LG L602i, Service Manual

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3. TECHNICAL BRIEF
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3.2.2 GSM Transmitter
The shared GSM Low-band (EGSM900) and High-band (DCS1800, PCS1900) transmit path begins
with the baseband inputs from the MSM6250A IC. These differential analog input signals are buffered,
lowpass filtered, corrected for DC offsets then applied to the GSM quadrature upconverter. The
upconverter LO signals are generated from the transceiver VCO signal by the LO distribution and
generation circuits within RTR6250.
This upconverter translates the GMSK-modulated signal to a convenient intermediate frequency (IF)
that forms one input to a frequency/phase detector circuit. This IF signal is the reference input to an
offset phase-locked loop (OPLL) circuit as shown in Figure 1.2.2-1.
1. The dual Tx VCO output (operating in the desired RF output frequency range) is buffered within the
RTR6250 IC then applied to the mixer RF port.
2. The LO Generation and Distribution circuits that deliver the transmit path.s LO for the baseband-to-IF
upconversion also provides the .offset LO. signal that is applied to the feedback path.s mixer LO port.
Figure 1.2.2-1 Offset phase-locked loop interfaces
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