AK4641 Datasheet, PDF (24/51 Pages) Asahi Kasei Microsystems – 16 BIT CODEC WITH BLUETOOTH INTERFACE

ASAHI KASEI
[AK4641]
„ Manual Mode
The AK4641 becomes a manual mode at ALC1 bit = “0”. This mode is used in the case shown below.
1. After exiting reset state, set up the registers for the ALC1 operation (ZTM1-0, LMTH and etc)
2. When the registers for the ALC1 operation (Limiter period, Recovery period and etc) are changed.
For example; When the change of the sampling frequency.
3. When IPGA is used as a manual volume.
„ MIC-ALC Operation
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), the IPGA value
is attenuated by the amount defined in the ALC1 limiter ATT step (LMAT1-0 bits) automatically.
When the ZELM bit = “1”, the timeout period is set by the LTM1-0 bits. The operation for attenuation is done
continuously until the input 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 input signal level equals or exceeds LMTH.
When the ZELM bit = “0”, the timeout period is set by the ZTM1-0 bits. This enables the zero-crossing attenuation
function so that the IPGA value is attenuated at the zero-detect points of the waveform.
[2] ALC1 Recovery Operation
The ALC1 recovery refers to the amount of time that the AK4641 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. If the input signal does not exceed the “ALC1 Recovery Waiting
Counter Reset Level”, the ALC1 recovery operation starts. The IPGA value increases automatically during this operation
up to the reference level (REF6-0 bits). 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.
MS0301-E-00
- 24 -
2004/05