Motorola Timeport P8190, Руководство по обслуживанию

Страница: 124 / 149

Audio
Filter
Audio
Filter
MIC MIC_IN
MIC_BIAS
VAG
MICOUT
HDST_MIC
MIC_BIAS
AUX_OUT
AUX_MIC
Audio
Filter
AUDIO_IN
EXT_MIC
S
2.75V
AUX_BATT_THERM
AUX_THERM
THERM_BIAS
MAIN_BAT_THERM
MAIN_THERM
R1516
R1515
Q1515
EAR+
TDMA StarTAC
TM
P8190: Audio/Thermistor
A
26
Description
The cellular transceiver has the capability to support two batteries, a main battery and an auxiliary battery. Since a charger circuit is designed in this unit, there needs to be a form of
reading the thermistor values of each battery separately. The thermistor reading are used to determine the temperature of the battery cell which is being charged.
In order for the call processor(U1000) to read the thermistor values of the batteries, a voltage needs to be placed across the thermistor. As the temperature increases the thermistor will
decrease in resistance, causing the supply level at the thermistor to decrease. The thermistor line is pulled high by the THERM_BIAS line. The THERM_BIAS line is sourced from the
2.75V supply through Q1515. Q1515 is switched on only when S is present. If S is not present, Q1515 will be turned off, not allowing THERM_BIAS to be
sourced by 2.75V.
The D is used to supply drive the exciter circuits for the 800MHz and 1900MHz bands. Driver B+ is sourced from the B+ supply. Q1501 is used as a voltage clamping cir-
cuit prevent a voltage level higher than 3.4V from entering the PA driver stage.
In order for the MIC and HDST_MIC circuit to operate a biasing voltage needs to be provided. For this reason, MIC_BIAS is used. The AUDIO_IN circuit doesn't need to have a bias-
ing voltage because the signal entering this line is generated by an external audio generator. All three mic circuits go through an audio filter before entering the CODEC, which is inter-
nal to the GCAP2(U1500).
The transceiver supports three audio output ports; ear speaker(EAR-), headset speaker(HDST_SPKR), and external audio port(AUDIO_OUT). The audio path routing is controlled by
the GCAP2. The call processor(U1000) programs the GCAP2 to route the audio to its proper path.
When the transceiver determines that audio needs to be routed externally, the other two audio ports are disabled by the GCAP2(U1500). The audio comes from the EXT_OUT line and
passes through an audio filter before being sent to the external connector. Because the AUDIO_OUT line has two multiplexed functions, the audio filter also acts as an isolator to the
ON/OFF function which in the same line.
When the ear speaker is used, the EAR- and EAR+ lines are used . The audio signals between EAR+ and EAR- is 180° out of phase. This allows proper operation of the ear speaker.
When a headset is attached to the transceiver, a headset detect interrupt will have the audio only go to the headset speaker(HDST_SPKR). Since the same EAR- line is used for the
headset and the ear speaker, the ear speaker is disabled by inverting the EAR- signal 180°. This will present two signals to the ear speaker that have no phase shift, thus, not allowing
the ear speaker from functioning.