Rx Audio - Motorola V975 Service Manual

Theory of Operation
Audio Circuits

RX Audio

The mobile phone supports four audio output paths.
The output of PCAP's internal DAC drives the internal
PGA. The output of the PGA can be routed to one of
the four supported outputs via the internal multiplexer.
These outputs connect to the SPKR+/- amplifier (Hand-
set Earpiece Speaker), the ALERT+/- amplifier (Hand-
set Loudspeaker/Alert Speaker), the EXTOUT ampli-
fier (Accessory connector output), and the ARight/ALeft
Out amplifier (Headset Speaker). The single ended
Alert mode amplifier (A2) is not used in this design. All
outputs use the same D/A converter so only one output
can be active at one time. The user can adjust the gain
of the audio outputs with the volume control buttons.
The Handset Speaker is driven by PCAP's internal
SPKR differential amplifier. Following the speaker path
from the PCAP pins Speaker- and Speaker+, they are
routed through R34003 and R34002 respectively, and
Figure 3-27. RX Audio Block
CDC_EN
CDC_SW
Phone
DAC
ST_DAC_IN ST_DAC_SW
L
Stereo
DAC
R
PGA_IN_SW
PGA_INR
PGA_INL
3-20
PGA_R_EN
MONO_SW_CTL
Right
PGA
Mono
AUDOG
Adder
Left
PGA
MONO_SW_CTL
Motorola Confidential Proprietary
then connected to the transducer. Off the Speaker-
path, SPKR_IN is routed through C4002 for the in-
verting input of the speaker amp A1. SPKR_OUT1
from PCAP is routed through C4000 and C4002 to
Speaker- which is the DAC output of the CODEC.
SPKR_IN and SPKR_OUT1 will output their respec-
tive bias voltages on these pins during standby times.
This is to maintain the voltage across an external cou-
pling capacitor to avoid audio "pops" when the ampli-
fier is enabled.
Figure 3-28. Handset Speaker Path
Handset
Speaker
EARSPKR-
J4000
EARSPKR+
J4001
SPKR_OUT2
A4_EN
Amplitude
Control
A1_EN
SPKR_OUT1
A4_EN
ARIGHT_EN
HS_OUT_R
ALEFT_EN
HS_OUT_L
V975/V980
PCAP
SPKR-
Audio
A1
Filter SPKR+
Circuit
SPKR_IN
SPKROUT1
ALRT+
ALRT_IN
ALRT-
A2
ALRT-
A2
SPKR+
SPKR_IN
A1 SPKR-
EXT_OUT
A4
ARight_Out
AR_IN
ARIGHT
ALeft_Out
AL_IN
ALEFT
Draft 1.0