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?