WM8959
Pre-Production
MICROPHONE INPUTS
Up to four microphones can be connected to the WM8959, either in single-ended or pseudo-
differential mode. A low noise microphone bias is fully integrated to reduce the need for external
components.
In single-ended microphone input configuration, the microphone signal is connected to the inverting
input of the PGA (LIN1, LIN3, RIN1 or RIN3). The non-inverting input of the PGAs should be
internally connected to VMID in this configuration. This is enabled via the Input PGA configuration
register settings. In this configuration, LIN2, LIN4, RIN2 or RIN4 may be free to be used as line input
to the Input Mixer or directly to the Speaker Mixer.
In pseudo-differential microphone input configuration, the non-inverted microphone signal is
connected to the non-inverting input of the PGA (LIN2, LIN4, RIN2 or RIN4) and the inverted (or
noisy ground) signal is connected to the inverting input (LIN1, LIN3, RIN1 or RIN3).
Any PGA input pin that is used in either microphone configuration should not be enabled as a line
input path at the same time.
The gain of the input PGAs is controlled via register settings. Note that the input impedance of LIN1,
LIN3, RIN1 and RIN3 changes with the input PGA gain setting, as described under “Electrical
Characteristics”. (Note this does not apply to input paths which bypass the input PGA.) The input
impedance of LIN2, LIN4, RIN2 and RIN4 does not change with input PGA gain. The inverting and
non-inverting inputs are therefore not matched and the differential configuration is not fully
differential.
Figure 16 Single-Ended Microphone Input
LINE INPUTS
Figure 17 Differential Microphone Input
All eight analogue input pins may be configured as line inputs. Various signal paths exist to provide
flexibility, high performance and low power consumption for different usage modes.
LIN1 and RIN1 can operate as line inputs to the Input PGAs LIN12 and RIN12 to provide high gain if
required for small input signals.
LIN2 and RIN2 can operate as line inputs directly to the input mixers or to the speaker output mixer.
Direct routing to the speaker output minimises power consumption by reducing the number of active
amplifiers in the signal path.
LIN3 and RIN3 can operate as line inputs to the Input PGAs or as a line input directly to either of the
output mixers LOMIX and ROMIX.
LIN1+LIN3 and RIN1+RIN3 can also be used as fully balanced differential inputs via the Input PGAs
to one of the input mixers. (Note that these inputs have matched input impedances.)
LIN4/RXN and RIN4/RXP can operate as line inputs directly to the outputs OUT3 and OUT4,
providing an ultra-low power stereo or mono differential signal path (e.g. from an external voice
CODEC) to an ear speaker. LIN4/RXN and RIN4/RXP can also operate as a mono differential input
directly to the output mixer stages.
PP, May 2008, Rev 3.1
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
