–
After 9.3 V is divided by R255 and R264, a bias voltage of about 7 V is provided to the front panel
MIC. The external MIC is connected to the MIC_HED of the codec (U231) as a unidirectional input.
Both MICs are controlled by Q232.When the internal MIC is active, EXT_MIC_EN is at low level, bias
voltage of external MIC is disconnected, and the ADC in U231 samples voltage at the MICIN_HND.
When external MIC is active, EXT_MIC_EN is at high level, Q232 is turned on, bias voltage is
connected, and the ADC in U231 senses only audio data at pin MICIN_HED.
Audio signals input from the MMC interface and the accessory connector are fed to the Codec (U231)
and then are converted by the ADC into 16-bit PCM digital audio signals, which will be fed to U302
via the SSI.
When the mobile radio is set to Public Address mode, the audio signal will be generated by the
internal MIC, and then is buffered by U231, and finally is output via SPK2. The output audio signal is
amplified, and then is output as the two paths of audio PUB_Address1 and PUB_Address2.
5.3 RF Section
5.3.1
Transmitter Circuit
The transmitter circuit is composed of power amplifier circuit and power control circuit. The former is
used to amplify the voltage control oscillator (VCO) signal to the appropriate output power level, while
the latter can keep the output power at the appropriate level, so as to protect the power amplifier from
damage caused by overheating, antenna mismatch, and out-of-range voltage (over voltage or under
voltage may result in damage to Q111, Q805, Q804, Q802 and Q803).
Q805
PreDriver
Attenuator
Q802
Q803
Finalstage
Microstrip
Matcher
Q804
Driver
Q111
Firststage
Tx/Rx
Switch
Harmonic
Filter
Microstrip Dual
Directional Coupler
ANT
Rx_PORT
Tx_PORT
9V1A_TX
B+
B+
Forward
Detector
Reflect
Detector
Alarm to ADC
VSWR Protection
TV_APC
Temperature
compensation
High
Temperature
Protection
OMAP
Match
Match
Match
TXC
Final_Bias
Voltage
Detec
Switch’s Power
9.1V
ADC
Q810
Power Amplifier Circuit
The power amplifier circuit consists of four-stage power amplifier circuits and amplifies the signal output
from VCO to the required output power level.
TX Buffer Amplifier
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