wm8775 Wolfson Microelectronics plc, wm8775 Datasheet - Page 28

• Manufacturer Part Number: wm8775
• Description: 24-bit, 96khz Adc With 4 Channel I/p Multiplexer
• Manufacturer: Wolfson Microelectronics plc

WM8775
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TRANSIENT WINDOW (LIMITER ONLY)
To prevent the limiter responding to to short duration high ampitude signals (such as hand-claps in a
live performance), the limiter has a programmable transient window preventing it responding to
signals above the threshold until their duration exceeds the window period. The Transient window is
set in register TRANWIN.
ZERO CROSS
The PGA has a zero cross detector to prevent gain changes introducing noise to the signal. In ALC
mode the register bit ALCZC allows this to be turned off if desired.
MAXIMUM GAIN (ALC ONLY) AND MAXIMUM ATTENUATION
To prevent low level signals being amplified too much by the ALC, the MAXGAIN register sets the
upper limit for the gain. This prevents low level noise being over-amplified. The MAXGAIN register
has no effect on the limiter operation.
The MAXATTEN register has different operation for the limiter and for the ALC. For the limiter it
defines the maximum attenuation below the static (user programmed) gain. For the ALC, it defines
the lower limit for the gain.
Limiter Control
ALC Control 2
REGISTER
ADDRESS
REGISTER
REGISTER
R18(12h)
Control 3
ADDRESS
ADDRESS
0010010
R20(14h)
R17(11h)
0010100
0010001
ALC
BIT
3:0
7:4
BIT
BIT
6:4
7
DCY [3:0]
ATK[3:0]
LABEL
TRANWIN
LABEL
LABEL
ALCZC
[2:0]
DEFAULT
0010
0011
DEFAULT
DEFAULT
(disabled)
010
0
ALC mode
0000: 8.4ms
0001: 16.8ms
0010: 33.6ms…
(time doubles with
every step)
1010 or higher:
8.6s
ALC mode
0000: 33.5ms
0001: 67.2ms
0010: 134.4ms
….(time doubles for
every step)
1010 or higher:
34.3ms
LC attack (gain ramp-down) time
Length of Transient Window
000: 0us (disabled)
001: 62.5us
010: 125us
…..
111: 4ms
PGA zero cross enable
0 : disabled
1: enabled
LC decay (gain ramp-up) time
DESCRIPTION
DESCRIPTION
DESCRIPTION
PD, Rev 4.4, October 2008
Limiter Mode
0000: 250us
0001: 500us… 0010:
1ms
(time doubles with
every step)
1010 or higher: 256ms
Limiter mode
0000: 1.2ms
0001: 2.4ms
0010: 4.8ms ….(time
doubles for every
step)
1010 or higher:
1.2288s
Production Data
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