Light-emitting diode (LEDs) have a promising prospect because of its outstanding advantages: 1) long lifetime, 2) environmentally friendly, 3) flexibility of color mixing, 4) high illumination efficiency, etc. Based on the electrical characteristics of LEDs, a constant current driver is needed to support the LED working performance. With the wide applications of LEDs, many new technologies are presented. In this paper, advantages and disadvantages of different LED drivers are discussed. A detailed technology review is presented which is good for researchers and engineers to make right choices in design and selection of LED drivers.

A Review of LED Drivers and Related Technologies

This paper presents the design and characterization of the first active matrix light-emitting diode (AMLED) microdisplay with an embedded visible light communication (VLC) transmitter, enabling LED digital signage for location-based applications such as information broadcasters and indoor positioning beacons. The driver system-on-a-chip (SoC) integrates four identical macro-cells, each containing a pixel driver array, a row driver, a column driver, and a first-in first-out memory, to drive a wide quarter-VGA (WQVGA) display featuring 400 × 240 blue micro-LED (µLED) pixels fabricated on a single gallium nitride (GaN) substrate. The size of each µLED pixel is 30 × 30 µm2. At the system level, pulse-width modulation (PWM) superimposed with on–off keying modulation is proposed to accomplish grayscale control for display and simultaneously transmit VLC signal by modulating the µLED array. At the circuit level, a pixel driver cell composed of three transistors and one capacitor (3T1C) with a novel VLC function is employed to implement the control scheme. Flip-Chip bonding is adopted to establish connections between the WQVGA microdisplay and the AMLED driver SoC. Implemented in a 0.5-µm 2P3M CMOS process, the driver SoC enables a high-resolution microdisplay module to achieve 4-bit grayscale at a 100-Hz frame rate, while supporting 1.25-Mb/s VLC for a bit error rate 500 cm.

Design and Characterization of Active Matrix LED Microdisplays With Embedded Visible Light Communication Transmitter

An amorphous indium-gallium-zinc-oxide (a-IGZO) pixel circuit with three transistors and one capacitor is proposed for use in high-speed-scan active-matrix organic light-emitting diode (AMOLED) displays. The proposed pixel circuit can compensate for the threshold voltage shifts in both normally-off and normally-on a-IGZO TFTs. Based on the simulation results with $\pm$ 1 V threshold voltage shifts of the driving TFT, the relative error rates of OLED currents are less than 4.46% for the entire range of data voltages $(-\hbox{9.9 V}{\sim}\hbox{5 V})$ .

New a-IGZO Pixel Circuit Composed of Three Transistors and One Capacitor for Use in High-Speed-Scan AMOLED Displays

High-performance vacuum-processed metal oxide thin-film transistors: A review of recent developments

This letter proposes a new voltage-programmed amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays. The proposed circuit detects the $\text{V}_{\mathrm {TH}}$ of the driving TFT only in a periodically executed compensation frame, allowing the other frames to perform only data input and emission for high-speed applications. An HSPICE model is also established based on the measured electrical characteristics of a fabricated a-IGZO TFT. The simulation results reveal that the proposed circuit can compensate for the degradation of the driving TFT and the OLED without external circuits. Moreover, the current error rates are <6.32%, so the proposed circuit is effective for use in AMOLED displays.

a-InGaZnO Active-Matrix Organic LED Pixel Periodically Detecting Thin-Film Transistor Threshold Voltage Once for Multiple Frames

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.

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

A new two-transistor pixel circuit in a current-biased voltage programming mode for active matrix-organic light emitting diode displays is proposed. The proposed circuit features a fixed current source and a conventional data line. The former offers a moderate bias current to compensate for the device performance variation or degeneration, and the latter provides pixels with voltage signals. It is demonstrated that both accurate and fast compensations can be realized in the proposed pixel circuit.

Two-Transistor Current-Biased Voltage-Programmed AM-OLED Pixel

The invention provides a self-aligned double-layer channel metallic oxide thin film transistor and a manufacturing method of the self-aligned double-layer channel metallic oxide thin film transistor. The manufacturing method comprises the following steps that a thick high-resistivity metallic oxide semiconductor layer and a thin low-resistivity metallic oxide layer deposit on a substrate, so that double layers of channels are formed; photoetching and etching are carried out on the double layers of channels, so that an active area graph is formed; a gate medium layer and a gate electrode are formed on the double layers of channels; a covering layer with H deposits on the whole substrate, then heat processing is carried out so that H can diffuse to metallic oxide outside the channel area not covered by the gate electrode and the gate medium, and a heavily doped low-resistivity source drain area is formed; a contact hole and a contact electrode are prepared. The self-aligned double-layer channel metallic oxide thin film transistor and the manufacturing method of the self-aligned double-layer channel metallic oxide thin film transistor adopt self-aligned double-layer channel top gate structure, can lower source drain resistance, lower the influence of ambient light on elements, lower off-state current, and improve on-state current and migration rate of the elements.

Self-aligned double-layer channel metallic oxide thin film transistor and manufacturing method thereof

We propose a new active matrix organic light-emitting diode (AMOLED) pixel circuit in which the compensation for the thin film transistor and OLED performance variation and/or degeneration is performed periodically in a separate frame time. In the other frame time, the AMOLED pixel works without any compensation operation, so that the whole row time is used for driving. Only three transistors and two capacitors are required to construct the pixel circuit. It is demonstrated that both accurate compensation and high driving speed can be realized in the separate frame compensated AMOLED pixel circuit.

Separate Frame Compensated Current-Biased Voltage-Programmed Active Matrix Organic Light-Emitting Diode Pixel

A multithreshold voltage amorphous indium- gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) technology based on the anodic oxidation (anodization) technique is demonstrated. It is shown that the characteristics of the a-IGZO channel layer can be considerably tailored by the anodization treatment. As a result, the threshold voltage of the a-IGZO TFTs depends on the anodization voltage, making it possible to fabricate both depletion and enhancement mode TFTs on the same substrate. The secondary ion mass spectrometry result shows that the oxygen content is noticeably increased in the anodized a-IGZO film, suggesting that the dependence of the threshold voltage on the anodization treatment is attributed to the anodization-induced reduction of oxygen vacancy concentration in the channel region, which also leads to an alleviated Vth shift under negative bias illumination stress in the anodized devices.

Chuanli Leng

Papers

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

Two-Transistor Current-Biased Voltage-Programmed AM-OLED Pixel

Self-aligned double-layer channel metallic oxide thin film transistor and manufacturing method thereof

Separate Frame Compensated Current-Biased Voltage-Programmed Active Matrix Organic Light-Emitting Diode Pixel

A Multi- $V_{\mathrm {th}}$ a-IGZO TFT Technology Using Anodization to Selectively Reduce Oxygen Vacancy Concentration in Channel Regions