26
TK-760G/
(
N
)
/762G/
(
N
)
■
Unlock Circuit
During reception, the 8RC signal goes high, the 8TC sig-
nal goes low, and Q16 turns on. Q18 turns on and a voltage
is applied to the collector (8R). During transmission, the
8RC signal goes low, the 8TC signal goes high and Q29
turns on. Q28 turns on and a voltage is applied to 8T.
The CPU in the control unit monitors the PLL (IC3) LD
signal directly. When the PLL is unlocked during transmis-
sion, the PLL LD signal goes low. The CPU detects this
signal and makes the 8TC signal low. When the 8TC signal
goes low, no voltage is applied to 8T, and no signal is trans-
mitted.
IC9
SHIFT
REG.
IC502
CPU
Q16
SW
Q18
SW
IC3
PLL
Q29
SW
Q28
SW
LD
CONTORL UNIT
8RC
8C
8R
8T
8TC
PLL lock
: LD "H"
Fig. 6
Unlock circuit
IC508
IC6
Q103
IC507(1/2)
MIC
AF AMP
NJM2904V
MIC KEY
INPUT
AF AMP,
IDC, LPF
TC35453F
IC502
CPU
30622M
4XXXGP
D/A
CONVERTER
M62363FP
IC1
SUM AMP
TA75S01F
X1
VCXO
16.8MHz
VCO
2SK508NV
(K52)
IC3
PLL
MB15A02
Q106
BUFFER
2SC4226
(R24)
Q9
BUFFER
2SC4215
(Y)
Q22
RF AMP
2SC3357
Q25
ANT
RF AMP
2SC2954
IC400
POWER AMP
M67741H-32
Q14
BUFFER
2SC4649
(N,P)
IC8
1/2
DIVIDER
UPB1509GV
Fig. 7
Transmitter system
Transmitter System
■
Outline
The transmitter circuit produces and amplifies the de-
sired frequency directly. It FM-modulates the carrier signal
by means of a varicap diode
■
Power Amplifier Circuit
The transmit output signal from the VCO is amplified to a
specified level of the power module (IC400) by the drive
block (Q22 and Q25). The amplified signal passes through
the transmission/reception selection diode (D16) and goes
to a low-pass filter. The low-pass filter removes unwanted
high-frequency harmonic components, and the resulting sig-
nal is goes the antenna terminal.
■
APC Circuit
The automatic transmission power control (APC) circuit
detects part of a power module output with a diode (D35,
D36) and applies a voltage to IC15. IC15 compares the APC
control voltage (PC) generated by the D/A converter (IC6)
and DC amplifier (IC7) with the detection output voltage to
control Q31 and Q32, generates DB voltage from B voltage,
and stabilizes transmission output.
The APC circuit is configured to protect over current of
the power module due to fluctuations of the load at the an-
tenna end and to stabilize transmission output at voltage
and temperature variations.
CIRCUIT DESCRIPTION
Fig. 8
APC circuit
RF
AMP
Q22
RF
AMP
Q25
POWER
AMP
IC400
APC
DRIVER
Q32
DB
+B
Q31
PRI
DRIVER
DC
AMP
IC7
ANT
SW
D34
LPF
ANT
POWER
DET
D35,36
IC15
APC
CONTROL
D16
PC
IC6
23pin
Q33
TEMP
PROTECT