SM5847 propagation delay - diyAudio
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Old 16th April 2008, 06:09 PM   #1
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Default SM5847 propagation delay

Hi everyone,

I'm currently designing a new dac based on sm5847 + pcm1704 (can't find ad1862s).

I want to use a master clock at 256fs for sm5847 and use that clock to directly feed the bck of the dacs, since this is the bck that really matters on these.

The question is:
does anyone know the delay between XTI (256 fs masterclock) and the bcko produced by the sm5847 (same freq with x8 os) ??

I measured the sm5842 at around 28ns, but I think the sm5847 is more powerful, maybe more delay ?

thanks to all

I'll post the schematic when it'll be over
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Old 16th April 2008, 09:16 PM   #2
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Why not look it up in the datasheet ?
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Old 17th April 2008, 08:51 AM   #3
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Sorry, I missed that part in the datasheet.

It's not explicitely said but it should be in phase. For this point, it's better than the previous 5842.
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Old 17th April 2008, 04:29 PM   #4
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Default Re: SM5847 propagation delay

Quote:
Originally posted by apolon34
Hi everyone,

I'm currently designing a new dac based on sm5847 + pcm1704 (can't find ad1862s).

I want to use a master clock at 256fs for sm5847 and use that clock to directly feed the bck of the dacs, since this is the bck that really matters on these.

Have you tried this with the SM5842-based dac ?
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Old 17th April 2008, 05:38 PM   #5
flshzug is offline flshzug  Antarctica
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hi, how to get those 47's ?
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Old 17th April 2008, 07:42 PM   #6
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for flshzug : I bought them from vcamerica.com (10)
I plan to resell some after the project is finished.


For the reclocking, I didn't try yet with the sm5842. I plan to do it before the project with the sm5847, as a prototype.

My problem is that I need a bit more logic cause my actual dac is 20bit, so I have to add a 12bit shift register and delay the sm5842 clock to be in sync with the dac one (delay around 28ns for my sm5842).

Temporary schematic:
here
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Old 17th April 2008, 07:47 PM   #7
flshzug is offline flshzug  Antarctica
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I'd want 2 if you want to resell recently, 3-4 weeks also ok ..!
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Old 19th April 2008, 06:22 PM   #8
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I finished wiring the reclocking board for the SM5842.
It is now working !


Here is the schematic:
Reclocker

The 30ns delay is inserted before the flip flops to be in phase with the output clock from sm5842 (bcko). It won't be needed for sm5847 cause the clock is already in phase.

The data are then processing through a 12bit shift register (20 bit dac) or 8 bits (24 bits dac).
The dac clock is the XTI one (the GOOD one).

I had to add some delay to wcko line so the falling edge is synced with the clock one.
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Old 19th April 2008, 07:09 PM   #9
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And the point of all this ?
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Old 19th April 2008, 07:35 PM   #10
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bit clock is directly the master clock and so contain less jitter than the one generated by the digital filter.
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