THREE TONE CALIBRATION SETUP
A calibration test setup consist of a test room (acoustical box)
with a loudspreaker (acoustical source) driven with the test
tone sequence from Figure 8. The test setup is shown in Fig-
ure 9. The distance 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.
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FIGURE 9. Three Tone Calibration Test setup
SUPPLY CURRENT DURING CALIBRATION
The Calibration function performs two main tasks in a se-
quence. First the AC characteristics of the microphones are
matched. Then in the second stage, if the PE pin is high, the
on-chip EEPROM is programmed.
During the first stage of this sequence the supply current on
the LMV1088 will increase to about 2.5 mA. During the writing
of the EEPROM the supply current will rise for about 215ms
to about 30 mA. This increased current is used for the on chip
charge pump which generates the high voltages that are re-
quired for programming the EEPROM.
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FIGURE 10. Supply current during calibration and
programming
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LMV1088
