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"Audio" DAC settling time - how to find out?

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kanonka

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In my device I need pretty fast DACs - ideally 16 bit, with less than 3.5 us settling time, SPI interface.
There are plenty of them, but all of them are quite expensive (for mass production; and I need 8 of them on a single board).
Then I noticed that there are a lot of "Audio" DACs with standard resolution of 24bit or better, and sampling rate of 192k to 384k.
But none of them provides "settling time" parameter in the datasheet.

Does it mean it's too large, or just nobody cares since it's "audio" DAC?
Is there any way to find out? Price on many of them is tempting...
 

I think they don't spec the settling time because those are probably sigma-delta DACs, not 'normal' ladder types.

You could just contact the manufacturer and ask them...
 

Modern audio DACs are SD-modulators with interpolating filters, usually FIR filters. Their length can be estimated from the delay specification in the datasheets. If the delay is e.g. 32/fs you can expect a pulse response respectively complete settling within 64/fs.
 
Ouch, this means none of them will satisfy my needs. Even when fs = 384k, fastest it can go is 1/fs = 2.6 us, and then required 2/fs = 5.2 us, which is too long for me. Am I right? On the other hand, I need settling time <3.5 us for 16 bit; if delay is given for 24 or, say, 32 bits, it should be faster if I'm interested in only 16 MSB, correct?
 

Re: &amp;quot;Audio&amp;quot; DAC settling time - how to find out?

Hi ... if you only need 16 bits you might be able to use some of the older audio DACs like AD1862, PCM1702, PCM56, PCM58, PCM63, PCM1704 or similar. E.g. the settling time for the PCM1704 is specified to be:

Settling Time ±0.0003% of FSR, ±1.2mA Step 200 ns

The PCM1704 is quite expensive, though, but some of the others have similar specs. They often are also able to be oversampled e.g. the PCM1704 should be able to work at 768 kHz (no oversampling but using the higher frequency sampling directly).

Best regards,

Jesper

kanonka said:
Ouch, this means none of them will satisfy my needs. Even when fs = 384k, fastest it can go is 1/fs = 2.6 us, and then required 2/fs = 5.2 us, which is too long for me. Am I right? On the other hand, I need settling time <3.5 us for 16 bit; if delay is given for 24 or, say, 32 bits, it should be faster if I'm interested in only 16 MSB, correct?
Click to expand...

- - - Updated - - -

P.S. Some of these DACs often can be found on ebay.

Jesper

PPS.: They don't have an SPI interface though ...
 
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Hi,

Audio DACs
* usually need a continous (jitter free) data stream within a fixed range of sampling frequency. This often is not usefull with industrial applications.
* usually use I2S interface instead of SPI.
* may have internal digital and/or analog filters. They have frequency dependent delay, groupl delay and latency.
* the internal filters may take care of the "preemphasis bit" in datastream. In that case you have two different "settling times" for set/cleared preemphasis.
* additionally the internal filters may change with sampling frequency (i´m not sure about this - but check this)

All in all i think an R2R ladder DAC is a better solution.


Klaus
 

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