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281, 282, 284
Users Manual
Introduction
Two or more channels in one multi-channel generator can be synchronized together and
precise phase differences can be set between the channels. Two separate generators can
also be synchronized, giving a maximum of 8 channels that can be operated
synchronously.
Inter-Channel Synchronization
This section covers the use of a multi-channel instrument to produce two or more
synchronous signals, and certain restrictions which apply to some specific waveform and
frequency combinations.
Synchronizing Principles
Frequency locking is achieved by using the clock output from a master channel to drive
the clock inputs of one or more slave channels. Any one channel can be the master and
any or all the others can be slaves; master, slaves and independent channels can be mixed
on the same instrument.
When frequency locking is switched on, an internal lock signal from the CPU locks the
channels at the specified inter-channel phase and re-locks them automatically every time
the frequency is changed. The clock and internal lock signals are shown in the Inter-
Channel Block Diagram in appendix F. Channels to be locked together must all be
operated in continuous mode.
For DDS-generated waveforms (refer to Principles of Operation in chapter 4) it is the
27.4878 MHz signal that is distributed from the master to the slaves, and channels can in
principle be frequency-locked with any frequency combination. However, the number of
cycles between the phase-referenced points will be excessively large unless the ratio is a
small rational number; for example a 2 kHz signal could be locked usefully with 10 kHz,
50 kHz, 100 kHz, etc., but not with 2.001 kHz.
For clock synthesized waveforms it is the PLL clock of the master which is distributed
from master to slaves; the clock frequency for master and slaves is therefore always the
same. The number of points comprising the waveforms should also be the same to ensure
that the waveforms themselves appear locked.
From the foregoing it is clear that only DDS slaves can be locked to a DDS master and
only clock synthesized slaves can be locked to a clock synthesized master. In practice the
constraints described are not severe as the most common use of synchronization is to
provide outputs of the same waveform at the same frequency, or a harmonic of it, often
with controlled phase offsets.
Master-Slave Allocation
Press the front panel INTER CHannel key to call up the inter-channel set-up screen.
mode: indep
phase: +000.0º
(actual: +000.0º
status: off view
The mode soft-key can be used to select between independent, master,
master/freq and slave; the default mode is independent. Only one
13-2
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