Datasheet
t
CC
1 kHz
0.3 kHz 3 kHz
PE
CAL
MIC1
MIC2
t
ST1
t
ET1
t
ST2
t
ST3
t
ET2
t
ET3
Start
Calibration
Calibration
Ready
LMV1089
SNAS441H –SEPTEMBER 2008–REVISED MAY 2010
www.ti.com
PERFORMING A THREE TONE CALIBRATION
In a system with two microphones in an enclosure there will always be a difference in the transfer function in
both gain and frequency response between the two channels. The LMV1089 has the capability to perform an
automatic calibration function to minimize these differences. To perform this calibration, a test sequence of three
tones is required right after the PE and CAL inputs are brought to a logic high level. At the end of this sequence
the calibration data is automatically stored in the internal EEPROM.
The three tones have to be applied as follows (see Figure 31):
• A first tone with a frequency of 1kHz
• A second tone with a frequency of 300Hz
• A third tone with a frequency of 3kHz
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 31 and Table 6 are ignored by the calibration system.
Between each tone pair there is a small time, indicated by a cross, to change the frequency. During that time the
input tone is ignored by the calibration system.
The total calibration sequence requires less than 790ms.
Figure 31. Calibration Timing
Table 6. Automatic Calibration Timing Parameters
(1)
Limits
Symbol Parameter Unitis
Min Max
t
ST1
Calibration Start Tone 1 10 ms
t
ET1
Calibration End Tone 1 200 ms
t
ST2
Calibration Start Tone 2 210 ms
t
ET2
Calibration End Tone 2 400 ms
t
ST3
Calibration Start Tone 3 410 ms
t
ET3
Calibration End Tone 3 600 ms
t
CC
Calibration Complete 790 ms
(1) Data specified by design
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