In-depth study of the semiconductor characteristics of LED devices, the realization of a gray-scale display solution for high-density L ED matrix display, and the test circuit to verify the solution. Experiments show that the LED gray scale display realized by this scheme can simultaneously consider the brightness and gray scale of the display screen.

Information display is one of the important links of information science and technology. Photoelectric integrated display has become more and more widely used as a bridge for human-machine communication. For a long period of time, information display technology has remained in the era of cathode ray tube (CRT), but CRT as a vacuum device has its own inherent shortcomings that limit its application in certain fields. In order to solve these problems brought by CRT monitors, the development and development of flat panel displays (FDPs) are intensifying at home and abroad. Among many FDPs, light-emitting diode (LED) displays have their own inherent advantages: low operating power, fast response, wide operating temperature range, low power consumption of all solid devices, small size, impact resistance, high reliability, and long life. Long wait. At the same time, it is a semiconductor device, so it can be fully compatible with the IC circuit. The control and drive circuit are easy to integrate in the flat panel display, further reducing the volume of the display, and also facilitating the multiplexing of signals. Based on the in-depth study of the luminescence characteristics of LED devices, a solution to realize gray scale display on high-level and high-density LED flat panel displays is introduced, and the scheme is verified by experiments. Experiments show that LEDs realized by this scheme The grayscale display can take into account both the brightness and grayscale of the display.

1, LED dot matrix gray level generation principle

Each pixel of the LED dot matrix consists of red (R), green (G), and blue (B) tri-color LEDs, corresponding to one pixel of the video image. When synchronously displayed with the computer CRT, if the luminance of the red, green, and blue LEDs of each pixel of the L ED dot matrix changes with the CRT corresponding pixel points R, G, and B signals, the corresponding CRT image can be simultaneously displayed. . If the gray level is used to describe the change of the brightness of the monochrome LED, the more the gray level, the more the image color and the richer the level. The forward volt-ampere characteristic of the LED is almost the same as that of the ordinary diode. The voltage has no current before the turn-on point. Once the voltage exceeds the turn-on point, it shows the conduction characteristic. At this time, the relationship between the forward current I and the forward voltage U is as follows:

Where m is the composite factor, I0 is the reverse saturation current, UT = kT/e is called the temperature voltage equivalent, and at the thermodynamic temperature T = 300 K, UT = 26 mV1 in the wide band gap semiconductor, when I <0. At 1 mA, the spatial composite current through the deep energy level in the junction dominates, when m = 2; when the current increases, the diffusion current dominates, m = 1.U is the applied voltage.

It can be seen from Figure 1 that the volt-ampere characteristics of L ED are generally linear from the start of conduction until the maximum current it is not burned. In this linear region, the luminous intensity of L ED is substantially proportional to its current intensity. There are two ways to achieve brightness control of L ED:

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