TLV320ADC6140: Wiring 2 analog MEMS microphones with Channel Summation

drs_i

Part Number: TLV320ADC6140

Tool/software:

Hi,

Can you elaborate on wiring 2 analog MEMS microphones with differential output to TLV320ADC6140 in Channel Summation mode?

Should I simply connect the first microphone Differential Output (+) to both IN1P and IN2P in parallel, Differential Output (-) to both IN1M and IN2M in parallel, and the second microphone Differential Output (+) to both IN3P and IN4P in parallel and microphone Differential parallel Output (-) to both IN3M and IN4M in parallel? Of course, I need to activate Summation mode (4--->2).

Thanks,
Ivan

3 months ago

+1 Jeff McPherson 3 months ago

TI__Mastermind 31075 points

Hi Ivan,

Yes that's correct. These shorts should take place after the AC coupling cap to your microphone, such that IN1P and IN2P (and so forth) are shorted together and the microphone connection is in parallel.

Best regards,
Jeff McPherson

0 drs_i 3 months ago in reply to Jeff McPherson

Prodigy 20 points

Hi Jeff,

Thanks a lot for the clarification.

Best regards,
Ivan

0 drs_i 3 months ago in reply to Jeff McPherson

Prodigy 20 points

Just to be 100% sure, is this correct?
Thanks

0 Jeff McPherson 3 months ago in reply to drs_i

TI__Mastermind 31075 points

Hi Ivan,

Your picture is not showing up for me, could you try sending it again?

Thanks,
Jeff McPherson

0 drs_i 3 months ago in reply to Jeff McPherson

Prodigy 20 points

Hi Jeff,

Sorry about that. Here is the picture again.
https://share.cleanshot.com/6TY38zpJy
5RZhPSvtYKz

+1 Jeff McPherson 3 months ago in reply to drs_i

TI__Mastermind 31075 points

Hi Ivan,

The symbol looks like it has a typo. Pin 11 should be IN3M.

Otherwise the connections are correct, but I would move your low pass filter to before the AC coupling caps. The coupling caps should be the last part of the input circuit before the device input pins.

Best regards,
Jeff McPherson

0 drs_i 3 months ago in reply to Jeff McPherson

Prodigy 20 points

Hi Jeff,

Yes, it was a typo. Pin 11 is IN3m.

Got it. Do you think low pass filter is even necessary in a setup with analog MEMS microphones? And what AC coupling cap value do you suggest if the microphone output impedance is 250ohm, or if the existing ones are suitable?

Thanks once more for your invaluable help!

Ivan

+1 Jeff McPherson 3 months ago in reply to drs_i

TI__Mastermind 31075 points

Hi Ivan,

I don't think the filter is necessary. This is a sigma delta ADC which means that out of band noise gets filtered out anyway by the ADC architecture. Even then the filter you have has a nearly 7MHz cutoff which is not doing much anyway in terms of filtering out non-audio signals.

The coupling cap value is okay. I ran a quick simulation and the high pass filter formed by it and the input impedance is outside the audio band and it'll dominate over the output impedance of the mic.

Best regards,
Jeff McPherson

0 drs_i 3 months ago in reply to Jeff McPherson

Prodigy 20 points

Hi Jeff,

Excellent, all very clear. Thanks a lot!

Ivan

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TLV320ADC6140: Wiring 2 analog MEMS microphones with Channel Summation