Teledyne PIXIS-XF, System Manual

Page: 55 / 116

Chapter 5 Operation 55
5.6.2 ADC Offset (Bias)
ADC offset, which is also known as Baseline Offset, provides another way of dealing
with dark charge.
REFERENCES:
Refer to Section 5.4.4, Dark Charge , on page 47 for
additional information.
By offsetting the baseline signal, much of the background is ignored during conversion.
Offsetting the baseline is accomplished by adding a voltage to the signal to bring the
A/D output to a non-zero value, typically 50-100 counts. 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 50-100 counts lower.
CAUTION!
!
If you observe a sudden change in the baseline signal you
may have excessive humidity in the camera's vacuum
enclosure. TURN OFF THE SYSTEM IMMEDIATELY. Contact
Teledyne Princeton Instruments Customer Support for
information on how to refresh the vacuum. See page 98 for
contact information.
NOTE:
Do not be concerned about either the DC level of the
baseline signal or its shape unless it is very high (i.e., > 1000
counts with 16-bit ADC).
The ADC Offset is pre-set at the factory and is not
user-changeable.