Tag Archives: Analog

Amp Hours of Aural Entertainment

Just this week I was in a conversation with someone and I found myself saying “Hey The Amp Hour interviewed someone in that field!” only kill the flow of the conversation with Google searching for the episode. Turns out it was Episode 71 with John Edmond of Cree.

I started listening to The Amp Hour way back when the number of episodes could be counted your fingers in decimal, not binary. Since then I remember the gist of a lot of shows but I haven’t gone back and replayed too many which is a shame since Chris and Dave have done a lot of really cool interviews as the show has grown. After that conversation I figured if I can go back and reread books at any point why not do the same with podcasts? So that’s my aim for the short-term, re-listen to some of the interviews that have stuck with me over the years. It will shock no one that a lot, but not all, of them are analog focused.

#54 – An Interview with Jack Ganssle – Embedded Elchee Epexegesis

#60 – An Interview with Joe Grand – Pancyclopaedic Prototyping Polymath

#71 – An Interview with John Edmond – Luciferous LED Lucubrator

#77 – An Interview with Dr. Howard Johnson – Winsome Waveform Wizardry

#84 – An Interview with Bunnie Huang – Bunnie’s Bibelot Bonification

#95 – An Interview with Øyvind Janbu – Feracious Fabless Facilitator

#115 – An Interview with Dr Greg Charvat – Watcher of Wraithlike Walls

#117 – Interview with Alan Wolke – Undulating Utensil Utility

#119 – An Interview with Dr. Kent Lundberg – Luculent Linear Legacy

#129 – An Interview with Brett Fox and Dr Jeroen Fonderie – Device Doubling Decretum

#133 – An Interview with Ron Quan – Tenacious Transistor Teacher

#135 – An Interview with Mike Harrison – X-ray Examining Xenogogue

#144 – An Interview with Bob Davidson – Hoodied HP Hijinks

#157 – An Interview with the SparkFun Team – Efficacious Engineering Ensemble

#165 – An Interview with Henry Ott – Forced FCC Filtering

#171 – An Interview with Forrest Mims – Snell Solisequious Scientist

#180 – An Interview with Dave Taylor – Multi-talented Meter Maker

#181 – An Interview with Dave Vandenbout – Xceptional XESS Xenagogue

#187 – An Interview with Elecia White – Wirewove Worshipping Wookieist?

#196 – An Interview with Mike Engelhardt – SPICE Simulator Synteresis

Assuming I’m doing routine tasks at work that don’t require me to be in full on troubleshooting mode I should be able to keep occupied for a few weeks at least. If anyone can think of a good interview I forgot or just wants to share their favorite interview with me I’ll be happy to add it to the list! Also, I’d like to somehow bundle all these files into one convenient download for whoever wants them but I don’t know how to go about doing that easily unfortunately. Please clue me in if you could be so kind.

Update: Dave pointed out to me that I could always just use The Amp Hour App to easily find the shows I’m looking for. Doh! I’d forgotten all about that. Check it out and support the show!


Circuit Notes – Part 1

The other week I impulse bought a bunch of Field Notes notebooks under the justification that they were a birthday gift to myself. I’ve been carrying a small pocket notebook on me for at least a year now so the regulator sized Field Notes won’t be stuffed in a drawer somewhere and forgotten but I also broke down and ordered a pack of the new limited release Arts & Sciences books too and needed a good use for them. They’re beautiful notebooks and I definitely recommend picking up a pack or two while you still can.

After brainstorming a bit I got the idea of using them to compose a circuit reference for myself. I seem to find my self deriving the same formulas over and over again at work so putting them all in one place where I can easily look back on them made the most sense. In order to keep this site from stagnating I figured I may as well also share them with whoever wants them. The Arts and Sciences books are the perfect size (7.5″ x 4.5″) and layout to fit a schematic on the blank left page and the derivation with some notes on the grid/lined right page. As an added bonus, writing out the circuits by hand with the idea of needing the info later will, ideally, help me to improve my normally atrocious penmanship as I have to take my time and focus on my writing.

Without further ado, here’s the Table of Contents and first entry into what I’m calling my Circuit Notes Series. I went with the transfer function for Type III compensation for switching regulators. Checkout the cool reference tables Field Notes threw on the inside cover too. Since this is just a reference I didn’t include all the math or in-depth details of how the circuit works, just some key notes to keep in mind. Think of this as an introduction to the circuit, not a be all end all treatise.

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For anyone who would like to save a digital copy of these derivations I’ve also posted these pages to Evernote (here and here) where you can add them to your own notebooks and search them using OCR. Hopefully someone finds these notes as useful as I do! The next note I do will be on an RC oscillator circuit and after that who knows? Recommendations for circuits are welcome too as I’m always willing to learn some new topology.

References:

http://www.intersil.com/content/dam/Intersil/documents/tb41/tb417.pdf

http://www.ti.com/lit/an/slva633/slva633.pdf


Office Tomfoolery

So Monday at work I successfully pulled a prank on the designer for the part that is currently occupying the majority of my time. Concept, planning, and execution took about two weeks or so as I had to fit this little side project in around my real work obviously. Ever since the part’s inception this designer had been claiming it was perfectly designed and any errors were clearly the fault of me, the Applications Engineer. He wasn’t being mean or anything, this sort of good-natured rivalry is pretty common between the Apps and Design departments at work, but being that this is my first part as lead apps since starting a year ago meant I got some extra abuse. I figured it would be a good idea to go on the offensive and show everyone I wasn’t such an easy target. My boss, who’s been good friends with the designer for a long time now, thought it would be pretty funny and approved the gag, eager to see how it would play out.

The part is a single phase buck regulator meant for Vcore applications in laptops and ultrabooks. Vcore means that the regulator provides the main voltage rail to the processor, specifically an Intel one in this case as AMD and other processors have different power requirements. My goal was to somehow screw with the regulator, cause the output voltage to glitch and go out of spec, and convince the designer this was a silicon bug and not a board issue. After a little brain storming I came up with the following circuit which could be cobbled together out of various parts in the lab:

Prank Circuit

My Prank Circuit

Without diving down the rabbit hole that is regulator compensation, the comp pin of any buck converter is the output of an error amplifier which connects to a networks of passives going back to its negative terminal (the Feedback pin) and is part of the control loop used to keep the output voltage stable and well-regulated. My circuit would periodically drive this pin away from its steady state operating point. This disturbance would propagate through the chip and result in a noticeable glitch on the output voltage until the compensation loop could regain control and bring the output voltage back into spec.

As phase switches merrily along at the frequency and duty cycle set by the controller it gets divided down by R1 and R2. When phase is high the output of this voltage divider is enough to forward bias the diode and cause current to flow into C1 for a brief period before going low again. C1, which also connects to the positive input comparator U1, charges over time and when the voltage across the cap gets to be higher than the reference voltage present on the comparator’s negative input the comparator’s output swings to 5V. When U1’s output goes high two things happen. One, comp is driven away from steady state through R5 and two, the gate of M1 goes high which discharges C1 below the reference voltage starting the cycle over again.

Prank Sims

Prank Circuit Sim Results (Click to view properly)

There really wasn’t much thought process behind the component values in my circuit; they were determined through trial and error in simulation. I didn’t care how often the circuit would trigger, only that it did and the disturbances it caused would appear on Vout. One of my only goals was to ensure that the resistor dividers wouldn’t draw enough current to interfere with the normal operation of the regulator and cause it not to start up. My second goal was to “break” the regulator just enough to cause concern but not enough to trigger any of various over voltage, current, or temperature protections built into the chip. This is why R5 had to be added; without it comp was driven too hard and the part simply shutdown (there’s no fun in that).

With the circuit idea solidified I headed into the lab to jury rig it into place underneath one of the eval boards. It was a messy hour after work one day, but I successfully placed each component and wired in the various signals and voltages from all across the board. Once things got going, there would be so many cables and probes attached to the board I knew it wouldn’t get turned over until I was ready to reveal what I’d done.

 

Holding my breath I powered up the board after making all the necessary modifications. Surprisingly enough it worked! I hadn’t made any disastrous mistakes when wiring it all up and the resulting waveforms basically match with my sims. All that was needed was some tweaking of R5 to find the right value and I was ready for action.

Cutting to Monday morning, I spent a little time taking scope captures of a good board and my doctored eval board. These were placed in a quick report which I shot off to my boss and the designer right after lunch. To add to the joke I took my clean scope caps using a part from an old rev of silicon and explained how the “bug” was only seen in the latest version of the chip. This caused the initial spark of concern in the designer as we’re currently waiting on a new rev of the chip to arrive from the fab and it was too late to make any changes. After getting some tests to run and tweaks to try, I actually went into the lab and did them! For one I was curious to see if any of them could actually fix the error (they didn’t) and secondly, this designer is pretty hands on and likes to come out to Apps Lab quite often. I knew that if he came out to see the glitch on the bench and none of his changes were made he would get suspicious. Fortunately, or unfortunately, other obligations kept him away for the day and he never came out to see the problem until the end of the day.

After running the initial list of tests the designer gave me I had a flash of brilliance that really threw him for a loop. I took a series of scope shots at each of the four switching frequencies our part could run at and varied the value of R5 at each one. Now I had created a problem that went away as switching frequency increased and could explain why we hadn’t seen this issue before as the majority of our testing had taken place at high frequency up until this point! Bingo.

By the end of the day, the designer was pretty much stumped. He’d done an initial check of his schematics, couldn’t spot an obviously fault he made, but thought it was a mistake somewhere in the core of the modulator. He told me that at this point he essentially resigned himself to hoping the new version of the chip came out okay and whatever changes he made would happen to fix this (remember it’s too late to make changes now as the part’s being fabricated).

Right afterwards I called him into the lab saying I’d found something interesting and he should come take a look. When I showed him the circuit on back of the board he didn’t get it at first. He asked why all this crap was added and what did it fix? I couldn’t hold back anymore and broke out in a smile and said that I just wanted to mess with him. Slowly realization dawned on him and he started laughing as did my boss and a few other guys in the lab who were in on the joke.

In the end the designer took it really well and thought it was pretty funny. He told my boss to give me more work as clearly I didn’t have enough to do since I could pull these elaborate pranks but mostly he just laughed. I now owe him a round or two the next time a bunch of us go out after work but that’s a price I’m more than willing to pay all things considered. In the end I caused him just enough trouble so he started to sweat but not enough to take him away from any real tasks he had to get done. A well executed prank overall in my opinion. Surely, there’s no way this will every come back to haunt me right?


Expanding the Analog Geek’s Toolkit

So I spent the other weekend in Washington, D.C. visiting a friend for his birthday. While I was waiting for my plane to take off in RDU Alan over at Tektronix was kind enough to provide me with some pre-flight entertainment. Back in 1987, Alan assembled The Ultimate Analog Engineer’s Toolkit designed to provide solace to engineers dealing with such problems as noise, the Miller Effect, and management, among other things. My personal favorites were the box of dBs (positive and negative flavors of course) and the Parasitic Pesticide. I tried to order some samples directly from Alan himself but he said his stock has run dry. I hope he can get another shipment delivered in time for the holiday season.

Anyways, as I was sitting in the terminal after reading it and I started to come up with a few additions to the toolkit and I present them to you here.

The Low Flow Current Adapter – We’re all familiar with the low flow shower heads installed in bathrooms nationwide to reduce water consumption. The Low Flow Current Adapter works in much the same way only on current instead of H2O. Plug this bad boy in between the power source and your circuit and watch as your product’s power consumption plummets before your very eyes.

Frequency Shaper Tool - Sometimes designs run over budget and when this happens you can’t always afford the box of high quality dBs needed to make a circuit meet the required specs placing a lot of “hertz” on you the designer. This is where the patented Frequency Shaper Tool comes in handy. While not as precise as a Box of dBs its low cost and reliable performance makes it ideal for the engineer on a budget. The Shaper allows a designer to grab a hold of an amplifier or filter’s frequency response and bend it to the desired shape. Need to nudge a zero in the stop band? Squeeze just a little more rolloff out of a filter? Reach for the Frequency Shaper and bend a transfer function into submission.

DocuGel – Come across an old PCB, product, or IC and have no idea what it does or how to use it? Did someone who’s clearly not as bright as you are forget to document their work and now the burden to upgrade the device is on you? Spread some DocuGel on the offending product and leave it sit overnight on your bench. Return the next morning and find datasheets, BOMs, gerber files, and schematics laying on your bench!

Grounding Stakes- Nasty PCB layout causing you problems? Is your circuit’s performance suffering at the hands of ground refusing to sit at 0V? Pound a ground stake into an open portion of your board and watch your problems disappear. Let your circuit know you only accept 0V, no more, no less.

I accept checks and all major credit cards :-)


A Call to Arms

I’m sure it’s not news anymore to most of the readers here but recently there has been not one, but two devastating blows to the analog electronics industry.  Legendary Linear Tech Applications Engineer Jim Williams passed away on June 10, 2011 and National Semiconductor’s Analog Wizard Bob Pease (the self crowned Czar of Bandgaps) also passed away on June 18, 2011.   EDN author and fellow analog engineer Paul Rako fondly remembers both analog giants in two heartfelt posts on EDN’s website here and here. You can also find a tribute to Williams on Linear Tech’s website (found here) which also links to a collection of his app note guaranteed to provide you with enough reading material for the foreseeable future. [Update] National Semi has also added a tribute to Bob Pease on their website found here.  There’s an excellent video to go along with it that’s well worth the time to watch it (if anyone from Maxim is reading I apologize but your product catalog as Pease’s floor mat was pretty funny).

No one can deny that their unexpected passing is a blow to EE’s everywhere and both men will be greatly missed.  It is unlikely that either Williams or Pease will ever be replaced. In his article on Pease, Rako mentions that there are still many great analog designers in the industry today and while I agree with him, I do claim that we as an industry are currently left with a void to fill in terms of engineers who are as vocal as both Pease and Williams were.  There is now a need for engineers and makers who possess the same passion as these two great men to step up and inspire and teach others with their writing.

My challenge to not only analog fans but all engineers, coders, makers, hackers, etc. is to carry on where Jim Williams and Bob Pease left off.  Be passionate about your work, take pride in it.  Look to teach. Look to inspire. Let your enthusiasm show through in every project. Let people know what we do as engineers may not be easy but the challenge it provides is both exhilarating and at times, fun.  These are the ideals that should be present each and every day you sit down at your bench. You don’t have to be a circuit junky to see  these principles shine through in Williams’ and Pease’s work, they’re pretty self-evident.

So grab your ‘scopes, grab your dev boards, your MakerBots, and your soldering irons (not by the hot end). Take them and make something.  If you’re not a maker, write an article on a bit of theory you’re knowledgeable on or just any topic that interests you.  Throw the results online for others to see be it in your own blog, an Instructable, up on Hack a Day, YouTube, whatever.  Carry on the legacies of passion, knowledge, and dedication left behind by Jim Williams and Bob Pease.  While they can’t be replaced, their memories can be honored through the work of those they inspired.

Sadly, I never had the opportunity to meet nor work with either Pease or Williams. However, the two have inspired me immensely through their countless publications.  Ever since I first stumbled across The Best of Bob Pease on National’s website and Analog Circuit Design: Art, Science and Personalities  a few years ago I’ve been hooked on reading everything these two have put into print.  Both of them have taught me a great deal on not only analog circuits, but also the passion required for really loving the work that you do.  As I prepare to go off into the real world after summer ends and start my own career as an apps engineer, I hope that perhaps one day a few of my own app notes can be as well regarded as those written by Williams and Pease and can inspire budding EE’s the way they have inspired me.

To Jim Williams and Bob Pease, may they rest in peace…


Filter Fiasco: Chapter 1

One of the circuits I have to design for my thesis is a bandpass filter.  Based off the specs I was presented with back in the early fall a filter with f_center = 100 MHz and Q = 250 was required; plus f_center needed to be tunable without changing Q. Not exactly the easiest design in the world but I studied up on a few topologies and settled on the Dual Amplifier Bandpass filter (pages 5.74 and 5.93).  According to Matlab and some hand calculations a 4th order filter was all I needed.

Figure 1: Dual Amplifier Bandpass Filter Schematic

Cut to Rev. 1 of the board and not a single aspect of the filter met spec or even remotely functioned as a bandpass filter.  Simply scoping the output showed my design self-oscillated around 50 MHz, fantastic.  Adjusting the potentiometer I put in place for R2 merely shifted the frequency of oscillation. No amount of debugging or rework could make the filter behave and according to one of my professors, my use pots in the first place was a recipe for disaster because of high parasitics along with poor overall performance at high frequencies. Another important thing to note was my use of a current feedback amplifier as opposed to a conventional voltage feedback amp  because of the higher bandwidth and slew rate they offer at high frequencies (foreshadowing, this will haunt me later on…).

After discussing things with my advisor we decided our first attempt was too ambitious and to spin a second revision of the board only this time with a few changes in the specs.  Mercifully, having a tunable center frequency was no longer required. It was determined that this feature wasn’t necessary in the prototype stage and that designing a new tuning method would take too much effort, thus preventing me from completing more important aspects of the project.  The center frequency was also dropped to 10 MHz which lowered Q down to 25 giving a much more achievable design.  Refining my Matlab simulations and hand calculations showed that I was actually incorrect on my first attempt (whoops) in regards to the number of stages.  With these new specs I would need a sixth order filter.  I decided to keep using a current feedback amplifier though I changed parts from Rev 1 and picked the THS3202 from TI.

With my first design having crashed and burned I turned to PSpice to see if I could get my design working in simulation before spending time in hardware chasing something that may prove to be a dead end.  Using  Intersil’s AN1613 (mentioned in my last post here) I downloaded the Spice model for the THS3202 from TI’s website, incorporated it into my schematic and began simulating.  I eventually got my filter working and meeting spec with the help of some compensation techniques from other app notes I discovered and got the results below in Figures 2 and 3.

BPF Mag Plot

Figure 2: Magnitude Plot of BPF

BPF Current Pulse Response

Figure 3: Vout of BPF to Current Pulse Input

From these figures everything appears to be in order, there’s a nice bandpass shape to the filter that met spec, a decent response to being hit with a 100 uA current pulse for 30 us, yadda yadda. All that should have been left was to slap it on a PCB and make sure it functioned right?  Stay tuned for Chapter 2 as our story continues…


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