Voltage-programmed Pixel Circuit Research Articles

A 6T1C pixel circuit compensating for TFT electrical characteristics variations, voltage drop, and OLED degradation

A voltage-programmed pixel circuit based on low-temperature poly-silicon (LTPS) thin-film transistors (TFTs) is presented for active-matrix organic light-emitting diode (AMOLED) displays. The circuit consists of six p-type transistors and one capacitor (6T1C). During the extraction stage, the circuit extracts the driving TFT’s threshold voltage and the power supply voltage. During the data input stage, the circuit generates a charging voltage, which is associated with the driving TFT’s mobility and the OLED’s threshold voltage. Consequently, the pixel circuit, using only one capacitor, compensates not only for the TFT’s electrical characteristics variations, i.e., the threshold voltage variation and mobility variation, but also for the power supply voltage drop and the OLED degradation. The circuit simulation results reveal that the OLED current error rates (CERs) are lower than 5.09% when the threshold voltage varies by ±0.5V, lower than 3.61% when the mobility varies by ±30%, and lower than 9.16% when the voltage drop varies by −0.5V in the data voltage range.

Novel Adjustable Self-Compensation Flipped Voltage Follower of ZnO TFTs for Transparent Pixel Circuits

A new flipped voltage follower (FVF) whose current source is realized by a depletion-mode thin-film transistor is proposed. It is successfully applied to a static voltage-programmed pixel circuit. The new FVF has good adjustable self-compensation (ASC) ability, which makes the pixel circuit can compensate for different threshold-voltage shifts of thin-film transistors in not only the driving but also the FVF circuits. The simulation results show that the proposed pixel circuit exhibits a tiny current variation ranging from 1.69% to 3.80% when “global” transistors shift by ±0.2 V or ±0.3 V. In the experiment, the excellent ASC ability of the new FVF is verified by measuring the voltage transfer curve under ultraviolet exposure. Finally, the proposed pixel circuit exhibits a current variation of 1.4% after a stress time of 40000 s.

Design of Pixel Circuit Using a-IGZO TFTs to Enhance Uniformity of AMOLED Displays by Threshold Voltage Compensation

This article presents a novel voltage-programmed pixel circuit using a-IGZO TFTs to effectively compensate threshold voltage (VTH) variations of driving TFT. The compensation is very important to maintain the pixel brightness of active-matrix organic light-emitting diodes (AMOLED) displays. The proposed pixel design uses four-phase clocking schemes: reset period, VTH detection period, data input period and emission period. To maintain uniformity in phases, the duration of all the phases is taken to be same which results in easier design of the multi-phase clock. Moreover, the switching speed of control signals is as high as 25 kHz, ensuring a high frame rate. The circuit has been simulated extensively, and the operation has been verified using SPICE models of a-IGZO TFT and OLED on Cadence Spectre. The circuit also achieves high contrast as OLED does not emit light in any periods except the emission period. The OLED current error in the proposed design for a VTH variation of 170% is below 0.1%. This circuit also provides a high aperture ratio of 51.6%, which ensures high resolution of AMOLED displays.

A Novel Voltage-Programmed Pixel Circuit with Poly-Si TFTs for AMOLED Displays

In this paper, we propose a novel voltage-programmed pixel circuit with polysilicon thin–flim transistors (poly-Si TFTs) for active matrix organic light-emitting diode (AMOLED) displays, which consists of one programming transistor, one driving transistor, four switching transistors and two storage capacitors, respectively. Specifically, the proposed pixel circuit is able to not only efficiently compensate for the threshold variations of TFTs, but also largely suppresses the electrical degradations of the devices caused by the long-term electrical stress. Moreover, the mobility variation of the driving transistor can be compensated as well. The simulation has been performed by HSPICE, and results indicate that the average values of nonuniformities are, respectively, 7.3% as the threshold-voltage varies by [Formula: see text][Formula: see text]V and 2.1%, as the mobility of the driving transistor varies by [Formula: see text]%, both of which are much lower than that of the conventional two-transistor and one-capacitor (2T1C) pixel. Furthermore, since the OLED is reverse-biased during the nonemission phases, the lifetime of OLED will be extended naturally. As a consequence, the proposed pixel circuit can substantially improve the display performance.

High Resolution a-IGZO TFT Pixel Circuit for Compensating Threshold Voltage Shifts and OLED Degradations

In this paper, we propose a novel voltage programmed pixel circuit based on amorphous-indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) for active-matrix organic light-emitting displays. Through the extensive simulation work based on a-IGZO TFT and OLED models, we confirm that the proposed pixel circuit can compensate for threshold voltage variations of TFTs and OLED degradation over wide dynamic range (~104) of OLED current as well as achieve a high pixel aperture ratio with the suppressed OLED current error rate below 9%.

Threshold Voltage Compensation Error in Voltage Programmed AMOLED Displays

A new accurate voltage-programmed pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays is presented. Composed of three TFTs and one storage capacitor, the proposed pixel circuit is implemented both in a-Si and a-IGZO TFT technologies for the same pixel size for fair comparison. The simulation result for the a-Si-based design shows that, during a programming time of ${\hbox{90}}~\mu \hbox{s}$ , the pixel circuit was able to compensate for a 3 V threshold voltage ( $V_{\rm th}$ ) shift of the drive TFT with almost no error. In contrast, the a-IGZO-based pixel circuit, has a larger current error (of around 8%), despite its proven three-fold higher speed.

P-44: A Current Source Free Separate Frame Compensated Voltage-Programmed Active Matrix Organic Light Emitting Diode Pixel Circuit

A current source free separate frame compensated voltage-programmed AMOLED pixel circuit is proposed. In the circuit a separate frame time is periodically assigned to compensate for the variation and/or degeneration of all driving transistors and OLEDs performance simultaneously and the pixel thereby is able to have enough compensation time which is not limited by the number of the row lines and frame rate. For the rest of operation time, the pixel circuit does not perform any compensation action, allowing sufficient time for light emission. Moreover, the current error can be suppressed below 2.50% provided that the threshold voltage shift of the driving transistor and OLED is 2V.

An Accurate and Fast Current-Biased Voltage-Programmed AMOLED Pixel Circuit With OLED Biased in AC Mode

A current-biased voltage-programmed (CBVP) pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays is proposed. The pixel circuit can not only ensure an accurate and fast compensation for the threshold voltage variation and degeneration of the driving TFT and the OLED, but also provide the OLED with a negative bias during the programming period. The negative bias prevents the OLED from a possible light emitting during the programming period and potentially suppresses the degradation of the OLED.

A novel current-biased voltage-programmed pixel circuit with low temperature polycrystalline silicon thin film transistors for AMOLED

A novel current-biased voltage-programmed pixel circuit with low temperature polycrystalline silicon thin film transistors for AMOLED

A Novel p-Type LTPS TFT Pixel Circuit Compensating for Threshold Voltage and Mobility Variations

In this paper, we propose a novel voltage programmed pixel circuit with p-type low temperature polycrystalline silicon thin-film transistors (LTPS TFTs) for active-matrix organic light-emitting displays (AMOLEDs) with an enhanced electrical stability and uniformity. Through extensive numerical analysis based on experimental data of p-type LTPS TFT and OLED, we confirm that the proposed pixel circuit can compensate for both the mobility variation and threshold voltage shift of TFTs.

In brief

PAGE 912 Researchers in South Korea propose a multi-functional highly isolated dual antenna with different Q-factors for controllable wireless charging and NFC communication. With antiparallel coil structure, the design has achieved more than 15 dB isolation between antenna ports. It also has a low-profile and compact structure for integration into mobile devices. PAGE 947 Research from Japan presents static and dynamic properties of 28-Gb/s directly modulated DFB lasers using asymmetric corrugation-pitch-modulated (ACPM) gratings. The gratings suppress longitudinal spatial hole-burning and the devices exhibit low threshold current with linear light-current characteristics and high-mask margin. The researchers believe this shows that the ACPM DFB laser is a good candidate for low power consumption light sources in 100-GbE applications. The dual NFC and wireless charging antenna is low-profile and compact for mobile device integration PAGE 932 Researchers in Brazil and the US propose a new formulation of a compact genetic algorithm. Modified by a mutation operator, based on the probability vectors of the algorithm, their results show that spectroscopy variable selection using the algorithm creates an efficient technique for determining protein concentration in wheat grain. ACPM DFB lasers are aimed at light sources for optical fibre communications PAGE 919 A method to address the problem of centre selection in radial basis function neural network regressors, using a cooperative game theoretic perspective, is presented in work from Brazil. The algorithm ranks training data points based on their marginal contribution to the network's accuracy, as calculated by the Shapley value. The mutation operator modified genetic algorithm creates an efficient technique for determining protein concentration in wheat grain PAGE 934 An AMOLED voltage-programmed pixel circuit (VPPC) that compensates for both threshold voltage and mobility variations of the driving TFT, to improve image quality, is presented in research from Korea. The proposed VPPC is aimed at addressing non-uniformity issues in low-temperature polycrystallinesilicon (LTPS) TFT displays, which are of interest for their good stability and high mobility. Training data points are ranked based on their marginal contribution to the network's accuracy, using the Shapley value Addressing the non-uniformity of LTPS TFTs is important for realising their use in mass produced AMOLED displays

An a-InGaZnO TFT Pixel Circuit Compensating Threshold Voltage and Mobility Variations in AMOLEDs

In this paper, we proposed a novel voltage-programmed pixel circuit based on amorphous indium gallium zinc-oxide thin-film transistor (a-InGaZnO TFT) for active-matrix organic light-emitting display (AMOLED) with an enhanced electrical stability and uniformity. Through an extensive simulation work based on a-InGaZnO TFT and OLED experimental data, we confirm that the proposed pixel circuit can compensate for both mobility variation and threshold voltage shift of the driving TFT.

A Novel a-InGaZnO TFT Pixel Circuit for AMOLED Display With the Enhanced Reliability and Aperture Ratio

In this paper, a novel voltage-programmed pixel circuit based on amorphous indium-gallium-zinc-oxide thin film transistor (a-InGaZnO TFT) for active-matrix organic light-emitting diode (AMOLED) displays with the enhanced aperture ratio is proposed. The proposed circuit consists of 5 TFTs and one capacitor. Through extensive simulation and layout works, we verified the proposed circuit compensates for the variation of the threshold voltage in a variety of harsh stress conditions. In addition, by removing one storage capacitor and one signal line, the proposed circuit can increase the aperture ratio as well as decrease the complexity of circuit operation in comparison to the conventional pixel circuit.

A Novel Voltage-Programmed Pixel Circuit Utilizing $V_{T}$-Dependent Charge-Transfer to Improve Stability of AMOLED Display

A novel voltage-programmed pixel circuit using hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) for active-matrix organic light-emitting diode (AMOLED) displays is proposed. The threshold voltage shift (ΔVT) of the drive TFT caused by electrical stress is compensated by an incremental gate-to-source voltage (ΔVGS) generated by utilizing the ΔVT-dependent charge transfer from the drive TFT to a TFT-based metal-insulator-semiconductor (MIS) capacitor. A second MIS capacitor is used to inject positive charge to the gate of the drive TFT to improve the OLED drive current. The non-ideality of the ΔVT-compensation, TFT overlap capacitance, programming speed, and OLED degradation are discussed. The effectiveness of the proposed pixel circuit is verified by simulation results.

High-Speed Voltage-Programmed Pixel Circuit for AMOLED Displays Employing Threshold Voltage One-Time Detection Method

This letter presents a high-speed, voltage-programmed pixel circuit for active-matrix organic light-emitting diode displays employing threshold voltage one-time detection method. The proposed pixel circuit that consists of one driving thin-film transistor (TFT), four switching TFTs, two capacitors, and four control signal lines can effectively compensate for the threshold voltage shift of the driving TFT and the OLED degradation. The threshold voltage of one-time detection method is realized by an ingenious application of capacitor coupling effect, and it is well-verified by comparing it with the conventional driving scheme. In this method, data is directly renewed without the periods of initialization and threshold voltage detection from the second-frame beginning. Moreover, this method can also be applied to other compensation pixel circuits.

Voltage‐programmed AM‐OLED pixel circuit to compensate threshold voltage and mobility variations

A novel voltage-programmed pixel circuit is proposed to achieve an active-matrix organic light-emitting display (AM-OLED) based on a low temperature polycrystalline silicon thin-film transistor (TFT) with an enhanced electrical stability and uniformity. The proposed pixel circuit consists of one driving TFT, one setup TFT, four switching TFTs, one capacitor, and four control signal lines. Through an extensive simulation work based on the HSPICE tool, it has been verified that the proposed pixel circuit can compensate for both mobility variations and threshold voltage shifts of the driving TFT.

A new AC driving circuit for a top emission AMOLED

A new voltage programmed pixel circuit with top emission design for active-matrix organic light-emitting 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.

A new LTPS TFT AC pixel circuit for an AMOLED

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 thin-film 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.

P‐16: 3‐TFT OLED Pixel Circuit for High Stability with In‐pixel Current Source

AbstractA new 3‐TFT voltage‐programmed pixel circuit with an in‐pixel current source is presented, which can be largely insensitive to the TFT threshold voltage shift. The fabricated pixel circuit provides OLED current ranging from 25nA to 2.9μA, an on/off ratio of 116 at typical QVGA display timing.

A New Voltage-Programmed Pixel Circuit for Enhancing the Uniformity of AMOLED Displays

This letter presents a new voltage-programmed pixel circuit for the active-matrix organic light-emitting diode (AMOLED) displays, which consists of one driving thin-film transistor (TFT), four switching TFTs, two capacitors, and three control signal lines. The proposed pixel circuit can effectively compensate for the threshold-voltage shift of the driving TFT and the OLED degradation, which is verified by the simulation work using SMART-SPICE software. It is shown that the average nonuniformity of the OLED current for the proposed pixel circuit is 5.7% compared with 85.7% for the conventional 2T1C pixel circuit, and thus, the brightness uniformity of AMOLED displays can be enhanced. 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.