Datasheet

t
CC
1 kHz
PE
CAL
MIC1
MIC2
t
ST1
t
ET3
Start
Calibration
Calibration
Ready
PE
Calibration
Start
Calibration
Ready
Calibrating in
progress
I
2
C
R[0]
LMV1089
www.ti.com SNAS441H –SEPTEMBER 2008–REVISED MAY 2010
• Apply Audio stimulus (single tone 1kHz or three tone sequence as described in PERFORMING A THREE
TONE CALIBRATION)
• Wait at least 790ms
• Remove Audio stimulus
• Write '0' into I
2
C to finish calibration
• Bring PE to a 'low' level (disable EEprom write)
A tone may be applied prior to the rising of PE or setting the I
2
C calibration bit . Signals applied to the
microphone inputs before rising of PE or setting the I
2
C calibration bit are ignored by the calibration system.
PERFORMING THE AUTOMATIC CALIBRATION
Automatic calibration can be performed as 'one tone' or as 'three tone' calibration. Three tone calibration is
preferred because the three tone calibration not only compensates for differences in the gain between the two
microphones, but this function also corrects for differences in the frequency response between in the two
microphones and compensates for the acoustical effects of the enclosure.
The one tone calibration only compensates for the gain difference between the two microphones at 1kHz and
can lead to less far field noise reduction when compared to three tone calibration.
PERFORMING A ONE TONE CALIBRATION
The easiest way to perform an automatic calibration with the LMV1089 uses a 1kHz tone. This tone can be a
steady state tone or a 1kHz tone that is switched on and off using the timing from Figure 30.
To perform a one tone calibration, a 1kHz test tone is required right after the PE and CAL inputs are brought to a
logic high level and that tone should be stable during the time as indicated in Table 6. At the end of this
sequence the calibration data is automatically stored in the internal EEPROM (see Figure 31).
A tone may be applied prior to the rising of CAL start signal and PE. Signals applied to the microphone outside
the limits shown in Figure 30 and Table 6 are ignored by the calibration system.
Figure 30. One Tone Calibration Timing
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