Image sticking prevention circuit for display device

#The invention relates to an image sticking prevention circuit and, in particular, to an image sticking prevention circuit for a display power-off mode.

#As shown in FIG. 1, a conventional liquid crystal display (LCD) 100 comprises a voltage converter 140, a gate driver circuit 110, a data driver circuit 120, and a pixel array 150. The pixel array 150 comprises a plurality of gate lines 112, a plurality of date lines 122, and a plurality of pixel driving circuits 130. The pixel driving circuit 130 comprises a driving transistor 132, a storage capacitor 134 and a liquid crystal cell 136. A gate and a source of the driving transistor 132 are respectively connected to one of the gate lines or data lines. When the gate drive circuit 110 raises a voltage of the gate line 112, the driving transistor 132 is turned on and a data signal on the data line 122 is transmitted to a drain of the driving transistor. Thereby, the data driver circuit 120 sends the data signal to the storage capacitor 134 via the data line 122 and the driving transistor 132. After the data signal is loaded into the storage capacitor 134, the gate driver circuit 110 decreases the voltage of the gate line 112 to its former level such that the liquid crystal cell 136 generates an image according to the data signal before the next data signal is loaded. However, when the LCD 100 enters a power-off mode, the data signal still remains in the storage capacitor 134, generating a residual image.

#A conventional solution shifts the current to voltage (I-V) curve of the transistor 132 (as shown in FIG. 2) to the left such that a threshold voltage of the transistor 132 is close to 0V. Thus, the transistor 132 is turned on even if a gate voltage of the transistor 132 is close to 0V. As a result, the data signal stored in the storage capacitor 134 is released to the data line 122. Image sticking is thus prevented, but current leakage is a major concern due to the decreased threshold voltage.

#FIG. 1 is a schematic diagram of a conventional liquid crystal display.

#FIG. 2 shows a current to voltage (I-V) curve of a driving transistor in the liquid crystal display shown in FIG. 1.

#FIG. 3A is a schematic diagram of a liquid crystal display comprising an image sticking prevention circuit according to one embodiment of the invention.

#Referring to FIG. 3A, an image sticking prevention circuit 300 is coupled to first and second voltage terminals (VDD and VEE) of a voltage converter 340. Two terminals of a gate driver circuit 310 are coupled to the first voltage terminal (VDD) and a second voltage terminal (VEE) of the voltage converter 340, respectively. The pixel array 350 comprises a plurality of gate lines 312 and a plurality of data lines 322.

#In addition, to facilitate the description of the present invention, the pixel driving circuit 330 is described first. In FIG. 3A, only one pixel driving circuit 330 is shown. Practically, there are a number of pixel driving circuits 330. In this embodiment, the pixel driving circuit 330 includes a driving transistor 332, a storage capacitor 334, and a liquid crystal cell 336. A gate 366 of driving transistor 332 is coupled to the gate line 312. A source 368 of the driving transistor 332 is coupled to the data line 322. A drain 370 of the driving transistor 332 is coupled to a first terminal 372 of the storage capacitor 334. A second terminal 374 of the storage capacitor 334 is coupled to a common voltage Vcom. One terminal of the liquid crystal cell 336 is coupled to the first terminal 372 of the storage capacitor 334. The other terminal of the liquid crystal cell 336 is coupled to the common voltage Vcom.

#A power supply provides power to a voltage converter 340 and the voltage converter 340 provides the gate driver circuit 310 with a high voltage VDD and a low voltage VEE. Preferably, the high voltage VDD is a positive voltage and the low voltage VEE is a negative voltage. For example, the high voltage VDD can be 12V, and the low voltage VEE −2V. When the data signal is received by the pixel driving circuit 330, the gate driver circuit 310 provides the high voltage VDD (12V) to turn on the driving transistor 332 via the gate line 312. After the driving transistor 332 is turned on, the data driver circuit 320 loads the data signal into the driving circuit 330 via the data line 322. After the data signal is loaded into the driving circuit 330, the gate driver circuit 310 provides the low voltage (−2V) to turn off the driving transistor 332. The data signal is stored in the storage capacitor 334 such that the liquid crystal cell 336 displays an image before the next data signal is loaded (i.e., the driving transistor 332 is turned on again). However, when the LCD enters a power-off mode, the data signal remains in the capacitor 334, generating a residual image.