LG VX8500 Service Manual page 31

VX8500
1.2.6 Down-converter Mixers (U107)
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 VX8500 Mixers is described below:
Parameter Low gain
Cellular PCS
Noise Figure 27
Input IP3 4
Input IP2 50
1.3 Description of Transmit Part Circuit
1.3.1 RFT6150 (U108)
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.
LG Electronics Inc.
High gain Units
Cellular PCS
27 11 11 dB
3 4 3 dBm
50 75 70 dBm
38