The Getting Started Guide for New Subscriber to the Signal Integrity Academy


First of all, congratulations on your personal or corporate subscription to the Signal Integrity Academy. If you are not sure if your company has a corporate subscription, it’s easy to check. Click on this link and enter your email (with your company domain) in the box on our web site:


Click the Subscription Check box. If your company has a corporate subscription, a new dialog box opens up with a link to follow to create your  account.


If you don’t see this invitation, talk to one of your managers about starting up a corporate subscription or consider purchasing a personal subscription. For less than 1/3 the registration price of a live class, you can view ALL the class content from six different courses I teach plus get soft copies of all the slides and download all the files to run all the hands on labs, all from the convenience of your desk.

While your subscription is current, you can view all the additional content I add through the year. And, you can ask any technical question about any lesson and I respond within a few days. It’s a pretty sweet deal.

If you are a new subscriber, follow the steps from the link above to enter your contact info. Here is where you will create a password. It is case sensitive. We use your email address as your user ID.

When you hit the last continue button, our site will send you an email to the address you entered. When you get this email, just click on the confirmation link and your account is set up and you are ready to go.

Come back to the Signal Integrity Academy and log in to then access all the lessons. There are three ways of logging in:

  • click on the subscriber log-in button on the very upper right of the web page
  • click on the big blue subscribe now button on the home page and enter your email in the subscription check box. If you have an account set up, you will be given a link to log in.
  • click on any of the lessons to open it up and you will see the subscribers click here to log in button:


Now you can click on any of the six courses which opens their landing page and view any lesson that looks interesting for you.

Now you are ready to Get The Most Out of the Signal Integrity Academy. Read this post.


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Check out Eric’s Latest publication, Synthesis of High Speed Channels from Shorter Elements


In my latest article in the May 2017 issue of IEEE Electromagnetic Compatibility Magazine, my former student, Karthik Radhakrishna, and I describe a simple process using an open source tool to concatenate S-parameter elements.

S-parameters are often called a behavioral model for interconnects. They describe everything there is to know about the electrical properties of an interconnect. A complex channel is often constructed of many individual components. When simulating a channel. we get models for each of these elements from different sources, 2D field solvers, 3D field solver, measurements, or even vendors.

How do we build a single, composite S-parameter model from all these different  models? S-parameters, by themselves, do not cascade together.

This articles explains the details of how to build a single composite S-parameter model, and how to evaluate if you have it correct.  You can access a copy from here.

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Video Interview With Eric At DesignCon 2017

When I was at DesignCon in January, 2017, I was interviewed by my friends at Sierra Circuits. This has become a tradition and is the third time I did extensive interviews with them.

They just posted this recent interview and I thought others might be interested in watching it. You can click here to view it:

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Download Your Copy of the PDN Resonance Calculator Spreadsheet

In the recently released book Larry Smith and I wrote, Principles of Power Integrity- Simplified, we offered a spreadsheet to go along with the book, especially the last chapter. You can download your copy of it by clicking here.

We advocate first doing analysis based on simple estimates using rules of thumb, then explore design space using analytical approximations and spreadsheets. Finally, to fill in the details, use a simulation tool.

This is the only real way of practicing safe simulation, which is really about applying rule #9. If you ever encounter one of my students, ask them what rule #9 is and they should immediately say, “Never do a measurement or simulation without first anticipating what you expect to see.” It’s by applying your engineering judgement based on rules of thumb and approximations that you know what to expect to see.

If my student does not give you the correct answer, please let me know and I will get into their University records and retroactively change their grade.

One of the principles we wanted to highlight in our book is how powerful simple models are in accurately predicting performance. You can often answer many of the bog picture questions using simple approximations. When design decisions interact, a spreadsheet is an invaluable tool to explore the tradeoffs.

Larry put together this very cool spreadsheet to take into account how the three typical resonances in a PDN might interact- the Bandini Mountain, the board caps and bulk cap parallel resonance and the VRM and bulk cap parallel resonance.

There’s a lot more to it as well, including the mounting inductance of the capacitors and the package based on their geometry.

It probably won’t mean much without the details outlined on chapter 10 which acts as sort of the user manual and shows a few examples of  using this spreadsheet to evaluate a design.  But, you can download the spreadsheet and if it tweaks your interest, go ahead and purchase the book. In the pdf version, all the figures are in color. I think you will find a few valuable nuggets that will help you in your next PDN design.

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Principles of Power Integrity–Simplified, Released!

The latest textbook I wrote with colleague Larry Smith, Principles of Power Integrity- Simplified, has just hit the streets. You can pick it up directly from Prentice Hall at their InformIT web site. While the hard cover version is in black and white, the pdf version is in color.

If you care about PDN design, this is the book for you.

I’ve known Larry Smith for many years. He was always one of my goto experts when it came to power integrity topics. I followed his work at IBM, then had a chance to work with him when we were both at Sun Microsystems, and then would correspond with him after he moved to Altera.

We met up at DesignCon 2009 after attending a panel discussion on power integrity. We walked out of the room shaking our heads after listening to the very naïve and confused questions from the audience.

Larry and I happened to walk out of the room and into the hallway together and remarked on how much confusion there was in the industry about power integrity.  This is not to say there aren’t plenty of experts already in the field, writing excellent papers and giving incredibly valuable talks, such as Istvan Novak, Scott Mc Morrow, Steve Sandler and the late, great Steve Weir, to name just a few.

It’s just that there were a lot of engineers who didn’t know about their work, or didn’t pay attention, or didn’t understand what they were saying.

Larry blurted out, “We should write a book together about PDN design.”  I think he meant it as a comment about the industry, and not a serious proposal.

But, as soon as he said it out loud, we looked at each other in astonishment and both said at the same time, “What a great idea!”

My latest textbook, the second edition of Signal and Power Integrity- Simplified had just come out and was becoming very popular. Some of the early reviews were pretty good. I was looking for my next textbook topic.

We ran off to a corner and spent an hour brainstorming ideas, missing our next talks. Between the two of us, we had different perspectives on the topic, different skill sets that complemented each other but the same drive to get it done, and get it done in a way we thought would be right.

With our enthusiasm still peaked, I dragged Larry over to the Prentice Hall Booth on the DesignCon show floor and we pitched the idea to my publisher, Bernard Goodwin. He was as excited as we were and signed us up with a book contract on the spot.

When he asked us how long it would take, I was about to say, “Oh we can do it in a year.” But I caught  myself and applied by standard factor of 2 increase to the estimate from what I realistically thought I could do. “Two years from now,” I said.  Both Larry and I thought this was very realistic. Boy, were we way off!

Over the next seven years, Larry and I meet by goto meeting every Thursday morning for up to 2 hours going over outlines, drafts and simulations. Some weeks, we would spend the whole two hours on the phone arguing over one little detail that we each had different, equally strong opinions about and could not reconcile.

What a pleasure it is working with a professional who puts science and engineering first and ego way in the back. Every debate ended in a resolution based on the evidence and good solid engineering or physics. One of us always ended up convincing the other he was right. Larry usually won the debates, but we both saw how much we learned from the process.

Each chapter went through multiple re-writes, sometimes whole sections thrown out or changed based on our new perspectives. We sent out the first five chapters to industry experts for review and bit our finger nails for their input to come back. Some of the very insightful comments were rather devastating, while others gave us relief that maybe we did understand at least some of these important design principles.

After 500 hours of conference calls, 5,00o hours of writing and editing and simulating, for each of us, three house and two job moves between us, a dozen in person day-long review and debate sessions, and three editors at Pearson Publishing House, the mother company of Prentice Hall, we had the first copies of the hardback book in our hands. And now you can to.

ps: Check out the dedication. When you get a chance, ask Susan or Marty about it. But be warned, you will get an earful.

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Only an Engineer Will Understand the Knack


You’re an engineer if…

You see a problem and your fingers itch to fix it.

You see a finely working machine and you think about how you could make one even better.

You have ever used a paperclip, a coat hanger and duct tape for other than clipping paper, hanging things and taping ducts.

If the sales people at Best Buy can’t answer your questions about the computer you want to buy.

If you think the real heroes of Apollo 13 were the mission controllers who figured out a solution to the Co2 filter with duct tape and file folders.

If, when you were a kid, you were diagnosed with “the knack.”

Note sure what the knack is, watch this video:

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Words Matter in Engineering


I think a significant reason why some aspects of engineering are so confusing to many is because we get sloppy with the words we use. Changing our habits will make us all less confusing and increase the signal to noise ratio in the industry.

Here are six examples of terms we use all the time, yet they inspire confusion and shaking of heads when casually dropped. The same word means different things to different folks. Let’s take a look at some of the qualifiers we should get in the habit of using. When we hear or see these words, don’t hesitate to ask for clarification.

Let’s look at “bandwidth”, “impedance of an interconnect”, “inductance”, “ground”, “speed”, and “insertion and return loss”.


Generally, bandwidth relates to the highest sine-wave frequency component that is significant. The confusion stems from what do we mean by “significant” and that bandwidth can refer to a signal, an interconnect, a measurement, and a model.

Bandwidth of a signal: The highest sine-wave frequency component in the signal, compared to an equivalent ideal square wave; usually the frequency at which the amplitude is below -3 dB of the square wave’s amplitude. Related to the rise time in the signal. To relate the bandwidth of a clock frequency, we are really making an assumption about the rise time of the clock signal.

Bandwidth of an interconnect: The highest sine-wave frequency that can be transmitted down the interconnect with acceptable attenuation. This is so dependent on the spec of what is acceptable. It is less ambiguous to refer to the -3 dB bandwidth of the interconnect, or the -10 dB bandwidth. This is unambiguous.

Bandwidth of a measurement: The highest sine-wave frequency component that is contained in the measurement. Easy to define for a frequency domain measurement, ambiguous for a time domain measurement. We usually define the -3 dB bandwidth of a measurement system as the frequency at which the measured frequency component is reduced to -3 dB of the input signal.

Bandwidth of a model: The highest sine wave frequency where the predictions of the model still match the actual measured response of the structure being modeled. How good the match is is very vague. Usually it is when the plotted simulation response is a few pen widths off from the measured response.

Impedance of an interconnect

Generally, impedance is always the ratio of a voltage to a current. But there are four different types of impedance relating to an interconnect.

Input impedance in the frequency domain: This is the impedance, at each frequency, looking between the signal and return connections at the front of the interconnect. At each frequency, the input impedance is about the total, complete, integrated effects from the entire interconnect including how it is terminated at the end. For an open transmission line, will look capacitive at low frequency and show the resonances of a typical transmission line.

Input impedance in the time domain: This is based on what a TDR might record. The initial input impedance will be the characteristic impedance, or a uniform transmission line, but only for a time less than the round trip time. After this time, there may be reflections which cause the input impedance to vary widely, ending up eventually at the impedance of the far end termination.

Instantaneous impedance of the transmission line: the impedance a signal will see each step along the way as it propagates down the transmission line. Will be constant if the cross section of the line is constant.

Characteristic impedance: Only applied to a uniform transmission line and is the one value of instantaneous impedance a signal will see on the transmission line. The one value of instantaneous impedance “characterizes” the transmission line.


Generally, inductance is the number of magnetic field line rings surrounding a conductor per amp of current through the inductor. It is a property of the geometry of the conductors.

Loop-self-inductance: Refers to a conductor in a complete loop, as the total number of rings of magnetic field lines around the conductor per amp of current in that loop.

Loop-mutual-inductance: Refers to two conductors each as complete loops, as the total number of rings of magnetic field lines around one conductor produced by the current in the other conductor, per amp of current.

Partial-self inductance: The number of rings of magnetic field lines around a part of a loop, per amp of current in that loop. Cannot be directly measured, but can be calculated mathematically.

Partial-mutual inductance: The number of rings of magnetic field lines around a part of a loop, per amp of current through another part of the loop. Cannot be directly measured, but can be calculated mathematically.

Total inductance: the total number of rings of magnetic field lines around a part of a loop from all the currents contributing magnetic field lines, usually the partial self-inductance of the section, minus the partial mutual to all other parts of the loop. Can be measured from the voltage generated from a dI/dt through the section of conductor.


Generally a specific conductor identified in a system based on how it is used.

Circuit ground. Generally, the circuit nodes or terminals which are the lowest voltage point in a unipolar supplied circuit, or the mid voltage point in a bipolar power supplied circuit. It is from this conductor that the voltage on other nodes is measured relative to. Other than being the reference conductor, there is nothing special about the circuit ground.

Digital ground. Usually the circuit ground conductor which is the return path for the digital signals. The return path can also be a conductor with a DC voltage on it.

Analog ground. Usually the circuit ground conductor which is the return path for analog signals. Other than extreme cases where fractions of a mV DC drop are important, analog and digital ground can be the same conductor if a continuous plane is used. The return currents will remain separate in the plane, following the location of the signal line. The idea of separating analog and digital ground applies when the return path is not a plane, like leads in a connector or pins in a package. In these cases, ground bounce from digital signals can create huge cross talk on the analog signals.

Chassis ground. This is the metal housing associated with the product. It often provides shielding to reduce EMI. It also acts as a safety shield to product any user who might touch the chassis. Cable shields should be connected to the chassis ground in order to reduce common currents on the shield. In this case, the cable shield becomes an extenuation of the chassis. Usually the circuit ground of the board is connected to the chassis ground at one point. If multiple points are used, there may be some low frequency return currents flowing in the chassis. Of course, if the enclosure is plastic, there is no chassis ground.

Earth ground. This is the connection that ultimately leads to a copper rod driven into the ground (literally) to provide a reference voltage throughout a house or building. This is a safety issue required by some building codes. The round hole in an AC outlet is connected to this copper rod. UL requires that chassis ground be connected to earth ground as a safety feature. Ground fault interrupter (GFI) sockets are designed to disconnect power to a device if more than a few micro amps of current from the low side of the power mains flows through the earth ground connection. Of course, a car, satellite or other portable device has no connection to earth ground.


The speed of a signal is the most confusing term as it is used in two completely different contexts. Speed is generally related to the velocity of the signal. But it is also used to refer to the rate of data transfer.

Speed of light in air: about 1 foot per nsec, 12 inches/nsec, or 30 cm/nsec

Speed of light in most laminates. Since the Dk of most laminates is about 4, the speed of a signal in the laminate is about 6 inches/nsec or 15 cm/nsec

Speed of electrons in a conductor. Even in the extreme of cases, the speed of an electron in a copper wire is about 1 cm/sec, the speed of an ant. It has nothing to do with the speed at which an electric and magnetic field will propagate in a transmission line.

The clock frequency of a system: The frequency, usually in MHz, of the repetitive reference signal to synchronize system operations. The clock frequency of many high end microprocessors has increased over the last 30 years from 16 MHz. to 2.5 GHz.

The Nyquist frequency of a serial link signal: This is the frequency of the underlying clock of a serial link signal. It is the clock frequency when the data transition rate is the highest, 10101010101. This looks like a square wave and its frequency is the Nyquist. Since there are two bits per clock cycle, Double Data Rate (DDR), the Nyquist frequency is half the data rate. A 10 Gbps NRZ (non-return to zero) data pattern has a Nyquist of 5 GHz. The Nyquist and the encoding scheme, determine the maximum rate of data transmission in the channel, or the channel capacity.

The data rate of a serial link: The rate at which the data is transmitted as bits per second. In an NRZ pattern, with just two voltage levels for the signal, referred to as PAM2, each clock cycle has 2 bits of information encoded on it. The channel capacity for the data rate is twice the Nyquist frequency. If the Nyquist is 5 GHz, the data rate is 10 Gbps.

The baud rate. We often refer to the data content in a signal as the data payload. When an encoding scheme uses extra bits to carry routing information or synchronization information, not all the bits are payload data. We use the term baud rate to refer to the rate at which symbol transitions are transmitted. A symbol is the smallest unit of modulation. The data rate of Ethernet may be 10 Gbps but with a small percentage of the possible symbols being non-payload data, the actual transmission rate of symbols, the baud rate,  is 10.3125 Gbps.

Insertion and return loss

These are throwback terms from the old days of how microwave measurements used to be performed. Two halves of a well matched fixture were measured separated and when connected together. When the device is inserted, the reflected signal and transmitted signal is measured.

The return loss is the loss in the returned signal of the open when the DUT is inserted. When open, all the signal returns. When the DUT is inserted, the better the match in the fixture, the less energy is returned; there is a large return loss, compared to an open. The larger the loss in the returned signal, compared to when the fixtures were open, the better the match.

The insertion loss is the ratio of the power received when the fixture is connected, compared with when the DUT is inserted. The less energy coming through the DUT, the more the insertion loss.

In both cases, the loss is defined as a positive dB value. The larger the value, the more loss. A large insertion loss means we lost a lot of signal when we inserted the DUT- not much gets through, not much is reflecting.

When we measure the S11 or S21 values of an interconnect, the magnitudes, in dB, are always negative for passive elements. Yet, we get in the habit of calling them return and insertion loss. To avoid the sign confusion, the industry is migrating to accepting return and insertion loss as either positive or negative.

The following terms apply to a uniform 2-port interconnect.

S11: the S-parameter = the reflection coefficient. The magnitude of S11, in dB, is the return loss, either as a positive or negative dB value. Referring to S11 as the reflection coefficient is unambiguous.

S21: the S-parameter = the transmission coefficient. The magnitude of S21, in dB, is the insertion loss, either as a positive or negative dB value. Referring to S21 as the transmission coefficient is unambiguous.

Attenuation = the attenuation in an interconnect, usually expressed in dB. It is usually a positive value. Larger values of attenuation in dB means more signal loss. Attenuation = -S21 in dB for a matched interconnect

Attenuation per length = dB/in or dB/m as a positive value.

These are just a few examples I encounter all the time. If we are not careful when we use these terms we leave confusion in our wake. Get in the habit of adding the qualifiers and it will help us communicate and think more clearly. Ultimately, we reduce the entropy in the universe and increase the signal to noise ratio in the industry.

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Why do Microwave Ovens Operate at 2.45 GHz?

Image result for microwave oven popcorn

I get this question all the time when we discuss dielectric loss in my classes. The common answer I get back is that this is the frequency for the resonance of a water molecule. It would make it the ideal frequency to run the oven so we get the most absorption.

But not always is the obvious answer the correct answer.

After all, is it a coincidence that 2.45 GHz is also the same frequency as 802.11ab wifi, the same as Bluetooth, and the Nyquist for PCIe gen 2, operating at 5 Gbps?

The use of 2.45 GHz is because this is in the center of the unlicensed ISM band of the FCC.  One of the frequency bands of the Industrial, Scientific and Medical (ISM) bands is from 2.4 GHz to 2.5 GHz. This band is reserved for non telecommunications applications and does not require an FCC certification of compliance.

If you use this band for communications, buyer beware. Your protocol must be robust to interference and the FCC will not help patrol emissions in this frequency range.

If microwave ovens use this band so they don’t have to be certified by the FCC, how is it related to heating water?

The frequency of 2.45 GHz is a wavelength in air of 122 mm or 12.2 cm. When we look at the absorption spectrum of liquid water, the frequency is usually reported as the wavelength, instead.

This low frequency is well below the energy of vibration bands, and is more related to the loose, rather “fluid” lattice of the water molecules, smeared out due to fluctuating hydrogen bonding.  Here is a typical absorption curve for liquid water, from 0 degC to 100 degC. There is a broad peak in the dissipation factor, around 3 cm which increases in frequency as temperature goes up.

Note that 12.2 cm, the wavelength of the microwave oven, is the black line. At 0 decC, the absorption of liquid water, the blue curve that is a measure of the dissipation factor, is actually sitting on the tail of the peak. It’s a very broad peak. As the water heats up, the absorption peak actually moves to higher frequency, shorter wavelength and the absorption for water actually gets worse.

The broad absorption by water, in the frequency range from 1 GHz to 100 GHz, is an important issue. This says that as an interconnect polymer absorbs water from the humidity in the air, we would expect the losses in the material to increase. This is why the humidity sensitivity to the dielectric loss of a laminate material is an important metric.

But why a microwave oven works at 2.45 GHz is more about the FCC than about the absorption resonance of water.

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Really Cool Signal Chart For Download


Every signal integrity engineer should be bilingual- able to speak in both the time domain and the frequency domain. This applies to signals and to the electrical properties of interconnects.

The basis of translating between the time domain and the frequency domain is the FFT and inverse FFT. If you have not done so, you should sit down and calculate the FFT of an ideal square wave in the time domain to see what its spectrum is in the frequency domain. After you do one by hand and see the underlying principles, its not important to do others by hand. Instead, you can use various simulation tools.

As a review, Teledyne LeCroy has put together a  handy little chart with a dozen time domain waveforms and what they look like in the frequency domain, as an amplitude histogram, and as an autocorrelation. You can download this simple chart here.

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Last 6 Columns by Eric on the Signal Integrity Journal Site

If you missed them, here is a list of the monthly columns I’ve written for the new Signal Integrity Journal. To get on the mailing list and get notification of new content on the journal’s site, click here.

DesignCon 2017 a cornucopia of information

Pop Quiz: When is an interconnect not a transmission line?

When Worlds Collide: Why RF Design is Very Different from High-Speed Digital Design

Six Cool things I saw at EDI CON 2016

Best Practices for Connector Models

Dispersion in Microstrip, Should I Care?

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My Rules for New Graduate Students

Image result for scroll rulesI am tired of telling my new graduate students the same things over and over again, so I wrote up the most important ones in a list, posted on the Signal Integrity Academy web site, for anyone to download.

There are currently 43 in the list and I reserve the right to add to them as I see needed.

I won’t repeat all of them here, but will mention a few of the ones I find the most important, especially as it relates to lab reports, or doing measurement or simulations.

9. Never perform a measurement or simulation without first anticipating the results you expect to see. Never believe a measurement or simulation blindly. If it doesn’t match what you expect, there is a reason for it. Either there is something wrong in the setup of the tool, or maybe your intuition is off, in which case this is an opportunity to re-calibrate your engineering intuition and move up the learning curve. Do not proceed with the result unless you can convince yourself it is reasonable.

10. Corollary to Rule #9: It is easy to perform a measurement or simulation. It is hard to eliminate errors and artifacts. There are so many ways a measurement or simulation can go wrong, you can never perform enough consistency tests. If you think you know why a result looks the way it does then ask, what else might be the case? Look for it to confirm you know what is going on and the measurement or simulation is consistent with the way you think the system should operate.

22. Never use auto scale on a plot. The only acceptable time is when you are taking a first look at the data and it does not come out on the scale you expected it to fit on. The purpose of a plot is to show patterns which can be immediately and easily interpreted by your engineering intuition. It should be displayed on a rational scale in units you can use to evaluate the quality of the result, and feed your engineering intuition. Use scales that are easy to use to get a “feel for the numbers.”

32. Never use a feature or function in a tool unless you know what it is really doing. No tool, measurement or simulation, is ideal. There are always hidden assumptions about what it is really measuring or calculating, written by an engineer no smarter than you. Always be aware of what the tool is actually doing to convert the result to what is displayed.

33. Often times, the documentation in a tool- simulator or instrument- is incomplete. You may have to spend appreciable time “reverse engineering” the tool in order to understand what it is really doing. Thinking of consistency tests you can do to confirm the tool is doing what you think it is, can be a very good investment of time. Always challenge the results of a tool. 

The corollary is, when using a tool or feature for the first time, ALWAYS run a problem for which you already know the answer. This way you know what to expect and can easily determine if the tool or feature is not giving you the answer you expect. If you don’t know what to expect, how can you evaluate the result?

39.Question authority. Just because someone says they are an expert doesn’t mean you have to believe everything they tell you. If it doesn’t sound right, it may not be. Become your own expert by tracing back the reasoning behind every statement to something you have high confidence in.

If you liked these, check out the whole list here.

Got one of your own not on my list, add a comment below.

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