Image display apparatus without occurence of nonuniform display
View Patent ↗A pixel drive circuit includes a drain voltage increase limiter circuit composed of a TFT device provided between a node and the drain of a TFT device serving as a current source, a capacitor and a switch. In a data write mode, switches are turned on to allow drive current to flow from a data line to the TFT devices. Then, respective gate voltages of the TFT devices are held in respective capacitors. In a display mode, only a switch is turned on to form a current path from a supply voltage to the TFT devices through a light-emitting diode. The voltage on a node is held constant regardless of channel modulation. Accordingly, desired electric current flows through the light-emitting diode.
1. An image display apparatus comprising:
a plurality of pixel circuits arranged in rows and columns and each having a current-driven light-emitting device;
a plurality of scan lines arranged correspondingly to respective rows of said plurality of pixel circuits and successively selected in constant cycles;
a plurality of data lines arranged correspondingly to respective columns of said plurality of pixel circuits; and
a constant current circuit provided correspondingly to said plurality of data lines and supplying, to said plurality of data lines each, drive current that is set according to a display brightness of a pixel circuit to be scanned among said plurality of pixel circuits, wherein
said plurality of pixel circuits each include:
a node electrically coupled to a corresponding data line in a first mode to allow said drive current to flow into/out of said node and electrically separated from said corresponding data line in a second mode performed subsequently to said first mode;
a pixel drive circuit connected between said node and a first voltage supply, writing said drive current flowing into/out of said node in said first mode and supplying, to said current-driven light-emitting device, current according to said written drive current in said second mode; and
said current-driven light-emitting device provided between said node and a second voltage supply and rendered conductive in said second mode to be supplied with said current according to said drive current, and
said pixel drive circuit includes:
first and second transistors connected in series between said node and said first voltage supply and, in said first mode, said drive current passes through said first and second transistors; and
first and second capacitor elements connected to respectively hold, on respective gate electrodes of said first and second transistors, voltages determined by said drive current in said first mode.
2. The image display apparatus according to claim 1 , wherein
said plurality of pixel circuits each further include:
a first switch element provided between said corresponding data line and said node, turned on in said first mode and turned off in said second mode;
second switch elements provided respectively between the gate electrode and a first electrode of said first transistor and between the gate electrode and said first electrode of said second transistor, turned on in said first mode and turned off in said second mode; and
a third switch element provided between said node and said current-driven light-emitting device, turned off in said first mode and turned on in said second mode.
3. The image display apparatus according to claim 2 , wherein
said first switch element includes a first transistor of a first conductivity type electrically coupled between said corresponding data line and said node and having a gate coupled to said scan line (a corresponding scan line among said scan lines),
said second switch elements include second transistors of the first conductivity type electrically coupled respectively between respective gates and drains of said first transistor and said second transistor and each having a gate coupled to said scan line,
said third switch element includes a transistor of a second conductivity type electrically coupled between said node and said current-driven light-emitting device and having a gate coupled to said scan line, and
said first mode is performed in a select period of said scan line and said second mode is performed in a non-select period of said scan line.
4. The image display apparatus according to claim 3 , wherein
said constant current circuit includes a plurality of constant current sources provided correspondingly to said plurality of data lines to supply said drive current to corresponding data lines.
5. The image display apparatus according to claim 4 , wherein
said first transistor has said first electrode connected to said node and a second electrode connected to said first electrode of said second transistor,
said second transistor has said second electrode connected to said first voltage supply, and
said second switch elements are set to allow, in said first mode, the gate electrode and said first electrode of said first transistor to be electrically separated earlier than at least the gate electrode and said first electrode of said second transistor.
6. The image display apparatus according to claim 1 , wherein
said plurality of pixel circuits each further include:
a first switch element provided between said corresponding data line and said node, turned on in said first mode and turned off in said second mode;
second switch elements provided respectively between the gate electrode and a first electrode of said first transistor and between the gate electrode and said first electrode of said second transistor, turned on in said first mode and turned off in said second mode;
a third voltage supply provided opposite to said second voltage supply; and
a third switch element provided between said second voltage supply, said third voltage supply and said current-driven light-emitting device, electrically connecting said current-driven light-emitting device and said third voltage supply in said first mode and electrically connecting said current-driven light-emitting device and said second voltage supply in said second mode, and
when said third voltage supply is coupled to said current-driven light-emitting device, a voltage of said third voltage supply allows, relative to a voltage of said node, said current-driven light-emitting device to be in a reverse-biased state.
7. The image display apparatus according to claim 1 , wherein
said plurality of pixel circuits each further include:
a first switch element provided between said corresponding data line and said node, turned on in said first mode and turned off in said second mode;
second switch elements provided respectively between the gate electrode and a first electrode of said first transistor and between the gate electrode and said first electrode of said second transistor, turned on in said first mode and turned off in said second mode; and
a third switch element provided between said second voltage supply and said current-driven light-emitting device, electrically separating said current-driven light-emitting device from said second voltage supply in said first mode and electrically coupling said current-driven light-emitting device and said second voltage supply in said second mode.
8. The image display apparatus according to claim 1 , wherein
said plurality of pixel circuits each further include:
a first switch element provided between said corresponding data line and said node, turned on in said first mode and turned off in said second mode;
second switch elements provided respectively between the gate electrode and a first electrode of said first transistor and between the gate electrode and said first electrode of said second transistor, turned on in said first mode and turned off in said second mode; and
pulse signal input means provided between said second voltage supply and said current-driven light-emitting device for applying, to said current-driven light-emitting device, a pulse signal having a voltage of a third voltage supply in said first mode and having a voltage of said second voltage supply in said second mode, and
the voltage of said third voltage supply allows, relative to a voltage of said node, said current-driven light-emitting device to be in a reverse-biased state.