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mcs

    Denmark
Simple DAC
« on: November 06, 2004, 02:39:04 PM »
I need a DAC for testing some of my other projects. So I looked for a DAC chip that was simple to use, and had the features I need, and found the CS4340A. The features are 24bits, stereo and samplerates up to 192kHz BTW.

Here's the schematic: http://stiftsbogtrykkeriet.dk/~mcs/DAC1_sch.gif

It's mostly from the datasheet. I put in a mute relay instead of the transistors though. If anybody notices any errors please tell me about them before I make the PCB :wink:

Best regards,

Mikkel C. Simonsen


slash14

Simple DAC
« Reply #1 on: November 06, 2004, 04:07:05 PM »
Instead of R7, I would have placed a small inductance to avoid digital noise to pollute analog ground.

Just my 2 cents ;)

daArry

    londaaan
Simple DAC
« Reply #2 on: November 06, 2004, 04:31:36 PM »
speaking of noise I guess pcb layout can come into play here but this is a massive subject in its own right from what i've been reading/chin rubbin over so far...

What's ur thoughts for a regular dbl sided layout? Split A and D gnds (on both sides of the brd)? Then joined under the dac? what if your brd had 2, 4, 8 etc dac chips...

mcs

    Denmark
Simple DAC
« Reply #3 on: November 06, 2004, 04:37:08 PM »
Quote from: "daArry"
What's ur thoughts for a regular dbl sided layout? Split A and D gnds (on both sides of the brd)? Then joined under the dac?

That's what I would do yes.

Quote
what if your brd had 2, 4, 8 etc dac chips...

Perhaps you could place the chips so that half the board was analog and the other half digital?

Best regards,

Mikkel C. Simonsen

daArry

    londaaan
Simple DAC
« Reply #4 on: November 06, 2004, 04:41:57 PM »
Quote
Perhaps you could place the chips so that half the board was analog and the other half digital?


ye do that, but then if u join under each dac u'd create loops right - or just join in one spot i guess...or how about keeping them sep all the way bak to the psu?

mcs

    Denmark
Simple DAC
« Reply #5 on: November 06, 2004, 10:37:23 PM »
Quote from: "daArry"
or how about keeping them sep all the way bak to the psu?

Maybe that's the best method.

Best regards,

Mikkel C. Simonsen

mcs

    Denmark
Simple DAC
« Reply #6 on: November 06, 2004, 10:40:15 PM »
Here's my PCB drawing:



Actual size is only 7*4.2cm. I didn't do any groundplane on the top (I was too lazy), but I think it will still work...

Best regards,

Mikkel C. Simonsen

daArry

    londaaan
Simple DAC
« Reply #7 on: November 07, 2004, 04:00:11 AM »
Nice :thumb:. What size (mill) do u use for the various signals?

mcs

    Denmark
Simple DAC
« Reply #8 on: November 07, 2004, 08:26:00 AM »
I use the standard sizes in my software. The thin ones are 0.32mm and the thick ones are 0.95mm (you do the mill convertion :wink:). I use the thin traces most of the time, but I like to use the thicker ones for the audio path, power and ground - when there's space for it.

Best regards,

Mikkel C. Simonsen

mcs

    Denmark
Simple DAC
« Reply #9 on: November 07, 2004, 08:27:29 AM »
Quote from: "slash14"
Instead of R7, I would have placed a small inductance to avoid digital noise to pollute analog ground.

What size/type would you use? I placed R7 on the top layer, so I could use an SMD inductor instead of a resistor...

Best regards,

Mikkel C. Simonsen


Svart

    Atlanta GA USA
Simple DAC
« Reply #10 on: November 08, 2004, 07:49:43 AM »
MCS, I would use a small value ferrite bead for your coupling between Agnd and Dgnd.  I was troubleshooting a video device proto for my company and came across a grounding setup like this one only there was just a copper bridge, no ferrite.  the ground bounce was so bad that the analog power for the video circuit was actually causing severe noise on the video.  I cut the track and placed a ferrite there and it works like a dream now.  I don't remember what the value was though..  what are you using for your clk source?  as i remember, you can also run the clock through ferrite too but the values have to be spec'd properly.

hope this helps..?

 :guinness:
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

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mcs

    Denmark
Simple DAC
« Reply #11 on: November 08, 2004, 07:57:35 AM »
Quote from: "Svart"
what are you using for your clk source?

Since this is a test board, it could be either a "canned" crystal oscillator, the recovered clock from a CS841x or my PLL1707 board.

Quote
as i remember, you can also run the clock through ferrite too but the values have to be spec'd properly.

With a clock frequency that's not fixed, I guess that would be difficult.

Quote
hope this helps..?

Yes, thanks.

Best regards,

Mikkel C. Simonsen

slash14

Simple DAC
« Reply #12 on: November 08, 2004, 08:31:51 AM »
Svart has been faster than I to answer but his answer is complete ;)

I used an inductance between AGND and DGND on the same kind of project but I can't remember the value, sorry.


 

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