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Vacuum fluorescent display

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   Display used in consumer electronics
   A full view of a typical vacuum fluorescent display used in a
   videocassette recorder
   A close-up of the VFD highlighting the multiple filaments, tensioned by
   the sheet metal springs at the right of the image
   Vacuum fluorescent display from a CD and dual cassette Hi-Fi. All
   segments are visible due to external ultraviolet illumination.

   CAPTION: Different VFD tubes

                7 segments 8 segments (Sharp EL-8) 16 segments
   7 segments
   0 8 segments
   (Sharp EL-8) 16 segments
   0

   A vacuum fluorescent display (VFD) is a display device once commonly
   used on consumer electronics equipment such as video cassette
   recorders, car radios, and microwave ovens.

   A VFD operates on the principle of cathodoluminescence, roughly similar
   to a cathode ray tube, but operating at much lower voltages. Each tube
   in a VFD has a phosphor-coated carbon anode that is bombarded by
   electrons emitted from the cathode filament.^[1]^[2] In fact, each tube
   in a VFD is a triode vacuum tube because it also has a mesh control
   grid.^[3]

   Unlike liquid crystal displays, a VFD emits very bright light with high
   contrast and can support display elements of various colors. Standard
   illumination figures for VFDs are around 640 cd/m^2 with
   high-brightness VFDs operating at 4,000 cd/m^2, and experimental units
   as high as 35,000 cd/m^2 depending on the drive voltage and its
   timing.^[3] The choice of color (which determines the nature of the
   phosphor) and display brightness significantly affect the lifetime of
   the tubes, which can range from as low as 1,500 hours for a vivid red
   VFD to 30,000 hours for the more common green ones.^[3] Cadmium was
   commonly used in the phosphors of VFDs in the past, but the current
   RoHS-compliant VFDs have eliminated this metal from their construction,
   using instead phosphors consisting of a matrix of alkaline earth and
   very small amounts of group III metals, doped with very small amounts
   of rare earth metals.^[4]

   VFDs can display seven-segment numerals, multi-segment alpha-numeric
   characters or can be made in a dot-matrix to display different
   alphanumeric characters and symbols. In practice, there is little limit
   to the shape of the image that can be displayed: it depends solely on
   the shape of phosphor on the anode(s).

   The first VFD was the single indication DM160 by Philips in 1959.^[5]
   The first multi-segment VFD was a 1967 Japanese single-digit,
   seven-segment device. The displays became common on calculators and
   other consumer electronics devices.^[6] In the late 1980s hundreds of
   millions of units were made yearly.^[7]
   [ ]

Contents

     * 1 Design
     * 2 Use
          + 2.1 Use as amplifier
     * 3 Fade
     * 4 History
     * 5 See also
     * 6 References
     * 7 External links

Design[edit]

   Macro image of a VFD digit with 3 horizontal tungsten wires and control
   grid

   The device consists of a hot cathode (filaments), grids and anodes
   (phosphor) encased in a glass envelope under a high vacuum condition.
   The cathode is made up of fine tungsten wires, coated by alkaline earth
   metal oxides (barium,^[2] strontium and calcium oxides^[8]^[9]), which
   emit electrons when heated to 650 DEGC^[2] by an electric current.
   These electrons are controlled and diffused by the grids (made using
   Photochemical machining), which are made up of thin (50 micron thick)
   stainless steel.^[2] If electrons impinge on the phosphor-coated anode
   plates, they fluoresce, emitting light. Unlike the orange-glowing
   cathodes of traditional vacuum tubes, VFD cathodes are efficient
   emitters at much lower temperatures, and are therefore essentially
   invisible.^[10] The anode consists of a glass plate with electrically
   conductive traces (each trace is connected to a single indicator
   segment), which is coated with an insulator, which is then partially
   etched to create holes which are then filled with a conductor like
   graphite, which in turn is coated with phosphor. This transfers energy
   from the trace to the segment. The shape of the phosphor will determine
   the shape of the VFD's segments. The most widely used phosphor is
   Zinc-doped copper-activated Zinc oxide,^[2] which generates light at a
   peak wavelength of 505 nm.

   The cathode wire to which the oxides are applied is made of tungsten or
   ruthenium-tungsten alloy. The oxides in the cathodes are not stable in
   air, so they are applied to the cathode as carbonates, the cathodes are
   assembled into the VFD, and the cathodes are heated by passing a
   current through them while inside the vacuum of the VFD to convert the
   carbonates into oxides.^[2]^[9]

   The principle of operation is identical to that of a vacuum tube
   triode. Electrons can only reach (and "illuminate") a given plate
   element if both the grid and the plate are at a positive potential with
   respect to the cathode.^[11] This allows the displays to be organized
   as multiplexed displays where the multiple grids and plates form a
   matrix, minimizing the number of signal pins required. In the example
   of the VCR display shown to the right, the grids are arranged so that
   only one digit is illuminated at a time. All of the similar plates in
   all of the digits (for example, all of the lower-left plates in all of
   the digits) are connected in parallel. One by one, the microprocessor
   driving the display enables a digit by placing a positive voltage on
   that digit's grid and then placing a positive voltage on the
   appropriate plates. Electrons flow through that digit's grid and strike
   those plates that are at a positive potential. The microprocessor
   cycles through illuminating the digits in this way at a rate high
   enough to create the illusion of all digits glowing at once via
   persistence of vision.

   The extra indicators (in our example, "VCR", "Hi-Fi", "STEREO", "SAP",
   etc.) are arranged as if they were segments of an additional digit or
   two or extra segments of existing digits and are scanned using the same
   multiplexed strategy as the real digits. Some of these extra indicators
   may use a phosphor that emits a different color of light, for example,
   orange.

   The light emitted by most VFDs contains many colors and can often be
   filtered to enhance the color saturation providing a deep green or deep
   blue, depending on the whims of the product's designers. Phosphors used
   in VFDs are different from those in cathode-ray displays since they
   must emit acceptable brightness with only around 50 volts of electron
   energy, compared to several thousand volts in a CRT.^[12] The
   insulating layer in a VFD is normally black, however it can be removed
   to allow the display to be transparent. AMVFD displays that incorporate
   a driver IC are available for applications that require high image
   brightness and an increased number of pixels. Phosphors of different
   colors can be stacked on top of each other for achieving gradations and
   various color combinations. Hybrid VFDs include both fixed display
   segments and a graphic VFD in the same unit. VFDs may have display
   segments, grids and related circuitry on their front and rear plass
   panels, using a central cathode for both panels, allowing for increased
   segment density. The segments can also be placed exclusively on the
   front instead of on the back, improving viewing angles and
   brightness.^[13]^[14]^[15]^[16]^[17]^[18]^[19]^[20]^[21]

Use[edit]

   Besides brightness, VFDs have the advantages of being rugged,
   inexpensive, and easily configured to display a wide variety of
   customized messages, and unlike LCDs, VFDs are not limited by the
   response time of rearranging liquid crystals and are thus able to
   function normally in cold, even sub-zero, temperatures, making them
   ideal for outdoor devices in cold climates. Early on, the main
   disadvantage of such displays was their use of significantly more power
   (0.2 watts) than a simple LCD. This was considered a significant
   drawback for battery-operated equipment like calculators, so VFDs ended
   up being used mainly in equipment powered by an AC supply or heavy-duty
   rechargeable batteries.
   A digital dashboard cluster in a 1990s Mercury Grand Marquis, an
   American automobile

   During the 1980s, this display began to be used in automobiles,
   especially where car makers were experimenting with digital displays
   for vehicle instruments such as speedometers and odometers. A good
   example of these were the high-end Subaru cars made in the early 1980s
   (referred to by Subaru enthusiasts as a digi-dash, or digital
   dashboard). The brightness of VFDs makes them well suited for use in
   cars. The Renault Espace and older models of Scenic used VFD panels to
   show all functions on the dashboard including the radio and multi
   message panel. They are bright enough to read in full sunlight as well
   as dimmable for use at night. This panel uses four colors; the usual
   blue/green as well as deep blue, red and yellow/orange.

   This technology was also used from 1979 to the mid-1980s in portable
   electronic game units. These games featured bright, clear displays but
   the size of the largest vacuum tubes that could be manufactured
   inexpensively kept the size of the displays quite small, often
   requiring the use of magnifying Fresnel lenses.^[citation needed] While
   later games had sophisticated multi-color displays, early games
   achieved color effects using transparent filters to change the color of
   the (usually light blue) light emitted by the phosphors. High power
   consumption and high manufacturing cost contributed to the demise of
   the VFD as a videogame display. LCD games could be manufactured for a
   fraction of the price, did not require frequent changes of batteries
   (or AC adapters) and were much more portable. Since the late 1990s,
   backlit color active-matrix LCD displays have been able to cheaply
   reproduce arbitrary images in any color, a marked advantage over
   fixed-color, fixed-character VFDs. This is one of the main reasons for
   the decline in popularity of VFDs, although they continue to be made.
   Many low-cost DVD players still feature VFDs.

   From the mid-1980s onwards, VFDs were used for applications requiring
   smaller displays with high brightness specifications, though now the
   adoption of high-brightness organic light-emitting diodes (OLEDs) is
   pushing VFDs out of these markets.

   Vacuum fluorescent displays were once commonly used as floor indicators
   for elevators by Otis Elevator Company worldwide and Montgomery
   Elevator Company in North America (the former from the early 1980s to
   the mid-2000s in the form of (usually two) 16-segment displays, and the
   latter from the mid 1980s to the mid 1990s in the form of (usually 3)
   10x14 dot-matrix displays).

   In addition to the widely used fixed character VFD, a graphic type made
   of an array of individually addressable pixels is also available. These
   more sophisticated displays offer the flexibility of displaying
   arbitrary images, and may still be a useful choice for some types of
   consumer equipment.

   Multiplexing may be used in VFDs to reduce the number of connections
   necessary to drive the display.^[2]

Use as amplifier[edit]

   Several radio amateurs have experimented with the possibilities of
   using VFDs as triode amplifiers.^[22]^[23]^[24] In 2015, Korg released
   the Nutube, an analogue audio amplifier component based on VFD
   technology. The Nutube is used in applications such as guitar
   amplifiers from Vox^[25] and the Apex Sangaku headphone amplifier.^[26]
   The Nutube is sold by Korg but made by Noritake Itron.^[27]

Fade[edit]

   Fading is sometimes a problem with VFDs. Light output drops over time
   due to falling emission and reduction of phosphor efficiency. How
   quickly and how far this falls depends on the construction and
   operation of the VFD. In some equipment, loss of VFD output can render
   the equipment inoperable. Fading can be slowed by using a display
   driver chip to lower the voltages necessary to drive a VFD. Fading can
   also occur due to evaporation and contamination of the cathode.
   Phosphors that contain sulfur are more susceptible to fading.^[2]

   Emission may usually be restored by raising filament voltage.
   Thirty-three percent voltage boost can rectify moderate fade, and 66%
   boost severe fade.^[citation needed] This can make the filaments
   visible in use, though the usual green-blue VFD filter helps reduce any
   such red or orange light from the filament.

History[edit]

   Of the three prevalent display technologies - VFD, LCD, and LED - the
   VFD was the first to be developed. It was used in early handheld
   calculators. LED displays displaced VFDs in this use as the very small
   LEDs used required less power, thereby extending battery life, though
   early LED displays had problems achieving uniform brightness levels
   across all display segments. Later, LCDs displaced LEDs, offering even
   lower power requirements.

   The first VFD was the single indication DM160 by Philips in 1959. It
   could easily be driven by transistors, so was aimed at computer
   applications as it was easier to drive than a neon and had longer life
   than a light bulb. The 1967 Japanese single digit seven segment display
   in terms of anode was more like the Philips DM70 / DM71 Magic Eye as
   the DM160 has a spiral wire anode. The Japanese seven segment VFD meant
   that no patent royalties needed to be paid on desk calculator displays
   as would have been the case using Nixies or Panaplex neon digits. In
   the UK the Philips designs were made and marketed by Mullard (almost
   wholly owned by Philips even before WWII).

   The Russian IV-15 VFD tube is very similar to the DM160. The DM160,
   DM70/DM71 and Russian IV-15 can (like a VFD panel) be used as triodes.
   The DM160 is thus the smallest VFD and smallest triode valve. The IV-15
   is slightly different shape (see photo of DM160 and IV-15 for
   comparison).

See also[edit]

     * Nixie tube
     * Sixteen-segment display
     * LCD
     * LED Display

References[edit]

    1. ^ Shigeo Shionoya; William M. Yen (1998). Phosphor Handbook. CRC
       Press. p. 561. ISBN 978-0-8493-7560-6.
    2. ^ ^a ^b ^c ^d ^e ^f ^g ^h Chen, J., Cranton, W., & Fihn, M. (Eds.).
       (2016). Handbook of Visual Display Technology.
       doi:10.1007/978-3-319-14346-0 page 1610 onwards
    3. ^ ^a ^b ^c Janglin Chen; Wayne Cranton; Mark Fihn (2011). Handbook
       of Visual Display Technology. Springer. pp. 1056, 1067-1068.
       ISBN 978-3-540-79566-7.
    4. ^ "Fluorescent phosphorescent coating free from sulphur and
       cadmium".
    5. ^ (HB9RXQ), Ernst Erb. "DM 160, Tube DM160; Roehre DM 160 ID19445,
       INDICATOR, in gene". www.radiomuseum.org.
    6. ^ Joseph A. Castellano (ed), Handbook of display technology Gulf
       Professional Publishing, 1992 ISBN 0-12-163420-5 page 9
    7. ^ Joseph A. Castellano (ed), Handbook of display technology Gulf
       Professional Publishing, 1992 ISBN 0-12-163420-5 page 176
    8. ^ "VFD|Futaba Corporation". www.futaba.co.jp.
    9. ^ ^a ^b "Directly-heated oxide cathode and fluorescent display tube
       using the same".
   10. ^ Joseph A. Castellano (ed), Handbook of display technology, Gulf
       Professional Publishing, 1992 ISBN 0-12-163420-5 Chapter 7 Vacuum
       Fluorescent Displays pp. 163 and following
   11. ^ Elektrotechnik Tabellen Kommunikationselektronik (3rd ed.).
       Braunschweig, Germany: Westermann. 1999. p. 110. ISBN 3142250379.
   12. ^ William M. Yen, Shigeo Shionoya, Hajime Yamamoto (editors),
       Phosphor Handbook, CRC Press, 2007 ISBN 0-8493-3564-7 Chapter 8
   13. ^ "Front Luminous VFD|Futaba Corporation". www.futaba.co.jp.
   14. ^ "Bi-Planar VFD|Futaba Corporation". www.futaba.co.jp.
   15. ^ "Gradation VFD|Futaba Corporation". www.futaba.co.jp.
   16. ^ "Hybrid VFD|Futaba Corporation". www.futaba.co.jp.
   17. ^ "VFD (Vacuum Fluorescent Display) | Products | NORITAKE ITRON
       CORPORATION". www.noritake-itron.jp.
   18. ^ "Chip In Glass VFD(CIG VFD)|Futaba Corporation".
       www.futaba.co.jp.
   19. ^ "Double Layer Phosphor Printing VFD|Futaba Corporation".
       www.futaba.co.jp.
   20. ^ "Ultra-high luminance, full dot matrix display|Futaba
       Corporation". www.futaba.co.jp.
   21. ^ "Clear Background VFD|Futaba Corporation". www.futaba.co.jp.
   22. ^ N9WOS (29 July 2005). "VFD as an audio/RF amplifier?".
       Electronics Point forums. Archived from the original on 11 March
       2018. Retrieved 11 March 2018.
   23. ^ "H. P. Friedrichs, Vacuum Fluorescent Display Amplifiers For
       Primitive Radio, eHam.net December 2008, retrieved 2010 Feb 8".
       Eham.net. Retrieved 2012-12-11.
   24. ^ "Des. Kostryca, A VFD Receiver (Triodes in Disguise), eHam.net
       January 2009, retrieved 2010 Feb 8". Eham.net. Retrieved
       2012-12-11.
   25. ^ "Vox MV50 AC guitar amplifier". Retrieved 11 March 2018.
   26. ^ "The Sangaku headphone amplifier". Retrieved 11 March 2018.
   27. ^ "News | KORG INC and Noritake Co., Limited Release Innovative
       Vacuum Tube: The Nutube | KORG (USA)".

External links[edit]

   Wikimedia Commons has media related to Vacuum fluorescent displays.
     * Noritake's Guide to VFD Operation
     * Vacuum Fluorescent Display (VFD) (including How to drive the
       filament)
     * Photos and specs for antique Russian VFD tubes
     * Simple VFD Test Circuit
     * The DM70 VFD related Magic eye
     * The smallest Triode and earliest VFD, the DM160, with size
       comparisons
     * The Russian VFD indicator like a DM160

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   Display technology
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          + ALiS

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   generation
     * Quantum dot display (QLED)
     * Electronic paper
          + E Ink
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   Non-video
     * Electromechanical
          + Flip-dot
          + Split-flap
          + Vane
     * Eggcrate
     * Fiber-optic
     * Nixie tube
     * Vacuum fluorescent display (VFD)
     * Light-emitting electrochemical cell (LEC)
     * Lightguide display
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   Static media

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          + CEA-861
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   Related articles

     * History of display technology
     * Large-screen television technology
     * Optimum HDTV viewing distance
     * High Dynamic Range (HDR)
     * Color Light Output
     * Flexible display
     * Comparison of CRT, LCD, plasma, and OLED displays

   Comparison of display technology

   Authority control: National libraries Edit this at Wikidata
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