LG CU920 Manual page 22

3. TECHNICAL BRIEF
3.2.2 GSM Transmitter
The RTR6275 transmitter outputs(DA_HB2_OUT and DA_LB1_OUT)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 pass-band
symmetry about the band center frequency, the suggested starting value is shown in Figure 3-2-2
The RTR6275 IC is able to support GSM850/900 and GSM 1800/1900 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
6pF
82Ω
82Ω 82Ω
4pF
51Ω
110Ω 110Ω
Fig. 3.2.2 GSM Transmitter matching
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