On Wed, 30 May 2001, William Tan wrote:

> Hi, Mr. Vasile Surducan.
>
> I not very sure about a few things you mentioned:-
>
> (1) My question is after transformer , then bridge diodes, then voltage
> regulator (example 7812, 7912, 7805). Like my amp use +/-12V and my digital
> IC use +5V, is this mean that analog and digital power is seperated?

Yes, if your ground respect one point, low impedance connection.
Long routes means some resistence. The output of a good power supply has
output impedance almost 0 ohm . Conecting grounds with short routes in
that point will result a "low impedance point"

 Else the "garbage" ( noise, spikes etc ) will jump through ground layers,
from digital to analogic section.

 If said,
> my analog IC and digital IC also use +5V, then I need two voltage regulator?
>

 Only if your digital section is garbage generator ( ie: high frequency
digital circuits without good filtering capacitors ) with many integrated
circuits disposed on a large area.

>
> (2)  The analogic ground and digital ground must be tied together (only once!
> ) in the lowest impedance point ( usual near supply ).
>
> What do you mean about ( only once! ) and low impedance point??? Very
> confuse, can imaging that these two ground can be seperated???

Sorry for my poor english: only once in my imagination means only in one
point, near the power supply. You will have two grounds plane or layers
connected in one point.

I hope is much clear now.

Vasile





> > On Wed, 30 May 2001, William Tan wrote:
> >
> > > Hi, all.
> > >
> > > I like to know how to seperate the Analog and Digital Power and Ground?
> > >
> >
> >   In a few words: analogic section of your project must be supplied from
> > different GND and VCC lines like digital section. Usual the autorouter
> > can't produce correct layers connection, so these must be routed manually
> > or using all restriction that autorouter have.
> > The analogic ground and digital ground must be tied together (only
> > once! ) in the lowest impedance point ( usual near supply ) else nothing
> > will work ( you can't keep these grounds separated only if you are using
> > floated design, much expensive because need isolated ad converters )
> > The analogic and digital power ( VCC or +V ) could be from different
> > supply ( not necessary all the time).
> > However the analogic supply must be clean and stable.
> >  Pics have different power supply for analogic and digital function, so
> > you can easy separate this layers.
> >
> > Vasile
> >
> > --
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>
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