BUS is a bundle of signals that have the same signal attributes. DATA and ADDRESS lines are examples of BUS. In order to keep the same signal attributes, they have the same length, width and via. In case of source synchronous technology, send the clock (strobe) signal to be used to capture data with the data signal.

If the system design is done carefully by routing data and associated clock together, you can ensure all variations on the data path are also seen on the strobe path. Both static (process variation, package and board configuration included) and dynamic variations (caused by system operating voltage and temperature fluctuations) can be minimized by design in this way.

This type of design should be ensuring that all the data and associated strobe paths in the PCB are carefully balanced, so they track each other effectively as voltage and temperature variation occur over time. Thus:
  • Make lengths the same to make equal transmission speed (delay).
  • Make pattern widths the same to match impedances.
  • Make the number of via usage the same.
  • Make the routing path the same.

This DFE item checks routing symmetry of data lines and data strobe lines.

If the routing priority of BUS is low, it is difficult to accomplish those three objectives. Therefore, high speed signals and BUS should be routed first.
  • Item: Input item name.
  • Net: Select a target net group.
  • Base Net: Assign measurement reference net. (Clock, DQS, and so on)
  • Filter: Enter a filter to choose differential pair net from selected base net group. After entering a base net and pair net add them into the list by clicking Add Filter.
  • Start Component: Select Start Component. If field is blank, the part with the highest number of pins is automatically targeted.
  • Net Length Check:
    • Except Component: The component excluded during testing. For example, Test Point should be excluded.
    • Tolerance: Upon selecting, check pattern length difference with base net.
    • Max Length: Upon selecting, check trace maximum length.
    • Width Check: Upon selecting, check pattern width difference with base net.
  • Routing Check:
    • Inner Routing Ratio: Upon selecting, check inner routing ratio of all signals.
    • Routing Symmetry: Upon selecting, check inner routing ratio difference between all signals and base signal.
  • Via Check:
    • Via Check: Upon selecting, check via min/max quantity.
    • Via Symmetry: Upon selecting, compare base net’s via count difference with base net.
  • Include Via Length: Upon selecting this option, DFE will include via length for calculating trace length.