U.S. Philips Corporation

Koninklijke Philips Corporation N.V.

Chimei Innolux Corporation

Tpo Displays Corporation

Alan G Knapp

John M Shannon

Martin John Edwards

David Andrew Fish

Neil C Bird

Derek Washington

Daphne L Lamport

John R Mansell

Alfred W Woodhead

Mark Thomas Johnson

Steven Charles Deane

Nigel David Young

Roel Van Woudenberg

Jason Roderick Hector

Cornelis Van Berkel

Nijs Cornelis Van Der Vaart

Jeremy N Sandoe

Colin D Overall

Jurgen J L Hoppenbrouwers

Alexander D Annis

Ronald W Gill

Hugo Johan Cornelissen

Karel E Kuijk

Mark Johnathan Childs

Adrianus Sempel

Andrea Giraldo

Stephen J Battersby

John R A Ayres

Gerben Johan Hekstra

Iain M Hunter

Adrianus A Van Der Put

Kenneth G Freeman

Robert A Hartman

Oliver S Davies

Roger Pook

Peter B Wolfs

Catherina J H Van Dam

Henry D Stone

Richard A Slater

Harold W Ellis

David S George

Gerben J Hekstra

Mark T Johnson

An active matrix electroluminescent display device has an array of current&#x2014;driven electroluminescent display elements (), for example comprising organic electroluminescent material, whose operations are each controlled by an associated switching means () to which a drive signal for determining a desired light output is supplied in a respective address period and which is arranged to drive the display element according to the drive signal following the address period. Each switching means comprises a current mirror circuit () which samples and stores the drive signal with one transistor () of the circuit controlling the drive current through the display element () and having its gate connected to a storage capacitance () on which a voltage determined by the drive signal is stored. Through the use of current mirror circuits improved uniformity of light outputs from the display elements in the array is obtained.

Active matrix electroluminescent display devices

In an active matrix electroluminescent display device, comprising an array of display pixels, each pixel comprises an electroluminescent display element, active matrix circuitry including at least one drive transistor for driving a current through the display element, means for determining an overall brightness level of an image to be displayed in a frame period, means for controlling the at least one drive transistor of each pixel in dependence on, (1) a respective input signal providing a drive level for the pixel, and (2) the overall brightness level. The novel arrangement is capable of controlling the pixels to limit the maximum currents drawn by the pixels, thereby limiting cross-talk effects resulting from voltage drops along row or column conductors. If an image is bright, the pixel drive levels across the image, or at least part of the image, can be reduced, so that the maximum brightness is reduced.

System and method for determining an overall brightness level of an image to be displayed in a frame period in electroluminescent display devices

Each pixel of an active matrix electroluminescent display device has a first amorphous silicon drive transistor for intermittently driving a current through the display element and a second amorphous silicon drive transistor for intermittently driving a current through the display element. The aging effect of amorphous silicon TFTs can be reduced by sharing the driving of the display element between two drive transistors. Providing a duty cycle reduces the on-time for each drive transistor, but also provides a period during which there can be some recovery of the TFT characteristics.

The pixels of an active matrix display device have a current-driven light emitting display element, a drive transistor for driving a current through the display element, a storage capacitor for storing a pixel drive voltage to be used for addressing the drive transistor, a light-dependent device for detecting the brightness of the display element, and driver circuitry for providing data signals to the pixel external to the pixel array. This provides a pixel with optical feedback to compensate for display element ageing. The driver circuitry has a processing means for processing the feedback brightness signals and derives from them a threshold voltage for the drive transistor of the pixel as well as information relating to the performance of the display element, for ageing compensation.

Electroluminescent display devices

An active matrix display panel comprises a substrate, array of pixel circuits being arranged in a matrix of at least one column and a plurality of rows on the substrate, each pixel circuit comprising a light-emitting element, capable of emitting light of an intensity determined by the value of a current passed through it, and at least one column line, each column line arranged to conduct a reference current, provided by a current driving circuit, when connected to the panel. The pixel circuits in a column are divided into a plurality of groups of at least one pixel circuit. The active matrix display panel comprises at least one current mirror circuit associated with a first group, comprising a first current mirror, arranged to mirror a reference current flowing through a column line to a first current mirror output. Each pixel circuit in the first group comprises at least a first current-memory stage, having an output terminal connected to the light-emitting element, wherein the first current-memory stage is capable of drawing a current determined at least partly by the current mirrored to the first current mirror output through the output terminal. Each current mirror circuit comprises at least one additional current mirror, arranged to mirror a reference current flowing through an associated column line to an additional current mirror output, wherein each additional current mirror output is connected in parallel to the first current mirror output.

Method and device for driving an active matrix display panel

In an active matrix electroluminescent display device, an overall brightness level of an image to be displayed in a frame period is determined. A drive transistor of each pixel is controlled in dependence on an input drive signal for the pixel and on the overall brightness level, for example using a signal processor () to vary the pixel drive signals. This arrangement can control the pixels to limit the maximum currents drawn by the pixels, thereby limiting the cross talk effects resulting from voltage drops along row or column conductors. If an image is bright, the pixel drive levels across the image (or at least a part of the image) can be reduced, so that the maximum brightness is reduced.

Control of current supplied by a transistor to a pixel in an electroluminescent display device

An active matrix display has a column driver for providing signals to the pixels for driving the display elements, the column driver comprising digital to analogue converter circuitry providing a first number of display element drive levels. Within each pixel, the first number of display element drive levels is converted into a second, greater number, of pixel grey levels. This combines multi-level digital to analogue conversion with in-pixel level generation and enables the complexity of the DACs to be reduced so that they can be integrated onto the display substrate, for example using low temperature polysilicon processing.

Active matrix display

An autostereoscopic display device (), includes a display panel (), a lenticular sheet () and an electrically controllable diffuser (). The electrically controllable diffuser () includes an optical medium (), e.g. polyethyleneterephthalate (PET), with a structured surface () against an electro-optic medium (), e.g. a small droplet polymer dispersed liquid crystal (PDLC) layer. The electro-optic material () refractive index is varied with an applied electric field (or zero field) and is switchable between at least (i) a value (n) substantially matching that of the optical medium (), which provides a substantially non-diffusing mode, hence 3D operation of the display device, and (ii) a value (n) different to that of the optical medium () hence causing refraction at the structured surface (), the structured surface () providing different refraction angles (&#x3b8;) so as to provide an overall diffusing effect, hence 2D operation. The diffuser () may be provided as a stand-alone item.

Autostereoscopic display apparatus

An active matrix display device has column address circuitry for generating pixel drive signals. The column address circuitry has an output buffer for providing a pixel drive signal to a column conductor, and the positive and negative slew rates of the output buffer are different. By selecting the positive and negative slew rates independently in the design of the output buffer, the size of the transistors (), particularly those which pass the charging (or discharging) current of the column capacitance, can be kept to a minimum.

Active matrix display device

A liquid crystal display has a plurality of bufferscontrolling a plurality of column lines. The buffers have a bias current control inputwhich is controlled, in the example by timing circuitry, to current during the row period for writing to each row of pixels. In particular, the row period may be divided between a drive period with a high buffer bias current and a voltage maintenance period with a lower buffer bias current.

Display device with variable-bias driver

An active matrix electroluminescent display device has an array of pixels (), each pixel having a plurality of current-driven display elements (), for example comprising organic electroluminescent material, connected in a series arrangement with one another and with drive means () operable to control the current through the respective series arrangement. By sub-dividing each pixel in this way, the high voltage drops, that can occur along power supply lines, are reduced thus improving the uniformity of the light outputs from the display elements across the display area.

Active matrix electroluminescent display device

A data input system is described comprising a surfacepenand a plurality of transducersThe surface has a structuresuch that when the penis moved across the structurevibration is generated. This is detected by the transducers and the position of the penon the surfaceis calculated. In the preferred embodiment of the invention the structure of the surfacevaries across the surfaceThis means vibration signal waveforms may be associated with specific regions of the surface making identification of the pen location easier.

Data input system

A method of driving an active matrix liquid crystal display in a partial display mode is provided, together with a display operable in accordance therewith. A live portion ( ) of the display is driven to display image data ( ) and a dormant portion ( ) is driven to display a substantially constant grey scale level output. The method comprises applying a signal ( ) to each of the column address conductors ( ) associated with the dormant portion ( ) which comprises a combination of a signal substantially the same as the signal ( ) applied to the counter electrode and kickback correction, such that the resultant kickback correction applied to each of the picture elements associated with the dormant portion ( ) substantially corresponds to the grey scale level of the dormant portion. This serves to reduce the power consumption of the dormant portion ( ), whilst avoiding the application of a substantial DC across the picture elements of the dormant portion ( ).

An active matrix liquid crystal display device comprising display elements ( ) addressed via sets of row and column address conductors ( ) connected respectively to row and column drive circuits ( ) and with the column drive circuit ( ) being operable to transfer data signals for the display elements of a row to groups of column address conductors ( ) in sequence in respective group address periods in a multiplexing manner. The occurrence of undesirable display artifacts is alleviated by applying, during the group address period for one group, a pre-charging signal to the adjacent column address conductor of the next-addressed group according to the level (magnitude) of a data signal for a column conductor in that one group. This can be achieved conveniently by providing, in addition to a multiplexing switch ( ) for that adjacent column conductor, a supplementary switch (Tx) connected to a video input line (V , V , V ), and which operates simultaneously with the multiplexer switches of the

Active matrix liquid crystal display devices

An active matrix electroluminescent display device in which the drive current through an electroluminescent display element ( ) in each pixel ( ) in a drive period is controlled by a driving device ( ) based on a drive signal applied during a preceding address period and stored as a voltage on an associated storage capacitor ( ). In order to counteract the effects of display element ageing, through which the light output for a given drive signal level diminishes over time, the pixel includes electro-optic discharging means ( ) coupled to the storage capacitor and responsive to the display element's light output to leak stored charge and to control the integrated light output of the display element in the drive period. For improved control, the discharging means is arranged to rapidly discharge the capacitor at a controlled point in the drive period, upon the drive of the display element falling to a low level. A photoresponsive transistor can conveniently be utilised for this purpose.

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Crawley, United Kingdom

Alan G Knapp