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DAC Differential Outputs
DAC Differential Outputs
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Old 24th November 2020, 06:02 AM   #1
Xittenn is offline Xittenn  Canada
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Default DAC Differential Outputs

I bought a DAC AK4490EQ not knowing it has differential outputs. I was planning on creating a class A output stage using 2SA1313 to power some HIFIMAN HD5SE, but I don't know what actually comes out of a differential output? I am aware of the recommended circuits.
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Old 24th November 2020, 08:21 PM   #2
PRR is offline PRR  United States
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DAC Differential Outputs
> [i]I bought a DAC AK4490EQ[i]

The bare chip? Or a boxed product including the AK4490EQ chip?

Use of the differential outputs on the chip is covered in datasheet, page 62-.
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Old 1st December 2020, 10:08 AM   #3
Xittenn is offline Xittenn  Canada
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The bare chip. I'm building my own module for a Raspberry Pi 4 B 8GB sweet, this will simply be a DAC Amp module. I want to run pure class A on the output. This was the first time I'd looked at a DAC. I didn't expect a differential output, and I'm still not entirely sure which of several types of out is this differential output?

Is it a positive and a negative swing?


Is it they swing at the same time but in opposite directions?


I hear that there are design concerns because either the positive or negative are dominant over the other, is this an issue?


The recomended circuits requires an op-amp Low Pass Filter and a differential in single-ended pre-out. I considered alternatives and they weren't very good. I would've just used a coupling transformer but well I haven't given up on using a coupling transformer, but probably not.
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Old 1st December 2020, 11:07 PM   #4
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DAC Differential Outputs
Why do many DACs have differential output? - Electrical Engineering Stack Exchange
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Old 1st December 2020, 11:40 PM   #5
chris719 is online now chris719  United States
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DAC Differential Outputs
Quote:
Originally Posted by Xittenn View Post
The bare chip. I'm building my own module for a Raspberry Pi 4 B 8GB sweet, this will simply be a DAC Amp module. I want to run pure class A on the output. This was the first time I'd looked at a DAC. I didn't expect a differential output, and I'm still not entirely sure which of several types of out is this differential output?

Is it a positive and a negative swing?


Is it they swing at the same time but in opposite directions?

.
It is described completely on Page 61 of the datasheet and on Page 9. They are 2.8 Vpp centered on half of the reference voltage.

AOUT (typ.@0dB) = (AOUT+) - (AOUT-) = +/-2.8Vpp * (VREFHL/R - VREFLL/R) / 5

The outputs are 180 degrees out of phase with respect to each other.
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Old 2nd December 2020, 12:00 AM   #6
Xittenn is offline Xittenn  Canada
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lol . . . written in japanese
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Old 2nd December 2020, 12:57 AM   #7
Xittenn is offline Xittenn  Canada
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The little formula wasn't obvious to me, and the literature I read, though mostly supported the idea of a 180degrees out of phase, still didn't leave me with a solid answer.

At any rate thanks for clearing that up.

Last edited by Xittenn; 2nd December 2020 at 12:59 AM.
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Old 2nd December 2020, 02:10 AM   #8
chris719 is online now chris719  United States
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DAC Differential Outputs
You don't technically need to use both outputs, especially if you are not looking to preserve the best measured performance. It is highly recommended, though, since there is probably a lot of common-mode output that AKM intends for you to cancel.
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Old 2nd December 2020, 02:13 AM   #9
Xittenn is offline Xittenn  Canada
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As far as I understand, yes there is. . . .. my 1313's just came in yay.
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