ak5702 AKM Semiconductor, Inc., ak5702 Datasheet - Page 42

• Manufacturer Part Number: ak5702
• Description: 4-channel Adc With Pll & Mic-amp
• Manufacturer: AKM Semiconductor, Inc.

2. ALC Recovery Operation
The ALC recovery operation waits for the WTMA/B2-0 bits (Table 31) to be set after completing the ALC limiter
operation. If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 28) during the wait time,
the ALC recovery operation is done. The IVAL and IVAR values are automatically incremented by RGA/B1-0 bits
(Table 32) up to the set reference level (Table 33) with zero crossing detection which timeout period is set by ZTMA/B1-0
bits (Table 30). Then the IVA/BL and IVA/BR are set to the same value for both channels. The ALC recovery operation
is done at a period set by WTMA/B2-0 bits. If ZTMA/B1-0 is longer than WTMA/B2-0 and no zero crossing occurs, the
ALC recovery operation is done at a period set by ZTMA/B1-0 bits.
For example, when the current IVOL value is 30H and RGA/B1-0 bits are set to “01”, IVOL is changed to 32H by the
auto limiter operation and then the input signal level is gained by 0.75dB (=0.375dB x 2). When the IVOL value exceeds
the reference level (REFA/B7-0), the IVOL values are not increased.
When
during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When
the waiting timer of ALC recovery operation starts.
The ALC operation corresponds to the impulse noise. When the impulse noise is input, the ALC recovery operation
becomes faster than a normal recovery operation. When large noise is input to microphone instantaneously, the quality of
small level in the large noise can be improved by this fast recovery operation. The speed of fast recovery operation is
setted by RFSTA/B1-0 bits (Table 34).
MS0623-E-00
“ALC recovery waiting counter reset level (LMTHA/B1-0) ≤ Output Signal < ALC limiter detection level
(LMTHA/B1-0)”
“ALC recovery waiting counter reset level (LMTHA/B1-0) > Output Signal”,
WTMA/B2
ZTMA/B1
0
0
0
0
1
1
1
1
0
0
1
1
ZELMNA/B
WTMA/B1
0
1
0
0
1
1
0
0
1
1
ZTMA/B0
0
1
0
1
LMATA/B1
WTMA/B0
Table 31. ALC Recovery Operation Waiting Period
Table 30. ALC Zero Crossing Timeout Period
0
0
1
1
x
0
1
0
1
0
1
0
1
1024/fs
128/fs
256/fs
512/fs
Table 29. ALC Limiter ATT Step
LMATA/B0
16384/fs
1024/fs
2048/fs
4096/fs
8192/fs
128/fs
256/fs
512/fs
0
1
0
1
x
128ms
8kHz
16ms
32ms
64ms
- 42 -
Zero Crossing Timeout Period
ALC Recovery Operation Waiting Period
1024ms
2048ms
128ms
256ms
512ms
8kHz
16ms
32ms
64ms
ALC Limiter ATT Step
1 step
2 step
4 step
8 step
1step
16kHz
16ms
32ms
64ms
8ms
1024ms
16kHz
128ms
256ms
512ms
16ms
32ms
64ms
8ms
0.375dB
0.750dB
1.500dB
3.000dB
0.375dB
44.1kHz
11.6ms
23.2ms
2.9ms
5.8ms
44.1kHz
185.8ms
371.5ms
11.6ms
23.2ms
46.4ms
92.9ms
2.9ms
5.8ms
(default)
(default)
(default)
[AK5702]
2007/06