Pll Circuit; Power Supply Circuits - Icom IC-M2A Service Manual

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 (Q21, Q22, D22, D23). The
oscillated signal is amplified at the buffer-amplifiers (Q23,
Q25) and then applied to the PLL IC (IC1, pin 19).
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
(Q23, Q24) and is then applied to the receive 1st mixer
(Q150) or transmit buffer amplifier (Q50) via the TX/RX
switching diode (D50, D51).

• PLL CIRCUIT

Loop
filter
"2nd LO" signal (21.25 MHz)
to the FM IF IC (IC170)
X1
21.25 MHz

4-4 POWER SUPPLY CIRCUITS

VOLTAGE LINES
Buffer
VCO
Q21, Q22, D22, D23
Phase Programmable
13
detector counter
Programmable
17
divider
16
4 - 3
LINE
HV The voltage from the attached battery pack.
The same voltage as the HV line (battery volt-
VCC age) which is controlled by the power switch (RF
unit; [OFF/VOL] control).
Common 5 V converted from the VCC line by the
CPU5V regulator circuit (IC220).
CPU5V
The output voltage is applied to the CPU (MAIN
unit; IC360), REG5V regulator, etc.
Common 5V converted from the VCC line by the
5V regulator circuit (Q223–Q225).
5V
The output voltage is applied to the D/A convert-
er (IC190) and PLL IC (IC1), etc.
Receive 5V converted from the 5V line by the R5
regulator circuit (Q221).
R5V The regulated voltage is applied to the MOD
MUTE circuit (Q20, D20, D21) and receiver cir-
cuit.
Common 5V converted from the 5V line by the
V5 regulator circuit (Q220).
V5V
The regulated voltage is applied to the VCO cir-
cuit
Transmit 5V converted from the 5V line by the T5
regulator circuit (Q222).
T5V
The regulated voltage is applied to the transmit-
ter circuit.
D50
to transmitter circuit
Buffer
Q24
to the 1st mixer circuit
Q23
D51
Buffer
Q25
IC1 (PLL IC)
19
Prescaler
3
PLST
4
Shift register SCK
5
SO
DESCRIPTION