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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 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]

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]

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 31-inch 4K flexible active-matrix organic light-emitting diode (AMOLED) display integrating with gate driver on the array (GOA) technology has been proposed and fabricated on a polyimide substrate. The GOA circuits, composed of two series-connected thin-film transistors (TFTs) and dual low-voltage power structure, are introduced to decrease the leakage current in TFTs. They are arranged symmetrically along the sides of the display. Inkjet printing (IJP) OLED process is used to reduce the number of sub-pixels from four (R/G/B/W) in commercial white OLED process to three (R/G/B) and a high pixel density in the display (144 pixels per inch) is achieved. Moreover, top-gated (TG) amorphous indium-gallium-zinc oxide (IGZO) TFTs with good electrical and mechanical reliability, have been successfully utilized to decrease the capacitance load in the display and improve signal transfer speed in GOA. Finally, this 31-inch flexible AMOLED display was operated for 500h under accelerating test conditions of 60°C and 90% humidity. [ABSTRACT FROM AUTHOR]

A new pixel circuit is proposed for the realization of high resolution and high uniformity organic light-emitting diode on silicon (OLEDoS) microdisplays in this article. A compensation scheme is adopted to mitigate the influence of threshold voltage variation of the driving transistor on display uniformity. Furthermore, two coupling capacitors are used to reduce the voltage at the gate terminal of the driving transistor in order to extend the data voltage range. The performance of the proposed pixel circuit is verified in an industrial 0.18- $\mu \text{m}$ CMOS process. Simulation results show that the data voltage of the proposed pixel circuit ranges from 0.5 to 3.12 V, which is up to $4.37\times $ wider than the previously published pixel circuits. The emission current error of the proposed pixel circuit varies from −2.1% to 2.08%, under the condition of ±5 mV threshold voltage variation for the driving transistor. The maximum emission current error changes from −10.36% to −2.62% when the OLED turn-on voltage is increased by 5 to 20 mV due to device aging. Furthermore, the proposed pixel circuit only occupies a layout area of $8.1\,\,\mu \text{m}\,\,\times {4}\,\,\mu \text{m}$. [ABSTRACT FROM AUTHOR]

A new source driving circuit to compensate characteristics variations of thin-film transistors for AMOLED displays with high resolution is presented in this brief. The second-generation current conveyor is implemented for rapid current sensing of the feedback line, which is biased with a constant reference-voltage ($V_{{\mathrm{ REF}}}$). Further, the current difference between the current of the driving transistor (${I}_{ {D}}$) and the programming current, i.e., ${I}_{{\mathrm{ DATA}}}$ , is converted into switching voltage through an amplifier with a shorted resistor, to control the input of a ramp voltage (${V}_{{\mathrm{ RAMP}}}$). Thus, the degradations in electrical characteristics of the driving transistor can be compensated in real time, and both the influence of threshold voltage (${V}_{{\mathrm{ TH}}}$) shift and mobility (${ {\mu }}$) variation are effectively suppressed. The current-error rate of the proposed circuit is less than 3% with ${V}_{{\mathrm{ TH}}}$ shift of ±0.5 V or ${ {\mu } }$ variation of ±15%. In addition, the settling time is less than $4~{ {\mu } }{\text s}$ with the panel loading of 1.5 $\text{K}{ {\Omega }}$ and 100 pF at the OLED current (${I}_{{\mathrm{ OLED}}}$) levels ranging from 3 ${ {\mu }}\text{A}$ to 200 nA. [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 operational amplifier with indium-gallium-zinc oxide thin-film-transistors (InGaZnO TFTs) is proposed and investigated. The proposed amplifier features introduction of positive feedback with negative equivalent output resistance for high voltage gain. Biasing conditions for every TFTs and voltage gain are systematically discussed. In addition, influences of threshold voltage shift on both static and dynamic performances are discussed. Comparison results show that the voltage gain can be increased from 40 to 67 dB, and stability of the constant tail-current biasing is better than that of constant voltage biasing method. Further, an oscillating capacitance touch sensing circuit based on the proposed amplifier is shown, and sub-pF touching capacitance can be distinguished. The proposed InGaZnO TFTs integrated amplifier is promising for high performance system on panel designs. [ABSTRACT FROM PUBLISHER]

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]

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 hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) gate driver on array with low-level holding TFTs (LLH TFTs) biased under bipolar pulse is investigated. It is shown that the bipolar bias at low frequency significantly alleviates the threshold voltage shift of the LLH TFTs. As a result, the lifetime of the proposed gate driver is demonstrated to be several times of that under the conventional unipolar pulse bias. In addition, the improvement in the lifetime becomes more significant at the higher work temperature. The liquid crystal display television panels (32-in, 1366\times \textrm RGB\times 768 ) with the proposed a-Si:H gate drivers integrated on array are manufactured, and the feasibility of the proposed driving scheme is well verified. [ABSTRACT FROM PUBLISHER]

Threshold voltage shift ( \Delta V\mathrm{ TH} ) effect of hydrogenated amorphous silicon thin-film transistors under bipolar pulse bias stress (BPBS) is investigated. The dependence of the \Delta V\mathrm{ TH} effect on the signal pulsewidth, stress temperature, and negative pulse voltage magnitude of the BPBS is systematically measured, and explained by the charge trapping and detrapping theory. Results show that the BPBS leads to a noticeably suppressed \Delta V\mathrm{ TH} , compared with the conventional unipolar pulse bias stress. It is suggested that the BPBS with proper negative pulse voltage magnitude and low pulse frequency is an effective way of suppressing \Delta V\mathrm{ TH} , especially when the thin-film transistors work relatively at high temperature. [ABSTRACT FROM PUBLISHER]

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]

Using low-temperature poly-silicon thin-film transistors (LTPS TFTs) as a basis, a pixel circuit for an active matrix organic light-emitting diode (AMOLED) with narrow bezel displays was developed. The pixel circuit features mono-type scanning signals, elimination of static power lines, and pixel-integrated emitting control functions. Therefore, gate driver circuits of the display bezel can be simplified efficiently. In addition, the pixel circuit has a high-resolution design due to an increase of the pulse width of the scan signal to extend the threshold voltage and internal–resistance drop (IR drop) detection period. Further, regarding the influences of process–voltage–temperature (PVT) variation in the pixel circuit, comparison investigations were carried out with the proposed circuit and other pixel circuits with mono-type scanning signals using Monte Carlo analysis. The feasibility of the proposed pixel circuit is well demonstrated, as the current variations can be reduced to 2.1% for the supplied power reduced from 5 V to 3 V due to IR drop, and the current variation is as low as 10.6% with operating temperatures from –40 degrees to 85 degrees. [ABSTRACT FROM AUTHOR]