The invention utilizes a DC-to-AC converter to provide a larger current to drive active matrix organic light emitting diode (AMOLED) pixels.
The AMOLED 36 is coupled to a voltage source, such as a ground voltage GND. The transistor MP1 has a first terminal coupled to the data driving unit 32, and a control terminal coupled to the scan driving unit 34. The transistor MP2 has a first terminal coupled to a second terminal of the transistor MP1, and a control terminal coupled to the scan driving unit 34. The transistor MP3 has a first terminal coupled to the first terminal of the transistor MP2, a second terminal coupled to a first voltage, such as an operation voltage VDD, and a control terminal coupled to a second terminal of the transistor MP2. The transistor MP4 has a first terminal coupled to the AMOLED 36, a second terminal coupled to the operation voltage VDD, and a control terminal coupled to the control terminal of the transistor MP3. The capacitor C has a first terminal coupled to the control terminal of the transistor MP4, and a second terminal coupled to the second terminal of the transistor MP4.
In a writing timing stage, a scan signal Scan outputted from the scan driving unit 34 turns on the transistor MP1 and the transistor MP2. The transistor MP3 also generates a current IData according to the current IData possessed by the data driving unit 32. Because the transistor MP3 and the transistor MP4 form a current mirror circuit structure, the transistor MP4 generates a current IOLED in proportional to the current IData, and outputs the current IOLED to the active matrix light emitting diode 36 to make the active matrix light emitting diode 36 emit the corresponding luminance. Meanwhile, the capacitor C is also charged to a corresponding voltage level.
Then, in a displaying timing stage, the scan signal Scan turns off the transistor MP1 and the transistor MP2, so the transistor MP4 is electrically isolated from the data driving unit 32. A voltage difference between a source and a gate of the transistor MP4 is stably kept at the corresponding voltage level through the capacitor C, and the current IOLED is thus stably kept at a predetermined value.
In the AMOLED panel 30, the data driving unit 32 includes a switch 321, a DC-to-AC converter 322, a mirror output circuit 323, a mirror switch 324 and a buffer amplifier 325. The switch 321 has a first terminal coupled to the AMOLED pixel unit 31, and a second terminal coupled to the voltage source GND. The mirror output circuit 323 has a first terminal coupled to the switch 321. The mirror switch 324 has a first terminal coupled to a second terminal of the mirror output circuit 323, and a second terminal coupled to the voltage source GND. The buffer amplifier 325 has an output terminal coupled to the control terminal of the switch 321, a positive input terminal coupled to the DC-to-AC converter 322, and a negative input terminal coupled to the output terminal of the buffer amplifier 325.
The DC-to-AC converter 322 outputs a variable voltage V. Because the DC-to-AC converter 322 has n+1 bytes, the number of magnitude changes of the variable voltage V is 2n+1, wherein n is a positive integer. The buffer amplifier 325 amplifies the power of the DC-to-AC converter 322, and still outputs the variable voltage V after receiving the variable voltage V. The variable voltage V turns on the switch 321 to make the switch 321 operate in a linear operation region. Then the switch 321 outputs a data current I having a magnitude in directly proportional to a magnitude of the variable voltage V.
When the mirror switch 324 is turned on, the mirror output circuit 323 outputs a duplicated data current I′, which is proportional to the data current I. For example, I′=I. Thus, the magnitude of the current IData drafted from the data driving unit 32 by the AMOLED pixel unit 31 is the sum (i.e., 2I) of the data current I and the duplicated data current I′.
The position of the mirror switch 324 may also be changed. For example, the first terminal of the mirror switch 324 may be coupled to the mirror output circuit 323, and the second terminal of the mirror switch 324 is coupled to the AMOLED pixel unit 31.
In the AMOLED panel 30, the first to fourth switches may also be NMOS transistors.
The operational principle of the AMOLED panel 40 is the same as that of the AMOLED panel 30, and one of ordinary skill in the art may make any modification easily. So, detailed descriptions thereof will be omitted.
The AMOLED panel according to the embodiment of the invention utilizes a DC-to-AC converter to provide a larger current to drive the AMOLED pixels, and also to provide various currents with different magnitudes to drive the AMOLED pixels.
While the invention has been described by way of example and in terms of a preferred embodiment, 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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95119832 | Jun 2006 | TW | national |