WM8940
Pre-Production
OUTPUT SIGNAL PATH
The WM8940 output signal paths consist of digital application filters, up-sampling filters, a Hi-Fi
DAC, analogue mixers, speaker and mono output drivers. The digital filters and DAC are enabled by
bit DACEN. 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 WM8940, irrespective of whether the DACs are running or not.
The WM8940 DAC receives digital input data on the DACDAT pin. The digital filter block processes
the data to provide the following functions:
Digital volume control
A digital peak limiter.
Sigma-Delta Modulation
The high performance sigma-delta audio DAC converts the digital data into an analogue signal.
DAC DIGITAL FILTERS
DIGITAL
AUDIO
INTERFACE
DIGITAL
PEAK
LIMITER
DIGITAL
GAIN
DIGITAL
FILTERS
INTERP
SDM
DAC
Figure 19 DAC Digital Filter Path
The analogue output from the DAC can then be mixed with the AUX analogue input and the ADC
analogue input. The mix is fed to the output drivers, SPKOUTP/N, and MONOOUT.
MONOOUT: can drive a 16Ω or 32Ω headphone or line output or can be a buffered version of VMID
(When MONOMUTE=1).
SPKOUTP/N: can drive a 16Ω or 32Ω stereo headphone or stereo line output, or an 8Ω BTL mono
speaker.
DIGITAL HI-FI DAC VOLUME CONTROL
The signal volume from each Hi-Fi DAC can be controlled digitally. 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;
MUTE for X = 0
REGISTER
ADDRESS
BIT
7:0
LABEL
DEFAULT
DESCRIPTION
R11
DACVOL
[7:0]
11111111
( 0dB )
DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
DAC Digital
Volume
Table 29 DAC Volume
Pre-Production, Rev 3.0, February 2007
40
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
