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# Questions About Analog? Step Right Up

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3/28/2013 4:05:06 PM
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Blogger
Re: Real world grounding concern
And of course, real systems often must be configured in such a way that the single point star-ground cannnot be accomplished.

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2/12/2013 4:27:37 PM
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Blogger
Re: Modules can an have its own ground...
It's OK (in general) if there are different ground potentials - until you have so much difference that you push the receiving end circuitry's input way beyond its acceptable range. Then it either stops working until the common mode voltage comes back into range and the input circuitry comes out of sturation; or it gets damaged and never recovers.

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JAYARAMAN KIRUTHI VASAN
2/8/2013 8:09:06 AM
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Newbie
Re: Modules can an have its own ground...
amrutah,

I also can think of another situation where the ground can be different - the 4- 20 mA loop. When it is converted to voltage at the destination circuit, typically by a resistor of appropriate value, the lower (cold) end of the resistor would normally be the ground at the destination.

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SunitaT
2/7/2013 5:32:24 AM
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Student
Real world grounding concern
Brad, Thanks for the post.

In real world, primary concern is considering current flow and current paths. We need to have a different reference ground for high-speed clock signals than the reference ground for low-level audio signal, so that the transient current from switching does not affect the ground reference for tiny signals. The grounds are tied together at one point, so that there is no circuit path for current to travel between the paths, but they are at the same potential voltage.

Real ground paths often have resistance, inductance and capacitance and signals take time to travel from one part of the circuit to another. Different paths wouldn't be necessary if we had an ideal ground(zero volts).

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amrutah
2/6/2013 4:48:42 AM
User Rank
Master
Modules can an have its own ground...
@Brad: I agree, "Differential signaling on a twisted pair of wires..."

this helps reduce the common mode noise riding on the signal, but this also helps us by removing the dependance on the Suppy or ground references, the destination module can have different ground plane compared to the source ground plane.

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