Power Supply Routing root approach
The root approach: In this case the power line starts as wide as possible, and
as the power is connected to various blocks, the power supply lines become
thinner, similar to the roots of a tree.
• The width of the supply lines is based on the electromigration factor and
is tapered in proportion to the quantity of current being consumed along
each branch of the root.
• This approach is used when the resistance of the supply lines is not an
issue for any block along the chain.
• Historically, most power routers routed power using this approach