LG KE990 Service Manual - Page 20

3. TECHNICAL BRIEF 3.4 Off-chip RF Components 3.4.1 VCTCXO (X100 : TG-5010LH(19.2M)) The Voltage Controlled Temperature Compensated Crystal Oscillator (VCTCXO) provides the reference frequency for all RFIC synthesizers as well as clock generation functions within the ESM6270 IC. The oscillator frequency is controlled by the ESM6270 IC.s TRK_LO_ADJ pulse density modulated signal in the same manner as the transmit gain control TX_AGC_ADJ. A two-pole RC lowpass filter is recommended on this control line. The PM6635 IC controls the handset power-up sequence, including a special VCTCXO warm-up interval before other circuits are turned on. This warm-up interval (as well as other TCXO controller functions) is enabled by the ESM TCXO_EN line . The PM6635 IC VREG_TCXO regulated output voltage is used to power the VCTCXO and is enabled before most other regulated outputs. Any GSM mode power control circuits within the ESM6270 IC require a reference voltage for proper operation and sufficient accuracy. Connecting the PM6635 IC REF_OUT directly to the ESM6270 IC GSM_PA_PWR_CTL_REF provides this reference. This sensitive analog signal needs a 0.1 •ÏF low frequency filter near to ESM side, and isolate from digital logic and clock traces with ground on both sides, plus ground above and below if routed on internal layers. 3.4.2 Front-End Module (FL100 : LMSP43QA-538) This equipment uses a single antenna to support all handset operating modes, with an antenna switch module select the operating frequency and band. The active connection is ESM-selected by three control lines (GPIO[9] and GPIO[10]). These GPIOs are programmed to be ANT_SEL0 and ANT_SEL1 respectively. [Table 3.4.2] Front End Module control logic Copyright © 2008 LG Electronics. Inc. All right reserved. Only for training and service purposes - 21 - LGE Internal Use Only