CN100433087C - Pixel unit of flat panel display and driving method thereof - Google Patents

Abstract

A pixel unit of a flat panel display comprises at least one non-volatile memory, at least one scan line, at least one data line and at least one storage capacitor. The scan line is electrically connected to the gate of the non-volatile memory. The data line is electrically connected to the source of the non-volatile memory. The storage capacitor is electrically connected to the drain of the non-volatile memory. The driving method of the pixel unit comprises: providing a scan voltage and a data voltage to change the starting voltage of the non-volatile memory, thereby redefining the storage potential of the storage capacitor.

Description

Pixel unit of flat panel display and driving method thereof

technical field

The invention relates to a pixel unit of a flat panel display and a driving method thereof, in particular to a pixel unit using a non-volatile memory as an active component and a driving method thereof.

Background technique

When an existing display is playing the same static image, for example, when reading an article or an electronic letter, the driver chip must still transmit the same image information to each pixel unit multiple times. In other words, even if the picture is still, the driver chip is still constantly consuming power. However. For portable displays, it is necessary to use lower power consumption to display static images to reduce their charging times.

In order to reduce the power consumption of the display, it is proposed in the prior art to add a memory unit, such as a static random access memory (SRAM), in the pixel unit to achieve the power saving effect when displaying a static image.

Please refer to FIG. 1A , which is a pixel unit of a conventional flat panel display. The pixel unit 10 has a scan line 11 , a data line 12 , a thin film transistor 13 , a SRAM 14 and an electrode 15 . The scan line 11 is electrically connected to the gate of the thin film transistor 13 . The data line 12 is electrically connected to the source of the thin film transistor 13 . One end of the SRAM 14 is electrically connected to the electrode 15 , and the other end can be disconnected or electrically connected to the thin film transistor 13 as the user selects "normal mode" or "static power-saving mode".

In normal mode, the SRAM 14 is not electrically connected to the TFT 13 , so the pixel unit 10 only uses the TFT 13 as an active component to cooperate with a capacitor (not shown) to operate. If switched to the static power-saving mode, the static random access memory 14 is electrically connected to the thin film transistor 13 to jointly control the brightness or gray scale of the screen. In this way, the driver chip (not shown) does not need to transmit the same frame information to the pixel unit 10 multiple times, which can reduce power consumption.

The circuit structure of the SRAM 14 is shown in FIG. 1B , including an N-channel transistor 142 connected in series to two parallel inverters 144 and 146 , and then connected in series to another N-channel transistor 148 .

Referring again to FIG. 1C, the basic structure of the inverter will be described. The inverter 144 is formed by connecting an N-channel transistor 1441 and a P-channel transistor 1442 in parallel. The inverter 146 also has the same structure, so the SRAM 14 shown in FIG. 1B actually consists of 6 transistors.

Based on the above, since the SRAM needs to be composed of 6-8 transistors, the aperture ratio of the pixel unit will be reduced. When the display uses an organic light emitting diode (OLED) as a light-emitting component, if there is a static random access memory disposed below it, the bottom-emission method cannot be adopted. In addition, each sub-pixel configured with SRAM can only display two gray scales, bright and dark. Therefore, each pixel unit composed of three sub-pixels of red, green and blue (RGB) can only display 8 colors at most.

Contents of the invention

The purpose of the present invention is to provide a pixel unit which uses a non-volatile memory (non-volatile memory device) as an active component and has a relatively high aperture ratio.

Another object of the present invention is to provide a driving method for a pixel unit that uses a non-volatile memory as an active component. When the pixel unit is applied to a flat-panel display, the driving method can enable the flat-panel display to display static pictures with lower power consumption and produce color changes of more than 8 colors.

The pixel unit of the present invention includes at least one non-volatile memory, at least one scanning line electrically connected to the gate of the non-volatile memory, at least one data line electrically connected to the source of the non-volatile memory, And, at least one storage capacitor is electrically connected to the drain of the non-volatile memory.

In order to cooperate with the operation of the above-mentioned pixel unit, the present invention also provides a driving method. In normal mode, the non-volatile memory has a first initial voltage, so that the storage capacitor has a first storage potential. To switch to static power-saving mode, follow the steps below. Firstly, the first starting voltage is erased. Then write a second initial voltage into the non-volatile memory to replace the first initial voltage. A scan voltage is provided on the gate of the non-volatile memory, and a second storage potential of the storage capacitor is defined by the difference between the scan voltage and the second start voltage. And, provide a data voltage to the source/drain of the non-volatile memory to charge the storage capacitor, so that the first storage potential is changed to the second storage potential.

According to the present invention, the pixel unit has less static random access memory than the prior art, so the aperture ratio can be increased. After replacing the TFT with the non-volatile memory, combined with the above-mentioned driving method, the initial voltage can be flexibly changed to achieve the purpose of saving power and increasing the number of colors and gray scales. The invention is especially suitable for switching between the general mode and the static power-saving mode when displaying a static picture.

Description of drawings

FIG. 1A is a pixel unit of an existing flat panel display;

Fig. 1B is the circuit structure of static random access memory;

Fig. 1C is the basic structure of the inverter;

Fig. 2A is that the pixel unit of the present invention is applied in a liquid crystal display;

FIG. 2B is the result of operating three pixel units in a liquid crystal display according to the driving method of the present invention;

FIG. 3A is a pixel unit of the present invention applied to an organic electroluminescent display;

3B-3C are the pixel units of the present invention, which have a plurality of organic light emitting diodes;

Figure 4 is a pixel unit of the present invention, which has an N-channel thin film transistor;

Fig. 5 is a pixel unit of the present invention, which has an inversion type organic light emitting diode;

Fig. 6 shows that the pixel unit of the present invention is applied to a liquid crystal display, which can control static display and dynamic display respectively;

7A-7C show that the pixel unit of the present invention is applied to an organic electroluminescent display, which can control static display and dynamic display respectively;

Fig. 8 is a timing control diagram for a static picture;

Fig. 9 is according to the present invention, the power consumption curve of driving chip; And

FIG. 10 is a graph showing the relationship between power consumption and the ratio of the bright area of the panel.

Description of reference symbols

10-pixel unit 30-pixel unit

11 scan lines 31 data lines

12 data lines 32 scan lines

13 thin film transistor 33 non-volatile memory

14 static random access memory 34 storage capacitor

142 N-channel transistors 35 drive transistors

144 inverters 36 OLEDs

1441 N-channel transistor 40 pixel unit

1442P Channel Transistor 42 Organic Light Emitting Diodes

146 inverters 50 pixel units

148 N-channel transistors 52 organic light-emitting diodes

15 electrodes 60 pixel unit

20 pixel unit 62N channel thin film transistor

20a pixel unit 70 pixel unit

20b pixel unit 72 organic light emitting diodes

20c pixel unit 80 pixel unit

201 pixel electrodes 82 scanning lines

202 pixel electrodes 84 thin film transistors

203 pixel electrodes 90 pixel units

21 data lines 92 scan lines

22 scanning lines 94 switching transistors

23 non-volatile memory 100 pixel units

24 storage capacitors 102 N-channel thin film transistors

25 liquid crystal capacitors 104 organic light emitting diodes

25a liquid crystal layer 110 pixel unit

                                                                                 

                                                                                 

Detailed ways

The pixel unit and its driving method of the present invention are described in detail with reference to the diagrams, and preferred embodiments are given to illustrate the application of the pixel unit in flat-panel displays such as liquid crystal displays or organic electroluminescent displays.

Please refer to FIG. 2A , which shows that the pixel unit of the present invention is applied in a liquid crystal display. The pixel unit 20 includes at least one data line 21 , at least one scan line 22 , at least one non-volatile memory 23 , at least one storage capacitor 24 and at least one liquid crystal capacitor 25 . The scan line 22 is electrically connected to the gate terminal G of the non-volatile memory 23 . The data line 21 is electrically connected to the source/drain terminal S of the non-volatile memory 23 . The other source/drain terminal D of the non-volatile memory 23 is electrically connected to the storage capacitor 24 and a liquid crystal layer (not shown) through a pixel electrode (not shown). The other terminal of the storage capacitor 24 is provided with a reference potential Vref1, and the difference between the reference potential Vref1 and the potential of the source/drain terminal D forms a capacitor potential. One surface of the liquid crystal layer receives the potential of the source/drain terminal D, while the other surface of the liquid crystal layer is provided with another reference potential Vref2 to form a function like a capacitor, called a liquid crystal capacitor 25 . Here, the reference potentials Vref1 and Vref2 can be the same or different, and can also be grounded to form zero potential.

The difference between non-volatile memory 23 and static random access memory is that non-volatile memory 23 does not change its stored data state when the power supply disappears, but static random access memory will lose its stored data when the power supply disappears . Based on the above-mentioned characteristics, the present invention uses non-volatile memory 23, such as electronically erasable/writeable read-only memory (electrically erasable programmable read-only memory, EEPROM), flash memory (flash memory) or similar memory, to replace existing Some thin film transistors are used as active components of the pixel unit. In particular, when the flat panel display displays a static image, the driver chip no longer needs to transmit the same image information to each pixel unit multiple times. Therefore, the power required to drive the operation of the chip can be saved.

The specific operation of the pixel unit 20 is as follows. In the normal mode, the operation of the non-volatile memory 23 is like a general thin film transistor, and the initial voltage at this time is Vth1. If switching to the static power-saving mode, a voltage difference is formed between the gate and the source/drain to erase the initial voltage Vth1. Similarly, another voltage difference is formed between the gate and the source/drain to write a predetermined voltage into the floating gate of the non-volatile memory 23, such as FN tunneling mechanism. In this way, the initial voltage of the non-volatile memory 23 can be changed to Vth2.

In the flat panel display, the non-volatile memory 23 of each pixel unit 20 can have a different starting voltage Vth and the storage capacitor 24 can have a different capacitance potential through the above-mentioned writing mechanism of the starting voltage Vth. When the storage capacitor 24 is charged, a scan voltage Vscan is provided to all the scan lines 22 of the flat panel display, and a data voltage Vdata is provided to all the data lines 21 . When the data voltage is greater than the scan voltage (Vdata>Vscan). At this time, assuming that the reference potential Vref1 is zero, the charging voltage of the storage capacitor 24 is equal to the voltage difference (Vscan−Vth) between the scan voltage and the starting voltage. When the screen needs to be updated, the initial voltage is erased again; if the screen does not need to be updated, the scanning voltage Vscan and the data voltage Vdata can be kept in a stable state.

The magnitude relationship between the data voltage Vdata and the scan voltage Vscan is described as follows. When the data voltage Vdata is smaller than the “difference between the scan voltage Vscan and the starting voltage Vth”, the charging voltage of the storage capacitor 24 is equal to the data voltage Vdata. In this case, since the static power-saving mode provides all pixel units with the same data voltage Vdata, the capacitor potentials of all pixels are the same, and the gray scale brightness set by different pixels cannot be displayed. When the data voltage Vdata is greater than the scan voltage Vscan, the charging voltage of the storage capacitor 24 is fixed at the maximum value "Vscan-Vth", so the initial voltage can be adjusted to achieve different grayscale display.

Please refer to FIG. 2B , which illustrates the operation result of the present invention by taking three pixel units 20 a , 20 b and 20 c in a liquid crystal display as an example. Assume that the initial voltage of the non-volatile memory 231 is changed to 5V, the initial voltage of the non-volatile memory 232 is 2.5V, and the initial voltage of the non-volatile memory 233 is 0V by using the above method. A data voltage of 8V and a scanning voltage of 5V are provided to the entire liquid crystal panel. At this time, since the data voltage Vdata is greater than the scan voltage Vscan, the charging voltages of the storage capacitors 241, 242, and 243 are respectively 0V, 2.5V, and 5V based on "Vscan-Vth", which means that the potentials of the pixel electrodes 201, 202, and 203 are also 0V, 2.5V and 5V. If the reference potential Vref2 of the liquid crystal layer 25a is zero or grounded, the operating voltage of the pixel unit 20a becomes 0V, the operating voltage of the pixel unit 20b becomes 2.5V, and the operating voltage of the pixel unit 20c becomes 5V. In this way, the variable initial voltage of the non-volatile memory is matched with the stable voltage of the data line and the scanning line to produce various grayscale brightness and save power consumption when displaying static images.

Please refer to FIG. 3A , which shows that the pixel unit of the present invention is applied to an organic electroluminescence display. The pixel unit 30 includes at least one data line 31 , at least one scan line 32 , at least one nonvolatile memory 33 , at least one storage capacitor 34 , at least one driving transistor 35 and at least one organic light emitting diode 36 .

The scan line 32 is electrically connected to the gate terminal G of the non-volatile memory 33 . The data line 31 is electrically connected to one source/drain terminal S of the non-volatile memory 33 . The other source/drain terminal D of the nonvolatile memory 33 is electrically connected to the gate of the driving transistor 35 and the storage capacitor 34 . Two ends of the storage capacitor 34 are electrically connected to the gate and the drain of the driving transistor 35 respectively. The anode of the OLED 36 is simultaneously connected to the drain of the driving transistor 35 and the storage capacitor 34 .

In this embodiment, the driving transistor 35 is a P-channel thin film transistor, and its source is used to receive a high voltage level Vdd. The cathode of the OLED 36 is used to receive a low voltage level Vss. Here, the voltage at point D is also Vscan-Vth. If the Vth of the non-volatile memory 33 is changed, the voltage at point D can be adjusted, so the gate voltage of the driving transistor 35 can be determined, and the driving current of the OLED 36 can be determined at the same time.

Please refer to FIG. 3B , which is a pixel unit of the present invention, which has a plurality of organic light emitting diodes connected in series. 3A , the pixel unit 40 is provided with an organic light emitting diode 42 connected in series with the organic light emitting diode 36 .

Please refer to FIG. 3C , which is a pixel unit of the present invention, which has a plurality of organic light emitting diodes connected in parallel. Comparing with FIG. 3A , the pixel unit 50 is provided with an organic light emitting diode 52 connected in parallel with the organic light emitting diode 36 .

Please refer to FIG. 4 , and compare with FIG. 3A , the pixel unit 60 uses an N-channel thin film transistor 62 instead of the driving transistor 35 (P-channel). The anode of the OLED 36 is electrically connected to the source of the N-channel TFT 62 .

Please refer to FIG. 5 , which is a pixel unit 70 having an inverted organic light emitting diode. Comparing FIG. 4 , the cathode of the OLED 72 is electrically connected to the drain of the N-channel transistor 62 .

Figures 3B-3C, Figure 4, and Figure 5 all use a single non-volatile memory as an active component, and adjust the brightness of the pixel unit by changing its initial voltage. However, in order to control the static display and the dynamic display separately, a non-volatile memory and a thin film transistor can also be used as active components, please refer to the description of the following embodiments.

Please refer to FIG. 6 , which shows that the pixel unit of the present invention is applied to a liquid crystal display, which can control static display and dynamic display respectively. Comparing with FIG. 2A , the pixel unit 80 has an additional scan line 82 and a thin film transistor 84 . The data line 21 is connected to the source of the thin film transistor 84 and the nonvolatile memory 33 . The scan line 22 is electrically connected to the gate of the non-volatile memory 33 . The scan line 82 is electrically connected to the gate of the thin film transistor 84 . Both the thin film transistor 84 and the drain of the nonvolatile memory 33 are electrically connected to the storage capacitor 24 .

In normal mode, the operating voltage of the pixel unit 80 is controlled by the thin film transistor 84 to display the image. In particular, when a static image is displayed, the non-volatile memory 33 can control the operating voltage of the pixel unit 80 to switch to the static power-saving mode.

In addition, in the organic electroluminescent display, static display and dynamic display can also be controlled separately.

Referring to FIG. 7A , and comparing with FIG. 3A , the pixel unit 90 has an additional scan line 92 and a switching transistor 94 . The data line 31 is connected to the switch transistor 94 and the source of the non-volatile memory 33 . The scan line 92 is electrically connected to the gate of the switching transistor 94 . The source/drain of the switching transistor 94 and the source/drain of the nonvolatile memory 33 are commonly connected to the gate of the driving transistor 35 (P-channel) and the storage capacitor 34 . The anode of the OLED 36 is electrically connected to the drain of the driving transistor 35 . In this way, in the normal mode, the operating potential of the pixel unit 90 is controlled by the switch transistor 94 to control the image. However, when a static image is displayed, the non-volatile memory 33 can control the operating potential of the pixel unit 90 to switch to the static power-saving mode.

Similarly, the drive transistor 35 in FIG. 7A can also be replaced with an N-channel transistor, please refer to FIGS. 7B-7C. In the pixel unit 100 , the cathode of the organic light emitting diode 104 is electrically connected to the drain of the N-channel thin film transistor 102 , forming an inversion structure. In the pixel unit 110 , the anode of the OLED 114 is electrically connected to the source of the N-channel TFT 112 .

In the present invention, the thin film transistor can adopt amorphous silicon (α-Si) or low temperature polysilicon (LTPS) process. In order to avoid damage to the glass substrate caused by the high-temperature oxidation process, PECVD can be used to deposit the oxide layer in the non-volatile memory at a temperature lower than 650°C.

The common feature of all the above embodiments is that the pixel unit includes at least one non-volatile memory, at least one scan line is electrically connected to the gate of the non-volatile memory, and at least one data line is electrically connected to the non-volatile memory. The source of the volatile memory, and at least one capacitor is electrically connected to the drain of the non-volatile memory.

In normal mode, the non-volatile memory has a first initial voltage, so that the capacitor has a first storage potential. To switch to static power-saving mode, follow the steps below. Firstly, a voltage difference is provided between the gate and the source/drain of the nonvolatile memory to erase the first starting voltage. Similarly, providing a voltage difference between the gate and the source/drain of the nonvolatile memory to write a second initial voltage in the nonvolatile memory to replace the first initial voltage; providing a scanning voltage on the gate of the non-volatile memory, and defining a second storage potential of the capacitor by the difference between the scanning voltage and the second starting voltage; and providing a data voltage on the non-volatile memory The source/drain of the volatile memory is used to charge the capacitor to change the first storage potential to the second storage potential.

Based on the above, since the initial voltage of the non-volatile memory 23 is different in each pixel unit, the storage potential of the storage capacitor 24 is also different, which can be displayed in multiple colors. In addition, each pixel unit uses only one non-volatile memory to replace the function of static random access memory. Since each non-volatile memory is usually composed of two transistors, but the SRAM includes six to eight transistors, so the required number of transistors is less, so the aperture ratio of the pixel unit can be increased.

Please refer to FIG. 8 , which is a timing control diagram of a static image. In the period I, when switching from the normal mode to the static power-saving mode, a scanning voltage may be provided to reset the capacitor potential. During period II, a data voltage is provided for displaying images.

Please refer to FIG. 9, which is a power consumption curve of the driver chip. The horizontal axis is the input voltage (V); the vertical axis is the power consumption (mW). When the input voltage is between 3.0V and 3.6V, the power consumption is between 40mW and 60mW.

Please refer to FIG. 10 , which is a relationship curve between power consumption and the ratio of the bright area of the panel, and the saved power is calculated accordingly. The horizontal axis in the figure is the proportion of bright area of the panel; the vertical axis on the left is power consumption (mW); the vertical axis on the right is power saving (%). When the ratio of the bright area of the organic electroluminescence panel is 1/3-1/4, assuming a static display, the power consumed by the organic light-emitting diode is 240mW to 180mW, and the circuit design of the present invention can save the power consumption of the driver chip 40mW to 60mW.

The above detailed description is a specific description of the preferred embodiments of the present invention, but the above embodiments are not intended to limit the patent scope of the present invention, and any equivalent implementation or change that does not depart from the technical spirit of the present invention shall be included in within the patent scope of this case.

Claims (25)

1. A pixel unit of a flat panel display, comprising: at least one non-volatile memory as an active component; at least one scan line electrically connected to the gate of the non-volatile memory; at least one data line electrically connected to the source of the non-volatile memory; and At least one storage capacitor is electrically connected to the drain of the non-volatile memory. 2. The pixel unit as claimed in claim 1, further comprising a pixel electrode electrically connected to the storage capacitor, and the pixel electrode is in contact with a liquid crystal layer. 3. The pixel unit according to claim 1, further comprising: at least one thin film transistor having a gate electrically connected to the storage capacitor and the drain of the non-volatile memory; and At least one organic light emitting diode is electrically connected to one of the drain and the source of the thin film transistor. 4. The pixel unit as claimed in claim 3, wherein the thin film transistor is a P-channel thin film transistor. 5. The pixel unit as claimed in claim 3, wherein the thin film transistor is an N-channel thin film transistor. 6. The pixel unit as claimed in claim 4, wherein the anode of the organic light emitting diode is electrically connected to the drain of the P-channel thin film transistor. 7. The pixel unit as claimed in claim 5, wherein the cathode of the organic light emitting diode is electrically connected to the drain of the N-channel thin film transistor. 8. The pixel unit as claimed in claim 5, wherein an anode of the organic light emitting diode is electrically connected to a source of the N-channel thin film transistor. 9. The pixel unit according to claim 1, further comprising: at least one thin film transistor having a gate electrically connected to the storage capacitor and the drain of the non-volatile memory; and A plurality of organic light emitting diodes, one of which is electrically connected to one of the drain and the source of the thin film transistor, and each of the organic light emitting diodes is connected in series. 10. The pixel unit according to claim 1, further comprising: at least one thin film transistor having a gate electrically connected to the storage capacitor and the drain of the non-volatile memory; and A plurality of organic light emitting diodes are electrically connected to one of the drain and the source of the thin film transistor, and each of the organic light emitting diodes is connected in parallel with each other. 11. A pixel unit of a flat panel display, comprising: at least one thin film transistor; at least one first scan line electrically connected to the gate of the thin film transistor; at least one non-volatile memory as an active component; at least one second scan line electrically connected to the gate of the non-volatile memory; at least one data line electrically connected to the thin film transistor and the source of the non-volatile memory; and At least one storage capacitor is electrically connected to the thin film transistor and the drain of the non-volatile memory. 12. The pixel unit as claimed in claim 11, further comprising a pixel electrode electrically connected to the capacitor, and the pixel electrode is in contact with a liquid crystal layer. 13. The pixel unit according to claim 11, further comprising: at least one second thin film transistor having a gate electrically connected to the storage capacitor and the drain of the non-volatile memory; and At least one organic light emitting diode is electrically connected to one of the drain and the source of the second thin film transistor. 14. The pixel unit as claimed in claim 13, wherein the second thin film transistor is a P-channel thin film transistor. 15. The pixel unit as claimed in claim 13, wherein the second thin film transistor is an N-channel thin film transistor. 16. The pixel unit as claimed in claim 14, wherein the anode of the organic light emitting diode is electrically connected to the drain of the P-channel thin film transistor. 17. The pixel unit as claimed in claim 15, wherein the cathode of the organic light emitting diode is electrically connected to the drain of the N-channel thin film transistor. 18. The pixel unit as claimed in claim 15, wherein an anode of the organic light emitting diode is electrically connected to a source of the N-channel thin film transistor. 19. The pixel unit of claim 11, further comprising: at least one second thin film transistor having a gate electrically connected to the storage capacitor and the drain of the non-volatile memory; and A plurality of organic light emitting diodes, one of which is electrically connected to one of the drain and the source of the thin film transistor, and each of the organic light emitting diodes is connected in series. 20. The pixel unit of claim 11, further comprising: at least one second thin film transistor having a gate electrically connected to the storage capacitor and the drain of the non-volatile memory; and A plurality of organic light emitting diodes are electrically connected to one of the drain and the source of the thin film transistor, and each of the organic light emitting diodes is connected in parallel with each other. 21. A method for driving a pixel unit, the pixel unit comprising at least one non-volatile memory electrically connected to at least one storage capacitor, wherein the non-volatile memory has a first initial voltage, so that the storage capacitor has A first stored potential, the method comprising: erasing the first initial voltage, and then writing a second initial voltage into the non-volatile memory to replace the first initial voltage; providing a scanning voltage on the gate of the non-volatile memory, and defining a second storage potential of the storage capacitor by the difference between the scanning voltage and the second starting voltage; and A data voltage is provided to the source/drain of the non-volatile memory to charge the storage capacitor so that the first storage potential is changed to the second storage potential. 22. The driving method according to claim 21, wherein the step of writing the second initial voltage further comprises: A voltage difference is provided between the gate and the source/drain of the non-volatile memory. 23. The driving method of claim 21, wherein the data voltage is greater than the scan voltage. 24. The driving method as claimed in claim 21, further comprising erasing the first starting voltage before writing the second starting voltage. 25. The driving method according to claim 24, wherein the step of erasing the first starting voltage comprises: A voltage difference is provided between the gate and the source/drain of the non-volatile memory.

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