/a>LED” title=”LED”>LED Display screen is more and more widely used, and its footprint can be seen in financial securities, sports, traffic information, advertising delivery, etc. In recent years, the cost of LED has decreased and the brightness has increased. In addition, the LED Display has the advantages of less power consumption, long life, large viewing angle and fast response speed.
Moreover, it can customize the corresponding size according to different locations and needs, and it has rapidly emerged as a new generation of media darlings in the market, and its conditions are unmatched by other large-scale display devices. This article will further explain how to use the fast response advantage of the driver chip to achieve a high-quality LED display without changing the Circuit design.
Overall speed improvement – higher refresh rate and frame change rate
The LED is driven by the flowing current, and the pulse width can control the brightness and gray level of the LED. In short, if the design of the system side is not considered, the refresh rate (refreshrate) is determined by the addressing time (Tacc) and the current It is determined by the current speed through the LED; and the improvement of the frame rate (framerate) requires faster addressing time in addition to the support of the system, and the addressing time and the transmission frequency (DCLK) have a strong relationship with the number of addressing. positive correlation.
For example: There is a full-color outdoor display whose addressing number is 768. If different frequencies are used, the overall addressing time will be different. The working frequency is 10Mhz->768X0.1us=76.8us The working frequency is 30Mhz->768X0.033us =25.6us The addressing time of the two differs by 3 times.
The speed of the current flowing through the LED determines the refresh rate of the LED display. For example, if an LED display has a addressing number of 768, an operating frequency of 30Mhz, a grayscale adjustment of 8 bits, and a brightness adjustment of 2 Bits, the interval time of each subfield is 4us; the pulse width displayed by the traditional driver chip is 250ns, while the pulse width of the SnapDriveTM driver chip is 50ns, and the refresh frequency that can be achieved by the two is obviously different.
Display grayscale improvement The OE response time of the conventional driver chips generally used in the market is about 250ns. If the above example is used, the highest grayscale is 8 bits; that is, R, G, and B each have 256 grayscales. gradation. Its color is 256X256X256=166777216 about 16 million colors.If you want to increase the gray scale to 14 bits, that is, 16384X16384X16384=4.39 billion colors; the refresh frequency between the two will also be significantly different.
The following are the test conditions and results of the driver chip including SnapDriveTM technology launched by Taiwan Xunjie Technology. From Figure 1 and Figure 3, it can be clearly seen that the output current of the driver chip is still linear under the extremely small OE pulse width, while the traditional driver The chip cannot provide linear output.
Test conditions: Vcc=5V, Iout=38.3mA, RL=47Ω, CL=13pF
For the driver chips with different output current slopes, we use the simulation software (HSPICE2007) to obtain different results in terms of distortion rate.