Defining and Assigning Power Nets

What is a Power Net?

A net is considered to be a power net if both these points are true:

• It connects to a node that is capable of sourcing or sinking current in excess of a few milliamps without its voltage varying significantly
• Its voltage is at a level that could represent a digital signal in the circuit being tested

Typically, a power net will be associated with a regulator (either analogue or DC switching) or with a power connector on the unit being tested; or be connected to such a net via a device such as a ferrite bead, fuse, or power filter.

Voltage rails derived from a potential divider are not considered power nets because they cannot supply current without their output voltage varying significantly. The output of a termination voltage regulator would not be classified as a power net because it is typically mid-supply and therefore cannot convey a digital level (such nets need to be categorised as termination voltage nets instead).

How to Assign Power, Ground & Termination Voltage Nets in XJDeveloper

Power, ground, and termination voltage nets are assigned in XJDeveloper's Power/Ground Nets screen, which is located within the list of screens under the Setup header:

Figure 1: Opening the Power/Ground Nets Screen

The following process is used to tell XJDeveloper which nets are power, ground or termination voltages. This user guide describes these individual steps in detail.

• It is important to spend time early in a project setup to ensure voltage rails are correctly identified. Failure to do so can cause problems later for the reasons described above.

1. Review XJDeveloper's proposed net categorisations and assign the obvious power, ground and termination voltage nets to their categories
2. Categorise remaining power and ground nets using XJDeveloper's intelligent analysis of the circuit to find the less obvious ones
3. Check the categorised nets for any mistakes