LG KU250 Service Manual - Page 21

GSM Transmitter

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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. The 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 starting value is shown in Figure1.3. 6pF 51Ω 91Ω 12pF 91Ω 39 Ω 100Ω 100 Ω [Fig 1.3] GSM Transmitter matching The RTR6275 IC is able to support GSM 900 and GSM 1800/1900 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 - 22 -

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3.2.2 GSM Transmitter
The RTR6275 transmitter outputs(DA_HB2_OUT and DA_LB1_OUT)include on-chip output matching
inductors. The 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 Figure1.3.
The RTR6275 IC is able to support GSM 900 and GSM 1800/1900 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
3. TECHNICAL BRIEF
- 22 -
91
91
6pF
100
100
51
12pF
39
Ω
Ω
Ω
Ω
Ω
Ω
[Fig 1.3] GSM Transmitter matching