Active matrix type display apparatus and drive circuit thereof

• US 6,501,466 B1
• Filed: 11/13/2000
• Issued: 12/31/2002
• Est. Priority Date: 11/18/1999
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Yumoto, Akira, Yamagishi, Machio
• Primary Examiner(s): Shankar, Vijay
• Assistant Examiner(s): Said, Mansour M.
• Application Number:
  US09/709,533
• Time in Patent Office: 778 Days
• Field of Search: 345/42, 345/55, 345/87, 345/90, 345/92, 345/93, 345/95, 345/99, 345/100, 345/204, 345/206, 345/214, 345/82-83, 349/42-43, 349/151
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror

Abstract

Each of picture elements comprises an input transistor for accepting a signal current from a data line when a scanning line is selected, a conversion transistor for converting the signal current into a voltage and for holding thus converted voltage, and a drive transistor for driving a light emitting device with drive current corresponding to the converted voltage. The conversion transistor flows the signal current to its channel to generate the voltage corresponding to the converted voltage and a capacitor to restrain the generated voltage. Further the drive transistor flows the drive current corresponding to the voltage stored in the capacitor. In this case the threshold voltage of the drive transistor is set not to be smaller than the threshold voltage of the conversion transistor, and thereby a leakage current flowing through the light emitting device is suppressed.

Claims

1. An active matrix type display apparatus comprising:

a scanning line drive circuit for sequentially selecting scanning lines;

a data line drive circuit containing a current source for generating signal current having current level corresponding to an intensity information and for sequentially supplying thus generated signal current to “

data lines”

; and

a plurality of picture elements provided at each cross point of said “

data line” and

said scanning line and each of the picture elements having a current drive type light emitting device which emits light in response to drive current, wherein

each of said picture element comprises;

an accept section for accepting said signal current from the corresponding data line when a corresponding scanning line is selected;

a converting section for converting a current level of thus accepted signal current once into corresponding voltage and restoring the converted voltage; and

a drive section for supplying the drive current having a current level corresponding to the restored voltage to the corresponding light emitting device, said converting section includes;

a conversion thin film transistor having a gate electrode, a source electrode, a drain electrode and a channel; and

a capacitor connected to said gate electrode of the conversion thin film transistor, wherein said conversion thin film transistor generates at the gate electrode the voltage converted by flowing through said channel the signal current taken through said accept section and said capacitor holds the voltage generated at the gate electrode, said drive section contains;

a drive thin film insulated gate type field effect transistor including a gate electrode, a drain electrode, a source electrode and a channel, wherein said drive thin film insulated gate type field effect transistor supplies the drive current through the channel to the light emitting device and the drive current has the current level corresponding to the voltage restored in said capacitor and accepted at the gate electrode of the drive thin film insulated gate type field effect transistor, and

a threshold voltage of said drive thin film insulated gate type field effect transistor is set not to become lower than a threshold voltage of said conversion thin film insulated gate type field effect transistor corresponding to the picture element.

2. The active matrix type display apparatus as claimed in claim 1, wherein

a gate length of said drive thin film insulated gate type field effect transistor is set not to be shorter than a gate length of said conversion thin film insulated gate type field effect transistor within one picture element.

3. The active matrix type display apparatus as claimed in claim 1, wherein

a thickness of a gate insulator of said drive thin film insulated gate type field effect transistor is set not to be thinner than a thickness of a gate insulator of said conversion thin film insulated gate type field effect transistor within one picture element.

4. The active matrix type display apparatus as claimed in claim 1, wherein

a threshold voltage of said drive thin film transistor is set not to be lower than a threshold voltage of said conversion thin film insulated gate type field effect transistor within one picture element by adjusting impurity density injected in said channel of the drive thin film insulated gate type field effect transistor.

5. The active matrix type display apparatus as claimed in claim 1, wherein

said drive thin film insulated gate type field effect transistor works in a saturation range and supplies the drive current corresponding to the difference between the threshold voltage and the voltage given to the gate electrode into the light emitting device.

6. The active matrix type display apparatus as claimed in claim 1, wherein

a current mirror circuit is constituted by directly connecting the gate electrode of said drive thin film insulated gate type field effect transistor to the gate electrode of the conversion thin film insulated gate type field effect transistor, so that the current level of the signal current and the current level of the drive current are made to be a proportional relation.

7. The active matrix type display apparatus as claimed in claim 1, wherein

said accept section includes a switch thin film insulated gate type field effect transistor interposed between the drain electrode and the gate electrode of the conversion thin film insulated gate type field effect transistor,

said switch thin film insulated gate type field effect transistor is made ON when the current level of the signal current is converted into the voltage and then generates at the gate electrode of the conversion thin film insulated gate type field effect transistor said voltage referenced with the source electrode by electrically connecting the gate electrode and the drain electrode of the conversion insulated gate type field effect thin film transistor, and

said switch thin film insulated gate type field effect transistor is made OFF to disconnect the gate electrode of the conversion thin film insulated gate type field effect transistor and the capacitor when restoring the voltage to said capacitor.

8. The active matrix type display apparatus as claimed in claim 1, wherein

said light emitting device is an organic electro-luminescence device.

9. The active matrix type display apparatus as claimed in claim 1, wherein

said source, drain and channel of both said drive thin film insulated gate type field effect transistor and said conversion thin film insulated gate type field effect transistor are formed with poly-crystal semiconductor thin films.

10. A picture element drive circuit to be provided at each cross point of a data line for supplying a signal current having current level corresponding to an intensity information and a scanning line for supplying a selecting pulse and for driving a current drive type light emitting device which emits light by a drive current, comprising:

an accept section for accepting said signal current from the corresponding data line in response to said selecting pulse from said scanning line;

a converting section for converting thus accepted signal current once into corresponding voltage and restoring thus converted voltage; and

a drive section for supplying the drive current having current level corresponding to the restored voltage to the corresponding light emitting device, and

said converting section includes;

a conversion thin film transistor having a gate electrode, a source electrode, a drain electrode and a channel; and

a capacitor connected to said gate electrode of the conversion thin film transistor, wherein the conversion thin film transistor generates at the gate electrode the voltage converted by flowing through said channel the signal current taken through said accept section and said capacitor holds the voltage generated at the gate electrode of the conversion thin film transistor,

said drive section contains;

a drive thin film insulated gate type field effect transistor including a gate electrode, a drain electrode, a source electrode and a channel and the drive thin film insulated gate type field effect transistor, wherein the drive thin film insulated gate type field effect transistor supplies the drive current through the channel to the light emitting device and the drive current has the current level corresponding to the voltage restored in the capacitor and accepted at the gate electrode of the drive thin film insulated gate type field effect transistor, and

a threshold voltage of said drive thin film insulated gate type field effect transistor is set not to become lower than a threshold voltage of said conversion thin film insulated gate type field effect transistor corresponding to the picture element.

11. The picture element drive circuit as claimed in claim 10, wherein

a gate length of said drive thin film insulated gate type field effect transistor is set not to be shorter than a gate length of said conversion thin film insulated gate type field effect transistor within one picture element.

12. The picture element drive circuit as claimed in claim 10, wherein

a thickness of a gate insulator of said drive thin film insulated gate type field effect transistor is set not to be thinner than a thickness of a gate insulator of said conversion thin film insulated gate type field effect transistor within one picture element.

13. The picture element drive circuit as claimed in claim 10, wherein

a threshold voltage of said drive thin film transistor is set not to be lower than a threshold voltage of said conversion thin film insulated gate type field effect transistor within one picture element by adjusting impurity density injected in said channel of the drive thin film insulated gate type field effect transistor.

14. The picture element drive circuit as claimed in claim 10, wherein said drive thin film insulated gate type field effect transistor works in saturation range and supplies the drive current corresponding to the difference between the threshold voltage and the voltage given to the gate electrode into the light emitting device.

15. The picture element drive circuit as claimed in claim 10, wherein a current mirror circuit is constituted by directly connecting the gate electrode of said drive thin film insulated gate type field effect transistor to the gate electrode of the conversion thin film insulated gate type field effect transistor, so that the current level of the signal current and the current level of the drive current are made to be a proportional relation.

16. The picture element drive circuit as claimed in claim 10, wherein said accept section includes a switch thin film insulated gate type field effect transistor interposed between the drain electrode and the gate electrode of the conversion thin film insulated gate type field effect transistor,

said switch thin film insulated gate type field effect transistor is made ON when the current level of the signal current is converted into the voltage and generates at the gate electrode of the conversion thin film insulated gate type field effect transistor said voltage referenced with the source electrode by electrically connecting the gate electrode and the drain electrode of the conversion insulated gate type field effect thin film transistor, and

said switch thin film insulated gate type field effect transistor is made OFF to disconnect the gate electrode of the conversion thin film insulated gate type field effect transistor and the capacitor when restoring the voltage to said capacitor.

17. The picture element drive circuit as claimed in claim 10, wherein

said light emitting device is an organic electro-luminescence device.

18. The picture element drive circuit as claimed in claim 10, wherein said source, drain and channel of both said drive thin film insulated gate type field effect transistor and said conversion thin film insulated gate type field effect transistor are formed with poly-crystal semiconductor thin films.

19. A method for driving picture element to be provided at each cross point of a data line for supplying a signal current having a current level corresponding to an intensity information and a scanning line for supplying a selecting pulse and for driving a current drive type light emitting device which emits light by a drive current, comprising the steps of:

step for accepting said signal current from the corresponding data line in response to said selecting pulse from corresponding scanning line;

step for converting thus accepted signal current once into corresponding voltage and restoring the voltage; and

step for driving by supplying the drive current having the current level corresponding to the restored voltage to the corresponding light emitting device, and

said converting step includes;

step for using a conversion thin film transistor having a gate electrode, a source electrode, a drain electrode and a channel; and

a capacitor connected to said gate electrode of the conversion thin film transistor, wherein the conversion thin film transistor generates at the gate electrode the voltage converted by flowing through said channel the signal current taken through said accepting step and said capacitor holds the voltage generated at the gate electrode, said driving step includes;

step for using a drive thin film insulated gate type field effect transistor having a gate electrode, a drain electrode, a source electrode and a channel, wherein said the drive thin film insulated gate type field effect transistor supplies the drive current through the channel to the light emitting device, wherein the drive current has the current level corresponding to the voltage stored in the capacitor and accepted at the gate electrode of the drive thin film insulated gate type field effect transistor, and

a threshold voltage of said drive thin film insulated gate type field effect transistor is set not to become lower than a threshold voltage of said conversion thin film insulated gate type field effect transistor corresponding to the picture element.

20. The method for driving a picture element as claimed in claim 19, wherein

a gate length of said drive thin film insulated gate type field effect transistor is set not to be shorter than a gate length of said conversion thin film insulated gate type field effect transistor within one picture element.

21. The method for driving a picture element as claimed in claim 19, wherein

a thickness of a gate insulator of said drive thin film insulated gate type field effect transistor is set not to be thinner than thickness of a gate insulator of said conversion thin film insulated gate type field effect transistor within one picture element.

22. The method for driving a picture element as claimed in claim 19, wherein

a threshold voltage of said drive thin film transistor is set not to be lower than a threshold voltage of said conversion thin film insulated gate type field effect transistor within one picture element by adjusting impurity density injected in said channel of the drive thin film insulated gate type field effect transistor.

23. The method for driving picture element as claimed in claim 19, wherein

said drive thin film insulated gate type field effect transistor works in saturation range and supplies the drive current corresponding to the difference between the threshold voltage and the voltage given to the gate electrode into the light emitting device.

24. The method for driving picture element as claimed in claim 19, wherein

a current mirror circuit is constituted by directly connecting the gate electrode of said drive thin film insulated gate type field effect transistor to the gate electrode of the conversion thin film insulated gate type field effect transistor, so that the current level of the signal current and the current level of the drive current are made to be a proportional relation.

25. The method for driving picture element as claimed in claim 19, wherein

said accepting step includes

a step for using a switch thin film insulated gate type field effect transistor interposed between the drain electrode and the gate electrode of the conversion thin film insulated gate type field effect transistor, wherein said switch thin film insulated gate type field effect transistor is made ON when the current level of the signal current is converted into the voltage and then generates at the gate electrode of the conversion thin film insulated gate type field effect transistor said voltage referenced with the source electrode by electrically connecting the gate electrode and the drain

electrode of the conversion insulated gate type field effect thin film transistor, and

said switch thin film insulated gate type field effect transistor is made OFF to disconnect the gate electrode of the conversion thin film insulated gate type field effect transistor and the capacitor when restoring the voltage to said capacitor.

26. The method for driving a picture element as claimed in claim 19, wherein

said light emitting device is an organic electro-luminescence device.

27. The method for driving a picture element as claimed in claim 19, wherein

said source, drain and channel of both said drive thin film insulated gate type field effect transistor and said conversion thin film insulated gate type field effect transistor are formed with poly-crystal semiconductor thin films.

28. An active matrix type display apparatus comprising:

a scanning line drive circuit for sequentially selecting scanning lines;

a data line drive circuit for sequentially supplying signal current corresponding to an intensity information to data lines; and

a plurality of picture elements provided at each cross point of said “

data line” and

said scanning lines and each of the picture elements having a current drive type light emitting device which emits light in response to drive current corresponding to said signal current, wherein

each of said picture element comprises;

an input thin film transistor connected to said data line;

a conversion thin film transistor connected to said input thin film transistor for converting said signal current on said data line to corresponding voltage;

a switch thin film transistor connected between a gate electrode and a source electrode of said conversion thin film transistor;

a capacitor connected to said gate electrode of said conversion thin film transistor for restoring said corresponding voltage; and

a drive thin film transistor connected to said light emitting device and to aid capacitor, wherein

a threshold voltage of said drive thin film transistor is set not to become lower than a threshold voltage of said conversion thin film transistor within one the picture element.