Part a - Harmonic Balance Simulation in Advanced Design System

Uploaded by AgilentEEsof on 08.02.2010

In this short video on Harmonic Balance simulation, I’ll cover how to set up the simulation
controller, and also some of the most commonly used sources for Harmonic Balance. I’ll
show you a power sweep, and also another form of Harmonic Balance done strictly for compression
testing called XDB. I’ll show you the data, typically the spectrum, and how to plot it.
And I’ll give you a few important tips on doing Harmonic Balance simulation.
Here in the examples directory I’ve selected the microwave circuits folder and the large
signal amp project. This particular project has both the Harmonic Balance one-tone analysis
that you can see here and the swept power for Harmonic Balance, and those are the two
that we’ll be looking at. Let’s go ahead and start with the first one which is the
one-tone Harmonic Balance design.
So here’s our first example, and Harmonic Balance gives you the spectrum and the amplitude.
So what we have is a power source that’s feeding into an amplifier that has a bias
here. It has two wire labels, or node names, and simply by clicking here and then typing
in Vin, picking a wire and Vout, you get these labels and that way you can look at the spectrum
at both of these points. So because Harmonic Balance gives us the spectrum and the amplitude,
we want to set it up to calculate what we expect to be inserted into the circuit and
then a number of harmonics, which will account for the nonlinearities of our device or our
amplifier, and that’s what’s done here.
Let’s quickly look at this amplifier. I’ll push into it using this hierarchical push
into, and notice there’s a device and a lot of microstrip elements; you can see it’s
quite crowded. So zooming in you can see that these microstrip elements refer to a substrate,
FR4. Let’s pop back out and that’s this Msub and that’s defining all of the substrate
as FR4, so that’s the name of it.
So that’s what’s in this example, a Harmonic Balance controller set to 1 GHz with order
equal seven, that means a total of seven harmonics. So that’s the fundamental and six harmonics,
and it will calculate those and give you the spectrum at the input and the output. Before
we look at the results, I’m going to scroll down and insert a brand new Harmonic Balance
controller from the palette. When I do, the dialog opens and we want to cover this briefly.
Notice that it comes in in a default condition showing 1 GHz order three. So again, if we
look at the dialog, this is where we can change that. Increase the order, change the frequency,
and simply add it or cut and paste other fundamental tones and harmonics to this list. So again
you have a fundamental tone, freak, and then order. And the order is the total number of
Here, maximum mixing order, this is used when you calculate intermod products. So if you
had a mixer then you’d be using this, and once you had two tones then you get intermod
products. But because we only have one tone it’s grayed out. Status level refers to
the information that is written to the status window, and that’s true for all simulation
In the next tab, sweep, this is ready to sweep a parameter. Now, we’ll look at the other
example that sweeps RF power and that would be normally typed in here if it’s set up
as a variable. And to set up variables in ADS you simply select this variable block,
insert it, and then declare a variable. These other tabs for initial guess and oscillator
and small signal we’re not going to cover here because we’re only covering the basics,
and these are typically used only in certain situations.
Initial guess is for circuits that don’t converge, but that's rare, and oscillator
is for doing oscillator analysis with either a node specified or this os_port. For noise,
you can get nonlinear noise by simply turning on this checkbox and then going to these other
two buttons and they will open up giving you these selections.
Harmonic Balance also allows you to use these noise controllers so if you click this and
you were to insert a noise controller, such as this one here, then you’re really setting
up noise separately and then you would be able to get it from the list. And there it
is. That’s how you do that, and the purpose of doing that is to have a separate noise
simulation that you could turn on or off that is deactivated or activated easily for various
The parameters tab can give you for devices the DC values, the operating point, either
detailed or brief, and if you were to turn that on you’d simply go to the simulate
detailed or brief icons and commands that you see there and then you’d get that information.
And here the output tab is where you can select specific node voltages or current or measurement
equations. Again, if you leave this in the default condition you’ll get everything
that’s on the schematic, or there’s an add/remove button down below, simply use that
to add or remove individual currents and voltages or measurement equations. Now the display
tab is like the other controllers where you can select which parameters of the controller
you want displayed.
So, to review Harmonic Balance, most of the time if you want to get the spectrum or the
power you’ll be using the frequency tab, and that’s where you set up the frequency
so that it matches the frequency of your source and also the sweep, whether you’re sweeping
power or anything else, that would just be a variable.
Here, back at our design, I’m showing the simulation palette for Harmonic Balance, the
controller’s in the left corner and it has the same options, parameters, sweep, and sweep
plan that all the other simulation palettes have. It also has several measurement equations
that are used specifically for Harmonic Balance, and the os_port component in case you’re
doing oscillator analysis.
Here, for example, is IP3 out, you insert this measurement equation and then once you
learn a little bit about Harmonic Balance data with a Vout node that would have to be
spelled the same way, so we can’t have upper case and lower case. Simply spell it the same
way and then you could get the IP3 out value that’s the third-order intercept point for
your circuit.
So that’s the palette, and the main thing is the controller. Now let’s look at a few
sources. With Harmonic Balance we can go to the frequency domain and here you can see
the PN tone and the P1 tone, this is a P1 tone. So inserting it, it comes in just like
this and it has a function, polar function. Notice that’s different than the DBMTOW,
which is dBm to watts function. Because you can set the value in dBm, that’s in these
parentheses, and the phase, it has the polar function as a default. But most of the time
if you’re only interested in having the value in dBm you can insert your cursor, remove
all the other information in the arguments, and simply set the value like this in dBm.
Now it’s -10 dBm and this simply means dBm to watts for the simulator. Notice the frequency
is set to 1 GHz. Again, you can set the frequency to anything you want and if you have a simulation
controller you can use that frequency that will automatically override, and that’s
why this one’s blank. So those are the basics of using the power sources for Harmonic Balance.
Now let's look at the results for this simulation.