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Old 14th October 2002, 08:24 AM   #31
kenev is offline kenev  Greece
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Hi all,
I see that the discussion goes on. I was away on wekkend - couldn't follow discussion. Really deep and thorough analysis, especially from "expert" Guido Tent. Unfortunately, I' m not a digital wizard and cannot contribute to this.
My question arose from reading this thread in relation to the way I should design the ground plane on my TDA1541 DAC. This will be fed directly from the I2S output of my CD-PRO2 cdp. That means, no other chip on board except two TDA1541s. From what I have understood, I come to the following configuration:
-two ground planes, 1 analog, 1 digital
-AGND and DGND of dac chips connected both to analog ground plane
-on the digital ground plane will be connected all the digital power supply circuitry, i.e., TL431 shunt regulator circuitry and bypass caps
-analog and digital ground planes connected together at one point

Any comments are welcomed.

Regards,
Evangelos
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Old 14th October 2002, 10:51 AM   #32
guido is offline guido  Netherlands
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Question any better ?

Hi all,

Evangelos, i am still searching too. Have the same problem, only my source is not
directly I2S, i have some logic in between (split I2S and reclocking). But also
two TDA's connected to digital.

I made a new version of the boards, with a digital groundplane and two
planes surrounding the DAC's (with moats inbetween (?)).
These are connected together on the board, like the multipleadc document suggested.
I needed 6 wires on the digital secion to complete the routing off all tracks.

If you have a look at the pdf's you see three tracks going from digital to each
DAC crossing the borders of the gnd layer. These are the clock, ws and dataline.

I still have the analogue ground connected as a 'star' to the agnd pin. Separate tracks
for decouplingcaps, output, VCC connector and decoupling caps and track to DGND pin.
Bad idea ?? I am still facing the problem of the AGND from the output pins being connected
via the digital gnd section.. Maybe i should try to get one start gnd circuit on the
analogue side or use transformers on the output like some designs or even one agnd plane.

Suggestions please!

Greetings,

Guido B.
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Old 14th October 2002, 05:15 PM   #33
kenev is offline kenev  Greece
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Guido B.,
As I explained, I'm not a digital wizard. I was only hoping to get an idea of correct pcb design. I have not yet completed the pcb design, so, as you can figure out, I have not tested the project to report about.
What I have in mind, is to solder everything that is connected to ground directly on the graound plane and not on the traces side of the board. In this way, I will not have ground currents running through the bottom of the board. So, no star wiring on the traces side.
What I have designed so far seems to be well accommodated: that is, everything is above AGND plane except the digital supply section, which lies on top of the DGND plane.
The two ground planes will be connected together at one point - don't ask me where should that be, I have no idea - any suggestions?
Anyway, my design seems to be simpler than yours, since I don't have all the digital stuff proceeding the dac chip.

Regards,
Evangelos
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Old 14th October 2002, 06:31 PM   #34
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Default Re: any better ?

Quote:
Originally posted by guido B
If you have a look at the pdf's you see three tracks going from digital to each DAC crossing the borders of the gnd layer. These are the clock, ws and dataline.

I still have the analogue ground connected as a 'star' to the agnd pin. Separate tracks for decouplingcaps, output, VCC connector and decoupling caps and track to DGND pin.
Bad idea ?? I am still facing the problem of the AGND from the output pins being connected via the digital gnd section.. Maybe i should try to get one start gnd circuit on the
analogue side or use transformers on the output like some designs or even one agnd plane.
Guido B. [/B]
Guido

It does not look that bad at all !. Realize that the DA chip has its' groun pins as reference. The "local star" you made is OK !

Wrt outputs: Take them rom the chip. The ground of the outputs should not be hindered by digital currents, i'e' make sure by design these currents do not run here, and you will be comfortable

Guido
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