wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 58

• Manufacturer Part Number: wm8918
• Description: Ultra Low Power Dac For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8918
DIGITAL-TO-ANALOGUE CONVERTER (DAC)
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The WM8918 DACs receive digital input data from the AIFRXDAT pin and via the digital sidetone
path (see “Digital Mixing” section). 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 Wolfson SmartDAC™
architecture offers reduced power consumption, whilst also delivering a reduction in high frequency
noise and sensitivity to clock jitter. It also uses a Dynamic Element Matching technique for high
linearity and low distortion.
The analogue outputs from the DACs are sent directly to the output PGAs (see “Output Signal
Path”).
The DACs are enabled by the DACL_ENA and DACR_ENA register bits.
Table 30 DAC Enable Control
DAC DIGITAL VOLUME CONTROL
The output level of each DAC can be controlled digitally over a range from -71.625dB to 0dB in
0.375dB steps. The level of attenuation for an eight-bit code is detailed in Table 32.
The DAC_VU bit controls the loading of digital volume control data. When DAC_VU is set to 0, the
DACL_VOL or DACR_VOL control data is loaded into the respective control register, but does not
actually change the digital gain setting. Both left and right gain settings are updated when a 1 is
written to DAC_VU. This makes it possible to update the gain of both channels simultaneously.
Table 31 DAC Digital Volume Control
R18 (12h)
Power
Management
6
R30 (1Eh)
DAC Digital
Volume Left
R31 (1Fh)
DAC Digital
Volume Right
REGISTER
REGISTER
ADDRESS
ADDRESS
BIT
BIT
7:0
7:0
3
2
8
8
DACR_VOL [7:0]
DACL_VOL [7:0]
DACR_ENA
DACL_ENA
DAC_VU
DAC_VU
LABEL
LABEL
DEFAULT
1100_0000
1100_0000
DEFAULT
(0dB)
(0dB)
N/A
N/A
0
0
Left DAC Enable
0 = DAC disabled
1 = DAC enabled
Right DAC Enable
0 = DAC disabled
1 = DAC enabled
DAC Volume Update
Writing a 1 to this bit causes left
and right DAC volume to be
updated simultaneously
Left DAC Digital Volume
00h = Mute
01h = -71.625dB
02h = -71.250dB
… (0.375dB steps)
C0h to FFh = 0dB
(See Table 32 for volume range)
DAC Volume Update
Writing a 1 to this bit causes left
and right DAC volume to be
updated simultaneously
Right DAC Digital Volume
00h = Mute
01h = -71.625dB
02h = -71.250dB
… (0.375dB steps)
C0h to FFh = 0dB
(See Table 32 for volume range)
PD, Rev 4.0, September 2010
DESCRIPTION
DESCRIPTION
Production Data
58