ADAU1701 eval board measured noise (graph)
Hello,
I measured the idle noise (inputs grounded) of the board I designed and compared to ADAU1701 evaluation board. The code in both just connects the inputs directly to outputs. I was surprised how big difference there was between those two and I'm wondering now if the measurement is good.
Can anybody comment if the measured noise curve is most likely correct or not?
I also wonder if that 1/f noise which is best visible in red curve between 20Hz and 1kHz comes from DAC or from somewhere else? Not that it's really a problem, just curious.
CYAN curve: evaluation board + USB power
GREEN curve: evaluation board + battery power
RED curve: own board
Thanks,
Ari
Audio Signal Processors
noise
SigmaDSP Audio Processors
evaluationboard
adau1701
Hi Ari,
There's nothing in your measurement that strikes me as being out of place.
I'm not that surprised that your board is achieving better noise performance than the evaluation board. The evaluation board was designed more from the perspective of creating a compact, easy-to-use platform for the customer to try out the product, and to make the design flexible enough so that a majority of the chip's functions could be exercised. Therefore, the design had some artificial limitations placed on it, meaning that we could not achieve the best noise performance possible. For example, the USB power option injects quite a bit of noise into the board, and we did not go out of our way to use expensive isolation components. We refrained from placing components on the underside of the board entirely, instead opting to cram everything on to the top layer. Concessions were also made in trace routing in order to make the design as compact as possible.
So, as you can see, the evaluation board is certainly not an optimal design. I'm sure you were able to achieve better noise performance because you placed more emphasis on audio performance when laying out the PCB.
Hi Ari:
Do you have the same gain stage applied in your board comparted to the eval board. I would certainly expect better performance however your design is so much better that makes me wonder.
When you play audio through both, do you get the same gain regardless of the noise floor.
Thanks
Miguel
Hi Miguel,
The gains are different:
My board has +10dB gain before of DSP and +6dB gain after DSP.
Eval kit board does not have any gain as it just has passive filters in input and output.
In both boards the code directly links ADAU1701 inputs to outputs.
All other measurement results with both boards (freq response, THD,..) look 'normal', so I guess I shouldn't have any reason to doubt in general that the results are not valid. Just this big difference in idle noise made me doubt...
/ari
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Thank you,
EZ Admin
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