Patent Application
20150035736
This application claims the benefit of Taiwan Patent Application No. 102127747, filed on Aug. 2, 2013, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display, and more particularly to an OLED display in which a method for compensating voltages is used in order to improve display uniformity.
2. Related Art
As the formula (1) shown below, it denotes the driving current IOLED which passes through the OLED OD1.
I
OLED
=K(VGS−Vth)2=K(VG−VS−Vth)2=K(VDATA−VOLED−VSS−Vth)2 Formula (1)
Wherein, K is a process parameter (constant) of the driving TFT T2; VGS is a voltage between the gate and the source of the driving TFT T2; Vth is a threshold voltage of the driving TFT T2; VG is a gate voltage of the driving TFT T2; Vs is a source voltage of the driving TFT T2; VDATA is a data signal voltage; VOLED is a voltage between two ends of the OLED OD1; and Vss is a reference voltage.
Referring to
Therefore, it needs an OLED display which can avoid the reference voltage Vss to be raised so as to solve the above-mentioned problems.
In one aspect of the invention, it provides an OLED display which can avoid the voltage of the reference voltage line to be raised.
To achieve the objective, the present invention further provides an organic light emitting diode (OLED) display, comprising: a data driving circuit; a scan driving circuit; a display panel, comprising: a plurality of data lines, electrically connected to the data driving circuit; a plurality of scan lines, electrically connected to the scan driving circuit, and the scan lines being across the data lines; a plurality of pixel units, each of the pixel units electrically connected to the corresponding data line and the corresponding scan line and having an OLED element, wherein the pixel units are arranged in a form of array; a plurality of reference power lines, each of the reference power lines electrically connected to the corresponding pixel unit; and a plurality of reference voltage lines, each of the reference voltage line electrically connected to a cathode of the OLED element in the corresponding pixel units; a power supply circuit, electrically with the reference power lines; and a compensation device, electrically with the reference voltage lines, whereby a voltage of the reference voltage line becomes an ideal signal, and the ideal signal is a fixed voltage, and the compensation device comprises: a detecting circuit, being used for detecting the reference voltage line to obtain a pulsation signal; and a compensation circuit, electrically connected to the detecting circuit and being used for outputting a compensation signal to the reference voltage line according to the pulsation signal.
The present invention further provides a method for compensating voltages including steps as follows. A reference voltage line is detected to obtain a first pulsation signal. A phase of the first pulsation signal is shifted to obtain a shift signal. The shift signal is compared with an ideal signal to obtain a difference signal. A phase of difference signal is inverted, and the phase-inverted difference signal is summed up with the ideal signal, so as to obtain a compensation signal. The compensation signal is outputted to the reference voltage line when the reference voltage line sends a second pulsation signal, so that a voltage of the reference voltage line becomes the ideal signal, wherein the ideal signal is a fixed voltage.
In the present invention, a method is used for compensating the voltage of the reference voltage line of an OLED display; therefore, it can prevent the voltage of the reference voltage line to be raised, which can avoid the driving current passing through the
OLED element to be decreased and further stabilize the brightness of the OLED display, so that the image of the OLED display can have an excellent uniformity.
The present invention will become more fully understood from the detailed description given herein below for illustration only, which thus is not limitative of the present invention.
The display panel 110 includes a plurality of data lines 111, a plurality of scan lines 112, a plurality of pixel units 113, a plurality of reference power lines 114 and a plurality of reference voltage lines 115. The data lines 111 are electrically connected to the data driving circuit 102, and the scan lines 112 are electrically connected to the scan driving circuit 104. In addition, the scan lines 112 are across the data lines 111, each of the pixel units 113 is electrically connected to the corresponding data line 111 and scan line 112, and the pixel units 113 are arranged in a form of array. Besides, each of the reference power lines 114 is electrically connected to the corresponding pixel unit 113, and each of the reference voltage line 115 is electrically connected to a cathode of an OLED element OD1 of the corresponding pixel unit 113.
Each pixel unit 113 includes a switching thin-film transistor (TFT) T1, a driving TFT T2, a capacitor Cs, and an OLED element OD1. The switching TFT T1 and the driving TFT T2 have a gate, a drain, and a source, respectively. The gate of the switching TFT T1 is electrically connected to the scan line 112, the drain of the switching TFT T1 is electrically connected to the data line 111, and the source of the switching TFT T1 is electrically connected to the gate of the driving TFT T2. On the other hand, the drain of the driving TFT T2 is electrically connected to the reference power line 114, and the source of the driving TFT T2 is electrically connected to an anode of the OLED element OD1. One end of the capacitor Cs is electrically connected to the gate of the driving TFT T2, and the other end of the capacitor Cs is electrically connected to the drain of the driving TFT T2.
When the scan driving circuit 104 performs N (N is a nature number larger than 1) times scans from top to bottom, the switching TFTs T1 of the pixel units 113 at the same row will be ON in sequence. Then, the signals in the data driving circuit 102 will be transmitted to the corresponding pixel units 113 through the data lines 111 and then stored in the capacitors Cs of the pixel units 113, respectively. When the scan driving circuit 104 makes the switching TFTs T1 of the pixel units 113 OFF, the driving TFTs T2 will be ON and respectively generate a driving current to drive the OLED element OD1 according to the voltage stored in the capacitor Cs.
The power supply circuit 106 is electrically connected to the reference power lines 114 so as to provide a power voltage, and the compensation device 120 is electrically connected to the reference voltage lines 115 so as to stabilize the voltages of the reference voltage lines 115.
The compensation circuit 122 may further include a shift calculation circuit 123, a differential comparator 124, a difference compensator 125, and a voltage generator 126. The shift calculation circuit 123 is electrically connected to the detecting circuit 121 for receiving the pulsation signal and outputting a shift signal. The differential comparator 124 is electrically connected to the shift calculation circuit 123 and the voltage generator 126 for receiving the shift signal of the shift calculation circuit 123 and the ideal signal of the voltage generator 126. Here, the ideal signal is a fixed voltage. The shift signal and the ideal signal are compared to output a difference signal. The difference compensator 125 is electrically connected to the differential comparator 124 for receiving the difference signal and outputting the compensation signal. In the embodiment, the compensation device 120 and the power supply circuit 106 are separately disposed. In another embodiment, the compensation device 120 may be disposed in the power supply circuit 106.
In step S100: detecting a reference voltage line to obtain a first pulsation signal. When the driving TFT T2 is ON, the impedance is increased because the path length of the reference voltage line 115 is increased, so that the reference voltage of the reference voltage line 115 is raised and generates a pulsating voltage. In this step, the pulsation signal generated in a first period t1 is defined as a first pulsation signal 210. When the reference voltage line 115 generates the first pulsation signal 210, the detecting circuit 121 is used to detect the reference voltage line 115, so as to obtain the first pulsation signal 210. Then, the first pulsation signal 210 is transmitted to the shift calculation circuit 123.
In step S102: shifting a phase of the first pulsation signal to obtain a shift signal. In this step, a shift calculation circuit 123 is used to shift a phase of the first pulsation signal 210, and the phase-shifted first pulsation signal 210 is defined as a shift signal 230, so that there is a phase lag between the first pulsation signal 210 and the shift signal 230.
In step S104: comparing the shift signal with the ideal signal to obtain a difference signal. In this step, the shift signal 230 and an ideal signal 240 are compared by the differential comparator 124, so as to obtain a difference signal 250. Here, the difference signal 250 is obtained by subtracting the ideal signal 240 from the shift signal 230.
In step S106: inverting the phase of the difference signal and summing up the phase-inverted difference signal with the ideal signal to obtain a compensation signal. In this step, after receiving the difference signal 250, the difference compensator 125 inverts the phase of the difference signal 250, and then the phase-inverted difference signal 250 and the ideal signal 240 are sum up together, so as to obtain the compensation signal 260. The voltage value of the compensation signal 260 is less than or equal to the fixed voltage value of the ideal signal 240.
In step S108: outputting the compensation signal to the reference voltage line when the reference line generates the N pulsation signal (for example, the second pulsation signal). In this step, when the reference voltage line 115 generates a second pulsation signal 220 during the second period t2, the difference compensator 125 will output the compensation signal 260 at the same time, so that the second pulsation signal 220 and the compensation signal 260 are neutralized and the signal in the reference voltage line 115 becomes the ideal signal 240.
For example, please refer to
It can be known from above, in the present invention, a method is used for compensating the voltage of the reference voltage line of an OLED display; therefore, it can prevent the voltage of the reference voltage line to be raised, which can avoid the driving current passing through the OLED element to be decreased and further stabilize the brightness of the OLED display, so that the image of the OLED display can have an excellent uniformity.
It will be apparent to persons of ordinary art 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102127747 | Aug 2013 | TW | national |
