WM9713L_06 WOLFSON [Wolfson Microelectronics plc], WM9713L_06 Datasheet - Page 29

• Manufacturer Part Number: WM9713L_06
• Description: AC 97 Audio + Touchpanel CODEC
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

Pre-Production
AUTOMATIC LEVEL CONTROL
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The WM9713L has an automatic level control that aims to keep a constant recording volume
irrespective of the input signal level. This is achieved by continuously adjusting the PGA gain so that
the signal level at the ADC input remains constant. A digital peak detector monitors the ADC output
and changes the PGA gain if necessary.
Figure 11 ALC Operation
The ALC function is enabled using the ALCSEL control bits. When enabled, the recording volume
can be programmed between –6dB and –28.5dB (relative to ADC full scale) using the ALCL register
bits.
HLD, DCY and ATK control the hold, decay and attack times, respectively.
HOLD TIME
Hold time is the time delay between the peak level detected being below target and the PGA gain
beginning to ramp up. It can be programmed in power-of-two (2
10.67ms etc. up to 43.7s. Alternatively, the hold time can also be set to zero. The hold time only
applies to gain ramp-up, there is no delay before ramping the gain down when the signal level is
above target.
DECAY (GAIN RAMP-UP) TIME
Decay time is the time that it takes for the PGA gain to ramp up across 90% of its range (e.g. from
–15B up to 27.75dB). The time it takes for the recording level to return to its target value therefore
depends on both the decay time and on the gain adjustment required. If the gain adjustment is small,
it will be shorter than the decay time. The decay time can be programmed in power-of-two (2
from 24ms, 48ms, 96ms, etc. to 24.58s.
signal
signal
input
PGA
after
ALC
gain
hold
time
decay
time
attack
time
target
level
ALC
n
) steps, e.g. 2.67ms, 5.33ms,
PP Rev 3.0 June 2006
WM9713L
n
) steps,
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