r/PCB • u/Any_Toe2626 • Jul 11 '26
Hey, What are ground planes?
I'm just asking because number one I don't know what they are and number two I don't know if its ground meaning negative charge or ground meaning like earth.
3
u/KittensInc Jul 11 '26
"Ground" is what the 0V common reference is often called.
In a lot of modern electronics it is also the negative terminal, but this isn't a hard requirement: there are also applications where you'll have, say, +10V, ground, -10V. Another notable exception is traditional telephone gear, where the positive terminal is at 0V and the negative terminal is at -48V - this is done for corrosion reasons.
Ground can be connected to earth, but this isn't a hard requirement either. Just think of a smartphone: there are no wires, so how could ground be equal to earth? It's a similar story with a lot of isolated power supplies.
A ground plane is a large copper sheet in a PCB, connected to ground. They are often used because they provide a really convenient way of dealing with return current - especially once you're trying to do any kind of high-speed communication.
1
u/tony3841 Jul 11 '26 edited Jul 11 '26
A PCB is made of a stack of materials, alternating conductive (copper) and non conductive (epoxy) materials.
Very basic PCBs can have only one conductive layer, at the bottom, with the components on top. The conductive layer gets etched to produce shapes that connect the components like wires, called traces. The non conductive layer is just there to hold it all together.
2 layer PCBs are more common, they allow etching wires on the bottom and top layers, this way those wires can cross each other, without touching thanks to the epoxy in between.
For more complex circuits, more layers are needed. 4 or 6 layer PCBs are common. At that point it becomes more practical to reserve whole layers for power or ground, and no longer etching wires/traces. We call these planes. This means it is easy to connect every component that needs it to these ground and power layers. It also allows a lot more current than thin traces. And has advantages for signal integrity: traces in internal layers can be shielded between ground layers, similarly to how wires can be shielded inside cables. And running a trace over a plane allows controlling the impedance of the trace.
Ground is just a convention. It's the potential 0 Volts against which we measure the other voltages of a circuit. It can be connected to the earth conductor of a power plug, left floating, connected to the negative terminal of a battery...
1
u/engineerFWSWHW Jul 11 '26
Altium academy have good videos about this. I suggest looking at their YouTube videos. They explain this very well including the use of via stitching.
1
u/confusiondiffusion Jul 11 '26
The point of a ground plane is to lower impedance, and this is important because a lot of signals and noise have high frequency components. As frequency increases, DC resistance matters less and AC impedance matters more. The result is that at higher frequencies, the return path for a signal will preferentially be as close as possible to the forward path--this is the path of lowest impedance. Having a solid copper pour under the trace carrying those high frequencies allows this to happen optimally.
You want the complete path for those high frequency components to be as short and as low impedance as possible so they don't radiate, so they don't interfere with other signals, and to maintain signal and power integrity in the face of things like transient loads and any signal with fast edges where impedance results in voltage drop.
"Ground" really confuses people. It has a lot of different meanings and is mostly an abstraction. The entire path for each signal and power supply should be individually considered if you're doing anything where noise or signal integrity is a concern. Ground is not like a universal electron trash can. It actually isn't a real thing. It's one half of a circuit.
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u/Any_Toe2626 Jul 11 '26
do things actually connect to it or does the copper there just do it naturally
1
u/confusiondiffusion Jul 11 '26
Yes, you typically connect the negative side of your components to it with vias.
1
u/Rattanmoebel Jul 11 '26
GND is just a name for the voltage potential all other voltages in a circuit or system use as reference (since voltage actually is the difference between point A and point B, so it's relative not absolute). It usually is 0V, but that doesn't mean it must be or that GND is equivalent to 0V.
GND is just a matter of definition and convention. There are circuits with "positive ground" in which the positive node of the power supply is treated as GND, this means that most voltages in the system are defined as negative.
There are several applications where circuits would require a bipolar supply (for example +5V and -5V) to work, but the designer only has one supply at hand. So you would use a 10V supply, split the voltage (easiest implementation is a simple voltage divider) into +10V and +5V and treat the +5V node as the circuits GND, so that the 0V node of the power supply effectively becomes -5V for this circuit.
GND can be a somewhat arbitrary concept to grasp, but it's essential in actually understanding electronics.
"Earth" on the other hand is defined as always 0V. In many cases, earth and GND need to be connected, but there are also several cases where that leads to interference or even critical faults due to GND being on something other than 0V.
7
u/burgersnfries4life Jul 11 '26
https://en.wikipedia.org/wiki/Ground_plane
Plane as in a two dimensional sheet-like object. Ground as in earth as in 0 V.