Pll Circuits; Power Supply Circuits - Icom IC-F610 Service Manual

4-3 PLL CIRCUITS

4-3-1 PLL CIRCUIT
A PLL circuit provides stable oscillation of the transmit fre-
quency and receive 1st LO frequency. The PLL output com-
pares the phase of the divided VCO frequency to the refer-
ence frequency. The PLL output frequency is controlled by
the divided ratio (N-data) of a programmable divider.
The PLL circuit contains the RX VCO (Q13, D16) and TX
VCO (Q14, D17). The oscillated signal is amplified at the buf-
fer amplifiers (Q11, Q12) and then applied to the PLL IC (IC4,
pin 5) via the low-pass filter (L32, C298, C299).
The PLL IC (IC4) contains a prescaler, programmable coun-
ter, programmable divider and phase detector, etc. The ap-
plied signal is divided at the prescaler and programmable
counter section by the N-data ratio from the CPU (IC20). The
reference signal is generated at the reference oscillator (X2)
and is applied to the PLL IC. The PLL IC detects the out-of-
step phase using the reference frequency and outputs it from
pin 8. The output signal is passed thorough the loop filter and
is then applied to the VCO circuit as the lock voltage.
If the oscillated signal drifts, its phase changes from that of
the reference frequency, causing a lock voltage change to
compensate for the drift in the oscillated frequency.
4-3-2 VCO CIRCUIT
The VCO circuit contains a separate RX VCO (Q13, D16)
and TX VCO (Q14, D17). The oscillated signal is amplified
at the buffer amplifiers (Q11, Q10) and is then applied to the
T/R switch circuit (D14, D15). Then the receive 1st LO (Rx)
signal is applied to the 1st mixer (Q3) and the transmit (Tx)
signal to the YGR amplifier circuit (Q9).
A portion of the signal from the buffer amplifier (Q11) is fed
back to the PLL IC (IC4, pin 5) via the buffer amplifier (Q12)
and low-pass filter (L32, C298, C299) as the comparison sig-
nal.
• PLL CIRCUIT
Loop
filter
45.9 MHz signal
to the FM IF IC
RX VCO
Q13, D16
TX VCO
Q14, D17
Phase
8
detector
Programable
divider
Q34
16
×3

4-4 POWER SUPPLY CIRCUITS

LINE
HV The voltage from a DC power supply.
The same voltage as the HV line which is
controlled by the power switching circuit
(Q23, Q24). When the [ ] switch is pushed,
VCC
the CPU outputs the "PWR" control signal to
the power switching circuit to turn the circuit
ON.
Common 5 V converted from the HV line
at the CPU5V regulator circuit (IC10). The
CPU5V
output voltage is applied to the CPU (IC20),
EEPROM (IC23), etc.
Common 5 V converted from the VCC line at
the 5 V regulator circuit (Q27, Q28). The out-
5V
put voltage is applied to the FM IF IC (IC1),
PLL IC (IC4), etc.
Common 8 V converted from the VCC line
at the 8 V regulator circuit (IC9). The out-
8V
put voltage is applied to the buffer amplifi er
(Q11), AF amplifi er (IC16), etc.
Transmit 8 V controlled by the T8V regulator
circuit (Q25, Q29, D23) using the "TMUT"
T8V signal from the CPU (IC20, pin 17). The out-
put voltage is applied to the YGR amplifier
(Q9), driver amplifi er (Q10), etc.
Receive 8 V controlled by the R8V regulator
circuit (Q26, Q30, D24) using the "TXC" sig-
R8V nal from the CPU (IC20, pin 16). The output
voltage is applied to the RF amplifier (Q2),
1st IF amplifi er (Q4), etc.
Buffer
Q10
Buffer
Q11
Buffer
Q12
IC4 (PLL IC)
Programable
Prescaler
counter
Shift register
X2
15.3 MHz
4 - 4
DESCRIPTION
D14
to transmitter circuit
to 1st mixer circuit
D15
LPF
5
19
PLST
18
SO
17
SCK