Section IV
,====REF.
DIVIDER====>.
(P/0
A9
I
REF.
DIVIDER
(R79-R88)
-0.75V
E1QJ
-1.ov
BQl
-lo25V
BQ]
cw
-1.5V
BQ]
ILOG.
ldBI
-
'
-l.75V
8QJ
-2.ov
E?Ql
I
'
AMPLITUDE L
I
REF
LEVEL
-2.25V
EiQJ
-2.5V
[QI
y
ILOG
IOdBI
I
I
_._
I
LOG
' I
OFFSET
'
LIN OFFSET
3580A
-8-3604
OV
TO
+2o5V
VIDEO
IN
FROM
VIDEO FILTER
GAIN
I
GAIN
2
44o2K
OFFSET
402K
r! 20K
VIDEO
Model 3580A
Rl25
+5V
TO
OV
=-----v-.IKl'v------
VIDEO
TO
AS
FOR
ADAPTIVE
SWEEP
20K
,---
---'V\/\.-----1
I I
' I
>----------'Vvv-..-
1
---;
[
Rl
29
OV
TO
+4.75V
">-<>--""I
Kl'v--.__
VI
DEO
DC
OFFSET
ADJ
-V
Rl40
19olK
TO
DIGITAL
STORAGE
Rl28
IK
~'V'l'v---<.
OV
TO
+5V
r VIDEO
Figure 4-9. Video Output.
output
is
limited to +6.8 V
de
by Zener diode CR29. An
output between
+5
V and +6.8 V positions the CRT trace
at the bottom
of
the screen.
If
the positive video level
equals the negative offset voltage, the output
of
the
Summing Amplifier drops
to
0 V for full-scale deflection.
If
the video level exceeds the offset voltage, the Summing
Amplifier output
is
driven negative and
is
limited to - 0.6 V
by CR29. An output level between 0 V and -0.6 V peaks
the display. Table 4-2 lists the offset voltage, displayed
video levels, Summing Amplifier output levels and display
range for each AMPLITUDE REF LEVEL setting.
4-65. The output of the Summing Amplifier
is
applied
to
the
A8
Assembly through
RI
25
and to the Output
Amplifier. In the
A8
Assembly, the video output from the
Summing Amplifier
is
used
to
detect the presence of a
video response for Adaptive Sweep purposes.
4-66. At the inverting port
of
the Output Amplifier, the
+ 5 V
de
to 0 V output from the Summing Amplifier
is
summed with a - 5 V
de
offset from the wiper
of
the
DC
Offset Adj. potentiometer,
RI
I.
The
gain
of
the Output
Amplifier
is
XI and the resulting output ranges from 0 V
de
to + 5 V de, full scale. This output
is
attenuated to
+ 4.75 V
de
full scale by RI 29 and
RI40
and applied
to
the
Digital Storage section. The 0 V
to
+ 5 V output
is
also
applied to the rear panel Y-AXIS output connector.
4-67.
Frequency
And
Sweep
Section.
4-68. Figure 4-10
is
a functional block diagram
of
the
Frequency and Sweep Section. Elements shown on the
diagram are -described in the following paragraphs.
4-69. Linear Sweep Gerierator. Because
of
its Adaptive
Sweep capability, the 3580A Linear Sweep generator
is
considerably more sophisticated than conventional sweep
generators. The primary purpose
of
the Linear Sweep
Generator
is
to produce a 0 V to + 5 V linear ramp which
simultaneously sweeps the VTO frequency and the refresh
trace on the CRT.
In
the Adaptive Sweep process, however,
it
is
required
to
perform a sequence
of
operations in
response to video signals that rise above the baseline
threshold set on the CRT display. This sequence or
"algorithm"
is
illustrated and described in Figure 4-I
I.
Table 4-2. Video
Output
Circuits (Log 1 dB mode).
Reference Offset Displayed Video Summing
Amp
Display
Level
Voltage
Level
Output
Range
OdB
-2.50
v + 2 .25 V
to
+ 2 .50 V +5
Vto
0 V
-10
dB
to
OdB
-10
dB
-2.25
v
+
2.00
V
to+
2.25
V
+5VtoOV
-20dBto-10dB
-20dB
-
2.00
v
+
1.75
V
to+
2.00
V
+5VtoOV
-30
dB
to-20dB
-30dB
-1.75
v + 1 .50 V
to
+ 1 .75 V
+5
Vto
0 V
-
40
dB
to
-
30
dB
-40dB
- 1.50 v + 1 .25 V
to
+ 1 .50 V
+5
Vto
0 V -
50
dB
to
-
40
dB
-50dB
- 1.25 v + 1 .00 V
to
+ 1 .25 V
t5VtoOV
-
60
dB
to
-
50
dB
-60dB
-1.00
v
+
0.75
V
to+
1.00
V
+ 5
Vto
0 V
-
70
dB
to
-
60
dB
-
70
dB
-
0.75
v
+0.50Vto+0.75V
+5
VtoO
V
-80
dB
to
-70
dB
4-8
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