(No.RA015<Rev.002>)1-15
2.4.5 PLL Frequency Synthesizer
2.4.5.1
TCXO (X700)
TCXO (X700) generates a reference frequency of 19.2MHz for the PLL frequency synthesizer. This reference signal is buffered by
Q700 and IC700. And it is distributed to TX PLL (IC100), RX PLL (IC200), IF IC (IC600), GPS/Bluetooth (IC850), and IC702.
The frequency adjustment is achieved by adjusting a D/A converter (IC901) output in the voltage of the control terminal of TCXO.
2.4.5.2
VCO
F2,F3,K2,K3 types
There are TX VCO and RX VCO.
The TX VCO (Q140) generates the carrier for the transmitter. The VCO oscillation frequency range is 450 to 520MHz. The transmit
frequency range is 450 to 520MHz.
The RX VCO (Q240) generates the 1st local signal for the receiver.
The VCO oscillation frequency range is 400.05 to 470.05MHz. The 1st local signal frequency range is 400.05 to 470.05MHz.
The VCO oscillation frequency is determined by voltage control terminals "CV" and "ASSIST". The voltage control terminal "CV" is
controlled by PLL IC (IC100 for TX PLL, IC200 for RX PLL). The voltage control terminal "ASSIST" is controlled by the control voltage
from D/A converter (IC901).
For the modulation input terminal, "VCO_MOD" of TX VCO (Q140), the output frequency changes according to the applied voltage.
This is used to modulate the VCO output.
F5,F6,K5,K6 types
There are TX VCO _L, TX VCO_H, RX VCO_L and RX VCO_H.
The TX VCO_L (Q160) and TX VCO_H (Q140) generates the carrier for the transmitter. The oscillation frequency range of TX VCO_L
is 380 to 413.5MHz. The oscillation frequency range of TX VCO_H is 413.5 to 470MHz. The transmit frequency range is 380 to
470MHz.
The RX VCO_L (Q260) and RX VCO_H (Q240) generates the 1st local signal for the receiver.
The oscillation frequency range of RX VCO_L is 330.05 to 363.55MHz. The oscillation frequency range of RX VCO_H is 363.55 to
420.05MHz. The 1st local signal frequency range is 330.05 to 420.05MHz.
The VCO oscillation frequency is determined by voltage control terminals "CV" and "ASSIST". The voltage control terminal "CV" is
controlled by PLL IC (IC100 for TX PLL, IC200 for RX PLL). The voltage control terminal "ASSIST" is controlled by the control voltage
from D/A converter (IC901).
For the modulation input terminal, "VCO_MOD" of TX VCO_H (Q140) and TX VCO_L (Q160), the output frequency changes according
to the applied voltage. This is used to modulate the VCO output.
E,E2 types
There are TX VCO _L, TX VCO_H, RX VCO_L and RX VCO_H.
The TX VCO_L (Q160) and TX VCO_H (Q140) generates the carrier for the transmitter. The oscillation frequency range of TX VCO_L
is 400 to 413.5MHz. The oscillation frequency range of TX VCO_H is 413.5 to 470MHz. The transmit frequency range is 400 to
470MHz.
The RX VCO_L (Q260) and RX VCO_H (Q240) generates the 1st local signal for the receiver.
The oscillation frequency range of RX VCO_L is 350.05 to 363.55MHz. The oscillation frequency range of RX VCO_H is 363.55 to
420.05MHz. The 1st local signal frequency range is 350.05 to 420.05MHz.
The VCO oscillation frequency is determined by voltage control terminals "CV" and "ASSIST". The voltage control terminal "CV" is
controlled by PLL IC (IC100 for TX PLL, IC200 for RX PLL). The voltage control terminal "ASSIST" is controlled by the control voltage
from D/A converter (IC901).
For the modulation input terminal, "VCO_MOD" of TX VCO_H (Q140) and TX VCO_L (Q160), the output frequency changes according
to the applied voltage. This is used to modulate the VCO output.
2.4.5.3
PLL IC
There are TX PLL IC and RX PLL IC. PLL ICs compare the difference in phases of the VCO oscillation signal and the TCXO reference
frequency. And it returns the difference voltage to the VCO CV terminal and realizes the "Phase Locked Loop". This allows the VCO
oscillation frequency to accurately match (lock) the desired frequency.
When the frequency is controlled by the PLL, the frequency convergence time increases as the frequency difference increases when
the set frequency is changed. To supplement this, the MPU is used before control by the PLL IC to bring the VCO oscillation frequency
close to the desired frequency. As a result, the VCO CV voltage does not change and is always stable at approx. 2.5V.
The desired frequency is set for the PLL IC by the MPU (IC702) through the 3-line "SDO1", "SCK1", "/PCS_R" serial bus for RX PLL
and "SDO1", "SCK1", "/PCS_T" serial bus for TX PLL. The MPU monitors through the "PLD_R" and "PLD_T" signal line, whether the
PLL IC is locked or not. If the VCO does not lock to desired frequency (unlock), the "PLD_R" and "PLD_T" logic is low.
2.4.6 Control Circuit
The control circuit consists of MPU/DSP (IC702) and its peripheral circuits. IC702 mainly performs the following;
(1) Switching between transmission and reception by PTT signal input.
(2) Reading system, zone, frequency, and program data from the memory circuit.
(3) Sending frequency program data to the PLL.
(4) Controlling the audio mute circuit by decode data input.
Summary of Contents for Nexedge NX-5300
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