Active matrix type display apparatus and drive circuit thereof

Claim 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 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 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.

Claim 4

An apparatus or a circuit according to any one of the preceding claims, 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.

Claim 5

An apparatus or a circuit according to any one of the preceding claims, 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.

Claim 6

An apparatus or a circuit according to any one of the preceding claims, 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.

Claim 7

An apparatus or a circuit according to any one of the preceding claims, 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.

Claim 8

An apparatus or a circuit according to any one of the preceding claims, 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.

Claim 9

An apparatus or a circuit according to any one of the preceding claims, wherein said light emitting device is an organic electro-luminescence device.

Claim 10

An apparatus or a circuit according to any one of the preceding claims, 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.

Claim 11

A method for driving picture element 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 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 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.

Claim 14

A method according to any one of claims 11 to 13, 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.

Claim 15

A method according to any one of claims 11 to 14, 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.

Claim 16

A method according to any one of claims 11 to 15, 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.

Claim 17

A method according to any one of claims 11 to 16, 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.

Claim 18

A method according to any one of claims 11 to 17, wherein said light emitting device is an organic electro-luminescence device.

Claim 19

A method according to any one of claims 11 to 18, 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.