WO1993007609A1 - Avionics display incorporating a light valve - Google Patents

Avionics display incorporating a light valve Download PDF

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Publication number
WO1993007609A1
WO1993007609A1 PCT/US1992/008067 US9208067W WO9307609A1 WO 1993007609 A1 WO1993007609 A1 WO 1993007609A1 US 9208067 W US9208067 W US 9208067W WO 9307609 A1 WO9307609 A1 WO 9307609A1
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WO
WIPO (PCT)
Prior art keywords
liquid crystal
light valve
displaying information
light
crystal display
Prior art date
Application number
PCT/US1992/008067
Other languages
French (fr)
Inventor
George Michael Gayda
Original Assignee
Allied-Signal Inc.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Allied-Signal Inc. filed Critical Allied-Signal Inc.
Publication of WO1993007609A1 publication Critical patent/WO1993007609A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/13725—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on guest-host interaction
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • 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
    • G09G3/34—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 by control of light from an independent source
    • G09G3/3406—Control of illumination source
    • 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
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G09G2320/0633—Adjustment of display parameters for control of overall brightness by amplitude modulation of the brightness of the illumination source
    • 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
    • G09G3/34—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 by control of light from an independent source
    • G09G3/36—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 by control of light from an independent source using liquid crystals
    • G09G3/3611—Control of matrices with row and column drivers

Definitions

  • This invention relates to the field of liquid crystal displays which are used in applications where the display is subjected to a wide variety of lighting conditions.
  • Liquid crystal displays that are used in aircraft are subjected to a wide variety of lighting conditions.
  • the lighting can be very bright at high altitudes where it is desirable to enhance the contrast of the display.
  • When flying at night it is desirable to dim the backlight of the liquid crystal display.
  • pilots often use night vision goggles which require even a greater dimming of the backlight of the liquid crystal display.
  • Hot cathode tubes can be dimmed over a very wide range, but have a shorter life than cold cathode tubes.
  • hot cathode tubes are inefficient at low light levels because they require using energy to maintain a hot cathode.
  • Cold cathode tubes are more reliable and more efficient, but is difficult to control their dimming over a wide range. At low light levels, there is insufficient ionization of mercury atoms for a cold cathode tube to maintain an arc.
  • the invention is an apparatus for displaying information to a viewer and comprises a fluorescent backlight positioned behind a liquid crystal display that displays information which will be viewed by the viewer.
  • a light valve In front of the liquid crystal display, and position between the display and the viewer, is a light valve.
  • the light valve contains a liquid crystal material which is used to attenuate light.
  • the present invention solves the aforementioned problems by allowing a broad range of dimming without requiring high voltages.
  • the brightness of a cold cathode fluorescent tube is controlled by an amplitude modulated input current to achieve a range of backlight dimming.
  • An additional range of dimming is controlled through the use of a light valve.
  • the light valve reduces reflections of ambient light from the liquid crystal display and thereby enhances the contrast of the display.
  • Figure 1 illustrates a backlight, a liquid crystal display and a light valve
  • Figure 2 illustrates a cross section of the light valve
  • Figure 3 illustrates the control circuitry used to control the fluorescent tube and the light valve.
  • backlight 10 provides light which passes through liquid crystal display 12.
  • Liquid crystal display 12 is positioned in front of backlight 10.
  • Light valve 14 is positioned between viewer 16 and liquid crystal display 12.
  • Backlight 10 comprises fluorescent tube 17 which produces the light for the display. Any type of fluorescent tube can be used but it is preferable to use a cold cathode tube rather than a hot cathode tube. It is also possible to use electroluminescent materials in backlight 10.
  • Liquid crystal display 12 is positioned in front of backlight 10. Any type of liquid crystal display can be used, but it is preferable to use a dichroic liquid crystal material. This material is preferable because it has a fast response time. Positioned in front of liquid crystal display 12, and between the display and viewer 16, is light valve 14. Figure 2 illustrates a cross section of light valve 14. Light valve 14 comprises rear glass panel 20 and front glass panel 22. Glass panels 20 and 22 are separated by gasket 23. Positioned between glass panels 20 and 22 is liquid crystal material 24. Liquid crystal material 24 can be any type of liquid crystal material including twisted nematic type, but it is preferable to use dichroic liquid crystal material.
  • dichroic liquid crystal material having a black dye it is most preferable to use dichroic liquid crystal material having a black dye, however, any convenient color may be used.
  • the liquid crystal material 24 can be distributed between panels 20 and 22 in any convenient manner, but it is preferable to use a uniform distribution.
  • Inside surface 26 of glass panel 20 and inside surface 28 of glass panel 22 are coated with indium tin oxide. These coatings act as conductors which are used to provide an electric field across liquid crystal material 24 to control the amount of light attenuation provided by the material.
  • the electrical connection to the conductor on surface 26 is made at end portion 27, and the electrical connection to the conductor on surface 28 is made at end portion 29.
  • Outer surface 30 of front panel 22 has a high efficiency anti-reflective coating. Any convenient anti-reflective coating can be used on outer surface 30.
  • light ray 38 illustrates how light valve 14 controls dimming the display.
  • Light ray 38 originates at backlight 10. It then passes through liquid crystal display 12 and through light valve 14 before reaching viewer 16. As light ray 38 passes through light valve 14, it is attenuated based on the transparency of light value 14. The amount of attenuation provided by light valve 14 is controlled by the electric field applied between surfaces 26 and 28. The attenuation provided by light valve 14 can be adjusted over a range of 20 to 1.
  • Light valve 14 also enhances the contrast of the display. Since outer surface 30 of front panel 22 has a high efficiency anti-reflective coating, most of ambient light 40 enters light valve 14 rather than reflecting off front panel 22. As ambient light 40 passes through light valve 14, it is attenuated based on the strength of the electric field applied between surfaces 26 and 28, however, the minimum attenuation is 50%. After passing through light valve 14, ambient light 40 is reflected off the front surface of liquid crystal display 12 as reflected light 42. Reflective light 42 passes through light valve 14 as it proceeds towards viewer 16. In passing through light valve 14 reflected light 42 is attenuated as was ambient light 40. This results in reflected ambient light being attenuated twice by light valve 14.
  • Fluorescent tube 17 and light valve 14 are controlled in a manner that maximizes the life of fluorescent tube 17.
  • the life of a fluorescent tube is maximized by running it at a minimal brightness whenever possible.
  • the brightness of the display is first decreased by decreasing the amount of drive to fluorescent tube 17.
  • the brightness of the fluorescent tube is decreased until the point is reached where attempting to further decrease the brightness of the tube will result in the tube extinguishing itself. After the tube has been reduced to minimal brightness, display brightness is decreased further by decreasing the transparency of light valve 14.
  • FIG. 3 illustrates the control circuitry that is used to control the brightness of fluorescent tube 17 and the transparency of light valve 14.
  • Display brightness is controlled by microprocessor 40.
  • the output of microprocessor 40 is connected to the input of digital to analog converter 42 which produces an analog output that varies between + 10 and -10 volts.
  • the output of digital to analog converter 42 is connected to buffer 44 which provides current drive.
  • the output of buffer 44 is connected to amplifier 46 which provides an offset so that no negative voltages are produced at the output of amplifier 46.
  • the offset introduced by amplifier 46 is adjusted through the use of potentiometer 48.
  • the output of amplifier 46 is connected to amplifier 50.
  • the gain introduced by amplifier 50 is controlled using potentiometer 52.
  • the output of amplifier 50 is connected to Buck regulator 54.
  • Buck regulator 54 acts as a current amplifier to amplify the current produced by amplifier 50.
  • the output of Buck regulator 54 is connected to terminal 55 of the primary coil of transformer 56. Terminal 57 of the primary coil of transformer 56 is connected to ground through field effect transistor 62. The gate of field effect transistor 62 is operated at 33 kHz so that the DC signal produced by Buck regulator 54 is chopped at 33 kHz.
  • the secondary coil of transformer 56 is connected across the contacts of fluorescent tube 17. Since transformer 56 has a 20 to 1 rums ratio, the voltage presented to the fluorescent tube is 20 times greater than the voltage at the output of Buck regulator 54.
  • the output of buffer 44 is also connected to the input of voltage sense 64. Voltage sense 64 comprises a resister divider and a voltage comparator. Voltage sense 64 detects when the output of buffer 44 is less than +5 volts.
  • the output of voltage sense 64 is connected to CMOS analog switch 66.
  • analog switch 66 When the voltage at the output of amplifier 44 is less than 5 volts, analog switch 66 is closed and pulls the input of amplifier 50 to ground.
  • the input to Buck regulator 54 When the input to amplifier 50 is at ground, the input to Buck regulator 54 is approximately zero volts, however, Buck regulator 54 produces a 5 volt DC output which will keep fluorescent 17 tube operating at a minimal brightness.
  • the fluorescent tube is maintained at a minimum brightness independent of the voltage produced at the output of buffer 44.
  • Operational amplifier 68 is configured as a summing amplifier, and it sums the inputs received through resistors 70 and 72.
  • Operational amplifier 68 receives the output of buffer 44 through resistor 70, and it receives the output of CMOS analog switch 74 through resistor 72.
  • CMOS analog switch 74 is controlled using voltage sense 64.
  • the output of voltage sense 64 is connected to inverter 76 which inverts the output of voltage sense 64.
  • the output of inverter 76 is connected to the switching input of analog switch 74.
  • Analog switch 74 is controlled so that it is closed and provides -15 volts to amplifier 68, via resistor 72, whenever the output of buffer 44 is above +5 volts.
  • analog switch 74 When the output buffer 44 is below +5 volts, analog switch 74 is open and provides a zero input to amplifier 68 via resistor 72. The output of amplifier 68 is connected to ground through resistor 80 and bipolar transistor 82. The base of transistor 82 is operated at a 120 kHz. The signal available at the collector of transistor 82 is used to control the light valve. One terminal of the light valve receives a signal from the collector through capacitor 84. The other terminal of the light valve receives the signal from the collector through inverter 86 and then through capacitor 88. Whenever analog switch 74 is closed summing amplifier 68 produces a maximum output and thereby provides a maximum voltage to light valve 14. When light valve 14 receives a maximum voltage, it is at maximum transparency.
  • analog switch 74 opens and no longer forces operational amplifier 68 to produce a maximum output.
  • the output of amplifier 68 decreases as the output of buffer 44 decreases. Therefore, the signal that drives light valve 14 decreases as the output of buffer 44 decreases.
  • Transistor 82 is operated at a 120 kHz to avoid damaging liquid crystal material 24 in light valve 14. Apply DC voltage to light value 14 would slow the response time of liquid crystal material 24.
  • microprocessor 40 can vary the brightness of the display over a range of 400 to 1 by providing a number between zero and 255 to digital to analog converter 42. Maximum brightness is achieved when a value of 255 is provided to digital to analog converter 42, and a minimal brightness is achieved when a value of zero is provided to digital to analog converter 42.

Abstract

An avionics display comprising a fluorescent backlight, a liquid crystal display positioned in front of the backlight and a light valve positioned between the liquid crystal display and a viewer. The fluorescent backlight comprises a cold cathode fluorescent tube that is controlled using amplitude modulation. The light valve has a substantially uniform distribution of a dichroic liquid crystal material containing a black dye.

Description

AVIONICS DISPLAY INCORPORATING A LIGHT VALVE
Background of the Invention
Field of the Invention:
This invention relates to the field of liquid crystal displays which are used in applications where the display is subjected to a wide variety of lighting conditions.
Description of the Related Art:
Liquid crystal displays that are used in aircraft are subjected to a wide variety of lighting conditions. The lighting can be very bright at high altitudes where it is desirable to enhance the contrast of the display. When flying at night it is desirable to dim the backlight of the liquid crystal display. In military applications, pilots often use night vision goggles which require even a greater dimming of the backlight of the liquid crystal display.
Many liquid crystal displays used in aircraft have a backlight which incorporates a fluorescent tube. Fluorescent tubes come in two varieties, hot cathode and cold cathode. Hot cathode tubes can be dimmed over a very wide range, but have a shorter life than cold cathode tubes. In addition, hot cathode tubes are inefficient at low light levels because they require using energy to maintain a hot cathode. Cold cathode tubes are more reliable and more efficient, but is difficult to control their dimming over a wide range. At low light levels, there is insufficient ionization of mercury atoms for a cold cathode tube to maintain an arc.
In the past, this problem was addressed by applying a high voltage to the outside of a cold cathode fluorescent tube. This caused the tube to glow without an arc being formed inside. This solution proved to be unsatisfactory. The high voltages required to produce the glow were between 1200 and 1400 volts, and therefore required a great deal of insulation which added to the cost of construction. In addition, at high altitudes these voltages tended to cause arcing which created carbon paths and short circuits.
Summary of the Invention The invention is an apparatus for displaying information to a viewer and comprises a fluorescent backlight positioned behind a liquid crystal display that displays information which will be viewed by the viewer. In front of the liquid crystal display, and position between the display and the viewer, is a light valve. The light valve contains a liquid crystal material which is used to attenuate light.
The present invention solves the aforementioned problems by allowing a broad range of dimming without requiring high voltages. The brightness of a cold cathode fluorescent tube is controlled by an amplitude modulated input current to achieve a range of backlight dimming. An additional range of dimming is controlled through the use of a light valve. In addition to the above mentioned advantage, the light valve reduces reflections of ambient light from the liquid crystal display and thereby enhances the contrast of the display.
Brief Description of the Drawings
Figure 1 illustrates a backlight, a liquid crystal display and a light valve; Figure 2 illustrates a cross section of the light valve; and Figure 3 illustrates the control circuitry used to control the fluorescent tube and the light valve.
Description of the Preferred Embodiment In reference to figure 1, backlight 10 provides light which passes through liquid crystal display 12. Liquid crystal display 12 is positioned in front of backlight 10. Positioned in front of liquid crystal display 12 is light valve 14. Light valve 14 is positioned between viewer 16 and liquid crystal display 12.
Backlight 10 comprises fluorescent tube 17 which produces the light for the display. Any type of fluorescent tube can be used but it is preferable to use a cold cathode tube rather than a hot cathode tube. It is also possible to use electroluminescent materials in backlight 10.
Liquid crystal display 12 is positioned in front of backlight 10. Any type of liquid crystal display can be used, but it is preferable to use a dichroic liquid crystal material. This material is preferable because it has a fast response time. Positioned in front of liquid crystal display 12, and between the display and viewer 16, is light valve 14. Figure 2 illustrates a cross section of light valve 14. Light valve 14 comprises rear glass panel 20 and front glass panel 22. Glass panels 20 and 22 are separated by gasket 23. Positioned between glass panels 20 and 22 is liquid crystal material 24. Liquid crystal material 24 can be any type of liquid crystal material including twisted nematic type, but it is preferable to use dichroic liquid crystal material. It is most preferable to use dichroic liquid crystal material having a black dye, however, any convenient color may be used. The liquid crystal material 24 can be distributed between panels 20 and 22 in any convenient manner, but it is preferable to use a uniform distribution. Inside surface 26 of glass panel 20 and inside surface 28 of glass panel 22 are coated with indium tin oxide. These coatings act as conductors which are used to provide an electric field across liquid crystal material 24 to control the amount of light attenuation provided by the material. The electrical connection to the conductor on surface 26 is made at end portion 27, and the electrical connection to the conductor on surface 28 is made at end portion 29. Outer surface 30 of front panel 22 has a high efficiency anti-reflective coating. Any convenient anti-reflective coating can be used on outer surface 30.
Referring back to figure 1, light ray 38 illustrates how light valve 14 controls dimming the display. Light ray 38 originates at backlight 10. It then passes through liquid crystal display 12 and through light valve 14 before reaching viewer 16. As light ray 38 passes through light valve 14, it is attenuated based on the transparency of light value 14. The amount of attenuation provided by light valve 14 is controlled by the electric field applied between surfaces 26 and 28. The attenuation provided by light valve 14 can be adjusted over a range of 20 to 1.
Under low light conditions and especially when the pilot is wearing night vision goggles, it is very desirable to provide a great deal of dimming so that the display does not interfere with the pilot's vision. By using amplitude modulated current to control the brightness of fluorescent tube 17 in backlight 10, a 20 to 1 range in brightness control can be achieved. Unfortunately, 20 to 1 does not provide sufficient dimming. An additional 20 to 1 range in attenuation or dimming can be achieved through light valve 14. By providing the amplitude modulation control of backlight 10, and the attenuation of light valve 14, a dimming range of 400 to 1 can be achieve. This wide dimming range provides sufficient lighting when a strong backlight is required and provides sufficient dimming when the pilot is using night vision goggles or when he desires dimming in low ambient light conditions.
Light valve 14 also enhances the contrast of the display. Since outer surface 30 of front panel 22 has a high efficiency anti-reflective coating, most of ambient light 40 enters light valve 14 rather than reflecting off front panel 22. As ambient light 40 passes through light valve 14, it is attenuated based on the strength of the electric field applied between surfaces 26 and 28, however, the minimum attenuation is 50%. After passing through light valve 14, ambient light 40 is reflected off the front surface of liquid crystal display 12 as reflected light 42. Reflective light 42 passes through light valve 14 as it proceeds towards viewer 16. In passing through light valve 14 reflected light 42 is attenuated as was ambient light 40. This results in reflected ambient light being attenuated twice by light valve 14. As a result of being attenuated twice, the ambient light reflected from liquid crystal display 12 's surface is greatly reduced. This results in an enhanced contrast which improves display performance even under the very bright ambient conditions that are sometimes encountered by high altitude aircraft. Fluorescent tube 17 and light valve 14 are controlled in a manner that maximizes the life of fluorescent tube 17. The life of a fluorescent tube is maximized by running it at a minimal brightness whenever possible. To achieve this goal, the brightness of the display is first decreased by decreasing the amount of drive to fluorescent tube 17. The brightness of the fluorescent tube is decreased until the point is reached where attempting to further decrease the brightness of the tube will result in the tube extinguishing itself. After the tube has been reduced to minimal brightness, display brightness is decreased further by decreasing the transparency of light valve 14.
Figure 3 illustrates the control circuitry that is used to control the brightness of fluorescent tube 17 and the transparency of light valve 14. Display brightness is controlled by microprocessor 40. The output of microprocessor 40 is connected to the input of digital to analog converter 42 which produces an analog output that varies between + 10 and -10 volts. The output of digital to analog converter 42 is connected to buffer 44 which provides current drive. The output of buffer 44 is connected to amplifier 46 which provides an offset so that no negative voltages are produced at the output of amplifier 46. The offset introduced by amplifier 46 is adjusted through the use of potentiometer 48. The output of amplifier 46 is connected to amplifier 50. The gain introduced by amplifier 50 is controlled using potentiometer 52. The output of amplifier 50 is connected to Buck regulator 54. Buck regulator 54 acts as a current amplifier to amplify the current produced by amplifier 50.
The output of Buck regulator 54 is connected to terminal 55 of the primary coil of transformer 56. Terminal 57 of the primary coil of transformer 56 is connected to ground through field effect transistor 62. The gate of field effect transistor 62 is operated at 33 kHz so that the DC signal produced by Buck regulator 54 is chopped at 33 kHz. The secondary coil of transformer 56 is connected across the contacts of fluorescent tube 17. Since transformer 56 has a 20 to 1 rums ratio, the voltage presented to the fluorescent tube is 20 times greater than the voltage at the output of Buck regulator 54. The output of buffer 44 is also connected to the input of voltage sense 64. Voltage sense 64 comprises a resister divider and a voltage comparator. Voltage sense 64 detects when the output of buffer 44 is less than +5 volts. The output of voltage sense 64 is connected to CMOS analog switch 66. When the voltage at the output of amplifier 44 is less than 5 volts, analog switch 66 is closed and pulls the input of amplifier 50 to ground. When the input to amplifier 50 is at ground, the input to Buck regulator 54 is approximately zero volts, however, Buck regulator 54 produces a 5 volt DC output which will keep fluorescent 17 tube operating at a minimal brightness. As a result, when the output of buffer 44 is below 5 volts, the fluorescent tube is maintained at a minimum brightness independent of the voltage produced at the output of buffer 44.
Operational amplifier 68 is configured as a summing amplifier, and it sums the inputs received through resistors 70 and 72. Operational amplifier 68 receives the output of buffer 44 through resistor 70, and it receives the output of CMOS analog switch 74 through resistor 72. CMOS analog switch 74 is controlled using voltage sense 64. The output of voltage sense 64 is connected to inverter 76 which inverts the output of voltage sense 64. The output of inverter 76 is connected to the switching input of analog switch 74. Analog switch 74 is controlled so that it is closed and provides -15 volts to amplifier 68, via resistor 72, whenever the output of buffer 44 is above +5 volts. When the output buffer 44 is below +5 volts, analog switch 74 is open and provides a zero input to amplifier 68 via resistor 72. The output of amplifier 68 is connected to ground through resistor 80 and bipolar transistor 82. The base of transistor 82 is operated at a 120 kHz. The signal available at the collector of transistor 82 is used to control the light valve. One terminal of the light valve receives a signal from the collector through capacitor 84. The other terminal of the light valve receives the signal from the collector through inverter 86 and then through capacitor 88. Whenever analog switch 74 is closed summing amplifier 68 produces a maximum output and thereby provides a maximum voltage to light valve 14. When light valve 14 receives a maximum voltage, it is at maximum transparency. When the output of amplifier 44 falls below 5 volts, analog switch 74 opens and no longer forces operational amplifier 68 to produce a maximum output. As a result, the output of amplifier 68 decreases as the output of buffer 44 decreases. Therefore, the signal that drives light valve 14 decreases as the output of buffer 44 decreases.
Transistor 82 is operated at a 120 kHz to avoid damaging liquid crystal material 24 in light valve 14. Apply DC voltage to light value 14 would slow the response time of liquid crystal material 24.
By using the above circuit, microprocessor 40 can vary the brightness of the display over a range of 400 to 1 by providing a number between zero and 255 to digital to analog converter 42. Maximum brightness is achieved when a value of 255 is provided to digital to analog converter 42, and a minimal brightness is achieved when a value of zero is provided to digital to analog converter 42.

Claims

I claim:
1. An apparatus for displaying information to a viewer, comprising:
(a) a fluorescent backlight means for producing light;
(b) a liquid crystal display means for displaying information to the viewer, said liquid crystal display means being positioned in front of said fluorescent backlight means; and
(c) a light valve means for attenuating light that passes through said light valve means, said light valve means being positioned between said liquid crystal display means and the viewer, and having a substantially uniform distribution of a liquid crystal material contained therein.
2. The apparatus for displaying information of claim 1, wherein said liquid crystal material is a dichroic liquid crystal material.
3. The apparatus for displaying information of claim 2, wherein said liquid crystal material contains a black dye.
4. The apparatus for displaying information of claim 1, wherein said light valve means comprises an outer front surface having an anti-reflective coating.
5. The apparatus for displaying information of claim 1, wherein said fluorescent backlight means comprises a fluorescent tube having a cold cathode.
6. An apparatus for displaying information to a viewer, comprising:
(a) a fluorescent backlight means for producing light having a brightness being controlled by amplitude modulation;
(b) a liquid crystal display means for displaying information to the viewer, said liquid crystal display means being positioned in front of said fluorescent backlight means; and
(c) a light valve means for attenuating light that passes through said light valve means, said light valve means being positioned between said liquid crystal display means and the viewer, and having a liquid crystal material contained therein.
7. The apparatus for displaying information of claim 6, wherein said liquid crystal material is a dichroic liquid crystal material.
8. The apparatus for displaying information of claim 7, wherein said liquid crystal material contains a black dye.
9. The apparatus for displaying information of claim 6, wherein said light valve means comprises an outer front surface having an anti-reflective coating.
10. The apparatus for displaying information of claim 6, wherein said fluorescent backlight means comprises a fluorescent tube having a cold cathode.
11. An apparatus for displaying information to a viewer, comprising:
(a) a fluorescent backlight means for producing light having a brightness being controlled by amplitude modulation, said fluorescent backlight means comprising a fluorescent tube having a cold cathode;
(b) a liquid crystal display means for displaying information to the viewer, said liquid crystal display means being positioned in front of said fluorescent backlight means; and
(c) a light valve means for attenuating light that passes through said light valve means, said light valve means being positioned between said liquid crystal display means and the viewer, and having a substantially uniform distribution of a liquid crystal material contained therein, said liquid crystal material being a dichroic liquid crystal material containing a black dye.
PCT/US1992/008067 1991-09-30 1992-09-23 Avionics display incorporating a light valve WO1993007609A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US77007691A 1991-09-30 1991-09-30
US770,076 1991-09-30

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1030209A2 (en) * 1999-02-17 2000-08-23 Mannesmann VDO Aktiengesellschaft Variable intensity display device
CN110646990A (en) * 2019-10-23 2020-01-03 南京中电熊猫平板显示科技有限公司 Display panel and control method thereof

Citations (3)

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Publication number Priority date Publication date Assignee Title
EP0182639A2 (en) * 1984-11-19 1986-05-28 Tektronix, Inc. Optical filter having variable transmission characteristics
US4655553A (en) * 1984-12-24 1987-04-07 Mcdonnell Douglas Corporation High contrast back lit liquid crystal display system
US4945350A (en) * 1985-07-09 1990-07-31 Mitsubishi Denki Kabushiki Kaisha Liquid crystal display unit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0182639A2 (en) * 1984-11-19 1986-05-28 Tektronix, Inc. Optical filter having variable transmission characteristics
US4655553A (en) * 1984-12-24 1987-04-07 Mcdonnell Douglas Corporation High contrast back lit liquid crystal display system
US4945350A (en) * 1985-07-09 1990-07-31 Mitsubishi Denki Kabushiki Kaisha Liquid crystal display unit

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1030209A2 (en) * 1999-02-17 2000-08-23 Mannesmann VDO Aktiengesellschaft Variable intensity display device
EP1030209A3 (en) * 1999-02-17 2002-01-16 Siemens Aktiengesellschaft Variable intensity display device
CN110646990A (en) * 2019-10-23 2020-01-03 南京中电熊猫平板显示科技有限公司 Display panel and control method thereof

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