is measured
5. 2 is subtracted from 4 to get real signal
This process is commonly referred to as CDS (Correlated Double Sampling) and is done in the analogue
domain before digitization. The reason it is required is due to what is known as reset noise, this arises because
every time the node is reset it does not settle at exactly the same level and hence the actual level must be
measured (
Step 2.
above) and subtracted from the signal level (
Step 4.
above) to get the real signal.
For rolling shutter, charge transfer happens on a per row basis; therefore each row follows steps 1 – 5 above,
until the entire sensor is read out. The disadvantage of this is that the start and end exposure time moves by
the row read out time for each subsequent row. So whilst each row of pixels is exposed for exactly the same
length of time they do not all start and end at exactly the same time.
In Global Shutter mode, the start and end of the exposure do occur at exactly the same time for every pixel (not
just for pixels in the same row); therefore
Step 3.
has to occur for all the pixels at the same time. Because of
this, the reset and reference read occur before this global transfer for every row. Since the same read out
circuitry is used for every row there is nowhere to store the measured reference level for every pixel and so a
reference frame is actually digitized and read out from the sensor and then the signal is digitized and read out
from the sensor. The two are subtracted to get the ‘real signal’. Reading two frames to get a real signal frame
effectively halves the Cycle Time when compared to Rolling Shutter.
Содержание Neo sCMOS
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Страница 17: ...INTRODUCTION Neo SECTION 1 Page 17 1 5 1 Mechanical drawings...
Страница 79: ...APPENDIX Neo APPENDIX Page 79 APPENDIX A1 DECLARATION OF CONFORMITY...
Страница 80: ...APPENDIX Neo APPENDIX Page 80...
