Icom IC-M1EURO V Service Manual - page 10
4 - 3
4-3 PLL CIRCUIT (RF UNIT)
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 a VCO (Q4, Q5, D4, D6). The oscil-
lated signal is amplified at the buffer-amplifiers (Q6, Q7) and
then applied to the PLL IC (IC1, pin 2).
The PLL IC contains the prescalers, programmable counter,
programmable divider, phase selector and etc. The entered
signal is divided at the prescaler and programmable counter
sections by the N-data ratio from the CPU. The divided sig-
nal is detected on phase at the phase detector using the ref-
erence frequency.
If the oscillated signal drifts, the phase of its frequency
changes from the reference frequency, causing a lock volt-
age changes to compensate for the drift in the oscillated fre-
quency.
A portion of the VCO signal is amplified at buffer-amplifiers
(Q6, Q8) and is then applied to the receive 1st mixer (Q14)
or transmit driver via the TX/RX switching diode (D7, D8).
The lock voltage is also used for the receiver tunable band-
pass filter to match the filter’s center frequency to the
desired receive frequency. The lock voltage is amplified at
the buffer-amplifier (Q1) and then applied to the CPU (MAIN
unit; IC9, pin 93).
The amplified signal is controlled by the CPU (MAIN unit;
IC9), and is then applied to bandpass filters (D13–D18) as
“T1”, “T2”, “T3”, “T4” signals via the D/A converter (IC2).
Shift register
Prescaler
Phase
detector
Loop
filter
Programmable
counter
Programmable
divider
X1
21.25 MHz
"2nd LO" signal (21.25 MHz)
to the FM IF IC (MAIN unit; IC1)
Q4, Q5, D5, D6
VCO
Buffer
Buffer
Buffer
Q8
D8
D7
Q7
Q6
3
4
5
PLST
IC1 (PLL IC)
SCK
SO
to transmitter circuit
to 1st mixer circuit
17
16
8
2
Buffer
"LVIN" signal to the CPU
(MAIN unit; IC9)
Q1
PLL CIRCUIT
LINE
HV
VCC
4V
R4V
T4V
S4V
DESCRIPTION
The voltage from the attached battery pack.
The same voltage as the HV line (battery volt-
age) which is controlled by the power switch
([OFF/VOL] control).
Common 4V converted from the VCC line by the
4V regulator circuit (MAIN unit; Q8–Q10).
The output voltage is applied to the D/A convert-
er (RF unit; IC2) and PLL IC (RF unit; IC1), etc.
Receive 4V converted from the 4V line by the R4
regulator circuit (MAIN unit; Q5).
The regulated voltage is applied to the MOD
MUTE circuit (RF unit; Q2, D2) and receiver cir-
cuit.
Transmit 4V converted from the 4V line by the T4
regulator circuit (MAIN unit; Q6).
The regulated voltage is applied to the transmit-
ter circuit.
Common 4V converted from the 4V line by the
S4V regulator circuit (MAIN unit; Q7).
The regulated voltage is applied to the optional
scrambler unit, limiter amplifier (MAIN unit; IC4),
etc.
4-4 POWER SUPPLY CIRCUITS
VOLTAGE LINES