wm8988 Wolfson Microelectronics plc, wm8988 Datasheet - Page 26

• Manufacturer Part Number: wm8988
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8988
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OUTPUT SIGNAL PATH
The WM8988 output signal paths consist of digital filters, DACs, analogue mixers and output drivers.
The digital filters and DACs are enabled when the WM8988 is in ‘playback only’ or ‘record and
playback’ mode. The mixers and output drivers can be separately enabled by individual control bits
(see Analogue Outputs). Thus it is possible to utilise the analogue mixing and amplification provided
by the WM8988, irrespective of whether the DACs are running or not.
The WM8988 receives digital input data on the DACDAT pin. The digital filter block processes the
data to provide the following functions:
•
•
•
Two high performance sigma-delta audio DACs convert the digital data into two analogue signals (left
and right). These can then be mixed with analogue signals from the LINPUT1/2 and RINPUT1/2 pins,
and the mix is fed to the output drivers, LOUT1/ROUT1 and LOUT2/ROUT2.
•
•
DIGITAL DAC VOLUME CONTROL
The signal volume from each DAC can be controlled digitally, in the same way as the ADC volume
(see Digital ADC Volume Control). The gain and attenuation range is –127dB to 0dB in 0.5dB steps.
The level of attenuation for an eight-bit code X is given by:
0.5 × (X-255) dB for 1 ≤ X ≤ 255;
The LDVU and RDVU control bits control the loading of digital volume control data. When LDVU or
RDVU are set to 0, the LDACVOL or RDACVOL control data is loaded into an intermediate register,
but the actual gain does not change. Both left and right gain settings are updated simultaneously
when either LDVU or RDVU are set to 1.
Table 17 Digital Volume Control
R10 (0Ah)
Left Channel
Digital Volume
R11 (0Bh)
Right Channel
Digital Volume
REGISTER
ADDRESS
Digital volume control
Graphic equaliser and Dynamic Bass Boost
Sigma-Delta Modulation
LOUT1/ROUT1: can drive a 16Ω or 32Ω stereo headphone or stereo line output.
LOUT2/ROUT2: can drive a 16Ω or 32Ω stereo headphone or stereo line output
8
7:0
8
7:0
BIT
LDVU
LDACVOL
[7:0]
RDVU
RDACVOL
[7:0]
LABEL
MUTE for X = 0
0
11111111
( 0dB )
0
11111111
( 0dB )
DEFAULT
Left DAC Volume Update
0 = Store LDACVOL in intermediate
latch (no gain change)
1 = Update left and right channel
gains (left = LDACVOL, right =
intermediate latch)
Left DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
Right DAC Volume Update
0 = Store RDACVOL in intermediate
latch (no gain change)
1 = Update left and right channel
gains (left = intermediate latch, right
= RDACVOL)
Right DAC Digital Volume Control
similar to LDACVOL
DESCRIPTION
PD, Rev 4.0, October 2008
Production Data
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