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Geometry and Focus Control Section
AN1290
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STMicroelectronics Confidential
6.2
Application Hints
6.2.1
E/W Output Stage
An output inverting amplifier has been designed to ensure the interface with an E/W diode
modulator (see
Here are some explanations on its design.
This is a simplified power op-amp with high, sink-only current capability.
Design data: R
15
= 1k
Ω
, R
9
= 470
Ω,
R
38
= 2.2
Ω
(negligible)
If V
i
is the input voltage and since we have an op-amp, the following relation holds:
or,
On pin 24, a parabolic voltage with minimum value approximately 2V is available. The peak value is
approximately 8.5V with VAmp, Breathing, Pincushion, Keystone and Corner corrections set to their
maximum value. We must choose the various resistors so that the output voltage will be
approximately 0V when the input is 2V, and will be at the maximum value when the input is 8.5V.
The maximum output is estimated at 40V for the maximum frequency (to be compared with
approximately 200V of B+); less is needed at lower frequencies.
The output must be able to go down to near ground when V
i
= 2V, therefore:
Figure 17: E/W Amplifier
24
To diode
modulator
TIP 122
38
19
17
15
33
9
18
220p
Vd
Vi
Vs=12V
To sub-HSize DAC
470k
V
d
V
i
–
R
19
-------------------
V
s
V
i
–
R
17
------------------
+
è
ø
ç
÷
æ
ö
V
i
R
18
-----------
=
V
d
R
19
-----------
V
i
1
R
19
-----------
1
R
17
-----------
1
R
18
-----------
+
+
è
ø
æ
ö
×
V
s
R
17
-----------
–
=
0
V
i
1
R
19
-----------
1
R
17
-----------
1
R
18
-----------
+
+
è
ø
æ
ö
×
V
s
R
17
-----------
–
è
ø
ç
÷
æ
ö
=