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ADAU1442 with 2 SRC creating noise on other inputs

Question asked by Nbenpaz on Aug 28, 2014

Hi all

I have a board uses the ADAU1442 for controlling the audio of a switcher.

8 of the inputs are analog so they are routed through ADCs to the DSP . The DSP generates the clock for the ADCs and these inputs are clock masters.

The other 2 inputs are digital that I get from a video Encoder ADV7842 so one of them is I2S and connected directly to the left 9 input of the DSP, The second is routed as SPDIF to the SPDIF input of the dsp. these tow are routed in the DSP through 2 SRC .

All is working fine when we deal with the analog inputs but when the I2S or the SPDIF inputs are connected to their source (even they are not selected inside the DSP switch) they couse the analog signal to be disturbe. when i loook on the scop  it looks like spikes over the sine wave of the analog source . it does not happanes all the time but when I switch the source on and off some times it start and does not stop unless the power is switched off.

I attach the design for evaluation.

 

thanks for any help.

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