All electronic devices, such as televisions and telephones, have one or more Printed Circuit Boards or PCBs. A typical PCB contains a large number of electronic components connected together through traces on the board. To operate the circuit, some power supply provides the voltage. For the circuit to function properly, the ground of all the components on the board should be equal to the ground of that power supply.
Ground Plane
A ground plane is a piece of copper on the board covering a large area. It is a good practice to cover all places on the board that do not contain a component or a trace with the ground plane. A trace is a thin piece of copper on the board that connects two components together. It acts like a copper wire. Generally the ground plane is made on both sides of the board, but the component side plane is sometimes kept at the supply voltage while the plane on the other side is grounded. The ground plane should be connected to all the ground pins of components and connectors. This helps keep the ground voltage at the same level throughout the board.
Ground Plane Vias
If both sides of the board have ground planes, they should be connected together through vias at a large number of points on the board. A via is a hole through the board that connects both sides. If the original PCB layout does not contain vias, use a small drill machine to drill multiple holes. Small copper wires can then be passed through these holes and soldered on both sides to make connections.
Connector Grounds
All connectors on the board must be connected to the PCB ground. A good practice is to use more than one connector pin for ground. A common mistake is to assume that one connector pin is enough, but this may cause impedance mismatch issues leading to signal oscillations. Impedance refers to electrical resistance --- when two conductors are connected together, their impedance should match. If there is a mismatch, the current flowing through the conductor may bounce back and forth, causing oscillations. These oscillations can affect the performance of the system. For example, when the signal is supposed to stay at a constant level but instead goes up and down or oscillates, the circuit will not work as intended.
Decoupling
All PCBs contain one or more integrated circuit chips. Each of these chips requires power to operate. The supply and ground pins are provided on these chips to connect them with external power. The ground pin of the chip should be connected directly to the ground plane. A decoupling capacitor should be installed between the supply pin and the ground plane. The purpose of this decoupling capacitor is to smooth out oscillations in the voltage going into the chip. The other end of the decoupling capacitor should be directly connected to the ground plane.
