Chapter 3. Circuit Description; Rf Transmit/Receive Part - LG KD3500 Service Manual

LG-KD3500

CHAPTER 3. Circuit Description

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 3-1].
RF signals received through the antenna are fed QSC6010 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, are demodulated by the modulator / demodulator.
In the case of transmission, QSC6010 modulates, interpolates, and converts the digital signal into an
analog baseband before upconverts the Tx analog baseband into RF.
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
LGE
LG Electronics Inc.
14/21