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APPLICATION BULLETIN
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DRIVING VIDEO OUTPUT STAGES
WITH MONOLITHIC INTEGRATED AMPLIFIERS
By Christian Henn, Burr-Brown International GmbH
Increasingly powerful computers and the rapidly expanding
use of picture processing and CAD/CAM systems in almost
all industry branches have combined to generate a greater
and greater demand for higher resolution graphic monitors.
Controlling the video output stages of these graphic moni-
tors is a key to producing such high resolutions. Until
recently, only highly complex, expensive systems have been
available to drive hybrid video output stages. But using the
monolithic amplifiers OPA623 and OPA2662 from Burr-
Brown, new methods are possible that make complicated
solutions a thing of the past. The OPA623 allows rise (t
RISE
)
and fall (t
FALL
) times of 3ns and 2.3ns, respectively, at the
output, while the OPA2662 is even more impressive at t
RISE
= 2.4ns and t
FALL
= 2.15ns. With this kind of performance,
the OPA623 and OPA2662 can be used in graphic systems
with resolutions of 1600
x
1200 pixel and more.
HIGH-RESOLUTION PICTURE
PROCESSING SYSTEMS: AN OVERVIEW
The various standard resolutions range from the commonly
used VGA standard with 640
x
400 pixels to the super VGA
with 800
x
600 pixels to CAD/CAM and radar systems with
over 1600
x
1200 pixels. But while radar and computer
tomography systems generally use high-resolution 1600
x
1200 color graphic monitors, monochrome displays with
2k
x
2k resolution and 500MHz bandwidth are now in
development. To achieve such high resolutions, the moni-
tors use horizontal deflection frequencies for electron rays
between 64kHz and 96kHz, as well as data rates between
100Mbit/s and 250Mbit/s, which are read out from the video
RAM card. Raising the vertical deflection frequency to more
than 70Hz causes the horizontal frequency and data rate to
increase while the resolution remains the same. Controlling
the pixels by the video controller adds to the demands on the
video amplifier, and significantly increases the power con-
sumption during video signal processing. Instead of a con-
tinuous video signal, the video card produces pulse se-
quences that return to zero between every two pulses. The
amplitude of each pulse is equal to the luminance of the
respective color (R, G, B). An additive optical mixing
process produces the correct color on the screen. For this
reason, displaying the color white at the maximum ampli-
tude is the toughest job for the video amplifier in graphic
monitors.
Table I summarizes the various timing requirements
necessary to produce the most commonly used graphic
formats. The T
H ACTIVE
can be calculated by multiplying the
horizontal cycle time by 0.8, and it includes time for the
electron ray to return from the right side to the left side of the
screen during the horizontal retrace time. When calculating
t
RISE
and t
FALL
, it was assumed that each was one third of the
pixel time. The 鈥?dB bandwidth (f
鈥?dB
) is dependent upon
the rise time and can be calculated as 0.35/t
RISE
.
The video signal levels at the interface between the video
card and monitor are standardized at +0.7Vp for the video
signal and 鈥?.3Vp for the synchronization pulse. A high-
resolution cathode ray tube (CRT) functions with bias volt-
ages between +65V and +75V and a modulation voltage of
+0.7V
Graphic Card
0V
鈥?.3V
T
H ACTIVE
T
H
+65V
Cathode Voltage
50Vp-p Contrast
max
+15V
0V
FIGURE 1. Pulse Sequences from a Signal Graphic Cathode.
PIXEL/CLOCK
FREQUENCY
(Hz)
25M
38M
102M
152M
SYSTEM
STANDARDS
VGA
Super VGA
CAD/CAM
Work Station
RESOLUTIONS
H
x
V
640
x
400
800
x
600
1280
x
1024
1600
x
1200
f
H
(Hz)
31.5k
38k
64k
76k
f
V
(Hz)
70
70
60
70
t
H
(
碌
s)
31.74
26.31
15.62
13.15
t
ACTIVE
(ns)
25.39
21.04
12.49
10.52
TIME/PIXEL
(ns)
39.67
26.30
9.75
6.57
t
RISE/FALL
(ns)
13.22
8.76
3.25
2.19
鈥?dB BW
(Hz)
26.47M
40M
107M
160M
TABLE I. Timing Requirements.
漏
1993 Burr-Brown Corporation
AN-184
Printed in U.S.A. November, 1993
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