User manual

Chapter 3.
Operating Features
Cooling
CoolSNAP
HQ
and CoolSNAP
fx
cameras are cooled to -30°C, minimizing the
dark charge below 0.05 e-/pixel/sec. CCD temperature is regulated to +/-0.05°C
and is settable between room temperature and -30°C.
CoolSNAP
HQ
and CoolSNAP
fx
are implemented with 10 MHz and 20 MHz
analog-to-digital conversion rates. At 20 MHz, they offer greater than 10 frames
per second (fps), whereas the 10 MHz operation allows lower read noise at the
expense of frame rate. (For more information, please refer to the product data
sheet).
Dual-Mode
Operation
(CoolSNAP
HQ
Only)
A unique feature of CoolSNAP
HQ
is that it allows two different CCD
clocking modes that allow you choose between speed and NIR sensitivity. In
the PVCAM
®
implementation, the clocking modes are referred to as "normal"
and "alternate normal".
Normal mode In "Normal" mode, the CCD is optimized for maximum anti-blooming protection
and frame rate. In this mode, the CCD can be clocked so that exposure and
readout happen simultaneously as shown in the example below.
Example: Consider a situation where the full frame readout time is 96 msec (at 20
MHz) and the exposure time is 200 msec. The readout of a frame will occur
during the exposure of the next frame. This is possible because the CCD has
alternate columns of sensitive and masked areas. While charge is integrating in
the sensor area, the previous frame, which is in the masked area, can be read out
(Figure 1). In this example, the time required to acquire the three-image sequence
is 696 ms (3 x 200 + 96) and the frame rate is approximately 4.3 fps.
200ms
96ms
Exposure
Readout
200ms 200ms
96ms 96ms
Figure 1. Normal Mode, Overlapped
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 6.84 fps (1/[0.05+0.096]). 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.
Exposure
Readout
50ms
96 ms
96 ms 96 ms 96 ms 96 ms
50ms 50ms 50ms 50ms
50ms
Figure 2. Normal Mode, Nonoverlapped
9