        |
Ground Impedance
The primary cause of most high-frequency (EMC, EMI, RF) issues, whether related to emissions, immunity or self-compatibility are due to high ground return impedance.
- Wires and traces innately have high impedance. Hence: ground return plane should be used at high frequencies
- High-frequency effects begin to be noticed around 1 MHz
- Wire inductance in free space = ~ 20 nH/in.
- A 1" wire (or trace) has an impedance of 2 * Π * f * l = 12 ohm at 100 MHz
EMI/RF-penetrating “slot” found in a design review (this is the long “channel” under handle)
Shield integrity: An example of poor design
Above: Copper-plated module halves: An attempt to shield this module did
not connect halves!
This guide was adapted from Agilent by Kenneth Wyatt, DVD, Colorado Springs
| Was this article useful? | del-icio.us | Digg-it |
 |
 |
(none) |  |
EMC Top Ten: 2 | |