An Interview with Dr. Howard Johnson - Winsome Waveform Wizardry

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• • Welcome Dr. Howard Johnson!

• • He has published two reference books that are a must-have for the field of high speed signal propagation:
    • High Speed Digital Design: A Handbook of Black Magic
    • High Speed Signal Propagation: Advanced Black Magic
  • Howard hails from Twisp, WA.
  • Martin Graham, the co-author of his book, was also his longtime mentor at ROLM.
  • Howard teaches a class at Oxford every summer. He also teaches classes throughout the US, both in public and private forums.
  • He also has published articles regularly at EDN and other technical magazines.
• Other things mentioned during the show:
  • Chris mentioned his article about Bell Labs and the Trickle Down Techonomy.
  • Howard mentioned how the Voyager Space Craft actually experienced some cosmic ray data corruption, though it doesn't happen often on earth.
  • As connectors get scale smaller, signals get better. However, on boards as traces get longer, they also need to get wider.
  • To continue increasing the speed of modern day comms, Howard believes we need to move to Multi-Level Communication (as we always do with every medium).
  • The limits of channel capacity are governed by the Shannon-Hartley Law (referred to as Shannon's Theory on the show).
  • In "The Early History of Data Networks" by Gerard J. Holzmann and Bjorn Pehrson (there's a "synopsis" here...), they talk about torches being used in single and multichannel modes.
  • Howard helped define the Gigabit Ethernet Standard (with no help from "Ernie"!)
  • Howard suggests "The Theory and Practice of Modem" Design, by John Bingham as a good starter text on the subject of encoding and data transfer.
  • If you need a place to talk about signal issues, check out the SI-list, part of freelists.org.
  • The IEEE EMC society also is a great place to meet other designers.
  • At EMC meetings, they often watch related videos, such as the ones on Howard's website!
  • Howard responded to silliness relating to claims of "skin effect in audio cables".
• The 90 degree question: Is it wrong to make right angles on your board layout?
  • This rule was propagated by microwave designers who were designing with 120 mil line widths.
  • Your board already has tons of 90 degree turns...in the vias on your board.
  • It's the added material in a right angle turn (beyond the normal width of a trace) that can add parasitic capacitance.

We had a wonderful time talking with Dr. Howard Johnson. It was great getting to know the kinds of work he does and the kinds of signal integrity problems he works with regularly. Please leave any questions you might have about the show or for Dr. Johnson in the comment section.