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question about two power wires

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vadim888

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question about power wire

Hi all,


I have few questions about vdd and gnd wires placement.

Is it better to place vdd over gnd?
  • f.e. m3 is gnd, m4 (top) is vdd.
What do you think about distance between analog vdd/gnd and digital vdd/gnd in typical cmos 1.8u process? How better to place analog and digit wires.

Thank you all,

Vadim.
 
Last edited:

Re: question about power wire

vadim888 said:
Is it better to place vdd over gnd?
  • f.e. m3 is gnd, m4 (top) is vdd.
Click to expand...

In pad rings the power lines usually are on same metal level (because the space beneath is used by I/O and ESD protection circuitry). But there's no reason why not to put them over each other, with the additional (desirable) effect to achieve some (tiny) parasitic capacitance between them.

vadim888 said:
What do you think about distance between analog vdd/gnd and digital vdd/gnd in typical cmos 1.8u process?
Click to expand...
Just use the width-dependent design rules.

vadim888 said:
How better to place analog and digit wires.
Click to expand...
Depends on your requirements: for shielding analog signals use min. spacing. Use wider spacing to keep parasitic capacitance low, if necessary.
 
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