Electroluminiscent display and driver circuit to reduce photoluminesence

Display driver circuitry for providing an improved contrast electroluminescent display, the electroluminescent display comprising a plurality of electroluminescent (EL) display elements, the display driver circuitry comprising:

• a first driver to apply a first polarity drive to at least one first display element of said EL display elements to cause said at least one first display element to electroluminesce;
• a second driver to apply a second polarity drive to at least one second display element of the EL display elements to at least partially quench photoluminescence from said at least one second display element wherein said second driver comprises a voltage generator to generate a voltage from a positive voltage power supply to said display driver circuitry,
• a plurality of column switches to connect each column electrode to the first polarity drive or to ground;
• and
• a plurality of row switches to selectively connect each row electrode to the second polarity drive or to ground;
• wherein said first and second display elements comprise different display elements and said first and second polarity drives at least partially overlap in time,
• wherein the display driver circuitry is configured to address said display by row-wise scanning by selectively connecting a row to ground and selectively connecting at least one column electrode to the first polarity drive whereby said at least one display element is illuminated;
• wherein the second driver is configured to provide sufficient reverse bias drive so that all non-scanned display elements connected to the same column electrode as said at least one illuminated first display element are reverse biased even though the non-scanned display elements are connected to the first driver which provides said forward drive to said at least one first display element;
• wherein the output of the second driver is greater than the output of the first driver;
• and
• wherein the difference between said output of the second driver and the output of the first driver is controlled to provide a reduction in photoluminescence, with all display elements off;
• of at least 50% under an illuminance of at least 1000 lux from a source approximating a black body at a temperature of 5400K.

A method of using a display driver to improve contrast in a display comprising a plurality of light emitting diode display elements addressed by row-wise scanning, the method comprising:

• applying a forward bias to at least one display element to illuminate the display element and
• operating the display driver to reverse-bias all non-scanned non-emitting display elements to at least partially quench photoluminescence from said non-scanned non-emitting display elements whereby said display contrast is enhanced;
• wherein the reverse bias is greater than an amount equal to the forward bias applied to the at least one illuminated element, wherein a reverse bias is applied to display elements except said at least one illuminated display element even when the forward bias is also applied to the display elements;
• and
• wherein a difference between the bias applied to a non-scanned non-emitting display element and the forward bias is controlled to provide a reduction in photoluminescence, with all display elements off, of at least 50% under an illuminance of at least 1000 lux from a source approximating a black body at a temperature of 5400K.

A method for improving the contrast of a display comprising a plurality of light emitting diode display elements addressed by row-wise scanning, comprising:

• using a display driver to apply a forward bias to at least one display element to illuminate the display element and
• using the display driver to reverse bias all non-emitting display elements to at least partially quench photoluminescence from said non-emitting display elements;
• wherein the reverse bias is greater than an amount equal to the forward bias applied to the at least one illuminated element, wherein a reverse bias is applied to display elements except said at least one illuminated display element even when the forward bias is also applied to the display elements and
• wherein a difference between the reverse bias applied to a non-scanned non-emitting display element and the forward bias is controlled to provide a reduction in photoluminescence, with all display elements off, of at least 50% under an illuminance of at least 1000 lux from a source approximating a black body at a temperature of 5400K.