Po Syun Chen

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

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 ±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 (-9.9 V ~ 5 V).

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

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 VTH 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 Three-Transistor Pixel Circuit to Compensate for Threshold Voltage Variations of LTPS TFTs for AMOLED Displays

This work presents a new pixel circuit adopting low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) for active-matrix organic light-emitting diode (AMOLED) displays. The proposed pixel circuit can compensate for the threshold voltage variations of the LTPS TFTs with a simple structure. Simulated results demonstrate that the OLED currents over the entire data voltage range are uniform for ±0.5 V variations in the threshold voltage of the driving TFT, unlike in a conventional circuit. Furthermore, the relative current error rates for parasitic loads in the 1280 ×720 resolution AMOLED display are less than 6%.

A Charge-Pump-Based Current Feedback Method for AMOLED Displays

This work presents a new external driving scheme that uses the current feedback method with a 3T1C pixel circuit. The proposed circuit provides a stable OLED driving current by compensating for the threshold voltage shift of amorphous-silicon thin-film transistors (a-Si TFTs). For fabricated a-Si TFTs and the 0.35 μm CMOS process associated with the proposed driving scheme, measurements reveal that the normalized OLED current degradation is less than 5% after 60 hours of operation at 60°C. Moreover, for a data line load of 1.69 K Ω/110 pF, the relative error rates between data currents and OLED currents are less than 4% within a settling time of 19 μs.

Insertion of Simple Structure Between Gate Driver Circuits to Prevent Stress Degradation in In-Cell Touch Panel Using Multi-V Blanking Method

This letter proposes a simple structure for in-cell touch thin-film transistor liquid crystal displays (TFT-LCDs) that are driven by the multi-V blanking method. The proposed structure is designed to activate the gate driver circuit after the touch sensing period to prevent the driving TFT of the gate driver circuit from exhibiting long-term stress during this period. Measured electrical characteristics of a fabricated hydrogenated amorphous silicon TFT are used to develop a model for the use in a HSPICE simulation. Based on the specifications of a 5.5 in FHD in-cell touch panel, the simulation results demonstrate that when the proposed structure is applied to a gate driver circuit, the error rates of the rising time and falling time between the output waveforms, which respectively precede and follow the touch sensing period, are both less than 2.14%.

Optical Pixel Sensor of Hydrogenated Amorphous Silicon Thin-Film Transistor Free of Variations in Ambient Illumination

This paper presents a primary color optical pixel sensor circuit that utilizes hydrogenated amorphous silicon thin-film transistors (TFTs). To minimize the effect of ambient light on the sensing result of optical sensor circuit, the proposed sensor circuit combines photo TFTs with color filters to sense a primary color optical input signal. A readout circuit, which also uses thin-film transistors, is integrated into the sensor circuit for sampling the stored charges in the pixel sensor circuit. Measurements demonstrate that the signal-to-noise ratio of the proposed sensor circuit is unaffected by ambient light under illumination up to 12 000 lux by white LEDs. Thus, the proposed optical pixel sensor circuit is suitable for receiving primary color optical input signals in large TFT-LCD panels.

Gate Driver Circuit Using Pre-Charge Structure and Time-Division Multiplexing Driving Scheme for Active-Matrix LCDs Integrated with In-Cell Touch Structures

This paper presents a new gate driver circuit for active-matrix liquid crystal displays with an in-cell touch structure designed by hydrogenated amorphous silicon thin-film transistors. To increase the reporting rate of a touch panel, the proposed circuit can be used to pause display operations to perform touch sensing operations several times per frame. The proposed circuit exploits a pre-charge structure that alleviates the leakage current and long-term stress of a driving TFT during the touch sensing operation. Simulation results confirm that the proposed gate driver circuit can generate a highly uniform output waveform after each touch sensing operation that lasts for 200 μs when the circuit is operate at 85 °C. The variations of the rising and falling time are suppressed below 3.71%, confirming the feasibility of use of the proposed gate driver circuit for an in-cell touch panel.

Hydrogenated Amorphous Silicon Thin-Film Transistor-Based Optical Pixel Sensor With High Sensitivity Under Ambient Illumination

This letter develops an optical pixel sensor that is based on hydrogenated amorphous silicon thin-film transistors. Exploiting the photo sensitivity of the photo TFTs and combining different color filters, the proposed sensor can sense an optical input signal of a specified color under high ambient illumination conditions. Measurements indicate that the proposed pixel sensor effectively reacts to the optical input signal under light intensities from 873 to 12,910 lux, proving that the sensor is highly reliable under strong ambient illumination.

Pixel Circuit With Parallel Driving Scheme for Compensating Luminance Variation Based on a-IGZO TFT for AMOLED Displays

This work proposes a new pixel structure based on amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) and a parallel addressing scheme for high-resolution active-matrix organic light-emitting diode (AMOLED) displays. The proposed circuit compensates for the nonuniformity of luminance that is caused by shifts in the threshold voltage (<inline-formula><tex-math notation=LaTeX>

Novel Pixel Circuit With Compensation for Normally-Off/On a-IGZO TFTs and OLED Luminance Degradation

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