ak4651 AKM Semiconductor, Inc., ak4651 Datasheet - Page 27

• Manufacturer Part Number: ak4651
• Description: 16bit ?? Codec With Mic/hp/spk-amp
• Manufacturer: AKM Semiconductor, Inc.

ASAHI KASEI
The ALC (Automatic Level Control) of MIC input is done by ALC1 block when ALC1 bit is “1”.
(1) ALC1 Limiter Operation
When the ALC1 limiter is enabled, and IPGA output exceeds the ALC1 limiter detection level (LMTH bit: Table 15), the
IPGA value is attenuated by the amount defined in the ALC1 limiter ATT step (LMAT1-0 bits: Table 16) automatically.
When the ZELMN bit = “1”, the timeout period is set by the LTM1-0 bits (Table 17). The operation for attenuation is
done continuously until the IPGA output signal level becomes LMTH or less. If the ALC1 bit does not change into “0”
after completing the attenuation, the attenuation operation repeats while the IPGA output signal level equals or exceeds
LMTH.
When the ZELMN bit = “0”, the timeout period is set by the ZTM1-0 bits (Table 18). This enables the zero-crossing
attenuation function so that the IPGA value is attenuated at the zero-detect points of the waveform.
MS0503-E-00
MIC-ALC Operation
LMTH
Note: When IPGA gain is 0dB or less, ALC1 limiter ATT step is fixed to 1 regardless as LMAT1-0 bits.
0
1
LTM1
ZTM1
0
0
1
1
0
0
1
1
Table 17. ALC1 Limiter Operation Period at zero crossing disable (ZELMN bit = “1”)
Table 15. ALC1 Limiter Detection Level / Recovery Waiting Counter Reset Level
ALC1 Limiter Detection Level
ADC Input ≥ −6.0dBFS
ADC Input ≥ −4.0dBFS
LTM0
ZTM0
0
1
0
1
0
1
0
1
LMAT1
0
0
1
1
1024/fs
Table 16. ALC1 Limiter ATT Step Setting
128/fs
256/fs
512/fs
0.5/fs
Table 18. Zero Crossing Timeout Period
1/fs
2/fs
4/fs
LMAT0
0
1
0
1
ALC1 Limiter Operation Period
Zero Crossing Timeout Period
128ms
125µs
250µs
500µs
8kHz
8kHz
16ms
32ms
64ms
63µs
ALC1 Recovery Waiting Counter Reset Level
- 27 -
−6.0dBFS > ADC Input ≥ −8.0dBFS
−4.0dBFS > ADC Input ≥ −6.0dBFS
ATT STEP
1
2
3
4
16kHz
16kHz
125µs
250µs
16ms
32ms
64ms
31µs
63µs
8ms
Default
44.1kHz
44.1kHz
11.6ms
23.2ms
2.9ms
5.8ms
11µs
23µs
45µs
91µs
Default
Default
Default
[AK4651]
2006/04