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this is more of a concept question than a physical circuit question. I am not an electronic engineer and only build electronics as a hobby in my free time so I do apologize if I am missing something simple. Before continuing with my question I did try and search around for a answer to my question but was unable to find it.

In general if you are using a transformer (not a battery powered circuit) your "ground" or "neutral" connection is not physically connected to the neutral wire from your outlet (even if it was I think my question would still apply). In any case if you are driving a load with a lot of wattage wouldn't there be voltage transients (I think I am using the words "voltage transients" correctly) on the ground plane? We use decoupling capacitors near a IC due to the fact that there are resistances and inductances in the VCC/VEE planes which cause the voltage to drop when current is drawn (also not to mention the fact that no regulator would be able to perfectly handle this issue anyway). But if for example you have a motor or speaker load wouldn't the current passing through the load cause the voltage on the ground place to change as well (I mean the ground plane isn't magical it would also have resistance/inductance)? Also, the fact that the ground plane would just travel straight back to the transformer.

On to the dead straight question. Would it be worthwhile to create a "regulated" ground (for example with a lm317/337) if your project was noise sensitive (1mV of noise would be noticeable)? Or does something I am not understanding come into play that makes it irrelevant and the ground will always be 0 volts?

Thanks for reading this far, and thank you for answering if you do so!

Edit:

Regulated Ground Plane Example: Regulated Ground Plane

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    \$\begingroup\$ You are correct in your understanding that a physical ground plane is not exactly 0 V throughout (if current is flowing). The best way to reduce the noise is by reducing the ground plane impedance/resistance, and making sure that high-current pulses do not tend to follow a return path directly next to very sensitive circuits. I don't see any way that you could "regulate" ground as you describe though. \$\endgroup\$
    – Justin
    Jul 30 '20 at 14:48
  • \$\begingroup\$ @Justin - For example if you use a lm336 in the center of a voltage divider (with two resistors of equal value) you would have 1.25v and -1.25v. You can use a lm317 from the positive rail referenced to the -1.25v to give you near zero and the lm337 referenced to the +1.25v from the negative rail to also give you near zero. Throw in some very low value resistors to account for slight offset and you would have a "regulated ground" such that if the voltage increased or decreased the regulators would keep the voltage at near 0. \$\endgroup\$
    – Boeggs
    Jul 30 '20 at 14:56
  • \$\begingroup\$ So it may be possible to have several points on the circuit board be regulated to an average voltage closer to ground than you would otherwise get with a normal ground plane. I'm suspect it would be more complicated than the way you describe, but I'm sure there is a way. However, there's almost never a good reason to do this. What we are usually more concerned about is high frequency signals causing temporary disturbances in the ground plane. The regulator would have some delay responding to this temporary disturbance. ... \$\endgroup\$
    – Justin
    Jul 30 '20 at 15:04
  • \$\begingroup\$ ...This would end up causing voltage spikes that would probably be larger (probably much larger) than the simple continuous ground plane method. The other thing to keep in mind is that if you need an very precise supply voltage at a certain circuit (supply voltage minus ground voltage), you could just put a local supply regulator near the circuit that regulates relative to the local ground and achieve the same thing with more normal methods. \$\endgroup\$
    – Justin
    Jul 30 '20 at 15:06
  • \$\begingroup\$ @Justin I see, so for example in a audio amplifier having a regulator for both positive and negative voltages in close proximity to the power stage would be better due to the fact that the positive and negative regulator will respond to any voltage changes on the nearest spot on the ground plane anyway, keeping the voltage regulated. Also I added a schematic above of a regulated ground that I tested working. I was originally using it to split a single ended supply and produce a virtual ground. \$\endgroup\$
    – Boeggs
    Jul 30 '20 at 15:11
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The Ground can be clean, if designed to be clean.

Or, as you suspect, horribly dirty with OHMS Law predicting

  • V = I * R (for DC; where the R is 0.0005 ohms per square of foil on a PCB)

and

  • V = I * Z (for AC; you should use the 0.0005 ohms, plus any inductance)

or

  • V = L_inductance * dI/dT (for transients --- the real world)

voltages.

The inductance of a square Ground will be low low nanoHenries, or even high picoHenries.

But 100 milliAmps changing in 2 nanoSeconds (a MCU driving a heavy load), and that current seeking a return path (to the VDD bypass cap, etc) will have this voltage in the Ground

V = L * dI/dT = 2 nanoHenries * 0.1 amp/2 nanoSeconds = 0.1 volts.

Sometimes you can use SLITS in the GROUND foil, to steer return_currents into regions that tolerate lots of Ground Spikes.

Consider this

Should I really divide the ground plane into analog and digital parts?

======================================================

If you establish "local batteries" for separate circuits, with large capacitors to supply the local transient currents, with series resistors of value 1 Ohm or 10 ohms that insure some separation of the sensitive circuit's VDD and the bulk/global DC, then variation of the GROUND currents can be very small.

I've discussed the "local battery" in a number of stackX answers.

By using differential_pairs in your pre_amplifiers (most opamps use diff_pairs in the input stage), you can take advantage of the substantial Power Supply rejection ratio (PSRR).

Note that transformers for audio signals will inherently provide a useful isolation of Ground DC currents.

Using separate power supplies for Preamps and for power Amps is a good idea.

Power transformers will have 100s of microAmps at 60Hz coupled into the secondary winding, and that current WILL FIND A RETURN PATH.

Notice high end phono turntables include a 5th wire from the turntable chassis, to be attached to the Preamp chassis. That helps reduce the 60Hz current (from power transformers) that use the cartridge wires as return paths.

Even if the cartridge is totally floating; there are still EFIELDS from the wires or cartridge shell to other metal parts in the turntable.

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  • \$\begingroup\$ Hey @analogsystemsrf, thank you for validating my understanding that there is in fact voltage transients on the ground plane. Also after reading your post that you linked I will definitely take that into account when designing my next pcb. A single question I have remains. Lets say in a amplifier design where you have a opamp pre-amp stage, and 2 separate bjt buffer stages. Then lets say for the pre-amp and each individual buffer stage you have a lm317/337 creating +-17 volts and then use the circuit I exampled above to create the ground plane for each sub-circuit. Would giving each.... \$\endgroup\$
    – Boeggs
    Jul 30 '20 at 16:13
  • \$\begingroup\$ individual sub-circuit it's own ground plane referenced from the +- rails be worthwhile? (No connection to the primary ground from the transformer other than the +-17volt regulators, the ground planes would not have any connection at all to the incoming ground from the transformer and instead all be separated) \$\endgroup\$
    – Boeggs
    Jul 30 '20 at 16:13

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