LG LG-MC2670, Service Manual

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LG-
MC
26
7
0
Parameter Gain Mode 0(G0) Gain Mode 1(G1) Gain Mode 2(G2) Gain Mode 3(G3) Unit
Gain 16 4 -5 -20 dB
Noise Figure 1.5 5 5.5 20 dB
Input IP3 10 7 15 15 dBm
1.2.3 Rx RF SAW FILTER (F103)
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.
1.2.4 Down-Converter Mixers (U106)
The RFR6122 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. RFR6122 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 MSM6000.
The specification of RD26
7
0 Mixers are described below:
Parameter High Gain Mode Low Gain Mode Unit
Noise Figure 10 25 dB
Input IP3 4 0 dBm
Input IP2 56 30 dBm
1.3 Description of Transmit Part Circuit
1.3.1 Description on the Internal Circuit of MSM6000 (U201) and RFT6122 (U105)
For the transmit data path(Tx), the MSM6000 modulates, interpolates, and converts the digital signal
into an analog baseband before sending it to the RFT6122. The RFT6122 upconverts the Tx analog
baseband into RF. The MSM6000 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 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
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