dirty DAC output AD1938 in Adau1452eval
By setting a fixed reference voltage from SigmaStudio and applying it to ADAU1452REVBZ, I can see a four or more level noise on AD1938 DAC output. Frequency of that noise seems fixed, and related to MCLK.
Instead of 200mVpp noise, I expected a constant voltage output because a single value is written to the codec.
This happens also when a signal is sent to DAC, noise is still present.
What about this behaviour?
Thanks
hardware
ad1938
Integrated/Special Purpose A/D Converters
Sigma DSP 4.6 + Adau1452RevBz
Audio CODECs
Hello RadioS,
If you are using a DC cell to send a fixed static value out of the DACs it will not work on the eval board. Because the eval board is capacitor coupled on the outputs:
Here is the schematic from the user guide.
From your screenshot it looks like you have the scope connected to the DAC1L and DAC1R test points that are right on the very output of the DAC. There you will see the DC level coming out of the DAC but you will also see all the out-of-band energy and that is what you are seeing on the scope. This is normal. Connect the scope to the OUT1L and OUT1R test points which is after the reconstruction filter so most of the out-of-band energy will be filtered out but it is after a 10uf cap so you will not see the DC output.
Also, where you ground the scope will also make a difference.
Dave T
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