Crosstalk and Noise in VLSI Layout Design
Switching of the signal in one net can interfere with the neighboring net due to cross-coupling capacitance known as cross-talk. Cross-talk may lead to setup or hold violation.
What is Cross talk noise?
If one net is switching and the other is at a constant value, the switching net may cause voltage spikes on the other Net. This is called cross-talk noise. Cross-talk noise is evolving in degrading the performance and reliability of high-speed integrated circuits.
Cross-talk Delay
Cross-talk delay depends on the switching direction of the aggressor and victim nets.
Cross-talk in Data Path
If the aggressor and victim both switch in the same direction, the victim transition becomes fast and resulting in data arriving early, which may cause a hold violation. This is good for setup and bad for hold.
If both switch in opposite directions, victim transition slows down which increases the delay and may result in a setup violation. This is bad for setup and good for hold.
Cross-talk in the clock path
If the aggressor and victim both switch in the same direction, the victim will see the improved transition and makes the clock arrive early which may result in a setup violation. This is bad for setup and good for hold.
If both aggressor and victim switch in opposite directions, the clock will arrive late because of a badly degraded transition which may lead to a holding violation. This is good for setup and bad for hold. In short, we can say that Cross-talk in the clock path is exactly the opposite of that in the data path.
Clock path
The clock path is the path wherein the clock traverses is known as the clock path. can have only clock inverters and clock buffers as its elements.
Data path
The path wherein data traverses are known as the data path. The data path is a pure combinational path. It can have any basic combinational gates or group of gates.
How do reduce cross-talk effects?
To avoid cross-talk or minimal cross-talk effect, we should
- Increase the spacing between wires
- Insert buffer if wire run length is too long.
- Jump to different metal layers.
- Shielding
- Do up-sizing the driver of the victim net or downsizing the driver of the aggressor net.