The invention provides an AMOLED pixel circuit driving an LED to produce the corresponding luminance by using a current mirror circuit structure. Referring to
The first switch T1 has a first terminal for receiving a data signal Data, and a control terminal for receiving a scan signal Scan. The second switch T2 has a first terminal coupled to a second terminal of the first switch T1 and a control terminal for receiving the scan signal Scan. The first transistor T3 has a drain coupled to a second terminal of the second switch T2, a source for receiving a second supply voltage, such as an operational voltage VDD and a gate coupled to a second terminal of the first switch T1.
The second transistor T4 has a drain coupled to an anode of the LED 22, a source for receiving the operational voltage VDD, and a gate coupled to the gate of the first transistor T3. The LED 22 has a cathode for receiving a first supply voltage, such as a ground voltage GND. The capacitor C has a first end coupled to the gate of the second transistor T4 and a second end for receiving the operational voltage VDD.
During a writing timing stage, the scan signal Scan turns on the first switch T1 and the second switch T2 and thus the first transistor T3 generates a data current Idata according to the data signal Data via the turned-on first switch T1 and the second switch T2. At the same time, owing that the second transistor T4 and the first transistor T3 form a current mirror circuit, the second transistor T4 generates a pixel current Ioled proportional to the data current Idata, and outputs the pixel current Ioled to the LED 22 to produce the corresponding luminance. During the writing timing stage, the capacitor C is charged via the turned-on first switch T1 to store the corresponding data voltage Vdata stably.
During a display timing stage, the scan signal Scan turns off the first switch T1 and the second switch T2, and consequently, the first transistor T3 is also turned off and the second transistor T4 is no longer electrically coupled to the data signal Data. However, owing that the capacitor C stably stores the data voltage Vdata, the second transistor T4 still outputs the pixel current Ioled to the LED 22 to produce the corresponding luminance.
In the above pixel circuit 20, the configuration of the capacitor C is not limited to having a first end coupled to the gate of the second transistor T4 and a second end for receiving the operational voltage VDD. Referring to
In the AMOLED pixel unit of the invention, the first switch T1, the second switch T2, the first transistor T3 and the second transistor T4 can also be n-type metal oxide semiconductor (NMOS) transistors. Referring to
During a writing timing stage, the scan signal Scan turns on the first switch T1 and the second switch T2 and a data current Idata is inputted to the first transistor T3 via the turned-on first switch T1 and the second switch T2 according to the data signal Data. At the same time, owing that the second transistor T4 and the first transistor T3 form a current mirror circuit, the second transistor T4 generates a pixel current Ioled proportional to the data current Idata, and outputs the pixel current Ioled to the LED 42 to produce the corresponding luminance. During the writing timing stage, the capacitor C is charged via the turned-on first switch T1 to store the corresponding data voltage Vdata stably.
During a display timing stage, the scan signal Scan turns off the first switch T1 and the second switch T2, and consequently, the first transistor T3 is also turned off and the second transistor T4 is no longer electrically coupled to the data signal Data. However, owing that the capacitor C stably stores the data voltage Vdata, the second transistor T4 still outputs the pixel current Ioled to the LED 42 to produce the corresponding luminance.
In the above pixel circuit 40, the configuration of the capacitor C is not limited to having a first end coupled to the gate of the second transistor T4 and a second end for receiving the ground voltage GND. Referring to
The pixel circuit disclosed by the above embodiments of the invention drives the LED to produce the corresponding luminance by using a current mirror circuit structure and maintains the LED to have the luminance during the displaying timing stage.
While the invention has been described by way of example and in terms of four embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
Number | Date | Country | Kind |
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95123206 | Jun 2006 | TW | national |