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Noise of DAC output of ADAU1372 too high on evaluation board

Question asked by HankCodec on May 6, 2016
Latest reply on Sep 18, 2017 by MarcvE

Hi all,


We have used the ADAU1772 codec in our prototype design and found that the noise is too high. Then we ordered the evaluation board EVAL-ADAU1372z (the ADAU1372 is the same as the ADAU1772 without the DSP core that we are not using anyway)  and  measured the noise on the DAC output. Even without input signal the noise level was 4.4 mV RMS and with a full scale value of 0.97 V RMS this gives a SNR of 47 dB, which is much lower than the specified 102 dB. The measurement was done under the same conditions as the conditions in the specifications: single-ended line output (J22 on the board), AVDD = 3.3 V, with flat 20 Hz to 20 kHz filter. We used Sigma Studio for the settings (the project file is attached) and the USBi board for communication and power supply. Our measurement setup is limited to a noise floor of 0.4 mV RMS (about 67 dB SNR, which is measured with S7 on the board if OFF position), but this can not be the problem if the measured noise is 47 dB.


Is the SNR specification of the ADAU1372 not correct or what else is going on here?


Kind regards,