Display device having current-addressed pixels
AssigneeKoninklijke Philips Electronics N.V.
InventorsIain M. Hunter, Neil C. Bird
Life of this patent
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Abstract
A display device has current-addressed pixels, with the currents being supplied by driver circuitry which comprises a transistor (10) for applying a charging voltage to a switched capacitor arrangement (Ci, S1, S2) arranged to selectively charge and discharge the capacitor (Ci) at a predetermined rate to a charging voltage. A transistor control voltage (Vref) is applied to a control terminal of the transistor which is adjusted depending on the transistor threshold voltage to ensure that the capacitor (Ci) is charged to the charging voltage irrespectively of the value of the threshold voltage. This enables an accurately controllable current to be provided which is used to drive the current-addressed pixels.
Claims10
A display device comprising:
- an array of pixels arranged in rows and columns, each pixel comprising a current-addressed display element;
- driver circuitry for generating current signals corresponding to desired outputs from the display elements, the driver circuitry comprising a transistor switching device for applying a charging voltage to a switched capacitor arrangement, which comprises a capacitor and a switch arrangement enabling the capacitor to be selectively charged and discharged at a predetermined rate to the charging voltage,
- wherein a transistor control voltage is applied to a control terminal of the transistor switching device so as to provide the charging voltage to the switched capacitor arrangement, and wherein the transistor control voltage is adjusted depending on the transistor threshold voltage thereby to ensure that the capacitor is charged to the charging voltage irrespectively of the value of the threshold voltage.
A display device as claimed in any preceding claim, wherein the switched capacitor arrangement comprises a first pair of switches and first associated capacitor, and a second pair of switches and second associated capacitor, wherein the switches are operated to provide charging of one capacitor simultaneously with discharging of the other capacitor.
A display device as claimed in any preceding claim, wherein the switched capacitor arrangement comprises a column capacitor which is charged during an initial operation period of the driver circuitry.
A display as claimed in any preceding claim, wherein each pixel comprises an electroluminescent display element.
A display as claimed in any preceding claim, wherein each pixel comprises first and second switching means, and being operable in a first mode in which the input current is supplied by the first switching means to the second switching means, a control level being stored for the second switching means corresponding to the input current, and in a second mode in which the stored control level is applied to the second switching means so as to drive a current corresponding to the input current through the display element.
Dependencies are inferred from the claim text.