Chapter 3
79
Theory of Operation
Theory of Operation
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mm. The resulting skew is small and repeatable. If desired, the skew can be
measured and calibrated (along with any phase shifts in cables on the AWG
outputs) by adding fixed delay offsets to the waveforms.
The SYNC clock is used internal to the AWG to clock the internal data
generator and to clock in the synchronous triggers. When using the internal
clock, the SYNC clock has a frequency of 1/8th the sample clock rate
(156.25 MHz). When synchronizing multiple units, the SYNC clock output
must be enabled in software (in the Master) and the external SYNC clock
input selected in all the modules. The SYNC clock signal is split passively
and distributed with low skew. The SYNC clock output level and the input
sensitivity support up to a 1 to 8 split (fan-out) using matched 50 Ohm
splitters (6 dB loss per 1 to 2 splitter). There is a specific SYNC cable length
that is required as a function of the sample clock frequency. Several different
lengths can be used, provided they are integer multiples of one half of a
SYNC clock period.
The trigger cables should all be the same length. The trigger inputs are high
impedance and several inputs can be driven in parallel without matched
passive splitters. The synchronous trigger timing can be determined in the
same way as any synchronous trigger into the AWG. The timing is specified
relative to the SYNC clock out. This is easily observed on the slave
modules, where the SYNC clock out is unconnected.
The multiple AWGs are configured to have an internal start trigger to begin
play. A software start marker event is used to initiate the synchronized play.
Marker 4 and Trigger 4 are used for this purpose.
Synchronization Using an External Clock
In synchronizing multiple modules using an external clock, one unit is
designated as the Master and the other units are designated as Slave units.
The external clock is split with low skew and distributed to all units. The
Master unit sources the following signals: SYNC clock, and the Sync
Marker. These signals are all split and fed to each of the synchronized
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