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Why do we use ground shields for noise?

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mince

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Sometimes ground shields are used to shield from noise. Why do we use ground? Why not Vdd?
 

neoflash

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Shielding question

You can use both.

Sometimes, different chips use different power supply, but they share the same ground. That make ground shielding more common.
 

bjeservice

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Shielding question

also i think that if you use Vdd it may has internal resistance to supply the noise to sink.
 

Teddy

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Re: Shielding question

cause ground is considered "ideal" unlike VDD. On VDD is usualy more noise due to the switching.
 

VSMVDD

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Re: Shielding question

to get rid of noise

you decouple it to ground

becouse all energy take's the shortest return path in an effort to balance its self somewhere else

so the noise goes with it


hopefully....


i like your use of 'sometimes ' :D

if you decouple to vdd your adding noise to the rest of the circuit again

instead of taking it away some where else more negative then vdd

+ noise 180 deg out of phase with the same negative noise
= 0 noise
 

neoflash

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Re: Shielding question

Teddy said:
cause ground is considered "ideal" unlike VDD. On VDD is usualy more noise due to the switching.

There should be no difference between GND/PWR on noise wise.
They are one loop. Your decoupling strategy should depend on your receiver is referenced to GND or PWR.
 

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