PCIe Gen4 Signal Integrity Analysis using ANSYS SIwave & Circuit Tools

Hello, this is Ibrahim Nassar with Ozen Engineering. In this demo, we will be using ANSYS SIwave to perform PCIe Gen4 signal integrity analysis to ensure reliable high-speed data transmission.

We will be using the SI Wizard, which has an automated workflow to set up a signal integrity analysis by dynamically linking the SIwave solver and the ANSYS circuit transient solver. We will be starting with this SIwave project, which has this layout file.

The first step we need to do is to define the nets. Next, we will show you how to set up the extended nets. We will make it simple by simulating one extended net for TX and one RX net. To define an extended net, we can click here on the Extended Nets tab. Then we click Auto Identify.

And we will be identifying them as underscore cap. Click Auto Identify. So these are the nets that we found in the total nets that we have. So we hit OK. Now let's define the differential nets.

To define the differential nets, we click also on Auto Identify and let's make the net name, and the differentiator should be my underscore P and N. So click Auto Identify and we click OK. So now we kind of modified the nets to the way we want.

Next, we can go to the simulation tab and click on SI Wizard. Okay, so from the differential nets, we will be selecting this net. You can just select any net and click add, and you can remove them by clicking enter, is click remove.

And we will take so we will take one differential net for our RX and we will take one of the differential nets of TX. Okay, and we hit next. Here we will have to define which nets are the transmitter and which one are the receivers. So you can do that by clicking and selecting the nets by Ctrl key.

And here you can specify which one do you want. If you want it to be receiver or driver, then you click update. So here I already defined them. So we need those RX nets to be the receivers. and these are the drivers.

So the PCIe Gen4 that connected to the TX and connected to these part numbers will be the drivers. So after we specify the drivers, we can identify include models or we can define the excitation source according to the PCIe Gen4 standards.

To do that, we can click here and select which excitation source we need. If you don't have them already listed here, you can define them by clicking on Manage Sources, and here you can select Add New, and then you define the parameters according to the standard. So here let's hit Cancel.

So now the excitation sources are selected, the drivers and receivers are selected, so we click Next. Here we don't have to modify anything, so click next as well. Here also we don't have to modify anything, so click next. And here we basically have to select which analysis do we need to do.

So here we need to use the ANSYS Electronics Desktop with SIwave Dynamic Link. Okay, and the step size is already defined based on the excitation source that If you don't have that, you can define them based on the standard rise time.

And we want to check all these boxes to include them in the simulation. For the S-parameter sweep, we can click on Edit to modify it.

So this is the frequency sweep that we will be doing, which is automatically created here based on the excitation source and the PCIe Gen4 standard that were selected.

and we notice here that we have an 18 picosecond rise time which is according to the standards, you can modify this if it's not correctly defined, but it should be all these settings should all be created automatically when you select the right standards.

Okay, and we hit OK, and now if we click OK, the SIwave simulation will start and the Electronics Desktop setup will be. Now we see the analysis is being created. Now the AEDT project is being created. Now it's building the circuit. The reports that we need to look at are all automated.

And now the transient simulation started. So what this SI Wizard is doing, basically it's running the signal integrity, the SIwave simulation to extract the S-parameters and it placed them in this block that links to the SIwave project.

Then here we define the I source since we have two extended two nets selected, two differential nets selected, so we have two sources, two I sources, and on the other end, we have the I props, so we can create the I diagram and plot the voltage on these props.

We can create the Idergram and plot the voltage on these props. We can check the source definition, so if we double click on the I source, we can go to the bets. So here the data automatically got filled according again to the excitation source that got defined.

So we see a rise time and fall time of 18 picosecond and we see the VLow and VHigh. And these are kind of most of the parameters that need to be included here. Click cancel.

And here is the IProp, which basically has to specify basically which one it's looking at, and the other one is looking at the I source of this site. And this one is looking at the other site. Okay, so now the simulation is completed, so we can look at the results.

We can go back to the SIwave tool and we can look at the S-parameter data here by right-click on the SYPsim, and, for example, plot the magnitude. and here we can see the S-parameters, Y-parameters, or Z-parameters. We can select which ones do we want to include.

You can select self terms, transmission terms, or cross-talk terms for example. And we can select, change the scale here, put markers and everything. We can also use the network data export to plot the results, or if we click on plot in Electronics Desktop.

So, let's go back to the circuit and start to look at the transient simulation and the I-Diagrams. So here we see the voltage versus time at both of the I-Probs for the RX and the TX. And we can also look at the I-Diagram, which is created here for RX and here for TX.

In the circuit simulation, actually, there is two analysis that were performed. So we have the quick eye analysis, which is a faster way to create the eye diagrams by looking at many more bits by using different kind of simulation technique.

And we have also the transient setup, which is defined also again, according to the PCIe Gen4 standards automatically through the SI wizard.

So if we were to create these I-Diagram plots, we can right-click on results, create I-Diagram report, rectangular plot, and here we select basically when I look at the transient solution or the quick eye. So let's select, for example, the quick eye.

And here we specify basically which prop, the RX1 or the TX 1. And here you have to specify the unit interval, but it comes here automatically again according to the PCIe Gen4 standards. So we click new report, so this is the one for Tx.

If we want, we can also add the mask here to look at the results against it. So we can select this plot here, then in the properties window go to the mask and we click on edit. And if we click on edit here, or you can import it if you already have it in a file, but let's click edit here and add one.

To add it, we just need to find where is the center point, so here is around 60 ps, and according to the PCIe Gen4 standards, the eye width is 18.75 ps and the eye height is 15 mV.

So in case we need to do an equalization, which obviously here we don't need for this kind of data, but let me show you how to do that. So let's copy the design and paste it. To define the equalization, so we have to modify the sources. So let's modify the first source.

And you can go here to the equalization tab.

and we need to get the FFE data according to the standard, so if we click here, so according to the standard, the gen PCIe, the PCIe gen 4 would have three ones, and if we specify them, it would be minus one and zero and one, okay, and for this one, it would be for the source that is here, which is 6050. Okay, that's all that we need to do the source, now we need to do the same thing for the other source.

So three tabs, minus one, zero, one, and connect it to the other probe, which is 1860, this one. Now we also need to modify the probe. So we double click here, and we select the DFE data.

and here we have for the DFE, I think we have two, okay, and for the CTLE data, we can select it according to the standards, so the PCIe Gen4 is here, so we have these two pole data at 4 gigahertz and 16 gigahertz, and we hit okay.

Okay, now we modify the other probe similarly, so we have two tabs for the probe, for the DFE data, and the CTLE select this PCIe gen4, and we hit okay. And that's it. Then we can repeat the simulation and see how the diagram changes. So I hope you find this demo useful.

That's it for this demo, and thank you for watching. Please contact us at https://ozeninc.com/contact for more information.