steps to implement physical compensation
1. Route signals as you would any other signal, and reserve space for length
compensation and shielding lines. Route all lines using a single width of line.
2. Determine the longest line among the group to be compensated and increase
the length of all other signals to match. Serpentining signal lines is appropriate
as long as adequate shielding is maintained.
3. If different routing layers are used, match the length of interconnect on each
layer for each signal. It is not necessary to place the different layer routing
in the same place along the line, but it is important to use the same number
of vias within each signal.
Match the relative transistor loading or fanout for each line. This means
that the ratio of the size of the transistor load relative to the driver should
be the same for every line. Additional transistor loads should be added to
the appropriate signal to match the fanout ratio.
4. Run layout extraction tools to verify the results and adjust the layout if
necessary.