Roper CoolSnap, ES manual Antiblooming, Normal Mode, Nonoverlapped

Alternate Normal mode

Antiblooming

If the exposure time is 50 ms, which is less than the readout time, the camera operates in "nonoverlapped" mode (see Figure 2). The effective frame rate for this is 7.14 fps (1/[0.05+0.090]). While in normal mode, the camera firmware automatically calculates the readout times, taking into account binning and/or subregion, and carries out the exposure-readout sequence to maximize the frame rate.

50ms 50ms 50ms 50ms 50ms 50ms

Exposure

90ms 90ms 90ms 90ms 90ms

Readout

Figure 2. Normal Mode, Nonoverlapped

In "Alt-Normal", it is possible to achieve higher QE in the NIR (peak QE of approximately 65%) by manipulating the CCD clock voltages. Also, in this high-sensitivity mode, the preamplifier is switched off during the exposure to eliminate the background generated by preamplifier glow. In this clocking mode, irrespective of what the exposure time is, the camera operates in "nonoverlapped" or "sequential" mode.

	70
	60					alternate-normal - high sensitivity
	50
(%)	40
QE	30
	20			normal - high frame rate
	10
	0	300	400	500	600	700	800	900	1000	1100
	200

Wavelength (nm)

Figure 3. QE for Normal and Alternate Normal Modes

Typically, interline CCD devices are designed with antiblooming capabilities. To prevent excess electronic charge from migrating to adjacent pixels, "drains" are built into the CCD. These drains remove any excessive charge generated from an overexposed pixel. Sony interline CCDs will prevent blooming for optical signals greater than 1000 times the full-well capacity of a single pixel. However, the extended QE capabilities of the Sony ICX285 in the CoolSNAPES reduce the antiblooming suppression for certain modes. In normal mode, the CCD operates with typical antiblooming suppression. But in alternate normal mode, the enhanced sensitivity causes a reduction in antiblooming to greater than 100 times single-pixel full-well capacity.

10CoolSNAPcf /CoolSNAPES