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AssigneeU.S. Philips Corporation
InventorsNeil Christopher Bird, Alan George Knapp
Estimating the term…
A TFT active matrix display device comprising an array of display elements (12), e.g. LC display elements, each connected to the drain of a TFT (17) whose gate and source are connected respectively to a row conductor (18) to which selection signals are applied by a scan drive circuit (21) and a column conductor (19) to which display data signals are applied by a data signal drive circuit (25) in the form of time dependent signals comprising pulse width modulated signals derived from an input digital video signal and representing video sample values. During the selection period the TFTs are biased to act as current sources such that their associated display elements (12) are charged to a level dependent on the duration of the applied signals. The digital to analogue conversion of the video signal is thus completed at the picture elements. In an initial part of the selection period a reference potential, which alternates between two levels in successive fields, is applied to the column conductors to reset the display elements to a predetermined level.
A method of driving an active matrix display device having sets of row and column conductors and an array of display elements each comprising first and second electrodes with electro-optical material therebetween, the first electrodes being connected to the drain of a respective TFT whose source and gate are connected respectively to a column and a row conductor, in which selection signals are applied to the row conductors and in which video information signals are converted into corresponding time dependent signals, characterised in that the time dependent signals are applied to the column conductors and in that during the application of a selection signal to a row of TFTs the TFTs are biased to act as current sources such that their associated display elements are charged to a level dependent on the duration of the applied time dependent signal.
An active matrix display device comprising sets of row and column conductors, an array of display elements each comprising first and second electrodes with electro-optical material therebetween, the first electrodes being connected to the drain of a respective TFT whose source and gate are connected respectively to a column and a row conductor, and a drive circuit for driving the display elements comprising a scan drive circuit for applying selection signals to the row conductors and a data signal drive circuit connected to the column conductors which includes means for providing time dependent pulse signals representing video information, characterised in that the data signal drive circuit is arranged to supply the time dependent pulse signals to the column conductors and in that the data signal drive circuit includes means for biasing the TFTs during the application thereto of a selection signal such that the TFTs act as current sources.
Dependencies are inferred from the claim text.
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No related US applications are recorded in the indexed filing history.
Details of drivers for data electrodes: suitable for active matrices only
Control of matrices with row and column drivers: using an active matrix
Display of intermediate tones: by modulation of the duration of a single pulse during which the logic level remains constant
Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light…:…
Term ended 22 Dec 2015 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to an active matrix display device comprising sets of row and column conductors, an array of display elements, each comprising first and second electrodes with electro-optical material therebetween, the first electrodes being connected to the drain of a TFT whose source and gate are connected respectively to a column conductor and a row conductor, and drive means comprising a scan drive circuit for applying selection signals to the row conductors, and a data signal drive circuit connected to the column conductors which drive circuit includes means for providing time dependent signals representing video information. The invention relates also to a method of operating such a display device.
Active matrix liquid crystal display devices of the above kind are known, both for analogue and digital video signals. Data signal drive circuits operating with digital video signals can offer certain advantages over those operating with analogue video signals, which comprise analogue sample and hold circuits. Particularly in larger area displays having increased numbers of rows and columns of display elements, limitations for example in the operating speeds of these analogue circuits become apparent. Digital video signals can also be advantageous, especially in data-graphic display apparatuses, in that digital video processing circuits can offer greater flexibility than their analogue counterparts. The digital video signal could be supplied for example from a RAM store of a computer. Alternatively, it could be provided by converting analogue TV video signals into digital form.
Examples of such display devices for operating with digital video signals are described in EP-A-0391654 and EP-A-0298255. In the data signal drive circuits described in these specifications, the digital video signals are converted into analogue (amplitude modulated) signals in the data signal drive circuit before being supplied to the column conductors of the display device, and hence to the TFTs associated with the display elements which operate as switches to transfer the analogue voltages to the display elements. This digital to analogue conversion typically involves translating the digital signals into time dependent pulse signals, e.g. pulses whose width are determined by the multibit digital signals, which are used to sample a time-varying reference voltage, either stepped or continuous, so as to obtain output voltages whose amplitudes are determined by the durations of the time dependent signals.
Active matrix display devices and methods of driving such in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic block diagram of an active matrix liquid crystal display device according to the present invention;
FIG. 2 is a schematic block diagram of a typical stage of a data signal drive circuit of the display device connected to a respective column conductor;
Referring to FIG. 1, the active matrix liquid crystal display device comprises a row and column array of liquid crystal display elements 12 defining a display area 14. Each display element 12 comprises a capacitive element consisting of two spaced electrodes carried respectively on the opposing surfaces of two spaced substrates with TN liquid crystal material disposed therebetween. The display element electrodes on the one substrate are constituted by respective regions of a continuous counter electrode layer, denoted 15, common to all display elements in the array. The other electrodes, 16, of the display elements comprise individual electrodes each of which is connected to the drain of an associated TFT 17 carried together with the electrode 16 on the other substrate and through which the display element is driven. The TFTs 17 of the array are addressed via sets of row and column address conductors, 18 and 19, also carried on that substrate, with the associated display elements and TFTs being located adjacent a respective intersection of the row and column conductors. The gates of all TFTs in the same row are connected to a respective row conductor 18 and the sources of all TFTs in a column are connected to a respective column conductor 19. There are r rows and c columns of display elements, providing a total of r.c display elements in the array.
The display element array is driven by peripheral drive means which includes a scan drive circuit 21 which scans the rows of TFTs successively in a known manner, for example, by applying a selection (gating) pulse signal to each of the row conductors 18 in turn, which operation is repeated in successive field periods. The scan drive circuit 21 is of conventional form, comprising for example a digital shift register circuit, and is controlled by timing signals provided from a timing and control circuit 23 along a bus 24 which also supplies the necessary potential levels defining the selection and non-selection signal levels.
The drive means further includes a display data signal drive circuit 25 to which a digital video information signal is applied along a bus 26 and which operates to supply to the set of column conductors 19 appropriately in parallel for each video line in turn data signals in digital form.