High Luminance Uniformity Research Articles

LTPS Pixel Driving Scheme to Improve Motion Blur for AMOLED Displays

This article proposes a new driving scheme based on an n-type low-temperature polycrystalline silicon (LTPS) four-transistor-two-capacitor (4T2C) pixel circuit to improve the quality of motion images of active matrix organic light-emitting diode (AMOLED) displays. The proposed driving scheme can prevent the effect of the lateral leakage current flowing through the OLED common layer by keeping the pixels in the upper and lower row lines in a nonemitting hold period during the program period. The simulation results show that all RGB colors maintain a shooting amount ratio (SAR) below 1% from the first frame when the image is switched from black to white, even for a concentration of the high p-doped hole transport layer (p-HTL). In addition, the parasitic capacitances of the 4T2C pixel circuit that causes OLED current errors are thoroughly analyzed for high luminance uniformity. A 1.5-in 326 pixels per inch (PPI) AMOLED panel based on the proposed driving scheme was fabricated. The results of our measurements show that the SARs of RGB colors are 0.8%, 0.2%, and 0.9%, respectively, and the average <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> -coordinate shift of the color is 0.007 during the transition between black and white images due to the effective suppression of the lateral leakage current. Therefore, we demonstrate that the proposed driving scheme is suitable for AMOLED displays that require high-quality motion images.

Removing crosstalk effect for high efficient polymer light emitting diode display

For passive matrix organic light emitting diodes, crosstalk effect is serious problem. This problem adversely affects the image quality of display with driver circuit operation. In this study, 16x16 pixel monochrome green emissive passive matrix (PM) OLED Display Module was successfully fabricated which exhibits high efficiency, high luminance uniformity and MIL-STD-3009 night vision (NVIS) compatibility. Current efficiency, power efficiency and external quantum efficiency has been obtained as 22.79 cd/A, 10.23 lm/W and 4.61%, respectively. Additionally, crosstalk effect was removed by adjusting spin rate of the hole injection layer so that display image quality optimally has been achieved.

Thin mini-LED backlight using reflective mirror dots with high luminance uniformity for mobile LCDs.

A new mini light-emitting diode (mini-LED) backlight with reflective dots is proposed for high luminance uniformity, high contrast ratio, and low power consumption for use in mobile liquid crystal displays. The proposed backlight, comprising a small number of mini-LEDs, was verified as having high luminance uniformity and high light use efficiency, due to the optimized reflective dots, backlight thickness and light distribution of the mini-LEDs. Moreover, the light leakage to adjacent segments was reduced by cutting a slit between each segment, improving the light use efficiency per segment and suppressing halo artifacts.

Fabrication of Large-area, Planar, UV Lighting Devices Based on flat Cs3Sb Photocathode Emitters

Planar lighting devices are ideal for many applications. Requirements for planar lighting devices are high luminance and good luminance uniformity, together with low power consumption. In this article, a large-area, planar lighting device with high luminance, excellent luminance uniformity, and controllable luminance characteristic that was successfully demonstrated for visible light emission is discussed. The same device with sufficient UV intensity and tunable intensity for UV light emission is also discussed. The design concept involves a diode panel structure that utilizes photocathodes operated in a reflection mode with an external excitation light source. The excitation light source is in the blue-visible light range. Commercially available phosphors are used as light sources for both visible and UV emissions. The light emission characteristic of the devices is investigated by measuring the optical and the electrical parameters as functions of the applied anode voltage. The results show that the luminance is high for visible light emission and that the intensity is sufficient for UV light emission. In particular, UV emission exhibits a characteristic of cold-UV light with a near-monochromatic spectrum. The optical and the electrical properties of the large-area planar device are good enough for many industrial applications.

A Temperature Compensation Method by Adjusting Gamma Voltages for High Luminance Uniformity of Active Matrix Organic Light-Emitting Diode Displays

In this paper, a temperature compensation method is proposed for active-matrix organic light-emitting diode (AMOLED) displays to achieve high luminance uniformity over a wide operating temperature range. The proposed temperature compensation method compensates for variation in OLED luminance according to temperature by adjusting the gamma voltages. To verify the proposed method, a built-in test circuit, which includes temperature sensors, current calculation block, current adjustment block, and gamma voltage generator, was fabricated using 90 nm complementary metal-oxide semiconductor process technology with 6 V high-voltage devices. The measurement results show that the proposed method achieves a high luminance uniformity with an OLED luminance variation of less than 1.54 cd/m 2 over the temperature range of -45°C to 60°C. Therefore, the proposed temperature compensation method is suitable for AMOLED displays requiring high luminance uniformity.

Design of Mini-LED Backlight Using Reflective Mirror Dots with High Luminance Uniformity for Mobile LCDs

Design of Mini-LED Backlight Using Reflective Mirror Dots with High Luminance Uniformity for Mobile LCDs

Design of Mini-LED Backlight Using Reflective Mirror Dots with High Luminance Uniformity for Mobile LCDs

Design of Mini-LED Backlight Using Reflective Mirror Dots with High Luminance Uniformity for Mobile LCDs

A Driving and Compensation Method for AMLED Displays Using Adaptive Reference Generator for High Luminance Uniformity

In this brief, we propose a driving method for an active matrix micro-pixelated light-emitting diode (AMLED) display in an attempt to achieve highly uniform luminance using an adaptive reference generator. The proposed driving method compensates for all resistance mismatches not only in a row line but also between the row lines by generating respective reference voltages for all row lines. To verify the proposed driving method, the pixel circuit ICs and pixel driver ICs were fabricated using a $0.18~\mu \text{m}$ standard CMOS process with 6 V high voltage devices. In the measurement, a micro-pixelated LED array with $16\times 16\times $ RGB was driven by the fabricated ICs, and its pixel currents were measured for luminance uniformity of the AMLED display. The measured average deviation of the pixel current for all 768 sub-pixels was 0.79% at a measured average pixel current of $12.003~\mu \text{A}$ , demonstrating that the proposed AMLED display achieved highly uniform luminance. Therefore, the proposed driving method is suitable for AMLED display applications requiring high image quality.

Improvement of the microprism distribution expression of an integrated light guide plate.

In our lab, the coefficient relational expressions called A(L,H), B(L,H), and C(L,H) between the coefficients in the microprism distribution expression and the structural parameters of the integrated light guide plate, which is to realize high luminance uniformity, have been proposed previously. Yet, there are some deficiencies in these coefficient relational expressions, such as numerical item redundancy and inconspicuous physical characterization. On this basis, the revised coefficient relational expressions of A(L,H), B(L,H), and C(L,H) are further studied. As a result, the numerical items of A(L,H), B(L,H), and C(L,H) are reduced by one-quarter, one-third, and one-half, respectively. The redundant high-order items are reduced, and C(L,H) is no longer a piecewise function. After revision, the effect of each numerical item on the coefficient values is highlighted, and it makes the physical characterization of each numerical term clearer. Moreover, by applying the revised coefficient relational expressions to acquire the microprism distribution, the luminance uniformities of all designed integrated backlight modules of 7.0 in. or less in size are totally higher than 85%. Taking a 5.0 in. integrated backlight module as an example, the performance of the integrated backlight module designed by the revised coefficient relational expressions is also improved over that before the revision. It verifies the correctness, effectiveness, and universality of the revised coefficient relational expressions, which will save a lot of design time.

73‐2: Wearable Display System Combined Directional Scattering Holographic Waveguide with Goggle

This paper presents a wearable display system combined directional scattering holographic waveguide (DSHW) with goggle for augmented reality. DSHW and goggle are used to form a suitable exit pupil and a large field of view with high luminance uniformity, respectively. The results of design and experiments are given in detail.

A 4410-ppi Resolution Pixel Circuit for High Luminance Uniformity of OLEDoS Microdisplays

This paper proposes a pixel circuit with high resolution and high luminance uniformity for organic light emitting diode-on-silicon (OLEDoS) microdisplays. The proposed pixel circuit employs a simple structure that consists of four n-channel MOSFETs and one capacitor, resulting in high resolution. In addition, this circuit compensates for the threshold voltage ( $V_{th}$ ) variation of the driving transistor caused by the body effect, which increases the $V_{th}$ as the source-to-body voltage of the driving transistor increases, thus reducing the emission current deviation, resulting in a high luminance uniformity. Moreover, the proposed pixel circuit extends the data voltage range using the capacitive coupling of the storage capacitance and the parasitic capacitance at the gate node of the driving transistor to precisely control the emission current. To verify the performance of the proposed pixel circuit, a test pattern with an array of the proposed 4T1C pixel circuits was fabricated on a single-crystalline silicon wafer as a backplane using a 110 nm standard CMOS process with 5.5 V high-voltage devices. The proposed pixel circuit occupies a unit sub-pixel area of $5.76 \mu \mathrm {m} \times 1.92 \mu \text{m}$ , which corresponds to a resolution of 4410 pixels per inch. The measurement results show that the emission current deviation error of the proposed pixel circuit ranges between −1.16% and +1.14%, which is improved from between −45.97% to +45.42% achieved in the conventional current-source type 2T1C pixel circuit, which does not compensate for the $V_{th}$ variation of the driving transistor. Moreover, the measured data voltage range of the proposed pixel circuit is extended to 1.618 V, which is 8.17 times wider than that of the conventional pixel circuit. Therefore, the proposed pixel circuit is very suitable for high resolution and high luminance uniformity of OLEDoS microdisplays.

Two-dimensional distribution design of micro-prism for partial integrated light guide plate

The microstructure distribution on the bottom surface of the partial integrated light guide plate (PILGP) is the key to affecting the uniformity of the output light from the backlight module (BLM), which is one of the important factors in the BLM design. Based on the development trend of the BLM in light-weight and integration, many research institutes have realized the requirement for high luminance and luminance uniformity in the BLM by setting micro-prism structure on the surface of the light guide plate (LGP). In most of these studies, the length of the micro-prism structure is the same as the width of the LGP, and the optimization of the micro-prism distribution is performed only in the length direction of the LGP, which is a one-dimensional distribution. So, the long strip micro-prism structure cannot modulate the light in the axial direction, resulting in large area identity in the width direction of the LGP, thereby the luminance uniformity of the BLM is affected. In this paper, a design idea of two-dimensional distribution of the micro-prism on the bottom surface of the PILGP, which improves the luminance uniformity of the BLM, is proposed to solve the problem that the luminance uniformity is affected by large area identity caused by one-dimensional distribution design of the micro-prism. The small length micro-prism structure is used to break the limit of the axial distribution of the long strip micro-prism structure, and it can modulate the light in the axial direction. The Lighttools software is used to optimize the two-dimensional distribution of the micro-prism on the bottom surface of a 5.0-inch PILGP. Comparing with the PILGP with one-dimensional distribution of the micro-prism on the bottom surface, the simulation results show that the utilization of light energy, illuminance uniformity and luminance uniformity in the BLM with optimized two-dimensional distribution of the micro-prism on the bottom surface of the PILGP respectively reach 92.03%, 87.07% and 91.94%, which meet industry standards. And the illuminance uniformity increases by 10%. Meanwhile, the luminance diagram shows that the overall luminance uniformity of the BLM is improved effectively. Moreover, the distribution principle of the micro-prism on the bottom surface of the PILGP is analyzed and the physical mechanism is reasonably explained . The simulation results above show that the design concept of the two-dimensional distribution of micro-prism is feasible. The study results have a certain referential value for the development of the BLM in light-weight and integration.

Two-dimensional distribution expressions of micro-prism on bottom surface of partial integrated light guide plate

The design of the microstructure distribution on the bottom surface of the partial integrated light guide plate (PILGP) is one of the key factors to improve the luminance uniformity of the partial integrated backlight module (BLM). In this paper, the two-dimensional micro-prism expressions on the bottom surface of the small-sized PILGP are presented. The two-dimensional micro-prism expressions make the micro-prisms spread out on a two-dimensional scale of the bottom surface of the PILGP. By fitting and analyzing a large number of simulation data, the relationship expressions between the coefficients of the two-dimensional micro-prism expressions and the structural parameters of the PILGP are established. The above expressions are directly applied to the two-dimensional distribution design of micro-prism on the bottom surface of small-sized PILGPs with different structural parameters. Without the help of the designers’ experience and the multiple simulations of the software, the average value of luminance uniformity in the partial integrated BLMs is obtained to be 84.94%. The simulation results show that the two-dimensional micro-prism expressions and coefficient relation-expressions presented in this paper have important application value. Take the 5-inch partial integrated BLM for example. The two-dimensional distribution of the micro-prism on the bottom surface of the PILGP with high luminance uniformity can be obtained directly by using the above expressions. By fine-tuning the coefficients of two-dimensional micro-prism expressions, calculated by the coefficient relation-expressions, the utilization of light energy, illuminance uniformity and luminance uniformity of the partial integrated BLM respectively reach 90.69%, 88.02% and 92.17%, which meet the practical requirements. The optimization and design time of the partial integrated BLM are both greatly saved. Further, the two-dimensional micro-prism expressions on the bottom surface of the PILGP are analyzed and the physical mechanism is explained reasonably. This work is of significance for the distribution design of the microstructures on the surface of the LGP.

An Active Matrix Micro-Pixelated LED Display Driver for High Luminance Uniformity Using Resistance Mismatch Compensation Method

This brief proposes an active matrix micro-pixelated light-emitting diode (AMLED) display driver to achieve a high luminance uniformity. The proposed AMLED display driver enhances the forward current uniformity of micro-LEDs by compensating for resistance mismatch between the micro-pixel circuits. The proposed AMLED display driver ICs were fabricated using a standard 0.18- $\mu \text{m}$ CMOS process with 6-V high voltage devices. They were assembled with a micro-LED array having a resolution of $16 \times 16 \times \text{RGB}$ and measured to verify the luminance uniformity of the AMLED display. The measured average deviation of the micro-LED forward current over all 768 pixels was 0.91% with an average current of 12.03 $\mu \text{A}$ , indicating that the proposed display driver achieved highly uniform luminance. Therefore, the proposed AMLED display driver is suitable for high-end display applications, offering high image quality.

28‐3: Distinguished Paper: New Pixel Driving Circuit Using Self‐discharging Compensation Method for High‐Resolution OLED Microdisplays on a Silicon Backplane

A novel 4T2C pixel circuit is proposed to realize a high‐resolution 7.8‐µm pixel pitch OLED microdisplay. In order to achieve high luminance uniformity, the pixel circuit compensates its Vth variation of the MOSFET for the driving transistor internally by using self‐discharging method. 0.5‐inch Quad‐VGA and 1.25‐inch Wide Quad‐XGA microdisplays with the proposed compensation architecture are also presented.

New pixel driving circuit using self‐discharging compensation method for high‐resolution OLED micro displays on a silicon backplane

AbstractA new 4T2C pixel circuit formed on a silicon substrate is proposed to realize a high‐resolution 7.8‐μm pixel pitch AMOLED microdisplay. In order to achieve high luminance uniformity, the pixel circuit compensates its Vth variation of the MOSFET for the driving transistor internally by using self‐discharging method. Also presented are 0.5‐in Quad‐VGA and 1.25‐in wide Quad‐XGA microdisplays with the proposed pixel circuit.

Backside Contacting for Uniform Luminance in Large-Area OLED

ABSTRACTWe have investigated organic light emitting diode (OLED) backside contacting for the enhancement of luminance uniformity as a superior alternative to gridlines. In this approach, the low-conductivity OLED anode is supported by a high-conductivity auxiliary electrode and vertically contacted through via holes. Electrical simulations of large-area OLEDs have predicted that this method allows comparable luminance uniformity while sacrificing significantly less active area compared to the common gridline approach.The method for fabricating backside contacts is comprised of five steps: (1) Thin-film encapsulation of the OLED, (2) Patterning of the OLED surface with lithography (resist mask defining via hole positions), (3) Via hole formation to the bottom anode by a plasma etching process, (4) Organic residues removal and sidewall insulation. (5) Contacting of the anode with a high-conductivity auxiliary electrode.Backside-contacted OLEDs processed by organic vapor phase deposition show high luminance uniformity. Scanning electron microscopy pictures and electrical breakthrough measurements confirm efficient sidewall insulation.

Development of multiple-surface optical elements for road lighting

The development of LED secondary optics for road illumination is quite a challenging problem. Optical elements developed for this kind of application should have maximal efficiency, provide high luminance and illuminance uniformity, and meet many other specific requirements. Here, we demonstrate that the usage of the supporting quadric method modification enables generating free-form optical solution satisfying all these requirements perfectly. As an example, two optical elements for different roadway types are computed, manufactured by injection molding, and then measured in a photometry bench. Experimental data demonstrate that the obtained light distributions meet ME1 class requirements of EN 13201 standard. The obtained directivity patterns are universal and provide high performance with different configurations of luminaires' arrangement: the ratio of pole altitude to distance can vary from 2.5 up to 3.6.

A Luminance Compensation Method Using Optical Sensors with Optimized Memory Size for High Image Quality AMOLED Displays

This paper proposes a luminance compensation method using optical sensors to achieve high luminance uniformity of active matrix organic light-emitting diode (AMOLED) displays. The proposed method compensates for the non-uniformity of luminance by capturing the luminance of entire pixels and extracting the characteristic parameters. Data modulation using the extracted characteristic parameters is performed to improve luminance uniformity. In addition, memory size is optimized by selecting an optimal bit depth of the extracted characteristic parameters according to the trade-off between the required memory size and luminance uniformity. To verify the proposed compensation method with the optimized memory size, a 40-inch 1920x1080 AMOLED display with a target maximum luminance of 350 cd/m2 is used. The proposed compensation method considering a 4σ range of luminance reduces luminance error from ± 38.64%, ± 36.32%, and ± 43.12% to ± 2.68%, ± 2.64%, and ± 2.76% for red, green, and blue colors, respectively. The optimal bit depth of each characteristic parameter is 6-bit and the total required memory size to achieve high luminance uniformity is 74.6 Mbits.

A 2822-ppi Resolution Pixel Circuit With High Luminance Uniformity for OLED Microdisplays

In this paper, a pixel circuit comprising four p-channel mosfet s and one capacitor is proposed for a high-resolution organic light emitting diode on silicon microdisplays with high luminance uniformity. The proposed pixel circuit improves the luminance uniformity by compensating for the threshold voltage $\rm{(V}_{\rm{th}}\rm{)}$ variation of the driving transistors. In addition, it extends the data voltage range to precisely control the emission current $\rm{(I}_{\rm{em}}\rm{)}$ . The test pattern of the proposed pixel circuit is fabricated on a single-crystalline silicon wafer as a backplane using a 90 nm CMOS process and occupies a subpixel area of 3 μ m × 9 μ m, corresponding to a resolution of 2822 pixels per inch. To verify the performance of the proposed pixel circuit, $\rm{I}_{\rm{em}}$ is measured from 24 fabricated test patterns. When the $\rm{V}_{\rm{th}}$ variation is not compensated for, the deviation of the measured $\rm{I}_{\rm{em}}$ ranges from –17.48% to +14.40% with a deviation of $\rm{V}_{\rm{th}}$ from –7.19 mV to +7.19 mV. On the other hand, when the $\rm{V}_{\rm{th}}$ variation is compensated for, the deviation of the measured Iem only ranges from –1.63% to +1.15%. Moreover, the proposed pixel circuit extends the data voltage range up to 1.289 V, which is 1.81 times wider than the source-to-gate voltage of the driving transistor which generates the maximum $\rm{I}_{\rm{em}}$ . In addition, the maximum organic light-emitting diode luminance of the proposed pixel circuit is constantly maintained between 292.5 and 303.8 cd/m 2 in the temperature range of –45 °C to 60 °C.