AK4569 Datasheet, PDF (17/45 Pages) Asahi Kasei Microsystems – 20-Bit Stereo CODEC with IPGA & HP-AMP

ASAHI KASEI
[AK4569]
„ ALC Operation
[1] ALC Limiter Operation
During the ALC limiter operation, when either Lch or Rch exceeds ALC limiter detection level (LMTH), IPGA value is
attenuated by ALC limiter ATT step (LMAT1-0) automatically. The IPGA is then set to the same value for both channels.
When ZELMN = “1”, the timeout period is set by LTM1-0 bits. The attenuation operation is done continuously until the
input signal level becomes LMTH or less. After finishing the attenuation operation, if ALC bit does not change to “0”, the
operation repeats when the input signal level exceeds LMTH.
When ZELMN = “0”, the ALC limiter operation is attenuated by the ZTM1-0 bits setting. The IPGA value is
automatically attenuated using zero crossing detection.
The ALC operation of the AK4569 corresponds to the impulse noise. If the impulse noise is supplied at ZELMN = “0”,
the ALC limiter operation becomes faster period than a set of ZTM1-0 bits. In case of ZELMN = “1”, it becomes the same
period as LTM1-0 bits.
[2] ALC Recovery Operation
The ALC recovery operation waits for the WTM1-0 bits to be set after completing the ALC limiter. If the input signal
does not exceed “ALC recovery waiting counter reset level (LMTH)”, the ALC recovery operation is done. The IPGA
value is automatically incremented by this operation up to the set reference level (REF6-0) with zero crossing detection
which timeout period is set by ZTM1-0 bits. Then the IPGA value is set for both Lch and Rch. The ALC recovery
operation is done at a period set by WTM1-0 bits. When zero cross is detected at the IPGA output during the wait period
set by WTM1-0 bits, the ALC recovery operation waits until WTM1-0 period and the next recovery operation is done.
During the ALC recovery operation or the recovery waiting, when either input signal level of Lch or Rch in IPGA exceeds
the ALC limiter detection level (LMTH), the ALC recovery operation changes into the ALC limiter operation
immediately.
When
(ALC recovery waiting counter reset level: LMTH) ≤ (IPGA output level) < (ALC limiter detection level: LMTH)
during the ALC recovery operation, the ALC recovery operation wait timer is reset. Therefore, when
(ALC recovery waiting counter reset level: LMTH) > (IPGA output level),
the ALC recovery operation wait timer starts.
The ALC operation of the AK4569 corresponds to the impulse noise. If the impulse noise is supplied, the ALC recovery
operation becomes faster period than a set of ZTM1-0 or WTM1-0 bits.
Others:
When either channel enters the limiter operation while waiting time for a zero crossing, the present ALC recovery
operation stops, according as the small value of IPGA (a channel waiting zero crossing), the ALC limiter operation is
done. When both channels are waiting for the next ALC recovery operation, the ALC limiter operation is done from the
IPGA value of a point in time.
ZTM1-0 bits set zero crossing timeout and WTM1-0 bits set the ALC recovery operation period. When the ALC recovery
waiting time (WTM1-0 bits) is shorter than zero crossing timeout period (ZTM1-0 bits), the ALC recovery is operated by
the zero crossing timeout period. Therefore, in this case, the ALC recovery operation period is not constant.
MS0292-E-01
- 17 -
2005/07