LG VX5400, Service Manual

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1.3 Description of Transmit Part Circuit
1.3.1 RFT6100 (U112)
The RFT6100 baseband-to-RF Transmit Processor performs all Tx signal-processing functions required
between digital baseband and the Power Amplifier Modulator (PAM). The baseband quadrature signals are
upconverted to the Cellular or PCS frequency bands and amplified to provide signal drive capability to the PAM.
The RFT6100 includes an mixers for up-converting analog baseband to RF, a programmable PLL for generating
Tx and Rx LO frequency, cellular and PCS driver amplifiers and Tx power control through an 85 dB VGA. As
added benefit, the single sideband upconversion eliminates the need for a band pass filter normally required
between the upconverter and driver amplifier.
I, I/, Q and Q/ signals proceed from the MSM6100 to RFT6100 are analog signal. In CDMA mode, These
signals are modulated by Offset Quadrature Phase Shift King (OQPSK). I and Q are 90 deg. out of phase, and I
and I/ are 180 deg. The mixers in RFT6100 converts baseband signals into RF signals. After passing through
the upconverters, RF signal is inputted into the Power AMP.
z
RFT6100 Cellular and PCS CDMA RF Specifications
Condition Min. Typ. Max. Units
Rated Output Power Average CDMA Cellular
Average CDMA PCS
8
10
dBm
dBm
Min Output Power Average CDMA Cellular
Average CDMA PCS
-80
-78
dBm
dBm
Rx band noise power CDMA Cellular
CDMA PCS
-133
-132
dBm/Hz
ACPR
Cellular: Fc
±
885kHz
PCS: Fc
±
1.25MHz
-56
-56
dBc/
30kHz
1.3.2 Power Amplifier(U108,109)
The power amplifier that can be used in the PCS and CDMA mode has linear amplification capability and
high efficiency. For higher efficiency, it is made up of one MMIC (Monolithic Microwave Integrated Circuit)
for which RF input terminal and internal interface circuit are integrated onto one IC after going through the
AlGaAs/GaAs HBT (heterojunction bipolar transistor) process. The module of power amplifier is made up of an
output end interface circuit including this MMIC. The maximum power that can be inputted through the input
terminal is +17dBm and conversion gain is about 28dB. RF transmit signals that have been amplified through
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Only for training and serving purposes
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