AK4635 datasheet(46/81 Pages) AKM

46 / 81 page

[AK4635]

Rev. 0.6

2007/10

- 46 -

2. ALC Recovery Operation

The ALC recovery operation waits for the WTM2-0 bits (Table 28) to be set after completing the ALC limiter operation.

If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 25) during the wait time, the ALC

recovery operation is executed. The VOL value is automatically incremented by RGAIN1-0 bits (Table 29) up to the set

reference level (Table 30, Table 31) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 27).

The ALC recovery operation is executed in a period set by WTM2-0 bits.

For example, when the current VOL value is 30H and RGAIN1-0 bits are set to “01”(2 steps), VOL is changed to 32H by

the auto limiter operation and then the input signal level is gained by 0.75dB (=0.375dB x 2). When the VOL value

exceeds the reference level (IREF7-0 or OREF5-0), the VOL values are not increased.

When

“ALC recovery waiting counter reset level (LMTH1-0)

≤ Output Signal < ALC limiter detection level (LMTH1-0)”

during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When

“ALC recovery waiting counter reset level (LMTH1-0) > Output Signal”,

the waiting timer of ALC recovery operation starts.

The ALC operation corresponds to the impulse noise. When the impulse noise is input, the ALC 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. The speed of first recovery operation is set

by RFST1-0 bits (Table 32).

ALC Recovery Operation Waiting Period

WTM2

WTM1

WTM0

8kHz

16kHz

44.1kHz

128/fs

16ms

8ms

2.9ms

(default)

256/fs

32ms

16ms

5.8ms

512/fs

64ms

32ms

11.6ms

1024/fs

128ms

64ms

23.2ms

2048/fs

256ms

128ms

46.4ms

4096/fs

512ms

256ms

92.9ms

8192/fs

1024ms

512ms

185.8ms

16384/fs

2048ms

1024ms

371.5ms

Table 28. ALC Recovery Operation Waiting Period

RGAIN1

RGAIN0

GAIN STEP

0.375dB

(default)

0.750dB

1.125dB

1.500dB

Table 29. ALC Recovery GAIN Step

AK4635 Scheda tecnica(PDF) 46 Page - Asahi Kasei Microsystems

AK4635 Scheda tecnica(HTML) 46 Page - Asahi Kasei Microsystems

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

Scheda tecnica Scarica

Link URL