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Tektronix FG 5010 User Manual

Tektronix FG 5010
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C
C
A
C
П
П
7
Frequency
DAC
The
Frequency
DAC
receives
the
dc
voltage
from
the
DAC
Referensce
Amplifier
,
the
input
of
which
is
the
+10
V
reference
either
alone
or
summed
with
the
FM
control
volt
age
.
The
Frequency
DAC
produces
a
dc
output
voltage
that
is
proportional
to
both
the
value
of
the
input
dc
voltage
and
the
digital
word
applied
from
the
CPU
.
The
Frequency
DAC
consists
of
two
DAC
circuits
,
the
coarse
-
tune
DAC
and
the
fine
-
tune
DAC
.
The
coarse
-
tune
circuit
consists
of
12
bit
DAC
U1612
,
amplifier
U1631
,
and
related
components
.
Feedback
resistance
for
U1631
is
through
the
input
,
pin
18
,
using
the
internal
resistance
in
U1612
.
The
input
resistance
is
through
the
digitally
con
trolled
resistance
ladder
internal
to
U1612
,
a
programmable
DAC
that
has
12
bits
of
resolution
.
The
dc
voltage
from
the
DAC
reference
is
applied
to
the
V
input
,
and
is
the
drive
signal
for
the
frequency
DAC
.
To
demonstrate
the
sealing
between
the
two
stages
,
assume
that
the
applied
data
is
equal
to
0.5
decimal
multiplier
,
and
the
V
applied
is
-10
V.
The
output
at
U1631
pin
6
would
be
5
V
,
which
is
divided
by
R1611
-
R1612
-
R1621
to
produce
a
Thevinine
equivalent
of
+2.5
V
to
drive
into
R1723
.
REF
REF
The
fine
-
tune
DAC
consists
of
DAC
U1721
,
amplifier
U1731D
,
and
related
components
.
The
circuit
operates
in
the
same
way
as
the
first
circuit
,
except
that
U1721
is
an
eight
-
bit
DAC
,
as
opposed
to
the
12
bit
resolution
of
U1631
.
Also
,
the
divider
at
the
output
of
U1731D
is
1/2048
as
op
posed
to
the
1/2
division
of
the
coarse
-
tune
DAC
.
Thus
,
with
the
same
input
conditions
,
the
Thevinin
output
of
the
fine
tune
DAC
will
only
be
0.0024
V
,
as
opposed
to
the
2.5
V
output
calculated
in
the
last
paragraph
.
Together
,
the
two
DAC
circuits
operate
with
two
bits
of
overlap
to
produce
an
output
current
that
relates
to
frequen
cy
that
has
18
bits
of
resolution
.
The
composite
current
is
applied
through
input
resistor
R1723
to
the
summing
ampli
fier
in
the
Frequency
Reference
Selector
.
The
Thevinin
out
put
resistance
of
the
Frequency
DAC
stages
is
5
k
;
thus
,
the
gain
of
this
leg
of
the
summing
amplifier
is
two
:
40.0k
15.0k
+
5.0k
DAC
Reference
Amplifier
The
purpose
of
the
DAC
Reference
Amplifier
is
to
sum
the
output
of
U1731A
,
the
+10
V
reference
,
with
the
output
of
transmission
gate
U1821C
,
which
,
when
selected
,
is
the
FM
control
voltage
from
amplifier
U1731B
.
The
DAC
Refer
ence
Amplifier
consists
of
operational
amplifier
U1731C
and
Theory
of
Operation
-
FG
5010
related
components
.
The
amplifier
is
configured
as
an
in
verting
operational
amplifier
with
nearly
unity
gain
.
Potenti
ometer
R1734
is
used
to
adjust
the
overall
main
loop
gain
.
The
output
voltage
is
sent
to
the
Frequency
DAC
circuits
for
use
as
the
V.
voltage
.
REF
SYMMETRY
CIRCUITS
Introduction
Refer
to
Fig
.
4-4
,
which
is
a
simplified
diagram
of
the
symmetry
circuits
.
The
principal
circuits
depicted
on
Dia
gram
11
are
the
Up
Symmetry
DAC
,
the
Down
Symmetry
DAC
,
the
Up
Ramp
Current
Source
,
the
Down
Ramp
Source
,
and
the
Digital
Control
Circuits
.
The
Digital
Control
Circuits
are
discussed
just
following
the
Loop
1
Block
Dia
gram
Description
.
The
Frequency
Control
Voltage
,
which
is
the
summation
of
the
Lock
Freq
control
voltage
,
the
VCF
voltage
,
or
the
Frequency
DAC
output
voltage
,
is
applied
to
the
Up
Sym
metry
DAC
and
Down
Symmetry
DAC
,
which
are
identical
circuits
.
Each
DAC
consists
of
a
10
bit
resistance
-
ladder
DAC
and
an
amplifier
.
Through
the
latch
inputs
to
the
DAC
,
the
Frequency
Control
Voltage
is
modified
by
the
factor
pro
grammed
into
the
DAC
,
and
the
output
voltage
from
the
DAC
is
fed
to
the
Up
Ramp
Current
Source
and
Down
Ramp
Current
Source
,
respectively
,
as
the
V
and
V.
voltages
.
Both
voltages
are
sent
to
the
Shrink
Control
Am
plifier
;
in
addition
,
the
V
voltage
is
applied
to
the
input
of
the
U1042C
(
Diagram
14
)
,
part
of
the
Clamp
Phase
Voltage
Generator
.
UP
DN
UP
The
two
current
sources
are
also
identical
.
Each
consists
of
an
amplifier
and
current
driver
.
The
circuits
convert
the
V.
and
V
voltages
to
the
I
and
I.
currents
that
are
fed
UP
DN
UP
DN
to
the
Transistor
Bridge
Circuit
of
the
Main
Loop
,
where
the
two
currents
are
switched
in
and
out
of
the
Loop
Capacitor
charge
path
.
Up
Symmetry
DAC
UP
The
Up
Symmetry
DAC
produces
the
V
voltage
that
is
applied
to
the
Up
Ramp
Current
Source
,
the
Shrink
Control
Amplifier
,
and
the
Clamp
Phase
Voltage
Generator
.
The
cir
cuit
consists
of
DAC
U1511
,
amplifier
U1521
,
and
related
components
.
The
Freq
Control
Voltage
from
the
Frequency
Reference
Selector
is
applied
through
R1633
to
the
V
input
of
U1511
.
The
adjustment
at
the
input
is
to
ensure
proper
REF
4-9

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Tektronix FG 5010 Specifications

General IconGeneral
BrandTektronix
ModelFG 5010
CategoryPortable Generator
LanguageEnglish

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