WM8940CGEFLSLASHRV datasheet(44/91 Pages) WOLFSON

44 / 91 page

WM8940

Production Data

PD, Rev 4.3, November 2011

DAC OUTPUT LIMITER

The WM8940 has a digital output limiter function. The operation of this is shown in Figure 20. In this

diagram the upper graph shows the envelope of the input/output signals and the lower graph shows

the gain characteristic.

Figure 20 DAC Digital Limiter Operation

The limiter has a programmable upper threshold which is close to 0dB. Referring to Table 33, 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

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.

WM8940CGEFL/RV 数据表(PDF) 44 Page - Wolfson Microelectronics plc