ADAU1797 and AIN0 noisy mic input

Hi Bruno,

Thanks for reaching out.

I believe you have configured the jumper settings as per the userguide (Section: ANALOG INPUTS, Table 3 page 14) and schematics (Page 19 of userguide). You will also have to change the ADC_CTRL2 register under ADC_CTRL tab in Sigma Studio+ accordingly (ie Single Ended or Differential). Please let me know if this works.

Hello Joseph, 

I've done those changes but without success.

when not running any program trough the HIFI processor there is no noise, but when adding something in it, i don't know why, the output of the ADC becomes noisy.

Routing the ADC output straight to the DAC is not changing anything, looks like a power supply issue, but no idea from where to start, I believe the Evboard from analog is well designed and should not have power supply issues.

Hello PtiBruno,

Yes, your asumption is that the power supply that came with the eval board is a good assumption but any power supply can fail. In addition, you might not be just dealing with one power supply if you are using other eval boards? I assume you are connecting the speaker directly so no issue there. Can you answer a few questions and provide couple of things?

1) draw up a schematic of how you are exactly connecting the microphone to the eval board? The mic will have a ground connection, where are you tying that ground connection on the eval board? Also, give us a link to the mic info. What are you doing with the other pin on the mic input header?

2) How are you powering the mic? This is I guess also included in my last question which is how you are wiring/connecting the mic?

3) Can you perform an experiment. Short the mic input to ground and see if you have noise. Let me clarify. If you are grounding the mic to a ground pin on the eval board and connecting the positive output of the mic to pin-2 of the mic input header, then disconnect the microphone and the cable. then connect a jumper from pin 2 to the ground pin. This will short out the mic power but it should not be a problem. See if you still have this high level of noise? 

4) Also, what is the nature of the noise? High frequency? Low frequency? Is it broadband or mostly a few frequencies and the harmonics?

Thanks,

Dave T

Hi dave, thanks for your support.

I'm facing this noise issue either with my own designed board and the Evboard.

here are the answers : 

1- on my board i'm using the differential mode schematics shown on my 1st post.

on the Ev board i'm connecting the mic to J25, J11 is mounted,  a 2k resistor on J48 header, nothing on J58 : 

2- either on my board and the Evkit i'm powering it with the 1.8V powering the ADAU, I've tried to power with an external stabilized power supply but no effect.

3-  short cut the mic to ground : the noise still present, same when disconnecting the mic or removing the bias voltage.

4- The noise is mostly130Hz, bellow a link of the recorded file.

https://we.tl/t-L4JhpRmVgX