LG LG-MC2670, Service Manual

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1. RF Transmit/Receive Part
1.1 Overview
The RF transmit/receive part employs the direct conversion architecture (ZIF, Zero Intermediate
Frequency). The transmit/receive frequency is respectively 824.04~848.97MHz and 869.04~893.97
MHz. The block diagram is shown in [Figure 1-1].
RF signals received through the antenna are fed into RFR6122 through the duplexer. And then, they
pass the low noise amplifier (LNA), combined with the signals of local oscillator (VCO) at the
frequency mixer in order to create baseband signal directly.
Baseband signals created are changed into digital signals by the analog / digital converter (ADC, A/D
Converter) and then, auto gain controlled and, sent to the MSM6000 (Mobile Station Modem) of the
digital circuit part. Then, they are demodulated by the modulator / demodulator.
In the case of transmission, MSM6000 modulates, interpolates, and converts the digital signal into an
analog baseband before sending it to the RFT6122.
RFT6122 receives OQPSK-modulated anlaog baseband signals from the MSM6000’s Tx part. The
RFT6122 upconverts the Tx analog baseband into RF.
The RFT6122 connects directly with MSM6000 using an analog baseband interface. In RFT6122, the
baseband quadrature signals are upconverted to the Cellular Tx 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.
CHAPTER 1. Circuit Description
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