Tuesday, January 9, 2018

Test and Measurement Metaphors

To prepare for an upcoming sales meeting, I was ask to explain the value proposition of the Tektronix AWG5208.  The question was - why did it accomplish a task for our customer that no competing product could perform?

For those who don't know, an AWG, or Arbitrary Waveform Generator, is like a reverse-oscilloscope.  It takes samples in memory and "plays" them in the real world.  They are very popular for developing new types of signal processing, such as MIMO Radar.  Anything you can dream can be played.  Later, hardware engineers can create a device based on the signals you create.  AWG's are defined by basic specifications like sample rate (highest frequency signal) and dynamic range (or how small of a signal you can create in the presence of a large signal).

Sample rate and high dynamic range are fairly easy to understand, but I was asked, "Why is having 8 channels in one box a value?  Can't you just use 8 signal generators tied together?"

In fact, we often do just that.  To generate 8 radar signals, a customer could use 8 signal generators:

Or you could use 4 two channel AWG's:

Apart from the logistical problem of 8 signal generators, what is wrong with this approach?  In T&M, I often look for a simple metaphor.  So I grabbed this one.  Suppose I want to measure this piece of wood?

But I only have four 12 inch rulers.

I count 3 complete rulers (3x12=36 inches) plus another 8 inches on the last ruler make 44 inches in total.

But suppose I have the correct tool, a tape measure.  That tape measure is like 4 rulers in one.

Now I can easily see that the wooden block is really 45.5", not 44".  Why did using 4 rulers not give me the same result as a single tape measure?

First, there is offset error.  Turns out each ruler doesn't start precisely at 0.  By lining up the wood block with the end of the ruler, I was adding a small amount of error with each 12 inch measurement.  I laid the rulers end to end, compounding the offset error and also creating a synchronization error because each 12 inch section was not the same.  And because the amount of "extra ruler" beyond the digits is different on each ruler, I might get a DIFFERENT measurement if I repeat and line the rulers up in a different order.

Offset error, synchronization error, lack of repeatability - all of these problems plague multiple instruments when they are tied together, whether oscilloscopes or signal generators.  You can try locking references, but you can get high frequency phase problems.  You can also get synchronization errors when executing complex multi-step AWG sequences as one can trigger slightly ahead of the other.

Can I work really hard to make 4 rulers take the place of a tape measure?  Of course!  But what is the fastest, most accurate, and most repeatable way to measure the wood?  With the right tool!

On a side note, 8 channel oscilloscopes are also pretty useful....

Monday, January 8, 2018

Joel Avrunin's Advice for College Hire Job Interviews

In my position managing the US AE team, I have the opportunity to interview engineers at various levels of experience, from new college hires to senior level engineers.  Having conducted more interviews than I can count, there are certain pieces of advice I would like to give to engineers looking for their first job out of school.  My list applies mostly to engineers going into sales, but of course, much of this applies to any job interview.

Main caveat here - I am not a career coach or counselor.  I'm just an employer sharing what I find are best practices in a college interview.
  • Make your resume relevant.
If you are a college hire, that resume should only be 1 page and should contain only things relevant to the job at hand.  Internships, jobs, notable group projects, etc.  If your resume goes to 2 pages, don't go to a small font or make the margins smaller.  Delete delete delete!  Your college admissions counselor cared that you were an Eagle Scout and in the National Honors Society, but frankly, it isn't very relevant to me unless you can work that into the story of why you are well suited for the job.  If you can make being an Eagle Scout into a good story, then by all means include it!  Also, if you have a college degree, I don't need to know where you went to high school.  Every single line of your resume should somehow communicate to me why you'd be good for this job.

By the way, not every piece of experience must be directly relevant as I mentioned with the Eagle Scout.  Work experience such as internships or even unrelated jobs that show your work ethic do count!  One of my favorite interviewees worked at Rite-Aid in college.  Everything on a resume is fair game, so I asked him about it.  He explained all of the roles he played in the store, and kept me occupied as he described the various aspects of the jobs.  He was a good story teller about his experience (a plus in sales), and I knew that the attention he put on a job as seemingly mundane as operating a cash register would mean he'd be effective in a sales engineering job.
  • Ensure your resume is true.
Everything on your resume is fair game to ask about.  I had one candidate write "RF Transmission Line Design" under "Classes".  Most candidates do not list their classes, and frankly I think it is a bad practice.  Especially if you just have a Bachelor's Degree, I don't need to know every class you took.  But since he did, I asked him to define impedance.  He couldn't.  I wrote out Z=sqrt(L/C) and asked him to explain it.  He couldn't.  I explained the whole equation, and then asked if I made a microstrip wider, how would that impact the impedance.  Blank stare.  Finally the candidate said, "I didn't think I had to know this for this job".  I told him, "You wrote you took a class on Transmission Lines on your resume, and this is fairly basic transmission line question.  If you couldn't discuss it, then it shouldn't be on your resume.  What else can't I trust on this resume?"

My favorite new college hire question is about group projects.  Tell me about it.  I then ask further questions on how the project worked.  Or how it could be improved if given more time or resources.  Very quickly I realize the difference between the group leader, and someone who was on the team but didn't do much.  In other words, if you can't discuss a line item multiple levels deep, then don't put it on there.
  • Look up your interviewer on LinkedIn
Especially for sales jobs, you must realize that an interview is a sales call where you are selling yourself.  Look up your interviewer.  First, the interviewer gets an alert when you look at his or her profile.  I am always impressed when a candidate looks me up prior to the interview.  I have only had 3 new college hires do this, and I hired 2 of them.  You can see your interviewers past experience, connections you may share, even personal interests.  If you looked me up, you'd find my blog and see everything you needed to know to have a successful interview with me.  Last week I even posted the answer to my favorite interview question!
  • Research the company on their website and LinkedIn
Spend some time on the company's website learning what they do.  Read some white papers, news articles, etc.  I am always impressed when a candidate has already been on the website.  People want to hire people who want to work for them.  If you put effort into learning about our company, it will reflect favorably on you.
  • Act like you want the job
Continuing on the last point, you are under zero obligation to actually take a job offer.  Therefore, there is no reason to equivocate during the interview.  During the interview, make it clear how much you want to work for my company.  Tell me why you want to work here.  If you decline my offer, you won't be "in trouble" for acting like you really wanted to work here.  If you are a good candidate, I will likely do some of my own selling during the interview.  But the interview is not the time to play hard to get.  If I don't think you really want to work here, I likely won't be too excited about hiring you.
  • Don't drone on and on - answer questions succinctly
I had one manager who, as a rule, did not interrupt people he was interviewing.  I witnessed him do this, and watched a candidate give a great answer in 30 seconds, and spend the next 5 minutes undoing their great answer.  Give the answer and then be quiet and let the interviewer talk.  As an interviewer (especially in phone interviews), it is frustrating when I can't get in a word edgewise.
  • Dress for success
Yes - even for telephone interviews.  Dress nicely, wear shoes, and stand up.  You'll sound so much more energetic over the phone.  I "meet" with customers over the phone, and I always dress as if I am meeting them in person even when I am in my home office.
  • Bring questions and ask them, even if you know the answer already
When I asked you, "What questions do you have for me?", that is actually an interview question.  Better phrased, I could say, "What questions did you prepare to show you are interested in this job and have thought about working here seriously?"  Saying, "I have no questions" is the wrong answer.  Even if you asked your questions to other interviewers, ask them again.  I always leave at least 10 minutes out of a 60 minute interview for questions.  Use those 10 minutes wisely and have questions to ask.  And no - don't ask me how much vacation you get.  The questions should be about the company, the work, our future vision, etc.  Or get personal - ask, "Why do you like working for Tektronix?  What's kept you here so long?"  People like talking about themselves.  I recognize these questions as good sales questions, and I give credit to interviewers who use them.  They are all fair game and show you have a genuine interest in the company.
  • Close - ask if you are right for the job and if not, why not?
If an interview is a sales call where you are selling your services, then you should close the interviewer like a sales person.  Ask the interviewer to tell what your strong points are and where you are weaker.  Ask if you are a good fit.  The interviewer may refuse to tell you, or may share a potential red flag that you can alleviate.  "You seem like a great fit, but I am concerned you've never had any leadership positions."  "Oh?  We didn't discuss my time as college debate team captain.  Let me tell you about that....."  I always give candidates credit for closing me, and the process can allow you one more chance to tell your story.
  • Send a thank you e-mail
This one should be obvious.  Send a quick follow-up thank you e-mail.  Send it immediately because the interview debriefs are often the same day.  Include a few bullet points if you must about why you'd be the best for the role.  But get it sent quickly.

Hope that helps.  And if you are interviewing with me and find this blog, not only have you done your research well, but you'll be ready to nail the interview.

Monday, January 1, 2018

The Why and not the What of Receiver Test

It is important for an engineer in technical sales to be able to explain not just what "what" of test and measurement technology, but the "why".

I use this question in almost all of my interviews now for sales engineers, and it helps me see how well an engineer can explain a concept at a high level.  The conversation goes something like this...

Joel Avrunin: "Many Gen 1 and Gen 2 high speed serial standards only involve transmitter test (TX), requiring an oscilloscope.  Receiver test (RX) is limited or non-existent.  I am an engineering manager putting someone else's silicon into my design, and I am concerned about the cost of test.  So why do Gen 3 standards such as USB3.1 require RX test?"

Here is the wrong answer.

Applicant: "Because it is required by the compliance test."

Joel Avrunin: "But WHY does the compliance test require it?"

Applicant: "To make sure the eye diagram is open at the receiver."

Joel Avrunin: "So I'll use an oscilloscope like I've always done to make sure the eye is open!"

Applicant: "But you can't do that - they are closed eye standards"

Joel Avrunin: "Why are they closed eye standards?"

Applicant: "Because there is too much high frequency insertion loss in the dielectric of the cable, jitter from random noise sources, ISI, and you need to make sure your CTLE is......"

Joel Avrunin: "WHOAH!  Hold on... why can't I just use a better transmitter, higher quality cable, better interconnects, and get an open eye?"

Applicant: "Ummmmmm.... because it's a closed eye standard and the compliance test requires receiver test."

A sales engineer who works for me has to be able to explain the purpose of the test.  We are entering an era where more attention is paid to cost of test than ever.  When budgeting a new project, the cost of buying $1M of new test equipment (or even $100k) looms large over project budgets.  Astute managers see labs full of equipment that was "new" just 5 years ago - why isn't that good enough?  Especially outside the silicon world, receiver tests with products such as the Tektronix BERTScope just were not performed.

Everything the applicant said above was correct.  But nothing there explained why receiver test is required.

Here is the simple answer.

Cost of interconnect.

It drives everything.  Moving a high frequency signal 1mm across a piece of silicon is (relatively) simple.  Moving it from the silicon, through a package, into a PCB, through a via - complex but still (relatively) simple.  But get it to leave the safe world of the PCB and into a flexible cable and you start talking real cost to keep the signal intact.

This is a high quality, precision machined 2.92mm connector.  USB3.1 is a 10GB/s standard, and this is what test and measurement companies like Tektronix suggest you use to qualify your designs.

It has bandwidth to 40GHz+, must be screwed in and torqued with a precision calibrated torque wrench to exactly 8lb-inch (no more, no less).  The cable assembly itself has many layers to transmit the signal with little loss - most of these can cost in excess of $1000 and must be kept with rubber caps on the end to protect the threads of the connector.

We need that because fast data rates require fast edges from 0 to 1 and 1 to 0.  A fast edge is a combination of frequencies.  Fast edges with little jitter or ISI yield clear 1's and 0's (on the left below).  Remove the high frequency content, and the edge slows down.  Slow the edge down enough, and the eye "closes" and the data link fails to transmit data (on the right below).

This is a USB3.1 portable hard drive.  2TB of storage for $50 (as of the end of 2017), and it comes with a cable.  You will likely stick this in the pocket of your cargo pants along with dryer lint and half a Clif Bar you are saving for later.  Yet when you plug it into your computer, you expect to get 10GB/s of data transfer.

How do we pay $50 for the hard drive instead of $1000?

As you see below, the USB connector and cable assembly are not "lab grade".  You can see that instead of 1 shielded and controlled impedance cable with a machined precision connector that is torqued exactly, we have a bundle of wires (shielded, but nowhere near as controlled as the cable assembly above), with a connector that uses pins that pressure-fit onto a PCB in a shield that is stamped and wrapped around the connector.  It is a commercial quality connector, not a lab quality connector.

So how do we keep pushing data rates faster but keep the cost of our devices down?  Better silicon receivers - we keep the magic in the silicon!  That portable hard drive doesn't come with $1000 cable and a torque wrench.  It comes with a $5 cable that you plug in and the silicon inside handles all of the impairment.

Let's revisit the interview:

Joel Avrunin: "I am an engineering manager putting someone else's silicon into my design, and I am concerned about the cost of test.  So why do Gen 3 standards such as USB3.1 or PCIe require RX test?"

Applicant: "We want to move data rates faster than we did in the past, but we need to keep the cost of our interconnects down.  In some cases we have legacy backplanes or CEM connectors that can't be easily upgraded.  In other cases, we need consumer grade cable assemblies.  Receivers need to handle impaired signals, and a BERTScope Receiver test ensures that these faster standards can still be transmitted over lower quality interconnects".

What do you think?  Is there a better answer to this interview question?  Please let me know in the comments section below.