I am facing this problem when using an EVAL-ADAU1X61EBZ.
The manual of the ADAU1761 clearly states that
- there is 4 bit available internally that provide 24 dB of extra headroom before saturating the DSP core internally.
- the typical available input in the ADC is 1 Vrms
Please correct me if I am wrong but I am assuming that with 1 Vrms input I will have +24 dB inside the DSP before I clip the signal.
So I would expect to be able to boost a 1 Vrms input signal by 24 dB before I clip it.
But this is not what I experience, nor what I see inside SigmaStudio. I only seem to have 4 dB of headroom before the signal clips internally.
here is the experiment I am doing that does not give me the expected results:
- I am feeding 1 Vrms input in IN1 of the EVAL-ADAU1X61EBZ
- In the "Record Input Signal Path" of SigmaStudio I am using PIN10 of IN1 to pass the signal through the DSP
- Inside the Schematic my design looks like this:
- in the "Playback Output Signal Path" my comfiguration looks like this:
- When I am measuring the DIFF OUT L output of the EVAL-ADAU1X61EBZ I am measuring 400 mV rms.
My questions are:
1) where is the 24 dB of headroom?
2) Why is there only 4dB of headroom appearing in the Schematic?
3) I would expect that my output would would also be 1 Vrms. Instead, it is 400 mV. Where is this attenuation coming from?
thank you for your time