Kyong-Hwan Oh

An Advanced External Compensation System for Active Matrix Organic Light-Emitting Diode Displays With Poly-Si Thin-Film Transistor Backplane

An advanced method for externally compensating the nonuniform electrical characteristics of polycrystalline silicon thin-film transistors (TFTs) and the degradation of organic light-emitting diode (OLED) devices is proposed, and the method is verified using a 14.1-in active matrix OLED (AMOLED) panel. The proposed method provides an effective solution for high-image-quality AMOLED displays by removing IR-drop and temperature effects during the sensing and displaying operations of the external compensation method. Experimental results show that the electrical characteristics of TFTs and OLEDs are successfully sensed, and that the stained image pattern due to the nonuniform luminance error and the differential aging of the OLED is removed. The luminance error range without compensation is from -6.1% to 9.0%, but it is from -1.1% to 1.2% using the external compensation at the luminance level of 120 cd/m2 in a 14.1-inch AMOLED panel.

A luminance adjusting algorithm for high resolution and high image quality AMOLED displays of mobile phone applications

A luminance adjusting algorithm using light sensing scanner is proposed for small-sized high resolution and high image quality active matrix organic light emitting diode (AMOLED) displays such as smartphone applications. By using simple pixel structure with the proposed algorithm, high aperture ratio in high resolution display can be achieved. Experimental results show that the standard deviation of luminance improves from 7.07 to 1.81 LSB when the proposed adjusting method is used to 3.5-inch AMOLED display with 8-bit gray scale.

P‐166: Successive Cross Emission Driving for 3‐Dimensional Active‐Matrix Organic Light Emitting Diode Displays

We propose a pixel structure and its driving scheme for stereoscopic 3-dimensional (3D) active-matrix organic light emitting diode (AMOLED) displays. The proposed pixel structure and its driving scheme have merits that are longer emission and programming time than simultaneous emission scheme by successive cross emission of left and right images. Moreover, it can reduce flicker by reducing interval between emission times. For 3D AMOLED displays of 40-inch full high definition TV (1920×1080), the emission current error rate of the proposed pixel structure is from −0.961% to 1.013% when the threshold voltage variation of driving TFT varies from −0.8 V to 0.8 V, and that the error is less than 2% when the VDD-IR drop voltage becomes 2.0 V.

Lifetime Extension Method for Active Matrix Organic Light-Emitting Diode Displays Using a Modified Stretched Exponential Decay Model

In this letter, we propose a compensation method for organic light-emitting diode (OLED) degradation occurring in a digital driving scheme for active-matrix OLED displays. The proposed method, in which we are the first to propose, employs the modified stretched exponential decay (SED) model to characterize the OLED degradation and compensates for the associated luminance decrease; the lifetime of an OLED panel can thereby be extended. The OLED panel is fabricated using low-temperature poly-Si thin-film transistors, and measured to verify the modified SED model and the proposed compensation method. The measurement results show that the luminance degradation with and without the proposed method is 0.3% and 6%, 4% and 17.8%, and 7.4% and 30.4%, for red, green, and blue OLEDs, respectively. This measurement is taken after 40 h of operation under a 350 cd/m2 initial luminance. Accordingly, the proposed compensation method extends the lifetime of the OLED panel up to 72.5, 15.5, and 20.75 times longer in red, green, and blue OLEDs, respectively, compared with the conventional method.

A pixel structure for simultaneous programming and emission method for shutter‐glasses‐type stereoscopic 3‐D AMOLED displays

— A pixel structure for shutter-glasses-type stereoscopic 3-D active-matrix organic light-emitting-diode (AMOLED) displays is proposed. The proposed pixel programs data to the pixel during the light-emission time of an OLED. Because the emission time of the proposed pixel is extended, it is expected that the proposed pixel not only decreases the peak current of the OLED during the emission period but also reduces flicker. Moreover, the aperture ratio of the proposed pixel is 58.69% for a 50-in. full-high-definition (FHD) condition by minimizing the number of thin-film transistors (TFTs), capacitors, and control signal lines as seven TFTs, two capacitors, two power lines, and four control lines per unit pixel. Simulation results show that the error in the emission current of the proposed pixel is from −0.82% to +0.90% when the threshold-voltage variation of the driving TFT is ±1.00 V, and the maximum variation of the emission current is −1.35% when a voltage drop in the power line is −0.50 V on a full-white-image display.

A Pixel Structure Using Block Emission Driving Method for High Image Quality in Active Matrix Organic Light-Emitting Diode Displays

In this paper, we propose a pixel structure and timing diagram using the block emission (BE) driving method to improve the image quality of high-resolution active matrix organic light-emitting diode (AMOLED) displays. The proposed pixel structure reduces the boundary error pattern between blocks by adjusting the timing of the compensation (comp) signal for the threshold voltage variation. The test patterns, which include a pixel array and unit pixels, are designed for a 10-inch quadruple high-definition resolution format and are fabricated to verify the image quality of the AMOLED displays. The measurement results show that the emission current error at the boundary between blocks is reduced from +11% to less than ±1% by adjusting the timing of the comp signal. Also, the emission current error caused by the threshold voltage variation of the driving thin film transistors is reduced from ±8.36% to ±2.77% at a gray level of 175 by using the BE driving method. Therefore, the proposed pixel structure improves image quality in high-resolution AMOLED displays.

A Luminance Compensation Method Using Optical Sensors with Optimized Memory Size for High Image Quality AMOLED Displays

This paper proposes a luminance compensation method using optical sensors to achieve high luminance uniformity of active matrix organic light-emitting diode (AMOLED) displays. The proposed method compensates for the non-uniformity of luminance by capturing the luminance of entire pixels and extracting the characteristic parameters. Data modulation using the extracted characteristic parameters is performed to improve luminance uniformity. In addition, memory size is optimized by selecting an optimal bit depth of the extracted characteristic parameters according to the trade-off between the required memory size and luminance uniformity. To verify the proposed compensation method with the optimized memory size, a 40-inch 1920x1080 AMOLED display with a target maximum luminance of 350 cd/m2 is used. The proposed compensation method considering a 4σ range of luminance reduces luminance error from ± 38.64%, ± 36.32%, and ± 43.12% to ± 2.68%, ± 2.64%, and ± 2.76% for red, green, and blue colors, respectively. The optimal bit depth of each characteristic parameter is 6-bit and the total required memory size to achieve high luminance uniformity is 74.6 Mbits.

27.4: Distinguished Student Paper: Simultaneous Programming and Emission Driving Using External Compensation Method for 3D AMOLED Displays

Simultaneous programming and emission driving using external compensation method for 3D active matrix organic light emitting diode (AMOLED) displays is proposed. The emission current uniformity is improved by compensating threshold voltage and mobility variations of driving TFTs. Simulation results show that the maximum emission current error range of the proposed method is from −1.6% to 0.6% in 40-inch full HDTV condition when the threshold voltage of driving TFT variation is form −1 V to 1 V and mobility variation of driving TFT is from −10% to 10%. The emission and programming time of 3D AMOLED display is also increased by simultaneous driving method.

Memory reduction method of luminance compensation algorithm for mobile AMOLED display applications

A memory reduction method of luminance compensation algorithm using luminance sensor is proposed for high resolution mobile active matrix organic light emitting diode (AMOLED) display applications. The proposed method can be applied to AMOLED panels which have poor luminance uniformity even though compensation pixel circuit is used. Measurement results show that the deviation of luminance error is reduced from 18.1% to 3.8% when the proposed algorithm is applied to 5.3-inch AMOLED panel using threshold voltage compensation pixel structure.

Threshold-Voltage-Shift Compensation and Suppression Method Using Hydrogenated Amorphous Silicon Thin-Film Transistors for Large Active Matrix Organic Light-Emitting Diode Displays

A threshold-voltage-shift compensation and suppression method for active matrix organic light-emitting diode (AMOLED) displays fabricated using a hydrogenated amorphous silicon thin-film transistor (TFT) backplane is proposed. The proposed method compensates for the threshold voltage variation of TFTs due to different threshold voltage shifts during emission time and extends the lifetime of the AMOLED panel. Measurement results show that the error range of emission current is from -1.1 to +1.7% when the threshold voltage of TFTs varies from 1.2 to 3.0 V.