In the work of the LED full-color display, the function of the driver IC is to receive the display data (from the receiving card or video processor and other information sources) that conform to the protocol, internally produce PWM and current time changes, and refresh the output and brightness grayscale. and other related PWM currents to light up the LEDs. The peripheral IC composed of driver IC, logic IC and MOS switch acts together on the display function of the LED display and determines the display effect it presents.
LED driver chips can be divided into general-purpose chips and special-purpose chips.
The so-called general-purpose chip, the chip itself is not specially designed for LED, but some logic chips with some logic functions of LED display screen (such as series-2-parallel shift register).
The special chip refers to the driver chip specially designed for the LED display according to the luminous characteristics of the LED. LED is a current characteristic device, that is, under the premise of saturation conduction, its brightness changes with the change of current, rather than by adjusting the voltage across it. Therefore, one of the biggest features of the dedicated chip is to provide a constant current source. The constant current source can ensure the stable driving of the LED and eliminate the flickering of the LED, which is the prerequisite for the LED display to display high-quality images. Some special-purpose chips also add some special functions for the requirements of different industries, such as LED error detection, current gain control and current correction.
Evolution of driver IC:
In the 1990s, LED display applications were dominated by single and double colors, and constant voltage driver ICs were used. In 1997, the first dedicated drive control chip 9701 for LED displays appeared in my country, which spanned from 16-level grayscale to 8192-level grayscale, realizing WYSIWYG for video. Subsequently, in view of LED light-emitting characteristics, constant current driver has become the first choice for full-color LED display driver, and 16-channel driver with higher integration has replaced 8-channel driver. In the late 1990s, companies such as Toshiba in Japan, Allegro and Ti in the United States successively launched 16-channel LED constant current driver chips. Nowadays, in order to solve the PCB wiring problem of small-pitch LED displays, some driver IC manufacturers have introduced highly integrated 48-channel LED constant current driver chips.
Performance indicators of the driver IC:
Among the performance indicators of LED display, refresh rate, gray level and image expressiveness are one of the most important indicators. This requires high consistency of current between LED display driver IC channels, high-speed communication interface rate and constant current response speed. In the past, the refresh rate, gray scale and utilization ratio were a trade-off relationship. To ensure that one or two of the indicators can be better, it is necessary to appropriately sacrifice the remaining two indicators. For this reason, it is difficult for many LED displays to have the best of both worlds in practical applications. Either the refresh rate is not enough, and black lines are prone to appear when shooting with high-speed camera equipment, or the grayscale is not enough, and the color and brightness are inconsistent. With the advancement of technology of driver IC manufacturers, there have been breakthroughs in the three high problems, and these problems have been solved.
In the application of LED full-color display, in order to ensure the user’s eye comfort for a long time, low brightness and high gray have become a particularly important standard to test the performance of the driver IC.
Post time: Oct-09-2022