Motorola V820, Service Manual

Page: 24 / 47

Theory of Operation
V810
2003 Motorola Confidential Proprietary Page 24
Receive Path Audio Circuits
The mobile phone supports three audio output paths. The output of
MSM’s internal DAC drives the internal AMP SEL. The outputs can
be routed to one of the three supported outputs via the internal
multiplexer. These outputs connect to the EAR1OP, EAR1ON
amplifier (Ear Speaker), the EAR2O amplifier (Headset boom
speaker), and the AUXOP, AUXON amplifier (Accessory connector
output). 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. Forward link audio path
block diagram is as below.
Rx Volume
RX FIR
Codec
Rx Gain
(+15~- 81dB)
Digital
filtering
13bit
D/A
AMP
SEL
001
010
100
Codec
ST Gain
(0~- 96dB)
Sidetone from
Input Path
ESEC
or
AEC
AAGC
DTMF
Detection
DTMF
Generation
EVRC
13K CELP
DFM
MSM6050
Packet/DFM
Loopback
RX
Interface
Internal
Speaker
Headset
Speaker
External
Speaker
Audio
Loopback
To TX
DTMF_RX_GAIN
Rx FIR Filter
A type-I 13-tap FIR (Finite Impulse Response) filter is supported on
the Tx and the Rx paths. Both filters are software programmable and
can be reconfigured during Vocoder or DFM operation. Tx FIR is
programmable 13-tap FIR filter whose coefficients can be
programmed through the QDSP4000 parameters txPcmFiltLoad and
Tx PcmFiltCoeff. Each filter consists of 7 coefficients with the outside
taps, h[0] and h[12], h[1] and h[11], h[2] and h[10], h[3] and h[9],
h[4] and h[8], and h[5] and h[7], using the same coefficient value. The
Rx and Tx filters are intended to equalize the frequency response of
the microphone (Tx), the earphone (Rx), and the frequency
characteristics of the mechanical housing of the subscriber unit.
Codec Rx Gain
The Rx audio path contains a programmable gain stage, with a range
of +15 dB to –81 dB, after the audio front end of the QDSP4000 and
prior to the Digital-to-Analog conversion. The QDSP4000 DMA
parameter CodecRxGain sets the Rx gain.
Ear Speaker Path
The Ear Speaker is driven by MSM’s internal SPKR differential
amplifier. This amplifier is powered by voltage VREG_MSMA and
Speaker outputs from MSM are routed through the speaker path
) and EAR1ON(-), that are routed to 40 pin B-B connector
through main board and then connected to the transducer in the flip
assembly.
Headset Speaker Path
The headset uses a standard 2.5mm phone jack. The phone will detect
the presence of a headset using pin 2 on the headset jack, which is