What I Learned this Month

Even though we’ve provided signal integrity training classes for more than 20 years, we are constantly evolving them based on the changing needs of the industry and feedback from our customers, our students.

Our most successful experiment has been the introduction of hands on labs to all of our classes. These are based on three different tools which we’ve arranged to give to all of our students.

QUCS is the easiest to use SPICE-like circuit simulator I’ve ever found. We provide the software and all the lab exercises using this tool.

Mentor’s HyperLynx is the most popular advanced circuit simulator with integrated field solver. Recently Mentor has announced cloud access to HyperLynx. Through special arrangement, we give our students access to their cloud server and the special labs we’ve created that run on this server.

LeCroy’s SI Studio is a powerful signal analyzer which has an S-parameter viewer, a signal synthesizer, a channel simulator and clock recovery algorithms which can implement FFE, DFE and CTLE algorithms. Additional analysis tools can be applied to extract useful parameters from the eye, such as jitter decomposition.

By special arrangement with Mom and Dad at LeCroy, we give a fully licensed version of SI Studio to all students who attend our classes. This software tool has a $5,000 list price.

Starting in 2012, all students to any of our classes will receive:

• A color copy of each slide in the handouts
• An e-book copy of Signal and Power Integrity Simplified viewable on ANY device
• A copy of the QUCS software and the QUCS hands on labs
• Access to the Mentor Graphics cloud server and the HyperLynx hands on labs
• A licensed copy of the LeCroy SI Studio software and the SI Studio hands on labs
• Breakfast, snacks and lunch
• A certificate of completion

Check out the schedule of classes and all the course details on our web site.

Standing room only crowd at Eric Bogatin’s Speed Training Session, photo courtesy of Jeremy Graef.

DesignCon 2012 has come and gone, leaving in its wake a core dump of new and useful information that can be immediately applied to help solve signal integrity problems at the “bleeding edge” of bandwidth and data rate. Over the next few weeks, I will post a series of summary and review columns about what I learned at this DesignCon.

Let me start this series with one of my session, the Speed Training Event, How Return Loss Gets its Ripples. If you want a copy of the slides, you can download them here. If you missed the event, I covered this topic in a recent webinar on Reading S-parameters like a book. You can view the recorded webinar here. 

As an experiment, the speed training event was held on the show floor at the Chip Head Theater. Seating was limited to the first seventy folks, and the crowd spilled over into the aisles.

The theme of this presentation was to illuminate the basic, fundamental mechanism that leads to the ripples in all measured or simulated return loss plots. What is it about the interconnect structures under consideration that cause this distinctive feature, and why do ripples appear sometimes in insertion loss, but not other times?

The punch line is that it is all about the interference between the reflected waves from the ends of the interconnect- wherever there  is an impedance mismatch. In a uniform transmission line, this is usually at the ends of the line, where it connects to the 50 Ohms of the ports.

When the waves reflecting from the front interface and the back interface combine at the receiver, they will either constructively or destructively add together, depending on the total path length.

When the interconnect length is an even multiple of a quarter of a wave, they subtract and there is a minimum of reflected signal. When they are an odd multiple of a quarter of a wave, the reflections from the front of the interconnect and the back of the interconnect add and the reflected signal, the return loss, is a maximum.

The strength of the min and max signals depends on how large the impedance mismatch is, at that frequency.

If return loss and insertion loss are important properties of interconnects for your applications, you might want to check out the S-parameters for SI class I am teaching, now scheduled for Longmont, CO and San Jose CA in the next few months.

Hope to see you there!

Jim Williams in his lab at Linear Tech, with his beloved Tek scopes and assorted breadboards.

I was saddened to learn last year of the passing of Jim Williams. He died on June 10, 2011 of a massive stroke. As a young, impressionable MIT undergraduate physics student, I met Jim, who was working on a slew of exciting instrumentation projects for various groups around the Institute.

Even though it was nearly 40 years ago, I remember so vividly many of the occasions he came to the Molecular Beams Lab or I visited him in his lab in Bld 20.

He used to say that temperature affected everything and had this foot diameter spherical ball of Styrofoam in which he embedded thermistors. We sat and watched slow thermal pulses travel through the sphere as he pulsed a thermistor as a heater and used the others as sensors.

Our lab used Keithley 602 Electrometers, with incredibility high input resistance tubes as the front end, to measure sub pico amps of current. He came to our lab one day with a new electrometer opamp chip (maybe it was from ADI) which we immediately used to build our own electrometers. He demonstrated it by building a 24 hour analog clock, with a simple ammeter dial as the indicator, which charged up a Teflon capacitor through a 10^10 Ohm resistor. He came to our lab just before midnight one night so we could all stand around and watch the clock reset after it reached 24. We cheered!

He worked for a few years with the Nutrition and Food Sciences Dept at MIT, building equipment for them. Once he built a scale that was so sensitive he could stand on it, take a bite out of a donut and measure the weight of the bite. He had to add a low frequency notch filter to take out the heartbeat of the user as the blood flowed up and down the femur arteries, modulating the weight on the scale.

He told me once of a consulting job he picked up at an art museum in Boston. He noticed they had wires connecting each painting in series. He figured it was just a series resistance connection with a sensor looking for an open. He walked into the director’s office, told him he could defeat their system and could show them how to fix it to protect it from this method of attack.

Sure enough, he said he used clip leads on either side of the wires connecting a painting, cut the painting from the leads and took it off the wall without their security system reacting. All he did was add a very sensitive 4-point low resistance Ohm meter to the sensor circuit that could detect a change in resistance of less than 1 milliohm and could tell if a wire were shorted.

When you walked into his lab in bld 20, you would hear a pulsing beat, once every 5 seconds. He had a three foot long Plexiglas tube with speakers at the ends. He sent a pulse down the tube with one speaker, using the other as the sensor, measured the time delay precisely, and then translated this into a speed and then a temperature and displayed the temperature to 0.1 deg F on a 4 digit LED display.

I learned most of what I know about the art of analog design from late night impromptu visits over coffee and donuts. And here I am, almost 40 years later, and still remember the impact he had on so impressionable a newbie physicist-to-be-kid.

Now, more than ever, time is a valuable commodity. Product design is just as much about meeting performance targets and cost targets as schedule targets. This means getting to an acceptable answer quickly is critically important.

This is the focus of the signal integrity classes offered by Bogatin Enterprises. We present not just specific design guidelines but also a design methodology based on identifying the potential signal integrity problems that will come up in all high speed designs, and implementing features which prevent these problems.

The details of our design philosophy and how our training will help you get to the right answer faster, are presented in a new brochure, available for download here. A list of the specific advanced signal integrity classes are also included.

New in 2012, we introduce hands on labs for all the classes, leveraging Mentor Graphics HyperLynx. By special arrangement, we give all registered students access to a cloud server running our specific labs in HyperLynx. These have been specially designed to illustrate and reinforce the design principles introduced in each class.

Also new in 2012, our most popular class, Essential Principles of Signal Integrity (EPSI) has been turned into a 1-day class and offered at a greatly reduced price so that more engineers can get a jump start on eliminating their SI problems.

All of our other classes are advanced, 2-day classes, with specific hands on labs.

All registered students receive, in addition to a copy of the handouts, a pdf copy of all class notes, an e-book version of Signal and Power Integrity- Simplified, a copy of the hands on labs using QUCS and access to the Mentor Cloud server running the HyperLynx hands on labs. Finally, students also receive a licensed copy of LeCroy’s SI Studio.

It is often said, “There are two kinds of engineers, those who have signal integrity problems and those who will.”

With the skills you gain from Bogatin Enterprises classes, you will become a “Signal Integrity Ninjaneer” and beat all of your SI problems into submission.