This short video on S-parameter simulation will cover the controller setup, ports and
sources for S-parameter simulation, some of the measurement equations and the data that
results, including S-parameters, circles, noise, etc., and other miscellaneous information.
And so to demonstrate S-parameter simulation, I’ve chosen the examples, and you can see
that here in the examples directory, the microwave circuit’s folder LNA 1 GHz project. This
low-noise amplifier has many designs and data displays. As you can see here it has designs
for setting up the bias, the matching networks, even stability and S-parameter with noise,
and that’s the one we’re selecting.
This particular design not only has the data display but also has the basics for S-parameter
simulation and some extras. So, let’s take a look at it right now.
Here is the design. It has a device, which is based on an S-parameter file you can see
here, and two terminations. For any two-port measurement you want to have two terminations.
They can also be sources, which are used as ports. The key to knowing what you can use
is that they have the parameter “NUM,” which means port number, and you see that
here. And also a box around the resister to indicate there is an impedance.
For example, here is a P one-tone source, so you can specify the power in one tone.
Notice it has the same box around it, like this one, and it has NUM for port number.
So that could also be used as a port. But keep in mind that these terminations are typically
located in the S-parameter simulation palette right here, and the sources that could be
used as terminations for an S-parameter simulation are in the sources palette, such as the frequency
domain.
Now I’m going to open up the simulation controller, and we’ll go over the tabs.
Keep in mind that frequency is setup for a sweep. Of course you could have a single point
or a log. And if you want to set the number of points then that will automatically calculate
the step size. Or you can set the step size, and that’ll calculate the number of points.
Sweep plan, if that’s checked, means that you’ve inserted a separate sweep plan here,
and that would sweep frequency, for example, within this broad range.
Looking at our palette, where we inserted our controller, there’s an SP lab, things
like S-parameter test benches and sequencing of various different networks to get the S21,
for example, of a lot of separate networks where you may have 8 or 10 or 12 ports, that
can be done.
Parameter sweeps mean that even though you’re sweeping frequency, you can sweep something
like the value of a capacitor or the value of a parameter for a model. And that’s what
this parameter sweep is. So you could sweep that. Along with your frequency, you’d get
S21 with varying values of that parameter. And typically that would be done with a variable.
Simply insert it and assign the value.
Looking again in this S-parameter simulation palette, there are a lot of measurements,
including circles, power and you can see stability and so on. But back to our basics here that’s
our frequency tab, so you set the frequency. And here in the parameters tab, S-parameters
are defaulted, but you can also have Y or Z parameters calculated and available in a
dataset, or even Group Delay.
This frequency conversion setting is strictly for our behavioral mixers. Those are system
components, and that way if you want S21 you don’t have to worry about the up or down
conversion.
Finally we have the status level. That’s the information written to the status window
during the simulation, defaulted to two. Typically not any reason for S-parameter simulation
why you’d want more, and device operating point level means if you have devices in there
that are biased then you can get all of the information about those devices and the operating
levels around them. So you simply select one of those, and then you can go to the command
up here, simulate, and then you can see detailed or brief and get that information.
And now for our noise tab, calculate noise is turned on, and you can see that here. If
you have more than two ports, and you want a different input or output port simply type
those in here. And noise contributors means how they’re setup in the dataset to be viewed.
So if you insert a list you can get them by value or by other details, and you can see
that here.
And next is the output tab, and as you can see here you can select if you want measurement
equations sent to the Data Display. The default with the checkbox here is to send them all.
Or you could add or remove individual measurement equations. Normally the pin and the node voltages,
the DC voltages don’t show up here because it’s an S-parameter simulation. So, if you
needed that you simply insert a DC controller, and you get all those DC values. But that’s
the only difference here. Otherwise all these output tabs are basically the same.
And then the display tab, you can set all the parameters that you want displayed on
the screen for the simulation controller.
So just in review, if you insert the S-parameter simulation controller and set the sweep, all
you need are ports for any device or any circuit, and be sure that the numbers, Num1, Num2,
and so on are consecutive. And you can have the impedance set to anything you want. In
this case it’s defaulted at 50 ohms, but that can be swept or even tuned.
So those are the basics. Remember you get the terminations here if you’re not using
ports that also have this number.
And finally, with this example, we have the noise circle built-in measurement equation.
Let’s take a closer look at it.
Here is an exploded view of the noise circle measurement equation. And I’ve also inserted
from the simulation palette a gain circle and VSWR. Notice that each of these has a
function – this is a measurement function, GA underscore circle for gain circles, with
the arguments, S, meaning the complete S matrix; two, meaning 2 dB and 51 points to draw the
circle in the data display.
VSWR has the function, VSWR, and in parenthesis, S11, which is all the measurement it would
need to calculate this. And our noise circles has several more. And these arguments are
as follows for the NS underscore circle function, 1.5 to 3.5. These are all values in dB for
our circles when we plot them on the Smith chart. NFmin, this is noise figure minimum,
which is automatically generated from the S-parameter simulation, so you don’t have
to do anything. That’s just a default. S-opt, which means the optimum source match. And
our noise resistance here. And then finally 51 points, and that’s the number of points
to draw the circle. You can say the same thing here.
So now I’m going to go to the data display and show you the results for this S-parameter
simulation of two ports setup for noise.
And here’s the data. As you would expect there is a Smith chart. It has all of the
circles. Remember the arguments, 1.5 to 3.5, so they’re all here. And because it’s
an example, it has a built-in marker slider, so you can place a marker on some parameter
value, such as our frequency sweep, and then simply move the marker and notice the circles
will change over here, and that’s because it’s for a different frequency.
It also has our Smith chart where we’re going to see S11 and S22 plotted, plus the
optimum source match. And notice that the dataset contains these values, so you simply
insert them, and that’s what you see here. And these traces are for all of the frequency
points.
Here’s our transmission measurement, our rectangular plot that was inserted. And here
you can see all of the dataset contents. Of course on a rectangular plot we’re going
to put our transmission measurement, dB of S21, there’s a noise figure minimum on there,
and of course the resistance value for the noise, and that’s what you see plotted here.
And for any of the data that’s in an S-parameter measurement, you can always insert a list,
like you see me doing here, and when the list comes in to the data display window then you
can list any values, and they’re all here. So, once again, we have the basic S-parameters
that you see here, plus what we got from noise, such as S-opt and NFmin. There’s also the
port impedances and the noise circles.
And that concludes our look at basic S-parameter simulation in ADS.