LG KF700Q Service Manual page 19

3. TECHNICAL BRIEF
3.2.2 GSM Transmitter
The RTR6280 transmitter outputs(HB_RF_OUT1 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 RTR6280 IC is able to support GSM850/EGSM900 and DCS1800/PCS1900 mode transmitting.
This design guideline shows a Quad-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.
LGE Internal Use Only
[Fig. 3.3] GSM Transmitter matching
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