Static DC output from audio DAC

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Hello,

I want to create a high precision voltage source, +/- 2.5 volts with < 1 microvolt steps. To do this I need a high bit depth DAC, 26+ bit. But the DACs that have that high of a bit depth are usually labeled as 'audio' and have filters. Can I output static DC levels? I assume if there is only a low pass filter then I am able to do this. But a lot of these have DSP filters and I do not know anything about DSP.

Thank you in advance.

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Professionally designed precision voltage sources use a hybrid of several techniques. For example, you can use two or three DACs and sum them (with different scale factors) in a good op-amp. The op-amp circuit would have to be well designed, compensating for input bias currents, and such.

Another way would be to use a DAC that can have a reference applied to both ends of the DAC ladder. Then use a second DAC to feed one end of the first DAC ladder and a third DAC to feed the other end of the first DAC ladder. This avoids much of the precision needed for the first idea. In a sense, the first DAC simply "interpolates" between the second and third ones.

There are MORE techniques that are possible.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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You know the DAC alone won't cut it? You need a very precise and stable reverence voltage source, too. 1 µV in a 5 V range is 0.2 ppm. Your reference source would have to be better than 0.2 ppm, like 0.02 ppm or better. Do you have such a source? Over the full temperature range you need it?

Stealing Proteus doesn't make you an engineer.

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26-bits resolution over 2.5V is 37nV precision. Now what in the world could that be used for, considering you are someone that "knows nothing about DSP's"? I mean noise levels emitted from your circuit are likely to near a few mV, so what would nV's matter?

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dustin_kreft wrote:

I want to create a high precision voltage source, +/- 2.5 volts with < 1 microvolt steps. To do this I need a high bit depth DAC, 26+ bit.

Is your power supply to your DAC going to be that good?
Is your reference going to be that good?
Are any analog parts going to be that good?
Even resistors make a lot of noise at that kind of level...

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Yes, there are many ways to do this. I know there will be noise and I know there are ways around that. The question I had was can an audio DAC output a constant static DC voltage even when they have filters installed inside the IC. All other circuit considerations are appreciated but are not my main focus. I don't want to spend money on parts and find out they don't work as expected.

Thank you.

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ka7ehk wrote:
Professionally designed precision voltage sources use a hybrid of several techniques. For example, you can use two or three DACs and sum them (with different scale factors) in a good op-amp. The op-amp circuit would have to be well designed, compensating for input bias currents, and such.

Another way would be to use a DAC that can have a reference applied to both ends of the DAC ladder. Then use a second DAC to feed one end of the first DAC ladder and a third DAC to feed the other end of the first DAC ladder. This avoids much of the precision needed for the first idea. In a sense, the first DAC simply "interpolates" between the second and third ones.

There are MORE techniques that are possible.

Jim

These are very good suggestions. I had a few things like this in mind. Thank you for your input.

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ArnoldB wrote:
You know the DAC alone won't cut it? You need a very precise and stable reverence voltage source, too. 1 µV in a 5 V range is 0.2 ppm. Your reference source would have to be better than 0.2 ppm, like 0.02 ppm or better. Do you have such a source? Over the full temperature range you need it?

Yes, I know this. I have already have ways of handling this that will ensure accuracy.

Thank you

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Quote:
For example, you can use two or three DACs and sum them (with different scale factors) in a good op-amp.

Problem with this approach usually is, that the
DAC with the largest scale must already have full precision (=output step size).

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Quote:
Yes, I know this. I have already have ways of handling this that will ensure accuracy.
Oh sure, you have ways of handling this. Sure, sure. You have a 5.0000000 V reference with a total error of ± 0.0000001 V (including temperature drift and long-term stability).

Stealing Proteus doesn't make you an engineer.

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If Agilent can make this nanovolt meter then it must be possible :)

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Fascinating piece of equipment, but I don't think it will cut it. If I take the most accurate voltage measurement range (10.000000 V), then I interpret the datasheet, that I get an accuracy of ± (2 ppm of the reading + 1 ppm of the range) over 24 hours at 23°C ± 1°C, after two hours of warmup.

For 5 V that would then be 5 V ± (10 µV + 10 µV). Worse than what we look at.

Still I want one of those multimeters :-)

Stealing Proteus doesn't make you an engineer.

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I always wonder what equipment do you use to verify equipment? A picovolt meter? How do you verify that one? with a femtovolt meter? :)

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With equipment like this:
Fluke 5440A
you get very good accuracy.

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I would like to see what's inside it :)

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My precision "dac" is a L&N K5 8-) Almost a half-century old and has 1/100 of a microvolt resolution!

Tom Pappano
Tulsa, Oklahoma

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jayjay1974 wrote:
I always wonder what equipment do you use to verify equipment? A picovolt meter? How do you verify that one? with a femtovolt meter? :)

People at Volt-Nuts could answer that:

https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts

Volt-Nuts is an off-shoot of Time-Nuts:

https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

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Quote:
Fluke 5440A
And how do they calibrate a Fluke 5440A? Ok, trick question. Fluke has Josephson voltage standards, which is the same stuff national laboratories use to keep the official Volt. http://assets.fluke.com/appnotes...

Stealing Proteus doesn't make you an engineer.

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Nist still uses banks of standard cells for the Standard Volt. Their website does suggest that they use the Josephson effect for monitoring the cell banks. Customer cells are compared to the "standard" using hi-res voltmeters. From their price list I can get one of my 4-cell banks checked for only $7022.00!

Tom Pappano
Tulsa, Oklahoma

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ArnoldB wrote:
Fascinating piece of equipment, but I don't think it will cut it. If I take the most accurate voltage measurement range (10.000000 V), then I interpret the datasheet, that I get an accuracy of ± (2 ppm of the reading + 1 ppm of the range) over 24 hours at 23°C ± 1°C, after two hours of warmup.

For 5 V that would then be 5 V ± (10 µV + 10 µV). Worse than what we look at.

Still I want one of those multimeters :-)

Look, people use these devices all of the time for quantum computing measurements, quantum dots, quantum point contacts, etc. There are plenty of products out there so this has been done many times before and there are plenty of circuit methods to compensate for error.

So, shut the hell up if your not going to help. Any idiot can be negative.

And your still not answering my question if an audio DAC can output a static DC voltage.

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Please specify a part number for your audio DAC. I'll look at a spec sheet and see if I can figure out what it does.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Oh, I see, you work in quantum computing. Is it normal for people working in quantum computing of not being able to read the datasheet?

If you still haven't got the hint - and this is indeed meant to help you - doing what you want requires real skills and experience. Skills and experience you apparently lack, as it is easily detectable from your question.

Until now I was friendly, even when you lied to me with your "I have ways of handling this" lie. You come here because you don't want to waste money on a simple audio DAC if it doesn't work, but you have absolutely no clue that the cost for an audio DAC will be minor compared to the rest.

If your can't afford the DAC, if you can't even make an initial judgment of the DAC based on the datasheet, and if you really believe this is just a matter of "circuit methods to compensate for error" then you are way out of your league.

You didn't even have the mental capacity to follow my calculation, you don't have the mental capacity of reading a datasheet, and you want to pull this off? HAHAHAHAHAHAHA

Stealing Proteus doesn't make you an engineer.

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Arnold, you just had the can of "shut the f*** up" opened on ya!

Dustin - I'd suggest you ask the manufacturer your question. Most of us would use an audio DAC for, hmmm, audio. Arnold does counter with a reasonable response - you want premium performance, but you're worried about investing a few dollars. Anyway, if you're really serious about saving dollars - why don't you scrounge an audio dac from an old soundblaster sound card or dud dvd player. Hook that up and do your tests. Chicks dig guys with skills.

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ArnoldB wrote:
Oh, I see, you work in quantum computing. Is it normal for people working in quantum computing of not being able to read the datasheet?

If you still haven't got the hint - and this is indeed meant to help you - doing what you want requires real skills and experience. Skills and experience you apparently lack, as it is easily detectable from your question.

Until now I was friendly, even when you lied to me with your "I have ways of handling this" lie. You come here because you don't want to waste money on a simple audio DAC if it doesn't work, but you have absolutely no clue that the cost for an audio DAC will be minor compared to the rest.

If your can't afford the DAC, if you can't even make an initial judgment of the DAC based on the datasheet, and if you really believe this is just a matter of "circuit methods to compensate for error" then you are way out of your league.

You didn't even have the mental capacity to follow my calculation, you don't have the mental capacity of reading a datasheet, and you want to pull this off? HAHAHAHAHAHAHA

LOOK, I want to be able to create a PC controlled voltage source. In our lab we have ones that can do 100 nV steps and are very accurate with no glitch transitions. According to your mental capacity and calculations, this isn't possible. Yet our lab is filled with these devices. I don't want to get back into a pissing match since YES there are devices like this and obviously companies are making money off of them. I know there is a lot more than the DAC, the DAC is about 1% of the total circuitry, if that. Since I already know that, and know how to work around other problems, I push forward with this since I already found my answer on my own.

And ArnoldB, quick being such a jackass so stuck in your ways and talking this project down. Get a clue, equipment with these capabilities have existed for awhile. Listen to what everyone is saying, wake up.

Amazing how a simple question got completely out of hand and no one answered it. But I did learn some stuff and THANK YOU to everyone for your input, except ArnoldB.

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So what was the outcome? Can you use an audio dac? What does your lab devices use to implement a high resolution DAC? What is the manufacturer/part number of such items?

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I would also like to know!

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Quote:

So what was the outcome? Can you use an audio dac?

I dug into that a while back. The attraction of the audio parts seems compelling at first glance: Given the "compact audio" industry--cell phones, MP3 players, and the like--we microcontroller peeps can piggy-back on that and get great spec devices at low prices for "off label" use. Another example is the Analog Devices ADE7xxx "energy meter" chips that do a better job than we could ever hope to with AC currents and voltages all for a couple $$.

Anyway, what you want to look for is devices that allow you to disable the low-pass filter (LPF). As I recall I was looking at streaming ADC channels versus the DAC channel(s). I don't remember whether any models had DAC configurable that way. I'd suggest starting at TI.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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No it can not! At least not with any DC accuracy