Pixel driver circuit with load-balance in current mirror circuit
A pixel circuit for use in a display comprising a plurality of pixels is provided. The load-balanced current mirror pixel circuit can compensate for device degradation and/or mismatch, and changing environmental factors like temperature and mechanical strain. The pixel circuit comprises a pixel drive circuit comprising, switching circuitry, a current mirror having a reference transistor and a drive transistor, the reference transistor and the drive transistor each having a first and second node and a gate, the gate of the reference transistor being connected to the gate of the drive transistor; and a capacitor connected between the gate of the reference transistor and a ground potential, and a load connected between the current mirror and a ground potential, the load having a first load element and a second load element, the first load element being connected to the first node of the reference transistor and the second load element being connected to the first node of the drive transistor.
1. A pixel driver circuit for use in a display, comprising:
a light emitting device (LED) comprising a first terminal connected to a source of a first potential and at least one second terminal;
a current mirror configured to provide a drive current to the LED based on a reference current; and,
a switching circuit configured to convey the reference current to the current mirror;
wherein the current mirror comprises:
a reference transistor comprising a source terminal, a gate terminal connected to the switching circuit, and a drain terminal connected to the switching circuit,
a drive transistor comprising a gate terminal connected to the gate terminal of the reference transistor, a source terminal, and a drain terminal, the drive transistor configured to convey the drive current to the LED;
wherein one of the drain terminal and the source terminal of the reference transistor and a corresponding one of the drain terminal and the source terminal of the drive transistor are connected to the at least one second terminal of the LED; and
a capacitor connected to the gate terminal of the reference transistor for accumulating a program voltage while the reference current is conveyed to the reference transistor.
2. The pixel driver circuit of claim 1 , wherein the switching circuit comprises:
a switch transistor comprising a gate terminal connected to a first select line, a first terminal connected to a data line, and a second terminal; and
a feedback transistor comprising a gate terminal connected to the first select line or a second select line, a first terminal connected to one of the first terminal or the second terminal of the switch transistor, and a second terminal;
wherein one of the second terminal of the switch transistor and the second terminal of the feedback transistor is connected to the gate terminal of the reference transistor, and the other of the second terminals of the switch transistor and the feedback transistor is connected to the drain terminal of the reference transistor.
3. The pixel driver circuit of claim 1 , wherein the source terminal of the reference transistor and the source terminal of the drive transistor are connected to a common node, and wherein the at least one second terminal of the LED is connected to said common node.
4. The pixel driver circuit of claim 1 , wherein the at least one second terminal of the LED comprises two LED terminals connected to the source terminal of the reference transistor and the source terminal of the drive transistor, respectively.
5. The pixel driver circuit of claim 4 , wherein the LED comprises a light emitting diode having a bottom electrode partitioned to form the two LED terminals.
6. The pixel driver circuit of claim 4 , wherein the LED comprises a first light emitting diode connected between the source terminal of the reference transistor and the source of the first potential, and a second light emitting diode connected between the source terminal of the drive transistor and the source of the first potential.
7. The pixel driver circuit of claim 1 , wherein the at least one second terminal of the LED comprises two LED terminals connected to the drain terminal of the reference transistor and the drain terminal of the drive transistor, respectively.
8. The pixel driver circuit of claim 4 , wherein the LED comprises a light emitting diode having a bottom electrode partitioned to form the two LED terminals.
9. The pixel driver circuit of claim 7 , wherein the LED comprises a first light emitting diode connected between the drain terminal of the reference transistor and the source of the first potential, and a second light emitting diode connected between the drain terminal of the drive transistors and the source of the first potential.
10. The pixel driver circuit of claim 7 , wherein the LED comprises a first light emitting diode connected between the drain terminal of the reference transistor and a source of a second potential, and a second light emitting diode connected between the drain terminal of the drive transistors and the source of the first potential.
11. The pixel driving circuit of claim 7 , wherein the first potential is a biasing potential that is sufficient to operate the drive transistor in a saturation regime.
12. The pixel driving circuit of claim 11 , wherein the source terminal of the drive transistor and the source terminal of the reference transistor are connected to a source of a ground potential.
13. The pixel driving circuit of claim 3 , wherein the first potential is a ground potential and wherein the drain terminal of the drive transistor is connected to a source of supply voltage that is sufficient to operate the drive transistor in a saturation regime.
14. The pixel driving circuit of claim 4 , wherein the first potential is a ground potential and wherein the drain terminal of the drive transistor is connected to a source of supply voltage that is sufficient to operate the drive transistor in a saturation regime.
15. The pixel driver circuit according to claim 1 , wherein the reference and drive transistors are thin film transistors.
16. The pixel driver circuit according to claim 15 , wherein the thin film transistors are formed using amorphous silicon or polycrystalline silicon or an organic material.
17. The pixel driver circuit according to claim 15 , wherein the reference and drive transistors are p-type.
18. The pixel driver circuit according to claim 15 , wherein the reference and drive transistors are n-type.
19. The pixel driver circuit according to claim 1 , incorporated in an active matrix organic light emitting display (AMOLED).