Pre-Production
WM8976
INPUT SIGNAL PATH
The WM8976 has flexible analogue inputs. An input PGA stage is followed by a boost/mix stage
which drives into the hi-fi ADC. The input path has three input pins which can be configured in a
variety of ways to accommodate single-ended or differential microphones. There is an auxiliary input
pin which can be fed into to the input boost/mix stage as well as driving into the output path. A
bypass path exists from the output of the boost/mix stage into the output left/right mixers.
MICROPHONE INPUTS
The WM8976 can accommodate a variety of microphone configurations including single ended and
differential inputs. The inputs to the differential input PGA are LIN, LIP and L2.
In single-ended microphone input configuration the microphone signal should be input to LIN and the
internal NOR gate configured to clamp the non-inverting input of the input PGA to VMID.
In differential mode the larger signal should be input to LIP or RIP and the smaller (e.g. noisy ground
connections) should be input to LIN or RIN.
Figure 7 Microphone Input PGA Circuit
The input PGA is enabled by the IPPGAENL/R register bits.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
Input PGA enable
R2
2
INPPGAENL
0
Power
Management
2
0 = disabled
1 = enabled
Table 3 Input PGA Enable Register Settings
PP Rev 3.0 April 2006
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
