PLL
(Phase
Lock
Loop)
CIRCUIT
DESCRIPTION
The
PLL
(Phase
Lock Loop)
circuit
used
in
the
TRC-457 consists
of
6 major components; Voltage
Controlled Oscillator (VCO), 1/N Divider, Refer-
Fvco
34.7625 MHz
I
35.2075 MHz
IC 5
V.C.O.
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- -
--
--
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--
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--
--
-- - -
200mv
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1 /
f
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1.9VC"lC~
FET 4
Mixer 0.91 MHz
I
1.35 MHz
33.
8575
MHz
I
33.8525 MHz
ence Oscillator, 111024 Divider,
Phase
Detector
and
Low
Pass
Filter.
AMP
---
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----
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le7
TR
31
Buffer Amp.
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1
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ov
70
.
91
~
1.35 MHz
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X'tal3
a TR 34
OSC
11
.
2858MHzT
1....-----'
TR
35
Filter
TR
40
I Filter PHASE
Oetector
10 kHz
1/1024 I
Divider
r--_-.lf10
kHz •
I 10.24 MHz I
Programmable Divider REF.
OSC
I
X'tal4
r---
Cl
TR
38
OSC
Tripier
l /N (91-135) l
f---
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_____
J
11.2842 MHz T
X'tal6
r---
C
11.2850 MHz T TR 39
OSC
I[J
Channel Selector
X'tal5
The VCO
is
an
oscillator which
controls
oscilla-
·
tion
frequency in accordance
with
input
voltage
changes.
The VCO
output
is
mixed
with
a signal in
the transmitter
or
receiver
circuitry.
A
portion
of
the VCO frequency
is
fed
to
FET4
and
mixed
with
a 33.8525 -33.8575 MHz frequency
from
X3,
X4
or
X6
and
then
goes
through
TR30
Amplifier
and
TR31
Buffer
Amp
and
then
added
to
the
1/N
Divider. This
is
applied
to
one
input
of
the
Phase
Detector.
"N"
for
the 1/N Divider
is
determined
by the Channel Selector Switch
(by
BCD)
and
varies
from
91
to
135.
On the other hand, a 10.24 MHz frequency
from
the Reference Oscillator
is
divided
to
10kHz
by
1/1024
Divider
and
applied
to
another
input
of
the
Phase
Detector. The
Phase
Detector detects the
difference
of
these
two
input
signals
and
produces
a voltage which controls the VCO frequency. The
Low
Pass
Filter
integrates the
outpuf
voltage
of
the
Phase
Detector which controls the VCO
frequency
and
the 1/N Divider produces a
10kHz
frequency.
Thus the
Phase
Detector receives
two
input
signals
(both 10 kHz).
It
compares the
phase
difference
of
the
two,
generating
an
error voltage, which acts on
the VCO
to
bring the
two
frequencies exactly in-
phase.
When this
condition
occurs, the
PLL
circuit
is
"Iocked".
Switch 10.
24
MHz
WAVE FORM O,F
le7
IC7
Pin No.
Wave
Form
IC7
?inNo.
WiNe
Form
H -
UN
L
OCKED
L =
LOCKED
where
H = 3.5 -
6V
L = 0 - 1.
0V
a
2&3
5&6
7 &
12
\0
1illl
5V
NJ
5V
lli10
5V m5V
\ -
T\
-
-,.(
2V
_
__V _V_
15V
--
- - -
-0------
-0
--
-
--0
-
--
- 0
-------0
Note:
Pin
No.
13
through 18, 20 &
21
are
as
in frequency
chart.
Pin
No. 19, 22 & 23
are
fixed
to
Low level.
By varying the constant N, the
output
frequency
from
the VCO
can
be
locked and varied one
10kHz
step at a time. The constant N
is
controlled
by
the Channel Selector Switch. A frequency
shift
of
2.5 kHz (required
for
AM
RX, USB and
AM
TX
and
LSB
RX/TX)
is
obtained
by
switching
to
X3,
X4
or
X6
as
shown in Frequency Chart.
For
a more detailed description
of
how
this
circuit
functions, refer
to
Abbreviated Block Diagram
as
well
as
the
full
Block
Diagram and Schematic.
-10
-
