5
TK-3130/3131
CIRCUIT DESCRIPTION
■
IF Amplifier
The IF circuit is integrated in the FM IC (IC2). The IF IC
contains local input, mixer, limiter amplifier, FM DET, and
low-frequency amplifier.
The IF signal coming from the IF amplifier (Q20) goes to
the IF IC mixer and is mixed with the second local signal
(38.4MHz) to produce a second IF signal.
(38.85MHz – 38.4MHz = 450kHz)
The tripled PLL reference oscillation (12.8MHz x 3) is
used for the second local signal.
The second IF signal passes through ceramic filter (CF1)
to remove unwanted signals.
The second IF signal passing through the ceramic filter
passes through the limiter amplifier consisting six differen-
tial amplifiers and is detected.
The FM detection is quadrature detection method. The
phase of the output signal from the limiter amplifier is
shifted by 90 degrees by a quad coil (L36) and compared
with the original waveform to produce detection output.
■
Squelch Circuit
A squelch circuit is provided to prevent no-signal noise or
weak signals from outputting to a speaker during transmis-
sion.
■
AF Circuit
The FM IC output passes through the base band IC
(IC205), mute (Q213), and amplifier (IC207). After go to AF
power amplifier IC (IC208). This IC have BTL amplifier func-
tion and electrical Volume. At internal speaker, BTL ampli-
fied. At external speaker, IC switch off the 1 channel ampli-
fier by connectors information.
MIX
Amp
Amp
Amp
Amp
DET
IC2
IC205
IC208
CF1
450kHz
16
MIXIN
38.85
MHz
1st IF
9
AFOUT
38.4MHz
X3
TCXO
Q22
12.8MHz
PLL
X1
HPF LPF
23
RXIN
MUTE
Q213
IC207
Amp
SW
VR202
AF VR
INT. SP
J200
EXT. SP
AF
Q21
Noise amp
D16
DET
BUSY
19
24
52
RSSI
IC204
CPU
6
AF MUTE
Q212
Q214
SW
SP AMP
Q20
IF amp
Fig. 4
IF amplifier, squelch and
AF amplifier circuits
Transmitter System
■
Microphone Amplifier Circuit
The audio signal from the microphone passes through
the MIC amplifier (IC207). Then, the signal goes through the
base band IC (IC205) that has the 6dB/oct pre-emphasis cir-
cuit, band-pass filter (300 to 3kHz), amplifier, and limiter.
The distortion components outside the audio band are re-
moved by the splatter filter.
■
Modulation Circuit
The MIC amplifier (IC207) output passes through VR201
for modulation adjustment and goes to the modulation input
of the VCO circuit for variable reactance phase modulation.
■
Transmission Output Circuit
The VCO output is amplified by a high-frequency ampli-
fier (Q7~Q10), passes through a high-frequency antenna
switch, passes through a low-pass filter and goes to the an-
tenna.
The transmission output is about 1W with 3.8V DC sup-
ply at battery terminal.
■
Low-Pass Filter Circuit
A three-stage Chebyshev type low-pass filter is located
between the antenna and transmit/receive switching circuit.
It removes harmonic components contained in the transmis-
sion output.
Fig. 5
Transmitter section configuration
Fig. 6
Microphone amplifier circuit
ANT
LPF
ANT SW
D12,13
DRIVE
AMP
Q9
PRE-DRIVE
AMP
Q8
RF AMP
Q7
VCO
Q4, Q5
VR201
MIC AMP
IC207
MIC
FINAL
AMP
Q10
Amp
IC205
LPF
IDC
DET
D205
SW
D204
MIC
MUTE
Q210
IC207
MIC amp
MIC
