Icom IC-E91, Руководство по обслуживанию

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5 - 7
5-3-2 PLL CIRCUITS (RF AND MAIN UNITS)
The PLL circuit provides stable oscillation of the transmit frequency
and receive 1st LO frequency. The PLL circuit compares the phase
of the divided VCO frequency with the reference frequency. The
PLL output frequency is controlled by the divided ratio (N-data)
from the CPU.
• A_BAND PLL CIRCUIT
The buffer amplified signals from the buffer amplifier (VCO UNIT;
Q202) are applied to the PLL IC (RF UNIT; IC800, pin 4). The applied
signals are divided at the prescaler and OSC counter according to
the “PLLDATA” signal from the CPU (LOGIC UNIT; IC1, pin 94).
The divided signal is phasecompared with the reference frequency
at the phase detector.
Input Register
OSC
Counter
Pre-
scaler
Phase
Detector
Charge
Pump
Loop
filter
6
Buffer
amp.
LO
amp.
Buffer
amp.
Q201
Doubler
Q850
Q202
Q200
10
12
13
“CK”
9
“UNLK” signal to the CPU
(LOGIC UNIT; IC1, pin 92)
from the CPU (LOGIC UNIT; IC1)
PLL IC control signals
PLL IC (IC800)
VCO BOARD
RF UNIT
“PLLDATA”
“APLLSTB”
Reference frequency
signal 15.3 MHz
from the TCXO
(MAIN UNIT; X450)
2 4
Q51,D51,D54,D55
VHF BAND VCO
Q1,D1,D3,D5,D6
BC BAND VCO
Q101,D100,D101,D104
UHF BAND VCO
Reference
Counter
BCLV VLV
R815 R811
ULV
D850
PLLOUT
LOOUT
×
2
D100
transmit signal
to the transmit
amplifiers
1st LO signals to the
1st mixer (IC900, pin 3)
IC100
4 1
• A_BAND PLL AND VCO CIRCUITS
The phase difference is output from pin 2 as a pulse type signal
after being passed through the internal charge pump. The output
signal is applied to the BC/VHF/UHF BAND VCOs (VCO UNIT)
after being converted into the DC voltage (lock voltage) at the loop
filter (RF UNIT; C820–C823, R806–R808).
The lock voltage for BC BAND VCO (“BCLV”) from the loop filter
is applied to the VCO (VCO UNIT) via R815 and pin 1 of J800
(RF UNIT). The lock voltage for VHF BAND VCO (“VLV”) from the
loop filter is applied to the VCO (VCO UNIT) via R811 and pin 6
of J800 (RF UNIT). The lock voltage for UHF BAND VCO (“ULV”)
from the loop filter is applied to the VCO (VCO UNIT) via pin 16 of
J800 (RF UNIT).