Production Data
WM9715L
Figure 2 Microphone Bias Schematic
PHONE INPUT
Pin 20 (PHONE) is a mono, line level input designed to connect to the receive path of a telephony
device.
The pin connects directly to the record selector for phone call recording (Note: to record both sides of
a phone call, one ADC channel should record the PHONE signal while the other channel records the
MIC signal). The RECVOL PGA adjusts the recording volume, controlled by register 1Ch or by the
ALC function.
To listen to the PHONE signal, the signal passes through a separate PGA, controlled by register
0Ch. The signal can be routed into the headphone mixer (for normal phone call operation) and/or the
speaker mixer (for speakerphone operation), but not into the phone mixer (to prevent forming a
feedback loop). When the phone input is not used, the phone-in PGA can be switched off to save
power (see “Power Management” section).
PHONE is biased internally to the reference voltage VREF. Whenever the input is muted or the
device placed into standby mode, the input remains biased to VREF using special anti-thump
circuitry to suppress any audible clicks when changing inputs.
REGISTER
ADDRESS
BIT
15
LABEL
P2H
DEFAULT
DESCRIPTION
0Ch
1
Mute PHONE path to headphone mixer
1: Mute, 0: No mute (ON)
Mute PHONE path to speaker mixer
1: Mute, 0: No mute (ON)
PHONE input gain
Phone Input
14
P2S
1
4:0
PHONE
VOL
01000
(0dB)
00000: +12dB
… (1.5dB steps)
11111: -34.5dB
Table 4 Phone Input Control
PD Rev 4.0 December 2007
17
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
