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white noise from ADMP441 I2S digital mic.


When using ADMP441 evaluation board connected to FPGA, the noise exceeds the sound signal ( audio sample attached).  3.3 DC supply is clean,+- 100 mV variation.  followed data sheet recommendations e,g, 100Kohm between serial data & GND.

Bit clk = 500 KHz:

serial data waveform:

Notice that serial data gets distorted during left channel acquisition.  This is because it is high impedance between right channel acquisition.

What causes the noise?

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