wm9714l Wolfson Microelectronics plc, wm9714l Datasheet - Page 45

• Manufacturer Part Number: wm9714l
• Description: Ac?97 Audio Codec
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
MICROPHONE INPUT
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MICROPHONE PRE-AMPS
There are two microphone pre-amplifiers, MPA and MPB, which can be configured in a variety of
ways to accommodate up to 3 selectable differential microphone inputs or 2 differential microphone
inputs operating simultaneously for stereo or noise cancellation. The microphone input circuit is
shown in Figure 20.
Figure 20 Microphone Input Circuit
The input pins used for the microphones are MIC1, MICCM, MIC2A and MIC2B. Note that input pins
MIC2A and MIC2B are multi-function inputs and must be configured for use as microphone inputs
when required. This is achieved using MICCMPSEL[1:0] in register 22h (see Table 23). The input to
microphone pre-amp A can be selected from any of the three microphone inputs MIC1, MIC2A and
MIC2B using MPASEL[1:0]. Each pre-amp has independent boost control from +12dB to +30dB in
four steps. This is controlled by MPABST[1:0] and MPBBST[1:0].
When not in use each microphone pre-amp can be powered down using the Powerdown register bits
MPA and MPB (register 3Eh, bits [1:0]). When disabled the inputs are tied to Vmid (for MIC2A and
MIC2B this only applies when they are selected as microphone inputs, otherwise they are left
floating).
Table 23 Microphone Pre-amp Control
22h
REGISTER
ADDRESS
MICCM
MIC2A
MIC2B
MIC1
15:14
13:12
11:10
9:8
BIT
MICCMPSEL
MPASEL
MPABST
MPBBST
LABEL
Vmid
Vmid
Vmid
13-12
22h:
00 = +12dB
11 = +30dB
00 = +12dB
11 = +30dB
22h:11-10
00
00
00
00
DEFAULT
22h:9-8
MICA
MICB
MIC2A/MIC2B Pin Function Control
00 = MIC2A and MIC2B are mic inputs
01 = MIC2A mic input only
10 = MIC2B mic input only
11 = MIC2A and MIC2B are not mic inputs
MPA Pre-Amp Source Control
00 = MIC1
01 = MIC2A
10 = MIC2B
11 = Reserved
MPA Pre-Amp Volume Control
00 = +12dB
01 = +18dB
10 = +24dB
11 = +30dB
MPB Pre-Amp Volume Control
As MPABST
DESCRIPTION
PP, Rev 3.2, October 2008
WM9714L
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