wm8903 Wolfson Microelectronics plc, wm8903 Datasheet - Page 55

• Manufacturer Part Number: wm8903
• Description: Ultra Low Power Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

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DAC BIAS CONTROL
The analogue circuits within the DAC use the Master bias current (see “Reference Voltages and
Master Bias”). The DAC bias currents can also be reduced using the DACBIAS_SEL and
DACVMID_SEL fields as described in Table 33. These can be used to reduce power consumption,
but may have a marginal impact on audio performance in some usage modes.
The DAC bias currents can be increased using the DAC_BIAS_BOOST field. Setting this bit doubles
the bias level of DACBIAS_SEL and DACVMID_BIAS_SEL. This offers a performance improvement,
but also an increase in power consumption.
Note that the increased DAC VMID buffer bias is unlikely to give better performance; when
DAC_BIAS_BOOST is set, it is recommended to set DACVMID_BIAS_SEL = 01 in order to restore
the Normal DAC VMID buffer bias level.
Table 33 DAC Bias Control
DAC OVERSAMPLING RATIO (OSR)
The DAC oversampling rate is programmable to allow power consumption versus audio performance
trade-offs. The default oversampling rate is low for reduced power consumption; using the higher
OSR setting improves the DAC signal-to-noise performance.
Table 34 DAC Oversampling Control
R33 (21h)
DAC Digital 1
R8 (08h)
Analogue
DAC 0
REGISTER
ADDRESS
REGISTER
ADDRESS
4:3
2:1
BIT
5
BIT
0
DAC_BIAS_BOO
ST
DACBIAS_SEL
DACVMID_BIAS_
SEL
LABEL
DAC_OSR
LABEL
DEFAULT
DEFAULT
00
00
0
0
DAC Bias boost
0 = Disable
1 = Enable
When DAC Bias boost is enabled, the
bias selected by DACBIAS_SEL and
DACVMID_BIAS_SEL are both
doubled.
DAC bias current select
00 = Normal bias
01 = Normal bias x 0.5
10 = Normal bias x 0.66
11 = Normal bias x 0.75
DAC VMID buffer bias select
00 = Normal bias
01 = Normal bias x 0.5
10 = Normal bias x 0.66
11 = Normal bias x 0.75
DAC Oversampling Control
0 = Low power (normal oversample)
1 = High performance (double rate)
PP, Rev 3.1, August 2009
DESCRIPTION
DESCRIPTION
WM8903
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