Kenwood TK-2160 - Manual (Page 9)

TK-2160
9
CIRCUIT DESCRIPTION
PLL DATA
X1
16.8MHz
REF OSC
1M
1N
PLL IC IC1
PHASE
COMPARATOR
CHARGE
PUMP
LPF
5kHz/6.25kHz
D3, 5, 7, 8
D4, 6, 9, 10
Q6
TX VCO
Q5
RX VCO
Q9
BUFF AMP
Q11
RF AMP
Q7
DOUBLER
Q8, 12
T/R SW
5kHz/6.25kHz
LPF
RX
TX
Fig. 6 PLL circuit
3) Unlock Detector
If a pulse signal appears at the LD pin of IC1, an unlock
condition occurs, and the DC voltage obtained from C19,R6
and Q1 causes the voltage applied to the microprocessor
to go high. When the microprocessor detects this condition,
the transmitter is disabled, ignoring the push-to-talk switch
input signal. (See Fig. 7)
Fig. 7 Unlock detector circuit
5C
R6
Q1
C19
R7
IC805
IC1
LD
UL
PLL IC
CPU
R16
4. Transmitter System
1) Microphone Amplifier
The signal from the microphone passes through the IC601.
When encoding DTMF, it is turned OFF for muting the
microphone input signal by IC601.
The signal passes through the Audio processor (IC601) for
the maximum deviation adjustment, and goes to the VCXO
modulation input.
Fig. 8 Microphone amplifier
Fig. 9 Drive and final amplifier and APC circuit
3) APC Circuit
The APC circuit always monitors the current flowing through
the RF power amplifier (Q211) and keeps a constant current.
The voltage drop at R264, R265 and R270 is caused by the
current flowing through the RF power amplifier and this
voltage is applied to the differential amplifier IC201(1/2).
IC201(2/2) compares the output voltage of IC201(1/2) with
the reference voltage from IC805. The output of IC201(2/2)
controls the VG of the RF power amplifier, drive amplifier
and pre-drive amplifier to make both voltages the same.
The change of power high/low is carried out by the change
of the reference voltage.
4) Encode Signalling
(1) QT/DQT
QT,DQT data of the LSDTCXO Line is output from pin 22 of
the CPU. The signal passes through a low-pass CR filter
and goes to the TCXO(X1).
The QT,DQT data of the LSDVCO Line is output from pin
2) Drive and Final Amplifier
The signal from the T/R switch (D201 is on) is amplified by
the drive amplifier (Q207) to 50mW.
The output of the drive amplifier is amplified by the RF power
amplifier (Q211) to 5.0W (1W when the power is low). The
RF power amplifier consists of two MOS FET stages. The
output of the RF power amplifier is then passed through
the harmonic filter (LPF) and antenna switch (D204 and
D206) and applied to the antenna terminal.
From
T/R SW
(D201)
DRIVE
AMP
RF
POWER AMP
LPF
ANT
SW
D204
D206
ANT
VG VG
Q207 Q211
Pre-DRIVE
AMP
Q206
VDD
VG
R264
R265
R270
+B
IC201
(2/2)
IC201
(1/2)
PCTV
(IC805)
IC601
IC805
LPF DTMF/2 TONE
LSDTCXO
LSDVCO
CPU
AGC
VCO
MIC
X1
TCXO LPF
IC606
BUFFER
LPF
AQUA