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LGE Internal Use Only
Copyright © 2010 LG Electronics. Inc. All right reserved.
Only for training and service purposes
3. TECHNICAL BRIEF
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3.6.2 19.2MHz VCTCXO (X250, KT3225L19200DCW28RA0)
The Voltage Controlled Temperature Compensated Crystal Oscillator (VCTCXO) provides the reference frequency for
all RFIC synthesizers as well as clock generation functions within the MSM6285 IC. The oscillator frequency is
controlled by the MSM6285 ICs.
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 MSM7227 IC require a
reference voltage for proper operation and sufficient accuracy. Connecting the PM7540 IC REF_OUT directly to the
MSM7227 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.