Pll Circuits; Power Supply Circuits - Icom IC-T81E Service Manual

The APC sensor (R911) detects driving current from the
drive voltage at the YGR (Q138), drive (Q921) and power
(Q922) amplifiers. The detected current is converted into DC
voltage at Q913, then applied to the APC control circuit
(IC901, pin 2). The applied voltage is compared with a
"PSET" voltage from the CPU via the D/A converter (LOGIC
unit; IC5), and the APC control circuit outputs "VGGC" volt-
age from pin 1 to control the YGR, drive and power ampli-
fiers.
When the driving current is increased, input voltage of the
differential amplifier (IC901, pin 2) will be increased. In such
cases, the differential amplifier output voltage (IC901, pin 1)
is decreased to reduce the driving current.

4-3 PLL CIRCUITS

4-3-1 50 MHz BAND PLL CIRCUIT (RF UNIT)
The osillated signal at the 6MVCO (Q341, D341) is amplified
at the buffer amplifiers (Q342, Q343). The amplified signal is
applied to the PLL IC (IC801, pin 2) via the buffer-amplifier
(Q813).
The signal which is applied to the PLL IC (IC801) is divided
by N-data from the CPU and phase-detected with the divid-
ed reference frequency (5 kHz) then output from pin 8. The
output signal is converted into DC voltage at the active filter
(Q804, Q805) and is fed back to the 6MVCO as the lock volt-
age.
4-3-2 144 MHz BAND PLL CIRCUIT
(VCO BOARD AND RF UNIT)
The osillated signal at the 144-VCO circuit (VCO unit; Q311,
Q312, D302 and D311) is amplified at the buffer amplifiers
(VCO unit; Q313).The amplified signal is applied to the PLL
IC (IC801, pin 19) via a buffer-amplifier (Q807).
The applied signal is divided by serial data from the CPU (N-
data) and phase-detected with the divided reference fre-
quency (5 kHz) at the phase detector section in the PLL IC.
The phase-detected signal is output from IC801 (pin 13) and
converted DC voltage at the active filter (Q811, Q812). The
converted DC voltage is fed back to the VCO board as the
"VLV" signal of the lock voltage.
While operating in the 144 MHz band, the lock voltage is
applied to the CPU (LOGIC unit; IC1) via the tune control cir-
cuit (Q803) to track the center frequency of the tunable
bandpass filters (D306, D309, D310) as the "TUNE" signal.
4-3-3 440 MHz BAND PLL CIRCUIT
(VCO BOARD AND RF UNIT)
The osillated signal at the 440-VCO circuit (VCO unit; Q321,
Q322, D321 and Q322) is amplified at the buffer-amplifiers
(VCO unit; Q323).The amplified signal is applied to the PLL
IC (IC801, pin 19) via a buffer-amplifier (Q807).
The applied signal is divided by serial data from the CPU (N-
data) and phase-detected with the divided reference fre-
quency (5 kHz) at the phase detector section in the PLL IC.
The phase-detected signal is output from IC801 (pin 13) and
converted DC voltage at the active filter (Q811, Q812). The
converted DC voltage is fed back to the VCO board as the
"VLV" signal of the lock voltage.
4-3-4 1200MHz BAND PLL CIRCUIT
(VCO BOARD AND RF UNIT)
The osillated signal at the 1200-VCO circuit (VCO unit;
Q350, D351 and D352) is amplified at the buffer-amplifiers
(VCO unit; Q351 and Q353). The signal passes through the
buffer amplifier (Q354), the high-pass (C376–C380, L334
and L335) and the low-pass filter (C381–C385, L336 and
L337). The filtered signal is applied to the PLL IC (IC802, pin
1) via the buffer amplifier (Q816).
The applied signal is divided by serial data from the CPU (N-
data) and phase-detected with the divided reference fre-
quency (5 kHz) at the phase detector section in the PLL IC.
The phase-detected signal is output from IC801 (pin 13) and
converted DC voltage at the active filter (Q811, Q812). The
converted DC voltage is fed back to the VCO board as the
"VLV" signal of the lock voltage.

4-4 POWER SUPPLY CIRCUITS

VOLTAGE LINE
LINE
The voltage from the external power supply or
HV
attached battery pack.
The same voltage as the "HV" line (external
power supply or battery pack) passed through a
VCC
diode (RF unit; D1).
Common 3V converted from the "VCC" line by
+3C CPU regulator IC (LOGIC unit; IC141). The
+3CPU
output voltage is supplied to the +3C regulator
circuits, etc.
Common 3V converted from the "VCC" line by
the +3C regulator circuit (LOGIC unit; Q142 and
+3C
Q145) using the +3CPU regulator (LOGIC unit;
IC141.)
Common 3V converted from the "VCC" line by
the +3 regulator circuit (LOGIC unit; IC5, Q1, Q2
+3
and Q3) using the +3C regulator (LOGIC unit;
Q142 and Q145).
3V for receiver circuit converted from the "VCC"
line by the "R+3" regulator circuit (RF unit; Q7
R+3
and Q8).
4V for transmitter circuit converted from the
"VCC" line by the T4 regulator circuit (RF unit;
Q901–Q903 and D901). The T4 regulator circuit
T4
is controlled by the CPU (LOGIC unit; IC1, pin
21) via the "TXC" line.
4 - 5
DESCRIPTION