wm8903 Wolfson Microelectronics plc, wm8903 Datasheet - Page 31

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

Pre-Production
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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 ADC has differential signal inputs, it has
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 ADC 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
INL_CM_ENA
INR_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)
PP, Rev 3.1, August 2009
DESCRIPTION
WM8903
31