LG VX9100 Maroon, Service Manual

Page: 31 / 169

- 30 -
VX9100
LGE Internal Use Only
Copyright © 2007 LG Electronics. Inc. All right reserved
Only for training and service purposes
1.2.5 RFR6500 - Down-converter Mixers part (U108)
The RFR6500 device performs signal down-conversion for Cellular, PCS and GPS tri-band applications. It contains
all the circuitry (with the exception of external filters) needed to support conversion of received RF signals to Base-
band signals. The three down-converting Mixers (Cellular, PCS and GPS), and a programmable PLL for generating
RX LO frequency and an RX LO Buffer Amplifier and RX Voltage Controlled Oscillator. The GPS LNA & mixers
offer the most advanced and integrated CDMA RX solution designed to meet cascaded Noise Figure (NF) and Third-
order Intercept Point (IIP3) requirements of IS-98D and J-STD-018 specifications for Sensitivity, Two-Tone Inter-
modulation, and Single-tone Desensitization.
Operation modes and band selection are specially controlled from the Mobile Station Modem
MSM6550A.
The specification of VX9100 Mixers is described below:
Low gain High gain Units
Cellular PCS Cellular PCS
Noise Figure 25 27 7.9 12 dB
Input IP3 -5 -11 4 4 dBm
Input IP2 30 30 56 56 dBm
Parameter
1.3 Description of Transmit Part Circuit
1.3.1 RFT6150 (U109)
The RFT6150 Base-band to RF Transmit Processor performs all TX signal-processing functions required between
digital Base-band and the Power Amplifier Modulator (PAM). The Base-band quadrate signals are up-converted to
the Cellular or PCS frequency bands and amplified to provide signal drive capability to the PAM. The RFT6150
includes mixers for up-converting analog Base-band to RF, a programmable PLL for generating TX LO frequency a
TX LO Buffer Amplifier and TX Voltage Controlled Oscillator, cellular and PCS driver amplifiers and TX power
control through an 85 dB VGA. As added benefit, the single sideband up-conversion eliminates the need for a band
pass filter normally required between the up-converter and driver amplifier.
I, I/, Q and Q/ signals proceed from the MSM6550A to RFT6150 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 RFT6150 converts baseband signals into RF signals. After passing through the upconverters,
RF signal is inputted into the Power AMP.