Service Manual
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4.2 RF part Description
The RF part consists of power part, synthesizing part, transmission and reception part.
4.2.1 Description of Frequency Synthesizer Circuit
The UHF band frequency synthesizer is composed of an indirect frequency synthesizer, Phase Locked
Loop (PLL IC, U2), VCO(U102) with the center frequency of 966.88MHz for CDMA mode and Loop Filter.
PLL IC(U2)’s phase detector compares the reference clock frequency (19.68MHz, TCXO(U104) clock)
divided down to 30kHz by the reference divider with a signal divided by the PLL IC(U2) main divider from
the VCO(U102), and generates a local oscillation signals with zero phase difference. These local oscillation
signals are used for Tx and Rx. The other PLL synthesizer controls Tx IF frequency and is implemented on
the TX_BBA(U112). The Tx phase detector receives Tx IF local oscillation signal(260.76MHz) within the
TX_BBA(U112). In Rx IF synthesizer, UHF PLL synthesizer support dual frequencies. Thus
RX_BBA(U109) use UHF PLL to generate the Rx IF frequency(170.76MHz).
Voltage Control Temperature Compensation Crystal Oscillator (VCTCXO, U104)
The temperature variation of reference frequency in a mobile phone can be compensated by
VCTCXO(U104). The reference frequency of a mobile phone is operated stably from –30 to +60 °C. The
VCTCXO(U104) receives frequency tuning signals called TRK_LO_ADJ from MSM(U125) through low-
pass filter in order to generate the reference frequency of 19.68MHz and is used for system main clock.
Frequency stability depending on temperature is within ±1.5 ppm.
RF Frequency Synthesizer
The RF PLL is consisted of the dual mode PLL IC(U2), loop filter, VCO(U102) and VCTCXO(U104). It
generates the RF local frequency of 954.38 ~ 979.38 MHz.
RX IF Frequency Synthesizer
The Rx IF PLL is consisted of the dual mode PLL IC(U2), Rx IF VCO included in the RX_BBA(U109),
loop filter and VCTCXO(U104). The Rx IF VCO included in the RX_BBA(U109) oscillates twice Rx IF
frequency as 170.76MHz and then generates the RX IF frequency of 85.38MHz by dividing the Rx IF
VCO output frequency by two.
TX IF Frequency Synthesizer
The Tx IF PLL Loop is consisted of the Tx IF PLL synthesizer, VCO(U108) that are internally installed in
the TX_BBA(U112), loop filter and VCTCXO(U104). The Tx IF VCO included the TX_BBA(U112)
generates Tx IF local frequency of 260.76MHz and then generates the Tx IF frequency of 130.38MH by