基于低温多晶硅薄膜晶体管的AMOLED交流像素电路

This work presents a new voltage programmed pixel circuit for an active-matrix organic light-emitting diode(AMOLED) display.The proposed pixel circuit consists of six low temperature polycrystalline silicon thinfilm transistors(LTPS TFTs),one storage capacitor,and one OLED,and is verified by simulation work using HSPICE software.Besides effectively compensating for the threshold voltage variation of the driving TFT and OLED,the proposed pixel circuit offers an AC driving mode for the OLED,which can suppress the degradation of the OLED.Moreover,a high contrast ratio can be achieved by the proposed pixel circuit since the OLED does not emit any light except for the emission period.     

具有顶部发光结构的AMOLED交流驱动电路

A new voltage programmed pixel circuit with top emission design for active-matrix organic lightemitting diode(AMOLED) displays is presented and verified by HSPICE simulations.The proposed pixel circuit consists of five poly-Si TFTs,and can effectively compensate for the threshold voltage variation of the driving TFT.Meanwhile,the proposed pixel circuit offers an AC driving mode for the OLED by the two adjacent pulse voltage sources,which can suppress the degradation of the OLED.Moreover,a high contrast ratio can be achieved by the proposed pixel circuit since the OLED does not emit any light except for the emission period.     

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.     

Poly-Si TFTs integrated gate driver circuit with charge-sharing structure

A p-type low-temperature poly-Si thin film transistors (LTPS TFTs) integrated gate driver using 2 non-overlapped clocks is proposed. This gate driver features charge-sharing structure to turn off buffer TFT and suppresses voltage feed-through effects. It is analyzed that the conventional gate driver suffers from waveform distortions due to voltage uncertainty of internal nodes for the initial period. The proposed charge-sharing structure also helps to suppress the unexpected pulses during the initialization phases. The proposed gate driver shows a simple circuit, as only 6 TFTs and 1 capacitor are used for single-stage, and the buffer TFT is used for both pulling-down and pulling-up of output electrode. Feasibility of the proposed gate driver is proven through detailed analyses. Investigations show that voltage bootrapping can be maintained once the bootrapping capacitance is larger than 0.8 pF, and pulse of gate driver outputs can be reduced to 5 μs. The proposed gate driver can still function properly with positive V_TH shift within 0.4 V and negative V_TH shift within-1.2 V and it is robust and promising for high-resolution display.     

Mobility impact on compensation performance of AMOLED pixel circuit using IGZO TFTs

The suitability of indium gallium zinc oxide (IGZO) thin-film transistors (TFT) for implementation of active matrix display of organic light emitting diodes (AMOLED) compensation pixel circuits is addressed in this paper. In particular, the impact of mobility on compensating performance for the implementation in AMOLED pixel circuits is investigated. Details of the effective mobility modeling using the power law of gate-to-source voltage are provided, and parameters are extracted according to the measured current-to-voltage data of IGZO TFT samples. The investigated AMOLED pixel circuit consists of 4 switching TFTs, 1 driving TFT, and 1 capacitor. A " source-follower” structure is used for the threshold voltage extraction of the driving transistor. A new timing diagram is proposed; thus the current error of the pixel circuit is almost independent of the effective mobility. But, to improve the precision of the threshold voltage extraction of the driving transistor, the mobility is required to be greater than 5 cm²V⁻¹s⁻¹. On the other hand, the optimized storage capacitance is reversely proportional to the effective mobility. Thus, the layout area of the pixel circuit can be decreased from 100 × 100 to 100 × 68 μm², with the effective mobility increased from 10 to 50 cm²V⁻¹s⁻¹. Therefore, IGZO TFT is a good alternative backplane technology for AMOLED displays, and a higher effective mobility is preferred for high compensation performance and compact layout.     

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.     

一种基于低温多晶硅薄膜晶体管的交流AMOLED像素补偿电路

This paper presents a new poly-Si pixel circuit employing AC driving mode for active matrix organic light-emitting diode （AMOLED） displays. The proposed pixel circuit, which consists of one driving thin-film tran- sistor （TFT）, three switching TFTs, and one storage capacitor, can effectively compensate for the threshold voltage variation in poly-Si and the OLED degradation. As there is no light emission, except for during the emitting period, and a small number of devices used in the proposed pixel circuit, a high contrast ratio and a high pixel aperture ratio can be easily achieved. Simulation results by SMART-SPICE software show that the non-uniformity of the OLED current for the proposed pixel circuit is significantly decreased （〈 10%） with an average value of 2.63%, while that of the conventional 2T1C is 103%. Thus the brightness uniformity of AMOLED displays can be improved by using the proposed pixel circuit.     

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。     

High-speed low-power voltage-programmed driving scheme for AMOLED displays

A new voltage-programmed driving scheme named the mixed parallel addressing scheme is presented for AMOLED displays, in which one compensation interval can be divided into the first compensation frame and the consequent N-1 post-compensation frames without periods of initialization and threshold voltage detection. The proposed driving scheme has the advantages of both high speed and low driving power due to the mixture of the pipeline technology and the threshold voltage one-time detection technology. Corresponding to the proposed driving scheme, we also propose a new voltage-programmed compensation pixel circuit, which consists of five TFTs and two capacitors(5T2C). In-Zn-O thin-film transistors(IZO TFTs) are used to build the proposed 5T2C pixel circuit. It is shown that the non-uniformity of the proposed pixel circuit is considerably reduced compared with that of the conventional 2T1C pixel circuit. The number of frames(N) preserved in the proposed driving scheme are measured and can be up to 35 with the variation of the OLED current remaining in an acceptable range. Moreover, the proposed voltage-programmed driving scheme can be more valuable for an AMOLED display with high resolution, and may also be applied to other compensation pixel circuits.     

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.     

基于砷化镓工艺的集成式功分器

A compact lumped integrated power divider with low insertion loss using 0.5 μm GaAs pHEMT technology is presented. The proposed power divider uses the π-type LC network for transmission line equivalence and a thin film resistor for isolation tuning simultaneously. The quality factor of the inductor is analyzed and synthesized for insertion-loss influence. The measured insertion loss is less than 0.5 dB when the operating frequency is within the range of 5.15-6.15 GHz. The return loss and isolation are better than 15 dB and 20 dB, respectively. The compact dimension of the power divider is as small as 0.9 × 0.85 mm^2. The measured results agree well with the simulated ones.     

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.