LG MX8550, Service Manual

Page: 31 / 190

- 30/148 - LG Electronics Inc.
M X8550
1.2.6 RFR6500 - Down-converter Mixers part (U110)
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
MSM6500.
The specification of VX8550 Mixers is described below:
dBm 56 56 30 30 Input IP2
dBm 4 4 -11 -5 Input IP3
dB 12 7.9 27 25 Noise Figure
PCS Cellular PCS Cellular
Units High gain Low gain Parameter
1.3 Description of Transmit Part Circuit
1.3.1 RFT6150 (U111)
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 RFT6100
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 MSM6500 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.
Z3X-BOX.COM