Motorola V820, Service Manual

Page: 23 / 47

Theory of Operation
V810
2003 Motorola Confidential Proprietary Page 23
Internal
MIC
Headset
MIC
External
MIC
MIC
SEL
01
10
11
MIC
AMP1
external
components
MIC
AMP2
MIC AMP2
BYPASS
13bit
A/D
Digital
filtering
Codec
Tx Gain
(0dB~- 96dB)
TX FIR
Tx Volume
Sidetone to
Output Path
MSM6050
MIC_AMP1_GAIN
00 - 2dB
01 +6dB
10 +8dB
11 +16dB
ESEC
or
AEC
NS &
AAGC
nsSwitch
EVRC
13K CELP
DFM
DTMF
Detection
DTMF
Generation
DTMF_TX_GAIN
Packet/DFM
Loopback
AUDIO
Loopback
TX
Interface
A/D converter & Filtering
A/D is 13-bit linear two’s complement converter. MIC AMP1
and MIC AMP2 gains should be selected to maximize the
dynamic range without overloading the A/D (3.63Vpp max
range). The transmit data from the microphone input is
digitally filtered with an ITU G.712 compliant filter. The filter
attenuates the input signals outside the 3400 Hz baseband and
decimates the data rate to 8 kHz. The MSM6050 has two
optional digital filters on the Tx path prior to the Vocoder, a
slope filter and a high-pass filter. The slope filter is designed to
provide pre-emphasis for the high frequency audio prior to the
Vocoder.
Tx Volume Control
The Tx and Rx audio path have separate volume controls to adjust the
loudness levels on the Tx and Rx audio paths. The Rx and Tx volume
controls are programmable multipliers
Headset Microphone Path
The Headset Microphone is pin 4 of EAR200, which is a 2.5mm jack.
MICBIAS 1.8V from MSM is used for headset Mic bias. The single-
ended MIC2P signal is fed to MSM headset Mic input and this line is
shared as headset SEND/END detect signal from headset.
External Microphone Path
The External Microphone input is connected to pin 16 of CN300
(AUDIO_IN), the accessory connector for the mobile phone. The path
is routed through IC301 to protect ESD and to the AUXIP pin on
MSM. This single-ended signal feeds directly to the input MIC select
multiplexer without an intervening gain stage. The audio signal shall
have a nominal level (-27dBv) of 43.5mVrms at 1 kHz, between 300
Hz and 3 kHz.