Research On Open-loop External Compensation Method For AMOLED Displays

In recent years,active-matrix organic light emitting diode(AMOLED)displays is taking increasing share of global display markets,proving to be the next generation display which will substitute the traditional liquid crystal displays(LCDs).Compared with LCDs,AMOLED owns the advantages like high display quality,low power consumption and flexibility.However,current AMOLED technologies mainly suffers from display uniformity issue.The characters of driving TFTs in display arrays will shift along with the bias-stress time,causing a series of uniformity issues like image-sticking and aging.As a result,compensation is vital important for maintaining high quality AMOLED displays.Currently,the most effective and promising method is external compensation method,which will utilize external drivers to sense the working states of driving TFTs and accordingly adjust the output driving signals.Generally,there are mainly two drawbacks exists in the current existing external compensation methods,the first is compensation timing issue,and the second is the long-term effectiveness issue.For the compensation timings,it is challenging to achieve sensing and fully compensation in a single gate scan time during normal display periods,especially for gate scan time limited high resolution displays.As a result,most of the commercialized products will choose to sense and compensate in non-display periods.This approach avoids the scan timing issues,but the display quality will continuously drop during display.Hence,achieving displaying-synchronous compensation with reduced timing requirements is still a problem remains to be solved.Besides,for the effectiveness verification of long-term compensation effectiveness verifications,most of the existing works adopt single pixel circuit with pre-set shifts to verify the compensation effectiveness in one or few frame times.However,this method is far different from the real display situations.The verification method of the long-term effectiveness should be close to the real situations.The simulation should be based on the entire display,generating the intrinsic TFT shift based on display contents,which will be a more effective approach to verify the compensation methods.This paper carried out a series of research aimed to solve the above issues.Firstly,a displaying-synchronous open-loop compensation method is proposed,able to perform displaying-synchronous sensing and open-loop compensation in backstage during normal display period to maintain display quality.This method is not limited by scan times since the sensing and compensation stage are separated.Secondly,a system level simulation method for displays is proposed.This simulation method will measure the compensation effectiveness by displaying videos and image evaluation algorithms in the simulated high resolution display arrays.This method is also applied to measure the proposed intermittent compensation method.The overall results represent that the proposed external compensation method and universal display simulation method could achieve satisfying performance.