Display apparatus

• US 7,221,339 B2
• Filed: 10/10/2002
• Issued: 05/22/2007
• Est. Priority Date: 02/17/1997
• Status: Expired due to Fees

• Current Assignee: Intellectual Keystone Technology LLC
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kimura, Mutsumi, Ozawa, Tokuroh
• Primary Examiner(s): Hjerpe; Richard
• Assistant Examiner(s): LESPERANCE, JEAN E
• Application Number:
  US10/267,834
• Publication Number:
  US 20030098827A1
• Time in Patent Office: 1,685 Days
• Field of Search: 345/92, 345/93, 345/97, 345/98, 345/204, 345/206, 345/210, 345/211
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0408 Integration of the drivers onto the display substrate
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0439 Pixel structures
• 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 2300/08 Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
• 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 2300/0847 being a dynamic memory without any storage capacitor, i.e. with use of parasitic capacitances as storage elements
• CPC Class Codes: G09G 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• 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 2310/0283 Arrangement of drivers for different directions of scanning
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3266 : Details of drivers for scan electrodes
• CPC Class Codes: H10K 2102/3026 : Top emission
• CPC Class Codes: H10K 50/81 : Anodes
• CPC Class Codes: H10K 50/828 : Transparent cathodes, e.g. comprising thin metal layers
• CPC Class Codes: H10K 50/86 : Arrangements for improving contrast, e.g. preventing reflection of ambient light
• CPC Class Codes: H10K 50/865 : comprising light absorbing layers, e.g. light-blocking layers
• CPC Class Codes: H10K 59/12 : Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/1213 : the pixel elements being TFTs
• CPC Class Codes: H10K 59/122 : Pixel-defining structures or layers, e.g. banks
• CPC Class Codes: H10K 59/131 : Interconnections, e.g. wiring lines or terminals
• CPC Class Codes: H10K 71/135 : using ink-jet printing

Abstract

A display apparatus, that includes current driving type luminescent elements, has a driving system that takes the conduction types of TFTs to control the emission of the luminescent elements into consideration. In order to reduce driving voltage and improve display quality simultaneously, the arrangement is provided such that if the second TFT which performs the “on-off” function of the current for the luminescent element is of an N channel type, the potential of the common power supply line (“com”) is lowered below the potential of the opposite electrode (“op”) of the luminescent element to obtain a higher gate voltage (“Vgcur”). In this case, if the first TFT connected to the gate of the second TFT is of a P channel type, when using the potential of the potential-holding electrode (“st”) at the “on” state as a reference, potentials of the scanning signal (“Sgate”) at the lower potential and the common power supply line (“com”) are rendered of the same polarities with respect to this potential of the potential-holding electrode (“st”). Therefore, the potential of the image signal (“data”) to turn “on” can be shifted within the range of the driving voltage in the display apparatus in the direction to reduce resistances at the “on” states of the first TFT and the second TFT to reduce driving voltage and improve display quality.

Claims

1. An electroluminescent apparatus comprising:

a plurality of scanning line;

a plurality of data lines intersecting said plurality of scanning lines;

a plurality of common power supply lines; and

a plurality of pixels,

each pixel of the plurality of pixels comprising;

a first transistor having a first gate electrode that is connected to one of the plurality of scanning lines;

a holding capacitor holds a signal supplied through one of the plurality of data lines and the first transistor;

a second transistor having a second gate electrode connected to the holding capacitor, the second transistor being of N channel type; and

a luminescent element provided between a pixel electrode of the each pixel and an opposite electrode opposed to the pixel electrode, the luminescent element being disposed in series with the second transistor, and the luminescent element emitting light due to direct current that flows between the pixel electrode and the opposite electrode when the pixel electrode is electrically connected to one common power supply line of the plurality of common power supply lines through the second transistor,

a potential of the one common power supply line being set at a lower level than a potential of the opposite electrode when the luminescent element emits light, and

a potential of the pixel electrode is always lower than the potential of the opposite electrode whether the luminescent element emits light or not.

2. The electroluminescent apparatus as claimed in claim 1,

a potential oft signal supplied through said one of the plurality of data lines and the first transistor to said pixel to be put in an “

on”

state being lower than or equal to the potential of said opposite electrode.

3. The electroluminescent apparatus as claimed in claim 1,

a potential of the signal supplied through said one of the plurality of data lines and the first transistor to said pixel to be put in an “

off”

state being higher than or equal to the potential of said one common power supply line.

4. The electroluminescent apparatus as claimed in claim 1,

the first transistor being of a P channel type.

5. The electroluminescent apparatus according to claim 1,

one of multiple electrodes of said holding capacitor, opposite to an electrode that is electrically connected to said second gate electrode of said second transistor, being supplied with a pulse, and

a potential polarity of the pulse being opposite to a selecting pulse supplied through said one scanning line.

6. The electroluminescent apparatus according to claim 1,

the luminescent element including emitting film formed of an organic semiconductor film.

7. The electroluminescent apparatus according to claim 1,

the second transistor being formed so as to operate in a saturated region.

8. The electroluminescent apparatus according to claim 1,

the second transistor being formed so as to operate in a linear region.

9. A electroluminescent apparatus comprising:

a plurality of scanning line;

a plurality of data lines intersecting said plurality of scanning lines;

a plurality of common power supply lines; and

a plurality of pixels,

each pixel of the plurality of pixels comprising;

a first transistor having a first gate electrode that is connected to one of the plurality of scanning lines;

a holding capacitor holds a signal supplied through one of the plurality of data lines and the first transistor;

a second transistor having a second gate electrode connected to the holding capacitor, the second transistor being of N channel type; and

a luminescent element provided between a pixel electrode of the each pixel and an opposite electrode opposed to the pixel electrode, the luminescent element being disposed between the opposite electrode and the second transistor, and the luminescent element being able to emit a light due to driving current that flows between the pixel electrode and the opposite electrode when the pixel electrode is electrically connected to one common power supply line of the plurality of common power supply lines through the second transistor,

a potential of the one common power supply line being set at a lower level than a potential of the opposite electrode when the luminescent element emits light, and

a potential of the pixel electrode is always lower than the potential of the opposite electrode whether the luminescent element emits light or not.

10. A electroluminescent apparatus comprising:

a plurality of scanning line;

a plurality of data line intersecting said plurality of scanning lines;

a plurality of common power supply lines; and

a plurality of pixels;

each pixel of the plurality of pixels comprising;

a first transistor having a first gate electrode that is connected to one of the plurality of scanning lines;

holding capacitor holds a signal supplied through one of the plurality of data lines and the first transistor;

second transistor having a second gate electrode connected to the holding capacitor, the second transistor being of an N channel type; and

a luminescent element provided between a pixel electrode of the each pixel and an opposite electrode opposed to the pixel electrode, the luminescent element being able to emit a light due to driving current that flows between the pixel electrode and the opposite electrode when the pixel electrode is electrically connected to one common power supply line of the plurality of common power supply lines,

a potential of the one common supply line being set at a lower level than a potential of the opposite electrode when the luminescent element emits light, and

a potential of the pixel electrode is always lower than the potential of the opposite electrode whether the luminescent element emits light or not.

11. The electroluminescent apparatus according to claim 10,

the first transistor being of a P channel type.