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The demo has three routing topics. Start with '45° Routing'. The first pattern shows why 90° corners are bad — they create sharp acid-traps and increase EMI radiation from the corner region.
Show hint
Modern EDA tools (KiCad, Altium) will flag 90° bends in DRC. Some fab houses explicitly require 45° routing.
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Step 2 compares 45° chamfers vs smooth arc routing. Arcs are slightly better electrically at very high frequencies (>10 GHz) because they minimise impedance discontinuities. Either is acceptable for most designs.
Show hint
KiCad's interactive router automatically creates 45° bends. Enable 'smooth curves' in router settings for arc routing.
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Step 3 shows stub traces. A stub is a dead-end trace segment that was once connected to something now removed. It creates a transmission line resonance. Always clean up stubs with DRC.
Show hint
Backdrilling is used in high-speed designs (>5 Gbps) to remove through-via stubs that would cause resonances.
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Switch to 'Differential Pairs'. Step 1 shows why spacing must be kept consistent. Widening gaps between the two traces breaks the coupling and allows noise to enter differentially, degrading CMRR.
Show hint
USB, HDMI, LVDS, MIPI CSI, and PCIe all use differential pairs. Always route them together, never split to different layers without a via pair.
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Step 2 shows length matching with a meander. At 1 Gbps, even 100 ps of skew (≈ 15 mm length mismatch) can corrupt the differential signal. Add meanders to the shorter trace to equalise lengths.
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Match lengths within λ/10 of the fastest edge rate. At 1 GHz in FR4, λ ≈ 150 mm, so match within 15 mm.
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Switch to 'Return Path'. Return current is the other half of every signal current loop. At high frequencies it flows directly under the signal trace on the nearest reference plane — this minimises loop inductance.
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This is why inner planes are always GND/PWR in a 4-layer stackup: they provide return paths for both surface layers.
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The split plane example shows what happens when you route a signal across a gap in the GND plane. The return current must travel all the way around the gap, creating a large EMI-radiating loop. Never route high-speed signals over plane splits.
Show hint
Use stitching capacitors (100 nF) to bridge plane transitions near layer-change vias. Add a GND via close to every signal layer-change via.