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In recent years, the active-matrix organic light-emitting diode (AMOLED) displays have been greatly required. A voltage compensation pixel circuit based on an amorphous indium gallium zinc oxide thin-film transistor is presented for AMOLED displays. The circuit is composed of five transistors–two capacitors (5T2C) in combination with an OLED. In the circuit, the threshold voltages of both the transistor and the OLED are extracted simultaneously in the threshold voltage extraction stage, and the mobility-related discharge voltage is generated in the data input stage. The circuit not only can compensate the electrical characteristics variation, i.e., the threshold voltage variation and mobility variation, but also can compensate the OLED degradation. Furthermore, the circuit can prevent the OLED flicker, and can achieve the wide data voltage range. The circuit simulation results show that the OLED current error rates (CERs) are lower than 3.89% when the transistor's threshold voltage variation is ±0.5V, lower than 3.49% when the mobility variation is ±30%. [ABSTRACT FROM AUTHOR]

A voltage-programmed pixel circuit based on low-temperature poly-silicon (LTPS) thin-film transistors (TFTs) is presented for active-matrix organic light-emitting diode (AMOLED) displays. The circuit consists of six p-type transistors and one capacitor (6T1C). During the extraction stage, the circuit extracts the driving TFT's threshold voltage and the power supply voltage. During the data input stage, the circuit generates a charging voltage, which is associated with the driving TFT's mobility and the OLED's threshold voltage. Consequently, the pixel circuit, using only one capacitor, compensates not only for the TFT's electrical characteristics variations, i.e., the threshold voltage variation and mobility variation, but also for the power supply voltage drop and the OLED degradation. The circuit simulation results reveal that the OLED current error rates (CERs) are lower than 5.09% when the threshold voltage varies by ± 0. 5 V , lower than 3.61% when the mobility varies by ± 30 % , and lower than 9.16% when the voltage drop varies by − 0. 5 V in the data voltage range. [ABSTRACT FROM AUTHOR]

Design and synthesis of novel mono- and dimeric quinazoline derivatives (+)-6-methyl-6-pyridin-2-yl-5,6-dihydrobenzo[4,5]imidazo[1,2- c ]quinazoline ( 1 ) and (+)-6-[(6-methyl-5,6-dihydrobenzo-[4,5]imidazo[1,2-c]quinazolin-6-yl)-pyridin-2-yl]-6-methyl-5,6-dihydro-benzo-[4,5]imidazo-[1,2- c ]quinazoline ( 2 ) have been described. Both 1 and 2 have been characterized by elemental analyses, FT-IR, 1 H and 13 C NMR, HRMS spectroscopic studies and their structures authenticated by X-ray single crystal analyses. Photophysical properties of these compounds have been studied by UV/VIS absorption and fluorescence spectroscopy and transient photoluminescence analysis in solution, powder, and non-doped (neat) and doped vacuum-deposited films. A broad emission spectrum spanning most of the visible range and good thermal stability indicated promising application of 1 and 2 as OLED emitters. Unfortunately, under current flow we observed rapid device degradation, presumably to be related to free –N H moiety in these compounds. [ABSTRACT FROM AUTHOR]

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 $\left({{3840} \times {2160}} \right) AMOLED panel, with one horizontal time of 7.7\,\upmu \texts at a scan frequency of 60 Hz, simultaneously senses the TFT current for back-end TFT variation compensation. Due to external compensation, a simple 3T1C pixel circuit is employed in each pixel. Accurate current sensing and high panel noise immunity is guaranteed by a proposed current-sensing circuit. By reusing the hybrid column-driver circuitries, the driver embodies an 8 bit current-mode ADC to measure OLED V–$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. [ABSTRACT FROM PUBLISHER]

This paper proposes a new pixel circuit for an active matrix organic light-emitting diode (OLED) display, which consists of five thin-film transistors (TFTs) and one capacitor. This circuit develops techniques of pulsed drive and reverse bias to achieve desired emitted brightness levels and elongate OLED life times, respectively. A current mirror is also adopted in the circuit to minimize emission nonuniformity of the OLED panel. The required input data voltages for varied displayed gray levels are calculated based on analytically known TFT and OLED models and the designed circuit architecture. The designed pixel circuit is simulated with realistic TFT models for validating expected performance to realize 256 gray levels and minimizing nonuniformity. The designed circuit is implemented in a 2.4-in quarter video graphics array panel, which shows favorable performance for minimizing display nonuniformity and alleviating OLED degradation. In addition, a closeness is clearly observed among analytical predictions, simulations, and experimental measurements. [ABSTRACT FROM AUTHOR]

This paper describes how a reversed-bias voltage affects organic light-emitting diodes (OLEDs) with green emitting \Alq3:C545T (40 nm). The luminance efficiency and the active area of the test OLED devices are 8–11 cd/A and 2.5 mm \times 2.5 mm, respectively. The OLED lifetime under an ac driving scheme can be apparently improved, in contrast with that under a dc driving scheme. Experimental results indicate that adjusting the duty ratio of the ac driving scheme can ameliorate the brightness uniformity; meanwhile, the normalized luminance of a 20% duty ratio after a 3600-s stress is 94.3%, and that of dc stress is 76.4%. Therefore, a novel pixel circuit with three p-type thin-film transistors (TFTs) for an active-matrix OLED application is proposed to ameliorate the brightness uniformity. Variations of the threshold voltage of the driving TFT are compensated for, and the performance and lifetime of the OLED are improved by using an ac driving method. Simulation results indicate that the output current is almost constant over the data range. Furthermore, the current error rate of the proposed pixel circuit is less than 6.5%. [ABSTRACT FROM AUTHOR]

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/ \mathrmm^\mathrm \mathbf 2 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. [ABSTRACT FROM AUTHOR]