WM8750BL_12 Datasheet, PDF (29/60 Pages) Wolfson Microelectronics plc – Stereo CODEC for Portable Audio Applications

Production Data
WM8750BL
DIGITAL TO ANALOGUE CONVERTER (DAC)
After passing through the graphic equaliser filters, digital ‘de-emphasis’ can be applied to the audio
data if necessary (e.g. when the data comes from a CD with pre-emphasis used in the recording). De-
emphasis filtering is available for sample rates of 48kHz, 44.1kHz and 32kHz.
The WM8750BL also has a Soft Mute function, which gradually attenuates the volume of the digital
signal to zero. When removed, the gain will return to the original setting. This function is enabled by
default. To play back an audio signal, it must first be disabled by setting the DACMU bit to zero.
REGISTER
ADDRESS
R5 (05h)
ADC and DAC
Control
BIT
LABEL
2:1 DEEMP
[1:0]
3 DACMU
Table 19 DAC Control
DEFAULT
DESCRIPTION
00
De-emphasis Control
11 = 48kHz sample rate
10 = 44.1kHz sample rate
01 = 32kHz sample rate
00 = No De-emphasis
1
Digital Soft Mute
1 = mute
0 = no mute (signal active)
The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital
interpolation filters. The bitstream data enters two multi-bit, sigma-delta DACs, which convert them to
high quality analogue audio signals. 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.
In normal operation, the left and right channel digital audio data is converted to analogue in two
separate DACs. However, it is also possible to disable one channel, so that the same signal (left or
right) appears on both analogue output channels. Additionally, there is a mono-mix mode where the
two audio channels are mixed together digitally and then converted to analogue using only one DAC,
while the other DAC is switched off. The mono-mix signal can be selected to appear on both
analogue output channels.
The DAC output defaults to non-inverted. Setting DACINV will invert the DAC output phase on both
left and right channels.
REGISTER
ADDRESS
R23 (17h)
Additional
Control (1)
BIT
LABEL
5:4 DMONOMIX
[1:0]
DEFAULT
00
1 DACINV
0
Table 20 DAC Mono Mix and Phase Invert Select
DESCRIPTION
DAC mono mix
00: stereo
01: mono ((L+R)/2) into DACL, ‘0’ into
DACR
10: mono ((L+R)/2) into DACR, ‘0’ into
DACL
11: mono ((L+R)/2) into DACL and
DACR
DAC phase invert
0 : non-inverted
1 : inverted
w
PD, Rev 4.1, August 2012
29