Pll Circuit - Alinco DJ-G1T Service Manual

3) PLL Circuit

1. Reference Freq.
Circuit
2. Phase Comparator
Circuit
3. Loop Filter Circuit
4) VCO Circuit
VR308 and the middle power setting variable resistor VR307 located in the
IF unit. The radio has no low power setting variable resistor.
High Middle
Power
D306A OFF ON
D306B ON OFF
The PLL serial data (clock, data, strobe) is sent from CPU IC401. The Pin9
of IC2 is clock, Pin10 of IC2 is data, Pin 11 of IC2 is strobe. The VCO signal
is amplified by RF amplifier Q19, and input to the Pin8 of IC2. The program­
mable divider of IC2 is determined by frequency data, and it divides (1/N)
input signal of IC2. Resulting signal will be 5kHz or 6.25kHz.
There are 8 channel steps (5, 10, 12.5, 15, 20, 25, 30 and 50kHz) of DJ-
G1T/E. The reference frequency is obtained by divided by 2560 or 2048
reference oscillator (12.8MHz). The reference frequency (5kHz) uses a
channel step of 5, 10, 15, 20, 25, 30 and 50kHz. The reference frequency
(6.25kHz) uses a channel step of 12.5kHz.
The reference frequency of the IC2 is 5kHz or 6.25kHz.
The VCO output frequency divided by N is compared with 5kHz or 6.25kHz
in the phase comparator.
If the phase error should occur in PLL, the charge pump (Pin5 of IC2)
outputs the pulse. This signal is converted into DC voltage by PLL loop filter
(C84, C85, C86, R70, R71, R72 and R73), and input to the varicap diode
(D202, D203, D204 and D205) in the VCO unit for the frequency control.
The frequency control voltage from the PLL circuit is input to the cathode of
the varicap diode D202 (VC01), D203 (VC01), D204 (VC02) and D205
(VC02).
The output frequency of VCO is amplified by RF amplifier Q203, and output
from VCO unit. The circuit is Colpitts oscillator. To get the wide band receive
range, the radio has two VCO's. To get the wide oscillation frequency range,
the fixed capacitance in the VCO is set to the smallest value.
Oscillator
VC01 Q201
VC02 Q202
Low
OFF
OFF
Modulation
Tune Varicap
Varicap
D202, D203
D206
D204, D205
Shift
Switch
D201