Hi Don,
Thanks for the reply . I've done some testing based on them .
First, to analyze whether the problem was caused by the disconnected input microphone, using the I2C buis I sent POWER SAVE command to ADC. ( ADPSV bit register 67 ) . This should turn off the ADC. Interference on a signal sent from the DSP is maintained .
To verify that the I2C working correctly , I sent POWER SAVE command to DAC and as expected, the interference and the test signal disappeared.
This led me to think that the problem is in the DAC , it tried to verify several configurations:
- I Enable and disable the de- emphasis filter , the test signal and the interference continued to exist .
- I Inverted phase output signal of the DAC , the test signal and the interference continued to exist.
- I sent my MUTE SOFT ON command (bits MUT1 MUT2 registry and 68) and the test signal disappeared , but the interference was maintained.
Regarding the PCB Layout , I've had the design is very similar to working prototype . I have divided the dough flat digital analog ( codec ) and ( DSP ) by a 2.2 Ohm resistor and have been careful not to generate induction loops . The only significant change is that the models have joined the AGND1 , AGND2 , AGND3 and DGND pin to plane below the codec mass plane in this model .
Anyway, I will analyze the PCB with the EMI expert of the team .
I hope to be close to solving the problem , hopefully with these measurements is possible to detect the problem. If you have news , the notify by this route .