Kenwood TK-8360 Service Manual page 15

4. PLL Frequency Synthesizer
The PLL circuit generates the fi rst local oscillator signal
for reception and the RF signal for transmission.
4-1. PLL Circuit
The frequency step of the PLL circuit is 5, 6.25, 10 or
12.5kHz.
A 19.2MHz reference oscillator signal is divided at IC2
by a fixed counter to produce the 5, 6.25, 10 or 12.5kHz
reference frequency. The voltage controlled oscillator (VCO)
output signal is buffer amplifi ed by Q12, then divided by a
programmable counter in IC2.
The divided signal is compared in phase with the 5, 6.25,
10 or 12.5kHz reference signal in the phase comparator in
IC2. The output signal from the phase comparator is fi ltered
IC2: PLL IC
1/N
PLL
DATA
REF
OSC
1/M
19.2MHz
4-3. Unlock Circuit
During reception, the 9RC signal goes high, the 9TC sig-
nal goes low, and Q400 turns on. Q402 turns on and a volt-
age is applied to the collector (9R). During transmission, the
9RC signal goes low, the 9TC signal goes high and Q401
turns on. Q403 turns on and a voltage is applied to 9T.
The MCU in the control unit monitors the PLL (IC2) LD
signal directly. When the PLL is unlocked during transmis-
sion, the PLL LD signal goes low. The MCU detects this
signal and makes the 9TC signal low. When the 9TC signal
goes low, no voltage is applied to 9T, and no signal is trans-
mitted.
Q402
9R
SW
Q400
SW
9RC
IC704
MCU
Fig. 9 Unlock circuit
TENTATIVE
CIRCUIT DESCRIPTION
Phase Charge
comparator pump
ASTC
AMP
Fig. 8 PLL circuit
9C
Q403
9T
SW
Q401
SW
9TC
LD
IC2
PLL
PLL lock
: LD "H"
TK-8360/8360H/8360H
through a low-pass fi lter and passed to the VCO to control
the oscillator frequency.
4-2. VCO Circuit
The operating frequency is generated by Q6 in transmit
mode and Q8 in receive mode. The oscillator frequency is
controlled by applying the VCO control voltage, obtained
from the phase comparator to the varactor diodes (D7 in
transmit mode and D9 in receive mode) and assist voltage
to the (D10, D12 and D13 in transmit mode and D11, D14
and D15 in receive mode).
The TX/RX pin is set high in receive mode causing Q7 to
turn off, and turn Q10 on. The TX/RX pin is set low in trans-
mit mode. The outputs from Q8 and Q6 are amplified by
Q12 and sent to the RF amplifi ers.
D10,D12,D13
LPF
D7
D9
IC3
Assist
voltage
OP
D11,D14,D15
5. Control Circuit
The MCU carries out the following tasks:
1) Controls the WIDE, NARROW, TX/RX outputs.
2) Controls the Baseband IC (IC702).
3) Controls the PLL (IC2).
4) Controls the display unit.
BLED
GLED
RLED
MBL
BLC
Display unit
Fig. 10 Control circuit
Q6
TX VCO
Q12
BUFF
AMP
Q8
RX VCO
Q7,Q10
T/R SW
IC2
PLL
C.DATA
SCLK
SLK
IC704 IC702
MCU Baseband IC
IRQ
CSN
IC1
LCD driver
U
( )
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