AK4665A Datasheet, PDF (19/52 Pages) Asahi Kasei Microsystems – 20-Bit Stereo CODEC with MIC/HP-AMP

ASAHI KASEI
[AK4665A]
2. ALC1 Recovery Operation
The ALC1 recovery operation waits for WTM1-0 bits (Table 12) to be set after completing the ALC1 limiter operation. If
the input signal does not exceed “ALC1 recovery waiting counter reset level” (Table 9) during the wait time, the ALC1
recovery operation is done. The IVOL value (same value for Lch and Rch) is automatically incremented by RGAIN1-0
bits (Table 13) up to the set reference level (Table 14) with zero crossing detection which timeout period is set by ZTM1-0
bits (Table 11). The ALC1 recovery operation is done at a period set by WTM1-0 bits. When zero cross is detected at both
channels during the wait period set by WTM1-0 bits, the ALC1 recovery operation waits until WTM1-0 period and the
next recovery operation is done. The setting period of WTM1-0 bits should be the same as ZTM1-0 bits or longer time.
For example, when the current IVOL value is 30H and RGAIN1-0 bits are set to “01”, the IVOL is changed to 32H by the
ALC1 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
“ALC1 recovery waiting counter reset level (LMTH1-0) ≤ Output Signal < ALC limiter detection level (LMTH1-0)”
during the ALC1 recovery operation, the waiting timer of ALC1 recovery operation is reset. When
“ALC1 recovery waiting counter reset level (LMTH1-0) > Output Signal”,
the waiting timer of ALC1 recovery operation starts.
The ALC1 operation corresponds to the impulse noise. When the impulse noise is input, the ALC1 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.
FS3 FS2 FS1 FS0
0000
0001
0010
1000
1001
1010
1100
1101
1110
Others
ALC1 Recovery Time
WTM=00
WTM=01
WTM=10
(Default)
384/fs (8.7ms) 768/fs (17.4ms) 1536/fs (34.8ms)
256/fs (8.0ms) 512/fs (16.0ms) 1024/fs (32.0ms)
384/fs (8.0ms) 768/fs (16.0ms) 1536/fs (32.0ms)
192/fs (8.7ms) 384/fs (17.4ms) 768/fs (34.8ms)
128/fs (8.0ms) 256/fs (16.0ms) 512/fs (32.0ms)
192/fs (8.0ms) 384/fs (16.0ms) 768/fs (32.0ms)
96/fs (8.7ms) 192/fs (17.4ms) 384/fs (34.8ms)
64/fs (8.0ms) 128/fs (16.0ms) 256/fs (32.0ms)
96/fs (8.0ms) 192/fs (16.0ms) 384/fs (32.0ms)
N/A
Table 12. ALC1 Recovery Operation Period
WTM=11
3072/fs (69.7ms)
2048/fs (64.0ms)
3072/fs (64.0ms)
1536/fs (69.7ms)
1024/fs (64.0ms)
1536/fs (64.0ms)
768/fs (69.7ms)
512/fs (64.0ms)
768/fs (64.0ms)
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 13. ALC1 Recovery GAIN Step
Default
MS0440-E-01
- 19 -
2006/05