U.S. patent number 3,833,832 [Application Number 05/372,543] was granted by the patent office on 1974-09-03 for electronic conditioning of gas discharge panels by inversion internal extension.
This patent grant is currently assigned to Owens-Illinois, Inc.. Invention is credited to Michael E. Fein, Jerry D. Schermerhorn.
United States Patent |
3,833,832 |
Fein , et al. |
September 3, 1974 |
ELECTRONIC CONDITIONING OF GAS DISCHARGE PANELS BY INVERSION
INTERNAL EXTENSION
Abstract
The conditioning or priming of multicelled gas discharge
display-memory panels, of the type in which a discharge in a
hermetically enclosed ionizable gas generates charges alternately
collectable on pairs of discrete areas of spaced dielectric
surfaces which are backed by conductors of first and second
conductor arrays to define a plurality of discharge cells, is
enhanced and their operation made more reliable by periodically
inverting the state of all cells in the panel. Extension of the
interval of inversion of the discharge state of the panel beyond
the half period of a normal sustainer voltage cycle increases the
probability that the cells normally in the "off state" will be
transferred to the "on state." This improvement permits less
frequent inversions of discharge state without detriment to the
cell writing reliability of the panel thereby enhancing the
contrast ratio between "on" cells and "off" cells. A clocking
circuit for regular sustainer voltage cycles and for a regular,
periodic, extended interval device inverting sustainer voltage is
shown with a number of sustainer wave form constructions for the
inverting condition.
Inventors: |
Fein; Michael E. (Toledo,
OH), Schermerhorn; Jerry D. (Swanton, OH) |
Assignee: |
Owens-Illinois, Inc. (Toledo,
OH)
|
Family
ID: |
23468588 |
Appl.
No.: |
05/372,543 |
Filed: |
June 22, 1973 |
Current U.S.
Class: |
315/169.4;
345/60; 315/174; 315/166; 365/116 |
Current CPC
Class: |
G09G
3/294 (20130101); G09G 3/297 (20130101); G09G
3/296 (20130101); G09G 2310/0254 (20130101); G09G
2320/0228 (20130101) |
Current International
Class: |
G09G
3/28 (20060101); H05b 041/29 () |
Field of
Search: |
;315/166,169R,169TV,174
;313/18B ;340/324M |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: LaRoche; Eugene R.
Attorney, Agent or Firm: Wedding; Donald Keith
Claims
What is claimed is:
1. The method of operating a gas discharge display/memory panel of
the type in which a discharge in an enclosed ionizable gas
generates charges alternately collectible on pairs of discrete
areas of spaced dielectric surfaces which are backed by conductors
of first and second conductor arrays respectively to define a
plurality of discharge cells, each including a pair of opposed
discrete charge storage areas comprising:
applying trains of a plurality of cycles of a first alternating
sustaining voltage wave form having a regular cycle period across
the first and second conductor arrays;
selectively interposing between said trains a second alternating
sustaining voltage wave form having levels displaced from the first
sustaining voltage to apply voltages across the first and second
conductor arrays tending to invert the discharge states of all
cells comprised of conductors of the first and second conductor
arrays from the discharge states established for those cells during
application of the first sustaining voltage; and
extending the time interval of application of an excursion of the
second sustaining voltage in the direction of the displacement of
the second sustaining voltage from the first sustaining voltage for
a time interval exceeding the time interval of an excursion in that
direction of the regular cycle of the first sustaining voltage wave
form.
2. The method according to claim 1 including the step of
maintaining each train of the first alternating sustaining voltage
wave form for a long interval relative to the interval of
application of the second alternating sustaining voltage wave
form.
3. The method according to claim 1 wherein the step of extending
the excursion of the second sustaining voltage is during the
initial excursion of the second sustaining voltage in the direction
of the displacement of the second sustaining voltage from the first
sustaining voltage.
4. The method according to claim 2 wherein the length of the
extended interval of excursion is a direct function of the length
of the interval the train of cycles of the first sustaining voltage
is maintained between applications of the second sustaining voltage
wave form.
5. The method according to claim 2 wherein the interval the train
of cycles of the first sustaining voltage wave form is applied is
of the order of a millisecond.
6. The method according to claim 1 wherein the regular period is of
the order of 20 microseconds and wherein the extension of the
excursion of the second sustaining voltage is of the order of 40
microseconds.
7. The method of operating a gas discharge display/memory panel of
the type in which a discharge in an enclosed ionizable gas
generates charges alternately collectible on pairs of discrete
areas of spaced dielectric surfaces which are backed by conductors
of first and second conductor arrays respectively, each pair of
opposed discrete charge storage areas comprising a discharge cell,
comprising:
imposing trains of a plurality of cycles of a first alternating
sustainer voltage wave form having a regular cycle period between
the first and second conductor arrays to develop a first "off" cell
wall voltage for cells in the "off" discharge state and a first
"on" discharge state periodic alternating wall voltage for cells in
the "on" discharge state having charges alternately collectible on
the dielectric surfaces;
between each train of the first alternating voltage shifting the
sustainer voltage level applied between the first and second
conductor arrays to an inversion level which has an inversion "off"
cell wall voltage for cells in the "off" discharge state which is
essentially at the cell wall voltage level of the first "on"
discharge state cell wall voltage and which has an inversion "on"
cell wall voltage for cells in the "on" discharge state which is
essentially at the cell wall voltage level of the first "off"
discharge state cell wall voltage, whereby those cells in the "off"
discharge state during imposition of the first sustainer voltage
tend to be shifted to the "on" discharge state during imposition of
the inversion level voltage and those cells in the "on" discharge
state during imposition of the first sustainer voltage tend to be
shifted to the "off" discharge state during imposition of the
inversion level voltage;
maintaining the sustainer voltage shift for a time interval
exceeding half the time interval of a regular period of the first
sustainer voltage wave form to facilitate the transfer of cells
which were in the "off" discharge state during imposition of the
first sustainer voltage to the "on" discharge state during the
period of said shift; and
shifting the sustainer voltage level to a level near the first
"off" cell wall voltage whereby the cells transferred to the "on"
state during the maintained shift of sustainer level have a cell
wall voltage level near the first "off" cell wall voltage.
8. The method according to claim 7 including the step of
maintaining the first alternating sustainer voltage wave form for a
long interval relative to the interval the shift of the sustainer
voltage level to the inversion level is maintained.
9. The method according to claim 8 wherein the length of the
interval of the shift of the sustainer voltage level to the
inversion level is a direct function of the length of the interval
the alternating sustainer voltage wave form is maintained.
10. The method according to claim 8 wherein the interval the first
alternating sustainer voltage wave form is maintained is of the
order of a millisecond.
11. The method according to claim 7 wherein the regular period is
of the order of twenty microseconds and wherein the maintained
interval is of the order of 40 microseconds.
12. The method according to claim 7 wherein the shift of the
sustainer voltage level near the first "off" cell wall voltage is
maintained for an interval of the order of one half the regular
period.
13. The method according to claim 7 wherein the interval the
sustainer voltage level is shifted to the inversion level is of the
order of 40 microseconds.
14. The method according to claim 7 wherein the first alternating
sustainer voltage is produced by:
alternately shifting the component of the sustainer applied to a
first array of conductors between a reference voltage and a first
small voltage displaced from the reference voltage;
alternately shifting the component of the sustainer applied to a
second array of conductors between a second small voltage of the
general magnitude and direction from the reference voltage of said
first small voltage and a third voltage at least equal to the
second voltage in magnitude and in a direction from the reference
voltage opposite the second voltage;
wherein the shift to said inversion level is produced by shifting
the component applied to the second array to the second small
voltage and shifting the component applied to the first array to a
fourth voltage displaced from the reference voltage opposite the
first voltage and of a value of the general magnitude of the third
voltage; and
wherein the shift to the first "off" cell wall voltage is produced
by shifting the component applied to the second array to the
reference voltage level and shifting the component applied to the
first array to the fourth voltage level.
15. The method according to claim 14 wherein the first voltage
equals the second voltage and the third voltage equals the fourth
voltage.
16. In a circuit for maintaining a distribution of starting charge
particles in a gas discharge display/memory panel of the type in
which a discharge in an enclosed ionizable gas generates charges
alternately collectible on pairs of discrete areas of spaced
dielectric surfaces which are backed by conductors of first and
second conductor arrays respectively to define a plurality of
discharge cells each including a pair of opposed discrete charge
storage areas comprising, means for applying successive trains of
cycles of a first level sustaining voltage across said first and
second conductor arrays alternating at regular cycle periods; means
effective between successive trains for selectively shifting said
sustaining voltage to a second-level to apply voltages across said
first and second conductor arrays tending to invert the discharge
state of all cells comprised of conductors of said first and second
conductor arrays; and means to extend the time interval of an
excursion of the shifted sustaining voltage in the direction
augmented by said shifted level for an interval exceeding the
interval of such excursion during a regular period for said first
level sustaining voltage.
17. The circuit according to claim 16 wherein said extending means
defines an interval which is at least several times said excursion
during a regular period.
18. The circuit according to claim 16 wherein said extending means
is operated during the initial excursion of said shifted sustaining
voltage.
19. The circuit according to claim 16 including means to actuate
said shifting means in response to the application of a
predetermined number of alternations of the first level sustaining
voltage by said applying means.
20. The circuit according to claim 18 wherein said shifting means
includes means for applying one cycle of alternation of the
sustaining voltage at the second level; means to terminate
application of the sustaining voltage at the second level and to
apply the first level sustaining voltage upon the completion of one
cycle of alternation of the sustaining voltage at the second
level.
21. The circuit according to claim 16 wherein said applying means
includes a first clock means having a given period which
establishes the regular periods of the sustaining voltage
alternations; and wherein said shifting means includes a second
clocking means having a second given period at least several times
said first mentioned given period.
22. The circuit according to claim 16 including means to generate
an excursion of the shifted sustaining voltage in the direction
opposite the shifted level for an interval equal to the interval of
an excursion in said direction of a regular period of the
sustaining voltage.
Description
RELATED APPLICATIONS
This application is related to applications for U.S. Pat., Ser. No.
372,553 entitled "Method of Driving and Addressing Gas Discharge
Panels by Inversion Techniques" (Case S-12513) and U.S. Pat. Ser.
No. 372,549 entitled "Circuits for Driving and Addressing Gas
Discharge Panels by Inversion Techniques" (Case S-13030) both of
which were filed herewith in the name of Jerry D. Schermerhorn.
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to gas discharge devices of the multiple
discharge display/memory type which have an electrical memory and
which are capable of producing a visual display or representation
of data and more particularly to methods of priming or conditioning
such devices for the institution of selective discharges.
2. DESCRIPTION OF THE PRIOR ART
Heretofore, multiple gas discharge display and/or memory panels
have been proposed in the form of a pair of opposed dielectric
charge storage members which are backed by electrodes, the
electrodes being so formed and oriented with respect to an
ionizable gaseous medium as to define a plurality of discrete gas
discharge units or cells. The cells have been defined by
surrounding or confining physical structure such as the walls of
apertures in a perforated glass plate sandwiched between glass
surfaces and they have been defined in an open space between glass
or other dielectric backed by conductive electrode surfaces by
appropriate choices of the gaseous medium, its pressure and the
electrode geometry. In either structure, charges (electrons and
ions) produced upon ionization of the gas volume of a selected
discharge cell, when proper alternating operating voltages are
applied between the opposed electrodes, are collected upon the
surface of the dielectric at specifically defined locations and
constitute an electrical field opposing the electrical field which
created them so as to reduce the voltage and terminate the
discharge for the remainder of the cycle portion during which the
discharge producing polarity remains applied. These collected
charges aid an applied voltage of the polarity opposite that which
created them so as that they aid in the initiation of a discharge
by imposing a total voltage across the gas sufficient to again
initiate a discharge and a collection of changes. This repetitive
and alternaing charge collection and ionization discharge
constitutes an electrical memory.
An example of a panel structure containing non-physically isolated
or open discharge cells is disclosed in U.S. Pat. No. 3,499,167
issued to Theodore C. Baker, et al. Physically isolated cells have
been disclosed in the article by D. L. Bitzer and H. G. Slottow
entitled "The Plasma Display Panel -- A Digitally Addressable
Display With Inherent Memory" Proceeding of the Fall Joint Computer
Conference, IEEE, San Franciso, California, November 1966, pp
541-547 and in U.S. Pat. No. 3,559,190.
One construction of a memory/display panel includes a continuous
volume of ionizable gas confined between a pair of dielectric
surfaces backed by conductor arrays typically in parallel lines
with the arrays of lines orthogonally related to define in the
region of the projected intersections, as viewed along the common
perpendicular to each array, a plurality of opposed pairs of charge
storage areas on the surfaces of the dielectric bounding or
confining the gas. Many variations of the individual conductor
form, the array form, their relationship to each other and to the
dielectric and gas are available, hence the orthogonally related,
parallel line arrays are discussed herein merely as
illustrative.
In prior art, a wide variety of gases and gas mixtures have been
utilized as the ionizable gaseous medium, it being desirable that
the gas provide a copious supply of charges during discharge, be
inert to the materials with which it comes in contact, and where a
visual display is desired, be one which produces a visible light or
radiation which stimulates a phosphor. Preferred embodiments of the
display panel have utilized at least one rare gas, more preferrably
at least two, selected from helium, neon, argon, krypton or
xenon.
In an open cell Baker etal. type panel, the gas pressure and the
electrical field are sufficient to laterally confine charges
generated on discharge within elemental or discrete dielectric
areas confined generally to a region in proximity to the
registering projections of opposed electrodes through the
dielectric layers and gas. The space between the dielectric
surfaces occupied by the gas is such as to permit photons generated
on discharge in a selected discrete or elemental volume of gas to
pass freely through the gas space and strike surface areas of
dielectric remote from the selected discrete volumes, such remote,
photon struck dielectric surface areas thereby emitting charged
particles so as to condition at least one elemental volume other
than the elemental volume in which the photons originated.
With respect to the memory function of a given discharge panel, the
allowable distance or spacing between the dielectric surfaces
depends inter alia, on the frequency of the alternating potential
imposed, the distance typically being greater for lower
frequencies.
While the prior art does disclose gaseous discharge devices having
externally positioned electrodes for initiating a gaseous
discharge, sometimes called "electrodeless discharge," such prior
art devices utilized frequencies and spacing or discharge volumes
and gas pressures such that although discharges are initiated in
the gaseous medium, such discharges are ineffective or not utilized
for charge generation and storage at higher frequencies. Although
charge storage may be realized at lower frequencies, such charge
storage has not been utilized in a display/memory device in the
manner of the Bitzer-Slottow or Baker et al. devices.
In operation of the display/memory device an alternating voltage is
applied, typically, by applying a first periodic voltage wave form
to one array and applying a cooperating second wave form,
frequently identical to and shifted on the time axis with respect
to the first wave form, to the opposed array to impose a voltage
across the cells formed by the opposed arrays of electrodes which
is the algebraic sum of the first and second wave forms. The cells
have a voltage at which a discharge is initiated. That voltage can
be derived from externally applied voltage or a combination of wall
charge potential and externally applied voltage. Ordinarily, the
entire cell array is excited by an alternating voltage which, by
itself, is of insufficient magnitude to ignite gas discharges in
any of the elements. When the walls are appropriately charged, as
by means of a previous discharge, the voltage applied across the
element will be augmented, and a new discharge will be ignited.
Electrons and ions again flow to the dielectric walls extinguishing
the discharge; however, on the following half cycle their resultant
wall charges again augment the applied external voltage and cause a
discharge in the opposite direction. The sequence of electrical
discharges is sustained by an alternating voltage signal that, by
itself, has been designated V.sub.s.
In addition to the sustaining voltage there are manipulating
voltages or addressing voltages imposed on the opposed electrodes
of a selected cell or cells to alter the state of those cells
selectively. One such voltage termed a "writing voltage" transfers
a cell or discharge site from the quiescent to the discharging
state by virtue of a total applied voltage across the cell
sufficient to make it probable that on subsequent sustaining
voltage half cycles the cell will be in the "on state." A cell in
the "on state" can be manipulated by an addressing voltage termed
an "erase voltage" which transfers it to the "off state" by
imposing sufficient voltage to draw off the surface or wall charges
on the cell walls and cause them to discharge without being
collected on the opposite cell walls so that succeeding sustainer
voltage transitions are not augmented sufficiently by wall charges
to ignite discharges.
A common method of producing writing voltages is to superimpose
voltage pulses on a sustainer wave form in an aiding direction and
cumulatively with the sustainer voltage, the combination having a
potential of enough magnitude to fire an "off state" cell into the
"on state." Erase voltages are produced by superimposing voltage
pulses on a sustainer wave form in opposition to the sustainer
voltage to develop a potential sufficient to cause a discharge in
"on state" cells and draw the charges from the dielectric surfaces
such that the cell will be in the "off state." The wall voltage of
a discharged cell is termed an "off state" wall voltage and
frequently is midway between the extreme magnitude limits of the
sustainer voltage, 2 V.sub.s. These manipulating signals are
applied in a timed relationship with the alternating sustaining
voltage, and through control of discharge intensity, accomplished
selective state transitions by changing the wall voltage of only
the cell being addressed.
Cells are transferred to the "on state" by applying a portion of
the manipulating signal superimposed on the sustaining voltage
termed a "select signal" on each of two opposed electrodes which
constitute the cell. Conventionally, like sustaining signals are
imposed on each electrode array so that half the sustaining voltage
is imposed on each array and half the select signal is imposed on
the addressed cell electrode in each electrode array at a time when
the sum of the applied voltages is sufficient to ignite a
discharge. Further, the partial select signals on each electrode
are limited to a value which will not impose a "turn on" potential
across other cells defined in part by that electrode and not
selected. A typical write signal for a cell is developed by
applying half select voltages to the addressed electrodes of the
cell to be placed in the "on state") at a time the sustaining
voltages are developing a pedestal potential somewhat below the
maximum sustaining voltage. Typically, a write signal is imposed on
each opposed electrode of the cell during the terminal portion of a
sustain voltage half cycle when any wall charging which may result
from the prior sustainer transient is substantially completed. The
manipulating signal thus ignites a single, and unique, cell at the
intersection of the selected two opposed electrodes. This ignited
discharge thus establishes the cell in the "on state" since a
quantity of charge is stored in the cell such that on each
succeeding half cycle of the sustaining voltage, a gaseous
discharge will be produced.
In order to erase a cell or transfer it to the "off state" the
charge stored in the cell is discharged at a time when the
sustaining voltage is imposing a voltage in opposition to the wall
charge voltage. As for writing, the erase manipulation is
facilitated if the sustaining voltage is at a pedestal level below
the level providing the maximum applied voltage so that the erase
half select voltages are at a convenient level. Typically an erase
signal is imposed on each opposed electrode of the cell during the
terminal portion of a sustain voltage half cycle, when the wall
charging from the prior sustainer discharge is substantially
completed, but preceeding the next half cycle alternation by enough
time so that the wall discharge of the selected cell is
substantially stabilized.
In the operation of a multiple gaseous discharge device, of the
above described type, it is necessary to condition or prime the
discrete elemental gas volume of each discharge cell by supplying
at least one free electron thereto such that a gaseous discharge
can be initiated when the cell is addressed with an appropriate
voltage signal.
One such means of panel conditioning comprises periodically
applying an electronic conditioning signal or write pulse to all of
the panel discharge cells. However, electronic conditioning is
self-conditioning and is only effective after a discharge cell has
been conditioned previously; that is electronic conditioning
involves periodically discharging a cell. Accordingly, one cannot
wait too long between the periodically applied conditioning pulses
since there must be at least one free electron present in order to
discharge and condition a cell.
External radiation can be employed to condition a panel, as by
flooding part or all of the gaseous medium of the panel with
ultraviolet radiation. This is sometimes inconvenient since
external radiation may not be available to the panel and at best,
requires auxiliary equipment.
A frequently employed conditioning termed "internal conditioning"
comprises using internal radiation such as from a radioactive
material.
Photon conditioning where photons excite electrons as by
impingement upon the dielectric surface of the cells is utilized by
providing one or more pilot discharge cells maintained in the "on
state" for the generation of photons. This is particularly
effective in an open cell construction as disclosed by Baker et al.
where the space between the dielectric surfaces occupied by the gas
is such as to permit photons generated on discharge in a selected
discrete or elemental volume of gas to pass freely through the
panel gas space so as to condition other elemental volumes of other
discharge units. In addition to or in lieu of the pilot cells,
other sources of photons internal to the panel may be used.
Internal photon conditioning may be unreliable when a given
discharge unit to be addressed is remote in distance relative to
the conditioning source. Accordingly, multiplicity of pilot cells
may be required for the conditioning of a panel having a large
area. In one highly convenient arrangement, the panel matrix border
is comprised of a plurality of such pilot cells.
The priming or conditioning mechanism for the gaseous discharge
devices involves metasable atoms, photons and electrons all of
which can impinge upon the cell walls to generate additional
starter electrons and/or collide with atoms in the gas of the cell
to generate such electrons.
It has been suggested from observation of the operation of
multicelled gaseous discharge display/memory devices that the
reliability of transfer of selected cells from an "off state" of
discharge to an "on state" is a function of the number of charged
particles available in the cell site at the time a "turn on" signal
is imposed on that cell. Even though the firing potential of the
cell is imposed, conventionally as a signal addressed to the
individual opposed conductors whose shadow region generally defines
the discharge site of the cell to superimpose a voltage upon the
sustainer voltage wave, not all cells so addressed will be turned
"on." The probability of turn on is enhanced by the spatial
proximity of an "on state" cell and the time proximity of that "on
state" to the application of a firing voltage. Thus, cells widely
spaced from an "on cell" or cells which have not either been in the
"on state" or had nearby cells in the "on state" shortly before the
application of a firing voltage will have less likelihood of
responding to an imposed firing voltage than cells which have a
nearby "on" cell or were recently exposed to an "on discharge
state."
The observed reliability of transfer as a monotonically decreasing
function of distance from a particle source suggests that the most
reliable conditioning method is to periodically place each cell in
the "on state" of discharge whereby conditioning particles are
generated and maintained in its vicinity. Periodic electronic
inversion of panels has been proposed for this purpose since such
inversion conditions all "off" cells to an "on state" at regular
intervals and, where the inversion interval is brief, those
normally "on" cells are only briefly in an "off state" and are
returned to the "on state" as the panel is reinverted.
Prior art electronic inversions have been performed by
superimposing a d-c signal level on one or both sustainer
components without altering the operating sequences of the
sustainer. When employed for conditioning, it has been observed
that electronic inversion must be imposed frequently in order to
achieve acceptable reliability of cell operation. Since each
inversion and reinversion of the panel generates at least two
bursts of light from each cell successfully transferred to the "on
state," a high rate of repetition of inversions increases the
background lighting of the images represented by normally "on"
cells and thus reduces the contrast for the display. A compromise
has, therefore, been forced upon utilizations of electronic
inversion conditioning between reliability and contrast ratio.
Inversion conditioning as disclosed in the aforenoted related
patent applications involves periodic, momentary shifting of all
cells of the panel which are normally in the "off state" to the "on
state" and of all cells which are normally in the "on state" to the
"off state" by an interchange of dissimilar sustainer component
wave forms applied to the opposed conductor arrays of the device.
In this manner the conditioning sources are distributed over the
panel field and thus are proximate to all cells in the field and
conditioning over the field is accomplished without loss of memory
since upon reinversion of the panel the cells which are normally
"on" will be returned to the "on state" and those normally "off"
will be returned to the "off state." Also as disclosed in the
related applications the inversion conditioning of the panel can be
combined with pilot cell or panel matrix border conditioning.
It is desirable that all cells of a panel matrix have the requisite
number of free electrons available at all times so that upon
imposition of a firing voltage across the cell it transfers to an
"on" discharge state. This suggests a relatively high frequency of
inversions of the panel where inversion is the mechanism supplying
free electrons. However, each change of discharge state in a cell
involves the emission of light. A burst of light is generated for
an "on" cell with each sustainer half cycle and when it is erased
or transferred to the "off state" a light burst is issued during
its discharge to the "off state" wall voltage level. As a result,
if inversion conditioning were employed for a single sustainer
cycle every other sustainer cycle, all cells would appear equally
illuminated since they would issue an equal number of light bursts
of like intensities for their respective transfers of state. No
useful display for visual observation would result at the
frequencies of sustainer employed.
It has been observed, when inversion of display panels is employed
for conditioning employing regular periods of normal and inverted
operation, that a single inversion interval of the regular
sustainer period does not place all normally "off" cells in an "on
state." These erratically operating cells then do not transfer to
an "on" state when subjected to normal write select signals or when
the call matrix has its discharge state inverted and cannot be
turned "on" by erasure during an inversion when operated according
to invert-erase writing technique of the aforenoted co-filed patent
applications. This marginal operation can be reduced or even
eliminated by increasing the frequency of the conditioning
inversions although such increase decreases the visual contrast
ratio of the display such that a doubling of the conditioning
inversions essentially makes the image of the "on" cells half as
bright relative to the background illumination.
In order to develop a visual contrast between "on" and "off" cells
it has been proposed that the frequency of inversion be reduced.
Ratios of four normal sustainer cycles to one inverted cycle and of
16 to 1 have been employed with acceptable visual contrast ratios
for certain utilizations although a background glow is evident.
Further, as the higher ratios are employed cell writing becomes
marginal since the long intervals between conditioning inversions
may result in erratic changes in discharge state from cell to
cell.
An object of the present invention is to enhance the write
reliability of cells in a multicelled discharge panel.
Another object is to enhance the contrast ratio of a display
panel.
A third object is to extend the interval between discharge panel
inversions where inversion conditioning is employed.
SUMMARY OF THE INVENTION
This invention involves apparatus for and a method of operating
multiple gas discharge display/memory devices conditioned by panel
inversion. More particularly it involves extending the inversion
interval beyond the normal sustainer voltage period whereby the
opportunity for "off" cells to achieve an "on discharge state"
during the inversion conditions is enhanced.
A feature of the invention is to apply the sustainer voltage which
induces inversion of the panel in the initial sustainer excursion
from a normal sustainer wave form for an interval substantially
greater than a normal half sustainer cycle period. This extended
interval preferrably is of a length sufficient to insure that all
cells normally in the "off state" fire to the "on state." The
succeeding half cycle of the inversion can be of normal sustainer
half cycle duration.
Another feature is a sustainer clocking control which extends the
conditioning inversion interval at regular intervals throughout the
application of a normal sustainer wave form applied to a multiple
gas discharge display/memory device.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially cut-away plan view of a gaseous discharge
display/memory panel as connected to diagrammatically illustrated
sources of operating potentials;
FIG. 2 is a cross-sectional view (enlarged but not to proportional
scale since the thickness of the gas volume, dielectric members and
conductor arrays have been enlarged for purposes of illustration)
taken on lines 2--2 of FIG. 1;
FIG. 3 is a plot of sustainer voltage applied across a display
panel and of "on" and "off" cell wall voltage for that panel
presented on a time base and illustrating two regular sustainer
periods of the sustainer voltage shifted to a level causing panel
inversion followed by a sustainer voltage shift to reinvert the
panel to the normal or preponderant sustainer voltage form;
FIG. 4 is a generalized sustaining voltage wave form applied across
a panel, typical cell wall voltages for such a wave form, and the
component wave forms making up the resultant sustainer wave form;
illustrating a resultant wave form comprised of two similar
component sustainer wave forms, the production of a panel inverting
condition by application of d-c voltage levels to the wave forms,
the cell wall voltage, and light emitted all as a function of
time;
FIG. 5 is a sustaining voltage wave form utilizing dissimilar
component wave forms on the opposed arrays of conductors of the
panel and including a means of shifting the resultant wave form by
interchange of the components on the arrays to cause an inversion
of discharge states in the panel for conditioning according to this
invention and illustrating the distribution of the transfer of
"off" cells to an "on state" with the time during the inversion
both as changes in wall charge and bursts of light for the
condition where none of cells in the panel were "on" during the
normal sustainer cycles;
FIG. 6 is a sustaining voltage resultant wave form and its
components utilizing dissimilar component wave forms and a
superimposed direct current level on one component as the means of
producing an inversion of the panel for conditioning;
FIG. 7 is a block diagram of a system applying the invention and
including a detailed logic diagram for clocking the sustainer for
an inversion conditioning cycle of extended length at regular
intervals; and
FIG. 8 is a plot of sustainer voltage applied across opposed
conductor arrays of a display/memory device and of "on" and "off"
cell wall voltages all as a function of time to illustrate the
cyclic extended inversion cycles between regular sustainer cycle
intervals which can be of greater length than has been practiced
theretofore.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The method of conditioning multicelled, gaseous discharge
display/memory devices according to this invention is applicable to
various forms of such devices and can be accomplished by various
techniques. Particular emphasis will be placed on the method as
applied to display panel devices having two opposed spaced
essentially planar parallel arrays of conductors each with their
proximate surfaces covered with a dielectric and each supported on
an individual spaced substrate. However, it is to be appreciated
that the conditioning method can be applied to other forms of
display/memory devices including those which have a single
substrate to sustain opposed arrays having dielectric overlays and
defining in their regions of proximity discrete discharge sites or
cells. Further the techniques of altering the sustainer wave form
to cause inversions in the discharge states of the cells will be
discussed in detail with respect to wave forms and controls
therefor wherein the change is by an interchange between the
conductor arrays of the display/memory device of dissimilar
sustainer component wave forms. Alternative wave forms will be
discussed briefly, it being understood that the conditioning by
discharge state inversion is accomplished by maintaining a long
inversion interval relative to the interval of a normal sustainer
half cycle for any of the techniques of sustainer voltage
manipulation.
One form of multicelled gas discharge display/memory device to
which the invention is applicable as illustrated in FIG. 1,
utilizes a pair of dielectric films 10 and 11 separated by a thin
layer or volume of a gaseous discharge medium 12, the medium
producing a copious supply of charges (ions and electrons) which
are alternately collectable on the surfaces of the dielectric
members at opposed or facing elemental or discrete areas, X and Y,
defined by the conductor array on non-gas contacting sides of the
dielectric members, each dielectric member presenting large open
surface areas and a plurality of pairs of elemental X and Y areas.
While the electrically operative structural members such as the
dielectric members 10 and 11 and conductor arrays 13 and 14 are all
relatively thin (being exaggerated in thickness in the drawings),
they are formed on and supported by rigid non-conductive support
members 16 and 17 respectively.
One or both non-conductive support members 16 and 17 pass light
produced by discharges in the elemental gas volumes unless only the
memory function is utilized, in which case they can be opaque.
Advantageously, they are transparent glass. Members 16 and 17
essentially define the over-all thickness and strength of the
panel. They serve as heat sinks for heat generated by discharges
and thus minimize the effect of temperature on operation of the
device. For example, the gas layer 12 is usually under 10 mils and
typically about 4 to 6 mils in thickness as determined by spacer
15. Dielectric layers 10 and 11 (over the conductors at the
elemental or discrete X and Y areas) are usualy between 1 and 2
mils thick. Conductors 13 and 14 are about 8,000 angstroms thick
and may be of transparent, semi-transparent, or opaque conductive
material such as tin oxide, gold or aluminum.
Spacer 15 may be made of the same glass material as dielectric
films 10 and 11 and may be an integral rib formed on one of the
dielectric members and fused to the other member to form a bakeable
hermetic seal enclosing and confining ionizable gas volume 12. A
separate final hermetic seal may be effected by a high strength
devitrified glass sealant 15S. Tubulation 18 is provided for
exhausting the space between dielectric members 10 and 11 and for
filling that space with the ionizable gas. For large panels, small
beadlike solder glass spacers 15B may be located between conductor
intersections and fused to dielectric members 10 and 11 to aid in
withstanding stress on the panel and maintain uniformity of
thickness of gas volume 12.
Conductor arrays 13 and 14 may be formed in situ on support members
16 and 17, typically as parallel lines of about 3 mils width spaced
17 mils center to center and having a resistance less than about
1,000 ohms per linear inch of conductor line and usually less than
50 ohms per inch.
Dielectric layer members 10 and 11 are formed of an inorganic
material and are preferrably formed in situ as an adherent film or
coating which is not chemically or physically affected during
bake-out of the panel. One such material is a solder glass such as
Kimble SG-68 manufactured by and commercially available from the
assignee of the present invention. This glass has thermal expansion
characteristics substantially matching the thermal expansion of
certain soda-lime glasses suitable, when in plate form, for support
members 16 and 17. Dielectric layers 10 and 11 must be smooth and
have a dielectric strength of about 1,000 volts per mil and be
electrically homogeneous on a microscopic scale (i.e., no cracks,
bubbles, crystals, dirt, surface films or other irregularities).
Also, the surfaces of dielectric layers 10 and 11 should be good
photo-emitters of electrons. Alternatively, dielectric layers 10
and 11 may be overcoated with materials designed to produce good
electron emission, as in U.S. Pat. No. 3,634,719, issued to Roger
E. Ernsthausen. Where an optical display is desired, at least one
of the dielectric layers and any overcoats should pass light.
The ends of conductors 14-1 . . . 14-4 and support member 17 extend
beyond the enclosed gas volume 12 and are exposed for the purpose
of making electrical connection to external circuitry generically
termed the "sustainer, interface and addressing circuitry" 19.
Likewise, the ends of conductors 13-1 . . . 13-4 on support member
16 extend beyond the enclosed gas volume 12 and are exposed for the
purpose of making electrical connection to sustainer, interface and
addressing circuitry 19.
In normal usage of a multicelled gaseous discharge device as a
display panel having memory, the preponderance of the cells is in
one state of discharge to form a field upon which selected cells
are in an opposite state of discharge. For example, the cells of
the field are normally in an "off state" while the selected cells
are in an "on state" to represent a desired bright image on a dark
background. As represented on the left side of FIG. 3, for two
cycles of alternation of the sustainer voltage S the selected "on
cells" have a wall charge voltage represented by the dot-dash line
D which follows the major sustainer voltage transitions to values
W. The values W approach the sustainer voltage levels and are of a
polarity tending to neutralize the sustainer voltage. Electrons
accumulate on the cell wall, the surface of dielectric 10 or 11 at
the interface with gas 12, at the area overlying the conductor of
the cell upon which the sustainer voltage imposes the more positive
potential while ions accumulate on the area overlying the conductor
which has the more negative sustainer imposed potential. Upon
reversal of the relative polarity of the sustainer voltage applied
to the conductor arrays the cell wall voltage of "on" cells
augments the sustainer sufficiently to cause those cells to again
institute a gaseous discharge at instant T and emit a burst of
light. At the frequency of alternations of a normal sustainer,
typically 50 kilohertz, the eye integrates these bursts of light as
a continuous glow localized to the cell area.
"Off" cells have a wall charge and a wall voltage resulting
therefrom which is between the extreme excursions of the sustainer
voltage as shown by the dashed line F and where the positive and
negative excursions are equal is centered between those extremes as
an essentially level value.
The discharge state of the cells in a display panel can be
interchanged by shifting the sustainer voltage whereby the
relationship of the wall charge levels to the sustainer voltage
levels are interchanged. This interchange has been termed "panel
inversion." Consider the sustainer wave form which is preponderant
as the "normal" wave form which dictates the "normal" cell states.
The sustainer voltage levels can be shifted as shown at the time
instant A in FIG. 3 so that one excursion of that sustainer voltage
is approximately 2V.sub.s from the normal "off" cell wall voltage
at N and no excursion of that shifted sustainer voltage from the
normal "on" on cell wall voltage is great enough to achieve a
discharge starting or sustaining value when the sustaining voltage
is augmented by the normal "on" cell wall voltage. In the example
the symmetrical wave form of the sustainer placed the "off" cell
wall voltage at N half way between the extremes of the excursions
V.sub.s1 and V.sub.s2 above and below N so that a shift of the
sustainer to alternate between the values N and V.sub.s3, a value 2
V.sub.s from N, places the value V.sub.s1 half way between the
extremes of the excursions. Since the value V.sub.s1 is essentially
the wall voltage level of a normally "on" cell, cells with that
wall voltage at the time of the sustainer voltage shift are at the
"off state" cell wall voltage for the shifted sustainer voltage and
discharges will not occur in the normally "on" cells during
sustainer transitions while the shifted sustainer is imposed upon
those normally "on" cells. Further, since the sustainer excursion
to the value V.sub.s3 is 2V.sub.s from the N level, the full
sustainer voltage is augmented by the cell wall voltage previously
established for the "off" cells during the normal cycles to cause
those cells to have discharges during each sustainer transition
while the shifted sustainer is imposed.
FIG. 3 illustrates a shift of the sustainer voltage for two cycles
preceded and followed by normal sustainer cycles. The normally "on"
cells having the wall voltage, wave form D, are in an "off state"
for the interval between A and B as evidenced by the constant level
wall charge during that interval. Normally "off" cells are
transferred to an "on state" with the first transition of their
wall charge shown for curve F at time A and are continued in that
state for three additional transitions whereby at the time B they
are at the wall charge voltage N.
At time B the sustainer is illustrated as returned to the normal
levels and the panel is reinverted such that the cells which were
"off" during the inversion interval have a wall charge voltage
which is essentially 2 V.sub.s from the excursion of the sustainer
to V.sub.s2. This wall charge is sufficient to augment the
sustainer voltage to institute a discharge in those cells. The
cells which were "on" during the shift of the sustainer voltage for
panel inversion are returned to the "off state" since their wall
charge level at N offers insufficient augmentation of the sustainer
transitions to sustain their discharges.
It is to be appreciated that while the inversion illustrated was by
a positive going shift of the sustainer, panel inversion can be
accomplished by a negative going shift, as, in fact, was the case
at instant B in FIG. 3. Further, it should be recognized that while
it is convenient to operate at or near ground external of the panel
as the reference value from which the sustainer voltage makes
positive and negative excursions, so far as the internal potentials
imposed on the panel are concerned the reference level can be at
any convenient level such that both the negative and positive going
excursions of the sustainer voltage can be at positive or negative
levels relative to external ground.
A generalized resultant sustainer wave form 21 showing an extended
half cycle which tends to invert the state of cells in the panel to
which it is applied is set forth in FIG. 4. That resultant
sustainer is made up of components 22 and 23 applied to the
conductors 13-1 . . . 13-4 of the x array and to conductors 14-1 .
. . 14-4 of the y array respectively. Each component has a
magnitude of V.sub.s so that when combined in phase opposition they
impose 2 V.sub.s or a sustaining voltage across the cell to which
they are applied, typically about 220 volts. By definition this
sustaining voltage is below the firing voltage of the panel cells
yet is of such magnitude as to maintain a cell in the "on state" of
discharge once it is placed in that state.
The resultant sustainer includes pedestals 24 developed by
restricting excursions from the reference levels 25 and 26 of the x
and y components to less than a half period, as illustrated for
about 135.degree.. Manipulation of the discharge state of
individual cells is accomplished by superimposing signals addressed
to the cells on the sustainer components to augment the sustainer
and increase the voltage across the cells above their firing
voltage in the case of a "write" or "turn on" manipulation and to
oppose the sustainer and draw off the wall charge of the cell
without collecting an opposite wall charge in the case of an
"erase" or "turn off" manipulation (all by well-known means, not
shown).
FIG. 4 represents a sustainer applied to a panel having all cells
in the "off state" as evidenced by the common "off state" wall
charge level 27 shown in dashed lines on the resultant wave form.
During normal sustainer cycles, as represented prior to the instant
28 and subsequent to the instant 29, the wall charge of all cells
in the "off state" remains approximately midway between the
extremes in the excursion of the resultant sustainer.
Since it is the voltage across the gas 12 which is significant in
determining the state of discharge of the cells, and the excursions
of the sustainer voltage in the resultant wave form from the "off
state" wall charge level of "off" cells is one half of the value
required to sustain an "on state" for the cells, a shift of the
sustainer to a value of 2 V.sub.s from the "off state" wall voltage
will place the normal "off state" wall charge voltage level 27 at a
value which augments the sustainer sufficiently to exceed the
voltage required to initiate a discharge in the cells. This firing
of the cells of the panel matrix is represented in FIG. 3 by
excursions 31 of the wall charge level from the normal "off state"
27 toward the displaced level 32 as at 33. In the example, the
sustainer voltage shift is accomplished by superimposing a negative
d-c level of V.sub.s on the y sustainer component (illustrated to
level 34 beginning at time 35) while maintaining the magnitude of
the x sustainer component 22 at V.sub.H. When the y sustainer
component is reduced to the reference voltage level V.sub.G,
illustrated at 26 at time 36, and shortly thereafter the x
sustainer component 22 is shifted from level V.sub.s to its
reference level 25 at time 37, a voltage which is effectively 2
V.sub.s augmented by the wall charge level 33 is imposed across the
cell and it is discharged to the opposite polarity as at 38. At
this wall charge level, a return to the normal sustainer voltage
wave form by removal of the V.sub.s d-c level will place the wall
charge at the normal "off state" wall charge level 27 and terminate
the "on state" of discharge established during the application of
that supplemental voltage.
The shift in sustainer resultant wave form during imposition of the
V.sub.s d-c level provides a transition condition from "on" to
"off" for the wall charge levels of cells which are in the "on
state" normally. Thus an "on" cell would have a wall charge level
(not shown) at or near the sustainer level 41. Upon the shift of
the sustainer by a value V.sub.s the level 41 is at the midpoint of
the displaced sustainer excursions effectively placing the normal
"on state" wall charge at the neutral level for the shifted
sustainer levels. As a result, the normally "on" cells have a wall
charge during the inverting interval which does not augment the
sustainer alternations to the cell firing potential and the cells
are in the "off state" with reference to the shifted wave form.
Upon return to the normal wave form at time 29, the wall charge
level of the cells which were "off" during inverting conditions is
retained and is therefore again at a level which augments the
sustainer transition at 42 sufficiently to impose the firing
potential across those cells and return them to the "on state."
The sustainer wave depicted is generated by clocking a group of
switches to the voltage levels on the sustainer component wave
forms such that each array is subjected to a pull up signal to
V.sub.H followed in a given interval by a pull down signal to the
reference level, typically ground or a slight offset from ground
V.sub.G followed by a repetition of the cycle. According to the
present invention reliable conditioning can be achieved where the
normal sustainer alternations are imposed for intervals of about a
millisecond provided the inversion producing interval is of the
order of 40 microseconds. Typically, a 50 kilohertz sustainer can
have 50 cycles of normal wave form between inversion cycles (a
single inversion cycle is illustrated between times 28 and 29 of
FIG. 4). It is to be appreciated that the values given here are
exemplary and that enhanced reliability of conditioning of the
cells is realized as a function of the increasing length of the
inversion producing interval.
The time relationships appear to be a function of the frequency of
conditioning. More frequent inversion producing intervals in a
panel having no normally "on" cells cause the cells to transfer to
an on state earlier in the inversion producing interval and to have
their times of transfer more bunched along the time axis than for
the same cell operated with widely spaced inversion producing
intervals. Since the inversion producing interval (the time from 28
to 29 in FIG. 4) should be of sufficient length to insure that all
cells in the panel are inverted under the most adverse conditions
of operation, with no cells "on" during the preceding normal
sustainer interval (the time from 29 to 28 of the next inversion
interval) a relationship between normal sustainer interval length
and inversion producing interval length exists dictating that the
inversion interval should be increased as the sustainer interval is
increased.
FIG. 4 illustrates a broad spread of the distribution of cell
discharges during the initial excursion period of the inversion
producing interval between the transitions at 35 and 36 which is
typical of a long interval of normal sustainer cycles preceding
each inversion producing interval. It will be noted that in the
absence of discharged cells during the interval of normal sustainer
cycles a delay is experienced before cells begin to discharge, the
greatest density of inversions is about a half a normal sustainer
period after the sustainer transition, and the density gradually
decays in a generally exponential form over the remainder of the
interval. The discharges are illustrated in FIGS. 4 and 5 in a
qualitative but not quantitative manner hence they should be
interpreted only as illustrative of general operating
characteristics for a panel. While the illustrations will
contemplate a 50 kilohertz sustainer having 20 microsecond periods
with an operating cycle of 50 normal sustainer cycles, a 40
microsecond inversion producing interval, a 10 microsecond half
cycle of alternation of the sustainer to discharge all cells which
have been placed in the "on state" to the opposite polarity, and a
return to the normal sustainer, it is to be understood that
sustainer frequency can be changed over a wide range. The inversion
producing interval can be changed within lower limits of achieving
the shift in discharge state for essentially all cells and upper
limits which are imposed in practice by system interfacing
constraints and brightness considerations. Further, the second half
cycle of the inverting sustainer voltage need not be at the normal
sustainer frequency although use of such frequency is
convenient.
FIG. 5 shows another combination of sustainer component wave forms
which produces a resultant sustainer of the same effective form as
that of FIG. 4 including a time extended first half cycle of an
inversion producing shift of the resultant sustainer. The sustainer
components in this instance are of the form set forth in the
aforenoted co-pending patent applications where they are
dissimilar. Typically, the x component 45 normally shifts between a
value V.sub.H above a reference level V.sub.G (ground) and a value
V.sub.L below the reference level an amount at least equal to
.vertline.V.sub.H .vertline. and preferrably about twice
.vertline.V.sub.H .vertline., and the y component 46 shifts between
V.sub.H and V.sub.G. Inverting conditions are imposed by an
interchange of the wave forms on the arrays at times 47 and 48 so
that the x component shifts between V.sub.H and V.sub.G and the y
component shifts between V.sub.H and V.sub.L. The inversion
producing interval effectively shifts the resultant sustainer an
amount V.sub.s so that the "off state" cell wall voltage for the
previously imposed sustainer is at the "on state" cell wall voltage
relative to the new sustainer level and the "on state" cell wall
voltage for the previously imposed sustainer is at the "off state"
cell wall voltage relative to that new sustainer level.
FIG. 5 also represents a panel having cells in the "on state"
during the normal sustainer interval. The wall charge 49 of those
normally "on" cells is shown in dot-dash lines. It involves a
transition with each normal alternation of the sustainer to a value
approaching the extreme of the flat topped sustainer. Each such
transition is accompanied by a burst of light, as illustrated in
dot-dash lines, utilized in the display function of the panel. Upon
shift of the sustainer to the inversion inducing state, the
conditioning effect of the cells which were "on" during the normal
sustainer quickly initiates discharges of the nromally "off" cells.
The distribution of discharges in this instance is more peaked and
tends toward completion earlier in the inversion producing
interval.
FIGS. 4 and 5 illustrate that the ranges of distribution and speed
of shift of "off" cells to the "on state" are a function of the
time proximity of "on state" cells in the panel to the inversion
producing interval. While it typically requires about a half
sustainer period (10 microseconds) for the density of inverting
cells to peak and may require 40 microseconds to essentially invert
all cells in the panel where no cells were in the "on state" and no
auxiliary conditioning is applied, when cells in significant
numbers and general distribution over the panel are "on" at the
time the inversion producing signal is imposed, the cells in large
measure respond within the normal operating speeds of regular
sustain manipulations. This produces a distribution of discharges
sharply peaked within a few microseconds of the sustainer shift and
essentially complete inversion of the panel in 10 to 20
microseconds.
A convenient feature of the wave form of FIG. 5 is electronic
exchange symmetry on the x and y arrays. Each can be controlled by
normally open transistor switches having emitter-collector circuits
coupled between sources of the desired voltage levels and busses
for the display connector lines to the arrays. Such circuits are
shown in the aforenoted co-pending applications so that the x and y
arrays each have a pull-up to V.sub.H circuit, a pull to ground
V.sub.G circuit, and a pull-down to V.sub.L circuit. The regular
operation of these circuits can be accomplished by conventional TTL
logic wherein clocking functions are performed by one-shot
multivibrators. In the illustrated wave form of FIG. 5 the extended
interval can be achieved by extending the interval between the turn
on of the pull to V.sub.L and the turn on of the pull to V.sub.H
circuits on the y component, in the example for 40 microseconds,
while holding the pull to ground V.sub.G in abeyance on the V.sub.H
level imposed on the x component during that interval. The second
half of the cycle for cell inversion is at the regular sustainer
half cycle period following which the sustainer components are
shifted back to their normal states. This returns the normally "on"
cells which have been "off" during the inversion to an "on state"
since their wall charge is at an "on" level and augments the
sustainer sufficiently at 51 to cause a discharge. Conversely, at
this time the normally "off" cells have their wall charge
transferred to a level 52 on the second half cycle of the inversion
producing sustainer at 53 so that with the return to a normal
sustainer, the level coincides with the normal "off state" level
and the cells are returned to their normally "off state."
Another wave form construction is considered in FIG. 6. The
sustainer components for FIG. 6 are normally those employed for
FIG. 5. However, inversion is accomplished by superimposing a
higher level on the x component as to level V.sub.HH, at time 55
while the y component is held at V.sub.G. The y component is raised
at 57 to V.sub.H and the x component is pulled to ground at 56 for
the second half of the inversion cycle. After the reverse discharge
of the "on state" cells has had an opportunity to stabilize, the
sustainer can be reinverted at 58 by shifting the x component to
V.sub.L and in due course switching the y component from V.sub.H to
V.sub.G, from which condition the regular sustainer sequence can be
continued.
A general block diagram with an extended inversion interval
clocking means is shown in FIG. 7. Signals for manipulating the
individual cells of the panel between their "on" and "off"
discharge states for useful display/memory purposes are derived at
a user interface 61 which can be a typewriter, a computer or even a
direct image source. The signals are decoded by means of selection
logic 62 to identify the row and column electrodes of the y and x
array which define the cells to be manipulated. Control logic 63
provides the clocking of the signals for the sustainer components
and synchronized therewith the addressed "write" and "erase" pulses
which augment or oppose the sustainer components at appropriate
times to place the selected cells in an "on" or "off" state.
Selection signals from the selection logic 62 control the
manipulating signals which are directed to the x and y display
lines 64 and 65 of panel 66 and are routed through a
transistor-diode matrix 67 as determined by signals on leads 68.
Sustainer sequencing signals are passed from control logic 63 on
leads 69 to the sustainer signal source and switch controls 71 from
which sustainer signal levels are issued to the transistor-diode
matrix 67 on a pull-up and pull-down buss for the x array 72 and 73
and similar busses 74 and 75 for the y array. The sustainer 71 and
the transistor-diode matrix 67 are shown in greater detail in the
co-pending aforementioned patent application entitled "Circuits For
Driving and Addressing Gas Discharge Panels By Inversion
Techniques" to produce wave forms as particularly set forth in FIG.
5.
The logic circuit for clocking the sustainer components is shown in
a generalized form within the control logic 63. It essentially
comprises a normal interval defining one shot 81 gated to an on
condition except during the extended inversion producing interval
defined by a long interval one shot 82. Each of the one-shots is
self-triggering. Assume that one-shot 81 operates on a 2.5
microsecond interval and that it has a gating signal on lead 83 and
a triggering signal is imposed on trigger lead 84. Upon expiration
of 2.5 microseconds a pulse is issued on output lead 85 to OR 86
which issues another trigger signal to 87 inverter 88 and trigger
input 84 for another cycle from 81. OR 86 also issues a pulse to
counter 89. Count on counter outputs 91 enters decoder 92 from
which decoded signals issued on leads 93, 94, 95 and 96 in the
sequence appropriate to turn on the normally open transistor
switches of the several pull-up, pull-down and pull-to-ground
circuits for the sustainer wave form generating sequence. The
output of the decoder is ored in OR 97 to gate 83 of one shot 81 to
maintain its operations for a number of wave form cycles between
the inversion producing cycle as determined by counter 98. Where 50
cycles are desired, counter 98 issues on output 99 a signal in
response to every fiftieth completion of a normal sustainer cycle.
The cycle completion is signified by the signal on lead 96 to
counter 98. When an output issues on lead 99, it inhibits the
transmittal of the gating signal from lead 93 through lead 101 and
AND 102 to input 103 for OR 97. The output signal on lead 99 is
inverted to an enable signal at inverter 104 and passed on lead 105
to AND 106. AND 106 is also subject to the gating signal on lead 93
so that the signal inhibited in AND 102 is enabled in AND 106. One
shot 82 is thus gated by the signal on output lead 107 from AND 106
and is triggered from lead 84 to begin its long interval defining
the initial long inversion producing interval. The signal at 107
also turns on the y array pull-down to V.sub.L switch at output 108
to develop the inversion producing sustainer level.
When one shot 82 times out, after 40 microseconds in the example,
it issues a signal at output 109 to OR 86 whereby a triggering
signal is passed on lead 87 through inverter 88 and trigger input
84 and one shot 81. That timed signal is also passed to the gate
lead 83 for one shot 81 since the inhibiting signal from counter 98
does not persist beyond the 2.5 microseconds of the next clocked
pulse issued on lead 93 of decoder 92 and subsequent pulses are
ORed through 97 to lead 83.
Decoder is thus pulsed at the clocking rate of one shot 81 for all
but the first inversion producing shift of the sustainer. That is
one shot 81 clocks the second half of the inversion interval as
determined in the decoder to pull the x component down to V.sub.G
at 111 of FIG. 5, then pull the y component up to V.sub.H at 112,
then pull the x component down to V.sub.L as it initiates its
regular routine for defining the next 50 normal sustainer
cycles.
The logic diagram is merely illustrative of a clocking arrangement
including means to regularly clock a predetermined number of normal
sustainer cycles, means to shift the sustainer to a cell inversion
producing condition for a long interval relative to a normal
sustainer half cycle, means to shift the polarity of the inversion
producing condition, and means to reinvert to the normal sustainer
form to initiate a repetition of the routine. Many other
arrangements can be utilized to produce the wave form of FIG. 5 and
the techniques illustrated can also be adopted for production of
wave forms as shown in FIGS. 4 and 6.
FIG. 8 represents the applied sustainer voltage levels for portions
of three intervals in which normal sustainer trains of alternations
have inverting sustainer cycles interposed between each train.
Prior to instant 111, a 50 cycle train of 50 kilohertz sustainer
cycles (i.e., an application of such a train for a millisecond) is
imposed on the display/memory device. The first half of the
inversion cycle between instant 111 and instant 112 represents an
extension of the time interval in which the excursion of the
inverting sustainer in the direction augmenting the inverting shift
(a positive going excursion for this example) is imposed which is
several times the period of a normal sustainer positive going
excursion. The second half of the inversion cycle between instant
112 and 113 corresponds in its duration to the duration of a
negative going half cycle of the normal sustainer. The wave form
between instants 113 and 114 is shown broken away for convenience
of illustration and is ordinarily a train of another 50 cycles of
normal sustainer followed at time 114 by an extended inversion
cycle of the same form as that between instants 111 and 113 for
conditioning the device. This sequence of plural cycle trains of
normal sustainer voltage cycles with interposed extended inversion
sustainer cycles can be repeated throughout operation of the
display/memory device to maintain it conditioned for reliable write
operations.
It is not intended that limits be set on the interval length or
number of normal sustainer cycles between the inversion producing
intervals or upon the length of the inversion producing intervals
other than that one interval, advantageously the first, is of a
length greater than the normal sustainer wave half period. With
increase in the length of this invention producing interval the
probability that a discharge will occur is improved for each cell
so that less frequent keep-alive inversions are required, resulting
in a greater contrast ratio for display panels, and so that more
reliability is achieved in addressing the cells to turn them to an
"on state." The technique of inversion interval extension is of
particular advantage in maintaining a sufficient metastable level
at every cell in the panel so that conditioning by remote cells,
the pilot or border cells, is not necessary. This extension of the
interval an inverting sustainer level is maintained appears to
allow time for conditioning of every cell of the panel. The
extended interval presumably has this effect for two reasons. First
of all, if the metastable density in an "off" cell has decayed to
the point where metastable action generates starting electrons
infrequently, the longer interval increases the probability that
one of these starting electrons will be effective during the
interval in initiating a discharge. Secondly, the long interval
allows for the propagation of conditioning from those cells which
fire early in the interval to others which fire later either by
photon conditioning or by step-by-step transfer of charged or
excited particles from each to its neighbors.
It is contemplated that a display device or panel can be
conditioned by an extended inversion time interval at regular
intervals each of which occurs between successive trains of normal
sustainer voltage cycles of a predetermined number of cycles. The
conditioning can also be performed by inversion intervals the
length of time spacing of application of which is adjusted
according to the interval or normal pulse train length between the
transfer of substantial numbers of cells to the "on state," such
transfers occurring, for example, where the inversion-erase-writing
technique of the aforenoted patent application disclosures is
employed.
In view of the variants available in the practice of this invention
it is to be understood that the above disclosure is to be read as
illustrative and not in a limiting sense.
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