Whenever the interconnect lines are running parallel in close proximity, signal on 1 line gets coupled to the signal on another line and may cause disturbance. This phenomenon is called cross-talk.
The coupling capacitance due to 2 parallel lines or interconnect line can be estimated using following empirical formula
where S is the spacing between the two lines.
Methods to reduce crosstalk:
- Double spacing.
- Reduce parallelism.
- Switch to other metal layer.
- Insert buffer in victim net.
- Upsize driver of victim.
- Downsize driver of aggressor.
- Shielding the victim net.
1) If at all possible, avoid floating nodes. Nodes are sensitive to cross-talk. Such as precharged busses, should be equipped with keeper devices to reduce the impedance.
2) Sensitive nodes should be well separated from full-swing signals.
3) In order to keep cross talk to a minimum, do not allow the capacitance between two signal wires to grow too large.
4) Use differential signalling in sensitive low-swing wiring networks. This turns the cross talk signal into a common mode noise source that does not impact the operation of the circuit.
5) Make the rise time as large as possible, subject to timing constraints. Be aware, however, of the impact this might have on the short-circuit power.
6) Adequate separation should be maintained between high speed clock lines. Also placing a power or ground rail between two high speed lines can be an effective measure.