True crosstalk aware incremental placement with noise map

Crosstalk noise has become an important issue as technology scales down for timing and signal integrity closure. Existing works to fix crosstalk noise are mostly done at the routing or post routing stage, which may be too late. Since placement determines the overall routing congestion, which correlates with the coupling capacitance, which in turn correlates with the crosstalk noise, placement shall be a good level to do early noise mitigation. The only existing work for the crosstalk aware placement (to our best knowledge) is by Lou and Chen (2004), which uses the coupling capacitance map to guide placement. However, crosstalk is determined not only by the coupling capacitance, but also by many other factors, such as the driver resistance of the victim net and the coupling location (near source vs near sink coupling) (Cong et al., 2001). We introduce a concept of noise map which takes those factors into account. Guided by this accurate noise map explicitly, we propose an incremental placement technique to mitigate noise without disturbing the global placement order. Our incremental placement has two key steps, namely noise aware cell inflation and local refinement. Experimental results on industrial circuits show that our approach is able to reduce the number of top noise nets by 25% and improve the timing (300ps on the worst slack), with no wire length penalty or CPU overhead. Our incremental approach is also able to maintain the placement stability.