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The differtial line in layout

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chang830

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Hi,
In the layout of the differtial line, is it the closer the differtial lines in layout then the better for the performance?

thanks
 

generally, yes, but you need to consider two more skills:
1. too close routings may introduce more line2line coupling, that means the capacitive loading of the signal may be bigger, so leave some space can be benificial.
2. pay attention to environmental noise coupling, sometimes for critical differential signals, ground shielding is necessary on both sides.
 

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    chang830

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chang830 said:
Hi,
In the layout of the differtial line, is it the closer the differtial lines in layout then the better for the performance?

thanks
Click to expand...


they must be. but this introduces capacitive coupling bet the 2 lines. to reduce the capacitive coupling, put dummy metal between them.
 

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    chang830

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sxunxs said:
chang830 said:
Hi,
In the layout of the differtial line, is it the closer the differtial lines in layout then the better for the performance?

thanks
Click to expand...


they must be. but this introduces capacitive coupling bet the 2 lines. to reduce the capacitive coupling, put dummy metal between them.
Click to expand...


Hi sxunxs

Can u elaborate ur statement please.I would like to know, how dis dummy metal is added in between and what its effects are .

regards
Brittoo
 

hi srieda

I am sorry but that link does not answer my question.When u say "a dummy metal", do you actually mean a shielded metal line?


Regards
Brittoo
 

Brittoo said:
hi srieda

I am sorry but that link does not answer my question.When u say "a dummy metal", do you actually mean a shielded metal line?


Regards
Brittoo
Click to expand...

the dummy metal acts as the common node of the parasitic capacitance bet the diff pair.
theredore, the parasitic capacitance will be seen as series from the first input to the common node and from the common node to the other input.
 

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