LG LG511C Service Manual page 35

LG511C
LN510
1.3 Description of Transmit Part Circuit
1.3.1 RF Transmitter (U2001)
The RF Transmitter(in QSC6075T, base-band-to-RF Transmit Processor) performs all Tx signal-processing
functions required between digital base-band and the Power Amplifier Module (PAM).
quadrature signals are up-converted to the Cellular or PCS frequency bands and amplified to provide signal drive
capability to the PAM. The RFT includes an RF mixer for upconverting analog baseband to RF, a programmable PLL
for generating Tx LO frequency, two cellular and two PCS driver amplifiers and Tx power control through an 85 dB
VGA. 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 proceed from the QSC6075 are analog signal. In CDMA mode, These signals are modulated
by Quadrature Phase Shift King (QPSK). I and Q are 90 deg. out of phase, and I and I/ are 180 deg. Tx IF signal can
be obtained by mixing analog signal with 228.6MHz (Cellular)/263.6(PCS) 1st local osillator frequency which is
generated by Tx VCO. The Tx IF signal is amplified by AGC controlled by QSC6075. The second mixer on RFT
converts IF signals into RF signals. After passing through the upconverter , RF signal is inputted into the Power
Amplifier Module.
1.3.1.1 Cellular CDMA transmit signal path performance specifications
LG Electronics Inc.
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The base-band