WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 38

• 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.

WM8978
INPUT LIMITER / AUTOMATIC LEVEL CONTROL (ALC)
w
Table 19 ADC Digital Volume Control
Figure 19 Input Peak Limiter Operation
The WM8978 has an automatic PGA gain control circuit, which can function as an input peak limiter
or as an automatic level control (ALC).
In input peak limiter mode (ALCMODE bit = 1), a digital peak detector detects when the input signal
goes above a predefined level and will ramp the PGA gain down to prevent the signal becoming too
large for the input range of the ADC. When the signal returns to a level below the threshold, the
PGA gain is slowly returned to its starting level. The peak limiter cannot increase the PGA gain
above its static level.
R15
Left channel
ADC Digital
Volume
R16
Right channel
ADC Digital
Volume
REGISTER
ADDRESS
7:0
8
7:0
8
BIT
ADCVOLL
[7:0]
ADCVU
ADCVOLR
[7:0]
ADCVU
LABEL
11111111
( 0dB )
Not
latched
11111111
( 0dB )
Not
latched
DEFAULT
Left ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
ADC left and ADC right volume do not
update until a 1 is written to ADCVU (in
reg 15 or 16)
Right ADC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
ADC left and ADC right volume do not
update until a 1 is written to ADCVU (in
reg 15 or 16)
DESCRIPTION
PTD Rev 2.6 November 2005
Preliminary Technical Data
38