LG GM200 Service Manual page 63

3. TECHNICAL BRIEF
Phase Frequency Detector (PFD)
The PFD ensures that the transmitted signal contains the required modulation and is accurately locked to
the desired GSM channel. The downconverted feedback signal from the TX VCO and the Quadrature
Modulator output are phase compared by the PFD.
The PFD charge pump generates a current pulse proportional to the difference in phase which is applied to
the loop filter.
Loop filter
To minimize complexity of the external PCB layout the TX loop filter is fully integrated into the IC. At power
up the filter is automatically calibrated as part of the baseband filter cal, eliminating process tolerances. The
calibration is fully integrated and requires no extra programming.
TX VCO
The Transmit Voltage Controlled Oscillator (TX VCO) and tank components are a fully integrated subsystem.
The subsystem includes PA drivers so the outputs are used to directly drive the external PAs. The low noise
oscillator design and internal filtering mean that external TX SAW filters are not required. In Low band
operation the TX VCO output is divided by two and filtered. The TX VCO is automatically calibrated to ensure
optimum performance over its operating frequency of 1648 to 1910 MHz.
Feedback Down-Converting Mixer
The feedback down converting mixer is used to translate the TX VCO output frequency to the TX IF. An
integrated band pass filter exists between the mixer and the PFD to filter the mixers unwanted side band
and higher order mixing products.
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Only for training and service purposes