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Browse Prior Art Database

Use of Tilted Arrays in Display Devices and Scanners

IP.com Disclosure Number: IPCOM000088541D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 77K

Publishing Venue

IBM

Related People

Garvin, RL: AUTHOR [+2]

Abstract

INTRODUCTION. In a rotating optical light-emitting diode (ROLED) display, a linear array of light-emitting diodes (LEDs) is scanned into an area display by a rotating mirror or similar device capable of scanning in a direction orthogonal to the array axis.

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Use of Tilted Arrays in Display Devices and Scanners

INTRODUCTION.

In a rotating optical light-emitting diode (ROLED) display, a linear array of light-emitting diodes (LEDs) is scanned into an area display by a rotating mirror or similar device capable of scanning in a direction orthogonal to the array axis. Fig. 1 illustrates the grid pattern obtained by pulsing all the LEDs in the array at a periodic rate. It is evident that the same grid may be obtained from other arrangements of LEDs if they are pulsed at appropriate intervals. Figs. 2-2D illustrate a number of possibilities of simple geometry. In each case, groups of LEDs are mounted in linear fashion at angles + or - Phi with respect to the horizontal axis of the display. The horizontal pitch Ph in the display is then less than the mounting separation S, and is given by: (1) Ph = Scos Phi Several advantages are gained by these arrangements:. 1) By increasing the spacing of the LEDs, the substrate area per LED is increased, thereby lowering the thereby lowering the operating temperature of the LEDs. 2) The emitting area of an LED is generally substantially smaller than the inter-LED distance, particularly if the LEDs are fabricated as separate chips. The above arrangements allow one to take full advantage of the inherent resolution, which can now be the same as the emitting area, without losing light intensity as would be the case if the entire chip were scaled down. 3) The configuration of Fig. 2D is available as a 5X7 matrix- addressed array in large production quantities. By using such an array,properly tilted and addressed, one can gain the usual economic advantages of mass production. TILT ANGLE.

The angle Phi determines the horizontal pitch in the display grid as given above. It does not directly determine the vertical pitch in the display grid--this is fixed by the interpulse time relative to the scanning rate. In practice, however, it will usually be convenient to pulse all or a simple fraction of the LEDs simultaneously. This requires that the scanned positions of the selected fraction of LEDs appear at grid positions simultaneously. Fig. 3 shows the display grid (open circles) for the general case of unequal horizontal and vertical pitch. The location of some of the LEDs (filled circles) are shown for arbitrary tilt angle. It is clear that the LEDs shown can only lie over grid positions if the vertical spacing in the array, SsinPhi is a multiple N of the vertical pitch Pv: (2) SsinPhi = NPv Combining with Equation 1, we find the allowable tilt angles: (3) tanPhi = NPv/Ph For a square grid (Pv=Ph), the angles are 45, 63,4, 71.6, 76.0, 78.7... (degrees). MATRIX-ADDRESSED ARRAYS.

It is frequently advantageous to connect the LEDs in matrix fashion in order to reduce the number of drive transistors. The standard rectangular array of Fig. 2D is an example, groups of 5 LEDs sharing a common connection controlled by a cluster drive transistor, 5 additional connections being...