Return Path
- Item: Input item name.
- Net: Select a target Net from the Net Class list.
- Reference: Select a Ground Net from the Net Class list to search for the Return Path.
- Pass/Fail Criteria: Define the value (Ratio or Distance) to detect the fail of Return Path and Signal.
- Check ratio: Check ratio between net length and return current path.
- Check distance: Check maximum allowable detour distance of return
path.
Figure 1.
- Check distance: Check maximum allowable detour distance of return
path.
- Consideration: Addition factors for Return Path search.
- Select Start Component in case of Branch net: When searching Return Path of multiple pin (more than 2 pins) net, a start component must be defined. Return paths are searched from the start component to all other components or pins.
- Except Component Group: Certain types of components or pins can be excluded from searching return path. (For example, Test Points)
- Flow current along via location: To search for the shortest return path one
multiple ground layers connected by via. When it is not checked, return path
is searched on a superimposed ground layer.
- Not checked: The return current always goes through capacitance
between two planes regardless of via existence.
Figure 2. - Check: The return current can go through only if there is stitching
via.
Figure 3.
- Not checked: The return current always goes through capacitance
between two planes regardless of via existence.
- Ignore return path for near area to pin: Complete the return path search to
the ground plane edge.
- Will not check pin area: Enter a radius of circular region around pins to be excluded for the rule check.
- Return path to pin: Select the way to complete the return path search.
- Consider Return Path from GND Pin to GND Pin: Complete the return path search to the ground pins that are closest to the signal pins. (Fig. below, path ‘B’)
- Force make return path to pin: Force return path to connect to
directly to GND pins as shown in Fig. below. (Fig. below, path
‘A’)
Figure 4. Return path connection compensation
![](../../../images/pollex/dfe_return_path_loop_antenna.png)
Figure 5.
The electrical field strength is proportional to loop size, so it is very important to reduce loop size of circuit in order to reduce EMI noise.