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Service Manual
given below:
Switch
LNA
PA
DVDD
AVDD
3.3~
4.8V
After entering RDA chip via MIC, the voice signal will undergo A/D conversion to get digital signal, which
will be delivered to DSP for further processing such as filtering, amplification, amplitude-limiting and
pre-emphasizing. Then the resulting voice signal is modulated to the internal VCO and output after being
amplified by the driver amplifier. At the RX end, the received RF signal will go to LNA for amplification
first, and then go to IF demodulation circuit to get demodulated voice signal. After gain control, such
signal is converted into digital signal, which will enter DSP for further processing such as filtering,
amplification and de-emphasizing.
The function of RDA is subject to MCU U622 and its reference clock signal is from 26MHZ crystal
oscillator. This chip is applicable to UHF (400~520MHZ) and VHF (134~174MHZ). The NF can be up to
3dB and IIP3 up to -6dBm, meeting GB and FCC requirements. Its RF output may reach up to 8dBm.
4.2.2
RF Power Amplifier Circuit (TX Section)
The block diagram of the RF power amplifier circuit is shown in the figure below:
+
-
0/90
-
+
PA_driver
LDO
Syntheizer
XTAL
I ADC
I PGA
Q ADC
Q PGA
VCO
RSSI
11
Circuit Description
DAC
DSP Core
Audio filter
Sub CH filter
FM Modem
AFC loop
ADC
GPIO
Interfac
e
BUS
I2C
MIC
MCU
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