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SECTION
5
GENERAL THEORY OF OPERATION
5.1
INTRODUCTION
5.1.1
This section describes the
general theory
of operation
for
the 1994.
5.1.2
The
theory of operation provided
is
based on
the
simplified overall
block
diagram
shown
in
Figure
5.1.
Key
circuit
blocks
of the
1994
are described
and supported
in
this
section
using
simplified
block
and schematic
diagrams.
These diagrams
supplement
the
complete schematics found
in
Section
7
of
this
manual.
As
much
as
possible,
the simplified
schematic
and block
diagrams
provided here are
annotated with
the
same
reference
designators found
in
the
complete
schematics. This should
facilitate
cross-referencing
between
this
section of
the
manual and
the
schematics
Integrated
circuits
(ICs)
in
the
following
circuit
descriptions
are
designated
by
circuit
references
provided on
the
supporting simplified
block
and
schematic diagrams.
The
IC
designations
employed
in
the
following
key
circuit
descriptions follow those
found
in
supplied
schematics.
When
an IC package
contains
more
than one
circuit,
suffix
letters
are
used
to
distinguish
them
(e.g.,
ICla).
Finally,
when
it
is
necessary
to identify
a
specific pin
in
an
IC, the
reference designator, with a
suffix letter
if
necessary,
is
followed
by
a
hyphen and
then
the required pin
number
(e.g.,
ICla-1).
5.2
FUNCTIONAL BLOCKS
5.2.1
The
1994 contains
the
following ten
main
functional blocks:
a.
Channel
A/B
block
(see
Subsection
5.3.1)
b.
Channel
C
block
(see
Subsection
5.3.2)
c.
Measurement
block (see
Subsection
5.3.3)
d.
Display block
(see
Subsection
5.3.4)
e.
Keyboard
block
(see
Subsection
5.3.5)
f.
Microprocessor block
(see
Subsection
5.3.6)
g.
Standby and
IRQ
block
(see
Subsection
5.3.7)
h.
Power
Supply block
(see
Subsection
5.3.8)
i.
Internal
Frequency Standard
block
(see
Subsection
5.3.9)
j.
GPIB
Interface
(see
Subsection
5.3.10)
5
'
2
*
2
The
functional relationship
between
the blocks
of the
1994
is
illustrated
in
Figure
5.1.
The measurement
block
is
internally
configured by
the
microprocessor
according
to
the
instructions
entered
via
the
keyboard
or
over
the
GPIB.
The
signal to
be
measured and
the
signal
from
the
frequency standard are
fed
to the
measurement
block.
The measured
result
is
passed
to
the
microprocessor.
If
mathematical manipulation
of
the result
is
required,
this
is
performed by
the microprocessor before the
final
output
is
passed
to
the display
or
system.
5-1
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