Method and apparatus for decoupling of unused power supply pins of a printed circuit board capable of operating at a plurality of predetermined voltages

In a printed circuit board (PCB) capable of operating at first and second predetermined voltages, the PCB including a plurality of layers, the PCB also including a first and second plurality of signal pins for operation of the first and second predetermined voltages, a method for decoupling the first plurality of signal pins when the PCB is operating at the second predetermined voltage comprising:

• dividing one of the plurality of metal layers such that two electrically isolated metal sections are provided on substantially the same plane, one of the electrically isolated metal sections being associated with the first plurality of signal pins;
• the other of the electrically isolated metal sections being associated with the second plurality of pins;
• and
• coupling at least one capacitor to a ground layer, the one of the electrically isolated metal section and the first plurality of signal pins to provide an alternating current return path.

An expansion board for use in a personal computer, the expansion board being capable of operating at 3.3 volt and 5 volt levels comprising:

• a plurality of metal layers, one of the metal layers being divided to provide two electrically isolated sections, the two electrically isolated sections being on substantially the same plane;
• one of the electrically isolated sections being a 5 volt power supply plane and the other of the electrically isolated sections being a 3.3 volt power supply plane;
• a first plurality of signal pins coupled to the 3.3 power supply plane, the first plurality of signal pins being unused when the expansion board is operating at the 5 volt level;
• and
• a plurality of capacitors coupled to a ground plane, the first plurality of signal pins and the one of the electrically isolated metal sections, the plurality of capacitors averaging at least 0.01 .mu.F per each of the first plurality of signal pins, each of the plurality of capacitors includes a trace length to each pin of the first plurality of signal pins which is less than 0.25 inches;
• wherein an alternating current path is provided.