Voltage compensation type pixel circuit of active matrix organic light emitting diode display device
A voltage compensation type pixel circuit of an AMOLED display device includes a driving transistor serially connected to a light emitting element between high-potential and low-potential power lines to drive the light emitting element in response to a voltage supplied to a first node, a first program transistor for supplying a data voltage of a data line to a second node in response to a scan signal of a scan line, a second program transistor for supplying a reference voltage from a reference voltage supply line to the first node in response to the scan signal of the scan line, a merge transistor for connecting the first and second nodes in response to a merge signal of a merge line, a storage capacitor connected between a third node and the second node interposed between the driving transistor and the light emitting element to store a voltage which corresponds to the data voltage in which the threshold voltage is compensated, and first and second reset transistors for initializing at least two of the first, second, and third nodes to an initialization voltage of an initialization voltage line in response to a reset signal of a reset line.
1. A voltage compensation type pixel circuit of an organic light emitting diode for driving a light emitting element, comprising:
a driving transistor serially connected to the light emitting element between a high-potential power line and a low-potential power line to drive the light emitting element in response to a voltage supplied to a first node;
a program transistor that supplies a data voltage of a data line to a second node in response to a scan signal of a scan line;
a merge transistor that connects the first node and the second node in response to a merge signal of a merge line;
a storage capacitor connected between a third node and the second node to store a voltage which corresponds to the data voltage in which the threshold voltage is compensated, wherein the third and second nodes are interposed between the driving transistor and the light emitting element;
first and second reset transistors that initialize at least two of the first, second, and third nodes to an initialization voltage of an initialization voltage line in response to a reset signal of a reset line; and
a capacitor connected between the scan line and the first node to supply a reference voltage to the first node according to variation of the scan signal.
2. The voltage compensation type pixel circuit of claim 1 , wherein a negative bias is applied to the light emitting element during the initialization period and the program period to use the light emitting element as the capacitor, and a positive bias is applied to the light emitting element only during the light emitting period to drive the light emitting element.
3. The voltage compensation type pixel circuit of claim 2 , wherein, during the program period, the capacitor of the light emitting element accumulates charges through the driving transistor until a potential of the third node reaches a voltage corresponding to a difference between the reference voltage and the threshold voltage, and the storage capacitor stores a voltage corresponding to a difference between voltages of the second and third nodes, and
during the light emitting period, the driving transistor supplies current proportional to the square of a voltage (Vdata−Vref) corresponding to a difference between the data voltage and the reference voltage to the light emitting element.
4. The voltage compensation type pixel circuit of claim 2 , wherein the transistors of the pixel circuit are n-type transistors and detect a positive threshold voltage or a negative threshold voltage during the program period.
5. The voltage compensation type pixel circuit of claim 2 , wherein the transistors of the pixel circuit are p-type transistors and detect a positive threshold voltage or a negative threshold voltage during the program period.
6. The voltage compensation type pixel circuit of claim 2 , wherein black luminance of the light emitting element is controlled by adjusting the reference voltage.
7. The voltage compensation type pixel circuit of claim 2 , wherein the driving transistor is always driven in a saturation region.