Hi everyone.
Welcome to Steam Academy.
My name is Avril.
In the previous video we talked about what is an AI diagram and how to construct it by superposition
of bits on a polar channel.
We have seen a couple of simulations as well on Security Topology Explorer.
In this video we will focus on what is an eye mask and how to create an eye mask using the datasheet
of Driver and Receiver ICS.
We will also discuss couple of demos to see how to apply it on security Sci viewer.
So let's get started.
There are so many signaling schemes and interfaces we use to send or receive data, either on single
ended or differential signals.
For example, DTR, HDMI, PCI, EDP, etc..
Now to evaluate signal quality or to confirm that signal meets specific standards, we use a method
called eye mask.
It can be either diamond shape, rectangular or hexagonal, which we can create using sampling time
or setup and hold time.
Minimum input high voltage or maximum input.
Low voltage jitter or distortion.
Accepted skew parameters given on the manufacturer's document, and we apply this eye mask on eye diagram
created using real world scenarios.
Based on that, we got to know the violations on eye pattern and we try to resolve those.
Now let's talk about different information or calculation we need to do to create eye mask.
As you can see in the image we need to find out these values from A to H to create an eye mask.
And very first condition is this complete eye mask should be within one UI or one unit interval.
So in case of single ended signals, or in case of SDR, it should be equal to one clock period.
But in case of DDR it should be either equal to one data period or one strobe period.
Alright, so let me explain these measurements to you in more detail.
Then we will go for the demonstration part on security.
ASI viewer first point that we should remember during calculation or noting down values from manufacturer's
datasheet and that is all measurements apply on eye mask are with respect to center of eye.
For example, if A is equal to 2.5 nanoseconds, then this point will be 2.5 nanoseconds away from the
center of eye mask.
As you can see on the screen.
Now we are good to go for all the formulas and measurement.
So first one is h is equal to t clock.
Or we can say t data period which will be equal to one unit interval where t clock is clock period in
this case.
Second one is O is equal to t clock by two plus t square.
Now this is very useful information here skew is skew between two buses.
Third point calculation can be done using OB is equal to rise time plus t setup plus t squared.
And here t setup is setup time that you will get with respect to clock.
Now fourth point which is OC is equal to OD is equal to t setup plus t by two plus t squared.
Here T is timing jitter that will get from the datasheet.
All right so this was left half of I mask.
Now we have to calculate right half point of I mask.
So first point is O is equal to O f is equal to t plus t jitter minus t skew.
Now from these formulas we got to know that we are adjusting or shifting.
I mask toward left side because on the left side we have added t skew, and on the right side we are
subtracting t skew.
So it is just to compensate time difference between I mask and I.
Alright, let's move to another point.
Next point is OG is equal to t hold plus four time minus t skew.
Now here.
The point is why I have.
I have not considered t jitter because in most of the cases Is when we create an eye mask.
We consider it as an ideal eye diagram.
All right.
And in that case, we are considering that t is almost equal to zero.
But if it is mentioned on the data sheet the acceptable t jitter we have to add it here as well.
And last point will be O which will be t minus t clock by two plus q.
So it is nothing just the subtraction of left part of the eye mask.
So using this equation we will get all the points on eye mask and apply them on eye diagram to validate
the pattern and find out violations.
Now before moving to the demonstration part here, I will conclude we need to get these values to create
an eye mask from manufacturer, datasheet or other documents.
And first one is clock rise time and fall time T jitter and setup and hold time.
If we have these six values we can able to create eye mask.
Apart from these timing information we also need some voltage information from manufacturer's Data sheet.
And that is output high voltage and output low voltage.
We also represent these voltages with vo min and vol max.
So in case of our topology which is a synchronized LVDS signal of 400mbps.
We have noted down all these values from the manufacturer's data sheet.
So in our case t clock will be one upon 400 Mbps, which will be 2.5 nanoseconds.
Set up and hold time.
Rise time.
Fall time.
Skew and jitter.
As mentioned on the data sheet, we are considering it almost negligible or zero.
The voltage values that we should note down from the data sheet is V common, which is 1.2V for LVDS
because we are following Ansi standard vo min is V common mode plus 100 volt and vol is V common mode
-100 Millivolt.
Now when we apply these values on the formulas that we have discussed on previous slide.
We got all these points from A to H.
And in the next step we are going to put these values on security topology explorers.
C viewer and implement I mask over I diagram.
So let's do that.
So let's open Topology Explorer and run the transient analysis and plot for I diagram.
Once the I diagram is there now we have to define the I mask.
To do that you have to click over mask and click on define button.
Let's delete this previous one.
And we are going to create a new mask.
Let's name it LVDS Synchronized channel.
And this will be a hexagonal mask.
Similarly you can plot for rectangular and diamond.
Now for hexagonal mask we have to put all these values that we have created in previous step.
So this will be point B, point C and point D, point E and point f and point g.
So we have to add all these values with respect to this center.
All right.
So let's put those values quickly.
So as you can see we have added all the time and voltages values for common mode voltage.
We have added 1.2V which is swinging around plus -100 millivolt.
So in the next step I'm just going to save this mask and click on okay.
So as you can see we have applied the eye mask here.
And here we can clearly see the violation of eye mask on the receiver waveform.
So this is happening because the driver waveform is also not that much clean because we are operating
at maximum data rate.
So I will attach this project in the description.
You can download it from that link.
And I would suggest just play along with the driver specification, change the data rate, play with
the termination resistors and try to minimize this violation.
So that's it about eye mask and how to implement it on security Topology explorer and C viewer.
See you in the next video.