wm9712l Wolfson Microelectronics plc, wm9712l Datasheet - Page 17

• Manufacturer Part Number: wm9712l
• Description: Ac?97 Audio And Touchpanel Codec
• Manufacturer: Wolfson Microelectronics plc

Production Data
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PHONE INPUT
Figure 2 Microphone Bias Schematic
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.
Table 4 Phone Input Control
0Ch
Phone Input
REGISTER
ADDRESS
CAP2
15
14
4:0
WM9712L
BIT
P2H
P2S
PHONE
VOL
LABEL
AGND
1
1
01000
(0dB)
DEFAULT
MICBIAS
= 1.8 x CAP2
= 0.9 X AVDD
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
00000: +12dB
… (1.5dB steps)
11111: -34.5dB
DESCRIPTION
PD Rev 4.5 August 2006
WM9712L
17