Datasheet
A-WEIGHTED
FILTER
Mic2+
Mic2-
Mic1+
Mic1-
470 nF
470 nF
470 nF
470 nF
OUT-
LPF
LMV1089
short
short
AC Voltmeter
OUT
+
LMV1089
www.ti.com
SNAS441H –SEPTEMBER 2008–REVISED MAY 2010
Figure 36. 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 LMV1089 is
programmed for 26dB of total gain (20dB preamplifier and 6dB postamplifier) with only Mic1 or Mic2 used. (See
also I
2
C Compatible Interface).
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 LMV1089 is disabled.
Copyright © 2008–2010, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Links: LMV1089