LMV1091 Datasheet, PDF (8/22 Pages) National Semiconductor (TI) – Dual Input, Far Field Noise Suppression Microphone Amplifier

LMV1091
SNAS481C – OCTOBER 2009 – REVISED MAY 2013
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Measuring Noise and SNR
The overall noise of the LMV1091 is measured within the frequency band from 10Hz to 22kHz using an A-
weighted filter. The Mic+ and Mic- inputs of the LMV1091 are AC shorted between the input capacitors, see
Figure 4.
LMV1090
Mic2+
short ^{470 nF}
Mic2-
470 nF
Mic1+
short ^{470 nF}
Mic1-
470 nF
LPF
OUT+
A-WEIGHTED
FILTER
AC Voltmeter
OUT-
Figure 4. Noise Measurement Setup
For the signal to noise ratio (SNR) the signal level at the output is measured with a 1kHz input signal of 18mV_P-P
using an A-weighted filter. This voltage represents the output voltage of a typical electret condenser microphone
at a sound pressure level of 94dB SPL, which is the standard level for these measurements. The LMV1091 is
programmed for 26dB of total 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.
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