WM8976 datasheet(39/83 Pages) WOLFSON

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Preliminary Technical Data

WM8976

PTD Rev 2.0 February 2005

Figure 18 DAC Digital Limiter Operation

The limiter has a programmable upper threshold which is close to 0dB. Referring to Figure 18, in

normal operation (LIMBOOST=000 => limit only) signals below this threshold are unaffected by the

limiter.

Signals above the upper threshold are attenuated at a specific attack rate (set by the

LIMATK register bits) until the signal falls below the threshold. The limiter also has a lower threshold

1dB below the upper threshold.

When the signal falls below the lower threshold the signal is

amplified at a specific decay rate (controlled by LIMDCY register bits) until a gain of 0dB is reached.

Both threshold levels are controlled by the LIMLVL register bits. The upper threshold is 0.5dB above

the value programmed by LIMLVL and the lower threshold is 0.5dB below the LIMLVL value.

VOLUME BOOST

The limiter has programmable upper gain which boosts signals below the threshold to compress the

dynamic range of the signal and increase its perceived loudness. This operates as an ALC function

with limited boost capability. The volume boost is from 0dB to +12dB in 1dB steps, controlled by the

LIMBOOST register bits.

The output limiter volume boost can also be used as a stand alone digital gain boost when the limiter

is disabled.

WM8976 数据表(PDF) 39 Page - Wolfson Microelectronics plc