Vco; Figure 15-4 Diagram Of Pll Ic - Hytera MD78X Service Manual

Service Manual VHF (136-174MHz 50W) Information

Figure 15-4 Diagram of PLL IC

The 19.2MHz frequency generated by the reference oscillator (X100) goes into the PLL IC (U100) for
division, generating the reference frequency. Meanwhile, the frequency generated by VCO goes into
PLL IC (U100) 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 and lock the frequency.
15.3.4

VCO

The VCO is composed of transistors (Q100, Q103, Q106 and Q110), varactors and four Colpitts
oscillators. There are four VCOs in all: two VCOs (Q100 and Q103) used to transmit excitation signals
and the other two VCOs (Q106 and Q110) to receive LO signals. U302 controls the operating
frequency of the VCO. Q102 and Q107 constitute the buffer amplifiers for the transmitter circuit, while
Q111 and Q109 for the receiver circuit. The digital-to-analog converter (U500) modulates the TX
oscillator signal.
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