WM9714L_06 Datasheet, PDF (38/94 Pages) Wolfson Microelectronics plc – AC 97 Audio CODEC

WM9714L
Pre-Production
SINGLE MIC OPERATION
Up to three microphones can be connected in a single-ended configuration. Any one of the three
MICs can be selected as the input to MPA using MPASEL[1:0] (Register 22h, bits 13:12). Only the
microphone on MIC2B can be selected to MPB. Note that MPABST always sets the gain for the
selected MPA input microphone. If MIC2B is the selected input for MPA it is recommended that MPB
is disabled.
DUAL MIC OPERATION
Up to two microphones can be connected in a dual differential configuration. This is suitable for
stereo microphone or noise cancellation applications. Mic1 is connected between the MIC2A and
MICCM inputs and mic2 is connected between the MIC2B and MICCM inputs as shown in Figure 13.
Additionally, another microphone can be supported on MIC1 selected through the MPA input mux.
Note that the microphones can be connected in a single-ended configuration.
Figure 13 Dual Microphone Configuration
MICROPHONE BIASING CIRCUIT
The MICBIAS output provides a low noise reference voltage suitable for biasing electret type
microphones and the associated external resistor biasing network. Refer to the Applications
Information section for recommended external components. The MICBIAS voltage can be altered via
MBVOL in register 22h. When MBVOL=0, MICBIAS=0.9*AVDD and when MBVOL=1,
MICBIAS=0.75*AVDD.
The microphone bias is driven to a dedicated MICBIAS pin 28 and is enabled by MPOP1EN in
register 22h. It can also be configured to drive out on GPIO8 pin 12 enabled by MPOP2EN in register
22h.
When not in use the microphone bias can be powered down using the Powerdown register bit
MICBIAS (register 3Eh, bit 14).
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PP Rev 3.0 June 2006
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