WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 41

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WM8978

Manufacturer Part Number
WM8978
Description
The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
Manufacturer
Wolfson Microelectronics Ltd.
Datasheet

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Preliminary Technical Data
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Table 20 ALC Control Registers
MINIMUM AND MAXIMUM GAIN
PEAK LIMITER
When the ALC is disabled, the input PGA remains at the last controlled value of the ALC. An input
gain update must be made by writing to the INPPGAVOLL/R register bits.
The MINGAIN and MAXGAIN register sets the minimum/maximum gain value that the PGA can be
set to whilst under the control of the ALC. This has no effect on the PGA when ALC is not enabled.
To prevent clipping when a large signal occurs just after a period of quiet, the ALC circuit includes a
limiter function. If the ADC input signal exceeds 87.5% of full scale (–1.16dB), the PGA gain is
ramped down at the maximum attack rate (as when ALCATK = 0000), until the signal level falls
below 87.5% of full scale. This function is automatically enabled whenever the ALC is enabled.
R34
ALC Control
3
REGISTER
ADDRESS
8
7:4
3:0
BIT
ALCMODE
ALCDCY
[3:0]
ALCATK
[3:0]
LABEL
0
0011
(13ms/6dB)
0011
(2.9ms/6dB)
0010
(832us/6dB)
0010
(182us/6dB)
DEFAULT
Determines the ALC mode of operation:
0=ALC mode
1=Limiter mode
Decay (gain ramp-up) time
(ALCMODE ==0)
0000
0001
0010
… (time doubles with every step)
1010
or
higher
Decay (gain ramp-up) time
(ALCMODE ==1)
0000
0001
0010
… (time doubles with every step)
1010
ALC attack (gain ramp-down) time
(ALCMODE == 0)
0000
0001
0010
… (time doubles with every step)
1010
or
higher
ALC attack (gain ramp-down) time
(ALCMODE == 1)
0000
0001
0010
… (time doubles with every step)
1010
Per
step
410us
820us
1.64ms
Per
step
90.8us
181.6us
363.2us
93ms
Per
step
104us
208us
416us
Per
step
22.7us
45.4us
90.8us
23.2ms
420ms
106ms
PTD Rev 2.6 November 2005
DESCRIPTION
Per
6dB
3.3ms
6.6ms
13.1ms
3.36s
Per 6dB
726.4us
1.453ms
2.905ms
744ms
Per 6dB
832us
1.664ms
3.328ms
852ms
Per
6dB
182.4us
363.2us
726.4us
186ms
WM8978
90% of
range
24.576s
6.18s
90% of
range
1.31ms
2.62ms
5.26ms
1.348s
24ms
48ms
192ms
5.39s
90% of
range
5.26ms
10.53ms
21.06ms
90% of
range
6ms
12ms
24.1ms
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