IR Drop

Example 1 pages

The paper has presented a theoretical approach to sizing the power straps in an integrated circuit. Not surprisingly there are some differences between what is desired and what is achievable, and these are considered here with reference to a real example.

The technology is 6 layer metal and the core size estimate before adding any power straps is 3.5×3.5mm. The table of relative power strap widths and resistivities, and the fixed block area is given below.

metal layer 1 2 3 4 5 6
 kan 100% 100% 100% 100% 200% 200%
power strap allocation coefficient
 kwn 100% 100% 100% 100% 200% 200%
power strap width coefficient
 rn 80 60 60 60 60 20
metal resistivities in Ω per sq.
 kcn  75% 100% 100% 100% 100% 300%
conductivity coefficient
 mn  50%  50%  50%  50%  50%   0%
core area blocked

Power straps are equally divided vertically and horizontally, and the metal-5 and metal-6 straps will overlap the standard cells, as shown in the Graal screen shots on the right.

In Graal, the power strap allocation is drawn with the TALU1-TALU6 layers.

metal-2 to metal-5 power strap allocation

Graal screen shots of (from l to r) metal-2/3,
metal-3/4 and metal-4/5 power strap allocations.

metal-5 and metal-6 power strap allocation

Graal screen shot of metal-5/6 power strap allocation.