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I am working on a PCB layout in which I have a 40cm long traces (bus of 4 traces). This traces will support between 50mA to 100mA and 5V. I want to minimize possible antenna effects that may occur due its length.

Could you provide me any tip on how to avoid this effect (width of trace affects?)? Or at least methods of how to protect the circuit?

Thanks.

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  • \$\begingroup\$ How many layers is your board? What are the edge-rates of your signals? If you are running pure DC on a 40cm trace, it won't be an antenna. Nothing is ever pure DC, of course, but the degree to which a trace acts like an antenna is dependent on the frequency content of the signal. \$\endgroup\$ – uint128_t Mar 13 '16 at 17:51
  • \$\begingroup\$ Are these data or power? If data, what is the rise and fall time? 40cm is long enough that they may be transmission lines. \$\endgroup\$ – Krunal Desai Mar 14 '16 at 6:52
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It's unclear from your question if you're more concerned with your traces generating EMI/RFI (creating interferance & possibly failing FCC compliance), receiving interference (causing unwanted/undefined circuit behavior), or inter-trace interference (one trace's signal interferes with its neighbors).

Fortunately however, if you were to split your signals into paired traces using differential signalling, you can reduce all three unwanted behaviors.

Other potentially useful approaches:

  • Placing your 4 signal traces 'interleaved' between 5 ground traces will give some interference improvement (emitted, received, and inter-trace), though somewhat less improvement for emitted & received EMI/RFI than "true differential" signalling.

  • 'Interleaving' 4 differential pairs between 5 ground traces (pattern: GND/S1+/S1-/GND/S2+/...) would further improve inter-trace interference performance over differential pairing alone.

  • Placing your data lines on an internal layer of a multiplayer PCB (with or without differential pairing &/or ground trace interleaving), with ground planes above & below will provide a high degree of shielding for emitted & received EMI/RFI.

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Using a groundplane is a good idea. The solid copper layer limits the loop area to the length of the track x layer distance. This minimizes the inductance of the loop. You could also use two groundplanes, one above and one below the tracks in question making it more like a full screen. You could also alternate send and return positions so as to form a twist a la twisted pair cables.

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