THEORY OF
OPERATION
3-22.
Amplitude Modulation
The
Generator allows amplitude
modulation depth
programming
from
0 to
99%
with
1
%
resolution.
However, the
maximum
calibrated
AM
depth is
90%.
Programming
an AM
depth greater than
90%
causes the 'UNCAU
indicator to light.
When the combination
of
signal
amplitude and programmed
AM depth
exceeds
+13 dBm
peak,
the ‘UNCAL’
indicator lights to warn
you the output level
is
no longer
guaranteed.
Amplitude
modulation depth is
programmed
using the
8-bit
AM DAC, with
a setting of
200
on the
AM DAC corresponding
to
100%
AM
modulation
of the
output frequency.
3-23-
Frequency
Modulation
Frequency
modulation (FM) is
programmable
with
three digits of
resolution
in the three
decade ranges. Table 4D-12,
FM Ranges,
lists
the three ranges.
3-24.
FM
Deviation
The FM DAC
is a 10-bit DAC
programmed
to the FM
deviation
in Hz divided
by the
resolution.
Table
4D-13 lists the settings
of the FM DAC.
3-25.
Self Test
At
power-on,
the
Generator
automatically
self tests its digital
and
analog circuits. If
the
Generator
fails
any self test, the test
results
are automatically
displayed as error
codes.
Several
special functions are available
for additional
tests.
(See section 4D-1
6.)
Also, the
Generator microprocessor
continuously
monitors
two status
signals,
UNLVL
(unleveled)
and UNLOK
(unlocked).
The self tests can also
be invoked
by using the
[SPCL]
[0][2]
keys.
The
results of the self
test can be displayed in the
four display fields
with
[SPCL]
[IJl] keys and can also
be
transmitted
using the optional IEEE-488
Interface.
Self tests I through
5 are digital checks
that
indicate the
general functionality
of
the
Controller
assembly. Self tests
6
through
10 use the
two status
signals
UNLVL and
UNLOK
to test the general
functionality
of the RF
circuitry.
During the self-test
sequence
all attenuators
are programmed
ON (maximum
attenuation) to prevent
unwanted signals at
the output. In
addition,
the Generator is
programmed to the
internal frequency
reference
because the
self tests fail if there
is
no
reference
supplied.
The
self-test error codes and
descriptions are
listed
in Section 4D.
A brief description of
the different Generator
self tests are described
in the following:
Test 1 . The
Generator RAM
is
verified by writing data
to
each
memory location
and checking that
the
same data can
be read
back. Both the off-chip
RAM and the
on-chip
RAM are tested
in
this way.
Test 2. The data in each
word of the two instrument
software EPROMs is
successively summed
and rotated by two. The
result
of this procedure is
compared with a checksum
for each EPROM.
Test 3. The data in each of the three calibration
EPROMs
(VCO, Output, and
Attenuator) is summed and compared with
a checksum.
Test 4. The
IEEE-488 (if
installed)
is verified
by the microprocessor writing
data
to the IEEE-488
chip and then
by reading it back
to see
if the response is
the
one
expected. The
operator is given
a report only if the test fails.
3-6
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