| With the development of science and technology,people's demand for mobile phones,tablets and other digital products is gradually increasing.Therefore,people's demand for high quality display in digital products is also increasing,and display technology is getting more and more attention.At present,liquid crystal display and light-emitting diode display are widely used in research and commercial fields.With the deepening of scientific research,Active Matrix Organic Light Emitting Diode(AMOLED)display technology is gradually known and sought after.AMOLED display technology is expected to become the main display technology for the third generation of flat panel due to its advantages such as autonomous luminescence,high speed response,low power consumption,thin and light structure,wide viewing Angle and so on.Among them,thin and light structure is also indispensable for the flexibility and transparency required by the display.Therefore,AMOLED also represents the latest trend in flat panel display technology.Yet despite the AMOLED display technology has many advantages,but due to time stress,manufacturing process,such as constraint factors,there are still some inevitable problems,such as driving transistor threshold voltage and mobility of drift problem caused by the parasitic resistance,addressing electrode produce the power supply voltage drop(I-R)reduction and OLED degradation problems,All these will affect the brightness uniformity of the display,so it is essential to design the corresponding compensation circuit in the development of AMOLED display technology.In this paper,based on the combined structure of Low Temperature Poly silicon-thin Film Transistor(LTPS-TFT)and capacitor,three different pixel compensation circuits are designed and improved.The detailed introduction is as follows:(1)An all-P pixel compensation circuit composed of 5 P-type LTPS-TFT and 2 capacitors is designed to compensate the threshold voltage and mobility drift of the drive transistor and the I-R drop of the power supply voltage.Simulation results show that in the threshold voltage and mobility of the change of ±0.5 V and ±30%,the drive transistor drive current produced by the error rate is within 6%,and when power cut 0.5 V,current error rate is only about 6%,indicating that the problems of the original circuit after compensation for the influence of the drive current smaller,increase the stability of the current.(2)Improved the pixels of a whole N compensation circuit,by 6N-type LTPS-TFT and of two capacitors,compared with before improvement,through the optimization of sequential adjustment and capacitance layout,based on the problem of threshold voltage drift compensation,a compensation function has been added,namely the compensation for migration rate,make the drive current more stability.The simulation results show that the error rate of the driving current is only 4% when the threshold voltage is changed by ±0.5 V.In the case of mobility change of ±30%,the current error rate generated by the driving transistor is not higher than 9%,compared with the original circuit has a better compensation effect and stability.(3)A new compensation method is designed to solve the problem of driving transistor threshold voltage drift in P-type AMOLED pixel circuits and OLED degradation in both N-type and P-type pixel circuits(all P-type is taken as an example in this chapter).The compensation circuit is composed of 6 P-type LTPS-TFT and 2 capacitors.Through the clever design of the circuit structure and reasonable arrangement of the timing sequence,the OLED is placed between the power supply and the source of the driving transistor to realize the compensation of OLED degradation and threshold voltage drift.The simulation results show that the driving current error rate is only 3% when the threshold voltage of the driving transistor is changed by ±0.5 V.And the problem of OLED degradation has been verified by repeated theoretical deliberations. |
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