Sharp Kabushiki Kaisha Corporation

Tong Lu

Michael James Brownlow

Tim Michael Smeeton

Adnan Heganovic

Naoki Ueda

Kohhei Tanaka

Christopher James Brown

Oliver James Beard

A pixel circuit for a display device may be operable in three phases, including an initialization phase, a combined threshold compensation and data programming phase, and an emission phase. The pixel circuit may include a drive transistor configured to control an amount of current from a first power supply to a light-emitting device during the emission phase depending upon a voltage applied to a gate of the drive transistor. The pixel circuit may also include a second transistor and a third transistor that are connected in series between the gate and a second terminal of the drive transistor and are configured to implement the three phases. The pixel circuit may also include two capacitors, with one capacitor connected between the gate of the drive transistor and a first node of the circuit, and another capacitor connected between the gate and a second node of the circuit.

Pixel circuit with threshold voltage compensation

A pixel circuit that drives a light-emitting device employs a diode-connection compensation scheme that compensates for threshold variations of the diode connecting switch that diode connects the drive transistor during a threshold compensation phase. The pixel circuit operates to reduce the impact of threshold voltage variations of the diode connecting switch to improve brightness uniformity and picture quality. The pixel circuit includes two compensation capacitors in addition to the storage capacitor for data programming to control the flow and magnitude of a rebalancing current through the diode connecting switch in such a way to cancel excess or deficit of charge caused by threshold voltage variations of the diode connecting switch due to capacitive coupling between the gate node of the switch and the storage capacitor. Therefore, the circuit configuration employs a triple-capacitor structure to significantly improve compensation performance and reliability.

Pixel circuit with reduced sensitivity to threshold variations of the diode connecting switch

A display system includes a display panel comprising a plurality of pixel circuits, and a measurement and data processing unit that is external to the display panel. Each pixel circuit includes a light-emitting device having a first terminal connected to a first voltage supply and a second terminal opposite from the first terminal; a first transistor connected between a data voltage supply line from the measurement and data processing unit and the second terminal of the light emitting device; and a second transistor connected between the second terminal of the light-emitting device and a sample line to the measurement and data processing unit. The measurement and data processing unit samples a measured voltage at the second terminal of the light-emitting device through the sample line and outputs a data voltage to the light-emitting device based on the measured voltage to compensate variations in properties of the light-emitting device.

Method of operating a pixel circuit using direct charging and that performs light-emitting device compensation

An enhanced pixel circuit for a display device provides separate compensation and data programming phases to permit minimization of the programming time. Variations in voltage supplies are accounted for by isolating the drive transistor from such power supply by using a second drive transistor configured as source follower relative to the first drive transistor. An on bias stress transistor is incorporated that can electrically connect the first drive transistor to the power supply during an on bias stress operation. During such operation, a voltage stress is applied to eliminate hysteresis effects associated with the drive transistor. The on bias stress operation may be performed as part of a refresh operation during which a data voltage is programmed to the pixel circuit, or as part of a low frequency operation during which a previously programming data voltage is maintained which reduces power consumption.

TFT pixel threshold voltage compensation circuit with a source follower

A pixel circuit for a display device provides enhanced performance by performing a partial threshold compensation during programming and performing further compensation independent of programming to achieve a short programming time while ensuring threshold compensation accuracy. The pixel circuit is operated in a relatively shortened duration first combined data programming and threshold compensation phase, and in a relatively prolonged duration second threshold compensation phase for improved compensation accuracy. During the combined programming and threshold compensation phase, a drive transistor is diode connected, and a data voltage is applied to a programming a capacitor that also stores a portion of a threshold voltage of the drive transistor. This permits a short programming time. During the prolonged threshold compensation phase, to further compensate the threshold voltage of the drive transistor for compensation accuracy, the drive transistor remains diode connected and a storage capacitor stores the threshold voltage of the drive transistor.

Fast data programming TFT pixel threshold voltage compensation circuit with improved compensation accuracy

A pixel circuit for a display device provides enhanced performance by performing a first threshold compensation phase that also operates to pre-charge a compensating storage capacitor, and then performing a further second threshold compensation combined with data programming during a shortened programming time. During the first threshold compensation phase, the threshold voltage of the drive transistor is stored in the compensating storage capacitor. During the combined data programming and second threshold compensation phase, the data voltage is stored in a programming capacitor, and the drive transistor threshold voltage is also stored in the programming capacitor. As the threshold voltage already is stored at the storage capacitor, and thus the node where the storage capacitor and the programming capacitor connect has been pre-charged with the threshold voltage, the pre-charging effect shortens the time needed for the programming capacitor to store the threshold voltage, which results in a short programming time while achieving high compensation accuracy.

Fast data programming TFT pixel threshold voltage compensation circuit with two phase threshold compensation

A pixel circuit compensates the threshold voltage variations of the drive transistor with an ultra-short one horizontal (1H) time, with additionally removing the possible memory effects associated with the light-emitting device and the drive transistor from the previous frame. An ultra-short 1H time (&#x3c;2 &#x3bc;s) is achieved via separation of threshold compensation of the drive transistor and data programming phases. The pixel circuit has a two-capacitor configuration, whereby a first capacitor is used for drive transistor threshold compensation, and a second capacitor is used to store the data voltage during a data pre-loading phase. Two transistors are employed to electrically connect the gate of the drive transistor to the second capacitor that stores the data voltage, wherein each transistor in this dual transistor configuration is controlled by a different control signal. A timing sequence of the different control signals is used to ensure that a mid node of the dual transistor configuration is refreshed before the data is applied to the gate of the drive transistor. An array of individual pixel circuits is controlled using a global compensation scheme in which global control signals are applied to the individual pixel circuits of the pixel array.

TFT pixel threshold voltage compensation circuit with global compensation

A pixel circuit for driving a light-emitting device for a display device is operable in an initialization phase, a compensation phase, a data programming phase, and an emission phase. The one horizontal time is minimized while maintaining accurate compensation of the threshold voltage of the drive transistor, and the pixel circuit further employs a varactor to compensate for variations in the threshold voltage of the drive transistor and for parasitic capacitances that arise within the pixel circuit. A capacitance of the varactor varies with a voltage at a node Nconstituting an electrical connection during the compensation phase of the drive transistor, the light-emitting device, a storage capacitor, and the varactor. The use of the capacitance variation of the varactor accounts for a variation in the threshold voltage of the drive transistor and for parasitic capacitances in the pixel circuit. The varactor may be implemented as a thin film transistor that operates as a variable capacitor.

TFT pixel threshold voltage compensation circuit using a variable capacitor

A pixel circuit for a display device provides enhanced performance by performing drain-side initialization and data programming with respect to the drive transistor. The pixel circuit is operable in an initialization phase, a combined threshold compensation and data programming phase, and an emission phase, the pixel circuit including a drive transistor configured to control an amount of current to a light-emitting device during the emission phase depending upon a voltage applied to a gate of the drive transistor, and the drive transistor having a first terminal and a second terminal with the first terminal being electrically connected during the emission phase to a first voltage supply line that supplies a driving voltage. The second terminal of the drive transistor is electrically connected to a data voltage supply line that supplies a data voltage during the initialization phase and the combined threshold compensation and data programming phase to compensate a threshold voltage of the drive transistor and to program the data voltage.

TFT pixel threshold voltage compensation circuit with data programming from drain of the drive TFT

A pixel circuit compensates the threshold voltage variations of the drive transistor with an ultra-short one horizontal (1H) time, with additionally removing the possible memory effects associated with the light-emitting device and the drive transistor from the previous frame. An ultra-short 1H time (&#x3c;2 &#x3bc;s) is achieved via separation of threshold compensation of the drive transistor and data programming phases. The pixel circuit has a two-capacitor configuration, whereby a first capacitor is used for drive transistor threshold compensation, and a second capacitor is used to store the data voltage during a data pre-loading phase. Two transistors are employed to electrically connect the gate and source of the drive transistor to a common initialization voltage during an initialization phase to reset circuit voltages for the current frame. In this manner, no current flows through the drive transistor to the light-emitting device during the initialization phase when the light-emitting device does not emit light, which saves power. An array of individual pixel circuits is controlled using a global compensation scheme in which global control signals are applied to the individual pixel circuits of the pixel array.

A display system includes a pixel circuit and an external compensation system that is operable with the pixel circuit to compensate for differences in a property of the drive transistor and/or light-emitting device. The pixel circuit includes a drive transistor configured to control an amount of current to a light-emitting device; a second transistor having a first terminal connected to the gate of the drive transistor and a second terminal connected to a data voltage input that is supplied by the external compensation system, and a gate of the second transistor is connected to a first control signal; a third transistor having a first terminal connected to a second terminal of the drive transistor and a second terminal connected to a second voltage supply input that is supplied from the external compensation system, wherein a current flow from the second voltage supply input is measured by the external compensation system, and wherein a gate of the third transistor is connected to a second control signal; and a fourth transistor having a first terminal connected to the second terminal of the drive transistor and a second terminal connected to a third voltage supply input, wherein a gate of the fourth transistor is connected to a third control signal. The external voltage compensation system is configured to adjust the data voltage input based on the measured current flow to compensate for a variation in a property of the drive transistor and/or the light-emitting device.

TFT pixel circuit for OLED external compensation using an adjusted data voltage for component compensation

A pixel circuit for a display device operable in an initialization phase, a compensation phase, a data programming phase, and an emission phase, whereby the one horizontal time is minimized while maintaining accurate compensation of the threshold voltages of the drive transistors, and further accounting for any variations in the voltage supplies. The pixel circuit includes a first drive transistor configured to control an amount of current to a light-emitting device during an emission phase depending upon voltages applied to a gate and a first terminal of the first drive transistor; and a second drive transistor that is configured as a source follower, wherein a first terminal of the second drive transistor is connected to a first power supply line and a second terminal of the second drive transistor is connected to a first terminal of the first drive transistor. The first drive transistor is one of a p-type or n-type transistor and the second drive transistor is the other of a p-type or n-type transistor. A light-emitting device is electrically connected at a first terminal to a second terminal of the first drive transistor during the emission phase and at a second terminal to a second power supply line.

A pixel circuit is operable in initialization, data programming, threshold compensation, and emission phases. The pixel circuit includes a drive transistor configured to control an amount of current to a light-emitting device during the emission phase depending upon a voltage applied to a gate of the drive transistor. A first ultra-low leakage oxide transistor is employed as a data switch device, and the data voltage is applied to the gate of the drive transistor through the first ultra-low leakage oxide transistor during the data programming phase. A second ultra-low leakage oxide transistor is employed as an initialization switch device. The second ultra-low leakage oxide transistor is in an on state during the initialization, data programming, and threshold compensation phases, and the initialization voltage is applied to the gate of the drive transistor through the second ultra-low leakage oxide transistor during the initialization phase.

TFT pixel threshold voltage compensation circuit with short data programming time and low frame rate

A pixel circuit for a display device is operable in a compensation phase, a data programming phase, and an emission phase, whereby the one horizontal time is minimized while maintaining accurate compensation of the threshold voltage of the drive transistor, and noise applied to the gate of drive transistor during the emission phase is substantially eliminated. The pixel circuit includes a drive transistor configured to control an amount of current from a power supply to a light-emitting device during the emission phase depending upon a voltage input applied to a gate of the drive transistor, and a threshold voltage of the drive transistor is compensated during the compensation phase. The pixel circuit further includes two transistors, one of which is connected between a data voltage input line and the other transistor, and the other transistor further is connected to the gate of the drive transistor, such that when the two transistors are in an on state during the data programming phase, the data voltage is applied to the gate of the drive transistor. The pixel circuit further may include another transistor that is connected between the power supply and a node Nbetween the two transistors, such that during the emission phase, the power supply is applied to the node Nto shield the drive transistor from noise from the data voltage input line.

TFT pixel threshold voltage compensation circuit with short data programming time

A pixel circuit has enhanced performance by minimizing noise effects from the data and reference voltage lines. To prevent data line noise from interfering with the drive transistor gate voltage during emission, a triple gate isolation is used between the data voltage line and the gate of the drive transistor by which three transistors are connected between the data voltage line and the gate of the drive transistor. To further improve the isolation, one of the middle nodes of the triple gate farthest from the data voltage line is connected to one floating node that is connectable to a reference voltage during the threshold compensation phase. A first capacitor is used for the threshold compensation, and a second capacitor is used to scale the data voltage during programming. The threshold compensation and data programming operations are thereby independent of each other to minimize programming time.

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Oxford, United Kingdom

Tong Lu