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Long digital MEMS microphone PDM line recommendations

Question asked by arvidjense on Jan 29, 2018
Latest reply on Jan 31, 2018 by Ken.M

I am building a system using multiple PDM MEMS microphones with a high acoustic overload point (>130dB) like Invensense INMP621, Infineon IM69D130 or Knowles SPH0644HM4H-1 (see diagram https://imgur.com/a/h5Z96). At the main pcb an Analog Devices ADAU 7002 will convert the PDM signal to TDM, to be processed by a dsp like ADAU1701. Each microphone will have a cable of max 1m to it. The recommended lengths for PDM lines seem te be under 20cm, so I was wondering what are your recommendations for ensuring robust operation?

Some constraints are that I am constrained in the pcb size on the microphone end (making it hard to add more than a few passive components) and I cannot make differential pairs as I can only use one wire per line on the CAT cable.

Next to using a source termination resistor, I have seen suggestions of using series ferrite beads and clock buffers, but I was wondering what are your recommendations?

Thanks a lot!

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