P_0_1011:A Novel Pixel Circuit to Compensate for the Degradation of OLED Luminance in High-Resolution AMOLED Displays National Cheng Kung University Department of Electrical Engineering IDBA Lab. Advisor.. Chih-Lung Lin Presenter.. Chia-en Wu 1
Outline What s AMOLED The conventional T1C pixel circuit The OLED lifetime Parallel addressing scheme Related researches for AMOLED displays The proposed circuit.. 4TC Simulation results Conclusions
What s AMOLED? AMOLED (Active Matrix Organic Light Emitting Diode) Advantages flexible fast response time high contrast ratio wide viewing angle and low power consumption Disadvantages short product lifetime Samsung's 55" OLED TVs in SID 01 LG s 55 AMOLED HD TV in CES 01 3
Conventional Pixel Circuit V DD Circuit feature.. Simple structure High aperture ratio Disadvantages.. T T1 I OLED V TH variation Power line IR drop Non-uniform luminance I OLED K( V SG_ T1 V TH _ T1 ) K( V DD V DATA V TH _ T1 ) Ref1. Ref. H.P.Shieh, Y.H. Tai, JDT EDL 007, 004, pp. pp. 399 78 I-R Drop V TH variation 4
Emitting Efficiency (cd/a) Lifetime OLED lifetime Defined as the time for the luminance to decrease to half of is initial value. OLED degradation Threshold voltage increase Emitting efficiency decrease 17.5 17.0 16.5 16.0 15.5 15.0 14.5 14.0 5
Driving scheme for pixel circuit Parallel addressing scheme, proposed by Chaji et al. (007) Extend the time for V TH compensation Suitable for application in high-resolution or large-size displays G. R. Chaji, and A. Nathan, Parallel Addressing Scheme for Voltage-programmed Active-Matrix OLED Displays, IEEE Trans. Electron Devices, vol. 54, no. 5, pp. 1095-1100, May. 007. (a)conventional and (b) parallel addressing schemes for voltage programming pixel circuit 6
Related researches for AMOLED displays 5T1C compensating pixel circuit of our prior work (007) C. L. Lin and Y. C. Chen, A novel LTPS-TFT pixel circuit compensating for TFT threshold-voltage shift and OLED degradation for AMOLED, IEEE Electron Device Lett., vol. 8, no., pp. 19-131, Feb. 007. 1 IOLED k ( VGS VTH _ DTFT ) 1 k ( VOLED _ 0 VOLED _1 VTH _ DTFT VDATA VOLED _1 VTH _ DTFT ) Characteristic: Luminance compensation 1 k ( VOLED _0 VDATA ) 7
Related researches for AMOLED displays 5T1C compensating pixel circuit of our prior work (007) C. L. Lin and Y. C. Chen, A novel LTPS-TFT pixel circuit compensating for TFT threshold-voltage shift and OLED degradation for AMOLED, IEEE Electron Device Lett., vol. 8, no., pp. 19-131, Feb. 007. X X 1 IOLED k ( VGS VTH _ DTFT ) 1 k ( VOLED _ 0 VOLED _1 VTH _ DTFT VDATA VOLED _1 VTH _ DTFT ) Characteristic: Luminance compensation 1 k ( VOLED _0 VDATA ) 8
Pixel circuit for luminance compensation V DD C T T1 B A C1 SCAN1 T4 T3 SCAN SCAN3 (a) Characteristics:1. 4TC. Luminance compensation 3. Parallel addressing driving scheme 4. Available for application for high-resolution and large-size displays (b) Operating Principle:Three periods 1) Compensation period ) Data input period 3) Emission period 9
Pixel circuit for luminance compensation V DD C T1 B SCAN1 T4 T C1 A T3 V OLED_0 SCAN SCAN3 Compensation: A V OLED _0 B V V OLED _ 0 TH _ T 4 10
Pixel circuit for luminance compensation V DD C T T1 B C1 A SCAN1 T4 T3 SCAN SCAN3 Data Input: is applied to node A A V DATA C1 B VOLED _ 0 VTH _ T 4 ( VDATA VOLED _ 0) C1 C 11
Pixel circuit for luminance compensation V DD C T1 B SCAN1 T4 T C1 A T3 I OLED SCAN SCAN3 Emission: T1 is turned; V B becomes VDD C C A VDD VTH _ T 4 VDATA VOLED _ 0 C1 C C1 C B V DD 1
Pixel circuit for luminance compensation V DD C T1 B SCAN1 T4 T C1 A T3 I OLED SCAN SCAN3 Emission: 1 IOLED k ( VSG VTH _ T 4 ) 1 ( ) Negative value; Control the corresponding gray level Increase with OLED decay k VB VA VTH _ T 4 1 C C k( VDD VDD VTH _ T 4 VDATA VOLED _ 0 VTH _ T 4 ) C1 C C1 C 1 C k[ ( V DATA VOLED _0)] C1 C 13
Pixel circuit for luminance compensation Pixel information: V DD T1 C B C1 T A SCAN SCAN1 T4 T3 SCAN3 Design Parameter Value SCAN Signal (V) -10~15 VDD (V) 15 (V) -5 C1 (pf) 1.5 C (pf) 1.5-1.~ -5.4 (W/L) T1,T,T3 (μm) 5/5 (W/L) T4 (μm) 5/10 Threshold voltage (V) -1 Mobility (cm /Vs) 44 14
Circuit simulation C T1 V DD B SCAN1 T4 T A C1 T3 SCAN SCAN3 Voltages on node B with varying threshold voltages of driving TFT (ΔV TH = -0.5 V, 0 V, and 0.5 V) 15
Circuit simulation Current error rate in proposed 4TC pixel circuit resulting from threshold voltage variations (ΔV TH = -0.5 V and 0.5 V ) Transient waveforms of OLED current variations when the supply voltage is degraded to 1 V 16
Circuit simulation Normalized OLED current as a function of shift in threshold voltage of OLEDs 17
Conclusion V DD Characteristics: Advantages 1)TFT V TH compensation )IR drop compensation 3)Suitable for application in high-resolution displays 4)Luminance compensation *Detecting OLED aging phenomena T1 C B C1 T A SCAN SCAN1 T4 T3 SCAN3 Disadvantages 1)Leakage current )Unsuitable for application in 3D displays 18
Reference 1. Y. C. Lin, and H. P. Shieh, Improvement of Brightness Uniformity by AC Driving Scheme for AMOLED Display, IEEE Electron Device Lett., vol. 5, pp. 78-730, November 004. H. Y. Lu, T. C. Chang, Y. H. Tai, P. T. Liu, and S. Chi A New Pixel Circuit Compensating for Brightness Variation in Large Size and High Resolution AMOLED Displays ", IEEE Journal of Display Technology, vol. 3, pp. 398-403,Dec. 007. 3. C. L. Lin and T. T. Tsai, A novel voltage driving method using 3-TFT pixel circuit for AMOLED, IEEE Electron Device Lett., vol. 8, pp. 489 491, Jun. 007. 4. B. Y. Chung, D. W. Park, Y. S. Park, D. Y. Chou, K. Kim, B. H. Kim, and S. S. Kim, Driving Method for a D-3D Switchable AMOLED Display Using Progressive or Simultaneous Emission, SID Symposium Digest, pp.68-71, (011) 5. H. S. Park, H. J. In, K. H. Oh, and O. K. Kwon, Successive Cross Emission Driving for 3- Dimensional Active-Matrix Organic Light Emitting Diode Displays, SID Symposium Digest, pp.175-178, (011) 6. Y. I. Hwang, T. S. Park, K. N. Kim, B. H. Kim, B. H. Berkeley, S. S. Kim, and B. D. Choi, New Simple Pixel Circuits for Threshold Voltage and IR-Drop Compensation for AMOLED Displays, IDW Tech. Dig., pp.635-638, (010) 19
Thanks for your attention 0