Description of Flicker Phenomenon
FLICKER is a common TFT display flicker phenomenon, which usually manifests itself as a rapid change in screen brightness. Ideally, the center values of Vcom (common electrode voltage) and Vpixel (pixel voltage) should be the same, and the difference between VoixelH and VpixelL should be equal to the difference between VcomH and VcomL. The FLICKER phenomenon may occur when the center value or difference of these voltages deviates.
Line Inversion
Horizontal stripes that appear when the screen is physically moving, and which diminish or disappear when the screen is stationary, especially in grayscale displays.
Frame Inversion
A flickering phenomenon that occurs when the entire screen alternates between light and dark, i.e., within the full screen.
Main Causes and Influencing Factors
Vcom interacts with Flicker
Vcom adjustment is critical to minimize Flicker. Negative Vcom shifts in constant white mode increase the brightness difference, while positive Vcom shifts in constant black mode decrease the brightness difference. Optimization can be found by precisely adjusting Vcom.
Effects of VGH and Flicker
VGH (Gate High Voltage) has a direct effect on the pixel fill level, too high or too low will change the brightness difference between frames, thus affecting the Flicker effect.
VGL and Flicker Correlation
VGL (Gate Low Voltage) affects the pixel current characteristics, and its improper setting can also cause Flicker fluctuation.
The Solution
Adjust the Vcom voltage:
Try to adjust Vcom and its associated values (e.g. VcomH) to find the direction that makes the flicker screen lightest and determine the optimal value.
Selection of polarity reversal method
Select the appropriate polarity inversion mode (e.g. frame inversion) to improve the display quality according to the specific situation.
Matching refresh direction
Ensure that the CPU data update direction matches the module refresh direction to avoid splash screen problems caused by inconsistent directions. Make the refresh frequency match the CPU write speed to ensure the screen stability.
Parameter Adjustment:
Adjust the GAMMA curve or optimize the VGH and VGL settings, etc. to further reduce the Flicker. in normal white mode, as the gray scale rises, the negative shift of Vcom will lead to an increase in the brightness difference; on the contrary, the positive shift of Vcom in normal black mode will reduce the brightness difference. By adjusting Vcom, the optimal flicker state can be found.
By the above method, the Flicker phenomenon in TFT displays can be effectively reduced or eliminated. By adjusting the values of the common electrode voltages Vcom and VcomH, we try to find the direction that makes the flicker screen the lightest and determine the optimum value. Since the adjustment of these values is jumpy, sometimes the flicker screen can only be adjusted to a very unobtrusive state, but not completely resolved. If the customer is not satisfied, try adjusting the GAMMA or changing to frame inversion mode, as splash screens larger than 100Hz are indistinguishable to the human eye.
