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E1437A User's Guide
Using the E1437A
Synchronizing Changes in Multi-module Systems
Multi-module systems require special treatment with respect to timing of frequency
and filter changes. Center frequency changes may involve synchronizing the local
oscillators of all modules in a system. Digital filters changes in multi-module systems
require that the decimation counters be synchronized.
Synchronous Digital Filter Changes
In multi-module systems where synchronous sampling is required, the decimation
counters in all the modules must be synchronous with each other. This condition
can be forced by preparing each module in the system in advance. Any
measurement in progress is terminated at this time and the module is placed in the
Idle state. After each module is prepared, the next SYNC line transition causes the
digital decimation counter to be reset and started at the same time. Once this is
done the decimation counters will stay synchronized as long as the same ADC clock
is used.
If you also intend to change the center frequency along with the digital filters, you
should synchronize the digitial filters first. Otherwise the center frequency phase
becomes unsynchronized when the digital filters are changed.
Synchronous Center Frequency Changes
In multi-module systems you may prepare each module in advance of a frequency
change, then perform the change synchronously by asserting the SYNC line. This
preserves the phase relationship of the local oscillators for all modules in the
system. Certain special considerations apply to multi-module frequency changes:
•
If all modules in a system are in the Idle state when the SYNC line transition
occurs, the LO frequency will be updated and the next measurement will be
armed.
•
If all modules are in the measurement state in continuous mode when the SYNC
line transition occurs, the LO frequency will be synchronously updated, and the
measurement will continue.
•
In continuous mode care must be taken to assure that all modules are in the
same state, either the Idle state or the Measure state, before the SYNC line
transition occurs, otherwise some modules will re-arm while others will continue
the current measurement.
•
In block mode the SYNC line transition will be ignored unless all modules are
currently in the Idle state.
•
If you also intend to change the digital filters along with the center frequency,
you should synchronize the digitial filters first. Otherwise the center frequency
phase becomes unsynchronized when the digital filters are changed.
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