Xiaomi added DC-Dimming Xiaomi Mi 9

Xiaomi's new DC-Dimming solution also uses a fixed brightness mode switching node, which uses the millet system integration and self-developing algorithm to integrate the “true hardware” DC dimming solution in the driver IC of the OLED screen. It can be clearly seen from the picture that the friends are different from ours, and the color is more transparent under low brightness. 

What is DC Dimming?

While there may be many pros of using an OLED panel, it begins to flicker when the brightness is set to low because OLED panels use Pulse Width Modulation to control backlight brightness, thus causing eye strain. This made OEMs take steps towards features like DC dimming

World main Research and development DC-Dimming method:

At present, the existing DC dimming on the tech world is based on the android system adopting the "software" or "hardware".

Software solutions, please refer to various anti-flicker protection apps, the effect is very poor
There are three hardware solutions

1. Fix the screen dimming level to the brightness mode switching node to ensure that the screen PWM dimming mechanism is not triggered, and then use the Qualcomm platform's pcc+dither scheme to compress the color data output to the screen while ensuring the screen display effect as much as possible. The gray scale value achieves the effect of reducing the brightness.

2, fixed screen dimming level to brightness mode switching node, to ensure that the screen PWM dimming mechanism is not triggered, and then modify the alpha channel described above, in the HWC hardware module, by adding a mask +dither solution with adjustable transparency , compressing the color grayscale value output to the screen to reduce the brightness of the screen

3, fixed screen dimming level to brightness mode switching node, to ensure that the screen PWM dimming mechanism is not triggered, using a third-party display chip, in the case of ensuring the screen display effect as much as possible, compressing the grayscale value of the color data output to the screen , to achieve the effect of reducing brightness. 

Why does OLED need PWM

Why does OLED need pwm (em duty) because in order to improve the yield of OLED, the main principle can be thought of as a lot of voltage control on the panel, different currents are different brightness.

The control current is expected to be very accurate. If it is inaccurate, the brightness will not be expected, and there will be some unevenness in the panel process. However, there are still some differences in the panel process, especially when the water volume is small, so it is in a certain brightness.

The following water volume will be more difficult to control, but the mobile phone must still have a uniform low-brightness picture, so there is a PWM, the more the off time, the smaller the brightness (PWM duty cycle). At present, if the industry is in active mode, it is 4cycle. With a frame rate of 60Hz, there will be 240hz. Currently, the oled product will turn on this function below some brightness. 

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