LG LG-YD636, Руководство по обслуживанию

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1. RF Transmit/Receive Part
1.1 Overview
The Tx and Rx part employs the Direct-Conversion system. The Tx and Rx frequencies are
824.04~848.97 and 869.04~893.97. RF signals received through the antenna are seperated by the
duplexer.
RF Signal fed into the RFR6122(RF receiver ) through the duplexer. The IF 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) 6025
processes the data from ADC. The digital processing part is a demodulator.
In the case of transmission, RFT6122 receives OQPSK-modulated anlaog signal from the MSM6025.
The RFT6122 connects directly with MSM6025 using an analog baseband interface. In RFT6122, 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.
1.2 Description of Receive Part Circuit
1.2.1 Duplexer ( EFSD836MD2S2 )
The duplexer consists of the Rx bandpass filter (BPF) and the Tx BPF which has the function of
separating Tx and Rx signals in the full duplex system for using the common antenna. The Tx part
BPF is used to suppress noises and spurious out of the Tx frequency band. The Rx BPF is used to
receive only Rx signal coming from the antenna, which is usually called preselector. It’s main function
is to limit the bandwidth of spectrum reaching the LNA and mixer, attenuate receiver spurious
response and suppress local oscillator energy. As a result frequency sensitivity and selectivity of
mobile phone increase. The specification of LG-YD636 duplexer described below ;
Tx Rx Tx to Rx (min)
Pass Band 824~849MHz 869~894 MHz
Insertion Loss 2.0dB max 4.0dB max
VSWR 2.2 max 2.2 max
Attenuation 45.0dB min (869~894MHz) 55.0dBmin(824~849MHz)
55.0dB (824~849MHz)
45.0dB (869~894MHz)
CHAPTER 2. Circuit Description