Pixel circuit and display apparatus

• US 20070152920A1
• Filed: 09/26/2006
• Published: 07/05/2007
• Est. Priority Date: 10/07/2005
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Uchino, Katsuhide, Yamashita, Junichi
• Granted Patent: US 7,659,872 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

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 for 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, 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.

Claims

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, and the additional capacitances in the respective pixel circuits have different capacitance values for the respective light-emitting devices for thereby uniformizing times requisite to operate the correcting means in the respective pixel circuits.

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 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.

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, said additional capacitance having 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, and a blue light-emitting device, and the additional capacitances in the respective pixels have different capacitance values for the respective light-emitting devices for thereby uniformizing times requisite to operate the correcting means in the respective pixels.

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.