WM8976 Wolfson Microelectronics Ltd., WM8976 Datasheet - Page 29

• Manufacturer Part Number: WM8976
• Description: The WM8976 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

Pre-Production
INPUT LIMITER / AUTOMATIC LEVEL CONTROL (ALC)
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The WM8976 has an automatic PGA gain control circuit, which can function as an input peak limiter
or as an automatic level control (ALC).
the amplitude of the input signal. A digital peak detector monitors the input signal amplitude and
compares it to a register defined threshold level (ALCLVL).
If the signal is below the threshold, the ALC will increase the gain of the PGA at a rate set by
ALCDCY. If the signal is above the threshold, the ALC will reduce the gain of the PGA at a rate set
by ALCATK.
The ALC has two modes selected by the ALCMODE register: normal mode and peak limiter mode.
The ALC/limiter function is enabled by setting the register bit R32[8] ALCSEL.
The Automatic Level Control (ALC) provides continuous adjustment of the input PGA in response to
R32 (20h)
ALC Control
1
R33 (21h)
ALC Control
2
REGISTER
ADDRESS
2:0
5:3
8:7
3:0
BIT
ALCMIN
[2:0]
ALCMAX
[2:0]
ALCSEL
ALCLVL
[3:0]
LABEL
000 (-12dB)
111
(+35.25dB)
00
1011
(-6dB)
DEFAULT
Set minimum gain of PGA
000 = -12dB
001 = -6dB
010 = 0dB
011 = +6dB
100 = +12dB
101 = +18dB
110 = +24dB
111 = +30dB
Set Maximum Gain of PGA
111 = +35.25dB
110 = +29.25dB
101 = +23.25dB
100 = +17.25dB
011 = +11.25dB
010 = +5.25dB
001 = -0.75dB
000 = -6.75dB
ALC function select
00 = ALC disabled
01 = Right channel ALC enabled
10 = Left channel ALC enabled
11 = Both channels ALC enabled
ALC target – sets signal level at ADC
input
1111 = -1.5dBFS
1110 = -1.5dBFS
1101 = -3dBFS
1100 = -4.5dBFS
1011 = -6dBFS
1010 = -7.5dBFS
1001 = -9dBFS
1000 = -10.5dBFS
0111 = -12dBFS
0110 = -13.5dBFS
0101 = -15dBFS
0100 = -16.5dBFS
0011 = -18dBFS
0010 = -19.5dBFS
0001 = -21dBFS
0000 = -22.5dBFS
DESCRIPTION
PP Rev 3.0 April 2006
WM8976
29