LG KS20 Operating Instructions Manual page 24

3. TECHNICAL BRIEF
3.5.2 VCTCXO (X500 : 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
MSM7200 IC. The oscillator frequency is controlled by the MSM7200 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 PM7540 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 MSM TCXO_EN line . The PM7540 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 MSM7200 IC require a reference voltage for proper
operation and sufficient accuracy. Connecting the PM7540 IC REF_OUT directly to the MSM6275 IC
GSM_PA_PWR_CTL_REF provides this reference. This sensitive analog signal needs a 0.1 µF low
frequency filter near to MSM side, and isolate from digital logic and clock traces with ground on both
sides, plus ground above and below if routed on internal layers.
3.5.3 Front-End Module (FL500 : LSHS-M090UE)
switch module select the operating frequency and band. UMTS operation requires simultaneous
reception and transmission, so the UMTS Rx/Tx connection is routed to a duplexer that separates
receive and transmit signals. The active connection is MSM-selected by three control lines (GPIO[75],
GPIO[74], and GPIO[731]). These GPIOs are programmed to be ANT_SEL0, ANT_SEL1, and
ANT_SEL2) respectively.
GSM 850/GSM 900 TX
GSM 1800/GSM 1900 TX
GSM 850 RX
GSM 900 RX
GSM 1800 RX
GSM 1900 RX
WCDMA
LGE Internal Use Only
ANT_SEL0
HIGH
HIGH
-
LOW
LOW
LOW
HIGH
[Table 1.2] Front End Module control logic
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ANT_SEL1 ANT_SEL2
HIGH
LOW
-
LOW
LOW
LOW
LOW
Copyright © 2007 LG Electronics. Inc. All right reserved.
Only for training and service purposes
LOW
LOW
-
LOW
LOW
HIGH
HIGH