Pixel circuit and display apparatus

Abstract

Disclosed herein is a pixel circuit that includes a correcting section configured to correct the input voltage sampled in the pixel capacitance in order to cancel out the dependency of the output current on the carrier mobility. In the pixel circuit, the correcting section operates depending on the control signal supplied from the scanning line to extract the output current from the drive transistor and introduce the extracted output current into a capacitance of the light-emitting device and the pixel capacitance, thereby correcting the input voltage. The pixel circuit further includes an additional capacitance added to the capacitance of the light-emitting device. In the pixel circuit, a portion of the output current extracted from the drive transistor flows into the additional capacitance to give a time margin to operation of the correcting section.

What is claimed is: 
     
       1. A pixel circuit for being positioned at a point of intersection between a row scanning line for supplying a control signal and a column signal line for supplying a video signal, comprising at least:
 a sampling transistor;   a pixel capacitance connected to said sampling transistor;   a drive transistor connected to said pixel capacitance;   a light-emitting device connected to said drive transistor;   wherein said sampling transistor is turned on in response to the control signal supplied from said scanning line to sample the video signal supplied from said signal line into said pixel capacitance,   said pixel capacitance applies an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor supplies an output current depending on said input voltage to said light-emitting device, said output current having dependency on a carrier mobility in a channel region of said drive transistor,   said light-emitting device emits light at a luminance level depending on said video signal in response to the output current supplied from said drive transistor,   said pixel circuit further including   correcting means for correcting the input voltage sampled in said pixel capacitance in order to cancel out the dependency of said output current on the carrier mobility,   wherein said correcting means operates depending on the control signal supplied from said scanning line to extract the output current from said drive transistor and introduce the extracted output current into a capacitance of said light-emitting device and said pixel capacitance for thereby correcting the input voltage, and   an additional capacitance added to the capacitance of said light-emitting device, wherein a portion of the output current extracted from said drive transistor flows into said additional capacitance to give a time margin to operation of said correcting means.   
     
     
       2. The pixel circuit according to  claim 1 , wherein said sampling transistor, said drive transistor, and said correcting means comprise thin-film transistors formed on an insulating substrate, and said pixel capacitance and said additional capacitance include thin-film capacitors formed on said insulating substrate. 
     
     
       3. The pixel circuit according to  claim 1 , wherein the output current of said drive transistor has dependency on a threshold voltage as well as the carrier mobility in the carrier region, and said correcting means detects a threshold voltage of said drive transistor and adds the detected threshold voltage to said input voltage in advance in order to cancel out the dependency of the output current on the threshold voltage. 
     
     
       4. The pixel circuit according to  claim 1 , wherein said light-emitting device comprises a diode-type light-emitting device having an anode connected to a source of said drive transistor and a cathode connected to ground, said additional capacitance having a terminal connected to the anode of said light-emitting device and another terminal connected to a predetermined fixed potential. 
     
     
       5. The pixel circuit according to  claim 4 , wherein said predetermined fixed potential to which another terminal of said additional capacitance is connected is selected from a ground potential on the cathode of said light-emitting device, and a positive power supply potential and a negative power supply potential of the pixel circuit. 
     
     
       6. The array of pixel circuits each according to  claim 1 , wherein each of said pixel circuits has either one of a red light-emitting device, a green light-emitting device, and a blue light-emitting device, or the additional capacitances in the respective pixel circuits have different capacitance values for the respective light-emitting devices for thereby making times requisite to operate the correcting means in the respective pixel circuits uniform. 
     
     
       7. The array of pixel circuits each according to  claim 6 , wherein a shortage of the capacitance value of the additional capacitance in one of said pixel circuits is made up for by a portion of the additional capacitance in an adjacent one of said pixel circuits. 
     
     
       8. The pixel circuit according to  claim 1 , wherein said correcting means extracts the output current from said drive transistor and supplies the extract output current to said pixel capacitance through a negative feedback loop to correct said input voltage while the video signal is being sampled in said pixel capacitance. 
     
     
       9. A display apparatus comprising:
 a pixel array having a matrix of pixels each positioned at a point of intersection between a row scanning line for supplying a control signal and a column signal line for supplying a video signal;   a signal unit for supplying a video signal to said signal line; and   a scanner unit for supplying a control signal to said scanning line to successively scan rows of the pixels;   each of said pixels including at least
 a sampling transistor, 
 a pixel capacitance connected to said sampling transistor, 
 a drive transistor connected to said pixel capacitance, 
 a light-emitting device connected to said drive transistor, 
 wherein said sampling transistor is turned on in response to the control signal supplied from said scanning line to sample the video signal supplied from said signal line into said pixel capacitance, 
 said pixel capacitance applies an input voltage to a gate of said drive transistor depending on the sampled video signal, 
 said drive transistor supplies an output current depending on said input voltage to said light-emitting device, said output current having dependency on a carrier mobility in a channel region of said drive transistor, 
 said light-emitting device emits light at a luminance level depending on said video signal in response to the output current supplied from said drive transistor, 
   each pixel of said pixels further including
 correcting means for correcting the input voltage sampled in said pixel capacitance in order to cancel out the dependency of said output current on the carrier mobility, 
 wherein said correcting means operates depending on the control signal supplied from said scanning line to extract the output current from said drive transistor and introduce the extracted output current into a capacitance of said light-emitting device and said pixel capacitance thereby correcting the input voltage, and 
 an additional capacitance added to the capacitance of said light-emitting device, wherein a portion of the output current extracted from said drive transistor flows into said additional capacitance to give a time margin to operation of said correcting means. 
   
     
     
       10. The display apparatus according to  claim 9 , wherein said sampling transistor, said drive transistor, and said correcting means comprise thin-film transistors formed on an insulating substrate, and said pixel capacitance and said additional capacitance include thin-film capacitors formed on said insulating substrate. 
     
     
       11. The display apparatus according to  claim 9 , wherein the output current of said drive transistor has dependency on a threshold voltage as well as the carrier mobility in the carrier region, and said correcting means detects a threshold voltage of said drive transistor and adds the detected threshold voltage to said input voltage in advance in order to cancel out the dependency of the output current on the threshold voltage. 
     
     
       12. The display apparatus according to  claim 9 , wherein said light-emitting device comprises a diode-type light-emitting device having an anode connected to a source of said drive transistor and a cathode connected to ground, and said additional capacitance has a terminal connected to the anode of said light-emitting device and another terminal connected to a predetermined fixed potential. 
     
     
       13. The display apparatus according to  claim 12 , wherein said predetermined fixed potential to which another terminal of said additional capacitance is connected is selected from a ground potential on the cathode of said light-emitting device, and a positive power supply potential and a negative power supply potential of the pixel circuit. 
     
     
       14. The display apparatus according to  claim 9 , wherein each of said pixels has either one of a red light-emitting device, a green light-emitting device, or a blue light-emitting device, and the additional capacitances in the respective pixels have different capacitance values for the respective light-emitting devices thereby making times requisite to operate the correcting means in the respective pixels uniform. 
     
     
       15. The display apparatus according to  claim 14 , wherein a shortage of the capacitance value of the additional capacitance in one of said pixels is made up for by a portion of the additional capacitance in an adjacent one of said pixels. 
     
     
       16. The display apparatus according to  claim 9 , wherein said correcting means extracts the output current from said drive transistor and supplies the extract output current to said pixel capacitance through a negative feedback loop to correct said input voltage while the video signal is being sampled in said pixel capacitance. 
     
     
       17. A pixel circuit for being positioned at a point of intersection between a row scanning line for supplying a control signal and a column signal line for supplying a video signal, comprising at least:
 a sampling transistor;   a pixel capacitance;   a drive transistor;   a light-emitting device;   wherein said sampling transistor is turned on in response to the control signal supplied from said row scanning line to sample the video signal supplied from said signal line into said pixel capacitance,   said pixel capacitance applies an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor supplies an output current depending on said input voltage to said light-emitting device,   said light-emitting device emits light at a luminance level depending on said video signal in response to said output current supplied from said drive transistor,   said pixel circuit corrects the input voltage sampled in said pixel capacitance,   wherein the output current from said drive transistor is extracted into said pixel capacitance, and   an additional capacitance added to said pixel capacitance, a portion of said output current from the drive transistor flowing into said additional capacitance.   
     
     
       18. The pixel circuit according to claim 17, wherein said sampling transistor and said drive transistor comprise thin-film transistors formed on an insulating substrate, and said pixel capacitance and said additional capacitance include thin-film capacitors formed on said insulating substrate. 
     
     
       19. The pixel according to claim 17, further including correcting means for correcting the input voltage sampled in said pixel capacitance in order to cancel out the dependency of said output current on the carrier mobility. 
     
     
       20. The pixel circuit according to claim 19, wherein the output current of said drive transistor has dependency on a threshold voltage as well as the carrier mobility in the carrier region, and said correcting means detects a threshold voltage of said drive transistor and adds the detected threshold voltage to said input voltage in advance in order to cancel out the dependency of the output current on the threshold voltage. 
     
     
       21. The array of pixel circuits each according to claim 20, wherein each of said pixel circuits has either one of a red light-emitting device, a green light-emitting device, and a blue light-emitting device, or the additional capacitances in the respective pixel circuits have different capacitance values for the respective light-emitting devices for thereby making times requisite to operate the correcting means in the respective pixel circuits uniform. 
     
     
       22. The array of pixel circuits each according to claim 21, wherein a shortage of the capacitance value of the additional capacitance in one of said pixel circuits is made up for by a portion of the additional capacitance in an adjacent one of said pixel circuits. 
     
     
       23. The pixel circuit according to claim 19, wherein said correcting means extracts the output current from said drive transistor and supplies the extract output current to said pixel capacitance through a negative feedback loop to correct said input voltage while the video signal is being sampled in said pixel capacitance. 
     
     
       24. A pixel circuit for being positioned at a point of intersection between a row scanning line for supplying a control signal and a column signal line for supplying a video signal, comprising at least:
 a sampling transistor;   a pixel capacitance;   a drive transistor;   a light-emitting device;   wherein said sampling transistor is turned on in response to the control signal supplied from said row scanning line to sample the video signal supplied from said signal line into said pixel capacitance,   said pixel capacitance applies an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor supplies an output current depending on said input voltage to said light-emitting device,   said light-emitting device emits light at a luminance level depending on said video signal in response to said output current supplied from said drive transistor,   said pixel circuit corrects the input voltage sampled in said pixel capacitance,   wherein the output current from said drive transistor is extracted into said pixel capacitance, and   an additional capacitance added to said pixel capacitance,   wherein said light-emitting device comprises an anode connected to a source of said drive transistor and a cathode connected to ground, said additional capacitance having a terminal connected to the anode of said light-emitting device and another terminal connected to a predetermined fixed potential.   
     
     
       25. The pixel circuit according to claim 24, wherein said predetermined fixed potential to which another terminal of said additional capacitance is connected is selected from a ground potential on the cathode of said light-emitting device, and a positive power supply potential and a negative power supply potential of the pixel circuit. 
     
     
       26. A display apparatus comprising:
 a pixel array having a matrix of pixels each positioned at a point of intersection between a row scanning line for supplying a control signal and a column signal line for supplying a video signal; a signal unit for supplying a video signal to said signal line; and a scanner unit for supplying a control signal to said row scanning line to successively scan rows of the pixels; each of said pixels including at least   a sampling transistor,   a pixel capacitance,   a drive transistor,   a light-emitting device,   wherein said sampling transistor is turned on in response to the control signal supplied from said row scanning line to sample the video signal supplied from said signal line into said pixel capacitance,   said pixel capacitance applies an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor supplies an output current depending on said input voltage to said light-emitting device,   said light-emitting device emits light at a luminance level depending on said video signal in response to said output current supplied from said drive transistor,   said pixel circuit corrects the input voltage sampled in said pixel capacitance,   wherein the output current from said drive transistor is extracted into said pixel capacitance, and   an additional capacitance added to said pixel capacitance, a portion of said output current from the drive transistor flowing into said additional capacitance.   
     
     
       27. The display apparatus according to claim 26, further including correcting means for correcting the input voltage sampled in said pixel capacitance in order to cancel out the dependency of said output current on the carrier mobility. 
     
     
       28. The display apparatus according to claim 27, wherein each of said pixels has either one of a red light-emitting device, a green light-emitting device, or a blue light-emitting device, and the additional capacitances in the respective pixels have different capacitance values for the respective light-emitting devices thereby making times requisite to operate the correcting means in the respective pixels uniform. 
     
     
       29. The display apparatus according to claim 28, wherein a shortage of the capacitance value of the additional capacitance in one of said pixels is made up for by a portion of the additional capacitance in an adjacent one of said pixels. 
     
     
       30. The display apparatus according to claim 27, wherein said correcting means extracts the output current from said drive transistor and supplies the extract output current to said pixel capacitance through a negative feedback loop to correct said input voltage while the video signal is being sampled in said pixel capacitance. 
     
     
       31. The display apparatus according to claim 26, wherein said sampling transistor and said drive transistor comprise thin-film transistors formed on an insulating substrate, and said pixel capacitance and said additional capacitance include thin-film capacitors formed on said insulating substrate. 
     
     
       32. The display apparatus according to claim 31, wherein the output current of said drive transistor has dependency on a threshold voltage as well as the carrier mobility in the carrier region, and said correcting means detects a threshold voltage of said drive transistor and adds the detected threshold voltage to said input voltage in advance in order to cancel out the dependency of the output current on the threshold voltage. 
     
     
       33. A display apparatus comprising:
 a pixel array having a matrix of pixels each positioned at a point of intersection between a row scanning line for supplying a control signal and a column signal line for supplying a video signal; a signal unit for supplying a video signal to said signal line; and a scanner unit for supplying a control signal to said row scanning line to successively scan rows of the pixels; each of said pixels including at least   a sampling transistor,   a pixel capacitance,   a drive transistor,   a light-emitting device,   wherein said sampling transistor is turned on in response to the control signal supplied from said row scanning line to sample the video signal supplied from said signal line into said pixel capacitance,   said pixel capacitance applies an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor supplies an output current depending on said input voltage to said light-emitting device,   said light-emitting device emits light at a luminance level depending on said video signal in response to said output current supplied from said drive transistor,   said pixel circuit corrects the input voltage sampled in said pixel capacitance,   wherein the output current from said drive transistor is extracted into said pixel capacitance, and   an additional capacitance added to said pixel capacitance,   wherein said light-emitting device comprises an anode connected to a source of said drive transistor and a cathode connected to ground, and said additional capacitance has a terminal connected to the anode of said light-emitting device and another terminal connected to a predetermined fixed potential.   
     
     
       34. The display apparatus according to claim 33, wherein said predetermined fixed potential to which another terminal of said additional capacitance is connected is selected from a ground potential on the cathode of said light-emitting device, and a positive power supply potential and a negative power supply potential of the pixel circuit. 
     
     
       35. A pixel circuit comprising:
 a sampling transistor;   a pixel capacitance;   a drive transistor; and   a light-emitting device;   wherein said sampling transistor is turned on in response to a control signal to sample a video signal into said pixel capacitance,   said pixel capacitance is configured to apply an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor is configured to supply an output current depending on said input voltage to said light-emitting device, and   said drive transistor is configured to supply a compensation current into said pixel capacitance and an additional capacitance before supplying the output current into said light-emitting device.   
     
     
       36. A display apparatus comprising: a pixel array having a matrix of pixels, each of said pixels including
 a sampling transistor,   a pixel capacitance,   a drive transistor, and   a light-emitting device,   wherein said sampling transistor is turned on in response to a control signal to sample a video signal into said pixel capacitance,   said pixel capacitance is configured to apply an input voltage to a gate of said drive transistor depending on the sampled video signal,   said drive transistor is configured to supply an output current depending on said input voltage to said light-emitting device, and   said drive transistor is configured to supply a feedback current into said pixel capacitance and an additional capacitance before supplying the output current into said light-emitting device.   
     
     
       37. The display apparatus according to claim 36, further comprising a vertical scanner and a horizontal selector. 
     
     
       38. The display apparatus according to claim 37, wherein said vertical scanner and said pixel array are formed on a glass substrate. 
     
     
       39. The display apparatus according to claim 37, wherein said vertical scanner is connected to a glass substrate by a flexible cable. 
     
     
       40. The display apparatus according to claim 36, wherein a period of supplying said feedback current into said pixel capacitance and additional capacitance is longer than 2.5 μs. 
     
     
       41. The display apparatus according to claim 36, wherein said sampling transistor is connected to said pixel capacitance directly. 
     
     
       42. The display apparatus according to claim 36, wherein each of said pixels has either one of a red light-emitting device, a green light-emitting device, or a blue light-emitting device, and thicknesses of each of light-emitting device are different.