Datasheet
Micro
phone 1
Micro
phone 2
Source
LMV1089
application
CAL PE
Start
Calibration
Test Tone
sequence
AWG
Acoustical Calibration Box
Calibration Pulse
LMV1089
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SNAS441H –SEPTEMBER 2008–REVISED MAY 2010
AUTOMATIC CALIBRATION SETUP
A calibration test setup consists of a test room (acoustical box) with a loudspeaker (acoustical source) driven with
the test tone sequence from Figure 31. The test setup is shown in Figure 32. The distances between the source
and microphone 1 and microphone 2 must be equal and the sound must travel without any obstacle from source
to both microphones.
The sound will travel with the limited speed of 300m/s from the loudspeaker source to the microphones. When
creating the calibration signals this time should not be ignored, 30cm distance will cause 1ms delay.
For an optimum automatic calibration the output level of the microphones and preamp gain must be set so that
the resulting signal at the output of the preamplifier is 100mV
P-P
± 6dB
Figure 32.
MANUAL CALIBRATION
You can manually program the gain compensation of the two mic inputs on the LMV1089 using the I
2
C interface.
Table 4 shows the control bits for I
2
C Register O and P with the corresponding gains. This can be easily done by
doing the following:
1) READ contents of the I
2
C register N immediately after powering up.
2) Set PE pin and T7 pin to Vdd.
3) WRITE to I
2
C register O and P to choose the calibration settings.
Bits O<7:4> control the two mics at 300Hz and bits O<3:0> control the two mics at 3kHz.
Bits P<7:4> control the right channel gain and bits P<3:0> control the left channel gain
4) WRITE a ‘0’ to I
2
C register Q<7> bit (storeBar) and the bits from I
2
C register N<6:0> to I
2
C register Q<6:0>
5) When I
2
C register N<7> (ready) goes high, then the EEPROM programming is complete. Now PE pin and
T7 pin should be set to GND and I
2
C register Q<7> (storeBar) should be returned to ‘1’.
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