46
Lansis
®
System Manual
Issue 1
EAR99
Technology
Subject
to
Restrictions
Contained
on
the
Cover
Page.
8.1.1
Speed
Because the readout noise for a CCD array increases with readout rate, it may be
necessary at times to trade off readout speed for high dynamic range.
Lansis supports the following digitization speeds:
•
100 kHz
•
2 MHz
8.1.2
ADC Offset (Bias)
With the camera’s light path completely blocked, the CCD accumulates a dark charge
pattern, dependent on the exposure time and camera temperature. The longer the
exposure time and the warmer the camera, the larger this background will appear. A
500-600 ADU offset is included to avoid loss of signal when noise and/or drift might
inadvertently result in a signal < 0 ADU. This offset value ensures that all the true
variation in the signal can really be seen and not lost below the A/D “0” value. Since the
offset is added to the signal, these counts only minimally reduce the range of the signal
from 65535 (16-bit A/D) to a value in the range of 500-600 counts lower.
WARNING!
If a sudden change in the baseline signal is observed, there
may be excessive humidity in the camera vacuum enclosure.
Turn off the camera and contact Teledyne Princeton
Instruments Customer Support. Refer to
on page 100 for complete information.
NOTES:
1. It is important to note that the bias level is not noise. It is
a fully subtractable readout pattern. Every device has
been thoroughly tested to ensure its compliance with
Teledyne Princeton Instruments' demanding
specifications.
2. The ADC Offset is pre-set at the factory and is not
user-changeable.
8.1.2.1
Correct Pixel Bias
By default, Pixel Bias Correction is ENABLED in LightField. Correct Pixel Bias
automatically corrects pixel bias drift that may be introduced.
Pixel bias correction operates by reading an artificially created row, which has
essentially no charge, at the start of the frame and subtracting the row average from all
following pixels in the frame. Therefore it adds one row readout time to the frame time.
This is particularly useful when data are to be collected over a long time and maximum
baseline stability is important.
This setting can be disabled by clicking
on the Analog to
Digital Conversion expander, and deselecting the Correct Pixel Bias option.
