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
MSB
LSB
RIGHT CHANNEL
HIGH-Z
HIGH-Z
HIGH-Z
1
2
3
4
24
25
26
32
33
34
35
36
56
57
58
64
WS
SCK (64 ×
f
S
)
SD (24-BIT)
MSB
LSB
LEFT CHANNEL
HIGH-Z
HIGH-Z
1
2
3
4
24
25
26
32
33
34
35
36
56
57
58
64
WS
SCK (64 ×
f
S
)
SD (24-BIT)
MSB
LSB
RIGHT CHANNEL
HIGH-Z
HIGH-Z
1
2
3
4
24
25
26
32
33
34
35
36
56
57
58
64
WS
SCK (64 ×
f
S
)
SD (24-BIT)
1.0
–1.0
–0.8
–0.6
–0.4
–0.2
0
0.2
0.4
0.6
0.8
0
0.9
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
D
IGITA
L A
M
P
LITU
D
E
(
D
)
TIME (ms)
Page 12 of 21
Document Number: DS-INMP441-00
Revision: 1.1