1. Field of Invention
The present invention relates to a pixel circuit, and more particularly relates to an AMOLED voltage type compensation pixel circuit.
2. Description of Related Art
The drawback of the conventional pixel circuit is that it needs a complicated design for variable power voltages and a reset signal.
According to one embodiment of the present invention, the pixel circuit has a light emitting diode, a driving transistor, a capacitor, and a switch unit. The driving transistor has a first source/drain coupled to one end of the light emitting diode. The capacitor is coupled between a gate of the driving transistor and the end of the light emitting diode. The switch unit couples the gate and a second source/drain of the driving transistor together, and couples the second source/drain of the driving transistor to a data line when a scan signal is asserted.
According to another embodiment of the present invention, the pixel circuit has a light emitting diode, a driving transistor, a capacitor, and a switch unit. The driving transistor has a first source/drain coupled to one end of the light emitting diode. The capacitor is coupled between a gate and a second source/drain of the driving transistor. The switch unit couples the gate and the first source/drain of the driving transistor together, and couples the second source/drain of the driving transistor to a data line when a scan signal is asserted.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
The switch unit has a first switch 241 and a second switch 242. The first switch 241 is connected between the second source/drain 222 and the gate 223 of the driving transistor 220. The second switch 242 is connected between the second source/drain 222 of the driving transistor 220 and the data line 250. Moreover, the pixel circuit has a third switch 260 controlled by a signal (SWN) to couple or decouple the second source/drain 222 of the driving transistor 220 to a power source end 270. The third switch 260 can be implemented outside the pixel circuit, such as the margin of the panel or the gat driver, to reduce the amount of the transistors inside the pixel circuit.
The signal SWN that controls the third switch 260 is opposite to the scan signal (SCAN). When the signal SWN is deasserted (i.e. the scan signal is asserted) in the data writing stage, the third switch 260 decouples the second source/drain 222 of the driving transistor 220 to a power source end 270. When the signal SWN is asserted (i.e. the scan signal is deasserted) in the display stage, the third switch 260 couples the second source/drain 222 of the driving transistor 220 to the power source end 270.
The second source/drain 222 of the driving transistor 220 floats when the third switch 260 is turned off (i.e. during the data writing stage). Therefore, the data signals can be written into the capacitor 230 of the pixel circuit more easily during the data writing stage. Compared with the pixel circuit of the prior art, the pixel circuit doesn't need an extra reset signal before data writing. Moreover, the power source end 270 can only supply a fixed voltage rather than the variable voltage of the conventional pixel circuit.
The first switch 241, the second switch 242, and the driving transistor 220 use NMOS transistors. If the first switch 241, the second switch 242, and the driving transistor 220 use NMOS transistors, the control signals have to be inverted.
Moreover, if the third switch 260 uses a different type of MOS from the first switch 241 and the second switch 242, the third switch 260 can be controlled by the scan signal (SCAN). For example, if the first switch 241 and the second switch 242 are NMOS transistors, and the third switch 260 is a PMOS transistor, the first switch, second switch and third switch can be controlled by the same scan signal (SCAN). Therefore, there are fewer control signals.
The switch unit has a first switch 341 and a second switch 342. The first switch 341 is connected between the first source/drain 321 and the gate 323 of the driving transistor 320. The second switch 342 is connected between the second source/drain 322 of the driving transistor 320 and the data line 350. Moreover, the pixel circuit has a third switch 360 controlled by a signal (SWP) to couple or decouple the second source/drain 322 of the driving transistor 320 to a power source end 370.
From the description above, the embodiments of this invention with the voltage compensation function has with three transistors have high aperture ratio. Otherwise, these embodiments can operate without an extra reset signal before writing data.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.