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Breaktru Forum  |  eCigarette Forum  |  Modding  |  Simplified Electronics  |  Topic: When GND Isn’t GND, Single-Ended Circuits Become Differential
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Author Topic: When GND Isn’t GND, Single-Ended Circuits Become Differential  (Read 3947 times)

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Online Breaktru

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Offline CraigHB

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Re: When GND Isn’t GND, Single-Ended Circuits Become Differential
« Reply #1 on: July 20, 2014, 02:56:01 PM »
Yes for sure that's an issue you have to constantly consider in PCB design.  For low current stuff it's less of an issue but when you get in to the higher currents, ground is only ground at one point on the PCB.  You have to consider variations in potential over your whole ground plane. 

Where the issue gets you is in control circuits or measurement circuits.  For example, you can't use a simple non-inverting amp when measuring current with a low side current sense resistor.  You have to use a differential amp that measures both the high and low side of the resistor even though the low side appears as a ground symbol in a schematic.  On the PCB, it's not ground at all and can be offset by several hundredths of a Volt which is a cavernous amount for a high gain amplifier.

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