Currently, the narrow pixel pitch (NPP) LED Display or Mini and Micro-LED products are generally for indoor application, especially the emerging of LED Wall, micro TV, small VIP cinema. These applications need the LED screen can achieve the ultra-low luminance designed for the dark surroundings.

Because human eyes are very sensitive in ultra-low brightness, the small brightness difference on LEDs is captured in this circumstance, so from LED drivers’ point of view, low current accuracy from channel to channel and from device to device will cause non-uniformity on low gray scale by column or matrix. In addition, When the turning-on pulse is getting smaller, the transient accuracy becomes another key issue. The transient current difference is mainly caused by the deviation of LEDs, such as forward voltage, parasitic capacitor.

Figure 2-7 shows the non-uniformity of NPP LED display in low gray scale.