English
Language : 

AK4373 Datasheet, PDF (51/98 Pages) Asahi Kasei Microsystems – Low Power Stereo DAC with HP/SPK-Amp
[AK4373]
2. ALC Recovery Operation
ALC recovery operation wait for the WTM2-0 bits (Table 25) to be set after completing ALC limiter operation. If the
input signal does not exceed “ALC recovery waiting counter reset level” (Table 22) during the wait time, ALC recovery
operation is completed. The AVL and AVR values are 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). Then
the AVL and AVR are set to the same value for both channels. ALC recovery operation is executed at a period set by
WTM2-0 bits. When zero cross is detected at both channels during the wait period set by WTM2-0 bits, ALC recovery
operation waits until WTM2-0 period and the next recovery operation is completed. If ZTM1-0 is longer than WTM2-0
and no zero crossing occurs, ALC recovery operation is made at a period set by ZTM1-0 bits.
For example, when the current AVOL value is 30H and RGAIN1-0 bits are set to “01”, AVOL 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 AVOL value exceeds
the reference level (REF7-0), the AVOL 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.
ALC operation corresponds to the impulse noise. When the impulse noise is input, ALC recovery operation is faster than
a normal recovery operation (Fast Recovery Operation). When large noise is input to microphone instantaneously, quality
of small signal level in the large noise can be improved by this fast recovery operation. The speed of fast recovery
operation is set by RFST1-0 bits (Table 28).
WTM2
0
0
0
0
1
1
1
1
WTM1
0
0
1
1
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
0
2048/fs
256ms
128ms
46.4ms
1
4096/fs
512ms
256ms
92.9ms
0
8192/fs
1024ms
512ms
185.8ms
1
16384/fs
2048ms
1024ms
371.5ms
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)
MS0991-E-00
- 51 -
2008/09