Device and method for operating a self-calibrating emissive pixel

Abstract

Self-calibrating emissive pixel circuit, device and method for operating pixel. Method for operating includes: establishing sensor capacitor at predetermined starting voltage, delivering current to photon emitting device to cause photons to be emitted at predetermined target photon emission level, exposing sensor having electrical properties that vary according to photon flux on sensor to the emitted photon emission during at least portion of display frame time, permitting sensor capacitor to either charge or discharge from predetermined starting state through the sensor so that portion of frame time and resistance of sensor during portion of frame time determine amount of charge on sensor capacitor, measuring voltage or charge remaining on sensor capacitor at end of portion of frame time as indication of integrated photon flux and pixel luminance, and modifying image voltage and/or current applied to pixel during any subsequent display frame time using measured voltage as feedback parameter.

1 . A method for operating a self-calibrating pixel, the method comprising: 
 establishing a sensor capacitor at a predetermined starting voltage;    delivering a current to a photon emitting device to cause photons to be emitted at a predetermined target photon emission level;    exposing a sensor device, having electrical properties that varies according to a photon flux on the sensor device, to the emitted photon emission during at least a portion of a display frame time;    permitting the sensor capacitor to either charge or discharge from the predetermined starting voltage through the sensor device so that the portion of the frame time and the average resistance of the sensor during the portion of the frame time determine the amount of charge on the sensor capacitor;    measuring the voltage or charge remaining on the sensor capacitor at the end of a portion of the frame time as an indication of the integrated photon flux and pixel luminance during the portion of the frame time used for measurement; and    modifying the image voltage and current to be applied to the same pixel and gray level during a subsequent display frame time using the measured sensor capacitor voltage as a feedback parameter.    
     
     
         2 . A method as in  claim 1 , wherein the sensor comprises a photoresistive device.  
     
     
         3 . A method as in  claim 1 , wherein the sensor comprises a photoconductive device.  
     
     
         4 . A method as in  claim 1 , wherein the sensor comprises at least one of a photodiode, a photoresistor, a photoconductor, and a phototransistor.  
     
     
         5 . A method as in  claim 1 , wherein the sensor comprises a phototransistor.  
     
     
         6 . A method as in  claim 1 , wherein the sensor comprises a photodiode.  
     
     
         7 . A method as in  claim 1 , wherein the established capacitor starting voltage is established by charging the sensor capacitor to a predetermined charging voltage.  
     
     
         8 . A method as in  claim 1 , wherein the established capacitor starting voltage is established at substantially zero volts.  
     
     
         9 . A method as in  claim 1 , wherein the predetermined capacitor starting voltage is a non-zero voltage having a voltage magnitude.  
     
     
         10 . A method as in  claim 1 , wherein for a sensor capacitor that was charged to a non-zero predetermined starting voltage and then permitted to discharge, the difference voltage remaining across the sensor capacitor is an indication of total photon integrated flux during the portion of the frame time.  
     
     
         11 . A method as in  claim 1 , wherein for a sensor capacitor that was uncharged at substantially zero volts or charged at a different voltage and then permitted to charge during the portion of the frame integration time, the difference of the starting voltage and the ending voltage across the sensor capacitor is an indication of total photon integrated flux during the portion of the frame time.  
     
     
         12 . A method as in  claim 1 , wherein the step of modifying the image voltage and current to be applied to the same pixel and gray level during a subsequent display frame further comprises comparing the measured sensor capacitor voltage with a reference calibration voltage stored in a memory and generating a correction using the difference between these voltages.  
     
     
         13 . A method as in  claim 1 , wherein the method is performed substantially in parallel for each pixel of a two-dimensional active-matrix pixel array.  
     
     
         14 . A method as in  claim 1 , wherein the current delivered is delivered by applying a voltage to a control device that delivers a current corresponding to that voltage to the photon emitting device to cause photons to be emitted at a predetermined target photon emission level.  
     
     
         15 . A method as in  claim 1 , wherein the portion of the frame time comprises the row address time or less.  
     
     
         16 . A method as in  claim 1 , wherein the portion of the frame time comprises substantially the entire frame time.  
     
     
         17 . A method as in  claim 1 , wherein the portion of the frame time comprises at least 50 percent of the entire frame time.  
     
     
         18 . A method as in  claim 1 , wherein the portion of the frame time comprises at least between 90 percent and 100 percent of the entire frame time.  
     
     
         19 . A method as in  claim 1 , wherein the portion of the frame time comprises at least 1 millisecond.  
     
     
         20 . A method as in  claim 1 , wherein the portion of the frame time is equal to or less than the row address time.  
     
     
         21 . A method as in  claim 1 , wherein the method further comprising charging a sensor coupled capacitor to a first predetermined voltage through a sensor line by a transistor and capacitor charging voltage source prior to an integration frame time.  
     
     
         22 . A method as in  claim 21 , wherein a capacitor charge voltage is applied over a sensor line and the sensor line only delivers current when a measurement is being made of the sensor capacitor voltage or when sensor capacitor is being recharged and the voltage is highly stable and not subject to variation.