Wider Trace

[Electronman]

Hi,

The ground wire (trace) in most PCB's tend to be wider than other traces.
I have heard that it is to cancel noises, and or make other traces to do not act like a capacitor with each others.
Can somebody explain it to me please?

Thanks in Advance

 

[Boncuk]

Supply traces have to carry a higher load than signal traces.

Not only the ground trace, but also the positive supply voltage should have a wider trace.

Boncuk

 

[Electronman]

So what will happen then??!

 

[mneary]

The trace named "ground" is usually used as a reference against which all (most) other signals are referred. It's good design practice to minimize the voltage potential between any two locations on "ground".

The "power" trace carries more current than the typical "signal". To achieve lower losses, it's made wider as required.

 

[Electronman]

Thanks but I am not sure if I got it!

Is that the whole story for it? It has nothing to do with noises?
I have seen SW selectors and intermediate frequency inductors have a metalic can/cover connected to ground too??

 

[dougy83]

As mneary said, the wider ground trace minimises the potential difference between different locations in the circuit by providing a lower impedance path. As ground is often used as the reference, any potential difference is the 'noise' you mentioned. Where amplifiers are used, the potential difference in the reference is often amplified as well.

 

[Electronman]

Oops!
What this means??: "any potential difference is the 'noise'".

What I seem to understand from your posts is that we make ground trace wider because
more current is following through it and so we try to choice a wider trace for the ground to have less RESISTANCE in the ground trace,right?

 

[Boncuk]

Just a short math example.

Consider you want to feed 10 ICs from the same power source each demanding 1mA for proper function.

Keeping the supply traces for the current flow of 1mA nine (most probably all) of the ICs will suffer from lack of power.

Widening the supply traces has nothing to do with noise being produced on a PCB because of poor engineering.

AF-circuits of poor design normally have feedback in the wrong direction, resulting in noise or other abnormal circuit behaviour - which might happen due to poor trace routing.

Boncuk

 

[crutschow]

For high speed circuits they often use a ground plane (sold copper plane) to minimize ground resistance and inductance, and thus minimize ground noise due to high speed signals.

 

[dougy83]

Oops!
What this means??: "any potential difference is the 'noise'".

What I seem to understand from your posts is that we make ground trace wider because
more current is following through it and so we try to choice a wider trace for the ground to have less RESISTANCE in the ground trace,right?

There's not necessarily any more current flowing in the ground trace, but yes, we want to reduce it's resistance/impedance so that currents flowing in it don't create much voltage drop. Ideally, the ground/reference voltage trace voltages should be the same at every point on the trace.

 

[ke5frf]

In other words, to the OP, you would not want to be able to take a voltmeter from any point on the ground trace and another point on the ground trace and read any potential whatsoever. With a trace that is physically too small, there will be a potential set up across it from one extremety to the other, therefore a series resistance. Since ground is the reference from which all points in your circuit work, it would be undesireable to have such a situation.

 

[Electronman]

I think I need an explanation paper about the philosophy of wide trace for ground and for metallic objects in a circuit (like a metallic covered inductor inside a radio).

 

[unclejed613]

wide traces have lower resistance. a ground plane has very low resistance..power traces are usually wider because they carry more current, just like power supply wires are usually thicker the wider trace lowers resistance, so the voltage drops are kept to a minimum. the purpose of the metal can is to prevent the component inside it from either picking up stray signals from another part of the circuit or radiating signals to another part of the circuit, and is 99.9% of the time grounded (don't worry about the other 0.1%, you will most likely never see it).

 

[Boncuk]

I think I need an explanation paper about the philosophy of wide trace for ground and for metallic objects in a circuit (like a metallic covered inductor inside a radio).

I guess you won't need an explanation paper about wider supply traces. Take a look at the attached sample PCB and decide what all other ICs will do if relay K1 pulls in.

Boncuk