A New Voltage Driving Pixel Circuit for Active Matrix Organic Light Emitting Diodes

Transcription

1 A New Voltage Driving Pixel Circuit for Active Matrix Organic Light Emitting Diodes Cheng-Chiu Chiu Pai 白承丘 ccpai.eo92g@nctu.edu.tw Department of Photonics & Institute of Electro-Optical Engineering, NCTU, Hsinchu, Taiwan

2 Organic Light Emitting Device Characteristics From : Light Thin Self emissive Wide viewing angle Fast response time High contrast ratio Low voltage DC drive Simple device structures

3 AMOLED Driving Methods National Chiao Tung University Voltage Current Digital Novel AC Self-Com.(Cvt) Match TFT Resistor Copy Mirror Scaling Time, Area Clamped Driving Active load Inverter Dawson IEDM98 Kodak Nam IDW01 Choi Komiya Type-B Choi Komiya Park Han Goh IDW01 EDL02 Pai IDMC05 Goh EDL03 Type A, B Goh Tam Epson Lee Kim Kim Euro02 Kwak Komiya Type-A Yeh ITRI Park AMLCD04 Jung Jung EDL04 Yujuan T-ED03 Sanford IBM Ono IDTech You Lee Lin EDL04 Wang ASID00 ITRI Kim Dawson IEDM98 Kodak He EDL00 JJAP01 T-ED01 Hong Lin Toppoly Bhowmick Shimoda NEC Kim Ohta Toshiba Tseng AUO Shirasaki Bae IDRC00 LG.Ph Sasaoka SID01 IDW01 Sony Wang IDW01 ITRI Chen IDW01 ITRI Chen Euro02 ITRI Wu Euro02 Sakariya Euro02 Fish Philips Lo Tseng AUO Lee EDL04 Lee Lee J Kimura IDW99 Epson Mizukami SID00 Inukai SID00 Ouchi Hitachi Tam Epson Nanmoto Epson Tanada Kimura Tagawa Sharp Akimoto Hitachi Kageyama Hitachi Kageyama Hitachi Casio

4 Comparison of Driving Methods Method Principle Advantage Disadvantage 1.Self-Com.(Cvt) 1.Great tolerance of 1.Non-uniformity of gray Voltage Driving 2.Match TFT 3.Clamped Inverter 4.AC Driving 5.R, Active load variations of Vth 2.Compatible with data drivers 3.Simple architecture of level due to μ variation drivers Current Driving 1.Current Copy 2.Current Mirror 3.Current Scaling 1.Great tolerance of variations of Vth and μ 2.Control the brightness of OLED directly 1.Driving speed is too slow 2.Complex driver circuit Digital Driving 1.Time period 2.Area period 1.Great tolerance of variations of Vth and μ 1.Need very fast addressing speed (low resolution) 2.Complex process

5 AMOLED Driving Methods National Chiao Tung University Voltage Current Digital Novel AC Self-Com.(Cvt) Match TFT Resistor Copy Mirror Scaling Time, Area Clamped Driving Active load Inverter Dawson IEDM98 Kodak Nam IDW01 Choi Komiya Type-B Choi Komiya Park Han Goh IDW01 EDL02 Pai IDMC05 Goh EDL03 Type A, B Goh Tam Epson Lee Kim Kim Euro02 Kwak Komiya Type-A Yeh ITRI Park AMLCD04 Jung Jung EDL04 Yujuan T-ED03 Sanford IBM Ono IDTech You Lee Lin EDL04 Wang ASID00 ITRI Kim Dawson IEDM98 Kodak He EDL00 JJAP01 T-ED01 Hong Lin Toppoly Bhowmick Shimoda NEC Kim Ohta Toshiba Tseng AUO Shirasaki Bae IDRC00 LG.Ph Sasaoka SID01 IDW01 Sony Wang IDW01 ITRI Chen IDW01 ITRI Chen Euro02 ITRI Wu Euro02 Sakariya Euro02 Fish Philips Lo Tseng AUO Lee EDL04 Lee Lee J Kimura IDW99 Epson Mizukami SID00 Inukai SID00 Ouchi Hitachi Tam Epson Nanmoto Epson Tanada Kimura Tagawa Sharp Akimoto Hitachi Kageyama Hitachi Kageyama Hitachi Casio

6 Device Modeling I D -V GS curves of poly-si TFTs I-V V characteristics of an OLED

7 Parameters used in the pixel circuit simulation T DV W/L Tsw W/L Cst Cvt Vdd Vscan1 Vscan2 Vscan3 ΔV TH TH of T DV 7μm/5μm 7μm/5μm 0.5pF 0.5pF 10V 0-10V 0-15V +/-0.33V

8 Conventional 2T1C Pixel Circuit I OLED I oled 1 = µ C 2 OX W L ( V V ) 2 GS TH Variations of threshold voltage (V( TH ) can affect the output current of Driving TFT(T DV Non-uniformity problems of display images DV ).

9 Variation of Vout due to V th

10 4T2C National Chiao Tung University IDW 01 IEEE EDL 02 Goh s s Pixel Circuit (Voltage Driving) x V in +ΔV e 1. initialization period 2. compensation period 3. data-input period x x ΔV e 1. The gate and the source of T DV are initialized to ground. a C VT _stored_δv = VTH _ T VTH OLED + V DV _ 1+ a 1+ a 1+ a 3. I OLED OLED = K(V GS - V TH_TDV ) 2 = K(V in + ΔV - V out - V TH_TDV TH_TDV ) a = OLED in K K T T DV

11 Transient simulation result The unnecessary OLED current during the compensation period. The output voltage can not been completely compensated by the voltage stored in Cvt, unless the parameter a is very large.

12 Modified IDW 03 Samsung SDI Modified Komiya s s Pixel Circuit (Voltage Driving) 2. Additional Scan line3 is used to increase the driving capability of Tsw1 5T2C 1. N-type TFT is used for T DV Komiya s s Pixel Circuit I OLED = K( V dd V in ) 2

13 Modified IDW 03 Samsung SDI Modified Komiya s s Pixel Circuit (Voltage Driving) 5T2C V in +V TH_TDV x 1. compensation period 2. data-input period x x V TH_TDV x 1. C VT 2. I OLED VT _stored_δv = V TH_TDV OLED = K(V GS - V TH_TDV ) 2 = K(V in + V TH_TDV - V out - V TH_TDV TH_TDV )

14 Transient simulation result

15 5T2C National Chiao Tung University Proposed Pixel Circuit (Voltage Driving) C ST :sustain the gate voltage of T DV against the leakage currents of T SW during a frame time C VT :store the V TH of T DV Data line Scan line 1 Scan line 2 (1) (2) (3) (1) initialization period (2) compensation period (3) data-input period T sw4 :prevents the current from flowing through the OLED during initialization and compensation period 1. improve the dark gray level 2. increase the contrast ratio 3. decrease power consumption of the panel

16 5T2C National Chiao Tung University Proposed Pixel Circuit (Voltage Driving) x V in +V TH_TDV e 1. initialization period 2. compensation period 3. data-input period x x e V Data line TH_TDV Scan line 1 x Scan line 2 (1) (2) (3) (1) initialization period (2) compensation period (3) data-input period 1. The gate and the source of T DV are initialized to ground C VT 3. I OLED VT _stored_δv = V TH_TDV OLED = K(V GS - V TH_TDV ) 2 = K(V in + V TH_TDV - V out - V TH_TDV TH_TDV )

17 Transient simulation result

18 Non-uniformity of Output Current I max -I min I avg

19 Conclusions A new voltage driving pixel circuit composed of five TFTs and two capacitors for AMOLED is proposed. Simulation results indicate that the pixel circuit is effective to provide a uniform output characteristic against the variation in the Poly-Si TFTs performances.

20 Thank You