Design, Driving, and Compensation for High-Resolution Active Matrix Displays

An approach for going towards high-resolution, uniform displays, with a high brightness range is presented. Before elaborating on this approach, general concepts for display driving and calibration are briefly touched. A design study, comparing analog and digital driving, concludes digital driving is mainly favorable for small, high-brightness displays with limited gray level accuracy, whereas other applications favor analog driving.

To enable good uniformity in AMOLED displays, compensation methods are required. Maintaining high-resolution stipulates a preference for external compensations schemes, with small pixel circuits. Two different external compensation methods are proposed, adopting a 3T2C pixel circuit, and a 2T1C pixel circuit respectively, the latter achieving current variations as low as 0.079% and showing significant improvement in optical uniformity. To increase the brightness range, allowing adequate image quality in different environments, a global dimming method is presented. Evaluating the proposed method on a test display shows promising results, i.e., maintaining image quality at different global brightness settings.

Further increasing the resolution is obtained by optimizing technology. A novel technology stack, combining two different transistor architectures in one flow, is developed. A design study confirms a further increase in resolution up to 1752 ppi is possible with current state-of-the-art tool capabilities. Furthermore, voltage drop and delay calculations validate the feasibility of the design.

Lastly, a design approach for LED walls is presented. Due to the different nature of LED walls, compared to AMOLED displays, other aspects flare up. The inherent wavelength shift with current, and tileability are taken into account in the proposed novel pixel design comprising a current mirror to accurately set the current through the LED, gray level control by PWM, and synchronous driving circuitry to allow updating all pixels in the display module simultaneously.