User`s guide

8 User’s and Service Guide Supplement

E4438C Option HEC

Repeatable Triggering for Multiple Baseband Sources

Using two or more baseband generators can present some challenges when it comes to

synchronizing the outputs and insuring a repeatable time-invariant relationship between

the outputs of the two generators.

Repeatable triggering between two or more baseband generators requires that the

baseband generators share a common clock source (Option HEC) and that the triggers to

the baseband generators are synchronized to the external clock.

NOTE

Tying the 10 MHz references of the external clock and the external trigger

source together is not sufficient to guarantee synchronization.

There are two possible configurations that differ by the method used to synchronize the

trigger to the external clock. The first method requires external hardware to synchronize

the trigger to the external clock. The second method uses the signal generator to

synchronize the trigger. The second method may be preferable, but introduces a time skew

between the output of the baseband generators. Both methods eliminate the 10 ns of jitter

associated with an unsynchronized trigger.

NOTE

The alignment of each baseband generators I/Q DACs can come up in one of

four states anytime the clock source is changed. The Align DACs function

insures that each I/Q DAC pair is aligned. However the I/Q DAC pairs

between multiple baseband generators may end up in one of four states as

well. It is necessary to measure the skew between multiple baseband

generators anytime the clock source is changed. Repeated pressing of the

Align DACs function on the second baseband generator can be used to see the

4 different states. Unfortunately, aligning the second baseband generator to

the first can only be accomplished by repeatedly pressing the Align DACs

function of the second ESG. The reason for this is that there is no way to reset

the clock dividers to a known state.