Signal Integrity (Crosstalk)
Signal - electrical signal or data or information. Integrity - complete or consistency or reliability of data. Signal integrity is the ability of an electrical signal to carry information reliably and resist the effects of high-frequency electromagnetic interference from nearby signals. Crosstalk is the undesirable electrical interaction between two or more physically adjacent nets due to capacitive cross-coupling. As semiconductor industry is moving towards smaller technologies, Crosstalk become increasingly more important than cell delay. Crosstalk can affect delay and static noise.
A) Crosstalk Delay
Crosstalk can effect signal delay by changing the time at which signal transition occurs. It can either increase or decrease delay depending on victim and aggressor transition. While crosstalk calculating tool (PrimeTime SI) usually show only worst-case delay that means in setup late crosstalk delay and hold show early crosstalk delay.
A and C net (Aggressor net) can affect transition of net B (Victim net). Rising transition of net A and falling transition of net B introducing small voltage bump which increase transition of net B and so its delay, which will lead to setup violation. Similarly, falling transition of net C can affect reducing falling transition of net B which will lead to hold violation. Basically, Similar transition will decrease delay and different transition will increase delay.
PrimeTime SI calculate crosstalk delta delay based on arrival window concept.
B) Crosstalk Noise
Crosstalk noise can affect design functionality. So, crosstalk noise is important factor of STA signoff. As you can see in fig, signal B is static, Transition in A can cause noise bump or glitch on static net B. If this noise bump is sufficiently large and wide, It will create incorrect logic value to propagate to next gate in path of net B.
Ways to fix crosstalk:
1) Increase victim net driver driving strength
2) Decrease aggressor net driver driving strength
3) Shielding victim net