The Mic+ and Mic- inputs of the LMV1091 are AC shorted
between the input capacitors, see Figure 11.
Measuring Noise and SNR
The overall noise of the LMV1091 is measured within the fre-
quency band from 10Hz to 22kHz using an A-weighted filter.
30092211
FIGURE 11: Noise Measurement Setup
For the signal to noise ratio (SNR) the signal level at the out-
put is measured with a 1kHz input signal of 18mVP-P using an
A-weighted filter. This voltage represents the output voltage
of a typical electret condenser microphone at a sound pres-
sure level of 94dB SPL, which is the standard level for these
measurements. The LMV1091 is programmed for 26dB of to-
tal gain (20dB preamplifier and 6dB postamplifier) with only
Mic1 or Mic2 used.
The input signal is applied differentially between the Mic+ and
Mic-. Because the part is in Pass Through mode the low-pass
filter at the output of the LMV1091 is disabled.
9
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