Chapter 9

Crosstalk & Signal Integrity

Crosstalk

Crosstalk is interference where switching on one net couples onto a neighbouring net through cross-coupling capacitance. It can push a path into a setup or hold violation.

KEY Crosstalk = coupling-cap interference between nets; it can cause setup or hold violations.

Avoiding Crosstalk

• Double spacing - more spacing means less coupling capacitance and less crosstalk.
• Multiple vias - lower resistance and lower RC delay.
• Shielding - holds the coupling capacitance constant, so crosstalk becomes a known value.
• Buffer insertion - boosts the victim net's drive strength.

KEY Fight crosstalk with spacing, shielding, multiple vias and victim buffering.

How Shielding Stops Crosstalk

• Shield lines are tied to VDD or VSS, so high-frequency noise (glitches) couples into VDD/VSS instead of the victim net.
• Because the shield is at a fixed potential, the coupling capacitance stays constant.

KEY Shields tied to VDD/VSS absorb glitches and keep coupling capacitance constant.

Spacing and Crosstalk Noise

Greater spacing between two conductors lowers the cross-coupling capacitance between them, which directly reduces crosstalk.

KEY More spacing -> less coupling capacitance -> less crosstalk.