LG KE990 Service Manual - Page 18
RTR6235, GSM PA
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3. TECHNICAL BRIEF 3.2.2 GSM Transmitter The RTR6235 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 Figure3.2.3. DA_HB2_OUT RTR6235 DA_LB1_OUT 6pF 91 68 91 5pF 51 Tx SAW 120 120 HB_IN HB_OUT GSM PA LB_IN LB_OUT [Fig 1.3] GSM Transmitter matching The RTR6235 IC is able to support GSM 850/900 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 Copyright © 2008 LG Electronics. Inc. All right reserved. Only for training and service purposes - 19 - LGE Internal Use Only