Hytera MD652, Service Manual

Page: 130 / 207

Circuit Description
VHF1 (136
‐
174 MHz)
22
HANDSET_AUDIO, RX_AUDIO, PUB_ADDESS1 and PUB_ADDESS2. The first two paths are
amplified by U3005, and the last two paths are amplified by U3006. Output of HANDSET_AUDIO,
PUB_ADDESS1 and PUB_ADDESS2 are controlled by Q3001, Q3006 and Q3003 respectively.
TX Audio Path
The audio processor U3001 has two MIC inputs: the internal MIC and external MIC. The internal MIC is
connected to the MICIN_HND of U3001, and is combined with AUX1 to provide differential input. After
9.3 V is divided by R3037 and R3039, 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 as a uni-directional input. Both MICs are
switched by Q3004. When the internal MIC is active, EXT_MIC_EN is at low level, bias voltage of
external MIC is disconnected, and the ADC in U3001 samples voltage at the MICIN_HND. When the
external MIC is active, EXT_MIC_EN is at high level, Q3004 is turned on, bias voltage is connected, and
the ADC in U3001 samples only audio data at MICIN_HED.
Audio signals input from the MMC interface or the accessory connector, are fed to the Codec (gain of
Codec is programmable via the CPS) and then are converted by the ADC into 16-bit PCM digital audio,
which will be fed to U1002 via the SSI interface.
When the radio is set to operate in loudspeaker mode, audio signal is generated by the internal MIC, and
then is buffered by U3001, 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
Transmitter Circuit
The transmitter circuit is composed of power amplifier circuit and power control circuit. The power
amplifier circuit is used to amplify the VCO signal to the appropriate output power level, while the power
control circuit can keep the output power at the appropriate level, so as to protect the power amplifier
from damage caused by over heat, antenna mismatch, and out-of-range voltage (over voltage or under
voltage may result in damage to Q7014, Q7012, Q7010 and Q7013).