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15-bit resolution of ADAU7002 in TDM mode

Question asked by EmilP on Jul 14, 2017
Latest reply on Jul 17, 2017 by EmilP

Dear Sirs,

we plan to use ADAU7002 as an interface between high-dynamic range PDM mics (INMP621) and processor with TDM input. I've expected, that it will behave as stated in the datasheet - with 20bit resolution and 110dB dynamic range.

Simple measurements showed us, that we are getting only 15-bit signal from ADAU7002 in TDM mode. First 5 bits after frame-sync are always zero, followed by sign of 2's complement format and 14 bits with audio information. Can you explain me, please, what's wrong there? Attached you can find our schematic + measurements on the scope.

Thanks and best regards,

Emil

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