Service Manual
converter, so as to ensure frequency accuracy.
9.3.2 PLL IC
PLL IC consists of the pre-divider, programmable divider, phase detector, charge pump and etc. The
voltage of analog circuit and digital circuit of PLL IC is 3.3V voltage, while the voltage of charge pump is
5V. See the following figure:
Figure 9-6 Block Diagram of PLL IC
SKY72310’s role is to generate appropriate frequency based on the data transmitted by OMAP of
baseband board. The 19.2MHz frequency generated by the reference crystal oscillator goes into the PLL,
to generate the reference frequency. Meanwhile, the frequency generated by VCO goes into PLL for
frequency division. The resulting frequency will be compared with reference frequency in terms of phase
difference in the phase detector. After comparison, the resulting frequency is converted to CV voltage via
the loop filter, to control the output frequency of VCO. In addition, as a key component of the modulation
circuit, PLL can directly obtain data from the MCSI port of OMAP for modulation.
9.3.3 VCO
s two transistors (Q101 and Q107), a varactor and four Colpitts oscillators. The VCO for RX unit comprise
Q105 and Q106 are the buffer amplifiers for the RX unit. The components of VCO for TX unit are the
same as those of RX unit. Q105 and Q106 are the buffer amplifiers for the TX unit.
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