LG Electronics Inc.
VX8560
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
824.04~848.97MHz and 869.04~893.97MHz for cellular and 1850~1910MHz and 1930~1990MHz for PCS.
The block diagram is shown in [Figure 1-1]. RF signals received through the antenna are seperated by
quintplexer. RF Signal fed into the low noise amplifier (in QSC6075) through the quintplexer. Then, they
are combined with the signals of local oscillator (VCO) at the down conversion mixer(in QSC6075) in order
to create Base-band frequency. 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 QSC(Qualcomm Single Chip)6075
processes the data from ADC. The digital processing part is a demodulator.
In the case of transmission, RF Transmitter(in QSC6075) receives QPSK-modulated anlog signal from the
QSC6055. In QSC6075, 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 coupler and quintplexer.
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