Operating instructions
This
section
of
the
manual
describes
the
circuitry
used
in
the
7880
Time-Base
unit
.
The
description
begins
with
a
discussion
of the
instrument,
using
the block diagram
shown
in
Figure
3-1
.
Next,
each
circuit
is
described
in
detail
with
a
block
diagram
provided
to
show
the
major
interconnections
between
circuits,
and
the
relationship
of
the
front-panel
controls to
each
circuit
.
Detailed
schematic
diagrams
of
each
circuit
are
located
in
the
diagrams
foldout
section
at
the
back
of
this
manual
.
Refer
to
these
diagrams
throughout
the
following
discussions
for
specific
electrical
values
and
relationships
.
The
following
discussion
is
provided
to
aid
in
understanding
the
overall
concept
of
the
time-base
unit
before
the
individual
circuits
are
discussed
in
detail
.
A
basic
block
diagram
is
shown
in
Figure
3-1
.
The
numbered
diamond
in
each block
refers
to
the
corresponding
circuit
diagram
at
the
rear
of
this
manual
.
TRIGGER
GENERATOR
The
Trigger
Generator
ensures
a
stable
crt
display
by
start-
ing
each
sweep
at
the
same
point
on
the
waveform
.
Circuit-
ry
is
included
for
selection
of
trigger
mode,
coupling,
and
source
.
The
output
of
the
Trigger
Generator
is
a fast-rise
gate
which
enables
the
Sweep
Generator
.
Symbols
SWEEP
GENERATOR
The
sweep
sawtooth
signal
is
initiated
when
the
Trigger
Generator
output
is
applied
to
the
Sweep
Generator
.
The
LOGIC
FUNDAMENTALS
Digital
logic
techniques
are
used
to
perform
many
functions
within
this
instrument
.
The
function
and
operation
of
the
logic
circuits
are
described
using
logic
symbologyand
termi-
nology
.
This
portion
of
the
manual
is
provided
to be an
aid
in
the
understanding
of
these
symbols
and
logic
concepts,
not
a
comprehensive
discussion of
the
subject
.
The
symbols
used
to
describe
digital circuits
in
this
instru-
ment
are
based
on
ANSI
standard
Y32
.14-1973
.
Table
3-1
provides
a
basic
reference
for
the
logic
devices
used
within
this
instrument
.
Any
deviations
from
the
standard
symbol-
ogy, or
devices
not
defined
by
the
standard,
are
described
in
the
circuit
description
for the
applicable
device
.
THEORY
OF
OPERATION
BLOCK
DIAGRAM
DESCRIPTION
DETAILED
CIRCUIT
DESCRIPTION
Section
3-71380
rate
of
change
(slope)
of
the
sawtooth
signal
is
determined
by
the
TIME/DIV
switch
setting
.
The
sawtooth
signal
pro-
vides
horizontal
deflection
for
the
mainframe
(oscilloscope)
.
The
Sweep
Generator
also
generates
a
Sweep
Gate
pulse
which
unblanks
the
crt
in
the
mainframe
.
LOGIC
The
Logic
circuits
control
the
sweep
modes
and
associated
functions
of
the
time-base
unit
(e
.g
.,
auto
sweep,
single
sweep,
hold
off,
etc
.)
.
The
Logic
circuits
also
generate
the
control
signals
for the
mainframe
.
The
operation
of
circuits
unique
to
this
instrument
is
described
in
detail in this
discussion
.
Circuits
commonly
used
in
the
electronics
industry
are
not
described
in
detail
.
The
following
circuit
analysis,
with
supporting
illustrations,
gives
the
names
of
individual
stages,
and
shows
how
they
are
con-
nected
to
form
major
circuits
.
These
illustrations
show
the
inputs
and
outputs
for
each
circuit
and
the
relationship
of the
front-panel
controls to
the
individual
stages
.
The
detailed
circuit
diagrams
from
which
the
illustrations
are
derived
are
shown
in
the
diagrams
foldout
section
.
Logic
Polarity
NOTE
Logic
symbols
used
on
the
diagrams
depict
the
logic
function
as
used
in this
instrument,
and
may
differ
from
the
manufacturer's
data
.
All
logic
functions
are
described
using
the
positive
logic
convention
.
Positive
logic
is
a system of
notation
where
the
more
positive
of
two
levels
(H
I) is
called
the
true
or
1-state
;
the
more
negative
level
(LO)
is
called
the
false
or
0-state
.
The
HI-LO
method
of
notation
is
used
in
this
description
.
The
specific
voltages
that constitute
a
HI or
LO
state
may
vary
between
individual
devices
.
Wherever
possible,
the
in-
put
and
output
lines
are
named
to
indicate
the
function
performed
when
at
the
HI
(true)
state
.