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Impedance Control: Formulas and Resources |
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This article summarizes the
impedance and related formulas for the four standard configurations (microstrip,
embedded microstrip, stripline, and asymmetric stripline) and points the
reader to several free resources for impedance related calculations,
including our own UltraCLC.exe, a
Transmission Line Calculator. The article appeared in the March, 1998
issue. |
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| Differential
Impedance: What's the Difference |
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This article explains the seemingly
complicated topic of differential impedance and removes the
"mystery" around it. Its relationship to common mode impedance is
also explained. Formulas are provided for estimating differential impedance.
The article appeared in the August, 1998 issue. |
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| Slots
in Planes: Don't Use 'Em! |
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This article covers three important reasons why
slots in planes should be avoided: (1) they can increase EMI, (2) cause a
loss of control over impedance, and (3) increase crosstalk. See the details
in this article that ran in the March, 1999, issue of the magazine. |
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| Impedance
Terminations, What's the Value? |
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We often talk about the fact that
adjustments must be made in the normal terminating resistance of
transmission lines in the case of differential signals. In fact, the bad
news is we ALWAYS must make an adjustment for coupled signals. but the good
news is that this adjustment is almost always zero except in the special
case of differential signals. This article, which ran in the June, 1999,
issue of the magazine, explains why. |
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What's All This Critical Length Stuff, Anyhow?? |
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Do you understand what
'critical length' means? Most others don't either! This article uses an
echoing sound analogy to illustrate what we mean by reflections, and why
shorter traces allow us to 'hear' better. The article appeared in the
October, 1999, issue of the magazine. |
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| Embedded Microstrip. |
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All the formulas for
the impedance of traces are approximations. But the usual formula for
embedded microstrip is more of an approximation than most! It doesn't help
that the formula normally used is wrong! This article, from the February,
2000, issue of the magazine, tells why I think so and what the correct formula
should be. |
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Differential
Signals, The Differential Difference. |
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There is much misunderstanding about how and why
differential signals are routed the way they are. This article, reprinted
from the May, 2001 issue of the magazine, explains the reasons behind the
routing guidelines commonly suggested in the industry. |
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Differential
Signals: Rules to Live By |
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We followed this last article up with two others
related to differential signals. This is the second one, a feature
article in the November, 2001, issue. It explores the reasons behind the various
design rules that exist related to differential signals. |
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