Fluke DDS Function Generator 271, User Manual

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271
Users Manual
13-2
Introduction
Two or more generators can be synchronized together following the procedure outlined
below; the number of generators that can be linked in this way will depend on the
clocking arrangement, cable lengths, etc., but there should be no difficulty with up to four
generators.
Synchronizing Principles
Frequency locking is achieved by using the clock output from a generator nominated as
the master generator to drive the clock inputs of another generator or generators as slaves.
The additional connection of an initializing
SYNC
signal permits each slave to be
synchronized such that the phase relationship between master and slave outputs is that
specified on each slave generator’s trigger menu.
Synchronization is only possible between generators when the ratio of the master and
slave frequencies is rational. For example 3 kHz can be synchronized with 2 kHz but not
with 7 kHz. The most practical use of synchronization will be to provide outputs at the
same frequency, or maybe harmonics, but with phase differences.
Connections for Synchronization
The preferred clock connection arrangement is for the rear panel
CLOCK IN/OUT
of the
master (which will be set to
CLOCK BNC=OUTPUT
) to be connected directly to each of
the
CLOCK IN/OUT
sockets of the slaves (which will be set to
CLOCK BNC=PHASE LOCK
).
The alternative arrangement is to ‘daisy-chain’ the slaves from the master using a BNC
T-piece at each slave connection, but reflections can cause clock corruption at the
intermediate taps under some circumstances.
Similarly the preferred synchronizing connection is from the rear panel
SYNC OUT
of
the master directly to each of the
EXT TRIG
inputs of the slaves. The alternative
arrangement is to ‘daisy-chain’ from each
SYNC OUT
to the next generator’s
EXT TRIG
in turn; this does not give rise to any data integrity problems but cumulative
hardware delays will degrade the phase-shift accuracy.
Generator Set-Ups
Each generator can have its main parameters set to any value, with the exception that the
ratio of frequencies between master and slave must be rational (see above).
The phase relationships between the slaves and the master are set individually on the
trigger menus of each slave, exactly as described in chapter 7,
Triggered Burst and Gate .
The convention adopted in synchronized mode is that a negative phase setting delays the
slave output with respect to the master; thus, for example, a phase setting of -90 ° will
delay the slave by a quarter-cycle with respect to the master. If the slave’s
EXT TRIG
inputs are all driven directly from the master then all phase shift is referenced from the
master; thus four generators set to the same frequency with the three slaves set to -90 °,
-180 ° and -270 ° respectively will give four evenly spaced phases of the same signal. If,
however, the synchronizing signal were daisy-chained from each
SYNC
to the next
generator’s
EXT TRIG
then the phase shifts become cumulative and each slave must be
set to -90 ° phase to achieve the same result.
Hardware delay becomes increasingly significant as frequency increases causing
additional phase delay between the master and slaves. However, these delays can be
largely nulled-out by ‘backing-off’ the phase settings of the slaves.
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