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For Circuit Envelope simulation I’ll cover the basics, how Circuit Envelope works, including
the controller set-up and sources that are used – typically, these are modulated sources
– and also plotting envelope data in the Data Display.
Here’s a simple circuit that I’ll use to demonstrate how Envelope works, and then
we’ll look at an example. Think of Envelope this say: It samples the envelope of the signal
and not the carrier. So, this means it’s very fast, and it does this because it samples
over time and it calculates the spectrum, and that’s why the Envelope controller is
set-up with both time and frequency; and here you see the frequency, and here you see the
time.
What I have here is a simple circuit. It’s a behavioral amplifier. It has 10 dB of gain.
It could represent any circuit. I’ve labeled these wires, or these nodes, V-in and V-out,
so we can look at the signal. And we have a pulse source here. It has a peak voltage,
a rise, a fall, a period, and a width.
So, to better understand how Envelope works, let me show you a slide from one of our courses.
I’ve taken this slide from the ADS Fundamentals course to show how Circuit Envelope works.
All of our courses cover a lot of details and spend a lot of time setting-up and running
simulations and plotting data. Basically, if you think of a time-varying spectrum, such
as a modulated source signal, that is input to your circuit with both linear and non-linear
devices, then knowing that signal source and all the models if we capture at any point
in time the spectral content of an envelope, then we can recreate that envelope. We can
do a transform on the data, such as the output data. And then, what you get is amplitude,
or phase, or frequency, harmonics versus time. So, in general, Circuit Envelope is like a
combination of time-domain analysis, or transient in ADS, with Harmonic Balance.
Next, let’s look at how the simulation controller is set up. Before I open up the controller
and show you the tabs, let’s quickly review what we have here, because we have a 1 GHz
signal. That’s the frequency injected into the amplifier. I’m going to set this up
like Harmonic Balance with a frequency of 1 GHz, and we’ll calculate a number of harmonics.
So, we need all our spectral components. Because this is a simple circuit and a demonstration,
I’ll just use the default of three, the fundamental, the second, and the third. However,
our time settings have to correspond with the time settings of the source. Because the
source rises over five nanoseconds and falls over ten nanoseconds, I’m going to set the
step for the sample rate such that it will be able to capture that rise. So, I’m setting
it to one nanosecond. So, every nanosecond the spectrum will be calculated.
If I were to set this to 20, for example, then we would already have the rise occur
before we’d even take one sample. So, we don’t want to do that. We always want to
set this at a rate that corresponds with how we think our envelope is going to appear.
Now, there are some details about doing this, and again, we cover that in our courses. The
stop time of 80 nanoseconds is long enough to capture two of these periods, so two of
these pulses. That covers the basics. Let’s open up the controller now, and those basics
are set up in this envelope set up tab, and you can see that here.
Set your time and enter the fundamental tones you want to calculate, and the harmonics,
just like Harmonic Balance. Here’s the status level, the information that’s reported to
the status window during simulation. These other tabs, “Envelope Parameters,” “Initial
Guess and Oscillator,” these are all advanced settings, and we won’t cover them here.
Most of the time you won’t need either of these. Just leave them in their defaults.
This is for oscillator analysis, and you can do oscillator analysis with Circuit Envelope
very similar to Harmonic Balance. The rest of these we don’t need to cover here. They’re
covered in some of the other simulation controllers, because most of them are all the same for
noise, params, solver. Except for fast co-simulation, but again, this is an advanced topic, so we
don’t cover that.
And now I’m going to run the Envelope simulation and show you what is at the output after running
Circuit Envelope. Here in the Data Display I’ve inserted a list, that’s this icon
here, and I’ve selected the V-out data. That’s our node that’s been labeled. And
notice that at every time point – and this list goes on – it calculates the three tones.
The DC is always calculated, and here are the three tones, our fundamental and the two
harmonics for an order or three. And at every point you get the complex voltage.
Next, let’s insert a rectangular plot.