Reducing Conducted and Radiated Emissions
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• Keep all metal structures at the same RF voltage.
• Do not use gaps in the return plane, except to control the location of low frequency (kHz) currents.
• Do not allow any traces to cross any gaps in the return plane.
• Most low frequency (kHz) I/O lines need HF(MHz) decoupling to the signal return (Ground) at the connector to reduce V DM applied to the cable.
• The circuit board signal return needs a HF (MHz) connection to any surrounding metal chassis at the connector to reduce V CM applied to the cable.
• Use the longest rise time possible for all pulse signals.
• Use logic families that are no faster than necessary.
• Use the lowest clock frequency possible.
• Keep all clock lines as short as possible.
• Tightly control the loop area of all high speed signals.
• Do not split or gap the return plane under any connector.
• For filter capacitors to be effective near 100MHz, essentially zero lead length is required. An “X” style lead connection may be necessary for a shunt capacitor.
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