Top 10 Reasons NOT to Care About Signal Integrity

(Syndicated content from: http://signal-integrity-tips.com/2009/top-10-reasons-not-to-care-about-signal-integrity/)

10. Hey! My chip meets spec. It’s the OEM’s job to design it in right.

9. The speed of light is 670,616,629.4 miles per hours. That’s really really fast.

8. I never had that problem on my last project, and this revision is only 30% faster.

7. The via stubs doesn’t connect to anything. What harm can they do?

6. My PCB vendor specs means I won’t have a problem: “Loss tangent – pretty close to zero. Roughness – almost no roughness. Metal resistivity – are you kidding? Copper’s a real good conductor.”

5. Skin effect? Isn’t that something to do with Photoshop?

4. S-parameters? No thanks. Don’t you have an RLC SPICE model?

3. 10 picoseconds? Listen to me: 10 picoseconds to ten decimal places is 0.0000000000 seconds.

2. If it doesn’t work we can always step up to Rogers’ material.

And the number 1 reason NOT to care about signal integrity is:

1. We’re hoping lower speed products will make a come back!

TGIF. Have a good weekend!

Signal Integrity Textbooks

(Syndicated content from: http://signal-integrity-tips.com/2009/signal-integrity-textbooks/)

Here are my thumbnail reviews of some signal integrity textbooks. They reflect my personal views, not those of Agilent. You can add your thoughts in the box below.

• Timing Analysis and Simulation for Signal Integrity Engineers by Greg Edlund
  This book takes a different approach to signal integrity then the “traditional” Bogatin and Johnson & Graham approach (see below) in that the starting point is not the interconnect, but the prima dona of signal integrity, the flip-flop in the receiving chip. “If I don’t see a clean zero or one during my set up and hold periods,” lectures the flip-flop, one hand on hip, the other wagging a threatening finger, “I’m going to go metastable.” And so the game begins. How to deliver on that demand? Greg’s twenty years – and counting – experience as a hands-on signal integrity engineer makes his textbook authoritative and his narrative style makes the book accessible.
• A Signal Integrity Engineer’s Companion Real-Time Test and Measurement and Design Simulation (Geoff Lawday, David Ireland, and Greg Edlund)
  Some of the chapters (2, 4, 9) in this books are the same (give or take a revision or two) as ones in the book above, so this book should be considered if the non-overlapping material is of value to you. Not sure why the publisher “double-dips” in this way.
• Signal Integrity – Simplified (2ed due for release July 27, 2009) by Eric Bogatin
  It was Eric who coined the phrases “There are two kinds of engineers — those who have signal integrity problems, and those who will.” and (with respect to all signal integrity issues) “It depends.”
  I haven’t seen the second edition yet, but the first edition has the “traditional” signal integrity focus on the properties of the interconnect, the impairments that it inflicts on the poor signal, and how to design around them within the limits imposed by physical laws. Eric also has a new book coming out in September, “Signal Integrity Characterization Techniques”, co-authored with my colleague Mike Resso. I’ll review it when I can.
• High Speed Digital Design: A Handbook of Black Magic and High Speed Signal Propagation: Advanced Black Magic by Howard Johnson and Martin Graham
  Published in 1993 and 2003 respectively, one frustration with these two very popular books is that I can never quite decided whether the latter is volume two of the former, or whether it’s the second edition. There’s certainly a lot of overlap between the two, but the second isn’t a true superset of the first. It smacks of another case of Prentice Hall “double-dipping.” Both volumes/editions have a “traditional” focus on the PRBS signal in the frequency- and time-domains, and its interaction with the interconnect. Personally, I prefer the flow of Eric’s book for “cover-to-cover” reading, but there’s a lot of good reference material and anecdotes here that I dip into when needed.

Other texts that are on my ever expanding to do list. I’ll try to add reviews here someday? Or p>

• The SPICE Book by Andrei Vladimirescu
• 
  Jitter, Noise, and Signal Integrity at High-Speed by Mike Peng Li
• Learn Signal Integrity Design Principles With Mathcad: Interactive textbook/CD for EMC/EMI/PI/SI by David Norte
• Semiconductor Modeling For Simulating Signal, Power, and Electromagnetic Integrity by Roy G. Leventhal and Lynne Green
• Power Integrity Modeling and Design for Semiconductors and Systems by Madhavan Swaminathan and A. Ege Engin

Signal Integrity Papers from Agilent ADS User Group Meetings in Rome and B?ngen

(Syndicated content from: http://ping.fm/0Mgo7)

The Agilent ADS User Group Meetings in Rome (13 May) and Böblingen (14-15 May) had three signal integrity papers that the authors have kindly given permission to post here.

• Francesco de Paulis and Antonio Orlandi, UAq EMC Laboratory, University of L’Aquila, Italy:
  Using Equivalent Circuits for the Analysis of Complex Power and Signal Integrity Problems
  .
  They compare fast circuit simulation with ADS to complex and time consuming 3D models and conclude that ADS is not only a tool for designing. Its flexibility allows its use as tool to investigate the fundamental mechanisms of relevant power and signal integrity issues and that it is a critical tool for engineering.
• Hermann Ruckerbauer, EyeKnowHow Signal Integrity Consulting:
  Signal Integrity Optimization of a Complex Memory Bus System
  .
  Hermann shows how to explore the system design space by applying the ADS optimizer to various pulse response goals.
• Karsten Drögemüller, ix-cad:
  High Speed Digital Signal Path Design for a 40 Gb/s Optical Receiver
  .
  Karsten shows how ix-cad achieved first pass success in designing the 40 Gb/s digital signal path for an optical receiver using ADS.

Using Equivalent Circuits for the Analysis of Complex Power and Signal Integrity Problems

(Syndicated content from: http://ping.fm/jBTWo)
Guest post from Francesco de Paulis and Antonio Orlandi, UAq EMC Laboratory, University of L’Aquila, Italy

At our ADS User Group meeting in Rome May 13th, Francesco de Paulis and Antonio Orlandi, UAq EMC Laboratory, University of L’Aquila, Italy presented a paper Using Equivalent Circuits for the Analysis of Complex Power and Signal Integrity Problems
.

They kindly gave me permission to post the slides here

They compare fast circuit simulation with ADS to complex and time consuming 3D models and conclude that ADS is not only a tool for designing. Its flexibility allows its use as tool to investigate the fundamental mechanisms of relevant power and signal integrity issues and that it is a critical tool for engineering

The Trouble With IFFT

(Syndicated content from: http://signal-integrity-tips.com/2009/the-trouble-with-ifft/)
Consider the following MATLAB code which models a lossless delay by its amplitude and phase frequency response, then applies a simple inverse discrete Fourier transform, then plots one period of the time domain response:

close all
clear all
npts = 256;
delta_t = 1e-9; % s
t = 0:delta_t:delta_t*(npts-1);
f = linspace(-(npts-1)/(2*npts*delta_t),1/(2*delta_t),npts); % Hz
amplitude = ones(size(f));
delay = 10.5e-9; %s
phase = -2 * pi * f * delay;
fresp = amplitude .* exp(j * phase);
tresp = ifft(ifftshift(fresp));
plot(t,tresp)

The resulting plot shows that this method cannot be used to create an accurate impulse response:

The pulse is spread out so badly that the skirt of the next period leaks into the end of this one.

The fundamental issues is that to get an impulse response, you have to do an inverse Laplace transform, not an inverse Fourier transform. (The output of an inverse Fourier transform isn’t an impulse response at all: it’s one period of the repeated pulse train response.) “But,” you say, “I don’t have the frequency response in the complex plane, I only have the steady state response on the upper half of the f = j ω line.” Kramers-Kronig relation to the rescue! This relation says that if you have a real physical system i.e. a causal system the frequency response it is possible to construct the impulse response (causal of course) from the steady state data alone.

If you don’t want to do the math (and I don’t blame you for that), don’t worry we’ve done it for you in ADS (US patent pending, application 20080281893).

Fifteenth Anniversary of the SI-List

(Syndicated content from: http://ping.fm/LnblX)

The si-list went “on the air” fifteen years ago today, on May 15, 1994 — an eon in Internet-years. It predates that milestone moment of the Internet: the IPO of Netscape on August 9, 1995.

The genesis was a short course on "Electrical Modeling, Simulation and Design of Electronic Packages" that was taught by Raj Mittra, Paul Franzon and Jose Schutt-Aine in San Jose, CA on May 9-12, 1994. During the last day of class we passed around a blank piece of paper collecting e-mail addresses from anyone who wanted to be included in a proposed signal integrity email list. When I returned to my office at Sun Microsystems the following Monday I put together the initial si-list with about 30 subscribers from the previous week’s short course.

Now 15 years later we have about 3,500 subscribers. They range from students just getting their feet wet in engineering to world-renowned experts in the field. They hail from both industry and academia in just about every country in the world that is involved in signal integrity related endeavors.

The original idea was to provide a forum for the exchange of technical conversation related to signal integrity and related fields. Over the years we have endeavored to keep the majority of the list traffic on the technical level and to control the use of the forum for advertising and head-hunting. To that end I think we have been remarkably successful. Let me take this opportunity to remind folk that working engineers and hiring managers looking to add to their staff may post job opening and that postings by ‘headhunters’ and HR departments are generally discouraged. Postings by vendors (hardware and software) should be primarily technical in nature and should not be mere advertisements. Si-list is not a marketing forum. Vendor postings about commercial products should refer those interested in further information to an e-mail, web address, or phone number for more detailed follow-up.

A bit of behind the scenes history:

• The original si-list incarnation was implemented as a simple Unix .forward file on an ancient Sparc2 workstation in my office. All list administration (additions, deletions etc.) was done manually.
• As the list grew,  we transitioned to the Majordomo listserver software and ran the list from a slightly less ancient Sparc4 box located in our SI lab.
• Over the years the subscriber database and the attendant bandwidth on the net increased. In order to head-off a cease and desist order from the keeper of the Sun LAN, si-list was moved to an external Linux server (freelists.org) running the Ecartis maillist manager software in June 2001. The list still resides on that server today. Thanks to the Freelists admins for years of fine service!

If you want to look back at the postings, archives are available at these locations:

• http://ping.fm/AuiCY or at our remote archives:
• http://ping.fm/3jBTF
• Posting in the period December 6 Dec 1995 to June 6, 2001 are viewable at http://ping.fm/ctAdE
• Posting prior to that were unfortunately consigned to the /dev/null

Thanks to all contributors over the past fifteen years.

Happy fifteenth anniversary si-list!

Ed: Related post What Social Media Web Sites Do Signal Integrity Engineers Use?

Newsletter and RSS Formats

(Syndicated content from: http://ping.fm/7i2JD)

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Circuit Simulation – Part Two – How Various Components and Analyses Are Handled

(Syndicated content from: http://ping.fm/mj40n)

In part one, we just covered DC analysis of conductances and current sources. What about other analyses and components?

It turns out that pure nodal analysis can’t handle voltages sources because they have infinite conductance. So the answer to puzzle event #3 is voltages sources. (Larry Nagel pointed out in a comment there that non-linear resistor is also a right answer if its current is not a well behaved function of its voltage. So give yourself credit that was your answer and you knew the bit about the current not being a well behaved function of its voltage. )

SPICE avoids the infinite conductance problem by modified nodal analysis (MNA). Nodes joined by infinite conductances are considered “super-nodes” whose constituent node voltages V_x and V_y move up and down in lock step. When SPICE creates a super-node the two individual KCL equations are eliminated and replaced by one KCL equation that sums all the currents into both nodes (into the blue dashed oval in the figure above) plus one internal constitutive equation, namely V_x = V_y + V_xy, where V_xy is the known value of the voltage source. Shorts and current sinks (i.e. the input ports of current controlled sources) can be treated similarly.

(MNA isn’t the only solution to the infinite conductance problem. For example Hachtel et al. proposed a sparse tableau method of where both branch currents and node voltages are considered unknown, both KCL and KVL equations are formulated. You then have to pick out a set of linearly independent equations.)

How about more than two terminals? It turns out that when the current source “stamped” its pattern-of-four into the conductance matrix, it was a special case of a more general four terminal “stamp.” The general case is the transconductance:

The “pattern of four” is simply displaced off-diagonal in the conductance matrix.

	Column a	Column b	Column x	Column y
Row a			+Gm	−Gm
Row b			−Gm	+Gm
Row x
Row y

Non-linear (”transient”) analysis

For transient analysis, components are represented in differential or integral form. See the table below. SPICE performs numerical ordinary differential equation (ODE) solution.
Non-linear elements are solved by an iterative method (e.g. Newton-Raphson) at each time step. An initial guess at the node voltages is created (usually all zeros). The slope and intercept of the tangent to the actual I-V curve is used to calculate a linear approximation of the non-linear element. The linear approximation (a conductance and a current source) is inserted into the conductance matrix as a proxy for the real device. Solution of the linear proxy yields better guess at the voltage vector. A new set of conductance/current source proxies is calculated using tangents at the new voltages. This is repeated until — hopefully! — convergence is reached for that time step.

SPICE uses variable time steps. The initial voltage vector guess for each time step is the converged solution of the previous step. If the time step causes accuracy problems, SPICE backtracks by disregarding that calculation and taking a small step from the previous time point.

AC Analysis

For DC analysis, reactive elements — inductors and capacitors — are treated as shorts and opens, respectively. For AC analysis, complex admittance is used in place of real conductance. For example admittance of a capacitor and inductor are jωC and 1/jωL, respectively. Again see the table below.

Table of branch constitutive equations for various components and various analyses in SPICE

Please give feedback on this article by leaving a comment below.

Eric Bogatin Webcast – S-Parameters, Signal Integrity and You

(Syndicated content from: http://ping.fm/AyRD0)

Eric Bogatin is offering a webcast “S-Parameters, Signal Integrity and You” on May 6th at 10am PST, 1pm EST.

Abstract

If you deal with interconnects but are not familiar with S-parameters, you will be left behind. They have become the de facto standard for interconnect characterization and are becoming popular as behavioral models in simulations. In this 45-minute webinar, we will explore what they are, why they are so valuable, and how to use them for single-ended and differential interconnects in both the frequency domain and the time domain. Whether they come from a measurement or a simulation, they contain “everything you ever wanted to know about interconnects”. We will show you how to data mine this rich motherlode of information. FREE for paid subscribers, only $40 for non-subscribers. Be sure to sign up by May 4th for this popular webinar series!

More info: http://ping.fm/Lf0hU

Puzzle Event 3 – Nodal Circuit Simulator

(Syndicated content from: http://ping.fm/Ge6a8)

In preparation for part two of our circuit simulator series, here is a quick puzzle for you. Click on your answer button and see an instant summary of the answers so far.

[poll id="27"]

Check back in few days for:
Everything you always wanted to know about SPICE^*
*But were afraid to ask.

PS:

In case you missed them, the puzzles and solution for events 1 and 2 are here

1. Puzzle Solution
2. Puzzle Solution