Hi everyone.
Welcome to esteemed PCB Academy.
My name is Avril.
In our previous video we talked about LVDS and different terminology we use for LVDS.
For example V differential v common and current mode drivers, along with couple of simulations on cadence
security tools.
We have also discussed different IEEE and Ansi standards for LVDS.
In this video we will focus on simulation part.
We will see how to set up the topology of LVDS driver and receiver along with lossy transmission line
on Security Topology Explorer.
Then we will add Stackup information and Ibis models to make it more realistic.
We will see how to do different measurements on output waveform and diagram.
So let's get started.
So before jumping to the simulation of high speed signals, we should be aware of why we are doing pre
layout simulations.
So let's understand that with an example.
Suppose in our case we need 0.4 GB data rate.
So are these drivers good enough to support that data rate with nice and clean waveform at receiver
side or parasitics and losses will destroy the waveform.
So in short, we do pre layout analysis to define constraints and design rules.
Now let me tell you about few of these constraints we simulate for.
First one is length of a transmission line.
So we simulate length of a transmission line to verify the effect of length or propagation delay on
the signal at receiver side.
Second one is impedance discontinuity.
So on our transmission line there can be impedance discontinuity due to stub and vars on the line.
Third one is stack up and material property.
So we basically analyze what stack up and material property are doing with the waveform by doing pre
layout analysis.
Fourth one is different type of losses like dielectric conductors crosstalk etc..
So now by running sweep analysis on these parameters We need to find the limit or break even points
for design rules, and we implement these design rules while layout.
Now let's talk about topology and requirement for simulating something.
So in our case we are simulating high speed LVDS drivers and receiver.
And for that I am using TS, DDS, LVDS 1047 driver and DDS LVDS 1048 receiver.
And because these driver and receiver follows Ansi standards.
So drivers differential output and receivers differential inputs should have 100 ohm differential impedance.
Plus we need to terminate it with 100 ohm resistor at the receiver's input.
So as you can see in the figure this is what we are going to simulate.
Now let's move to the simulation requirement part to simulate this topology or to make simulation more
realistic.
Instead of just following the default All simulation.
We need few information from chip manufacturer and PCB manufacturer.
And first one is Ibis model or Spice model, or other circuit models in general.
But in our case we need Spice models only.
Second is PCB stack up information.
So here I mean detailed stack up including materials, property, etc..
Third one is fixed or variable parameters like data rate, bit pattern, differential impedance, maximum
length supported, maximum number of vars, etc..
And last but not the least connector models.
So if we are using any connector in our design, we need to include those as well in our simulation
because those also has parasitics in it.
Now with all this information, we are ready for setting up our topology in Security Topology Explorer.
So in the step one we need to open Security Topology Explorer 17.4.
You will get it with couple of licenses.
I'm just going to use security Aurora license and click over.
Okay.
All right.
So now it is asking either you want to open an existing design or want to create a new one.
I'm just going to create new topology.
So here you can set your topology name.
In our case it is LVDS 1047 and 1048 receiver driver topology.
And I'm just going to save it in desktop.
After selecting the folder you have to select either you want to use some template or just go for the
blank topology.
So in our case we're going to create it from scratch.
So we'll just select blank topology and click over create button.
After creating the new topology we have to place driver block from Add block menu.
And if you'll try to place the driver you'll see it is single ended output as of now.
To make it make a differential output, you have to just select differential from here.
And now we are ready to place differential output driver.
Now in the next step we have to add Ibis model in this transmitter.
To do that you have to just double click to open Edit Property tab.
And here you have to select the Ibis file.
Now it will direct you to this load Ibis section.
So as of now you can see we have a default Ibis model assigned to change this to manufacturer's Ibis
model.
You have to just click over this three dot.
And in our case we have saved the Ibis file in desktop.
So I have to just go there and select the Ibis model for driver and open it.
As soon as you select the Ibis model it will direct you to differential pin tab.
And from here you have to select differential pairs.
So it has four channel.
And I am just going to use doubt four plus and doubt four minus channel.
In case you are going to use multiple channels, you can select multiple differential pairs.
I'm just going to uncheck those.
So for this type of topology what you have to do you have to just select the output pins which differential
pins you want to use for output.
So I'm just going to use ten comma nine and click over okay.
And our driver model is ready to use.
Similarly we can setup the receiver model.
So firstly we have to place our differential receiver model here.
Again double click on this one.
Select the Ibis file.
Click on these three dots and select RDS LVDS 1048 Ibis model.
Click on open.
Now for receiver we are going to use pin number two and pin number one as a differential input of receiver.
And we are going to place couple of single data pins which will be enable pins.
Just select those and we're not going to change anything on pin mapping and click on okay.
Alright.
So our receiver model is also ready to use.
So now in both case as of now I am seeing pin numbers on pins.
I just want to change it to net name.
It will be easy to identify which pin is for what purpose.
So I'm just going to slide it down here.
And just arrange positive and negative pins in front of each other.
All right.
And if you zoom in to receiver side we have to enable receiver.
To do that.
You have to just right click over enable pin and connect it to power.
Double click over power and change it to 3.3V.
Similarly, for enable asterisk you have to just connect it to ground and our receiver side is enabled
now.
Alright, so till now we have set up our driver and receiver model.
Now in the next step we have to add trace between transmitter and receiver.
To do that again make sure this differential block is selected and click over trace.
Now to edit the trace property.
As you can see it is 5000 mil longer trace which has 118.673Ω differential impedance.
To edit the trace property, you have to just select it and click over Trace Editor.
Now inside this trace editor, we have to add the stackup that we are going to use in our PCB.
So we'll get this information from our PCB manufacturer.
In my case I'm just going to use this Stackup which is a four layer 1.6mm thick Stackup.
So I'm just going to add it quickly.
All right.
So till here we have added our stack up in this trace editor.
Now in the next step I'm just going to place these tracks on the bottom layer.
To do that you have to just go to that layer name column and double click here and select bottom.
So you can see the traces are shifted to the bottom layer.
Now in the next step again I'm going to change the unit to mill.
So as of now if you see the impedance it is 104.917.
We have to make it more precise to 100 ohm characteristic impedance of differential pair signals.
To do that we have to change the trace width and spacing.
So I have already calculated what should be the trace width and spacing for this stackup from cross
section editor of PCB editor 17.4 tool.
So let's put that value here quickly.
So I have changed the trace width to five mil and spacing to 7.5 mil.
And again, if you're going to calculate the transmission line parameters here you can see the impedance
is very much close to 100 ohm.
Now in the next step you can put the length of the transmission line and change its reference plane
if you want.
So in our case, the reference plane is the nearest plane to bottom layer which is power plane.
So let it be power plane and length.
We are going to simulate for 5000 mil.
Now you can save this trace editor and stack up value.
Just name it stack up for LVDS and save it.
So after setting all this value, you have to just click over this generate element model.
And you can see we have implemented all the changes in trace.
Now after setting all the trace parameters, we have to just connect those to connect driver and trace.
You have to just click over or double click over this driver pin and connect it to a pin of the trace.
And similarly we can connect it to receiver.
Let's do that quickly.
Alright.
Why I'm connecting like this I'll tell you in a few seconds.
So once it is done now in the next step we have to add a termination register at the receiver side.
So to place a register you have to just select Ideal Elements.
Right click and select the register element.
To rotate it.
You have to again right click and click over.
Either you can rotate it left side or right side and place it here.
So as you can see as of now, it is not connected to any pin.
To connect it again you have to follow the same process.
So till now register element is also connected to receiver side.
Now we have to change its value to 100 ohm.
To do that, you have to just select the resistor, go to the Edit Properties section and change it
to 100 and enter.
All right.
So as you can see as of now the topology is ready to simulate.
But before running the simulation we have to add analysis options.
For that you have to just click over set analysis option tab from Workflow or Topology Explorer.
And here you will see three columns.
Data rate number of bits and stimulus pattern.
If you open the data sheet of DDS LVDS 1047, they will find this driver supports up to 0.4 GB data
rate.
So we are going to use the same value here.
As of now and number of bits we can change it to 32 bits.
And for setting the stimulus pattern you have to right click here.
Then left click over define pattern.
Make sure you have selected random from Data Pattern and click over preview.
So these 32 random bits we are going to send over driver differential line and click over okay.
Now in the next step at the receiver side make sure write receiver IO model assigned to write signal
name for example are in one positive should have R in positive receiver model and negative should have
R in minus receiver model.
Now in the next step we need to check the connectivity between transmitter and receiver.
To do that you have to click over check connectivity from Workflow of Topology Explorer and click over
check button.
So as you can see the simulation is ready to use and RX pin two comma one are connected to transmitter
pin or driver pin 910.
Now we can close these menus and we can go for the simulation part.
To simulate this topology, we have to click over Start transient analysis.
Let's click on that.
So as of now we can see three waveforms in this C viewer.
One is for Enable and Enable assist.
We're just going to disable it.
And the other waveform is for R in one plus minus r in one minus.
So this is the output or differential output of received differential signal.
Now to edit the property of this waveform you can just left click over here.
And here you can add the add different styles.
And if you want to add some marker on it you can do that.
And from here you can change the color.
Let's make it red and change the width to two unit and click on okay.
So now this waveform will be like more visible.
Apart from that you can do certain measurements on this one.
Let's suppose I want to measure the rise time and fall time, let's say 10 to 90% of the waveform.
To do that, let's just right click go to measure and click over rise and fall time.
Now here.
So here you will see all the waveform selected from this menu.
And this is the minimum and maximum voltage of this waveform.
And here you can add the percentage.
So when we measure the rise time and fall time for a particular waveform we get two information.
One is what is the rise time or fall time for 10 to 90%.
And what is the rise time and fall time for 20 to 80%.
Now, to do that measurement you have to just click over apply button.
And here you will get the minimum and maximum rise time and fall time for this particular waveform.
Similarly using the markers you can do amplitude measurement.
So we have to just select the vertical voltage measurement.
Okay.
And add these markers at the maximum value.
So from where we'll get peak to peak value of this particular waveform which is 0.671689.
Similarly you can measure the overshoot and undershoot on this waveform.
Now this all the measurement was for receiver output.
Similarly you can do certain measurements for receiver input and driver output.
Because we have added our longer transmission line between driver and receiver.
So we'll see some propagation delay between driver and receiver waveform.
So you can set the marker at a particular voltage.
And from there you will get the delay value.
To do that you have to just select a particular section of the waveform.
Right click go to Measure Difference and this time uncheck vertical.
Now let's set this marker at 1.25V.
And here you can see the clear time difference is 780 5.9 picoseconds.
And you can compare these measurements with the information given on the datasheet.
So this is one kind of waveform measurements.
Or from these measurements we can maintain the signal integrity of the waveform.
There is one more way to measure the signal integrity of the waveform.
And that is eye diagram.
We are going to learn more about eye diagram and jitter in the next video.
So I will add this project in the description.
You can download it.
And to run this simulation you need the free trial of Sigrity Aurora and other security tools.
I have added a link in the description.
You can go there and register for getting the free trial.
And there you can run these simulations.
So see you in the next video.