Patent ID: 7755580
Filing Date: 2010-07-13
Classification: G09G

Abstract:
1. A device for regulating the biasing voltage of column control circuits of an array screen made of LEDs distributed in lines and columns, the column control circuits comprising a current mirror having a reference branch and several duplication branches connected to the biasing voltage, each duplication branch being coupled to a column of the screen, the reference branch being connected at a reference node to a reference current source providing a desired luminance current, said device comprising: first measuring means coupled to the columns to measure a plurality of individual column voltages and provide a first signal representative of a maximum of the plurality of individual column voltages; second measuring means providing a second signal representative of the voltage of the reference node; and an adjustment circuit receiving the first and second signals and being adapted to increase the biasing voltage when the first signal is higher than the second signal and conversely; wherein the first measuring means comprises, for each column, a first diode having an anode connected to the column and a cathode connected to a first input of the adjustment circuit; wherein the cathodes of the first diodes are connected to the first input of the adjustment circuit by a switch, a capacitor being connected to the first input of the adjustment circuit; wherein the switch is controlled so as to be non-conductive when a screen line is black and no LED of the screen line is conductive; and wherein the capacitor holds a value of a voltage of a non-black screen line when the switch is non-conductive.