Part b - The Momentum 3D Planar EM Simulator in Advanced Design System

Uploaded by AgilentEEsof on 09.02.2010

Now before we set up the simulation, let me show you the mesh setup. By default, Momentum
will automatically create a mesh for you using the following.
It will have an edge mesh around the edges because it assumes that there’s current
bunched around the edges. It’s more dense, so that’s automatic. And then it will use
the highest simulation frequency, in our case it’s 10 GHz, and create 20 cells per wavelength
at that high frequency.
So this is the default, and we’re going to use this, but you could set it up any way
you want, for a coarser mesh or a denser mesh, with or without edge mesh. This sometimes
saves time, but you may tradeoff accuracy in some cases. You can mesh individual drawing
layers. You can mesh primitives. All of this is available, but we’ll use the global default
mesh as you see here.
Now let’s setup our simulation, and now we’ll complete our steps.
Using the command Momentum/simulation/S-parameters, a dialogue appears where you can setup the
sweep. Notice that there’s an adaptive type, also log, linear and single, but this adaptive
type is the default. I set a start of 1 GHz stop of 10 to match the circuit simulator
with 101 sample points as the limit. This adaptive sweep will take the first point and
the last point and points in between. And when the testing is done to the point where
it knows the S-parameters aren’t going to change anymore, it can then just interpolate.
It’s like a curve fitting. And you’ll get your data much faster than simulation
all the individual points.
Now, in this dialogue you can name the dataset or use the default, and there’s a presentation
template that will come up, and we’ll see that in a moment. So I’m going to click
the simulate button, and then we’ll get our Momentum results.
Here’s a Data Display that automatically appears with the presentation that’s a template.
I’m going to close this and go back to our other Data Display. And now I’m going to
double click, and that will bring up the plot traces and attributes dialogue. And now I
can select the dataset that I want, which in this case is this easyline_mom_A, A for
adaptive, and then we can select S21, add it in dB, click okay and here we can see the
We have a very close match between the circuit simulator and Momentum, and this is expected.
Next, I’m going to go back into the layout and show you the mesh pattern, and you can
see that here we have edge mesh along the edges both inside and out, and we have our
cells. I’m going to change the spacing now so that we have very closely spaced lines
and see what Momentum can do for us.
Let’s go ahead back to schematic, and that’s where I’ll set that spacing up with the
variable. The first thing I’m going to do though is use control A to select everything
in layout and delete it.
And here back in schematic I set the spacing up to 2 mils, and then I regenerate the layout
using this command, and here are the results. Now you can see the spacing is very close.
So I’ll put ports back on, and then we’ll run the simulation again, which is already
setup. And now we’ll change the dataset name so that we can identify it, underscore
2 mils, and simulate.
While the simulation is running I want to point out that ports always need to be on
the same layer as the metal. And in a moment we’ll have our results.
I select the 2 mil dataset, S21, and add it in dB. And here you can see that with the
closed spacing, once we get over about 2 GHz, there is a definite difference between what
we simulated with Momentum and what we simulated with the circuit simulator and Momentum where
the lines weren’t closely spaced. And the circuit simulator would not be able to give
you these results.
To prove this I’ve gone back to the circuit simulator where we have our 2 mil spacing,
and I use the command simulate/setup. And I have a new dataset name, circuit 2 mils,
and I ran the analysis, and here are the results. The 2 mil spacing from the circuit simulator
is very, very close again to the first results.
Only using Momentum can you take coupling into account for closely spaced lines. Now,
Momentum has a lot of other features and capabilities, but we’re going to use at the spiral inductor
next, and that will bring our video to a close.
Here in the ADS main window I’m going to the examples directory and then into the Momentum
folder microwave spiral project, and that’s what you see here. And I’ve opened up the
design spiral. So let’s take a look at it right now. And here’s the schematic.
As you can see the mesh has already been created and that’s because it’s been solved. As
with all of our examples there’s a Data Display, and everything in Momentum is already
setup. So let’s take this step by step. I’ll begin with the ports.
It has two ports. This one on the drawing layer that you see, it’s internal to the
structure, and then throughout all our windings there’s a via here. And the via comes up
into another drawing layer where we have Port 2. And zooming in, you can see the via here
is just a polyline via, and that’s what we recommend because it will solve better.
That’s the thin green line that you see here. That’s our via.
The results come from the simulation that was setup from zero to 5.2 GHz, as you can
see, with the adaptive technique. Let me show you the Data Display for this example. And
here it is. Notice that measured data is in this dataset. That’s the red trace. And
the blue trace is from Momentum. So for impedance S11, transmission S21 and our phase for both
of those respectively, you can see that the Momentum data is very close to measured data,
and that proves Momentum’s accuracy, especially for solving spiral inductors.
And so this covers the basics of ADS Momentum. Remember that we always have to have a layout
with ports. Then you can use the Momentum menus. There are two modes, full microwave
and RF. The substrate is defined right here in this command, or you can update it from
schematic, both the dielectric material and the individual drawing layers that are mapped
as strips, slots or vias.
Also in Momentum we define the ports. They can be single ports, internal ports, coplanar
waveguide ports. You can even renumber them using this command. We have box wave guide
setup. The component allows you to use the advanced model composer or create a lookalike
component, and we cover that a lot in our ADS Momentum and layout course.
You can preprocess everything. And here you can see the preprocessor dialogue, which we
won’t go into, but generally it will cleanup your layout. And for example, in this case,
what you see are two individual polygons, and there’s a very severe angle here. Well,
the preprocessor will clean up that angle so that you can then use it with Momentum
and avoid any potential problems.
The mesh can be calculated in advance. You can set it up for the global structure or
individual layers. And then when you simulate basically the S-parameter setup, post processing
includes visualization, radiation patterns. And then finally we have this command here,
which allows you to use these files for our 3D EM simulator.
So, all of this is covered in our Momentum course. And that brings our short video on
ADS Momentum to a close.