wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 56

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

WM8918
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DAC INTERFACE VOLUME BOOST
A digital gain function is available at the audio interface to boost the DAC volume when a small
signal is received on AIFRXDAT. This is controlled using register bits DAC_BOOST [1:0]. To prevent
clipping at the DAC input, this function should not be used when the boosted DAC data is expected
to be greater than 0dBFS.
The digital interface volume is controlled as shown in Table 27.
Table 27 DAC Interface Volume Boost
DIGITAL SIDETONE
A digital sidetone is available, allowing digital data from either Left or Right Digital Microphone (TX)
channels to be mixed with the audio interface data on the Left and Right DAC (RX) channels.
Sidetone data is taken from the DMIC high pass filter output, to reduce low frequency noise in the
sidetone (e.g. wind noise or mechanical vibration).
When using the digital sidetone, it is recommended that the DMIC paths are enabled before un-
muting the DACs to prevent pop noise. The DAC volumes and sidetone volumes should be set to an
appropriate level to avoid clipping at the DAC input.
When digital sidetone is used, it is recommended that the Charge Pump operates in Register Control
mode only (CP_DYN_PWR = 0). See “Charge Pump” for details.
The digital sidetone is controlled as shown in Table 28.
Table 28 Digital Sidetone Control
R24 (18h)
Audio
Interface 0
R32 (20h)
DAC Digital
0
REGISTER
REGISTER
ADDRESS
ADDRESS
11:8
BIT
7:4
3:2
1:0
10:9
BIT
DMICR_DAC_SVOL
DMICL_DAC_SVOL
DMIC_TO_DACR
DMIC_TO_DACL
DAC_BOOST
LABEL
LABEL
[3:0]
[3:0]
[1:0]
[1:0]
[1:0]
DEFAULT
DEFAULT
00
0000
0000
00
00
DAC Input Volume Boost
00 = 0dB
01 = +6dB (Input data must not
exceed -6dBFS)
10 = +12dB (Input data must not
exceed -12dBFS)
11 = +18dB (Input data must not
exceed -18dBFS)
Left Digital Sidetone Volume
(See Table 29 for volume range)
Right Digital Sidetone Volume
(See Table 29 for volume range)
Left DAC Digital Sidetone Source
00 = No sidetone
01 = Left DMIC
10 = Right DMIC
11 = Reserved
Right DAC Digital Sidetone Source
00 = No sidetone
01 = Left DMIC
10 = Right DMIC
11 = Reserved
PD, Rev 4.0, September 2010
DESCRIPTION
DESCRIPTION
Production Data
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