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WM8983
INPUT LIMITER / AUTOMATIC LEVEL CONTROL (ALC)
The WM8983 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.
Figure 19 Input Peak Limiter Operation
In ALC mode (ALCMODE bit = 0) the circuit 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.
PP Rev 1.1 August 2005
33
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
