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An analog pulse‐width‐modulation (A‐PWM) Micro‐LED (μLED) pixel circuit based on low‐temperature‐polysilicon (LTPS) thin‐film transistors (TFTs) for mobile displays is proposed. The progressive‐emission mode is implemented using a single Sweep (SW) signal by in‐pixel logic operation circuits. By adjusting the emission time of the progressive‐emission mode, the μLED is biased with the maximum quantum efficiency (EQE). Consequently, the static power consumption of proposed pixels is reduced by 29.2%, compared with conventional schemes. [ABSTRACT FROM AUTHOR]

A compact gate driver using p‐type low‐temperature polycrystalline silicon (LTPS) thin‐film transistors (TFTs) was proposed for Micro‐Light Emitting diodes (μLEDs) display using progressive emission analog pulse‐width modulation (A‐PWM) approach. The gate driver contains a simple waveform shaping module and outputs multiple sweep signals, including SW[n], EM[n], and S[n], by reusing the bootstrap node. Compared with conventional schemes, the proposed gate driver renders static power consumption reduction of the μLED display by 29.2%. [ABSTRACT FROM AUTHOR]

This paper studies high‐resolution AMOLED displays pixel and driving circuits using 3D stacking LTPS and oxide hybrid TFT integration technology systematically. It is demonstrated the OLED display resolution reaches 1167 PPI when the minimum line width/line spacing is reduced to 1 μm/0.5 μm. In addition, peripheral row and column drive circuits for the high display resolution were also illustrated. Good dynamic performance of the designed driving circuits was obtained thanks to the 3D TFTs. [ABSTRACT FROM AUTHOR]

A pulse‐width‐modulation (PWM) pixel circuit for Micro‐LED display based on low‐temperature poly‐silicon and oxide (LTPO) thin‐film transistor (TFT) is proposed. The PWM falling‐time is reduced to 10 μs, which is only 1/10 of conventional PWM pixel schematics, thanks to the high gain dynamic CMOS inverter for converting data voltage to PWM waveforms and an independent diode‐connected compensation structure for generating constant driving current. The maximum error of PWM conversion and driving current of Micro‐LED is less than 1%, despite VTH shift of oxide TFT ±2 V or VTH variation of LTPS TFT ±1 V. Furthermore, high display resolution above 270 PPI is obtained as the pixel layout reduced to 94 μm×94 μm due to the simplified pixel structure. [ABSTRACT FROM AUTHOR]

This paper presents a PAM and PWM combined Mini‐LED pixel circuit based on oxide TFTs. In the PAM part, a constant current (1mA) allows Mini‐LEDs work at peak efficiency and reduce power consumption. A source follower structure compensates for ΔVTH and VSS IR rise, which has only one TFT on current path, so that the pixel circuit works at low voltage. In the PWM part, a diode connected structure compensates for ΔVTH. Simulation results show that the current error rate is less than 0.81% when ΔVTH of PAM part is within ±3 V. When VSS rises less than 3 V, the current error rate is less than 7.22%. When ΔVTH of PWM part is +3 V, emission time variation is reduced by 99.29% compared with the circuit without compensation. The supply‐voltage can be reduced from 19.7 V to 15 V thanks to the proposed Mini‐LED pixel circuit. [ABSTRACT FROM AUTHOR]

Dynamic X‐ray detecting for large area medical imaging requires high‐gain and stable Active Pixel Sensor (APS) circuit integrated with Thin Film Transistors (TFTs). In this paper, the APS circuit using oxide TFTs is studied based on the small‐signal model, and the charge gain and effects of threshold voltage shift (ΔVth) are investigated. Detailed SPICE simulations show the charge gain of the APS circuit of the oxide TFTs is 234 × of that of the conventional a‐Si:H TFT PPS circuit. [ABSTRACT FROM AUTHOR]

A pulse-width-modulation (PWM) pixel circuit for Micro-LED displays is proposed based on low-temperature poly-silicon and oxide (LTPO) thin-film transistors (TFTs). The pixel circuit features fast PWM transition, as the PWM falling-time is less than 20 μs thanks to the high-gain dynamic inverter. Furthermore, the proposed pixel circuit can compensate the degradation and non- uniformities of TFT characteristics of LTPO TFTs through auto- zeroing configuration of the dynamic inverter and a diode- connected threshold voltage compensation structure. The error rate of luminous time is less than 3.2% and the error rate of current is less than 1% under VTH shift of oxide TFT ±2 V or LTPS TFT ±1 V. [ABSTRACT FROM AUTHOR]

A compact gate driver on array (GOA) was proposed for Micro‐Light Emitting diodes (Micro‐LED) display based on progressive‐mode pulse‐width modulation (PWM) using low‐temperature‐polysilicon (LTPS) thin‐film transistors (TFTs). Thanks to outputting line‐by‐line scanning (Scan) and emission control signals (EM) to address switching‐and emission‐transistors in Micro‐LED pixel circuit, the proposed GOA circuit enables an increased emission time by 60% with the frame rate of 120 Hz, compared with the conventional GOA circuit of simultaneous operating mode. Furthermore, the pulse‐width of EM signals are programmable simply by adjusting the number of input pulses. [ABSTRACT FROM AUTHOR]

A concise pixel circuit with interleaved Emit signals is proposed for active matrix organic light‐emitting diode (AMOLED) displays, on the basis of low‐temperature polycrystalline silicon oxide (LTPO) TFTs. The oxide TFT can be re‐used for both initialization and threshold voltage extraction periods, using interleaved Emit signals of adjacent lines with overlapped waveforms. The proposed pixel circuit consists of 1 oxide TFT and 5 p‐type LTPS TFTs, while only 2~3 types of line‐by‐line scanning driving signals, i.e. the Emit signal and the Scan signal, are required. Implementation of the proposed pixel circuit shows that the occupation can be reduced to 40 μm × 56.7 μm. Furthermore, optimization of the pixel circuit shows the emission current error is less than 2.3% with threshold voltage variation of ± 0.5 V, while refresh rate from 1 to 120 Hz can achieved. [ABSTRACT FROM AUTHOR]

A compact integrated gate driver using metal‐oxide TFTs is proposed for Micro‐LED display. The positive pulse generation module (i.e. Scan driver) and negative modules (i.e. Emit driver) are located at different side of the Micro‐LED display, respectively. While Emit signals are re‐used for low‐level‐maintaining of the Scan module, the gate driver design can be much simplified and area occupation of the single gate driver can be reduced to 90 μm(length)× 245 μm(height), while the length of conventional designs exceeds 1000 μm. The simulation results of cascaded gate driver show that the rising time and falling time of the circuit are reduced to 1.3 μs and 2.1 μs, respectively, with the gate loading of 1.5 kΩ and 150 pF. [ABSTRACT FROM AUTHOR]

A two‐mode pulse width modulation (PWM) pixel circuit is proposed for Micro‐LED display. The proposed driving method divides the consecutive 8 sub‐frames (256 gray levels) into low‐bit and high‐bit subframes, which are respectively driven by simultaneous emission (SE) and progressive emission (PE) modes. Compared with the traditional PWM driving scheme, the proposed one shows an increased effective luminous time ratio by 40% for a frame rate of 120Hz, which benefits higher power conversion efficiency. There are only 5 dual‐gate metal‐oxide transistors for the pixel circuit, while a source‐follower structure is adopted to extract the threshold‐voltage shift(ΔVth). Simulation results demonstrate that the current error rates can be reduced to 2% with ΔVth of ± 1 V for various grayscales. [ABSTRACT FROM AUTHOR]

A thin‐film transistors (TFTs) integrated gate driver circuit with bifunctional capacitors for in‐cell touch with horizontal blanking display mode is proposed in this paper. The coupling capacitor, which conventionally enables low‐level‐maintaining parts in display periods, is reused to store transfer charges during touch detection periods. Consequently, only nine TFTs and two capacitors are used for a single stage of the proposed gate driver for in‐cell touch display. Furthermore, the bifunctional capacitor scheme not only avoids the driving TFT from long‐time voltage stress but also suppresses the transfer charges leakage effectively. Therefore, the variation ratios of rising/falling time between adjacent gate driver stages are suppressed within 6%. For a 5.7‐in. display with HD+ resolution, the layout of a single gate driver stage is 623 μm (width) × 171 μm (height). The proposed gate driver circuit has been prepared with the state‐of‐the‐art hydrogenated amorphous silicon (a‐Si:H) TFT manufacturing process. The measured results verified the circuit functions. The gate driver output waveforms are well maintained and being almost independent of touch detection time interval from 100 to 300 μs. [ABSTRACT FROM AUTHOR]

In this paper, pixel circuit design method using low‐temperature poly‐silicon and oxides (LTPO) thin film transistors (TFTs) for active‐matrix organic light‐emitting diode (AMOLED) are derived in detail. Through calculation and SPICE simulation of a typical 7TFT‐1C LTPO pixel circuit, the optimum value for the capacitor is selected as 0.1 pF for accurate VTH compensation and high resolution above 490 pixels per inch (PPI). Moreover, to reduce the relative current error rate to 3 %, the maximum allowable threshold voltage shift is limited within −0.98 V and 0.44 V for IGZO TFT, and within −0.3 V to 0.31 V for the driving TFT (LTPS). This research provides guidelines for AMOLED display development using LTPO TFTs. [ABSTRACT FROM AUTHOR]

The a‐IGZO TFTs integrated gate driver circuit with inter‐frame memory module and isolated bootstrapping node structure is proposed for AMOLED display. The driver can provide progressive display signal, inter‐frame detection signal and standby detection signal. Compared with conventional ones, the proposed inter‐frame memory shows enhanced driving ability due to the introduce of voltage bootstrapping function. Besides, the proposed gate driver can tolerate larger threshold voltage variations (ΔVth) than the conventional circuit due to the isolated bootstrap node structure. [ABSTRACT FROM AUTHOR]

This paper demonstrates a novel low‐temperature‐poly‐Si thin‐film transistors (LTPS TFTs) gate driver with tunable width for low‐grey level brightness adjustment of active‐matrix organic light‐emitting diode (AMOLED) display. The width of output pulses can be tuned accordingly by changing the number of input pulses, to avoid changing the frequency, duty ratio, or increasing the numbers of the external clock‐lines. The proposed circuit still works well when outputting 10 ms pulse with leakage current above 1.45 nA. [ABSTRACT FROM AUTHOR]

An OLEDoS microdisplay system is proposed in this paper, which includes a voltage‐driving pixel circuit, an OLED threshold voltage detection method, and a fast‐progressive compensation scheme. The measurement result shows that the range of the programming display voltage of the proposed voltage‐driving pixel circuit is 5.15 times larger than the gate‐source voltage difference of the driving transistor. The measured lowest current of a pixel can be as low as 2.89 pA. [ABSTRACT FROM AUTHOR]

In this work, we proposed a voltage‐programmed AMOLED pixel circuit using amorphous InGaZnO thin‐film transistors (a‐IGZO TFTs). For every display frame, thanks to the capacitive coupling method, the gate‐source voltage of the driving transistor is programmed through a zero to a positive value process, i.e. a unipolar sweeping direction is maintained for the driving transistor, to suppress the electrical hysteresis effects. In addition, the threshold voltage variation of the driving transistor can also be compensated through a source follower structure. Simulation results indicate that the relative current error is less than 30% for threshold voltage variations of ± 0.4 V. [ABSTRACT FROM AUTHOR]

A hydrogenated amorphous silicon (a‐Si:H) gate driver circuit for vehicle displays is proposed. The new gate driver circuit features a separated bootstrapping structure to enhance the driving ability for low operating temperature. Electrical characteristics of the standard a‐Si:H TFTs are measured and modeled with ‐40 °C, 25 °C and 80 °C SPICE simulations of a 6 stages gate driver circuit show that, with the operation temperature of ‐40 °C, the high level of gate driver circuit (i.e. VGH) maintains above 17 V, while VGH is decreased to 0 V for the conventional schematic. [ABSTRACT FROM AUTHOR]

A robust a‐IGZO TFT integrated gate driver for AMOLED is proposed. The emission driver and dynamic inverter share the pull‐up and pull‐down parts, which features enhanced charging and discharging ability. The driver provides not only multiple control signals for internal compensation, but also increased threshold voltage margin. [ABSTRACT FROM AUTHOR]

In this work we present a DC‐DC converter based on metal oxide thin film transistors (TFTs) for passive radio frequency identification (RFID) tags. To increase the voltage conversion ratio, the cross‐coupled structure with positive feedback from adjacent stages is proposed. Compared with conventional DC‐DC converter with separation block, the proposed circuit features the decreased threshold voltage drop, the reduced on‐resistance of switch transistor, the improved driving capability and the increased power efficiency. The simulated results reveal that the output voltage and maximum power efficiency for proposed two‐stage DC‐DC converter are 16.6 V and 52% at a output current of 550 µA, which are 12.6 V and 42% at a output current of 250 µA for conventional designs. [ABSTRACT FROM AUTHOR]

An IGZO TFTs integrated gate driver with an independent bootstrapping structure and an independent control unit is proposed for AMOLED display. The driver can output both programmable multi‐pulse scan signals and normally‐high‐voltage emission control signals. Compared with the traditional bootstrapping node structure with a long rising time of 1.06 µs, and the diode‐connected bootstrapping node structure with a long falling time of 1.60 µs, the proposed driver has a short and symmetric rising and falling time of about 0.64 µs. Cascaded simulation results show that the driver may be applicable to 5.5‐in full HD AMOLED panel. [ABSTRACT FROM AUTHOR]

The a‐IGZO TFTs integrated gate driver being compatible depletion‐mode device is proposed for AMOLEDs. The circuit features a bootstrapping inverter, which is initialized by global signal and controlled by cascading gate‐driving signals. Two sets of clocks with different low voltages are employed. Enhanced stability and reduced power consumption is thus resulted. The circuit can generate ultra‐wide compensation signals for AMOLED displays even with Vth of ‐6 V. [ABSTRACT FROM AUTHOR]

The a‐IGZO TFTs integrated gate driver on array with depletion‐mode compatible is proposed for AMOLEDs. The driver features a bootstrapping inverter, which is initialized by global signal and controlled by cascading signals. Greatly enhanced stability and pull‐down ability of the circuit is thus resulted. The driver functions well even with Vth of ‐5V and ripple on the output is reduced to 27.4%. [ABSTRACT FROM AUTHOR]

A new OLEDoS pixel circuit is proposed for high resolution micro‐displays with improved image quality. The data voltage range is extended by using two coupling capacitors to raise the voltage at the source electrode of the driving transistor. Furthermore, the image quality is improved by a compensation scheme of the threshold voltage variation of the driving transistor. The simulations on the basis of CSMC 0.25 µm CMOS model are used to verify the performance of the proposed pixel circuit. It is shown that the data voltage of the proposed pixel circuit ranges from 1.5 V to 3.05 V, which is 2.5 times of that of the conventional 2T1C pixel circuit. The emission current error is decreased to −2.6% ~ 2.6% with ±5 mV threshold voltage variation of the driving transistor for the proposed circuit. [ABSTRACT FROM AUTHOR]

An a‐IGZO TFTs integrated gate driver with programmable output waveform for AMOLED display is proposed by shared input shift registers and output stages of multiple clock‐follower structure. The driver provides not only multiple scan and control signals for internal compensation, but also extended scan pulses for external compensation. [ABSTRACT FROM AUTHOR]

A reliable digital thin‐film transistors (TFTs) integrated ambient light sensor is proposed. The circuit structure is simple, as only 6 TFTs and 2 capacitors are required. The intensity of ambient light is presented by the number of voltage pulses at the output terminal of the light sensor. The operating principal of the sensor are detailed, and SPICE simulations are performed to explore the relationship between the number of output pulses and the light‐induced leakage current. The feasibility of the circuit is further proved by measurements of fabricated circuit samples with the standard a‐Si:H TFTs process. [ABSTRACT FROM AUTHOR]

A depletion‐mode amorphous indium‐gallium‐zinc‐oxide thin‐film‐transistor (a‐IGZO TFT) gate driver on array (GOA) integrated circuit has been proposed and fabricated for a 15‐inch active‐matrix organic light emitting diode (AMOLED) display in this work. The depletion‐mode a‐IGZO TFTs were turned off completely due to series‐connected two‐transistor structure and dual low‐voltage‐level power signal. For this reason, the window of Vth shift margin was wide with margin value from −5V to +10V by Spice simulation. Additionally, the proposed GOA circuit exhibited stable high‐voltage output pulse. Subsequently, GOA circuit was placed in a 15‐inch AMOLED display and the performance of the proposed circuit was confirmed. [ABSTRACT FROM AUTHOR]

A novel bootstrap method is proposed, which can significantly reduce the clock feedthrough effect and the dynamic power consumption. An ESL a-IGZO TFTs based gate driver using this technique is designed. It is shown that the ripple voltage and the power consumption of the proposed driver are only 22.9% and 23.86% of those of the earlier driver. [ABSTRACT FROM AUTHOR]

Analysis results demonstrates in this paper for gradation horizontal line (H-line) occurred in reliability (aging) test on amorphous silicon TFT-LCDs with integrated gate driver technology (short as GOA circuit). There are two factors that induce H-line: GOA gate output and data inversion type. Changing these two factors could eliminate or relieve H-line defect. [ABSTRACT FROM AUTHOR]

A stack buffer structure is proposed to suppress feed-through effects, which is caused by serious gate-to-drain capacitance of Etching-Stop-Layer (ESL) type InGaZnO (IGZO) TFTs. For low-level-maintaining periods, the stack buffer TFT can be modeled by reversely cascaded diodes for decreasing of noise voltage of internal nodes. Compared with conventional designs, the proposed buffer structure owns better stability and good driving ability. A robust gate driver using the proposed buffer structure is demonstrated, and only 7 TFTs and 1 capacitance are used. Thorough analysis and simulations are carried out, and the circuit performance is discussed concerning threshold voltage variation, different bootstrapping capacitance, and decreased driving pulse width. It is proven that the proposed gate driver is promising for high performance IGZO TFT display with high resolution for large dimension display. [ABSTRACT FROM AUTHOR]

This work presents a peripheral compensation scheme for AMOLED displays, in which threshold voltage and aging information of driving TFT, and the signal data voltage are analogously added in the pixel circuits without changing the gamma corrections and increasing the bit and voltage range of DAC. Without increasing the resolution and voltage range of DAC, the cost and power consumption are reduced. A driving scheme using current sensing method with adjustable settling time and peripheral compensation system are also proposed. [ABSTRACT FROM AUTHOR]

A TFT integrated gate driver with threshold voltage (Vth) shift compensable low-level holding (LLII) unit is proposed. The gate overdrive voltage (VGOV) of LLII TFTs is kept small and constant due to the compensation effect during the LLII period, leading to much suppressed AVTH and enlarged AVTH tolerance. Simulation results show that the proposed gate driver is able to work properly even the AVTH is up to around (VH-VI). This indicates that the proposed gate driver is of long life. [ABSTRACT FROM AUTHOR]

A current comparison scheme for external compensation circuit of AMOLED displays is proposed. In this scheme, a current comparator is designed to sense the difference between the reference current and the driving current of pixels and to output a corresponding digital signal to the compensation block. For the current comparator, a sense amplifier is used to amplify the current difference, which can effectively increase the accuracy of the current comparator. Simulation results show that the accuracy of the proposed current comparator is 1nA and the sensing error is lower than 0.224 %, when the reference current is 500 nA. [ABSTRACT FROM AUTHOR]

A low-power ESL a-IGZO TFT integrated gate driver, where the gate level of driving-transistor is kept lower than the source/drain level to suppress the serious dock-feed-through effect induced by the large parasitic capacitance of the ESL structured driving TFT Moreover, a new inverter is designed to minimize internal leakage current. Thus, the dependence of power consumption in the gate driver on the overlap-length between gate and source/drain of driving TFT anil the bootstrapping capacitor is much lessened. Simulation results verify the feasibility of the proposed gate driver with 16 stages and manifest that the power consumption is smaller than half of the conventional one whit the same simulation parameters. [ABSTRACT FROM AUTHOR]

Reliability issues of TFT integrated gate driver are still of great concern for large size (i.e. TV) display applications, especially for a‐Si:H TFT integrated panels with stressing test of high temperature and high humidity (HTHHO). In this paper, current detection method is proposed for gate driver failure identification. Measurements of 55‐inch UHD TV (4K) panel with integrated gate driver are carried out. It is found that gate driver failure after HTHHO are strongly associates with via‐hole open of clock bus‐lines. It is demonstrated that current through clock lines will be increased with prolonged falling edge due to multi‐pulses of gate driver outputs. And clock bus‐line open is caused by oxygen of Cu after long operating time during the stressing test. [ABSTRACT FROM AUTHOR]

A simple a-Si TFT integrated gate driver on array which can work at low temperature is proposed and studied. The circuit features a capacitor coupling gate bias at the TFT for suppressing feed-through effect. The bias allows the circuit output a well-formed waveform even at low temperature. [ABSTRACT FROM AUTHOR]

This paper presents an IGZO-TFT latch circuit featuring high stability and simple structure with only 5 TFTs per stage. Pass-transistor logic style with gate voltage bootstrapped is used to suppress voltage amplitude loss and achieve a full swing output. Comparison studies are carried out with conventional latch, and results show that the proposed one has compact layout, free DC stress and enhanced immunity to △VTH. [ABSTRACT FROM AUTHOR]

A high reliable amorphous silicon gate driver with shared dual pull-down units is proposed and fabricated for large-sized TFT-LCD applications. A special unit in the driver is designed to generate bipolar pulse bias for low-level holding TFTs to suppress the threshold voltage shift, which achieves 40.5% and 34.8% improvement compared with conventional DC and unipolar pulse bias respectively according to measurement results. [ABSTRACT FROM AUTHOR]

A digital-to-analog converter (DAC) working in a charge-cyclic mode and inplementable with IGZO TFTs for integrated data driver is proposed The DAC has the conversion accuracy determined by the ratio of loading capacitances of every two adjacent data lines and therefore independent of threshold voltages (VT) of integrated devices. Thus, high conversion accuracy can be achieved even if a significant VT shift or variation happens. [ABSTRACT FROM AUTHOR]