Driving schemes for a-Si and LTPS AMOLED displays

Design of stable active matrix organic light-emitting diode (AMOLED) displays comes with significant challenges that stem from the electrical property of the backplane materials, line parasitics in the matrix, and the opto-electronic property of the organic light-emitting diode (OLED). This paper reviews voltage and current programming schemes for AMOLEDs. Following a systematic review of pixel circuits, design considerations are examined for both current and voltage schemes with focus on stability and programming speed for both amorphous silicon (a-Si) and low temperature polysilicon (LTPS) pixel circuits. In particular, spatial parameter variations and stability, which hinder reliable operation of AMOLED display backplanes, are discussed. Analysis shows that while driving schemes reported hitherto maybe suitable for small and medium size displays, new schemes are critically needed for large-area high-resolution AMOLED displays.     

An integrated circuit for multiplexing and driving injection lasers

A monolithic silicon integrated circuit has been designed to provide feedback-stabilized biasing and high-speed modulation for semiconductor injection lasers. The circuit is capable of selecting and controlling any one of a group of four lasers, and in the event of laser darkening it automatically switches to a replacement laser. The laser driver consists of a high-speed modulator and a feedback loop that incorporates the selected laser and an external backlight photodetector. The feedback controls the bias current of the laser so as to stabilize its light output against variations due to aging, replacement, or environmental changes. The feedback loop itself is compensated to allow arbitrary variation in the duty cycle or frequency of the modulation signal. Prototypes of the laser driver have been integrated in a junction-isolated bipolar technology. The integrated circuit is capable of supplying bias currents of 500 mA and modulation currents as high as 100 mA. At lower currents, modulation rates in excess of 100 Mbits/s have been achieved.     

基于 P-Type 多晶硅TFT技术的集成型有源 OLED 驱动电路

低温多晶硅(LTPS:Low-temperature poly-Si)技术已经成为薄膜晶体管(TFT:thin film transistor)制作中最具吸引力的技术,并应用在AMOLED显示器中.P-type 技术能够简化 TFT 的制作过程.本文提出了一种应用 p-type 多晶硅 TFT的 AMOLED 驱动电路结构,包括栅极驱动器、数据驱动器以及像素阵列.数据驱动器采用分块方法,使得显示屏的输出线数大大减少.作者采用一种改进的 p-type 移位寄存器实现逐行选通的功能,并采用由 4 个 p-type 反相器级联构成的缓冲器来提高电路的驱动能力.为了验证上述电路结构的正确性,作者采用 HSPICE 软件进行仿真分析.结果表明,电路工作正常.利用韩国汉城国立大学及 Neo Poly 公司在多晶硅制作方面的优势,我们已经合作完成了应用上述电路结构的分辨率为96×3×128的有源 OLED 的制作.     

A novel a-Si:H AMOLED pixel circuit based on short-term stress stability of a-Si:H TFTs

This letter presents a novel pixel circuit for hydrogenated amorphous silicon (a-Si:H) active matrix organic light-emitting diode displays employing the short-term stress stability characteristics of a-Si:H thin film transistors (TFTs). The pixel circuit uses a programming TFT that is under stress during the programming cycle and unstressed during the drive cycle. The threshold voltage shift (V/sub T/-shift) of the TFT under these conditions is negligible. The programming TFT in turn regulates the current of the drive TFT, and the pixel current therefore becomes independent of the threshold voltage of the drive TFT.     

Design and realization of a flexible QQVGA AMOLED display with organic TFTs

We present a QQVGA top emitting monochrome AMOLED display with 85dpi resolution using an organic TFT backplane on low temperature PEN-foil. The backplane process flow is based on a 7 layer photolithography process that yields a final mobility of the OTFT of ～0.4 cm²/Vs. The aperture ratio of the top-emitting OLEDs is over 75%. For operation at 10 V supply voltage (V_DD), the brightness of the display using red and green OLEDs exceeds 200 cd/m².     

A new current scaling pixel circuit for AMOLED

A new active-matrix organic light-emitting diode (AMOLED) pixel design, composed of four polycrystalline silicon thin-film transistor (poly-Si TFT) and one capacitor, is proposed by employing a novel current scaling scheme. The simulation results, based on the measured characteristics of an OLED and poly-Si TFTs, show that the proposed pixel design would scale down the data current more effectively, so as to guarantee a lower charging time compared with the conventional current mirror structure, as well as successfully compensate the variation of the electrical characteristics of the poly-Si TFTs, such as the threshold voltage and mobility.     

一种LTPS-TFT AMOLED像素电路的理论研究

本文对一种LTPS-TFT AMOLED电压型阈值电压(V_(th))补偿像素电路进行了理论研究,分析了影响V_(th)补偿效果的主要因素。电路的补偿效果主要由驱动TFTV_(th)的获取精度和随后的保持精度决定。在V_(th)获取过程中,相关误差主要由驱动TFT转移特性电流对存储电容充电的充电率不足产生;在显示信号与V_(th)叠加过程中,与V_(th)保持节点连接的电容增量等因素会造成V_(th)保持精度的损失。根据分析的结果,本文解释了高分辨率像素电路补偿效果下降的原因。     

An integrated expandor circuit

Presents a bipolar monolithic version, for frequency division telephone multiplex equipment, that has a marked improvement in performance compared with discrete component versions. The principles of operation and the design criteria and limits are discussed in full detail, particularly with respect to CCITT recommendations. Special attention is devoted to the analysis of the circuit and technological solutions that have been implemented to achieve an overall operation accuracy of 0.2 dB together with a high level of reliability.     

Dependence of Photosensitive Effect on the Defects Created by DC Stress for LTPS TFTs

In this letter, the photosensitive effect of n-type low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) after dc stress was investigated. It was discovered that the photo-generated carrier behaviors under optical illumination are related to defect types created by different stress conditions of hot-carrier effect and self-heating effect. These two types of defect creation result in the different photosensitivity behaviors of LTPS TFT. A model considering the relation between photosensitivity and defect is proposed to explain the anomalous illumination behaviors after device degradation.      

An integrated circuit for GSM mobile communications

An integrated circuit for the Pan European GSM mobile communications system is described which performs GMSK digital modulation and front-end functions for both base and mobile stations. The circuit includes, as main functional blocks, a 10-bit D/A converter, a 13-MHz switched-capacitor interpolating filter, and a power buffer. A fully differential approach was used. The circuit has been fabricated using a 2-m CMOS process. The chip size is 6.7×5.3 mm². The overall circuit performance fully meets GSM specifications.     

An integrated electronic telephone circuit

An integrated electronic telephone circuit (ETC) providing all the necessary elements of a telephone station apparatus is described. The ETC includes a speech network, tone ringer, dual-tone multifrequency (DTMF) dialer and DC line interface circuit. A microprocessor port facilitates automatic dialing features under control of a separate microprocessor. The speech network and dialer circuits operate with instantaneous input voltage as low as 1.4 V. The DTMF generator incorporates a high-precision frequency synthesis technique. Because of the reduction of frequency errors, an inexpensive ceramic resonator can be used as the frequency reference for the dialer. A linear/I/SUP 2/L process with two-layer metal interconnects is used to fabricate the 125/spl times/146 mil ETC die.     

An integrated JK flip-flop circuit

An integrated JK flip-flop circuit, which is constructed using an RS flip-flop and four gates, is described. The circuit operation is based on an original concept, which is different from the conventional master-slave principle. Results of a monolithic integration using emitter-coupled logic (ECL) circuits are also given. As compared with the conventional master-slave-type JK flip-flop, which is constructed using ECL, a 40 percent improvement in speed-power product has been obtained.     

A new voltage-modulated AMOLED pixel design compensating for threshold voltage variation in poly-Si TFTs

A new voltage-modulated active-matrix organic light-emitting diode (AMOLED) pixel design, which successfully compensates for the threshold voltage variations in poly-Si thin-film transitors (TFTs), is proposed, and verified by SPICE simulation and experiments. In order to compensate for variations in OLED current, the proposed pixel design employs a new voltage modulation scheme using diode connections.     

An improved GaAs MESFET equivalent circuit model for analog integrated circuit applications

An improved equivalent circuit model of a gallium-arsenide (GaAs) MESFET that is optimized for the design and analysis of precision analog integrated circuits is described. These circuits entail different modeling requirements from digital or microwave circuits, for which existing equivalent circuit models are optimized. Improved techniques are presented to model the drain-to-source conductance, device capacitance, and the functional dependence of drain-to-source current.     

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.     

一种应用于AMOLED的阵列扫描控制电路

为了提高显示屏的成品率,降低成本,提出了AMOLED屏上行驱动电路的一种设计方案,以PMOS-TFT为行驱动电路的结构.该电路由阵列扫描控制电路构成,每个阵列扫描控制单元由2个时钟信号控制,并包含5个PMOS-TFT.通过HSPICE的仿真,结果得出电路的仿真结果与分析结果一致,验证了电路功能的正确性.     

An optical integrated circuit for time-division 2-D velocitymeasurement

An LiNbO₃ optical integrated circuit pigtailed with two single-mode fibres, which allows time-division two-dimensional velocity measurement, is discussed. To detect time-division multiplexed beat signals corresponding to velocity components v_X and v_γ of a moving object, a waveguide switch is integrated on a Z-propagating LiNbO₃ substrate of 28×7 mm² in addition to a waveguide interferometer with a frequency shifter. In the optical IC, either v_X or v_γ could be measured selectively with signal-to-noise ratio of 20 dB by driving an electronic gate placed after a photodiode in synchronization with the waveguide switch     

An X-band integrated circuit FET oscillator with dielectric resonator stabilization

Experimental results are presented for the performance of a MIC common drain GaAs FET oscillator and are compared with the performance of the same oscillator stabilized by using a high Q. temperature compensated dielectric resonator made from barium nonatitanate. The unstabilized oscillator gave 85 mW of Rf power at an efficiency of 20%. whilst the compensated oscillator gave 46 mW of power at an efficiency of 12%. with a line width of only 0.3 MHz as measured at 60 dB below the peak. Over the temperature range 0 to 60°C the frequency of the stabilized oscillator changed only 5 MHz, compared t0 the 30 MHz change found in unstabilized oscillators. Mechanical tuning was easily achieved, and careful choice of coupling between the resonator and oscillator eliminated the hysteresis observed in the mode of oscillation of designs previously reported.