wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 34

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

WM8918
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INPUT PGA COMMON MODE AMPLIFIER
In Differential Line Mode only, a Common Mode amplifier can be enabled as part of the input PGA
circuit. This feature provides approximately 20dB reduction in common mode noise on the differential
input, which can reduce problematic interference. Since the internal signal paths use a differential
configuration, they have an inherent immunity to common mode noise (see “Electrical
Characteristics”). However, the presence of Common Mode noise can limit the usable signal range of
the analogue input path; enabling the Common Mode amplifier can solve this issue.
It should be noted that the Common Mode amplifier consumes additional power and can also add its
own noise to the input signal. For these reasons, it is recommended that the Common Mode
Amplifier is only enabled if there is a known source of Common Mode interference.
The Common Mode amplifier is controlled by the INL_CM_ENA and INR_CM_ENA fields as
described in Table 5. Although the Common Mode amplifier may be enabled regardless of the input
PGA mode, its function is only effective in the Differential Line Mode configuration.
Table 5 Common Mode Amplifier Enable
R46 (2Eh)
Analogue Left
Input 1
R47 (2Fh)
Analogue
Right Input 1
REGISTER
ADDRESS
BIT
6
6
INR_CM_ENA
INL_CM_ENA
LABEL
DEFAULT
1
1
Left Input PGA Common Mode
Rejection enable
0 = Disabled
1 = Enabled
(only available for L_MODE=01 –
Differential Line)
Right Input PGA Common Mode
Rejection enable
0 = Disabled
1 = Enabled
(only available for R_MODE=01 –
Differential Line)
PD, Rev 4.0, September 2010
DESCRIPTION
Production Data
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