T3903
Page 12 of 21
Document Number: DS-000358
Revision: 1.0
This definition of a 0 dB FS signal must be understood when measuring the sensitivity of the T3903. A 1 kHz sine wave at a 94 dB SPL
acoustic input to the T3903 resul
ts in an output signal with a −2
6 dB FS level (low-power mode). 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 −2
9 dB FS; however, this is
not true because of the definition of the 0 dB FS sine wave.
Figure 11. 1 kHz, 0 dB FS Sine Wave
There is not a commonly accepted unit of measurement to express the instantaneous level, as opposed to the RMS level of the
signal, of a digital signal output from the microphone. Some measurement systems express the instantaneous level of an individual
sample in units of D, where 1.0 D is digital full scale. In this case, a −
26 dB FS sine wave has peaks at 0.05 D.
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
DIGITA
L A
M
PLITU
DE
(D
)
TIME (ms)
