STA321MPL1 datasheet(15/80 Pages) STMICROELECTRONICS

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STA321MPL1

Microphone interface

3.3

PDM recombination (dual-membrane microphone support)

Dual microphone scenario:

A dual-membrane microphone has two separate PDM signal paths:

•

Normal channel for moderate SPL (sound pressure level) acoustic signals

•

High channel for high SPL acoustic signals

The sensitivity of the high channel is configurable and is set by default to 20 dBSPL lower

than the sensitivity of the normal channel to avoid saturation in any part of the signal path.

The two channels can be combined together to enlarge the dynamic range and have a good

trade-off between the DNR and the noise floor (which is lower in the case of the normal

channel).

The main functionality is based on a signal level measurement and a dual-threshold system.

If the signal of the normal channel is:

•

above the upper threshold (TH_H), the output is taken from the high channel

•

under the lower threshold (TH_N), the output is taken from the normal channel

•

between TH_H and TH_N, the output is a combination of the high and normal

channels.

Figure 5. PDM recombination block diagram

3.4

Low-pass filter

A filter is provided (and needed) to suppress the noise outside the audio band that may be

still present before the recombination stage.

The filter is a 2nd order IIR (infinite impulse response) low-pass with a cutoff frequency of

20 kHz. It can be bypassed through the I2C bit.

Configuration registers: 0x62(6), 0x63(6), 0x64(6)

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