Beefy
Headphoneus Supremus
- Joined
- Mar 4, 2008
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The same thing I have been saying...... *deep breath*
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So current is being sourced/sunk current directly from/to ground. There is no guarantee that there is current right there from the opposite rail. So localised ground impedance means that the potential of ground will change as current flows.
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So current isn't being sourced/sunk from/to ground. Whatever is required by the positive rail is always right there on the negative rail.
The current just moves from one rail to the other, without ground actually needing to contribute. Whatever goes into ground goes straight back out again, right there locally, with much lower impedance than sourcing/sinking from the whole ground plane.
The signal ground, the reference point for the whole circuit, doesn't see any sourcing or sinking of current because it is always cancelled out locally.
Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif It depends on what you mean by passing "directly through" the caps. |
The same thing I have been saying...... *deep breath*
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Consider the reservoir cap on the positive side of the power supply in A, the passive ground example. Load current flows from the capacitor's negative plate, through the ground node, and then to the driver's negative terminal, and then on around the loop, where there is an equal amount of load current flowing into the capacitor's negative plate. |
So current is being sourced/sunk current directly from/to ground. There is no guarantee that there is current right there from the opposite rail. So localised ground impedance means that the potential of ground will change as current flows.
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Now let's consider B, the active ground example. Again, let's start with the reservoir cap on the positive side of the power supply. Load current flows from the capacitor's negative plate, through the ground node, just as it does in the passive ground example. The only difference here is that instead of flowing next into the driver's negative terminal, it flows into the positive plate of the reservoir cap on the negative side of the power supply. Of course that current can't flow into that cap's positive plate without an equal amount of current flowing out of it's negative plate. And this current flows through the negative rail, the output stage of the ground amp, finally to the load itself, and ultimately on back to the positive plate of the positive rail's reservoir cap. |
So current isn't being sourced/sunk from/to ground. Whatever is required by the positive rail is always right there on the negative rail.
The current just moves from one rail to the other, without ground actually needing to contribute. Whatever goes into ground goes straight back out again, right there locally, with much lower impedance than sourcing/sinking from the whole ground plane.
The signal ground, the reference point for the whole circuit, doesn't see any sourcing or sinking of current because it is always cancelled out locally.