Design of an organic pixel addressing circuit for an active-matrix OLED display

In this paper, we present a design of a flat-panel display (FPD) based on organic light-emitting diodes (OLEDs) and on organic thin-film transistors (OTFTs). Addressing mode, circuit topology, layout, and drive scheme are developed in order to reach the desired frame rate and to control the gray levels against the threshold voltage dispersions of OTFTs and OLEDs. The design shows that the current OLED and OTFT technology are suitable for FPD technology, though setting serious constraints on driver design.     

Mirrored OLED pixel circuit for threshold voltage and mobility compensation with IGZO TFTs

In this paper, pixel circuit using mirroring structure with Indium–Gallium–Zinc oxide (IGZO) thin film transistors (TFTs) for active matrix organic light emitting diode (AMOLED) display is proposed. This pixel circuit consists of only four TFTs, and one capacitor. Due to the mirroring structure, characteristic of the driving TFT can be precisely sensed by the sensing TFT, which is deployed in a discharging path for gate electrode of the driving TFT. This discharging process is strongly dependent on threshold voltage (V_T) and effective mobility of the sensing TFT. Circuit operating details are discussed, and compensation effects for threshold voltage shift and mobility variations are verified through numerical derivation and SPICE simulations. Furthermore, compared with conventional schematics, the proposed pixel circuit might have much simplified external driving circuits, and it is a promising alternative solution of high performance AMOLED display.     

一种新型的OLED像素补偿驱动电路

为了防止有机发光二极管(organic light-emitting diode,OLED)显示器随着使用时间增加而造成OLED像素驱动电路发生阈值电压和电源电压漂移,从而引起显示屏亮度不均匀和不稳定的现象,本文对OLED像素补偿驱动电路进行研究。首先对通用型的2T1C驱动电路进行分析,找出引起显示器亮度不均匀和不稳定的原因,然后以目前使用较多的4T1C像素补偿驱动电路为例,对该电路进行了深入的分析,指出这种电路结构的缺陷,最后针对这些缺陷,提出了改进的5T1C像素补偿驱动电路,并且对该电路进行了仿真,验证了其可行性。仿真结果表明,在显示阶段,输出电流稳定在2μA。基本可以改善OLED显示器亮度不稳定和不均匀的缺点。     

A new a-Si:H thin-film transistor pixel circuit for active-matrix organic light-emitting diodes

We propose a new pixel circuit using hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs), composed of three switching and one driving TFT, for active-matrix organic light-emitting diodes (AMOLEDs) with a voltage source method. The circuit simulation results based on the measured threshold voltage shift of a-Si:H TFTs by gate-bias stress indicate that this circuit compensates for the threshold voltage shifts over 10000 h of operation.     

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。     

一种支持OLED亮度补偿的电流型PWM像素驱动电路

OLED(organic light-emitting diode,OLED)微显示器长时间工作在高对比度、高亮度的状态下,OLED像素衰退不一致,发光亮度衰退也不一致,会产生残影现象。因此,提出了一种改进的电流型PWM像素驱动电路,保持了对OLED像素衰退补偿效果,同时可以读出OLED阳极电压,计算得到OLED衰退信息,以便于对OLED亮度衰退进行有效的补偿。文章中分析了改进的电流型PWM驱动电路结构,及其对OLED衰退补偿和亮度补偿的原理。通过模拟仿真,得到几个影响OLED衰退补偿效果的关键参数。当OLED像素衰退电阻R_oled小于40 MΩ时,该电流型PWM驱动电路电流衰退度与传统2T1C驱动电路相比,只为其衰退度的50%。     

A new a-Si:H TFT pixel circuit compensating the threshold voltage shift of a-Si:H TFT and OLED for active matrix OLED

We propose a new hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) pixel circuit for an active matrix organic light-emitting diode (AMOLED) employing a voltage programming. The proposed a-Si:H TFT pixel circuit, which consists of five switching TFTs, one driving TFT, and one capacitor, successfully minimizes a decrease of OLED current caused by threshold voltage degradation of a-Si:H TFT and OLED. Our experimental results, based on the bias-temperature stress, exhibit that the output current for OLED is decreased by 7% in the proposed pixel, while it is decreased by 28% in the conventional 2-TFT pixel.     

一种新的应用到硅基有机发光二极管微显示像素电路仿真的OLED SPICE模型

本文介绍了一种新的OLED器件等效电路模型。由于单二极管模型能和多二极管模型一样较好的模拟OLED特性,因此新模型是基于单二极管模型建立的。并且为了保证拟合数据和测试数据有很好的一致性,在新模型中将常量电阻替换成指数电阻。通过与测试数据和其他两种OLED SPICE模型的模拟数据对比,新的模型更符合OLED的电流电压特性。新的模型能直接整合到SPICE电路仿真器中去,并且在OLED整个电压工作范围内拥有较好的仿真精度。     

A novel current-scaling a-Si:H TFTs pixel electrode circuit for AM-OLEDs

Hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) pixel electrode circuit with a function of current scaling is proposed for active-matrix organic light-emitting displays (AM-OLEDs). In contrast to the conventional current mirror pixel electrode circuit, in this circuit a high data-to-organic light-emitting device (OLED) current ratio can be achieved, without increasing the a-Si:H TFT size, by using a cascade structure of storage capacitors. Moreover, the proposed circuit can compensate for the variations of TFT threshold voltage. Simulation results, based on a-Si:H TFT and OLED experimental data, showed that a data-to-OLED current ratio larger than 10 and a fast pixel programming time can be accomplished with the proposed circuit.     

Current-source a-Si:H thin-film transistor circuit for active-matrix organic light-emitting displays

In this letter, we describe a four thin-film-transistor (TFT) circuit based on hydrogenated amorphous silicon (a-Si:H) technology. This circuit can provide a constant output current level and can be automatically adjusted for TFT threshold voltage variations. The experimental results indicated that, for TFT threshold voltage shift as large as /spl sim/3 V, the output current variations can be less than 1 and 5% for high (/spl ges/0.5 /spl mu/A) and low (/spl les/0.1 /spl mu/A) current levels, respectively. This circuit can potentially be used for the active-matrix organic light-emitting displays (AM-OLEDs).     

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.     

Readout circuit for CMOS active pixel image sensor

The design and simulation results of a new readout circuit for a CMOS active pixel image sensor are presented. This scheme removes the fixed pattern noise and reduces the signal degradation while offering an increase in readout speed, compared with the conventional approach     

高功放高压联锁电路改进与测试

高压联锁性能的好坏直接影响设备能否正常工作。通过分析CPI高功放（HPA）的延时加高压程序、高压联锁电路和交流延时器工作原理,研究出一种新改进的高压联锁电路方案和用于交流延时器的测试方法。分析阐述表明,该方案和测试方法克服了CPI高功放的高压联锁方案的弊端。另外,根据分析结果设计了延时测试电路,它可对交流延时器性能参数进行定量测试。     

Simulation of pixel voltage error for a-Si TFT LCD regarding thechange in LC pixel capacitance

LC pixel capacitance C_lc, which changes with the director of liquid crystal molecules as a function of external applied voltage, has a most important impact on the pixel voltage error Δ V_p and therefore on the electro-optics (E-O) characteristics of the LC pixel for an a-Si TFT LCD. In this paper, the pixel voltage error has been simulated for 10.4" VGA (640×480) and SVGA (800×600) a-Si TFT LCD, and in this simulation, we especially took into account the change in LC dielectric constant. We found that Δ V_p changes with the data voltage V_p. In addition, E-O characteristics of LC pixel for an a-Si TFT LCD has been investigated. The result shows that the effect of Δ V_p on E-O characteristics is significant when V_p ranges from the threshold voltage to the saturation voltage     

GM-APD阵列高精度像素读出电路设计

提出并设计了一种适用于激光3D成像的盖革模式雪崩光电二极管（Geiger-mode avalanche photodiode,GM-APD）阵列像素读出电路。基于飞行时间（time-of-flight,TOF）原理,像素读出电路主要由两部分组成:有源淬火电路（active quenching circuit,AQC）和时间数字转换器（time-to-digital converter,TDC）。所采用的TDC是粗细结合的两段式计数方式,成功实现了时钟频率和时间分辨率间的折中。基于内插技术,由粗计数的线性反馈移位寄存器和细计数的延时线型TDC共同实现了高达18-bit的动态范围。同时两者的时钟频率分别降低至250 MHz和500 MHz,分别是常规设计频率的1/20和1/10,大大降低了设计和应用难度。电路采用SMIC 0.18 m工艺设计,后仿结果显示达到了200 ps的高精度时间分辨率,对应的距离分辨率为3 cm,完全能够满足3 km激光3D成像中的测距要求。像素电路版图面积小于5095 m2,总功耗为0.89 mW,具有小面积和低功耗的优势。     

锥状微结构阵列提高OLED出光效率的研究

为提高OLED出光效率,在OLED基底上设计锥状微结构阵列,通过几何光学和光线追迹方法分析了锥状微结构对OLED出光效率的影响。结果表明:锥状微结构阵列最大可以提高60%的出光效率;锥状微结构阵列的占空比、材料折射率和坡度角对出光效率有较大影响;锥状微结构阵列不会改变OLED的辐射角,且有一定的聚光作用。结果为提高OLED出光效率提供一种新的参考和方法。     

用于红外焦平面阵列的等效像元电路设计

提出了一种用于300×400红外焦平面阵列读出电路的等效像元电路结构。该电路与氧化钒(VOx薄膜)制成的微机械系统(MEMS)的电特性等效,并能够模拟MEMS像元改变时支路电流的变化。红外面阵探测器读出电路在流片后,生长MEMS物理结构(VOx薄膜)前,该等效像元电路结构用于读出电路的电性能测试,从而剔除不良品,减少封装成本。该电路采用了Global Foundry 0.35μm工艺设计并流片。测试结果表明,当积分电流为0~200nA时,该等效像元电路的电性能与MEMS像元一致。     

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.     

Characterization of AMOLED pixel circuit without power line

We fabricated and evaluated the simple active matrix organic light emitting diode (AMOLED) pixel circuits without power line and proved that it is useful for the AMOLED display. Without power line in the pixel circuit we got higher-aperture ratio of emission area than the pixel with power line and the pixel with high aperture ratio can give a long life time due to lower current density of organic light emitting diode. However, the lack of power line requires the verification of the driving scheme of the pixel circuit. After fabrication of two types of AMOLED with and without power line in the pixel, we evaluated the pixel currents under various conditions. The operation of the pixel circuit without power line gave similar characteristics to that of the pixel circuit with power line. By the comparison, we verified that the pixel without power line is acceptable for the application to the AMOLED display combined with feedback compensation scheme for the uniform brightness.     

In-process functional testing of pixel circuit in AM-OLEDs

This paper presents a functional testing scheme using a two-thin-film-transistor (TFT) pixel circuit of an active-matrix organic light-emitting display (AM-OLED). This pixel circuit and the co-operative electrical testing scheme can not only evaluate the characteristics of each TFT, but also determine the location of line and point defects in the TFT array. Information on defects can be used in a unique repair system that cutting and repairing these defects. Furthermore, the functional testing scheme can be applied as a part of yield management of the AM-OLED array process.