SNAA406 August   2024 LMK6C

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction and Test Methodology
  5. 2Routing Topologies and Simulation Results
    1. 2.1 Single-Line
    2. 2.2 Star Line
    3. 2.3 Split Line
    4. 2.4 Star Line vs. Split Line
  6. 3Summary
  7. 4References

2.1 Single-Line

This is the typical configuration for a single-ended signal. The single line configuration is recommended for the best signal integrity since the number of nodes are reduced to only one load per line. The single-line, single-load configuration is used as a benchmark for the other topologies that were tested.

Single Line, Single Load Topology Figure 2-1 Single Line, Single Load Topology

The single-line, multi-load configuration is a good option for driving multiple loads when the separation between them is small. Some common use cases for this topology include driving two clock input pins on the same device, or multiple devices that are closely located. To be considered a single-line in the context of this study, the distance between loads need to be limited to under 1". The assumption is that each load is an equal distance from the main line, therefore LS is the same length for each receiver.

Single Line, Multiple Loads Topology Figure 2-2 Single Line, Multiple Loads Topology
Single Line Simulation Results Figure 2-3 Single Line Simulation Results
Table 2-1 Single Line Rise or Fall Time
Number of Loads Trace Length - LM Rise Time (ns) Fall Time (ns)
1 6" 0.676 0.763
2 6" 0.938 1.105
4 6" 4.010 3.946

For single line configurations, driving two loads produces acceptable signal quality with only slightly longer rise and fall times and almost no measurable reflection artifacts.

With the addition of four loads, the rise/fall time slows significantly but there are still minimal reflections in the waveform.