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PDM to Analog

Category: Software

Dear Sir or Madam,

in my studies I am working on a project to measure 2 microphones.

For this purpose a small sound absorber chamber is built to measure with
measurement electronics an analog reference microphone (the b&k 4165) and a DUT
(e.g. the digital microphone Infineon IM69D130-DS).

The FFT Analyzer requires analog signals at the input and converts them to
digital signals with a sampling rate of 131kHz.

My problem is to pick up the digital microphone IM69D130-DS. This
MEMS micro gives as signal a 1-bit PDM signal, which I have to convert to an
analog signal, so that the FFT Analyzer recognizes it.

There have already been a few suggestions in the general forum (ez.analog.com/.../pdm-convert-to-analog) , there was also a similar topic here in the subforum.

The ADAU7002 chip or the ADAU1777 chip were discussed. Also an idea of combination of ADAU7002 and ADAU1701 was mentioned.

As a result, I would need a circuit that makes an analog signal from a PDM signal (with pre-amplification).

By the way, after consultation, I can't get behind the A/D converter, but is also not so wild for now. The problem with the multiple conversions is known to me, but is not so bad at this point.

Can you help me with this problem so that I can get further?

First of all, thanks already for the help.

best Regards,

Ovid

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  • Ovid,

    There is another way that you could go that might be simpler. One nice property of pulse density modulation (aka sigma-delta modulation) is that the analog signal can be recovered with just a low pass filter. This can be implemented as a combination of digital and analog, as in a DAC, or completely in analog. The required filter order depends only on the needs of the receiving device. For example, the output of our class-D amplifiers is, basically, a PDM signal with current drive. The voice coil and mechanical elements of the speaker do the filtering. I assume the input to your analyzer has an ADC, in which case it would also have some low-pass filtering already, though likely not enough on it's own. 

    Ken

  • Hi Ken and Dave,

    thanks for the super helpful suggestions, I will probably look at both.

    Thank you, you have helped me well!

    best regards

    Ovid

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