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iXon 3

Features & Functionality

3.3.2 - Variable Horizontal Readout Rate

The Horizontal Readout Rate denes the rate at which pixels are read from the shift register. The faster the horizontal

readout rate the higher the frame rate that can be achieved. The ability to change the pixel readout speed is important

toachievethemaximumexibilityofcameraoperation,particularlyintermsofdynamicrange.Slowerreadouttypically

allows lower read noise and higher available dynamic range, but at the expense of slower frame rates. There are number

of different horizontal readout rates available on all iXon3 models. Please refer to the performance sheet for readout rates

available on your particular model.

3.3.3 - Variable Vertical Shift Speed

The vertical shift speed is the time taken to vertically shift all pixels one row down, with the bottom row entering the

shift register. The ability to vary the vertical shift speed is important for several reasons. It is possible using the different

vertical speeds to better synchronize the frame rates to external events such as a confocal spinning disc. Faster vertical

shift speeds also have benets such as lower Clock Induced Charge (CIC). A drawback with faster vertical shift speeds

is that the charge transfer efciency is reduced, effectively reducing the pixel well depth. This is particularly important for

bright signals as a pixel with a large signal is likely to have some charge left behind if the vertical shift speed is too fast.

This will result in degraded spatial resolution.

Slower vertical clocks ensure better charge transfer efciency giving maximum pixel well depth but result in a slower

maximum frame rate. To improve the transfer efciency the clocking voltage can be increased using the vertical clock

voltage amplitude setting. However, the higher the voltage, the higher the clock-induced charge. Thus the user must

make a measured judgement as to which setting works best for their situation, for example:

• For low CIC: Use the fastest vertical shift speed that still transfers charge correctly (no image distortion),

without having to select excess vertical shift voltage amplitude

• For maximum pixel well depth: Use the slowest vertical shift speed, which will give an increase in CIC

• For maximum frame rate: Use the fastest vertical shift speed and increase the vertical shift voltage amplitude

to the minimum value that regains the full pixel well depth.

• To reduce vertical smearing during very short exposure: use a faster vertical shift speed. This vertical

smearing is due to the fact that light is still falling on the image area during the short time taken to transfer the

charge from the image area into the storage area. If the actual exposure time is of a similar magnitude to this

transfertimethenaspixelsareshiftedverticallythroughbrighterregionsoftheimagetheywillcollect“extra”

charge which will manifest itself as vertical streaking. NOTE: For extremely short exposure times, a fast

external shutter or pulsed light source may be required.

• For short exposures (e.g. 1ms): with high signal count and DC illumination, it may be necessary to increase

the vertical clock voltage to ensure that the keep clean cycle can fully remove the extremely high (saturated)

signal that may have accumulated during the sensor readout phase.

Andor Technology iXon3 Series User Manual

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