LG KU250 Service Manual - Page 24

3. TECHNICAL BRIEF 3.4 LO generation and distribution circuits The integrated LO generation and distribution circuits are driven by internal VCOs to support various modes to yield highly flexible quadrature LO outputs that drive all GSM and UMTS band upconverters and downconverters; with the help of these LO generation and distribution circuits, zero-IF architecture is employed in all GSM and UMTS band receivers and transmitters to translate the signal directly from RF to baseband and from baseband to RF. Two fully functional fractional-N synthesizers, including VCOs and loop filters, are integrated within the RTR6275 IC. The first synthesizer (PLL1) creates the transceiver LOs that support the UMTS 2100/1900/1800 transmitter, and all four GSM band receivers and transmitters including: GSM 850, GSM 900, GSM 1800, and GSM 1900. The second synthesizer (PLL2) provides the LO for the UMTS 2100/1900/1800 receiver. An external TCXO input signal is required to provide the synthesizer frequency reference to which the PLL is phase and frequency locked. The RTR6275 IC integrates most of PLL loop filter components on-chip except two off-chip loop filter series capacitors, and significantly reduces off-chip component requirement. With the integrated fractional-N PLL synthesizers, the RTR6275 has the advantages of more flexible loop bandwidth control, fast lock time, and low-integrated phase error 3.5 Off-chip RF Components 3.5.1 WCDMA PAM (U103: WS2512-TR1G) The UMTS PA output power is monitored by l power detector circuits(U100 : RTR6275) . This detector voltage can be used for transmitter calibration and monitor to meet RF system WCDMA Rev.D L404 1.8nH 0.5p L125 FL104 4 PGND 3 ANT RX 1 TX 2 ACMD-7602 C162 3.3p 51R119 4 1 50OHM OUT +VPWR C155 C158 4.7u 15p L123 1nH IN 2 3 COUP C164 0.5p 20dB U102 CP0402A1950DNTR R121 R120 130 47 7dB R122 130 PWR_DET Rev_1.0 C165 1p WS2512_TR1G U103 10 VCC2 1 VCC1 9 GND4 RFIN 2 8 RFOUT GND1 3 7 6 GND3 11 GND2 BGND VCONT 4 5 VREF C159 15p +VPWR C154 1.5p L122 NA Rev_1.0 C157 10nH FL102 4 5 EFCH1950TDF1 O1 G3 1 IN G2 G1 32 C192 100p 4 5 PA_R0 TR100 KRX102U 3 2 1 PA_ON Rev.B VREG_TCXO_2.85V C170 0.1u [Figure 1.5] WCDMA PAM, Duplexer, Coupler - 25 -