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Bruce Archambeault

The Ground Myth

Bruce Archambeault
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etnapowers
etnapowers
12/5/2013 4:55:06 AM
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Re: power ground and analog ground
@Ranasinghe:the post on power and analog ground is an example of the difference of theoretic design versus pratical realization. Theoretically you don't need two grounds, pratically yes, you need one ground to collect high pulsed current and one ground to be a reference to the logic signals, and you have to keep the two grounds at the same potential, by accordingly design your pcb layout. 

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SunitaT0
SunitaT0
11/30/2013 11:08:43 PM
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Re : The Ground Myth
@Bruce, thanks a lot for the post. I totally agree with you that term "ground" is probably the most misunderstood and misused term in electrical engineering. Your post definitely helps us to understand the concept of "Ground" clearly.

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Ranasinghe
Ranasinghe
11/30/2013 1:24:00 PM
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Re: power ground and analog ground
Thanks Bruce for the informative post.

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etnapowers
etnapowers
11/27/2013 10:49:47 AM
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Re: power ground and analog ground
@amrutah: thanks for your comment, this is the reason for why the designer's feedback is really important during the realization of the application board and the test board.

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amrutah
amrutah
11/20/2013 11:53:15 PM
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Finally the main sink is ground
Bruce,

   Thanks for an excellent post.

   You mentioned (w.r.t. the figure) that the electric lines of force may terminate on the VCC metal strip thereby causing a current flow into the VCC. Usually we will have a very good or wide Ground plane (usually 0V or near to it) metal strip, and that will form a capacitor with the VCC line.  The same switching current will then cause the electric lines from VCC metal to the ground plane thereby causing the current to return to ground?  So the final current is sunk in the ground plane.  Please let me know if I am wrong.

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amrutah
amrutah
11/20/2013 11:47:04 PM
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Re: power ground and analog ground

@etnapowers: Yes as you mentioned when designing IC's we have different grounds for Analog section, Digital section and substrate base.  This is done inorder to Isolate the return current paths for these sections so that the highly switching digital logic don't interfere/disturb the analog section.

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etnapowers
etnapowers
11/18/2013 9:59:39 AM
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ground paths as decouplers
When designing a PCB, a good strategy is to insulate two signal paths by surrounding the signals with ground planes. This will avoid cross talking and will provide a return path for the current.

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etnapowers
etnapowers
11/18/2013 9:27:01 AM
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power ground and analog ground
Many times I have engineered devices having two different ground pins: the analogic and the power ground.

In pcb traces, these path have to be separated but the potential has to be kept the same . The power ground has to dissipate an high pulsed current coming from power switches, and its potential can rise , hence the only chance to control the voltage is to force externally to a zero voltage the power ground pin, by checking the analog ground voltage, which acts as a feedback signal.

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etnapowers
etnapowers
11/18/2013 9:17:27 AM
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Voltage in maxwell equations
The voltage is a function that in static case is the scalar function that  originates the electrostatic field:

E=-grad V

being E a vector and V a scalar function.

 

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D Feucht
D Feucht
11/17/2013 10:18:27 PM
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Re: Co-planar waveguide and other tricks
Bruce,

In answer ot your friend who claimed that "Maxwell's equations, ... are accepted as the basis for all electromagnetic (and therefore circuit) theory", I would add that they are also not the completion of fields theory. Some physicists think that electric and magnetic potentials are more real than the fields.

There is still a concept of ground (0 V) in distributed-parameter circuits because even in them, currents flow in closed loops and somewhere in the loop(s) is a spatial point at which the electric potential is deemed to be 0 V. However, as you point out, one must be (spatially) careful in declaring such nodes in distributed-parameter circuits!

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