AK4650 Datasheet, PDF (30/86 Pages) Asahi Kasei Microsystems – 16Bit ΔΣ CODEC with MIC/HP/SPK-AMP & TSC

[AK4650]
(2) ALC1 Recovery Operation
The ALC1 recovery refers to the amount of time that the AK4650 will allow a signal to exceed a predetermined limiting
value prior to enabling the limiting function. The ALC1 recovery operation uses the WTM1-0 bits to define the wait
period used after completing an ALC1 limiter operation (Table 19). If the input signal does not exceed the “ALC1
Recovery Waiting Counter Reset Level” (LMTH: Table 15), the ALC1 recovery operation starts. The IPGA value
increases automatically by the recovery gain step (RGAIN bit: Table 20) with zero crossing operation (timeout is set by
ZTM1-0: Table 18) during this operation up to the reference level (REF5-0 bit: Table 21). The ALC1 recovery operation
is done at a period set by the WTM1-0 bits. Zero crossing is detected during WTM1-0 period, the ALC1 recovery
operation waits WTM1-0 period and the next recovery operation starts.
During the ALC1 recovery operation, when input signal level exceeds the ALC1 limiter detection level (LMTH), the
ALC1 recovery operation changes immediately into an ALC1 limiter operation.
In the case of
(Recovery waiting counter reset level) ≤ (IPGA Output Level) < (Limiter detection level)
during the ALC1 recovery operation, the wait timer for the ALC1 recovery operation is reset. Therefore, in the case of
(Recovery waiting counter reset level) > (IPGA Output Level),
the wait timer for the 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.
WTM1
0
0
1
1
WTM0
ALC1 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 19. ALC1 Recovery Operation Waiting Period
(default)
RGAIN
GAIN STEP
0
0.5dB
(default)
1
1.0dB
Table 20. ALC1 Recovery Gain Step Setting
REF5-0
GAIN (dB)
STEP
3DH
+26.5
3CH
+26.0
:
:
2DH
+19.0
0.5dB (default)
:
:
05H
+0.5
04H
+0.0
03H
−1.0
02H
−2.0
:
:
1.0dB
01H
−7.0
00H
−8.0
Table 21. Setting Reference Value at ALC1 Recovery Operation
MS0502-E-01
- 30 -
2007/04