Hi. I’m Bill Griffith and I’m an Application Engineer with Agilent Technologies.
Today I want to talk about synchronizing the output of a two-channel waveform generator.
This is necessary when you want to simulate two signals that are correlated in time.
An example of this is two clock signals. Even if they’re different frequencies, if they come from the
same source, they’ll be correlated in time. So let’s get started.
When we first start the waveform generator in its default mode, the two channels work independently.
We can set up different waveforms on each channel. We can have different amplitudes and different frequencies.
I’ve chosen the same frequencies for these signals and at this point they’re not phase-aligned.
And so what we need to do is we need to go into our phase menu and choose, “Sync Internal.”
Now the waveforms are aligned in phase and we can put a phase offset in if we want to
at this point from the same menu. We have some additional methods to align the waveforms as well.
The problem with this method is if we change the frequency – so I’m going
to go to 2 kHz on channel two – is that we’ll lose our phase alignment and
we’ll have to go back into the menu and align it one more time.
And so any time we change the frequency we have to realign it. So let’s look at some
other methods for aligning the phase. Okay, Method number two: let’s say we have two
clock signals and they’re a ratio of three to one. What we can do is we can use channel
coupling to go ahead and set that up. So I’m going to go ahead and turn on frequency coupling
and then I’m going to set the ratio of three to one. And now, as you can see, for every
period of our first signal we’ll get three periods of our second signal. We can go ahead
and synchronize them so they start with zero phase again, just like we did before.
Okay, and now when I adjust the frequency of channel one you’ll notice that channel two adjusts
along with it and they stay in phase as well.
So this is a unique feature of the 33500 series waveform generators; and another thing we
can do with our frequency coupling is we can use an offset instead. Right now we’re using
a ratio, but we could have an offset so that as we move channel one we would see channel two
move with that same offset. Another feature is we can also couple amplitude. So let me
go ahead and turn on amplitude coupling. It’s an independent setting, but as you can see
with the amplitude coupling on, when I go back and change the amplitude of channel one,
the amplitude of channel two changes. We also have a couple special cases for coupling the
channels and that is using the tracking feature.
And so with tracking on, what it does is it produces two identical signals and they’re
both in phase; and so as you can see, we now have two identical signals. It copied the
waveform, the amplitude and the frequency and the other special tracking mode we have
is to invert it so it’s 180 degrees out of phase and this is useful for creating a
differential signal. So the two channels can be combined to create a single differential channel.
Moving on to the third method, we’re going to use the optional IQ Player. So the
optional IQ planner can actually be used to play back any two-channel waveform, and so
we’re going to go ahead and show what that looks like.
So in Excel the way it would look is we would have in Column A all the data for channel one
and in Column B we’d have all the data for channel two. So each row would represent
a data pair and so what we’re going to send to the function generator is these data pairs
in a CSV file. So I’m going to go ahead and save the Excel spreadsheet as a CSV file
to a USB stick and then we can import the data from our USB stick. So I’ll go ahead
and show you what that looks like. Okay, so we’ll go ahead and go to “Waveforms,”
go to “Arbs,” and then I’m going to go ahead and import the data. So I’ll select
a data file, which is out of my USB stick. So I’ll select it and then I’m going to
select to bring in the data as an IQ waveform, even though it’s not an IQ waveform, but
this allows the data pairs to be imported, and I’m going to import my data.
Okay, so now we’ve imported our data. I’m going to say, “Yes.” We want to load the
file and I’m going to autoscale the oscilloscope so you can see both waveforms. As you can
see, I have a sine wave on channel one and I have a sine wave at twice the frequency
on channel two. So this could be used to represent a mechanical system with a gear ratio of two
to one. And so with this special option, when I change the amplitude, I change the amplitude
for both data pairs simultaneously. If I change the sample rate or frequency, I change it for
both channels. So this is one more method of creating data that’s synchronized with
a two-channel waveform generator.
So we looked at three different methods to synchronize waveforms using the new 33500B Series from Agilent.
We started by setting up the two channels independently and then using the sync internal function.
The second method was to use channel coupling. So the advantage to that was when
we changed the frequency on the first channel the second channel moved with it. In addition,
we can do the same thing with amplitude and we looked at the special case modes for tracking.
We created the identical signal and the inverted signal and then we moved on to the IQ Player,
which is optional, and downloaded our data pairs and created two synchronized waveforms
using the optional IQ Player. So these are very unique features to the 33500B.
I hope you found this useful. Thanks for watching.