Display apparatus

• US 6,522,315 B2
• Filed: 10/16/1998
• Issued: 02/18/2003
• Est. Priority Date: 02/17/1997
• Status: Expired due to Term

• Current Assignee: Intellectual Keystone Technology LLC (Samsung Electronics Co. Ltd.)
• 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:
  US09/171,224
• Publication Number:
  US 20020024493A1
• Time in Patent Office: 1,586 Days
• Field of Search: 345/204, 345/206, 345/210, 345/211, 345/92, 345/93, 345/97, 345/98
• US Class Current: 345/92
• 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 59/8051 : Anodes
• CPC Class Codes: H10K 59/80524 : Transparent cathodes, e.g. comprising thin metal layers
• 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 (1) 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. A display apparatus, comprising:

a substrate;

a plurality of scanning lines disposed on the substrate;

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

a plurality of common power supply lines; and

a plurality of pixels formed in a matrix by said scanning lines and said data lines, each of said pixels including;

a first thin film transistor having a first gate electrode which is supplied with a scanning signal through at least one scanning line of said plurality of scanning lines,

a holding capacitor which holds an image signal supplied through at least one data line of said plurality of data lines through said first thin film transistor,

a second thin film transistor having a second gate electrode which is supplied with said image signal held by said holding capacitor, and

a luminescent element provided between a pixel electrode corresponding to each of said pixels and an opposite electrode opposed to said pixel electrode, the luminescent element being disposed in series with the second thin film transistor, the luminescent element being able to emit light due to driving current which flows between said pixel electrode and said opposite electrode when said pixel electrode is electrically connected to at least one common power supply line of said plurality of common power supply lines through said second thin film transistor;

wherein said second thin film transistor is of a P channel type, and a potential of said at least one common power supply line is set at a higher level than a potential of said opposite electrode.

2. The display apparatus as claimed in claim 1, a potential of said image signal supplied through said at least one data line to said pixel to be put in an “

on”

state is higher than or equal to the potential of said opposite electrode.

3. The display apparatus as claimed in claim 1, a potential of said image signal supplied through said at least one data line to said pixel to be put in an “

off”

state is lower than or equal to the potential of said at least one common power supply line.

4. The display apparatus as claimed in claim 1, said first thin film transistor and said second thin film transistor being formed as thin film transistors which are of opposite conduction types.

5. The display apparatus as claimed in 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 thin film transistor, is supplied with a pulse, a potential polarity of the pulse being opposite to a selecting pulse of said scanning signal with a delay behind the selecting pulse.

6. The display apparatus as claimed in claim 1, the emitting thin film of the luminescent element being an organic semiconductor film.

7. The display apparatus as claimed in claim 1, said second thin film transistor being formed so as to operate in a saturated region.

8. The display apparatus as claimed in claim 1, said second thin film transistor being formed so as to operate in a linear region.

9. A display apparatus, comprising:

a substrate;

a plurality of scanning lines formed on the substrate;

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

a plurality of common power supply lines; and

a plurality of pixels formed by said scanning lines and said data lines in a matrix, each of said pixels including;

a first thin film transistor having a first gate electrode which is supplied with a scanning signal through at least one scanning line of said plurality of scanning lines,

a holding capacitor which holds an image signal supplied through at least one data line of said plurality of data lines via the first thin film transistor,

a second thin film transistor having a second gate electrode which is supplied with said image signal held by said holding capacitor, and

a luminescent element provided between a pixel electrode corresponding to each of said pixels and an opposite electrode opposed to said pixel electrode, the luminescent element being able to emit light due to driving current which flows between said pixel electrode and said opposite electrode when said pixel electrode is electrically connected to at least one common power supply line of said plurality of common power supply lines through said second thin film transistor, the luminescent element being disposed in series with the second thin film transistor;

wherein said first thin film transistor and said second thin film transistor are formed as thin film transistors which are of opposite conduction types.

10. The display apparatus as claimed in claim 9, a polarity of a gate voltage applied to said second thin film transistor that is in “

off”

state pixels is the same in polarity as the potential of said second thin film transistor which is “

on”

state, and also a value of said gate voltage does not exceed a threshold voltage of said second thin film transistor.

11. The display apparatus as claimed in claim 10,

said first thin film transistor is of an N channel type and said second thin film transistor is of a P channel type,

a potential of said scanning signal to put said first thin film transistor in the “ on”

state is the same as a potential of said at least one common power supply line, and

a potential of the gate electrode to be applied to said second thin film transistor of a pixel that is in the “

off”

state is lower than a potential which is obtained by subtracting a threshold voltage of said first thin film transistor from the potential of the scanning signal to put said first thin film transistor in the “

on”

state.

12. The display apparatus as claimed in claim 10,

said first thin film transistor is of a P channel type and said second thin film transistor is of an N channel type,

a potential of said scanning signal to put said first thin film transistor in the “

on”

state is the same as a potential of said at least one common power supply line, and

a potential of said gate electrode to be applied to said second thin film transistor of a pixel that is in the “

off”

state is higher than a potential which is obtained by adding a threshold voltage of said first thin film transistor to the potential of the scanning signal to put said first thin film transistor in the “

on”

state.

13. The display apparatus as claimed in claim 9, one of multiple electrodes of said holding capacitor, opposite to an electrode that is electrically connected to said second gate electrode of said second thin film transistor, is supplied with a pulse, a potential polarity of the pulse being opposite to a selecting pulse of said scanning signal with a delay behind the selecting pulse.

14. The display apparatus as claimed in claim 9, the emitting thin film of the luminescent element being an organic semiconductor film.

15. The display apparatus as claimed in claim 9, said second thin film transistor being formed so as to operate in a saturated region.

16. The display apparatus as claimed in claim 9, said second thin film transistor being formed so as to operate in a linear region.

17. A display apparatus, comprising:

a substrate;

a plurality of scanning lines disposed on the substrate;

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

a plurality of common power supply lines;

a plurality of pixels formed by said scanning lines and said data lines in a matrix, each of said pixels including;

a first thin film transistor having a first gate electrode which is supplied with a scanning signal through at least one scanning line of said plurality of scanning lines,

a holding capacitor which holds an image signal supplied through at least one data line of said plurality of data lines via said first thin film transistor,

a second thin film transistor having a second gate electrode which is supplied with said image signal held by said holding capacitor, and

a luminescent element provided between a pixel electrode corresponding to each of said pixels and an opposite electrode opposed to said pixel electrode, the luminescent element being able to emit light due to driving current which flows between said pixel electrode and said opposite electrode when said pixel electrode is electrically connected to at least one common power supply line of said plurality of common power supply lines through said second thin film transistor, the luminescent element being disposed in series with the second thin film transistor;

wherein one of multiple electrodes of said holding capacitor, opposite to an electrode that is electrically connected to said second gate electrode of said second thin film transistor, is supplied with a pulse, a potential polarity of the pulse being opposite to a selecting pulse of said scanning signal with a delay behind said selecting pulse.

18. The display apparatus as claimed in claim 17, the emitting thin film of the luminescent element being an organic semiconductor film.

19. The display apparatus as claimed in claim 17, said second thin film transistor being formed so as to operate in a saturated region.

20. The display apparatus as claimed in claim 17, said second thin film transistor being formed so as to operate in a linear region.

21. A display apparatus comprising:

a plurality of scanning lines;

a plurality of data 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 that 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 P channel type; and

a luminescent element provided between a pixel electrode of each pixel and an opposite electrode opposed to the pixel electrode, the luminescent element being disposed in series with the second transistor, the luminescent element being able to emit a light due to the 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 higher level than a potential of the opposite electrode.

22. A display apparatus comprising:

a plurality of scanning lines;

a plurality of data 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 that 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 P channel type; and

a luminescent element provided between a pixl 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 transitor, 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 higher level than a potential of the opposite electrode.

23. A display apparatus comprising:

a plurality of canning lines;

a plurality of data 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 that 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; 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 through the second transistor, the first transistor and the second transistor being of opposite conduction types each other.

24. A display apparatus comprising:

a plurality of scanning lines;

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

a second transistor having a second gate electrode connected to the holding capacitor; 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, the first transistor and the second transistor being of opposite conduction types each other.