Organic EL pixel circuit

• US 6,924,602 B2
• Filed: 02/12/2002
• Issued: 08/02/2005
• Est. Priority Date: 02/15/2001
• Status: Expired due to Term

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Komiya, Naoaki
• Primary Examiner(s): Lee, Wilson
• Application Number:
  US10/074,405
• Publication Number:
  US 20020158587A1
• Time in Patent Office: 1,267 Days
• Field of Search: 3151691-1694, 345/60, 345/65, 345 76- 80, 345/84
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with 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 2320/0257 Reduction of after-image effects
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

A discharge transistor (TFT3) which connects the upper end of an organic EL element (EL) and a negative power source (VEE) and a control transistor (TFT4) which connects the upper end of a storage capacitor (SC) with a power source (PVDD) are provided. These transistors (TFT3, TFT4) are turned on by the upper gate line, so that the capacitor of the organic EL element (EL) is discharged prior to the selection of the line for these transistors.

Claims

1. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, and

a driving transistor is provided between the organic EL element and a power source for controlling driving current to the organic EL element, and one end of the discharge transistor is connected between the driving transistor and the organic EL element;

and

the discharge transistor discharges charges that are accumulated on a node between the organic EL element and the driving transistor if the discharge transistor is turned on.

2. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, and

a drive transistor is provided between the organic EL element and a power source for controlling driving current to the organic EL element, and one end of the discharge transistor is connected between the driving transistor and the organic EL element, wherein

said organic EL pixels are arranged in a matrix and the pixels in a row direction are selected by a first gate line, and

said discharge transistor is driven by a second gate line which is selected at a timing prior to the selection of the first gate line at the row of the EL element to which said discharge translator is connected, to discharge the charges accumulated in the capacitor of the organic EL element.

3. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, wherein

said organic EL pixels are arranged in a matrix and the pixels in a row direction are selected by a same gate line,

said discharge transistor is driven by a dedicated discharge line which is activated at a timing prior to the selection of the gate line at the row of the EL element to which said discharge transistor is connected, to discharge the charges accumulated in the capacitor of the organic EL element, and

the discharge transistor discharges charges that are accumulated on a node between the organic EL element and a driving transistor if the discharge transistor is turned on.

4. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, and

a driving current to the organic EL element, and a power source for controlling driving current to the organic EL element, and one end of the discharge transistor is connected between the driving transistor and the organic EL element, wherein

said organic EL pixels are arranged in a matrix and each of the pixels emits light of a color which is predetermined for each pixel, and

a discharge transistor for a pixel which emits light of a color with a low emission efficiency is provided within a pixel which emits light of a color with a higher emission efficiency.

5. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, wherein

each of said pixels includes a storage capacitor for holding a control voltage to be applied to a drive transistor which controls application of a drive current to the organic EL element, and

each of said pixels further includes a control transistor for controlling the control voltage held in storage capacitor to turn the drive transistor off, and

the discharge transistor discharges charges that are accumulated on a node between the organic EL element and the driving transistor if the discharger transistor is turned on.

6. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, wherein

each of said pixels includes a storage capacitor for holding a control voltage to be applied to a drive transistor which controls application of a drive current to the organic EL element, and

each of said pixel further includes a control transistor for controlling the control voltage held in the storage capacitor to turn the drive transistor off, wherein

said control transistor is driven simultaneously with said discharge transistor to turn the drive transistor off at the time of driving said discharge transistor.

7. An organic EL pixel circuit for control application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, wherein

each of said pixels includes a storage capacitor for holding a control voltage to be applied to a drive transistor which controls application of a drive current to the organic EL element, and

each of said pixels further includes a control transistor for controlling the control voltage held in the storage capacitor to turn the drive transistor off, wherein

said control transistor is driven prior to said discharge transistor to turn the drive transistor off prior to driving of said discharge transistor.

8. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, wherein

each of said pixels includes a storage capacitor for holding a control voltage to be applied to a drive transistor which controls application of a drive current to the organic EL element, and

each of said pixels further includes a control transistor for controlling the control voltage held in the storage capacitor to turn the drive transistor off, wherein

said organic EL pixels are arranged in a matrix and each of the pixels emits light of a color which is predetermined for each pixel, and

a control transistor for a pixel which emits light of a color with a lower emission efficiency is provided within a pixel which emits light of a color with a higher emission efficiency.

9. An organic EL pixel circuit for controlling application of a drive voltage to a plurality of organic EL pixels, wherein a discharge transistor is provided for discharging charges accumulated in a capacitor of an organic EL element, and

a driving transistor is provided between the organic EL element and a power source for controlling driving current to the organic EL element, and one end of the discharge transistor is connected between the driving transistor and the organic EL element, further comprising a plurality of discharge transistors in the organic EL pixels located at rows selected by a first gate line are driven by a second gate line which is selected before the selection of the first gate line.

10. An organic EL pixel comprising:

an EL element;

a driving transistor for controlling driving current to be supplied to the EL element;

a selecting transistor for controlling the driving transistor,

a discharge transistor provided independently of the driving transistor and the selecting transistor for discharging charges accumulated in a parasitic capacitor of the EL element; and

the discharge transistor discharges charges that are accumulated on a node between the EL element and the driving transistor if the discharge transistor is turned on.

11. An organic EL pixel circuit according to claim 10, wherein

the discharge transistor is connected to a node connecting the driving transistor and the EL element.

12. An organic EL pixel circuit according to claim 11, wherein

the discharge transistor is turned on when the selecting transistor is turned off.