OL3.APR–Tektronix–wy
Oscilloscope makers ride the color bandwagon
New displays bring less-expensive color to digital scopes
Color displays offer substantial benefits to oscilloscope users. However,
with traditional CRT displays these benefits come at a price not everyone
is willing to pay. Two major scope manufacturers are addressing the
problem with new digital scopes using nontraditional color displays.
Two recent announcements will be welcomed by oscilloscope users who crave
the visual advantages of color displays, but don't want to pay large
premiums for them. The first involves a digital storage oscilloscope (DSO)
introduced by Tektronix (Beaverton, OR), that incorporates a proprietary
full-color shutter CRT display that Tektronix says is a breakthrough in
color display performance and price. The display is a major departure from
that of the traditional shadow-mask CRT display used in the few color
scopes that have been available and in color monitors for computers and
televisions. The second announcement, from Gould Test & Measurement
(Cleveland, OH), is that it will also soon introduce a color DSO that will
also depart from the traditional shadow-mask technology. The shadow-mask
color display has been around for about 40 years. In this display, three
electron beams–usually produced by three electron guns–excite either
stripes or dots of color on the display's phosphor screen (see diagram a).
When excited simultaneously by the three electron beams, the closely
positioned stripes or dots are blended by the viewer's eye, allowing for the
creation of a large number of colors on the CRT display. Although the
shadow mask can create a wide spectrum of colors, it does so at the cost
of display resolution. Furthermore, the three electron beams pose
substantial accuracy problems. To excite each set of color dots or lines,
the three electron beams must move closely in unison and converge
precisely. If they don't, they create blurred and falsely colored images.
Shadow-mask CRT displays also tend to be relatively power hungry, bulky,
and sensitive to shock and vibration. The Tektronix NuColor display, in
sharp contrast with a shadow-mask color display, uses a monochrome CRT
with a single electron beam (see diagram b). A liquid-crystal shutter,
incorporating ultra-thin liquid-crystal optical switches with color
polarizers and neutral polarizers, creates the color images.
How NuColor works The NuColor monitor produces color images by
sequentially displaying the red, green, and blue field information on the
CRT. The liquid-crystal switches, called pi cells, govern the display of
the three color fields. The color components of the image alternate so
rapidly that the eye integrates them to create a full-color image. By
using a color-field rate of 180 Hz for sequencing through the three color
fields, the NuColor system produces a complete color picture at the
conventional color CRT's 60-Hz frame rate. To generate the spectrum of
colors, the system simply varies the intensity of the electron beam in
each field. Capable of extremely high contrast, the NuColor system produces
a true white by displaying the same image in each field. The system
creates a deep black by not displaying an image at all during a
color-filter sequence. The NuColor approach provides far superior color
purity, convergence, and resolution than a shadow-mask CRT, according to
Chris Martinez, Tektronix's marketing manager for the TDS Series scopes.
In addition, the NuColor display, with only one instead of three electron
guns, should provide higher reliability and lower power requirements. The
first use of the NuColor display is in Tektronix's TDS 544A and TDS 644A
DSOs, the two latest members of its TDS family. These high-performance
scopes have four channels; 500-MHz bandwidth; sample rates of 1 Gsample/s
on the TDS 544A and 2 Gsamples/s on the TDS 644A; up to 15 Kpoints per
channel record length on the TDS 544A and 2 Kpoints on the TDS 644A; 8-bit
resolution, and 1% accuracy on the TDS 544A and 1.5% on the TDS 644. They
are priced at $16,790 and $21,490, respectively. These prices include a
broad range of very useful features, such as powerful logic triggering,
extensive digital signal processing, template generation, pass-fail
limits, and 25 automatic waveform measurements. The substantially lower
cost of the NuColor display when compared with traditional shadow-mask
displays played a big part in Tektronix being able to price the scopes so
aggressively. Shadow-mask displays used in color DSOs (including their
additional memory, power, and circuit needs) from Tektronix,
Hewlett-Packard, and LeCroy in the past have added about $2,000 to $3,000
to the cost of a color scope. The estimated added costs with the NuColor
display is only about $500 or so, according to Martinez. In another
announcement, Gould Test & Measurement (Cleveland, OH) said that the
company will introduce a color DSO starting at about $7,500 in May or
June. The scope, which will be available with up to four channels, will
have a 150-MHz bandwidth and 100-Msample/s sampling rate. This scope,
like the new scope from Tektronix, avoids the shadow-mask color CRT.
According to Gould sources, the scope will use a high-resolution backlit
color LCD display, the first use of such a color display in digital
scopes. For more information from Tektronix, call the Test and
Measurement Group in Pittsfield, MA, at 800-426-2200. For more from Gould,
call the Test & Measurement Div.at 216-328-7313 or . –Warren Yates
CAPTIONS:
A color display, such as the TDS 544A from Tektronix, can be of great
help to the user in interpreting the waveforms and data present on a
multiple-trace DSO.
DIAGRAM:
In Tektronix's DSOs using the NuColor display, the traditional three-gun
shadow-mask CRT (a) is replaced by a new type of color CRT developed by
Tektronix (b).
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