LG HB620 Service Manual page 22

3.2.2 GSM Transmitter
The RTR6275 transmitter outputs (HB_RF_OUT2 and LB_RF_OUT1) include on-chip output matching
inductors. 50ohm output impedance is achieved by adding a series capacitor at the output pins. The
capacitor value may be optimized for specific applications and PCB characteristics based on passband
symmetry about the band center frequency. The suggested circuit is shown in [Fig. 3.3].
The RTR6275 IC is able to support EGSM900 and DCS1800/PCS1900 mode transmitting. This design
guideline shows a tri-band GSM application.
Both high-band and low band outputs are followed by resistive pads to ensure that the load Presented
to the outputs remains close to 50ohm. The low-band GSM Tx path also includes a Tx-band SAW filter
to remove noise-spurious components and noise that would be amplified by the PA and appear in the
GSM Rx band.
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Only for training and service purposes
[Fig. 3.3] GSM Transmitter matching
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3. TECHNICAL BRIEF
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