The Basics on Signal Integrity

hello my name is Mike reso and I’m a signal integrity application scientist for keysight technologies in the internet infrastructure group I’d like to invite you to watch this snippet of our keysight educational forum that we did in santa clara for design con and we’re going to be showing snippet that preludes a full 40 minutes seminar and I wanted to mention the title of this is practical signal integrity analysis box simulation and measurement and so we have some nice basic foundational signal integrity topics and then we’re going to delve into some more advanced analysis for Hardware measurements and how to correlate to simulation and if you’re interested follow the link and go watch the whole 40 minute video and happy signal integrity thank you signal integrity is about the problems interconnects introduced and how to avoid them first we’ll have to understand signal integrity with a case that eat a failing virtual Channel I’ll talk about the three steps to solving any signal integrity problems when number one simulate the channel number two find the root cause like Eric said and number three explore design solutions here’s a via structure that I simulated it actually caused some transmission lines and let me tell you why if I take a look at this stub over here it’s about 75 mils right do the math given the date array and Nyquist I’m taking the five times as the bandwidth and the wavelength using six inch per nanosecond as the propagation fr4 our wavelength wavelength is about 75 mils what does that mean that means that entire wavelength is gonna fit in to that stop and by definition when the voltage and current is changing with a physical length that is definition of the transmission line now finally after we understand the root cause we can explore the design solution solution 1 or if the stub is a problem hey just throw it away we’ll just remove this stuff and that’s let’s see what it does right now on the Left we have the stub ice close and we take away the stuff I should be open and here we go the ice is open so we know now again for sure the stubs are the problem I’m solution number two what can add Equalization that’s fine right but if I’m doing decision feedback equalizer ssin well how many times why do I need that’s the frequent question that that we get right we do not know how many steps but here is another thing that would help us single pulse response we’ll be able to identify the number of tabs we need by looking at the single pulse response and ensure Singapore’s response is when we send a single pulse on the input with specific writes time and data rate and on the outside comes the single host response and if we carefully mark the single pulse response as such I name the maximum the cursor given one unit interval I separate them and the peak one I’ll call the cursor whatever is happening before the cursor is the precursor whatever I whatever is happening called the post cursor I’ll be able to identify number of precursors and post courses I need to do Equalization good now I’m gonna let Mike do a rapid testing example of plcs good morning first I have to apologize for my voice you can just imagine you’re getting a demo from the Godfather so we we tested a PCI 5 device and this to of physical layer test systems we have two input and two output so it was a four port via a measurement okay so we got a s4p file and so I’m gonna open up that file and this is this is the file here and you can look up the data in many different ways Multi domain analysis is possible time domain frequency domain eye diagrams are LCG or you can actually build a template that has multiple domains in one view and this is what we have here and so the s parameters are used as the base file and then we extract all of the different

domains and as you can see from from just one s-parameter measurement you can get eye diagrams you can get frequency domain information here is the insertion loss overlaid on the return loss and you can drop a marker and start trying to find things like the half power band width of your system so if you want to move a marker to the 3 DB point you can see that you’ve got about 4 gigahertz bandwidth inside this and likewise you can look at domain data when you auto scale you can look at the impedance profile both forward and reverse and there’s also some interesting playing ground that you have in this environment of course the the TDR is like a step response right you launch a very fast edge into your device under test and you look at reflections right so but you can also differentiate that and PRTs will warn you well okay you can’t use impedance to do the impulse response but that’s okay but you can look at the impulse using the same exact data and so here now you have the impulse response okay so after we found out that this standard eye diagram failed the original specification we said well let’s see what happens when we do emphasis pre emphasis or post emphasis and so here we added some F IR taps it was to post cursors and you can see the I opened up nicely so this is multi channel simulation built into P LTS now it’s not as powerful of a simulation engine as abs abs does everything active components passive components very powerful there’s pretty much this tool will focus on the passive interconnect what does that mean that planes PCBs cables connectors things like that and then likewise you can come in here and apply D F V also and see how much more it opens up so so using the two tools simulation and measurement you can import touchstone files city files and export back and forth between these two platforms and and that is really what we’re trying to do today with our hyper scale network infrastructure for the Internet we have to look at more ways to look at the data from different domains when we troubleshoot so measurements simulation and doing multi domain analysis will help solve design problems so I’m not gonna punish you anymore with listening to me so I’m gonna say at this point my co-author Tim and also thank you for coming this morning you