INMP441

Figure 8. Stereo-Output I²S Format

Figure 9. Mono-Output I²S Format Left Channel (L/R = 0)

Figure 10. Mono-Output I²S Format Right Channel (L/R = 1)

DIGITAL MICROPHONE SENSITIVITY

The sensitivity of a PDM output microphone is specified in units of dBFS (decibels relative to a full-scale digital output). A 0 dBFS sine

wave is defined as a signal whose peak just touches the full-scale code of the digital word (see Figure 5). This measurement

convention means that signals with a different crest factor may have an RMS level higher than 0dBFS. For example, a full-scale

square wave has an RMS level of 3dBFS.

Figure 11. 1 kHz, 0 dBFS Sine Wave

The definition of a 0 dBFS signal must be understood when measuring the sensitivity of the INMP441. An acoustic input signal of a

1 kHz sine wave at 94 dB SPL applied to the INMP441 results in an output signal with a −26 dBFS level. This means that the output

digital word peaks at −26 dB below the digital full-scale level. A common misunderstanding is that the output has an RMS level of

−29 dBFS; however, this is not the case because of the definition of a 0 dBFS sine wave.

MSB

LSB

LEFT CHANNEL

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RIGHT CHANNEL

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TIME (ms)

Page 12 of 21

Document Number: DS-INMP441-00

Revision: 1.1