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Looking for DAC: DC stable & accurate and high-end audio specs

Christian Erle
Intellectual 470 points
Other Parts Discussed in Thread: ADS127L01, DAC11001A, PCM5242, PCM5102A-Q1

Hello TI & forum-users,

I'm desperately looking for a DAC with very good DC specs and high-end audio specs (>=24bit, THD > 100dB, SNR > 110dB, fs >= 192kHz, ...).

On the ADC side TI has made me really happy with the greatest ADC of all, combining very good DC and audio specs, the ADS127L01 (especially the stop-band filters).

So is there a DAC equivalent to the ADS127L01?

I have already checked most audio DACs (and not only TI's), and there is none with really good DC specs and accuracy.

The non-audio DACs on the other hand usually fall short in resolution, THD, SNR.

Anything I might have overseen, or other ideas?

Thanks in advance!

  • 0
    TI__Guru 53773 points

    Hi Christian,

    I think you should look at our new 20-bit flagship precision DAC, the DAC11001A.  This device is an R-2R device, so it will have excellent DC specs.  In addition, it has a very capable track-and-hold subcircuit that keeps code-to-code glitch low, allowing excellent AC performance as well.  There is a pretty detailed thread discussing the AC performance over at diyaudio.com if you care to check that as well.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Intellectual 470 points

    Hi Paul,

    thanks for the suggestion.

    I already found that one, several problems: 20bit only, R2R -> aliasing filter and / or up-sampling needed.

    We basically have an audio application, which requires also very good (not ultra high precision) DC specs.

    Any idea which audio DAC has the best DC specs? At least best DC stability?
    We might be able to adjust any static offsets.

  • 0 in reply to Christian Erle
    TI__Guru 53773 points

    What DC specs are critical to you? 

  • 0 in reply to Paul_Frost
    Intellectual 470 points

    DC: offset, drift

    And I completely forgot to mention in my 1st post: AC & DC accuracy and stability (or gain error and gain drift, as it's called in the audio DACs' datasheets...)

  • 0 in reply to Christian Erle
    TI__Guru 53773 points

    Hi Christian,

    We do not have any audio DACs that we characterize or specify gain and offset drift.  You will likely need to look at our precision DAC portfolio.

    On your comment about the limitation of the DAC11001A: why is 24bit required? Your SNR requirement is only 110dB (or greater), so your least significant bits will not really be present under the noise level.  Assuming an ideal DAC, 24-bits would have a dynamic range of 146dB.  The 20-bit DAC11001 can have an ideal dynamic range of 122dB.  In my reference design, I was able to achieve a DR and SNR of >120dB.  

  • 0 in reply to Paul_Frost
    Intellectual 470 points

    Hi Paul,

    you're right, maybe I'm a little bit too fixed on the >= 24 bits, but just as I say that the marketing guys behind me start complaining about "only 20 bits!". ;-)

    I couldn't really find detailed noise specs in the datasheet, except for the 7nV/sqrt(Hz), but 120dB would definitely be good enough.

    But with such a low noise floor, maybe the harmonics due to the "missing" 4 bits might be problematic for very low output levels.

    There's still the bandwidth issue apart from noise: concerning user bandwidth we need 100kHz (so sampling rate >= 200kHz),

    and I really learned to appreciate the sigma-delta ADCs & DACs when it comes to anti-aliasing filters.

    So with this DAC, we would probably need a steep analog filter, and also some up-sampling of the audio-like input data in the digital domain to get the update rate to 1MHz.
    That's probably too much space and power on the analog side, not sure about the upsampling.

    So, back to TI's audio DACs:

    although these are not really DC specified, maybe someone can share their "DC experience" with the TI audio DACs? Apart from what we get from the datasheets.
    At least DC and gain drift should be low, static stuff can be adjusted more easily.

  • 0 in reply to Christian Erle
    TI__Guru 53773 points

    Hi Christian,

    I recommend you take a look at the PCM5242 and PCM5102A-Q1.  While we do not provide drift specifications on either of these devices, they do feature a true band-gap reference.  This is as opposed to some of the PCM17xx families of devices that usually rely on a simple voltage divider for the common mode and amplitude voltages.  The PCM5102A-Q1 is an automotive-qualified device, so some of these key specifications actually apply to a large temperature range.  For example, the gain error is shown to be a min/max of ±7% across the temperature range.  You can use that as guidance in your design.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Intellectual 470 points

    Hi Paul,

    thanks for the suggestions.

    Well, +-7% is... far from accuracy, but drift is okay.

    My main problem with these DACs is the stop-band attenuation.

    I'll have another look at some of your DACs with

    a) an external reference if that is the main cause for gain accuracy, and

    b) with stop-band attenuation >= 100dB (120dB preferred)

    Edit: the PCM5242's stop-band filter no. 4 with 100dB and stop-band at 0.45fs looks promising