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:
switching circuitry for providing a reference current input, the switching circuitry including:
a switch transistor having a gate connected to a first select line, a first terminal connected to a data line, and
a feedback transistor having a gate connected to a second select line, a first terminal connected to a second terminal of the switch transistor;
a light emitting device having a first terminal and a second terminal, the second terminal being connected to a first potential; and
a current mirror for providing a drive current to the light emitting device based on the reference current, the current mirror including:
a drive transistor for conveying the drive current through the light emitting device and having a first node;
a reference transistor for receiving the reference current, the reference transistor having a gate connected to a gate of the drive transistor, the reference transistor having a drain terminal connected either to a second terminal of the feedback transistor or to a second terminal of the switch transistor, wherein the first terminal of the light emitting device is connected to the first node and to a source terminal of the reference transistor; and
a capacitor for storing a program voltage independent of a transistor threshold voltage, the program voltage settling on the capacitor while the reference current is conveyed through the reference transistor, the capacitor having a first terminal connected to both the gate of the drive transistor and the gate of the reference transistor, the capacitor having a second terminal connected to the first potential.
2. The pixel driver circuit according to claim 1 , wherein the drain terminal of the reference transistor is connected to the second terminal of the feedback and a source terminal of the reference transistor is connected to a first terminal of the light emitting device.
3. The pixel driver circuit according to claim 2 , wherein a second terminal of the light emitting device is connected to a ground potential.
4. The pixel driver circuit according to claim 1 , wherein the drain terminal of the reference transistor is connected to the second terminal of the switch transistor and a source terminal of the reference transistor is connected to a first terminal of the light emitting device.
5. The pixel driver circuit according to claim 4 , wherein a second terminal of the light emitting device is connected to a ground potential.
6. The pixel driver circuit according to claim 1 , wherein the light emitting device is a light emitting diode.
7. The pixel driver circuit according to claim 6 , wherein the first potential is a ground potential.
8. The pixel driver circuit according to claim 1 , wherein the first potential is a ground potential.
9. The pixel driver circuit according to claim 1 , wherein the reference and drive transistors are thin film transistors.
10. The pixel driver circuit according to claim 9 , wherein the thin film transistors are amorphous silicon or polycrystalline silicon or organic.
11. The pixel driver circuit according to claim 10 , wherein the reference and drive transistors are p-type.
12. The pixel driver circuit according to claim 1 , wherein a first terminal of the drive transistor is connected to a supply voltage, and a second terminal of the drive transistor is connected to the light emitting device.
13. The pixel driver circuit according to claim 1 , incorporated in an active matrix organic light emitting display (AMOLED).