Direct detect sensor for flat panel displays

Abstract

Each sensor of a linear array of sensors includes, in part, a sensing electrode and an associated feedback circuit. The sensing electrodes are adapted to be brought in proximity to a flat panel having formed thereon a multitude of pixel electrodes in order to capacitively measure the voltage of the pixel electrodes. Each feedback circuit is adapted to actively drive its associated electrode via a feedback signal so as to maintain the voltage of its associated electrode at a substantially fixed bias. Each feedback circuit may include an amplifier having a first input terminal coupled to the sensing electrode and a second input terminal coupled to receive a biasing voltage. The output signal of the amplification circuit is used to generate the feedback signal that actively drives the sensing electrode. The biasing voltage may be the ground potential.

1 - 8 . (canceled) 
   
   
       9 . A method of testing a panel having formed thereon a plurality of pixels, the method comprising:
 capacitively coupling a sensing electrode to a pixel electrode at time T1 to sense the pixel electrode voltage; and   maintaining said sensing electrode pixel at a substantially constant voltage via a feedback signal generated in accordance with the sensed pixel electrode voltage, wherein said sensing electrode is disposed in a linear of array of sensors.   
   
   
       10 . The method of  claim 9  further comprising:
 supplying the sensed pixel electrode voltage to a first input terminal of an amplifying circuit; and   generating the feedback signal from an output voltage generated by the amplifying circuit.   
   
   
       11 . The method of  claim 10  wherein said amplifying circuit comprises an operational amplifier. 
   
   
       12 . The method of  claim 10  further comprising:
 supplying a biasing voltage to a second input terminal of the amplifying circuit.   
   
   
       13 . The method of  claim 12  wherein said biasing voltage is the ground potential. 
   
   
       14 . The method of  claim 12  further comprising:
 capacitively coupling the output terminal of the amplifying circuit to the first input terminal of the amplifying circuit.   
   
   
       15 . The method of  claim 10  further comprising:
 capacitively coupling a second sensing electrode to the pixel electrode at time T2 to sense the pixel electrode voltage; wherein T2 and T1 are spaced in time by a predefined value; and   maintaining said second sensing electrode pixel at a substantially constant voltage via a feedback signal generated in accordance with the pixel electrode voltage sensed by the second sensed electrode.   
   
   
       16 . The method of  claim 15  further comprising:
 capacitively coupling a third sensing electrode to the pixel electrode at time T3 to sense the pixel electrode voltage; wherein T3 and T1 are spaced in time by a predefined value; and   maintaining said third sensing electrode pixel at a substantially constant voltage via a feedback signal generated in accordance with the pixel electrode voltage sensed by the third sensed electrode.   
   
   
       17 . The method of  claim 16  wherein each of the second and third sensors further comprises:
 a sensing electrode adapted to be capacitively coupled to the pixel electrode disposed on the panel; and   an associated feedback network configured to maintain the voltage of the sensing electrode associated therewith at a substantially constant voltage when positioned in proximity of the pixel electrode to be capacitively coupled thereto.   
   
   
       18 . The method of  claim 9  wherein said pixel electrode receives a DC voltage before being capacitively coupled to the sensing electrode.