Technics ST-9038 Manual page 3

t
PART
II
PLL
SYNTHES]ZER
t
1.
PLL Synthesizer
1-1
Synthesizer
Dividing
or
multiplying
a
certain frequency
or
combining
frequencies
to
obtaín
the
desired
frequency is called "frequency
synthesis" A
frequency
synthesizer is a
unit
used
to
achieve this
purpose.
1-2
Block diagram of synthesizer section
98.3 (98.8)
-
118.6 MHz
1/A
1/983 (1/988)
-1/11a6
12.5 KHz
1
/
1024 Xtal
12.8 MHz
ü
o
l
Ð
"
Frequency
range
87.6 (88.1)
-
107.g MHz
.
Local
oscillator
frequency
gB.3
(gB.B)
-
118.6 MHz
.
1/8
prescaler
12.2815 (12.95)
-
14.B25MHz
"
Dividing ratio
of
programmable
frequency
divider
983 (988)
-
1
1Bo
.
Comparison
frequency
12.5
k1z
Note)
Values in
parentheses
are specif ied
for the
U.S.A.
When
a
broadcast signal
of
87.6 (88.1)
to
1Oj.g MHz
enters
the
receiver,
the
local oscillator
frequency (Vco) becomes
98.3
(98.8) to
118.6
MHz.
The frequency
is
divided ar rhe ratio
of
1/g
by the
prescaler
through
the
interface, and further divided
ar rhe rario
of 1/gB3 (1i98g)
-
1/11g6
by the programmable frequency divider according to
the input
frequency thus obtaining 12.5 KHz.
On the other hand, a12.8MHz frequency from a high precision crystal oscillator
is
divided at
the
ratio
of
1/1024
to
obtain
12.5
KHz,
the
standard comparison
frequency.
When these two
frequencies are added
to the
phase comparaTor, itsoutput
is
the
phase
difference. By
passing
the
output
through
the
low-pass
filter,
a positive
or
negative voltage can be obtained
in
proportion to
the
phase
difference between the two
frequencies. Vco
is
controlled by this voltage. As
is
evídent
in
the
above description,
the
composition
of
this circuit
is
that
of a
pLL synthesizer.
The
description of
each
section
ís
given
in the following.
1-3
lnterface circuit
This circuit connects Vco and
prescaler,
and
serves as
an amplifier
and
a
buffer.
TR901
is a
buffer
for Vco and ECL (Emitter Coupled Logic lC), and TRg02
is a
buffer/amplif ier
for
ECL and TTL.
Vco
I
nterface
Prescaler
Programmable frequäncy
d
¡vider
Low-pass
f
ilter
Phase
comparatof
F
req
uency
d ¡vid
er