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Parallel RC circuit for Chassis GND and Digital GND isolation

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haridharan

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hi in our design we've used a parallel RC circuit for Chassis ground and Digital ground isolation

the resistor value is 1M ohm and the capacitor is 1000pf_2KV

i was told that it's basically for "EMI ,EMC and ESD protection":?:

i would like to know why exactly it is used and how the the parallel circuit precisely works and helps preventing ESD and EMI/EMC noise


GND isolation.JPG




thanks in advance :-D
 

my assumption:
you have a electronic product which cannot be physically connect o the earth-so u use a chassis ground.
Now we have a Digital ground which is connected to a digital circuit and hence exposed to high speed switching which can cause EMI. This has to be prevented to go to the other digital circuits connected to the same digital gnd.
The cap offers very low impedance in high frequency and bypasses all the signal to chassis gnd and hence interference bet's digital circuits is prevented.

At zero frequency, the cap is open- but still you digital ground has to be connected to the chassis. Hence the resistor....
 

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