LG KD3500 Service Manual page 18

LG-KD3500
1.2.2 Rx RF SAW FILTER (F101)
The main function of Rx RF SAW filter is to attenuate mobile phone spurious frequency, attenuate
noise amplified by the LNA and suppress second harmonic originating in the LNA.
1.2.3 Down-Converter Mixers (U201)
The QSC6010 device performs signal direct-down-conversion for Cellular applications. It contains all
the circuitry (with the exception of external filters) needed to support conversion of received RF
signals to baseband signals. The LO Buffer Amplifier buffers the RF VCO to the RF Transmit
Upconverter. QSC6010 offers the most advanced and integrated CDMA Rx solution designed to meet
cascaded Noise Figure (NF) and Third-order Intercept Point (IIP3) requirements of IS-98C and
J-STD-018 specifications for Sensitivity, Two-Tone Intermodulation, and Single-tone Desense.
Operation modes and band selection are specially controlled from the Mobile Station Modem QSC6010.
1.3 Description of Transmit Part Circuit
1.3.1 Description on the Internal Circuit of QSC6010(U201)
For the transmit data path(Tx), the QSC6010 modulates, interpolates, and converts the digital signal
into an analog baseband, and upconverts the Tx analog baseband into RF. The QSC6010
communicates with the external RF and analog baseband to control signal gain in the RF Rx and Tx
signal paths, educe base band offset errors, and tune the system frequency reference.
The QSC6010 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 QSC6010 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. 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 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 QSC6010 converts baseband signals into
RF signals. After passing through the upconverters, RF signal is inputted into the Power Amplifier
Module.
The QSC6010 Cellular CDMA RF specifications are described below:
LGE
LG Electronics Inc.
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