wm8974gefl-v Wolfson Microelectronics plc, wm8974gefl-v Datasheet - Page 37

• Manufacturer Part Number: wm8974gefl-v
• Description: Mono Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

Production Data
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AUTOMUTE
Table 27 DAC Auto Mute Control Register
DAC OUTPUT LIMITER
The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital
interpolation filters. The bitstream data enters a multi-bit, sigma-delta DAC, which converts it to a
high quality analogue audio signal. The multi-bit DAC architecture reduces high frequency noise and
sensitivity to clock jitter.
The DAC output defaults to non-inverted. Setting DACPOL will invert the DAC output phase.
The DAC has an automute function which applies an analogue mute when 1024 consecutive zeros
are detected. The mute is release as soon as a non-zero sample is detected. Automute can be
disabled using the AMUTE control bit.
The WM8974 has a digital output limiter function. The operation of this is shown in Figure 19. In
this diagram the upper graph shows the envelope of the input/output signals and the lower graph
shows the gain characteristic.
The limiter has a programmable upper threshold which is close to 0dB. Referring to Table 28, in
normal operation (LIMBOOST=000 => limit only) signals below this threshold are unaffected by the
limiter.
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.
Figure 19 DAC Digital Limiter Operation
R10
DAC Control
REGISTER
ADDRESS
Signals above the upper threshold are attenuated at a specific attack rate (set by the
BIT
2
AMUTE
LABEL
0
DEFAULT
DAC auto mute enable
0 = auto mute disabled
1 = auto mute enabled
PD, Rev 4.5, September 2008
DESCRIPTION
WM8974
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