Silicon OLED microdisplay is a display solution using CMOS circuits on silicon panels to drive OLED pixels. In its operating mechanism, driving circuits play a crucial role, enabling the display to present colorful images. These circuits control pixel on/off and brightness, leading to digital and analog driving methods.
Analog driving adjusts pixel current by changing the gate voltage of the driving transistor, like fine-tuning a voltage knob for different gray-level brightness. The adjustment signal is continuous. An ideal analog driving circuit precisely provides the right current for each pixel.
Digital driving circuits supply power to pixel units. Instead of adjusting voltage or current, they keep the control voltage 100% constant and adjust the on-off time ratio of each pixel. This is like installing a switch for each pixel to control its lighting. Longer on-time results in a high-brightness pixel for high-gray-scale areas, while shorter on-time gives a low-brightness pixel for low-gray-scale areas. This is a discrete signal, achieving different brightness levels by controlling the number of on-time units.
Both driving methods aim to drive pixels to emit specific light. Ideal circuits can accurately regulate pixel brightness.
However, in practice, some characteristics of silicon OLED microdisplays affect the driving methods' adjustment effects.
The current required for actual light emission in silicon OLED microdisplays is extremely small (nA level), and that of low-gray-scale pixels is even smaller (pA level). The current differences between adjacent-brightness-level low-brightness pixels are slight. Analog signals, being continuously adjusted, can't accurately grade these pixels, resulting in gray-scale loss, lack of details in similar dark colors, and poor image quality.
Digital driving, not relying on continuous voltage or current adjustment, precisely controls pixel and sub-pixel brightness by adjusting the number of on-time units, even in low-gray-scale cases, presenting a smoother and more detailed image in the full-gray-scale range.
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