LG MX8550, Service Manual

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M X8550
CHAPTER 3. Circuit Description
CHAPTER 3. Circuit Description
1. RF Transmit/Receive Part
1.1 Overview
The TX and RX part employs the Direct-Conversion system. The TX and RX frequencies are respectively
824.04~848.97 and 869.04~893.97 for cellular and 1850~1910 and 1930~1990 for PCS. The block diagram is shown
in [Figure 1-1]. CDMA RF signals received through the antenna are separated by the Diplexer.
RF Signal fed into the low noise amplifier in RFR6500(LNA) through the duplexer. Then, they are fed into Mixer in
RFR6500. In RFR6500, the RF signal is changed into baseband signal directly. Then, this signal is changed into
digital signal by the analog to digital converter (ADC, A/D Converter), and the digital circuit part of the
MSM(Mobile Station Modem) 6500 processes the data from ADC. The digital processing part is a demodulator.
In the case of transmission, RFT6150 receives OQPSK-modulated analog signal from the MSM6500.
The RFT6150 connects directly with MSM6500 using an analog baseband interface. In RFT6150, the baseband
quadrature signals are upconverted to the Cellular or PCS frequency bands and amplified to provide signal drive
capability to the power amp.
After that, the RF signal is amplified by the Power Amp in order to have enough power for radiation. Finally, the RF
signal is sent out to the cell site via the antenna after going through the duplexer.
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