Issue link: https://iconnect007.uberflip.com/i/1457913
MARCH 2022 I DESIGN007 MAGAZINE 47 it there, and it is not making the isolation from the aggressor to the victim trace worse. Comparing the isolation curve of the original model simulation (Figure 3) with our properly stitched ground pour (Figure 8) shows that the added isolation of adding a properly grounded copper pour is about 8 dB in this simulation as shown in Figure 9. Certainly, to me, adding properly done copper pours to all my layers is worth doing for the improved isolation and the improved EM radiation performance of the PCB. You might now ask: "Since the stitching vias are at 0.5 inch spacing in this example, won't there be a new reso- nance at 6 GHz now?" And you would be right; extend- ing the sweep frequency of the structure of Figure 7 up to 8 GHz does indeed show a new resonance at 6 GHz, just as we predicted (Figure 10). We can continue pushing the undesired resonance fre- quency up by decreasing the space between the stitching vias, and this is one of the rea- sons I use the less than quar- ter wavelength as the rule of thumb on spacing in the first place, as it gives plenty of Figure 8: Simulating our structure of Figure 7 with the addition of stitching vias placed in the copper pours shows the resonances are now completely gone. Figure 10: Now, it is predicted that the properly stitched copper pours of Figure 7 will have a new resonance peak at around 6 GHz and that is exactly what we find. We can either place the stitching vias closer together or know that these simulations are done with lossless materials and any real FR-4 PCB will start to have significant losses above 3 GHz, which will be much less of an energetic peak than simulated here. Figure 9: Comparing the isolation curve of the original model simulation (blue curve) with our stitched ground pour (orange curve) shows that the added isolation of adding a properly grounded copper pour is about 8 dB in this simulation as shown. This is proof that properly done, adding ground pours to signal layers does indeed improve signal-to-signal isolation.