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1
SERVICE INFORMATION FROM HEWLETT-PACKARD
-
INSIDE
\
MARCH-MAY 1981
Elements and Terminology
In all X-Y display applications, the
purpose is to draw an image on the
screen for human interaction. How-
ever, before discussing the methods
of drawing these images, it is impor-
tant to discuss display-related ter-
All About CRT's minology and some of the important
elements of a picture. Once this
By Jim Bechtdd, Editor
common ground is established, the
methods of forming a picture can be
analyzed in detail.
The important aspects of any picture
are resolution, brightness and data
density.
An oscillompe is 811 in&rument
In 1879, William Crookes demon-
signals is applied to the horizontal
deflection (X-axis) sysbm, and the
strated the ability to deflect cathode
rays in a vacuuIll tube with a mag- beam spot divided i t
no
net. Cathode rays had earlier been
Sh e of causing phos- ity of a spot is not uni-
Ph the glass walls of a its diameter, measure-
vacuum tube, but control of the area ment of spot size is not an exact
of phosphorescencewas only possible SCienCe.
Csometimes called the vi& signal)
by using shaping masks (solid struc-
tures in the tube incapable of pro- appligd to %e Z-axis system. Such a
h
ducing dynamic deflection). The Minition includes not only oscillo-
combination of focusing elements to
scopes and other related electronic
produce a narrow electron beam (or
cathode ray) aimed at a fluorescent
target with dynamic electromag-
netic-beam deflection became known
as a Crookes tube. The Crookes tube, way the picture is formed on the
later to be commonly known as a screen ofthe CRT. In an ac3cillormpe,
cathode-my tube (CRT) or more pre- exted control the vertical
cisely as an electron-beam tube, of- and hsr movement of the
fered much promise for displaying electron beam. The path the beam
high-sspaed variations that could not traces on the phosphor e the CRT is
f lNTEGRATD CIRCUIT
be demonstrated on mechanical CROSS REFERENCE
atus. By 1897, CarlF. Bra-
cted a "variable current SERVICE NOTES
by using the Crookes
e first forerunner of the
modern dllwxope.
Prut No. 5952-0108
WWW.HPARCHIVE.COM
*'
`I
:I ALL ABOUT rqTS
To test spot size resolution, a raster Raster Electromagnetic
is displayed on the screen and re-
duced in size until the lines just be- Raster is a predetermined pattern of Magnetic deflection systems utilize
come indistinguishable. At that scanning lines that provides sub- an inductive coil (called a yoke) sur-
point, the size of the raster is meas- stantially uniform coverage of an rounding the neck of the CRT
ured and divided by the number of area. In other words, the raster is through which a current signal is
lines in the raster to determine the the rectangular pattern of light passed to generate a magnetic field
resolution. which appears on the CRT screen to deflect the electron beam (see
when the screen is scanned by the Figure 1).At high frequencies, in-
electron beam. ductors with few turns are necessary
to obtain fast current changes, and
Addressable resolution, on the other larger currents are required to
hand, has nothing to do with spot Z-Axis obtain the required field strength.
size, but simply is the incremental Consequently,above repetition rates
accuracy in which the beam can be This refers to that part of the display of 20 kHz, large power dissipations
positioned. The smallest positional that controls CRT intensity. It in- are required to obtain full-scan dis-
movement of the electron beam cludes the input circuit, an amplifier plays. Most television sets and com-
divided into the CRT dimensions (called the Z-axis amplifier), and the puter display terminals use the
then gives the addressable resolu- circuit that drives the CRT control magnetic deflection scheme.
tion. Unlike spot resolution, ad- grid. The control grid controls the Electrostatic
dressable resolution is an exact amount of beam current allowed to
computable number. It is important fall on the phosphor at the front of Electrostatic deflection systems con-
to realize that addressable resolu- the tube which varies the intensity sist of complex electron gun struc-
tion holds no fixed relationship to of the picture. tures containing two sets of deflec-
spot resolution. Addressable resolu- tion plates; one set for horizontal
tion can be either greater or less deflection and one set for vertical
than spot resolution. The relation- CRT Deflection deflection (see Figure 2). Electrosta-
ship of addressable resolution to spot Fundamentals tic deflection, involving voltage
resolution does play a significant charging of capacitive plates to de-
role in the perceived "quality" of a Now that some of the basic CRT flect the electron beam, is capable of
display or picture. More on this elements and terminology have been speeds several orders of magnitude
later. identified, let's discuss beam deflec- higher than electromagnetic for a
tion techniques. There are two comparable amplifier cost (but not
methods of deflecting the beam CRT cost). Since even inexpensive
inside the CRT; electromagneticand industrial oscilloscopes generally
Brightness electrostatic. are capable of displaying 500 kHz or
Brightness is simply the light output
of the picture being displayed. The
relative light output of a displayed
picture is significantly different
from the maximum light output
capability of the CRT as will become
apparent later.
Data Density
The amount of data displayed (data
density) is simply the area of the
CRT screen that is lit versus the en-
tire screen size (or the amount of lit
area versus dark area). The lit por-
tion of the screen consists of all the
alphanumeric characters and vec-
tors (lines) that comprise the picture
being displayed.
.I '
mechanical distance from
as feasible. This optimizes
sensitivity by providing the grea
deflection distance at the screen per
volt, or gauss, of applied deflection
field. In the electrostatic CRT, the
plates must also be reasonably close
together to achieve svfficient d d e e
tion field etrength with ail applied
voltage in the range of 300 volts. A
greater swing would create signifk-
ant X a n amplifier design
P
Electrostatic displays have fasterd&
and use less current
that electromagnetic displays. TAis
i the result of physics; the load of
s
the deflection plates is only the stray
capacitance of a few pieofma&. On
the other hand, the inductance ofthe
yoke is the load to t h e driving
amplifiers. The higher the induc-
tance (Le., more turns and stronger
magnetic field), the easier it is to de-
flect the beam; however, higher in-
ductance requires high power. To
lower the inductance reduces power
requirements but also reduces de-
flection sensitivity. This then
requires reduction in accelerating
potentials in the CRT so that the
Electromagnetic vs Electrostatic beam can be deflected full screen,
Given the same spot size, with dl which also reduces the light output.
The major differences between the other things equal, a n elec-
two systems are light output and tromagnetic CRT will be brighter Some further points of comparison
frequency response. The magnetic follow:
system generally offem more light due to the fact
output while the electrostatic sp- 1. LineurityiGeorne8ry: In order t~
tern offers high-speed response at achieve a linear deflection in a n
low power consumption. In addition, most of the beam current to pasns electromagnetic display, it is nec&&
magnetic deflection allows a wider through to the screen. The electro- sary to apply an "S"-shaped non-
beamdeflection angle than does static gun has a large number of linear voltage function to the deflec-
electrostatic deflection. Moreover, internal dements as shown in Fig- tion coils. To achieve good li
e full-screen deflection ure 2. Notice that the front-most
red is less than 20 element of the focus lens has a rela-
magnetic deflection tively small aperture, which strips
lifier and CRT) has a away 7040% of the beam current component caunt. For good geametay
t advantage over an just before the beam enters the de- (minimum barrel and pincushion
systan. This is one of f l d o n plate region. The gun is con- distortion1 in eleetrornagnetic dis-
telecwision sets, many
,and mme oscillo-
CIWB with elmi-
trontagaieeic deflection.
.I
a ALL ABOUT CRTS
.I
Electrostatic CRTs, on the other Vector If the beam is blanked (turned off)
hand, have inherently good linear- during movement and turned on at
ity. Only a variable dc voltage needs Other common names for vector rest, the picture will be comprised of
to be applied to an element in the drawing are "dot writing", "directed a series of dots on the CRT face (see
CRT for any minor geometric pat- beam", and "stroke writing." As the Figure4a). This type of "dot writ-
tern correction. name implies, the beam is succes- ing" lends itself well to the CRTs
sively moved to each new location by used in spectrum analyzers, air traf-
signals applied to the X (horizontal) fic control monitors, and other dis-
2. 2-Axis Delay: Since deflection and Y (vertical) inputs. In an oscillo- plays where annotation is displayed
coils act as a delay line, it is neces- scope, the directed-beam is linearly on the screen along with the main
sary to introduce delay into the Z- deflected to follow the signal pattern picture (see Figure 4b).
axis signal path in high-speed elec- in the vertical direction while often
tromagnetic displays. This coordi- using a constant deflectioh rate in
nates the blanking and unblanking the horizontal direction to represent
with the beam position; these delay time. If the beam is left on during Raster
lines are unnecessary in electro- the writing cycle (as in a standard
static displays. oscilloscope), the picture will be
comprised of curves or straight-line In a raster system, the beam follows
segments on the CRT face (see a fixed path covering the face of the
3. Resolution: In either type of CRT, Figure 3). tube in a series of interlaced parallel
there is a tradeoff of beam diameter lines (usually horizontal), with
vs brightness. Since a n elec- blanked (turned off) retrace lines
tromagnetic CRT passes so much (see Figure 5). In a raster system
more beam current, a much smaller there are two methods of modulating
spot size (higher resolution) can be the beam intensity; analog and
obtained a t the same level of digital.
brightness.
4. Weight: A high-speed elec- Analog modulation is used in televi-
tromagnetic display weighs 2-3 sion. The principle of operation in-
times more than a comparable elec- volves varying the intensity of the
trostatic display does. The power beam as it moves across the screen
transformer is bigger and more heat in aceordance with the picture im-
sinks are required to meet the pulses of the video signals applied to
higher power demands of elec- the grid of the CRT.
tromagnetic displays. The mass of
the yoke and the increased number
of components contribute t o the
The picture is traced line-by-line.
added weight.
The first odd-numbered line of the
picture is traced by one sweep from
left to right. When the beam reaches
5 . Cooling: Fast electromagnetic the right side of the screen, the hori-
displays require forced-air cooling; zontal blanking signal biases the
electrostatic displays require only tube beyond cut-off and the beam is
convective cooling. thus extinguished (blanked out).
The beam remains blanked out long
enough for it to move rapidly over to
CRT Picture Drawing the left-hand side of the screen
Fundamentals where it is in another position to
start the trace of the second odd-
numbered line of the picture. The
In addition to how the beam is de- horizontal blanking signal is now
flected inside the tube is the actual withdrawn and the beam moves
method in which the picture is across the screen as before, tracing
drawn. Again, two basic methods are another odd-numbered line of the
used; vector scan and raster scan. picture.
ALL ABOUT CRT'S
As this process is repeated again and
again, the vertical sweep signal is
applied to the vertical deflection sys-
tem of the CRT which causes the
beam to move gradually toward the
bottom of the screen. Due t o the
downward pull of the slowly moving
vertical sweep, each horizontal
scanning line will be slightly below
the preceding line.
is, the odd-line picture (first field) is
scanned in the first 1/6Oth of a sec-
method,.the face of to loeate d& and
titioned into r o w and columns of ond, the defiection
All of this scanning and modulation dots which are called "pixels." Refer
results in a picture of gray shades to Figure 6 Pixels are defined as the
.
where the beam intensity ranges smallest location on screen where
from full on to full off. In other the beam c81n be modulated on or off.
words, when the video signal The picture ia created from line
increases the beam intensity to full aots ptdaced by turn-
on, the phosphor on the CRT glows ing the beam intensity on and off at
brightly; and when the video cuts off appropriate times. Special effects
the beam intensity, the phosphor can be mated when the beam inten- minimize the power cons^^ of:
does not glow. Everything in be- sity is modulated at points between of aa energy-
tween is the gray range, which forms full on and off.
the picture.
' e "he other method of drawing the
p i d m in a raster format is by using
a digital signal to modulate the
For a low-cost alphanumeric display,
the raster ~UCBT). e h offers several
mtd
advantages over the directed beam.
First, it doesn't q u i r e accurate,
high-speed, and themfore expensive
1-k-analog e9nrverters. In-
it uses counter 88
.HPARCHIV$~%
I-
e
.- ALL ABOUT C R T S
I .
- -
The Final
Criterion - Resolution
In high resolution line drawing situ-
ations, continuous lines have sig-
nificant merit. It should be pointed
vector systems have con-
ines at all addressable reso-
lutions. Only the starting and stop-
ping point accuracy of the vectors is
sacrificed at lower resolutions. To
achieve continuous lines in a raster
system can place significant
requirements upon it. Since, in a
raster system, vectors are comprised
of a series of dots or pixels, in order
to achieve the effect of a continuous
cond Field - , line, the dots must be spaced so close
as to merge. In fact, they need to
Horizontal Spot M
overlap by approximately two-thirds
to three-quartersof the spot diame-
ter. This means that the addreisable
resolution (number of scan lines)
d
tion CRT requires 3 or 4 thowand
scan lines to achieve the same qual-
line in a vwbr
e, this has ex-
tremely adverse effecte on light out-
put, deflection systems, power, and
cost. Therefore, in high resolution
line drawing applications, the "qual-
ity" of the continuous line may also
become an issue.
Another example of resolution
restridion can occur when trying to
use a n alphanumeric raster-type
computer terminal to &play a volt-
age vs time phenomenon. Remember
modulated raster scan method used
to generate alphanumeric characters. that this type of CRT is the digital
This example shows a bask 7 pixel raster type with a fixed scan rate
wide by 9 pixel high character cell as that modulates pixels on and off
with a certain portion of time set
aside for retrace.
the 7 x 9 matrix are used for
descender areas of lower case letters
and underlining. one pixel is used on
either side for character-to-character If the event you are trying to capture
spacing. In this particular example the is nonrecurring, it may occur dur-
display screen has a low aspect ratio ing retrace, or if it is quick enough,
of 5 x 10 inches, for a capacity of 1920 in-between pixels. In either case, the
character cells partitioned into 24 CRT will not show the phenomenon.
rows of 80 characters each. That
equals 259,200 pixels (720 horizontal Remember that our example shown
by 360 vertical). in Figure 0 has ony 720 pixels of
visual horiumtal resolution.
t SERVICE TIPS ?
For Customers Who Repair Their Own
Accessory Kit
1 ee 3/32hex drive
1ea 16-pin I d i p
C
1 ea ZO-pin IC clip
I
a
New Test Procedures contained in either the 0854-90012
or 0854-90025 Operating and Ser-
vice Manuals.
8 5 3 Signal Generator
643
I
A new h c e note (8654B-1) has The new procedures require less test
that provides improved equipment, are faster and simpler,
pr-
e$ tests and a&uatmentcS and are more thorough and accurate
for the 8664B Signal Generator. than the procedures in the manuals.
Test set-ups, recommended test
The 30-page prformance test re- equipment and perfmmance test
places the correspanding procedures reeoLds 8 ~ a8 l p w i d d .
l
WWW.HP RCHIVE.COM
8662A Verification
Tape Available
I
A tape cartridge containing 1 pro-
1
grams w i h check the operation of
hc
the 8062A Synthesized Signal
Generator via H B now avail-
@ is
able. These programs run on the
9825 desktop computer and w e 811
8 6 r or 8566A Spectrum Analyzer
58A
a~the measuring instruInent. Them
pa
-, test all functiha of the
8622A except modulation &Won.
Although the tests are not complete
performance tests, they are very
~
thorough and should find most any
problem that an insbumkt might
have.
These programs are very easy to w
aad can rununattended. B i l am
aub
printad if a line
WWW. HPARCHIVE.COM
INTEGRATED CIRCUIT CROSS
Integrated Circuits
Replacement Part Cross Reference
When plelecting replaoement parts tance, etc. There may d o be slight
s To help you in these situations,
for your NP products, you may mechanical differences, such as the here's a cross-reference o HP inte-
f
notice that many manuals list only shaping or length of leads. In some grated circuik part numbers to man-
a n HP part number for the part, cases special quality checks are ufacturers "generic type" part num-
even though it appears that this part employed to ensure that high relia- bers (whom i n most cases is the
bility parts are qsd at the factory originah of the part), Even though
and at HP field ofti-. the crorss-reference only lists 011s)
Thedore, we suggest obtaining re- mmufiuturer, th- may actusrlly be
placement parts from HP to main- several approved mu~cces an HP
for
t i the quality that you have paid
an part. While every attempt was made
It is recommended that HP replace- for in your instrument. There may to ensure the accuracy of the list, it
ment parts be used to ensure that be situations however .where HP re- is advisable to compare the descrip-
the original perfommce of the pro- placement parts are not in etock and tion of the device being replaced
substituting parts will allow you t o with the description of the substi-
return the product to service im- tuted part. For example, if the serv-
identical to that mediately. In these cases it may be ice manual describes the device
chased at a local electronics dis- worthwhile to see if a substitute part being replaced 88 8 " d d J-K f i -
lp
tributor, many t m s parts will be
ie will work in the circuit. Perhaps an flop",check this against the descrip-
selected for certain characteristics, HP part could be ordered and in- tion of the replacement part.
such as gain, bandwidth, capaci- stalled at some later date.
oo(x39 Amperex E M . Corp. Semicon. EL MC Div.
00350 National semiconductor Corp.
00575 Tdedyne, PMlbrWc Nexus
015m opafrau lnc
01- knsltcan Mkro system Inc.
017s May Inc.
01870 wsystenv3corp.
01e1 E m Arrays, Inc.
01973 Inteoh Inc.
01s9l Adwnced M0 Devices Inc.
i
a
02a23 Motorda Inc.
(12037 Harris S e m i i . Div. Harris-Intertype
02180 l t corp.
nd
02237 M s& corp.
ot
02290 Monolithic M m re Inc.
e ois
02569 Nitron Dhr. McDormell Douglas corp.
02598 spm@wElectric Co.
02634 BunBromco.
02713 SGSAtes
02763 Lamwa Ekdroniar Corp.
02838 f3iwnms Corp. Components Group
0
- Data M y Devices
02883 zlloa fnc.
02910 Texas Instruments France
03183 Hybk Microsystems Inc.
03285
HP Pm 181s- 0 0 12882 zn 1 8 1%-OIL1 03195 niiis&-ionnz
1'11s- 0 0 13406 Lb 1811-0082 02598 PIC646
0950-9566 101J- E 0 13I95 K1 1813-0083 02S98 PIC601
09b0-056I 1813- 0I O 13195 I1 1813-0014 02598 C l C 6 1 1
0950-0.169 1813- I IO 13795 KI 1013-0083 83795 UiIOOA-27UWZ
O%O-0570 1813- 0 0 1379s K1 1813-009s OS*S6 OAC80-CCO-V
0960-0512 1813- EIO 11285 13 1813-0093 I 02257 UA111412X
0960-OS81 1015- IOI 12163 21 1813-0091I oms1 ~ D C ~ O I E - L ~
096B-Wll 1813- I 52
IO I3793 KI l e l 6 a l O lI 02237 UAIOWOSSC
0960-0632 1815. 9I1 53 11795 K1 1013-010