Appendix A
Overview of the Calibration Constants
A-2
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Internal Reference
The NI 54
XX
series devices have a high-precision voltage reference, which
is used during self-calibration. The value of this reference is subject to drift,
so its current value (as of the last external calibration) is stored as a
calibration constant.
Frequency Response
Several constants are used to store the frequency response of the analog
channel to compensate for attenuation at higher frequencies. A different set
of constants is held for the unterminated and terminated cases. For each
case, seventeen constants are stored, corresponding to the gain of the
channel at frequencies from 0 to 16 MHz, inclusive.
Duty Cycle
Duty cycle is the ratio of the duration of the logical high level of a signal to
the total period of the signal.The duty cycle of the SYNC TTL output is
adjustable from 20% to 80%. To set a desired duty cycle, the driver software
must use two calibration constants, called D0 and D1. Calibrating for these
constants involves iteratively converging on the proper values to achieve
specified duty cycles.
A7
The low frequency gain of the analog filter.
A8
The gain of the 10 dB attenuator in the analog channel.
A9
Unterminated
An array of constants corresponding to the gains of the six post-amplification
attenuators (1, 2, 4, 8, 16, 32 dB) when device is unterminated.
A9
Terminated
An array of constants corresponding to the gains of the six post-amplification
attenuators (1, 2, 4, 8, 16, 32 dB) when device is terminated with a 50
Ω
load.
A9TA
The gain of the device in the terminated state with no post-amplification
attenuators active.
Table A-1.
DC or Low-Frequency Gains and Offsets of Components within the Analog Channel (Continued)
Constant
Name
Description
