Low‐temperature poly‐Si TFT data drivers for an SVGA a‐Si TFT‐LCD panel

Low‐temperature poly‐Si TFT data drivers for an SVGA a‐Si TFT‐LCD panel have been developed. The data drivers include shift registers, sample‐and‐hold circuits, and operational amplifiers, and drive LCD panels using a line‐at‐a‐time addressing method. To reduce the power consumption of the shift register, a dot‐clock control circuit has been developed. Using this circuit, the power consumption of the shift register has been reduced to 36% of that of conventional circuits. To cancel the offset voltage generated by the operational amplifier, an offset cancellation circuit for low‐temperature poly‐Si TFTs has been developed. This circuit is also able to avoid any unstable operation of the operational amplifier. Using this circuit, the offset voltage has been reduced to one‐third of the value without using the offset cancellation circuit. These data drivers have been connected to an LCD panel and have realized an SVGA display on a 12.1‐in. a‐Si TFT‐LCD panel.     

Current programming pixel circuit and data‐driver design for active‐matrix organic light‐emitting diodes

Abstract— We propose a new pixel design for active‐matrix organic light‐emitting diodes (AMOLEDs) employing five polycrystalline thin‐film transistors (poly‐Si TFTs) and one capacitor, which decreases the data current considerably in order to reduce the charging time compared with that of conventional current‐mirror structures. Also, the new pixel design compensates the threshold‐voltage degradation of OLEDs caused by continuous operation and the non‐uniformity of poly‐Si TFTs due to excimer‐laser annealing. The proposed pixel circuit was verified by SPICE simulation, based on measured TFT and OLED characteristics. We also propose current‐data‐driver circuitry that reduces the number of shift‐register signals for addressing the current data driver by one‐half.     

Integrated a‐Si TFT row driver circuits for high‐resolution applications

Abstract— A 12.1‐in. tablet liquid‐crystal‐display (LCD) panel with integrated amorphous‐silicon row driver circuits has been developed using a standard TFT process and Advanced Fringe‐Field Switching (AFFS) technology. An XGA‐resolution 768‐stage shift‐register circuit with two‐phase clocks has been designed and fabricated. The circuit parameters were optimized in order to obtain a highly reliable a‐Si row‐driver‐circuit structure. Thermal Humidity Operation (THO) test results at 50°C and 80% humidity during 500 hours of operation shows that the fabricated panel is reliable during long‐term operation and any abnormal display phenomenon was not observed at 0°C.     

Evaluation of single‐, pre‐emphasis,and dual‐driving methods in large‐sized TFT‐LCDs

Abstract— As the panel size and the frame frequency of TFT‐LCDs increases, driving issues become much more important for larger‐sized and higher‐resolution TFT‐LCDs. In our previous paper, the pre‐emphasis driving method was proposed to shorten the driving time of the data line with heavy loads of the large‐sized TFT‐LCDs. This paper proposes a simulation model based on the evaluation results of the developed pre‐emphasis source driver, and the issues of driving the data line with heavy loads are reviewed. The single‐, pre‐emphasis, and dual‐driving methods are compared in terms of their driving time and power consumption for large‐sized TFT‐LCDs with various resistances and capacitances of the data lines. At a panel load of 250‐pF capacitance and 15‐kΩ resistance in full‐HD resolution, the pre‐emphasis driving can reduce the pixel driving time to 66% with a 54% increase in the analog power consumption.     

Vt Compensated voltage‐data a‐Si TFT AMOLED pixel circuits

Abstract— Active‐matrix organic light‐emitting‐diode (AMOLED) displays are now entering the marketplace. The use of a thin‐film‐transistor (TFT) active matrix allows OLED displays to be larger in size, higher in resolutions and lower in power dissipation than is possible using a conventional passive matrix. A number of TFT active‐matrix pixel circuits have been developed for luminance control, while correcting for initial and electrically stressed TFT parameter variations. Previous circuits and driving methods are reviewed. A new driving method is presented in which the threshold‐voltage (V_t) compensation performance, along with various circuit improvements for amorphous‐silicon (a‐Si) TFT pixel circuits using voltage data, are discussed. This new driving method along with various circuit improvements is demonstrated in a state‐of‐the‐art 20‐in. a‐Si TFT AMOLED HDTV.     

Low‐temperature poly‐Si TFT‐LCD with an integrated analog circuit

We have developed a 6‐bit D/A converter and amplifier integrated low‐temperature poly‐Si TFT‐LCD in which an integrated signal‐line driver is driven by a 5‐V power supply. We have employed a D/A converter including a new capacitor array and an original amplifier comprised of serially connected comparators to achieve high accuracy. The D/A converter performs gamma correction using upper significant bits of input data. Control signals for these circuits were generated by the integrated timing circuit. These advances in integration have been achieved for the first time using 3‐μm design rule and improved LTPS TFT technologies and provide an advanced display system with lower power consumption, smaller module size, and higher durability.     

Design of dual‐outputs‐single‐stage a‐Si:H TFT gate driver for high resolution TFT‐LCD application

A new gate driver has been designed and fabricated by amorphous silicon technology. With utilizing the concept of sharing the noise free block in a single stage for gate driver, dual‐outputs signals could be generated in sequence. By increasing the number of output circuit block in proposed gate driver, number of outputs per stage could also be adding that improves the efficiency for area reduction. Besides, using single driving thin‐film‐transistor (TFT) for charging and discharging, the area of circuit is also decreased by diminishing the size of pulling down TFT. Moreover, the proposed gate driver has been successfully demonstrated in a 5.5‐inch Full HD (1080xRGBx1920) TFT‐liquid‐crystal display panel and passed reliability tests of the supporting foundry.     

Active‐matrix organic light‐emitting diode using inverse‐staggered poly‐Si TFTs with a center‐offset gated structure

Abstract— A low‐cost active‐matrix backplane using non‐laser polycrystalline silicon (poly‐Si) having inverse‐staggered TFTs with amorphous‐silicon (a‐Si) n⁺ contacts has been developed. The thin‐film transistors (TFTs) have a center‐offset gated structure to reduce the leakage current without scarifying the ON‐currents. The leakage current of the center‐offset TFTs at Vg = ?10 V is two orders of magnitude lower than those of the non‐offset TFTs. The center‐offset length of the TFTs was 3 μm for both the switching and driving TFTs. A 2.2‐in. QQVGA (1 60 × 1 20) active‐matrix organic light‐emitting‐diode (AMOLED) display was demonstrated using conventional 2T + 1C pixel circuits.     

A new a‐Si:H TFT pixel circuit employing data‐reflected negative‐bias annealing for a stable and uniform AMOLED

Abstract— A new a‐Si:H pixel circuit to reduce the VTH degradation of driving a‐Si:H thin‐film transistors (TFTs) by data‐reflected negative‐bias annealing (DRNBA) is presented. The new pixel circuit compensates VTH variation induced by non‐uniform degradation of each a‐Si:H pixel due to various electrical stress. The proposed pixel circuit was verified by SPICE simulations. Although the VTH of the driving a‐Si:H TFT varies from 2.5 to 3.0 and 3.5 V, the organic light‐emitting diode (OLED) current changes by only 1.5 and 2.8% in the emission period, respectively. During the negative‐bias annealing period, the negative VGS is applied to the driving TFT by using its own data signal. It is expected that the VTH shift of the driving TFT can be effectively reduced and the VTH shift can be compensated for in our new pixel circuit, which can contribute to a stable and uniform image from an a‐Si:H TFT active‐matrix OLED.     

A small‐area and low‐power data driver IC using two‐stage DAC with a capacitor array for active matrix flat‐panel displays

A small‐area and low‐power data driver integrated circuit (IC) using a two‐stage digital‐to‐analog converter (DAC) with a capacitor array is proposed for active matrix flat‐panel displays. The proposed data driver IC employs a capacitor array in the two‐stage DAC so as to reduce the DAC area and eliminate the need for a resistor string, which has high‐power consumption. To verify the proposed two‐stage DAC, a 20‐channel data driver IC with the proposed 10‐bit two‐stage DAC was fabricated using a 0.18‐μm complementary metal–oxide–semiconductor process with 1.8 and 6 V complementary metal–oxide–semiconductor devices. The proposed 10‐bit two‐stage DAC occupies only 43.8% of the area of a conventional 10‐bit two‐stage DAC. The measurement results show that the differential nonlinearity and integral nonlinearity are +0.58/?0.52 least significant bit and +0.62/?0.59 least significant bit, respectively. The measured interchannel deviation of the voltage outputs is 8.8 mV, and the measured power consumption of the 20‐channel data driver IC is reduced to 7.1 mW, which is less than half of the power consumed by the conventional one.     

Displacement‐current analysis of organic light‐emitting diodes

Abstract— Organic light‐emitting diodes (OLEDs) having multiple organic layers were fabricated to analyze the physical phenomena occurring in an OLED according to the amplitude of the applied voltage. The staircase voltage with both an increasing period and a constant period was designed and applied to an OLED. The displacement current began to change at a voltage where the conduction current began to change, and partly originated from the formation of space charge due to the low mobility of the majority carrier. The displacement current was shown to be constant at low voltage and decreased after showing a maximum value as the applied voltage increased. The exact voltage for the injection of two types of carriers and light emission could be obtained from the variation in the displacement current.     

Compact and power‐saving polysilicon data driver with common‐decoder DA converter (CD‐DAC)

Abstract— A common‐decoder architecture for a data‐driver circuit fabricated by using a polysilicon process has been developed. The architecture achieves a compact circuit and low‐power consumption. In application to an integrated polysilicon data driver for small‐sized displays, this architecture reduces the area of the data driver by removing the vertical bus lines that occupy a large area. It also suppresses the power consumption of the data bus by reducing the number of driven lines in the data bus during word‐to‐word transitions from six to two. By using a conventional 4‐μm design rule, we fabricated an active‐matrix OLED (AMOLED) panel with an integrated six‐bit data‐driver circuit with 384 outputs. The driver circuit had a height of 2.6 mm and a pitch between output lines of 84 μm. The maximum power consumption of the driver was only 5 mW, i.e., 3.8 mW for logic‐data transfer and 1.2 mW for reference‐voltage source. Furthermore, we also fabricated an active‐matrix LCD (AMLCD) panel including driver circuits of the same type as the integrated elements. Six‐bit full‐color images were successfully displayed on both panels.     

Electro‐optic properties of an intrinsic half‐V‐mode FLCD and its application to field‐sequential full‐color LCDs using a poly‐Si TFT matrix array

Abstract— An intrinsic half‐V‐mode ferroelectric liquid‐crystal display (FLCD) exhibiting a high contrast ratio (300:1), owing to defect‐free gray‐scale capability, with a high response speed (τ ? 400 μsec) and good switchability with TFTs, has been developed. Furthermore, this FLCD features high‐temperature reliability owing to the use of a special hybrid alignment technique. We successfully fabricated an active‐matrix poly‐Si TFT field‐sequential full‐color (FS FC) LCD with XGA specifications and a 0.9‐in. diagonal using a half‐V‐mode FLCD and an RGB light‐emitting‐diode (LED) array microdisplay. It is shown that the fabricated active‐matrix FS FCLCD exhibits good moving‐image performance with high full‐color display capability.     

A semantic interoperability approach to health‐care data: Resolving data‐level conflicts

The integration of data from various electronic health record (EHR) systems presents a critical conflict in the sharing and exchanging of patient information across a diverse group of health‐oriented organizations. Patient health records in each system are annotated with ontologies utilizing different health‐care standards, creating ontology conflicts both at the schema and data levels. In this study, we introduce the concept of semantic ontology mapping for the facilitation and interoperability of heterogeneous EHR systems. This approach proposes a means of detecting and resolving the data‐level conflicts that generally exist in the ontology mapping process. We have extended the semantic bridge ontology in support of ontology mapping at the data level and generated the required mapping rules to reconcile data from different ontological sources into a canonical format. As a result, linked‐patient data are generated and made available in a semantic query engine to facilitate user queries of patient data across heterogeneous EHR systems.     

Preventing untestedness in data‐flow based testing

A large number of path‐oriented testing criteria have been proposed in the last twenty years. Surprisingly, almost all of them suffer from a serious weakness, which is called the untestedness syndrome: even though a criterion is satisfied, some statements of the program under test may remain ‘untested’, i.e., the observed test output does not depend on them. A new data‐flow based testing criterion is introduced which does not suffer from untestedness, called the All Program Function (APF) criterion. Intuitively, it requires that each possible computation to every output statement in a program be covered by some test; but for lots of programs APF would require an infinite number of tests. A second, applicable criterion is thus introduced, derived from APF and called the Basic Program Function (BPF) criterion. BPF leaves no statement untested and yields finite test suites. Some examples show the application of BPF and investigate the failure‐detection capability of the proposed criterion. Copyright © 2001 John Wiley & Sons, Ltd.     

Optimization of low‐temperature poly‐Si TFT‐LCDs and a large‐scale production line for large glass substrates

Abstract— An update of the progress of inherently low‐temperature poly‐Si (LTPS) technologies, such as ELA, ion doping, and activation in conjunction with chemical vapor deposition (CVD) and photolithography will be given. We will also discuss whether LTPS LCDs will be applied to a large‐scale production line using a large motherglass substrate. It was found that a more‐powerful excimer laser as well as photolithography with higher‐resolution and a more‐precise overlaid arrangement would enable a large‐scale production line handling motherglass of 4th generation size to be constructed in the very near future with reasonable investment and productivity costs.     

On‐demand data co‐allocation with user‐level cache for grids

Conventional remote data access middlewares usually provide client applications with either a pre‐staging scheme or an on‐demand access scheme to fetch data. The pre‐staging scheme uses parallel downloads to fetch a completed input file from multiple data sources, even when only a tiny file fragment is required. Such a transfer scheme consumes unnecessary data transmission time and storage space. In contrast, the on‐demand scheme downloads only the required data blocks from a single data source and does not fully utilize the downstream bandwidth of the computing nodes. This paper presents a middleware called ‘Spigot’ that facilitates legacy (grid‐unaware) applications to transparently access remote data by using native I/O function calls. Spigot uses the on‐demand concept to avoid unnecessary data transfer and adopts a co‐allocation download algorithm to improve the data transfer performance. Moreover, it uses the pre‐fetching strategy to reduce the data waiting time by overlapping data acquisition and data processing. It also provides the client application with its own user‐level cache, which is advantageous since a larger cache space is available in comparison with the kernel‐level cache. Further, it is easy to maintain data consistency between Spigot nodes. The experimental results indicate that Spigot achieves superior performance in reducing the data waiting time than the pre‐staging and the on‐demand access schemes. Copyright © 2010 John Wiley & Sons, Ltd.     

Driver‐circuits‐integrated LCDs based on novel amorphous In‐Ga‐Zn‐oxide TFT

Abstract— A liquid‐crystal panel integrated with a gate driver and a source driver by using amorphous In—Ga—Zn‐oxide TFTs was designed, prototyped, and evaluated. By using the process of bottom‐gate bottom‐contact (BGBC) TFTs, amorphous In—Ga—Zn‐oxide TFTs with superior characteristics were provided. Further, for the first time in the world, a 4‐in. QVGA liquid‐crystal panel integrated with a gate driver and a source driver was developed by using BGBC TFTs formed from an oxide semiconductor. By evaluating the liquid‐crystal panel, its functionality was successfully demonstrate. Based on the findings, it is believed that the novel BGBC amorphous In—Ga—Zn‐oxide TFT will be a promising candidate for future large‐screen backplanes having high definition.     

Examining the technological pedagogical content knowledge of Singapore pre‐service teachers with a large‐scale survey

This paper examined the profile of Singaporean pre‐service teachers in terms of their technological pedagogical content knowledge (TPACK). A total of 1185 pre‐service teachers were studied with a TPACK survey. An exploratory factor analysis found five distinctive constructs: technological knowledge, content knowledge, knowledge of pedagogy, knowledge of teaching with technology and knowledge from critical reflection. The participants of this study did not make conceptual distinctions between TPACK constructs such as technological content knowledge and technological pedagogical knowledge. There were some differences in their TPACK perceptions by gender. However, the influence of age and teaching level were not strong. The methodological and theoretical implications for the development of TPACK surveys were discussed.     

A 2‐in. a‐Si:H TFT‐LCD with embedded backlight control TFT sensors with various channel widths

Abstract— A 2.0‐in. a‐Si:H TFT‐LCD with embedded TFT sensors for the control of the backlight intensity according to the ambient light intensity has been developed. Two types of a‐Si:H TFT sensors with various channel widths were embedded into a TFT backplane with bottom‐ and top‐gate structures for measuring the ambient light and backlight illumination, respectively. The output signal, measured by a readout IC, increased with backlight intensity until 20,000 lux.