24 bit dual audio DAC - cheap but can in do DC?

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welshzadok
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Posted by welshzadok: Sun. Mar 30, 2008 - 12:29 AM
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I'm looking at a very cheap IC: PCM1753/4/5 which has two 24 bit DACs. I want to control a radio receiver with the voltage output, which needs to be steady and as high a resolution as possible. This IC looks just the ticket, but as it's intended for audio, I'm wondering if it can hold the DAC outputs steady? There are quite a lot of these stereo audio DACs out there - low cost because they are consumer parts. I wonder if anyone else has ever used one of these impressive DACs for a project other than audio?

Tried searching the AVR freaks forums and the net but it seems hard to get the right search terms!

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AVR Microcontrollers, megaAVR and tinyAVR
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ka7ehk
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Posted by ka7ehk: Sun. Mar 30, 2008 - 01:37 AM
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I looked over the spec sheet pretty closely and there does not seem to be anything limiting the low end. Frequency response plots show it going down to zero.

It is not clear what function "delta-sigma" has in the context of a DAC.

Jim

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

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bobgardner
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Posted by bobgardner: Sun. Mar 30, 2008 - 03:14 PM
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Is it three 8 bit dacs with their outputs summed and scaled??

Imagecraft compiler user

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ossi
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Posted by ossi: Sun. Mar 30, 2008 - 03:18 PM
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The datasheet has some entries under title:
DC-accuracy

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welshzadok
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Posted by welshzadok: Sun. Mar 30, 2008 - 09:35 PM
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Thanks for your comments, all. I'm looking at using the output voltage to control the local oscillator in a VHF mixer / amp SA (or NE) 612A. If I can get it accurate enough I can get away without an intermediate IF stage. This is the kind of stuff I should be discussing on a radio ham forum, but there doesn't seem to be many of those! I've just joined www.eham.net but they won't let me post yet. Anybody know any other good RF hangouts?

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ossi
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Posted by ossi: Sun. Mar 30, 2008 - 09:42 PM
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I think it's important here to clearly distinguish
between the following criteria:
a) resolution
b) accuracy
c) stability
d) ???
While the resolution of a sigma-delta DAC will
probably very high, the issue, whether accuracy
and stability are ok have to be discussed.
I have no conclusive answers.

If you want to adjust the frequency of a VCO and can
measure the frequency, so you operate it in a sort of
a "closed loop", you even would need no linearity in
the DAC !

Comments welcome !

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danni
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Posted by danni: Sun. Mar 30, 2008 - 10:39 PM
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I tried audio DACs to check for DC applications and it failed.
The offset voltage change big over temperature.

Audio DACs must only be short time accurate, so offset and gain drift plays no role.

Peter

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Kleinstein
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Posted by Kleinstein: Mon. Mar 31, 2008 - 09:18 PM
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If its just controlling a VCO then you need high resolution but linearity and drift don't have to be better than the vco. For stability some feedback from the frequency is probably needed anyway.
The one thing that can be a problem is low frequency noise.

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Jepael
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Posted by Jepael: Mon. Mar 31, 2008 - 09:42 PM
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Some audio DACs need constant feeding of data, or they will go into auto-mute operation. Feeding too many times the same sample can also do this if memory serves.

- Jani

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theusch
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Posted by theusch: Mon. Mar 31, 2008 - 10:34 PM
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I looked at this a while back from the "other end" of the sound chip, to get streaming A/D at a high[er than AVR] sample rate on several channels and higher resolution. They aren't all created equal in that respect; only certain of the chips would work on DC inputs. I suspect the same may be true on the DAC end.

For sound work, it is hard for an AVR to stream well on I2S or similar. For DAC work, if it holds the last level, that may not be important. For true streaming I2S I was going to use the SAM7 but the project got canceled. I think you could do a fine job with an Xmega, though. That might become moot as it already has DACs. ;)

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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