LG LG-RD2750, Service Manual

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LG-RD2750
LGE
LG Electronics Inc.
20/26
The RFT6122 baseband-to-RF Transmit Processor performs all Tx signal-processing functions
required between digital baseband and the Power Amplifier Module (PAM). The baseband quadrature
signals are upconverted to the Cellular frequency bands and amplified to provide signal drive
capability to the PAM. The RFT6122 includes an mixer for up-converting analog baseband to RF, a
programmable PLL for generating Tx and Rx LO frequency, cellular driver amplifier 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 MSM6000 to RFT6122 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 mixer in RFT6122 converts baseband signals into RF
signals. After passing through the upconverters, RF signal is inputted into the Power Amplifier Module.
The RFT6122 Cellular CDMA RF specifications are described below:
Condition Min. Typ. Max. Unit
Rated Output Power Average CDMA Cellular 6 dBm
Min Output Power
Average CDMA Cellular -75 dBm
Rx band noise power CDMA Cellular -132 dBm/Hz
ACPR Cellular: Fc
±
885kHz
Fc
±
1.98MHz
-52
-63
dBc
dBc
1.3.2 Power Amplifier (U102)
The power amplifier that can be used in the CDMA mode has linear amplification capability.
For higher efficiency, it is made up of one module (Monolithic Microwave Integrated Circuit) for which
RF input terminal and internal interface circuit are integrated onto one IC after going through the GaAs
HBT (heterojunction bipolar transistor) process.
The module of power amplifier is made up of an output end interface circuit including this module.
The maximum power that can be inputted through the input terminal is +7dBm and conversion gain is
about 28.5dB. RF transmit signals that have been amplified through the power amplifier are sent to
the duplexer.
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