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LGC-340/345W
1.4 Description of Frequency Synthesizer Circuit
1.4.1 Voltage Control Temperature Compensation Crystal Oscillator
The temperature range that can be compensated by VC-TCXO(X3) which is the reference frequency generator of
a mobile station is -30~+80 ° C.
VC-TCXO receives frequency tuning signals called TRK_LO_ADJ from MSM as 0.5V~2.5V DC via R and C
filters in order to generate the reference frequency of 19.68MHz and input it into the frequency synthesizer of
UHF band. Frequency stability depending on temperature is ¡ ¾ 2 .0 ppm.
1.4.2 Dual PLL Module
Reference frequency that can be inputted to PLL(U8) is 19.68MHz.
It is the dual mode frequency synthesizer (PLL) that can synthesize frequencies band 954MHz~980MHz and IF
oscilation frequency 170.76MHz. PLL that receives the reference frequency of 19.68MHz from VC-TCXO
creates the phase detect frequency of 30kHz with the use of internal program and then, changes the frequency of
900MHz band. And then, two signal differences are calculated from the internal phase comparator.
The calculated difference is inputted to DC for adjusting the frequency of PLL. In addition, outputs of other
PIN3 are inputted into IFR after going through the VRACTOR diode and tank circuit so that the outputs of IFR
internal receive end VCO are adjusted to 170.76MHz.
PLL that generates the LO frequency of a mobile station have good spurious characteristics (ref. supurious at
30kHz from carrier = -70dBc (Max)).
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LG Information & Communications, Ltd.
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