TK-5810
(
BG
)
/5810H
(
BG
)
29
Fig. 11 PLL block diagram
SW
5C
8C
ASSIST
VCO 1/2
8CL
RX VCO2
8CL
RX VCO1
8CL
TX VCO
MO
3.3V
MB
Q409
16.8MHz
8R
8C
5C
CV
ASSIST
STR
8CL
5C
TX
VCO
T/R
SW
Pre-drive
AMP
(Q150)
Local AMP
(Q203)
CV
8CL
RX
VCO1,2
VCXO
X400
SW
Q410
IC401
IC403
SW
Q406
Q411
SW
IC402
DC/DC
CONVERTER
RIPPLE
FILTER
Q404
Q405
Q407
Q408
SW
PLL
IC400
EP CLK DAT
POTENTIO
METER
VCO
TUNE
PCS
CLK
DAT
Buff
AMP
Q416
Q413
Q414,Q415
8C
8T
Buff
AMP
Q418
5C
RF AMP
Q417
5C
15CL
8CL
ASSIST
DOUBLER
Q403
D419,D420
CIRCUIT DESCRIPTION
The VCO oscillation frequency is determined by two sys-
tems of operation switching terminals “STR” and “VCO1/2”
and two systems of voltage control terminals “C/V” and
“ASSIST”.
The operation switching terminals, “STR” and “VCO1/2”,
are controlled by the control lines (STR, VCO1/2) output
from the ASIC (IC708). When the STR logic is high and the
VCO1/2 logic is high, the RX VCO1 output a 1st local receive
signal. When the STR logic is high and the VCO1/2 logic is
low, the RX VCO2 output a 1st local receive signal. When
the STR logic is low, the TX VCO output a transmit carrier.
The voltage control terminals, “C/V” and “ASSIST”, are
controlled by the PLL IC (IC400) and potentiometer IC (IC401)
and the output frequency changes continuously according
to the applied voltage. For the modulation input terminal,
“MOD”, the output frequency changes according to the
applied voltage. This is used to modulate the VCO output.
“MOD” works only when “STR” is low.
The oscillation frequency is controlled by the voltage of
the input terminals of the VCO, obtained from the potenti-
ometer IC applying to varactor diodes (D416, D417, D421,
D411, D412, D422, D405, D406, and D407), and from the
phase detector applying to diodes (D413, D414, D408,
D409, D402, and D403).
5-3. Potentiometer IC (IC401)
The potentiometer IC (IC401) is connected to the VCO
voltage control terminal, “ASSIST”, and quickly controls the
VCO oscillation frequency. However, its accuracy is low and
the VCO frequency cannot be matched accurately with the
desired transmit carrier or the 1st local receive signal.
The potentiometer IC is controlled by the ASIC (IC708)
through the 3-line “PCS”, “DAT”, “CLK” serial bus.
5-4. Lockup Accelerator
The lockup accelerator is a circuit composed of a potenti-
ometer IC (IC401) and a DC amplifi er (IC403) to compel the
oscillation frequency of the VCO to be close to the target.
The potentiometer IC outputs the voltage which meets
the target frequency, and the signal is connected to one of
two input terminals of the VCO through the DC amplifi er.
5-5. PLL IC (IC400)
PLL IC compares the differences in phases of the VCO
oscillation frequency and the VCXO reference frequency, re-
turns the difference to the VCO CV terminal and realizes the
“Phase Locked Loop” for the return control. This allows
the VCO oscillation frequency to accurately match (lock) the
desired frequency.
When the frequency is controlled by the PLL, the fre-
quency convergence time increases as the frequency differ-
ence increases when the set frequency is changed. To sup-
plement this, the potentiometer IC is used before control by
the PLL IC to bring the VCO oscillation frequency close to
the desired frequency. As a result, the VCO CV voltage does
not change and is always stable at approximately 2V.
The desired frequency is set for the PLL IC by the ASIC
(IC708) through the 3-line “EP”, “DAT”, “CLK” serial bus.
Whether the PLL IC is locked or not is monitored by the
ASIC through the “UL” signal line. If the VCO is not the de-
sired frequency (unlock), the “UL” logic is low.
5-6. Local Switch (D419, D420)
The connection destination of the signal output from the
amplifier (Q418) is changed with the diode switch (D420)
that is controlled by the transmission power supply, 8T, and
the diode switch (D419) that is controlled by the receive
power supply, 8R.
If the 8T logic is high, it is connected to a transmit-side
pre-drive amplifi er (Q150). If the 8R logic is high, it passes
through the local amplifi er (Q203) and then is connected to
a receive-side mixer (IC200).
