Active Matrix VFD CL Series


Active-Matrix VFD with phosphor on Chip
Allows Static Graphic Display Mode
Chip lighting vacuum fluorescent displays (CL Series), developed by Ise Electronics Corp. is a blend of semiconductor technology and conventional VFD technology. The manufactures build a 16x16-dot phosphor matrix on top of a semiconductor chip that integrates memory functions and display driver circuits. These chips are arranged in a single- or double- stage format, making it possible for highly precise graphic displays. (Fig.1 shows the dot structure of such chips.)
High precision means that complex characters appear vividly on the display. Also, the display uses a self-emitting design, so no back light-backlight is required. New technology has given these displays the additional benefits of low voltage (12 to 18V), high brightness (3500cd/cm2 when VDD2=15V), long life (20,000 hours) and low noise. There is another benefit. Blanking signals can control brightness. Thus, the most appropriate brightness for a given purpose can be obtained. (Table 1 shows the characteristics of the conventional model and the CLVFD.)

Fig.1 Dot Structure of CLVFD
Table 1 Comparison with small graphic VFD and CLVFD
Items for comparisonConventional small
size graphic VFD		 CL VFD
Brightness450cd/m2 or higher3500cd/m2
Matrix size To be determined by external size
and number of leads		 16x16 dot per chip
There is no restriction
in the horizontal direction,
but the maximum chip number
in the vertical direction is 2.
Life expectancy10KHrs. or more20KHrs. or more
Power consumption2W/10cm20.8W/10cm2
Drive voltageebc(+Ek)=60V to 130VVDD2=12V to 18V
Filament bias voltage(Ek)Ek=7V to 20VEk=0 to 1V
Optimal
controller		High speed CPU or advanced
function ASIC		 Controllable using generally
available CPU
Mounted on display tube(Pin)FPC or fine leads frames 2.0mm Pitch few lead pin
ApplicationsGeneral message display
Measurement control		 Information equipment
Industrial purpose
Medical purpose
Drive systemMultiplex driveStatic drive
Grid structureThin-width wire gridSingle-piece
honeycomb mesh
Anode Structure Completely Different
The basic structure of the new display device is the same as that of conventional VFDs. It consists of three electrodes - the cathode, grid and anode. However, the structure of the anode in the new tube is completely different from that in conventional tubes.
In conventional VFDs complex wiring, insulation and phosphor layers are fabricated directly on the glass plate no semiconductor devices are arranged internally and many lead wires are pulled out of the VFD (Fig. 2).
With the new technology, semiconductor chips on which the phosphor matrixes are fabricated and arranged on the glass plate. The chips and outer leads are connected by wire bonding. This technology reduces the number of lead wires pulled out of the VFD (Fig. 3). Therefore, mounting this device on printed circuit boards is easy compared to mounting conventional graphic VFDs.



Fig.2 Construction of
conventional graphic VFD

Fig.3 Construction of CLVFD
No Special Power Source Required
Since these graphic displays incorporate semiconductor driver ICs with embedded memory static display mode becomes available even for graphic display applications. Therefore, the grid and anode voltage can be set between 12 and 18V. Meaning no special power source is required. (Tables 2 and 3 show drive conditions and electric characteristics of P/N MW12832D.)

Table 2 Recommended operating conditions (P/N MW12832D)
ParameterSymbolMINTYPMAXUnit
Filament voltageEf2.52.83.1Vac
Grid voltageEc-15.016.5V
Filament bias voltageEk0.00.61.0V
Logic supply voltageVDD14.55.05.5V
Display supply voltageVDD210.015.017.0V
Hi-level input voltageVIH3.7-VDD1V
Low-level input voltageVIL-0.6-V
Clock frequencyfCLK--4MHz

Table 3 Electrical characteristics (Ta=25deg.C)
ParameterSumbolTest conditionsMINTYPMAXUnit
Filament currentIfAll segment OFF8392101mAac
Grid currentIcAll segment ON-12.024.0mA
Grid currentIDD1fCLK=1.25MHz-30.045.0mA
Display supply currentIDD2All segment ON-14.028.0mA
LuminanceLEnable="High"20003500-cd/cm2
Color of illuminationBlue-green-

Conventional tubes require drivers and multifunctional controllers, but CLVFDs do not because they contain internal semiconductor chips. They can easily be controlled using a generally available CPU. (Fig.4 shows a block diagram of the display system. Fig. 5 shows a block diagram of the inside of a chip.) The interface adopts a synchronized serial format and consists of data clock, latch and enabling logic. (Fig. 6 shows a timing chart for these logic devices.)
Fig.4 Block diagramFig.5 Internal logic
diagram of CL chip		Fig.6 Interface timing chart
Benefits of New Technology
The introduction of these technologies has produced a number of benefits. These benefits include lower noise, longer life, higher brightness, fewer soldering points on PCBs, improved mounting workability and stable operation under a wide range of operating temperatures.
Also, improved storage-temperature and humidty levels .

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