Emission Current Error Research Articles

12.2: High Performance AMOLED Pixel Circuit Using Interleaved Emit Signals Based on Low‐Temperature Poly‐Si and Oxide (LTPO) TFTs

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.

64‐4: Student Paper: MiniLED Driving Circuit with Power‐Saving Mechanism for Use in LCD Backlight Module

This work presents a Mini‐LED driving circuit with for backlight unit of liquid crystal display. Simulation results indicate that the emission current error rates are all below 9.9% to ensure the capability of the proposed circuit to improve the image quality of displays.

A Pixel Circuit With Wide Data Voltage Range for OLEDoS Microdisplays With High Uniformity

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 $8.1\,\,\mu \text{m}\,\,\times {4}\,\,\mu \text{m}$ .

A 4410-ppi Resolution Pixel Circuit for High Luminance Uniformity of OLEDoS Microdisplays

This paper proposes a pixel circuit with high resolution and high luminance uniformity for organic light emitting diode-on-silicon (OLEDoS) microdisplays. The proposed pixel circuit employs a simple structure that consists of four n-channel MOSFETs and one capacitor, resulting in high resolution. In addition, this circuit compensates for the threshold voltage ( $V_{th}$ ) variation of the driving transistor caused by the body effect, which increases the $V_{th}$ as the source-to-body voltage of the driving transistor increases, thus reducing the emission current deviation, resulting in a high luminance uniformity. Moreover, the proposed pixel circuit extends the data voltage range using the capacitive coupling of the storage capacitance and the parasitic capacitance at the gate node of the driving transistor to precisely control the emission current. To verify the performance of the proposed pixel circuit, a test pattern with an array of the proposed 4T1C pixel circuits was fabricated on a single-crystalline silicon wafer as a backplane using a 110 nm standard CMOS process with 5.5 V high-voltage devices. The proposed pixel circuit occupies a unit sub-pixel area of $5.76 \mu \mathrm {m} \times 1.92 \mu \text{m}$ , which corresponds to a resolution of 4410 pixels per inch. The measurement results show that the emission current deviation error of the proposed pixel circuit ranges between −1.16% and +1.14%, which is improved from between −45.97% to +45.42% achieved in the conventional current-source type 2T1C pixel circuit, which does not compensate for the $V_{th}$ variation of the driving transistor. Moreover, the measured data voltage range of the proposed pixel circuit is extended to 1.618 V, which is 8.17 times wider than that of the conventional pixel circuit. Therefore, the proposed pixel circuit is very suitable for high resolution and high luminance uniformity of OLEDoS microdisplays.

A Compensation Method for Variations in Subthreshold Slope and Threshold Voltage of Thin-Film Transistors for AMOLED Displays

In this paper, we propose a compensation method for variations in the subthreshold slope (SS) and threshold voltage (Vth) of the low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) in an attempt to improve the image quality of the active matrix organic light-emitting diode (AMOLED) displays for mobile applications. The proposed compensation method provides a uniform voltage to the OLED according to the gray level without being affected by variations in the SS and Vth of the LTPS TFTs. To verify the performance of the proposed compensation method, a test pattern, including two pixel circuits designed for 5.7-inch quadruple high-definition AMOLED display was fabricated and measured. The measurement results showed that the proposed compensation method achieved an emission current error of the pixel circuit of only ±3.1 LSB at the 255th gray level. Therefore, the proposed compensation method is very suitable for AMOLED displays requiring high image quality.

P‐47: An OLEDoS Pixel Circuit with Extended Data Voltage Range for High Resolution Micro‐Displays

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.

An AMOLED pixel circuit for high image quality of 1000 ppi mobile displays in AR and VR applications

AbstractIn this paper, an active‐matrix organic light‐emitting diode pixel circuit is proposed to improve the image quality of 5.87‐in. mobile displays with 1000 ppi resolution in augmented and virtual reality applications. The proposed pixel circuit consisting of three thin‐film transistors (TFTs) and two capacitors (3T2C) employs a simultaneous emission driving method to reduce the number of TFTs and the emission current error caused by variations in threshold voltage (Vth) and subthreshold slope (SS) of the low‐temperature polycrystalline silicon TFTs. Using the simultaneous emission driving method, the compensation time is increased to 90 μs from 6.5 μs achieved in the conventional six TFTs and one capacitor (6T1C) pixel circuit. Consequently, the emission current error of the proposed 3T2C pixel circuit was reduced to ±3 least significant bit (LSB) from ±12 LSB at the 32nd gray level when the variations in both the Vth and SS are ±4σ. Moreover, both the crosstalk errors due to the parasitic capacitances between the adjacent pixel circuits and due to the leakage current were achieved to be less than ±1 LSB over the entire gray level. Therefore, the proposed pixel circuit is very suitable for active‐matrix organic light‐emitting diode displays requiring high image quality.

Qualitative analysis of Copaifera oleoresin using comprehensive two-dimensional gas chromatography and gas chromatography with classical and cold electron ionisation mass spectrometry

Improved separation of both sesquiterpenes and diterpenic acids in Copaifera multijuga Hayne oleoresin, is demonstrated by using comprehensive two-dimensional gas chromatography (GC×GC) coupled to accurate mass time-of-flight mass spectrometry (accTOFMS). GC×GC separation employs polar phases (including ionic liquid phases) as the first dimension (1D) column, combined with a lower polarity 2D phase. Elution temperatures (Te) of diterpenic acids (in methyl ester form, DAME) increased as the 1D McReynolds’ polarity value of the column phase decreased. Since Te of sesquiterpene hydrocarbons decreased with increased polarity, the very polar SLB-IL111 1D phase leads to excessive peak broadening in the 2D apolar phase due to increased second dimension retention (2tR). The combination of SLB-IL59 with a nonpolar column phase was selected, providing reasonable separation and low Te for sesquiterpenes and DAME, compared to other tested column sets, without excessive 2tR. Identities of DAME were aided by both soft (30eV) electron ionisation (EI) accurate mass TOFMS analysis and supersonic molecular beam ionisation (cold EI) TOFMS, both which providing less fragmentation and increased relative abundance of molecular ions. The inter-relation between EI energies, emission current, signal-to-noise and mass error for the accurate mass measurement of DAME are reported. These approaches can be used as a basis for conducting of GC×GC with soft EI accurate mass measurement of terpenes, particularly for unknown phytochemicals.

A Pixel Structure Using Block Emission Driving Method for High Image Quality in Active Matrix Organic Light-Emitting Diode Displays

In this paper, we propose a pixel structure and timing diagram using the block emission (BE) driving method to improve the image quality of high-resolution active matrix organic light-emitting diode (AMOLED) displays. The proposed pixel structure reduces the boundary error pattern between blocks by adjusting the timing of the compensation ( comp ) signal for the threshold voltage variation. The test patterns, which include a pixel array and unit pixels, are designed for a 10-inch quadruple high-definition resolution format and are fabricated to verify the image quality of the AMOLED displays. The measurement results show that the emission current error at the boundary between blocks is reduced from +11% to less than ±1% by adjusting the timing of the comp signal. Also, the emission current error caused by the threshold voltage variation of the driving thin film transistors is reduced from ±8.36% to ±2.77% at a gray level of 175 by using the BE driving method. Therefore, the proposed pixel structure improves image quality in high-resolution AMOLED displays.

7-3: AMOLED Pixel Structure Using the Close Loop Negative Feedback Method for High Resolution Displays

A new 5T2C pixel circuit is proposed in this study to compensate TFT Vth variation, power line IR-drop, and OLED degradation in LTPS PMOS process and it also has The Close Loop Negative Feedback Method (CL-NFM) to compensate the gate voltage distortion of the driving TFT during the emission phase. The simulation showed that the emission current error are 4.85%, 9.02% and 39.25% separated for high, middle and low grey level compared between the current value in 1ms and 16ms, which is 12.51%, 38.14% and 97.8% for the conventional pixel structure, respectively.

Simple pixel circuits for high resolution and high image quality organic light emitting diode-on-silicon microdisplays with wide data voltage range

Two simple pixel circuits are proposed for high resolution and high image quality organic light-emitting diode-on-silicon microdisplays. The proposed pixel circuits achieve high resolution due to simple pixel structure comprising three n-type MOSFETs and one storage capacitor, which are integrated into a unit subpixel area of 3 × 9 µm2 using a 90 nm CMOS process. The proposed pixel circuits improve image quality by compensating for the threshold voltage variation of the driving transistors and extending the data voltage range. To verify the performance of the proposed pixel circuits, the emission currents of 24 pixel circuits are measured. The measured emission current deviation error of the proposed pixel circuits A and B ranges from −2.59% to +2.78%, and from −1.86% to +1.84%, respectively, which are improved from the emission current deviation error of the conventional current-source type pixel circuit when the threshold voltage variation is not compensated for, which ranges from −14.87% to +14.67%. In addition, the data voltage ranges of the proposed pixel circuits A and B are 1.193 V and 1.792 V, respectively, which are 2.38 and 3.57 times wider than the data voltage range of the conventional current-source type pixel circuit of 0.501 V.

7.2: A Pixel Structure Using Switching Error Reduction Method for High Image Quality AMOLED Displays

In this paper, an active matrix organic light emitting diode (AMOLED) pixel structure is proposed to improve the image quality by using the switching error reduction method. The switching error is decreased by floating the storage capacitor before it is induced. The simulation results show that the switching error and the emission current error of the proposed pixel structure are reduced by 91.4% and 77.5%, respectively, compared to those of the conventional pixel structure, when the threshold voltage of the switching TFT varies from ‐1.9 V to ‐1.1 V.

13.5L: Late‐News Paper: A Simple Pixel Circuit for Ultra High Resolution Active Matrix OLED‐on‐Silicon (OLEDoS) Microdisplays with Highly Uniform Luminance

In this paper, a simple pixel circuit is proposed for the high resolution organic light emitting diode‐on‐silicon (OLEDoS) microdisplay. The proposed pixel circuit achieves a wide input data voltage range using the body effect and suppresses the emission current deviation due to the threshold voltage variation of the driving transistor using the capacitive coupling effect. The proposed pixel circuit which consists of three n‐type MOSFETs and one storage capacitor occupies an area of 3 μm × 9 μm. The simulated results show that the proposed pixel circuit achieves maximum input data voltage ranges of 1.37 V, 1.51 V, and 1.34 V for red, green, and blue OLED, respectively, from 1‐gray to 255‐gray level, and the emission current error ranges from −2.85% to +2.96% under the threshold voltage variation of ±5 mV.

Pixel structures to compensate nonuniform threshold voltage and mobility of polycrystalline silicon thin-film transistors using subthreshold current for large-size active matrix organic light-emitting diode displays

We propose pixel structures for large-size and high-resolution active matrix organic light-emitting diode (AMOLED) displays using a polycrystalline silicon (poly-Si) thin-film transistor (TFT) backplane. The proposed pixel structures compensate the variations of the threshold voltage and mobility of the driving TFT using the subthreshold current. The simulated results show that the emission current error of the proposed pixel structure B ranges from −2.25 to 2.02 least significant bit (LSB) when the variations of the threshold voltage and mobility of the driving TFT are ±0.5 V and ±10%, respectively.

Pixel structures using the negative feedback method for high‐resolution active matrix organic light‐emitting diode displays

AbstractNovel two pixel structures are proposed for high‐resolution active matrix organic light‐emitting diode displays. The proposed two pixels (pixel structures A and B) use the negative feedback method for high‐resolution displays that requires to have small‐sized storage capacitance. The proposed pixel structures A and B improve the luminance uniformity by reducing the voltage distortion in the storage capacitor. However, the proposed pixel structure A is vulnerable to the organic light‐emitting diode (OLED) degradation because the anode voltage of the OLED affects the emission current. In order to compensate the OLED degradation, the proposed pixel structure B stores the turn‐on voltage of OLEDs in the storage capacitor. The simulation results show that the emission current error of the proposed pixel structure B is improved by four times in comparison with the proposed pixel structure A when the OLED turn‐on voltage increases by 0.1 V. Also, the emission current error of the proposed pixel structure B when the threshold voltage of driving thin‐film transistors varies from −2.2 to −1.8 V is from −0.69 least significant bit (LSB) to 0.13 LSB, which shows the excellent luminance uniformity. The proposed pixels are designed for 5.5‐in. full high‐definition displays.

35.1: High Resolution AMOLED Pixel Using Negative Feedback Structure for Improving Image Quality

AbstractAn active matrix organic light emitting diode (AMOLED) pixel structure is proposed to improve image quality of high resolution small sized displays. The proposed pixel structure increases luminance uniformity by decreasing the distortion of the voltage in the storage capacitors using negative feedback structure. The simulation results show that the distortion of the voltage in the storage capacitors with negative feedback structure decreases to 55.3% compared to that without negative feedback structure and the emission current error of the proposed pixel structure ranges from −0.71 LSB to 0.56 LSB when the threshold voltage of the driving TFT varies from −0.2 V to 0.2 V.

A Simple Pixel Structure Using Polycrystalline-Silicon Thin-Film Transistors for High-Resolution Active-Matrix Organic Light-Emitting Diode Displays

A simple pixel structure comprising two transistors and one capacitor and a novel driving method are proposed for small-sized and high-resolution active-matrix organic light-emitting diode displays on polycrystalline-silicon thin-film transistor (TFT) backplane. The proposed pixel increases the yield due to small number of TFTs and improves image quality by compensating threshold voltage variations of driving TFTs. The proposed pixel is designed as test pixels with 353 pixels per inch, and the measured emission current error range of -74.2% -60.6% is improved to the range of -2.5% -2.1% when the proposed pixel is used.

Novel Driving Method for Two-Dimensional and Three-Dimensional Switchable Active Matrix Organic Light-Emitting Diode Displays for Emission and Programming Time Extension

A novel driving method for two-dimensional (2D) and three-dimensional (3D) switchable active matrix organic light-emitting diode (AMOLED) displays is proposed to extend emission time and data programming time during 3D display operation. The proposed pixel consists of six thin-film transistors (TFTs) and two capacitors, and the aperture ratio of the pixel is 45.8% under 40-in. full-high-definition television condition. By increasing emission time and programming time, the flicker problem can be reduced and the lifetime of AMOLED displays can be extended owing to the decrease in emission current density. Simulation results show that the emission current error range from -0.4 to 1.6% is achieved when the threshold voltage variation of driving TFTs is in the range from -1.0 to 1.0 V, and the emission current error is 1.0% when the power line IR-drop is 2.0 V.

P‐166: Successive Cross Emission Driving for 3‐Dimensional Active‐Matrix Organic Light Emitting Diode Displays

AbstractWe propose a pixel structure and its driving scheme for stereoscopic 3‐dimensional (3D) active‐matrix organic light emitting diode (AMOLED) displays. The proposed pixel structure and its driving scheme have merits that are longer emission and programming time than simultaneous emission scheme by successive cross emission of left and right images. Moreover, it can reduce flicker by reducing interval between emission times. For 3D AMOLED displays of 40‐inch full high definition TV (1920×1080), the emission current error rate of the proposed pixel structure is from −0.961% to 1.013% when the threshold voltage variation of driving TFT varies from −0.8 V to 0.8 V, and that the error is less than 2% when the VDD‐IR drop voltage becomes 2.0 V.

27.4: Distinguished Student Paper: Simultaneous Programming and Emission Driving Using External Compensation Method for 3D AMOLED Displays

AbstractSimultaneous programming and emission driving using external compensation method for 3D active matrix organic light emitting diode (AMOLED) displays is proposed. The emission current uniformity is improved by compensating threshold voltage and mobility variations of driving TFTs. Simulation results show that the maximum emission current error range of the proposed method is from −1.6% to 0.6% in 40‐inch full HDTV condition when the threshold voltage of driving TFT variation is form −1 V to 1 V and mobility variation of driving TFT is from −10% to 10%. The emission and programming time of 3D AMOLED display is also increased by simultaneous driving method.