CA2247794A1 - Gray-scale driver for fixed-intensity electronic display - Google Patents
Gray-scale driver for fixed-intensity electronic display Download PDFInfo
- Publication number
- CA2247794A1 CA2247794A1 CA 2247794 CA2247794A CA2247794A1 CA 2247794 A1 CA2247794 A1 CA 2247794A1 CA 2247794 CA2247794 CA 2247794 CA 2247794 A CA2247794 A CA 2247794A CA 2247794 A1 CA2247794 A1 CA 2247794A1
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- CA
- Canada
- Prior art keywords
- intensity
- display
- gray
- fields
- refresh rate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/04—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of a single character by selection from a plurality of characters, or by composing the character by combination of individual elements, e.g. segments using a combination of such display devices for composing words, rows or the like, in a frame with fixed character positions
- G09G3/06—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of a single character by selection from a plurality of characters, or by composing the character by combination of individual elements, e.g. segments using a combination of such display devices for composing words, rows or the like, in a frame with fixed character positions using controlled light sources
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/02—Improving the quality of display appearance
- G09G2320/0247—Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
- G09G3/2022—Display of intermediate tones by time modulation using two or more time intervals using sub-frames
- G09G3/2025—Display of intermediate tones by time modulation using two or more time intervals using sub-frames the sub-frames having all the same time duration
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- General Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
Abstract
A method and a driver are provided for enabling a fixed-intensity electronic display, such as a BDVFD, to produce multiple levels of intensity or gray-scale on a pre-pixel basis. This is achieved by sequencing several fields at a rate that is at least double and preferably several times the normal minimum refresh rate set for the display.
Description
GRAY-SCALE DRIVER FOR FIXED-INTENSITY ELECTRONIC DISPLAY
1. Field of the Invention:
This invention relates to a method and driver for driving fixed-intensity electronic displays in such a way as to produce multiple levels of intensity (gray-scale) on a per-pixel basis. It applies in particular, but not exclusively, to built-in driver vacuum fluorescent display (BDVFD) products.
1. Field of the Invention:
This invention relates to a method and driver for driving fixed-intensity electronic displays in such a way as to produce multiple levels of intensity (gray-scale) on a per-pixel basis. It applies in particular, but not exclusively, to built-in driver vacuum fluorescent display (BDVFD) products.
2. Description of the Prior Art:
Some electronic displays are only available with fixed-intensity electronic drive circuitry, i.e. the pixels can only be driven in one of two states (bi-stable). A good analogy for the pixels of these displays would be a lamp that only has a simple on-off switch, while a lamp controlled by a dimmer would not fill that category since it can directly provide intermediate brightness levels. It should be noted that the word "pixel" refers to a picture element which is the smallest addressable component of the display.
This is the case, for example, of the BDVFD products manufactured by the Japanese company Noritake, which constitute an improvement on the previous generation of vacuum fluorescent display (VFD) devices by integrating within the glass display package the electronic driver circuits. VFDs act as a classic triode vacuum tube, with a cathode filament emitting electrons when heated, an anode at a relatively high voltage (around 55 volts) and a grid between the anode and cathode. In Noritake~s VFDs, the triode is used only in two discrete states, fully ON
or fully OFF, because logic circuits are used to control them. In the OFF state, the grid is driven at a voltage below that of the cathode to stop the electron flow from cathode to anode. In the ON state, the grid switches to a higher voltage than the cathode: the electrons are drawn toward the anode, hit the phosphor coating which emits the light. The phosphor used by Noritake emits a blue-green light when excited. Since the built-in driver circuit either switches the grid fully ON or fully OFF, it has no provision for varying the intensity of light on a per-pixel basis.
The standard circuit recommended by Noritake for controlling their BDVFD devices includes sections for power supply and logic waveform generation. The power supply must provide different voltages for the anodes (approximately 55 volts, Direct Current) and cathodes (approximately 4 volt RMS of Alternating Current, centered around the 6 volt DC level, to heat the filaments). The built-in driver inside the Noritake display receives logic data from the control inputs as a stream of serially shifted 0's and 1's, for two columns of pixels on the screen, then switches ON the grids for these columns while the data for the next two columns is shifted in. Eventually, all the pixels get addressed this way, to be turned on briefly if their corresponding data was a 1. The required refresh rate for the display (the addressing of all of its pixels) should be at a minimum of one hundred times per second to prevent flicker.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to improve upon present fixed-intensity electronic displays by providing multiple levels of intensity or gray-scale therefor, thus allowing for display of shades in such devices.
Another object is to achieve intermediate intensity levels in BDVFD products.
Other objects and advantages of the present invention will be apparent from the following description thereof .
The invention basically relies on inertia inherent to either the human vision neurosystem (referred simply as the eye hereafter) or the display technology used. The inertia of the eye is defined as the maximum speed at which changes in light intensity can be perceived. The peripheral vision is more sensitive to fast, small changes in light intensity and is used to measure the maximum rate of detectable changes in light intensity. If a point in the field of view changes states faster than this limit, the eye perceives a light intensity that is an intermediate value between the two states. The inertia of the display relates to some property, either mechanical, chemical or physical, that causes the pixels to resist abrupt changes in their state. Fluorescent lamps have negligible inertia compared to that of the human eye because luminosity ceases as soon as the excitation is removed, while phosphorescent materials (such as those used in the cathode ray tube of a TV or computer monitor) exhibit a decaying light output, called persistence, after the excitation stops.
The perceived light value from a point is the sum of all contributing emitted, reflected or refracted light sources. If two light sources vary their intensities at rates A and B, both above the rate detectable by the human eye, they could still exhibit a beating effect at a rate ~A - B~ that could be below the detectable rate, and therefore be observable; this is the principle behind stroboscope tachometers. This beating effect can be observed with computer monitors that have a refresh rate below 85 Hz in offices lit by fluorescent lamps (which have a frequency of 60 Hz in North America); this undesirable effect is called screen flicker and is most perceptible with a large white screen background.
The essence of the present invention is to have a much faster screen refresh rate and alternate between the ON and OFF states for each pixel according to the intermediate intensity level desired. The persistence of both the phosphor and human eye have an integrating (or averaging) effect on the intensity of the light emitted by the pixel and perceived by the observer. The perceived light intensity is directly controlled by the proportion of the time that the pixel is ON.
By sequencing several fields in which the pixels may have different states, at a rate that is at least double and preferably several times the normal minimum refresh rate, there is obtained the desired averaging effect and the perception of different intensities (or shades of blue-green) for each pixels. The number of fields defines the number of intensities perceived (plus one for the all-off, or black, intensity). Also, by spreading the ON
states as much as possible over time, the chances of perceptible flicker are minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
A non-limitative embodiment of the present invention will now be described with reference to the appended drawings, in which:
Fig. 1 shows a timing diagram that illustrates pixel state to field for each of 8 equally spaced brightness levels; and Fig. 2 shows a block diagram of a BDVFD module provided with the improved features of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The timing diagram of Fig. 1 illustrates one embodiment of the method of relating pixel state to field, for each of 8 equally spaced brightness levels from 0% (black) to 100% (full intensity). The ON states are deliberately spread over the repetitive period (the full sequence of fields) to minimize flicker. There could be some flicker remaining for the 14% intensity since it has only one ON state per repetitive period. The effect of this artifact is minimized since it occurs for the lowest intensity above the black level.
The block diagram of Fig. 2 illustrates one embodiment of the circuit that the applicant has implemented to validate the above described concept. It works off a single regulated 5V DC power supply. The included power circuitry uses a push-pull transformer drive whose duty cycle (and thus output levels) can be varied under software control for overall intensity control of the display.
The implementation described herein uses 4 bits of memory for each pixel. The controlling processor writes and reads the display memory while the display refresh circuitry only reads it. The logic allows synchronized accesses to the memory by both the processor and refresh circuitry.
For each pixel, one bit of memory is used to control blinking (turning the pixel ON and OFF at a slow rate) while the other three define which of the 8 possible shades is displayed (OOOb for black, lllb for maximum intensity).
In the diagram of Fig. 2, the various acronyms have the following meanings:
BDVFD - built-in driver vacuum fluorescent display CMOS - complimentary metal oxide semiconductor SRAM - static random access memory MOSFET - metal-oxide-semiconductor field effect transistor CPLD - complex programmable logic device FPGA - field programmable gate array.
Some electronic displays are only available with fixed-intensity electronic drive circuitry, i.e. the pixels can only be driven in one of two states (bi-stable). A good analogy for the pixels of these displays would be a lamp that only has a simple on-off switch, while a lamp controlled by a dimmer would not fill that category since it can directly provide intermediate brightness levels. It should be noted that the word "pixel" refers to a picture element which is the smallest addressable component of the display.
This is the case, for example, of the BDVFD products manufactured by the Japanese company Noritake, which constitute an improvement on the previous generation of vacuum fluorescent display (VFD) devices by integrating within the glass display package the electronic driver circuits. VFDs act as a classic triode vacuum tube, with a cathode filament emitting electrons when heated, an anode at a relatively high voltage (around 55 volts) and a grid between the anode and cathode. In Noritake~s VFDs, the triode is used only in two discrete states, fully ON
or fully OFF, because logic circuits are used to control them. In the OFF state, the grid is driven at a voltage below that of the cathode to stop the electron flow from cathode to anode. In the ON state, the grid switches to a higher voltage than the cathode: the electrons are drawn toward the anode, hit the phosphor coating which emits the light. The phosphor used by Noritake emits a blue-green light when excited. Since the built-in driver circuit either switches the grid fully ON or fully OFF, it has no provision for varying the intensity of light on a per-pixel basis.
The standard circuit recommended by Noritake for controlling their BDVFD devices includes sections for power supply and logic waveform generation. The power supply must provide different voltages for the anodes (approximately 55 volts, Direct Current) and cathodes (approximately 4 volt RMS of Alternating Current, centered around the 6 volt DC level, to heat the filaments). The built-in driver inside the Noritake display receives logic data from the control inputs as a stream of serially shifted 0's and 1's, for two columns of pixels on the screen, then switches ON the grids for these columns while the data for the next two columns is shifted in. Eventually, all the pixels get addressed this way, to be turned on briefly if their corresponding data was a 1. The required refresh rate for the display (the addressing of all of its pixels) should be at a minimum of one hundred times per second to prevent flicker.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to improve upon present fixed-intensity electronic displays by providing multiple levels of intensity or gray-scale therefor, thus allowing for display of shades in such devices.
Another object is to achieve intermediate intensity levels in BDVFD products.
Other objects and advantages of the present invention will be apparent from the following description thereof .
The invention basically relies on inertia inherent to either the human vision neurosystem (referred simply as the eye hereafter) or the display technology used. The inertia of the eye is defined as the maximum speed at which changes in light intensity can be perceived. The peripheral vision is more sensitive to fast, small changes in light intensity and is used to measure the maximum rate of detectable changes in light intensity. If a point in the field of view changes states faster than this limit, the eye perceives a light intensity that is an intermediate value between the two states. The inertia of the display relates to some property, either mechanical, chemical or physical, that causes the pixels to resist abrupt changes in their state. Fluorescent lamps have negligible inertia compared to that of the human eye because luminosity ceases as soon as the excitation is removed, while phosphorescent materials (such as those used in the cathode ray tube of a TV or computer monitor) exhibit a decaying light output, called persistence, after the excitation stops.
The perceived light value from a point is the sum of all contributing emitted, reflected or refracted light sources. If two light sources vary their intensities at rates A and B, both above the rate detectable by the human eye, they could still exhibit a beating effect at a rate ~A - B~ that could be below the detectable rate, and therefore be observable; this is the principle behind stroboscope tachometers. This beating effect can be observed with computer monitors that have a refresh rate below 85 Hz in offices lit by fluorescent lamps (which have a frequency of 60 Hz in North America); this undesirable effect is called screen flicker and is most perceptible with a large white screen background.
The essence of the present invention is to have a much faster screen refresh rate and alternate between the ON and OFF states for each pixel according to the intermediate intensity level desired. The persistence of both the phosphor and human eye have an integrating (or averaging) effect on the intensity of the light emitted by the pixel and perceived by the observer. The perceived light intensity is directly controlled by the proportion of the time that the pixel is ON.
By sequencing several fields in which the pixels may have different states, at a rate that is at least double and preferably several times the normal minimum refresh rate, there is obtained the desired averaging effect and the perception of different intensities (or shades of blue-green) for each pixels. The number of fields defines the number of intensities perceived (plus one for the all-off, or black, intensity). Also, by spreading the ON
states as much as possible over time, the chances of perceptible flicker are minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
A non-limitative embodiment of the present invention will now be described with reference to the appended drawings, in which:
Fig. 1 shows a timing diagram that illustrates pixel state to field for each of 8 equally spaced brightness levels; and Fig. 2 shows a block diagram of a BDVFD module provided with the improved features of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The timing diagram of Fig. 1 illustrates one embodiment of the method of relating pixel state to field, for each of 8 equally spaced brightness levels from 0% (black) to 100% (full intensity). The ON states are deliberately spread over the repetitive period (the full sequence of fields) to minimize flicker. There could be some flicker remaining for the 14% intensity since it has only one ON state per repetitive period. The effect of this artifact is minimized since it occurs for the lowest intensity above the black level.
The block diagram of Fig. 2 illustrates one embodiment of the circuit that the applicant has implemented to validate the above described concept. It works off a single regulated 5V DC power supply. The included power circuitry uses a push-pull transformer drive whose duty cycle (and thus output levels) can be varied under software control for overall intensity control of the display.
The implementation described herein uses 4 bits of memory for each pixel. The controlling processor writes and reads the display memory while the display refresh circuitry only reads it. The logic allows synchronized accesses to the memory by both the processor and refresh circuitry.
For each pixel, one bit of memory is used to control blinking (turning the pixel ON and OFF at a slow rate) while the other three define which of the 8 possible shades is displayed (OOOb for black, lllb for maximum intensity).
In the diagram of Fig. 2, the various acronyms have the following meanings:
BDVFD - built-in driver vacuum fluorescent display CMOS - complimentary metal oxide semiconductor SRAM - static random access memory MOSFET - metal-oxide-semiconductor field effect transistor CPLD - complex programmable logic device FPGA - field programmable gate array.
The above terms are generally known in the art.
The circuit illustrated in Fig. 2 has a refresh circuitry (consisting of SRAM, programmable logic and CMOS drivers) that enables much faster refresh rate and alternating between ON and OFF states than was previously proposed for fixed intensity electronic displays. Thus, the rate can be at least 200 times per second for 3 intensities, at least 300 times per second for 4 intensities and at least 400 times per second for 8 intensities with minimal flicker as illustrated in Fig.
1. It has been found, however, that for the BDVFD display arrangement shown in Fig. 2, the maximum field refresh rate is 420 times per second (Hz) which for seven fields (eight intensities) produces 60 full image refresh (screens) per second.
It should be noted that the invention is not limited to the specific embodiments described above, but that various obvious modifications can be made by those skilled in the art without departing from the invention and the scope of the following claims.
The circuit illustrated in Fig. 2 has a refresh circuitry (consisting of SRAM, programmable logic and CMOS drivers) that enables much faster refresh rate and alternating between ON and OFF states than was previously proposed for fixed intensity electronic displays. Thus, the rate can be at least 200 times per second for 3 intensities, at least 300 times per second for 4 intensities and at least 400 times per second for 8 intensities with minimal flicker as illustrated in Fig.
1. It has been found, however, that for the BDVFD display arrangement shown in Fig. 2, the maximum field refresh rate is 420 times per second (Hz) which for seven fields (eight intensities) produces 60 full image refresh (screens) per second.
It should be noted that the invention is not limited to the specific embodiments described above, but that various obvious modifications can be made by those skilled in the art without departing from the invention and the scope of the following claims.
Claims (6)
1. In a fixed-intensity electronic display, a gray-scale driver which comprises a refresh circuitry that produces sequencing of several fields at a rate which is at least double the normal minimum refresh rate set for said display, thereby producing multiple intermediate levels of intensity in said display.
2. A gray-scale driver according to claim 1, used with a built-in driver vacuum fluorescent display (BDVFD), and having a circuitry that produces sequencing of up to seven fields at a refresh rate of up to 420 fields per second for an overall refresh rate of at least 60 screens per second.
3. A gray-scale driver according to claims 1 or 2, wherein the sequenced fields have pixels with different ON-OFF states, which alternate, for each pixel, at a rate such as to achieve the desired intermediate intensity level.
4. A method of producing multiple levels of intensity or gray-scale on a per-pixel basis in a fixed-intensity electronic display, which comprises, sequencing several fields in which the pixels may have different ON-OFF
states, at a refresh rate at least double the normal minimum refresh rate set for said display.
states, at a refresh rate at least double the normal minimum refresh rate set for said display.
5. A method according to claim 4, in which sequencing of up to seven fields is performed at a refresh rate of up to 420 fields per second for an overall refresh rate of at least 60 screens per second.
6. A method according to claims 4 or 5, in which the ON-OFF states of each pixel are made to alternate at a rate such as to achieve the desired level of intensity.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2247794 CA2247794A1 (en) | 1998-09-25 | 1998-09-25 | Gray-scale driver for fixed-intensity electronic display |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2247794 CA2247794A1 (en) | 1998-09-25 | 1998-09-25 | Gray-scale driver for fixed-intensity electronic display |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2247794A1 true CA2247794A1 (en) | 2000-03-25 |
Family
ID=29409930
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2247794 Abandoned CA2247794A1 (en) | 1998-09-25 | 1998-09-25 | Gray-scale driver for fixed-intensity electronic display |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2247794A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101494021B (en) * | 2008-01-21 | 2010-10-27 | 普诚科技股份有限公司 | Vacuum fluorescent display device drive circuit and vacuum fluorescent display device |
-
1998
- 1998-09-25 CA CA 2247794 patent/CA2247794A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101494021B (en) * | 2008-01-21 | 2010-10-27 | 普诚科技股份有限公司 | Vacuum fluorescent display device drive circuit and vacuum fluorescent display device |
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| FZDE | Dead |