Importance

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Abstract

A circuit and method for controlling the brightness of a display screen implemented using a field emission display (FED) screen. Within the FED screen, a matrix of rows and columns is provided and emitters are situated within each row-column intersection. Rows are activated sequentially and separate gray scale information (voltages) is presented to the columns. When the proper voltage is applied across the cathode and anode of the emitters, they release electrons toward a phosphor spot, e.g., red, green, blue, causing an illumination point. The present invention includes specialized circuitry positioned across the row drivers for altering the applied voltage to the rows to cause a change in brightness cross the FED screen. In response to a variable brightness voltage signal, the row on-time window is pulse width modulated to alter the brightness of the FED screen. In an automatic brightness adjustment embodiment, an ambient light sensor supplies the brightness signal that changes in proportion to the light sensed. The FED screen brightness is increased in response to increases in the light sensor output and decreased in response to decreases in the light sensor output. Another embodiment uses the light sensor for brightness normalization where the FED screen is used as the reference light level and the FED screen brightness is compensated for due to variations caused by age and manufacturing differences. A manual brightness adjustment (override) and automatic brightness on/off switch are also provided.

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First Claim