Creating a differential output using a SigmaDSP with single-ended DACs

Hi Brett,

As a matter of interest, as I'm keen to do this with my project, what would the purpose of the capacitors be? With the differential drive surely the half rail DC output of the DACs would be canceled at the speaker? Unless there is a small random offset of the bias on each DAC that would cause a DC current to waste a small amount of power in the speaker?

Kind regards

Charles

Hi Charles,

Perhaps my original explanation was a bit misleading. The output of the DAC wasn't meant to go directly to a speaker; it is meant to go to an amplifier.

The ADAU1701 DAC doesn't have the ability to drive a speaker directly (it is only meant to drive high impedance loads), so you'll need to use some kind of amplifier in between the DAC and the speaker. Assuming that the bias point of the amplifier input does not match the DC offset of the DAC output, the AC coupling capacitor will become necessary. Hopefully that makes sense.

Hi Brett,

That does make sense, thanks. What I had meant though for a speaker is a headphone. Bob had confirmed in this thread that this is possible:

https://ez.analog.com/thread/36603?start=0&tstart=0

So the question now is, since this is not an amplifier input, could I drive a small headphone speaker differentially? From your above explanation, it seems this should be perfectly feasible.

Kind regards

Charles

Hi Charles,

I think it will depend on the characteristics of the particular speaker. You might want to give it a try with the evaluation board first before committing to your own design.

The EVAL-ADAU1701MINIZ uses a simple passive low pass filter on the output and still manages to drive headphones pretty well!