wm8940gefl-v Wolfson Microelectronics plc, wm8940gefl-v Datasheet - Page 28

• Manufacturer Part Number: wm8940gefl-v
• Description: Mono Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

WM8940
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INPUT LIMITER / AUTOMATIC LEVEL CONTROL (ALC)
The WM8940 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
3:0
BIT
ALCMIN
[2:0]
ALCMAX
[2:0]
ALCSEL
ALCLVL
[3:0]
LABEL
000 (-12dB)
111
(+35.25dB)
0
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 (see Note)
0 = ALC disabled
1 = 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
PD, Rev 4.2, April 2008
Production Data
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