In the LED display industry, the normal refresh rate and high refresh rate announced by the industry are usually defined as 1920HZ and 3840HZ refresh rates respectively. The usual implementation methods are double-latch drive and PWM drive respectively. The specific performance of the solution is mainly as follows:
[Double latch driver IC]: 1920HZ refresh rate, 13Bit display gray scale, built-in ghost elimination function, low voltage start function to remove dead pixels and other functions;
[PWM driver IC]: 3840HZ refresh rate, 14-16Bit grayscale display, built-in ghost elimination function, low voltage start, and dead pixel removal functions.
The latter PWM driving scheme has more gray-scale expressiveness in the case of doubling the refresh rate. The integrated circuit functions and algorithms used in the product are more and more complex. Naturally, the driver chip adopts a larger wafer unit area and a higher cost.
However, in the post-epidemic era, the global situation is unstable, inflation and other external economic conditions, LED display manufacturers want to offset the cost pressure, and launched 3K refresh LED products, but actually use 1920HZ refresh gear dual-edge trigger driver chip The scheme, by reducing the number of grayscale loading points and other functional parameters and performance indicators, in exchange for a 2880HZ refresh rate, and this type of refresh rate is commonly referred to as a 3K refresh rate to falsely claim a refresh rate above 3000HZ to match the PWM with a true 3840HZ refresh rate The driving scheme confuses consumers and is suspected of confusing the public with shoddy products.
Because usually the resolution of 1920X1080 in the display field is called 2K resolution, and the resolution of 3840X2160 is also usually called 4K resolution. Therefore, the 2880HZ refresh rate is naturally confused to the 3K refresh rate level, and the image quality parameters that can be achieved by the real 3840HZ refresh are not an order of magnitude.
When using a general LED driver chip as a scanning screen application, there are three main methods to improve the visual refresh rate of the scanning screen:
1. Reduce the number of image gray-scale sub-fields: By sacrificing the integrity of the image gray-scale, the time for each scan to complete the gray-scale count is shortened, so that the number of times the screen is repeatedly lit within one frame time is increased to improve its vision refresh rate.
2. Shorten the minimum pulse width to control LED conduction: by reducing the LED bright field time, shorten the cycle of grayscale counting for each scan, and increase the number of times the screen is repeatedly lit. However, the response time of traditional driver chips cannot be reduced Otherwise, there will be abnormal phenomena such as low gray unevenness or low gray color cast.
3. Limit the number of driver chips connected in series: For example, in the application of 8-line scanning, the number of driver chips connected in series needs to be limited to ensure that the data can be transmitted correctly within the limited time of fast scan change under high refresh rate.
The scanning screen needs to wait for the data of the next line to be written before changing the line. This time cannot be shortened (the length of time is proportional to the number of chips), otherwise the screen will display errors. After deducting these times, the LED can be effectively turned on. The lighting time is reduced, so within a frame time (1/60 sec), the number of times that all scans can be normally lit is limited, and the LED utilization rate is not high (see the figure below). In addition, the design and use of the controller become more complicated, and the bandwidth of internal data processing needs to be increased, resulting in a decrease in hardware stability. In addition, the number of parameters that users need to monitor increases. Behaving erratically.
The demand for image quality in the market is increasing day by day. Although the current driver chips have the advantages of S-PWM technology, there is still a bottleneck that cannot be broken through in the application of scanning screens. For example, the operation principle of the existing S-PWM driver chip is shown in the figure below. If the existing S-PWM technology driver chip is used to design a 1:8 scanning screen, under the conditions of 16-bit gray scale and PWM counting frequency of 16MHz, the visual refresh rate is about 30Hz. In 14-bit grayscale, the visual refresh rate is about 120Hz. However, the visual refresh rate needs to be at least above 3000Hz to meet the requirements of the human eye for picture quality. Therefore, when the demand value of the visual refresh rate is 3000Hz, LED driver chips with better functions are needed to meet the demand.
Refresh is usually defined according to the integer n times the frame rate of the video source 60FPS. In general, 1920HZ is 32 times the frame rate of 60FPS. Most of them are used in the rental display, which is a high-brightness and high-refresh field. The unit board displays in 32 scans LED display unit boards of the following levels; 3840HZ is 64 times the frame rate of 60FPS, and most of them are used on 64-scan LED display unit boards with low brightness and high refresh rate on indoor LED displays.
However, the display module on the basis of the 1920HZ drive frame is forcibly increased to 2880HZ, which requires 4BIT hardware processing space, needs to break through the upper limit of hardware performance, and needs to sacrifice the number of gray scales. Distortion and instability.
Post time: Mar-31-2023
