Pixel current driver for organic light emitting diode displays
A pixel current driver comprises a plurality of thin film transistors (TFTs) each having dual gates and for driving OLED layers. A top gate of the dual gates is formed between a source and a drain of each of the thin film transistors, to thereby minimize parasitic capacitance. The top gate is grounded or electrically tied to a bottom gate. The plurality of thin film transistors may be two thin film transistors formed in voltage-programmed manner or five thin film transistors formed in a current-programmed ΔV T -compensated manner. Other versions of the current-programmed circuit with different numbers of thin film transistors are also presented that compensate for δV T . The OLED layer are continuous and vertically stacked on the plurality of thin film transistors to provide an aperture ratio close to 100%.
1. A pixel current driver for an organic light emitting diode (OLED) having an OLED layer for emitting light, comprising:
an address line;
a data line; and
a plurality of thin film transistors (TFTs) forming a current mirror, each having dual gates and driving for the OLED layer, the plurality of thin film transistors comprising:
a switch thin film transistor, a first node of the switch transistor being connected to the data line and a first gate of the dual gates of the switch transistor being connected to the address line;
a feedback thin film transistor, a first node of the feedback transistor being connected to the data line and a first gate of the dual gates of the feedback transistor being connected to the address line;
a reference thin film transistor, a drain of the reference transistor being connected to a second node of the feedback transistor, a first gate of the dual gates of the reference transistor being connected to a second node of the switch transistor and a source of the reference transistor being connected to a ground potential; and
a drive thin film transistor, a first gate of the dual gates of the drive transistor being connected to the gate of the reference transistor,
a second gate of the dual gates of each thin film transistor being formed between a back electrode of the organic light emitting diode and the first gate of the respective thin film transistor.
2. The pixel current driver according to claim 1 wherein the thin film transistors are amorphous silicon.
3. The pixel current driver according to claim 1 wherein the thin film transistors are polycrystalline silicon.
4. The pixel current driver according to claim 3 , wherein each of the transistors is a p-channel thin film transistor.
5. The pixel current driver according to claim 1 , wherein the dual gates are fabricated in a normal inverted staggered TFT structure.
6. The pixel current driver according to claim 1 , wherein the second gate of the thin film transistor is grounded.
7. The pixel current driver according to claim 1 , wherein the second gate of the thin film transistor is electrically tied to the first gate of the thin film transistor.