Automatic Calibration
The full automatic calibration should only be required once,
when the product containing the LMV1088 has completed
manufacture, and prior to application packaging. The product
containing the LMV1088 will be calibrated to the micro-
phones, the microphone spacings, and the acoustical prop-
erties of the final manufactured product containing the
LMV1088.
The compensation or calibration technology is achieved via
memory stored coefficients when the FFNS circuitry activates
the calibration sequence. The purpose of the calibration se-
quence is to choose the optimized coefficients for the FFNS
circuitry for the given microphones, spacing, and acoustical
environment of the product containing the LMV1088.
A basic calibration can be performed with a single 1kHz tone,
however to take full advantage of this calibration feature a
three tone calibration (See the section PERFORMING A
THREE TONE CALIBRATION) is preferred .
The automatic calibration process can be initiated from either
a digital interface CALIBRATE pin (CAL) or via the I
2
C inter-
face.
The logic level at the PROGRAM ENABLE (PE) pin deter-
mines if the result of the calibration is volatile or permanent.
To make the result of the calibration permanent (stored in the
EEPROM) the PROGRAM ENABLE (PE) pin must be high
during the automatic calibration process.
AUTOMATIC CALIBRATION VIA CAL PIN
To initiate the automatic calibration via the CAL pin, the fol-
lowing procedure is required:
•
From the initial condition where both PE and CAL are at
'low' level
•
bring PE to a 'high' level (enable EEprom write)
•
bring CAL to a 'high' level to start Calibration
•
Apply Audio stimulus (single tone 1kHz or three tone
sequence as described in PERFORMING A THREE
TONE CALIBRATION)
•
Hold CAL 'high' for at least 770ms
•
Remove Audio stimulus
•
bring CAL to a 'low' level to stop Calibration
•
bring PE to a 'low' level (disable EEprom write)
A tone may be applied prior to the rising of CAL and PE. Sig-
nals applied to the microphone inputs before rising of CAL
and PE are ignored by the calibration system.
202130r1
FIGURE 6. Automatic Calibration via CAL pin
Note:
When the I
2
C is operated, make sure that register 'R' (address 0x12)
bit 0 is '0' before operating the CAL pin (default value for this bit).
When this bit is set '1' the calibration engine of the LMV1088 is started
and will remain active with a higher supply current than normal oper-
ation. The state of the calibration remains active until this bit is reset,
'0”. With the bit set the 'low' to' high' transfer of the CAL pin will be
ignored.
AUTOMATIC CALIBRATION VIA I
2
C COMMAND
To initiate the automatic calibration via the I
2
interface, the
following procedure is required:
•
From the initial condition where PE is 'low' level
•
Bring PE to a 'high' level (enable EEprom write)
•
Write '1' into I
2
C register 'R' (address 0x12) bit 0 to start
calibration
•
Apply Audio stimulus (single tone 1kHz or three tone
sequence as described in PERFORMING A THREE
TONE CALIBRATION)
•
Wait at least 770ms
•
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 CAL and PE. Sig-
nals applied to the microphone inputs before rising of CAL
and PE are ignored by the calibration system.
202130r2
FIGURE 7. Automatic Calibration via I
2
C COMMAND
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LMV1088
