AK5700 Datasheet, PDF (35/61 Pages) Asahi Kasei Microsystems – 16-Bit ΔΣ Mono ADC with PLL & MIC-AMP

ASAHI KASEI
[AK5700]
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM1-0 bits (Table 25) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 22) during the wait time, the ALC
recovery operation is done. The IVL value is automatically incremented by RGAIN1-0 bits (Table 26) up to the set
reference level (Table 27) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 24). The ALC
recovery operation is done at a period set by WTM1-0 bits. If ZTM1-0 is longer than WTM1-0 and no zero crossing
occurs, the ALC recovery operation is done at a period set by ZTM1-0 bits.
For example, when the current IVOL value is 30H and RGAIN1-0 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 (REF7-0), the IVOL values are not increased.
When
“ALC recovery waiting counter reset level (LMTH1-0) ≤ Output Signal < ALC limiter detection level (LMTH1-0)”
during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When
“ALC recovery waiting counter reset level (LMTH1-0) > Output Signal”,
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.
WTM1
0
0
1
1
WTM0
ALC Recovery Operation Waiting Period
8kHz
16kHz
44.1kHz
0
128/fs
16ms
8ms
2.9ms
1
256/fs
32ms
16ms
5.8ms
0
512/fs
64ms
32ms
11.6ms
1
1024/fs
128ms
64ms
23.2ms
Table 25. ALC Recovery Operation Waiting Period
Default
RGAIN1
0
0
1
1
RGAIN0
GAIN STEP
0
1 step
0.375dB
1
2 step
0.750dB
0
3 step
1.125dB
1
4 step
1.500dB
Table 26. ALC Recovery GAIN Step
Default
REF7-0
GAIN(dB)
Step
F1H
+36.0
F0H
+35.625
EFH
+35.25
:
:
E2H
+30.375
E1H
+30.0
0.375dB Default
E0H
+29.625
:
:
03H
−53.25
02H
−53.625
01H
−54.0
00H
MUTE
Table 27. Reference Level at ALC Recovery operation
MS0569-E-01
- 35 -
2006/12