AnyDATA DTS-800 CDK, Руководство по обслуживанию

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2.6. Description of Frequency Synthesizer Circuit
2.6.1 Voltage Control Temperature Compensation Crystal Oscillator(U174, VCTCXO)
The temperature range that can be compensated by U174 which is the reference frequency generator of mobile
terminal is -30 ~ +80 degrees. U174 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
±
2.0 ppm.
2.6.2 UHF Band Frequency Synthesizer (U172)
Reference frequency that can be inputted to U172 is 3MHz~40MHz. It is the dual mode
frequency synthesizer (PLL) that can synthesize the frequencies of UHF band 50MHz~1200MHz and IF band
20MHz~300MHz. U172 that receives the reference frequency of 19.68MHz from U174 creates 30kHz comparison
frequency with the use of internal program and then, changes the frequency of 900MHz band inputted from X200
which is the voltage adjustment crystal oscillator into the comparison frequency of 30kHz at the prescaler in U172.
Then, two signal differences are calculated from the internal phase comparator. The calculated difference is
inputted to DC for adjusting the frequency of U174 through U172 No.2 PIN and external loop filter in order to
generate UHF signals. In addition, outputs of other PIN17 are inputted into BBA after going through the VRACTOR
diode and tank circuit so that the outputs of BBA internal receive end VCO are adjusted to 170.76MHz.
2.6.3 Voltage Control Crystal Oscillator (U171)
U171 that generates the LO frequency (900MHz) of mobile terminal receives the output voltage of PLL U172 and
then, generates the frequency of 954MHz at 0.7V and the frequency of 980MHz at 2.7V. The sensitivity on control
voltage is 23MHz/v and the output level is 1dBm(maximum). Since LO frequency signal is very important for the
sensitivity of mobile terminal, they must have good spurious characteristics. U174 is -70dBc(maximum).
3. Digital/Voice Processing Part
3.1 Overview
The digital/voice processing part processes the user's commands and processes all the digital and voice signal
processing in order to operate in the phone. The digital/voice processing part is made up of a receptacle part, voice
processing part, mobile station modem part, memory part, and power supply part.