WM8985
Pre-Production
The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital
interpolation filters. The bitstream data enters the multi-bit, sigma-delta DACs, which convert it to a
high quality analogue audio signal. The multi-bit DAC architecture reduces high frequency noise and
sensitivity to clock jitter. It also uses a Dynamic Element Matching technique for high linearity and
low distortion.
The DAC output phase defaults to non-inverted. Setting DACLPOL will invert the DAC output phase
on the left channel and DACRPOL inverts the phase on the right channel.
AUTO-MUTE
The DAC has an auto-mute function which applies an analogue mute when 1024 consecutive zeros
are detected. The mute is released as soon as a non-zero sample is detected. Auto-mute can be
disabled using the AMUTE control bit.
DIGITAL HI-FI DAC VOLUME (GAIN) CONTROL
The signal volume from each Hi-Fi DAC can be controlled digitally. The gain 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
LABEL
DEFAULT
DESCRIPTION
R11 (0Bh)
7:0
DACLVOL
[7:0]
11111111
( 0dB )
Left DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
Left DAC
Digital Volume
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
8
DACVU
Not
latched
DAC left and DAC right volume do
not update until a 1 is written to
DACVU (in reg 11 or 12)
R12 (0Ch)
7:0
DACRVOL
[7:0]
11111111
( 0dB )
Right DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
Right DAC
Digital Volume
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
8
DACVU
Not
latched
DAC left and DAC right volume do
not update until a 1 is written to
DACVU (in reg 11 or 12)
Table 23 DAC Digital Volume Control
Note: An additional gain of up to 12dB can be added using the gain block embedded in the
digital peak limiter circuit (see DAC OUTPUT LIMITER section).
5-BAND EQUALISER
A 5-band graphic equaliser function which can be used to change the output frequency levels to suit
the environment. This can be applied to the ADC or DAC path and is described in the 5-BAND
EQUALISER section for further details on this feature.
3-D ENHANCEMENT
The WM8985 has an advanced digital 3-D enhancement feature which can be used to vary the
perceived stereo separation of the left and right channels. Like the 5-band equaliser this feature can
be applied to either the ADC record path or the DAC playback path but not both simultaneously.
Refer to the 3-D STEREO ENHANCEMENT section for further details on this feature.
DAC DIGITAL OUTPUT LIMITER
The WM8985 has a digital output limiter function. The operation of this is shown in Figure 24. In
this diagram the upper graph shows the envelope of the input/output signals and the lower graph
shows the gain characteristic.
PP, Rev 3.4, October 2006
56
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
