Abstract:
A novel driving method targeting area color organic light emitting diode display devices aims at resolving the problems of poor color balance and uneven luminosity on the display panel resulting from different luminous materials.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 090133354 filed in TAIWAN, R.O.C. on Dec. 31, 2001, which is herein incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a displaying technique for organic light emitting diode (OLED) and particularly a method for generating uniform luminosity and improved color balance for area color OLED display devices by controlling driver signals of various luminous materials in the diodes. 
   BACKGROUND OF THE INVENTION 
   According to color classification, OLED display devices may be grouped in monochrome type, area color type and full color type. The area color OLED display device consists of a plurality of monochrome display areas. Each display area is made from a selected monochrome luminous material. As every luminous material has different luminous efficiency, its luminosity also is different. As a result, the luminosity evenness and the color balance of the display panel are not desirable. This is the main problem now existing in the area color OLED display devices. 
   To resolve this problem, the most direct approach is to provide a separated and independent driving voltage or current to each luminous material. However such an approach requires to develop a driver circuit for each material. This not only increases the hardware cost, it is also not suitable for mass production. Thus its applicability is not high in the industry. 
   SUMMARY OF THE INVENTION 
   The primary object of the invention is to resolve the aforesaid problems of poor color balance and uneven luminosity that occur to the area color OLED display panel resulting from different materials. The invention provides a software design to enhance the uniform luminosity of the entire display panel without increasing the hardware cost. 
   In order to achieve the foregoing object, the method to achieve uniform luminosity for area color OLED display devices of the invention includes: obtaining the luminous efficiency Pi of every luminous material, and calculating the least common multiple Pm based on the luminous efficiency Pi; next, evenly dividing the original scanning cycle T of the scanning line driver circuit to Pm sub-scanning cycles to allow the scanning line driver circuit to scan sequentially and respectively all of the scanning lines in the Pm sub-scanning cycles; the scanning line driver circuit sequentially providing data signals to data lines in every sub-scanning cycle to drive every luminous material, and every luminous material being driven Pm/Pi times in the scanning cycle T. 
   Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a schematic view of a driver circuit of a conventional area color OLED display device. 
       FIG. 2  is the process flow chart of the method of the invention. 
       FIGS. 3A ,  3 B and  3 C are schematic views of an embodiment of the invention, including driving signal wave forms of the scanning signals and data signals. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Refer to  FIG. 1  for a driver circuit of a conventional area color OLED display device. The display device may be a passive OLED display device or an active OLED display device that includes a plurality of scanning lines  100 , a plurality of data lines  102  and a plurality of luminous materials (or pixels)  104  and  106  driven by the scanning lines  100  and the data lines  102 . Based on the present OLED technology, the red, blue and green light materials have been developed, while other luminous materials are under development.  FIG. 1  also includes a data line driver circuit  108  to provide data signals to the data lines  102 , and a scanning line driver circuit  110  to provide scanning signals to all scanning lines  100 . The scanning line driver circuit  110  has a scanning cycle T to periodically scan all scanning lines  100 . The scanning line driver circuit  110  may scan sequentially or alternately. Either way may be adopted to the invention. 
   Refer to  FIG. 2  for the process flow of the invention. First, at step  20 , obtain the luminous efficiency Pi of every luminous material, and calculate the least common multiple Pm based in the luminous efficiency Pi. Next, at step  22 , evenly divide the original scanning cycle T of the scanning line driver circuit  110  by the least common multiple Pm to obtain Pm sub-scanning cycles to allow the scanning line driver circuit  110  to scan sequentially and respectively all of the scanning lines  100  in the Pm sub-scanning cycles. Finally, at step  24 , based on every luminous efficiency Pi obtained at step  20 , the data line driver circuit  108  sequentially provides data signals to the data lines  102  in every sub-scanning cycle to drive every luminous material, and every luminous material is driven Pm/Pi times in the scanning cycle T. The step  22  and  24  adopt software design to control the scanning signals and the data signals that drive the luminous materials in the display device to achieve the effect of the invention. 
   Refer to  FIGS. 3A ,  3 B and  3 C for an embodiment of the invention, including the driving signal wave forms of scanning signals and data signals.  FIG. 3  is designed based on  FIG. 1 . It employs a luminous material  106  with three times of luminosity efficiency than the luminous material  104 . According to the invention, a least common multiple 3 may be obtained. Then evenly divide the original scanning cycle of the scanning line driver circuit  110  to T 1 , T 2  and T 3  sub-scanning cycles. The sub-scanning cycles T 1 , T 2  and T 3  correspond respectively to  FIGS. 3A ,  3 B and  3 C. In the sub-scanning cycle T 1 , the luminous material  104  driven by scanning line S 1  and the data line D 1 , and the luminous material  106  driven by scanning line S k+1 and the data line D 1  are ignited sequentially. Their effective currents are S 1 /D 1  and S k+1/D 1 . The shadow area indicates that illumination has been generated. In the sub-scanning cycle T 2 , the luminous material  104  driven by the scanning line S 1  and the data line D 1  is ignited again, but the luminous material  106  driven by the scanning line S k+1 and the data line D 1  is not ignited. Their effective currents are S 1 /D 1  and S k+1/D 1 . Similarly, in the sub-scanning cycle T 3 , only the luminous material  104  driven by the scanning line Si and the data line D 1  is ignited. Their effective currents are S 1 /D 1  and S k+1/D 1 . According to persistence of vision, the uniform luminosity of the picture viewed by human&#39;s eyes is caused by a plurality of overlapping original images that can enhance the gray level of the original image sensed by human eyes. The invention properly adjusts the illuminating times of different luminous materials based on their luminosity efficiency. The material which has a higher luminous efficiency is ignited with a fewer number of times, while the material which has a lower luminous efficiency is ignited with a greater number of times. Control of the ignition times for the luminous material is achieved by increasing the scanning frequency of the scanning line driver circuit and coupling with a pre-designed data line driving wave form. Details of the process have been explained previously, thus are omitted here. 
   While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart, from the spirit and scope of the invention.