Active Matrix Organic Light Emitting Diode Panel Research Articles

P‐67: Foldable Ultra‐High‐Resolution AMOLED Panel with Cascade Display‐Driver Integrated Circuit

Smart portable device equipped with active matrix organic light emitting diode (AMOLED) display is a trend in modern consumer market. In this paper, we present not only a 15.6‐inch foldable 4K ultra high definition (UHD) resolution of low temperature poly‐silicon thin film transistor (LTPS‐TFT) AMOLED panel, but also a display driver integrated circuit (DDIC) module which integrate the cascade structure and high‐magnification demura 6 times compression technology.

Achieving high sensing in 0.5 nA for the driving pixel currents in AMOLEDs with settling time of 7 µs by a new external current sensing circuit

A new external current sensing circuit with baseline compensation for the active matrix organic light emitting diode (AMOLED) display is developed herein to achieve the sensing precision of 0.5 nA in pixel with 7 µs of settling time. Current sensing circuit incorporates a new push–pull transient current feedforward whereas the current analog to digital converter (CADC) based digital baseline current compensation incorporates an 11-bit current digital-to-analog converter, a current comparator and a digital control circuit with an 11-bit successive approximation register. The proposed integrated mixed signal IC drives a 6T1C pixel-based AMOLED panel with one horizontal time of 7.7 µs at a scan frequency of 60 Hz. The design readout chip can simultaneously sense and compensate TFT baseline current variation. The readout circuit and the baseline compensation circuit are implemented in the integrated chip with chip area of 125 μm × 46 μm and fabricated via TSMC T18 process. With the standard 3.3 V supply, experimental result shows that the overall power consumption of the chip is 988 µW watt. The minimum LSB current for the CADC is 10 nA and the maximum achievable sampling rate is 500 KS/s. The measured INL and DNL of CADC is 0.84 and 0.98 respectively. Despite of heavy data line parasitic capacitances (2.6 KΩ/20 pF) of the AMOLED display, experimental results show that the proposed circuit can sense 0.5 nA current within 7 µs of settling time. The sensing precision of 0.5 nA within 7 µs are the best among all reported literature to date whereas the current sense range (0.5–500 nA), system sampling rate (142 KS/s), INL (0.84) and DNL (0.98) of the CADC is approximately comparable among all reported.

Optimal Color Lighting for Scanning Images of Flat Panel Display using Simplex Search

A system for inspecting flat panel displays (FPDs) acquires scanning images using multiline charge-coupled device (CCD) cameras and industrial machine vision. Optical filters are currently installed in front of these inspection systems to obtain high-quality images. However, the combination of optical filters required is determined manually and by using empirical methods; this is referred to as passive color control. In this study, active color control is proposed for inspecting FPDs. This inspection scheme requires the scanning of images, which is achieved using a mixed color light source and a mixing algorithm. The light source utilizes high-power light emitting diodes (LEDs) of multiple colors and a communication port to dim their level. Mixed light illuminates an active-matrix organic light-emitting diode (AMOLED) panel after passing through a beam expander and after being shaped into a line beam. The image quality is then evaluated using the Tenenbaum gradient after intensity calibration of the scanning images. The dimming levels are determined using the simplex search method which maximizes the image quality. The color of the light was varied after every scan of an AMOLED panel, and the variation was iterated until the image quality approached a local maximization. The number of scans performed was less than 225, while the number of dimming level combinations was 20484. The proposed method can reduce manual tasks in setting-up inspection machines, and hence is useful for the inspection machines in FPD processes.

Shaping the Spatial and Temporal Noise Characteristics of Driving Signals for Driving AMOLED Display

In this paper, a digital driving technique for generating binary driving signals to display a digital video on an active-matrix organic light-emitting diode (AMOLED) panel is proposed. The ideal spatial and temporal noise characteristics of the driving signal for an AMOLED panel to display high-quality video are first suggested. Based on the suggested characteristics, a digital driving technique is proposed to generate the driving signals for an AMOLED panel. Simulation results show that the proposed driving technique can generate driving signals having the desired spatial and temporal noise characteristics and, accordingly, allows an AMOLED panel to display video of better quality than other conventional driving techniques in terms of various measures.

A Hybrid AMOLED Driver IC for Real-Time TFT Nonuniformity Compensation

An active matrix organic light emitting diode (AMOLED) display driver IC, enabling real-time thin-film transistor (TFT) nonuniformity compensation, is presented with a hybrid driving method to satisfy fast driving speed, high TFT current accuracy, and a high aperture ratio. The proposed hybrid column-driver IC drives a mobile UHD $\left({{3840} \times {2160}} \right)$ AMOLED panel, with one horizontal time of ${7}.{7}\,{\upmu \text{s}}$ at a scan frequency of 60 Hz, simultaneously senses the TFT current for back-end TFT variation compensation. Due to external compensation, a simple 3T1C pixel circuit is employed in each pixel. Accurate current sensing and high panel noise immunity is guaranteed by a proposed current-sensing circuit. By reusing the hybrid column-driver circuitries, the driver embodies an 8 bit current-mode ADC to measure OLED $V$ – $I$ transfer characteristic for OLED luminance-degradation compensation. Measurement results show that the hybrid driving method reduces the maximum current error between two emulated TFTs with a 60 mV threshold voltage difference under 1 gray-level error of 0.94 gray level (37 nA) in 8 bit gray scales from 12.82 gray level (501 nA). The circuit-reused current-mode ADC achieves 0.56 LSB DNL and 0.75 LSB INL.

Depletion Mode Oxide TFT Shift Register for Variable Frame Rate AMOLED Displays

This letter demonstrates a shift register circuit at the backplane of depletion mode oxide thin-film transistors (TFTs), which can cover variable frame rates for low-power active matrix organic light emitting diode (AMOLED) displays. The proposed scheme focuses on the stable gate control of a pull-up TFT by securing the charging and discharging paths at the wide operating frequency range. In a prototype high-definition (HD: 1366 × 768) AMOLED panel, it is ensured that fabricated shift registers operate at the wide frame frequency range from 1 to 240 Hz. The measured current consumptions are 30, 4, 6, and 5.8 mA for four clock signals, VGH of 24 V, VGL1 of -6 V, and VGL2 of -14 V at a frame rate of 120 Hz.

The Method of 2/3 Sampled Sub-Pixel Rendering for AMOLED Display

Due to the capability of the AMOLED (Active matrix organic light emitting diode) display can provide superior color saturation, flexible utilization, slimmer screen profile and more impressive image quality, it has received increasing demand for application in electronic devices. The organic light emitting diode (OLED) is current driven device so that the characteristics of thin field transistor (TFT) influence panel uniformity. Multiple TFT of pixel circuitry has been designed to compensate the Vth (threshold voltage) variations of array process and other driving issues. The fine metal mask (FMM) used in the OLED evaporation is an accurate mask having physical margin limitations in the high PPI (pixel per inch) AMOLED application. This paper details the utilization of a 2/3 sampled sub-pixel rendering (SPR) method to liberate more 50% layout area than the RGB stripe configuration. The proposed algorithm utilizes edge detection and one-side color diffusion to improve display performance as well as RGB stripe compatibility. A 4.65” HD (720 ×1280) AMOLED panel with a 317 PPI retina display was implemented to realize the development of our SPR technology.

A Low-Power Contrast Enhancement Algorithm Using Histogram Segmentation and Circuit Implementation for AMOLED Applications

A low-power contrast enhancement algorithm is proposed for active-matrix organic light-emitting diode (AMOLED) applications in this paper. Compared with the conventional contrast enhancement on global images, the proposed contrast enhancement has been implemented for each histogram segment, respectively, which is better for local contrast. An effective power reduction method to conserve local details is also presented based on the histogram segmentation. Moreover, a self-adaptation power reduction mechanism is further employed to achieve the tradeoff between the image quality and the power consumption for videos. Finally, the algorithm has been implemented on a FPGA with a 2.8-in AMOLED panel. The simulation and experimental results demonstrate that power consumption is reduced by 30%-40% using the algorithm, while keeping a good image quality.

Life time extension method for simultaneous emission driving AMOLED displays

A life time extension method for simultaneous emission driving active matrix organic light emitting diode (AMOLED) displays is proposed. The proposed driving method extends emission time by driving even and odd row lines separately. The extended emission time reduces organic light emitting diode (OLED) degradation because the current density of the OLED decreases as emission time increases. The proposed driving method increases the emission time by 50% compared with the conventional simultaneous emission driving method. Measurement results show the proposed driving method increases the OLED life time by 70.07% when the target luminance of the OLED is 300 cd/m 2 and the life time is assumed that the time until the OLED luminance becomes 75% of the initial luminance. The proposed pixel structure using the even-odd separation driving scheme compensates the electrical characteristic variation of the polycrystalline-silicon thin film transistors and the maximum luminance error of pixel to pixel is 0.26% in a 3.8-inch AMOLED panel.

27.1: Integrated pMOS Gate Driver for a 3D AMOLED Display

AbstractSimultaneous Emission with Active Voltage control (SEAV) is a strong candidate for crosstalk‐free driving of 3D Active Matrix Organic Light Emitting Diode (AMOLED) displays. A gate driver for a SEAV 3D AMOLED panel needs two operating modes: the simultaneous switching mode and the progressive scanning mode. However, conventional gate drivers can operate in only progressive scanning mode. In this paper, a new integrated gate driver to support both of these modes is proposed and applied to a prototype 3D AMOLED display panel.

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 Synchronous Multioutput Step-Up/Down DC–DC Converter With Return Current Control

This brief presents a new return-current control method for a multioutput step-up/down dc-dc converter. Compared with prior multioutput dc-dc converters, the presently described converter can generate outputs higher or lower than the input voltage with simple control-loop compensation while guaranteeing stability in a wide load range. Using a 0.5-mum bipolar CMOS (BiCMOS) process, a converter having five outputs has been implemented for an LG active-matrix organic light-emitting diode (AM-OLED) display panel. The implemented converter operates at 1-MHz switching frequency with 4.7- muH inductor and 10-muF capacitor. Experimental results show that the proposed control method can generate tightly regulated stepped-up or -down outputs stably under a wide load variation. The conversion efficiency is higher than 80% at a typical AM-OLED panel grey level.

Improvement of Brightness Uniformity by AC Driving Scheme for AMOLED Display

We propose an AC voltage driving scheme which can improve the brightness uniformity of active-matrix organic light-emitting diode (AMOLED) displays. Through the use of a charge feed-through mechanism and an AC driving voltage, the voltage drop caused by the parasitic resistance can be compensated. A 2.2 in AMOLED panel with a resolution of 176/spl times/RGB/spl times/220 has been fabricated by low temperature polycrystalline silicon technology to evaluate the performance of the AC driving scheme. Experimental results show that a brightness uniformity of higher than 91.6%, achieved by the AC driving scheme, in contrast to that of 74% achieved by a DC driving scheme.