Circuit Description - Kenwood UBZ-LJ8 Service Manual

■ PLL Circuit
Frequency data is sent to the PLL IC (IC1) from MPU
(IC208) through common data line either when the set is
powered on, or when channel is changed, or when transmit
is required. This data sets the dividers and CP (Charge Pump)
of PLL IC.
The TCXO (X1) produces a 21.25MHz reference frequency
and passes to PLL IC. Reference frequency is divided to pro-
duce a 12.5kHz for comparison of frequency inside PLL IC.
The VCO output frequency is also passed to the PLL IC via
Fin. The divider of the PLL IC, which is set by MPU, also di-
vides this frequency. These two frequencies will be com-
pared by the phase comparator circuit of PLL IC so as to de-
tect the phase difference.
From the phase detection results, charge pump will be
able to output the PWM (Pulse Width Modulation) pulse.
This output voltage will then be used to control the VCO fre-
quency through PLL Loop Filter.
This control voltage passes through the loop filter which is
applied at the VCO control pin to control the oscillation fre-
quency. Basically, the loop filter removes unwanted harmon-
ics and noise produced at the output of the charge pump. It
also determines the PLL response by synchronizing the am-
plitude and phase characteristics.
■ Unlock Detection Circuit
If the PLL cannot synchronize for some reason during op-
eration, the PLL IC will output a low voltage level signal at LD
(pin 5) to the MPU. MPU will stop transmitting or receiving to
prevent wrong frequency transmitted or received.
Loop filter
3
CP1
+ +
+
LV (Lock Voltage)
1
Fin1
VCO
3C,T/R,MOD VCO out
Fig. 11 PLL circuit

CIRCUIT DESCRIPTION

C4
R3 L1 L3
LV
D1 C2
R5
R9
Q1
TX/RX 3C MOD
Fig. 10 VCO circuit
X1
11
Xin
TCXO
Vcon
3C
3C
IC1
PLL IC
IC208
MPU
54
5
LD UL
STB
PLL DATA
DATA
(MPU)
CK
C12
C15 C26
Q2 R16
Q4
L5 R17 L9
Q3
+
Control System
■ Reset Circuit
When a battery is inserted, the MPU power supply pro-
vides the operating voltage after about 0.5sec. The reset IC
(IC202) output a low signal to reset the MPU so that MPU
starts to work correctly.
When battery voltage is lower than 3.0V (set working volt-
age limits) or battery is removed, another reset IC (IC206) will
send a reset to MPU so as to prevent this unit from working
under non-guarantee low voltage condition.
■ Battery Voltage Indication Circuit
The unit contains a battery voltage detection circuit. This
circuit monitors battery voltage every half second and dis-
plays bars on LCD to indicate the battery level. Once battery
voltage drops below 3.2V, indicator will start flashing on LCD
and TX operation inhibits.
B 3M
IC207
IC206 IC202
8
60
VCC
BATTL RESET
3TC
63
IC208
BATT 3RC
MPU
SAVE
3MC
Fig. 12 Reset, battery voltage indication and
Power supply circuit
UBZ-LJ8
VCO
output
Q211
3MS
Q215
3C
Q212
3R
Q210
3T
VR4
14
PA
47
48
49
46
5