Ise Electronics Corp

Back to APN130 Index

CL VFDs Application Note APN130

1. STRUCTURE

CL VFDs is one of Chip-in-Glass(CIG) VFDs. CL VFDs contain multiple number of small silicon chips which include the driver and memory functions. One chip has about 5x5 mm size, and contains 16x16=256 dot matrix anodes(phosphors). In order to construct wide display area freely and economically, a small square silicon chips was developed and are precisely "tiled" on the glass plate. A 16x16 dot matrix phosphors were precisely formed on the top surface of the silicon chip.

Fig.1 Silicon Chip Array

1.1 Basic Structure

As well as conventional VFDs, CL VFDs have cathode (filaments) to emit electrons, mesh grids to diffuse electrons, and anodes coated with phosphor to collect electrons. The difference between CL and conventional VFDs can be seen on the anodes. Conventional VFDs have the anodes and phosphors printed on the glass plate directly, and on the other hand CL VFDs have them on silicon chip which is bonded on the glass plate. To make a continuous graphic area, many semiconductor chips can be arrayed horizontally (X direction), but only 2 chips can be put vertically (Y direction) due to the space for wire bonding. CL VFDs have made it easy to use a fewer number of lead pins, which contribute to easy assembly unlike the conventional graphic VFDs (shown in figure 3) that require numerous fine lead pins or FPCs. The CL VFDs have achieved high-resolution graphic display in a compact package. As number of lead pins are reduced, difficulty in assembly is need no longer a concern.

Fig.2 Structure of CL VFDs

Fig.3 Structure of Conventional Graphic VFDs

The driving method of CL VFDs is called "active matrix" type, and can be classified as static drive in a broad sense. (As for the details of "Static drive", please refer to Application Note APN201.) This static drive gives us the following advantages against the ordinary multiplex driven VFDs.

  • Easy to achieve high brightness with low driving voltage from 12V.
  • Extend life expectancy by the low driving voltage.
  • Lower noise because of low driving voltage and no Grid scanning.
  • Low power consumption since there is no switching power loss from Grid scanning.
  • No display flickering.

1.2 Silicon Chip

The silicon chip used in CL VFD contains 256 bit (16x 16 bit) driver, and can be arrayed to make larger graphic areas. The internal driver is made with C-MOS FET, and its logic circuit is similar to ordinary discrete driver ICs for VFDs. Figure 4 shows logic diagram of the silicon chip. The 256 bit drivers, latches and shift-registers are included in a silicon chip. When serial data output from each chip is fed to serial input of the next chip, the multiple number of silicon chips can be controlled as "one" large shift register and driver circuit.

Fig.4 Logic Diagram

Back to APN130 Index   2. Power Supply

APN130