CN100543820C - Active matrix organic light emitting diode display and its driving method - Google Patents

Abstract

The active matrix organic light emitting diode display comprises a plurality of data lines, a plurality of scanning lines, a plurality of pixel circuits, a source electrode driving circuit, a grid electrode driving circuit, a time sequence data control circuit and a gray scale circuit. The source driving circuit comprises a data line driving circuit for generating a driving current related to a pixel circuit to display an image. The current source is used to pre-charge the pixel circuit. The switch is coupled between the current source and the pixel circuit and used for electrically connecting or separating the current source and the pixel circuit. The gray scale circuit is used for controlling the switch according to the gray scale value of the image to be displayed by the pixel circuit on a scanning line. The time sequence data control circuit is used for controlling the source electrode driving circuit and the grid electrode driving circuit.

Description

Active matrix organic light emitting diode display and its driving method

technical field

The invention relates to an active matrix organic light emitting diode display and its driving method, in particular to an active matrix organic light emitting diode display capable of driving and precharging pixels through a current source and its driving method.

Background technique

The flat panel display (flat panel display) has the advantages of power saving, no radiation and small size, so it gradually replaces the traditional cathode ray tube (cathode ray tube, CRT) display. With the vigorous development of flat-panel display technology, global panel manufacturers are all committed to developing various emerging flat-panel display technologies to enhance market competitiveness. Among them, the organic light-emitting display using organic light emitting diode (OLED) has the advantages of self-illumination, high brightness, high luminous efficiency, high contrast, fast response time, wide viewing angle, low power consumption, and wide usable temperature range. Therefore, the market for flat panel displays is extremely competitive.

The organic light emitting diode itself is a current-driven component, and its luminous brightness is determined according to the magnitude of the current flowing through it. By controlling the magnitude of the driving current of the organic light emitting diode, the effect of displaying different brightness (also called gray scale value) can be achieved. According to the differences in driving methods, matrix displays can be divided into passive matrix (passive matrix) displays and active matrix (active matrix) displays. The passive matrix display uses the method of sequentially driving the scanning lines to drive the pixels located in different columns/rows (scanning lines/data lines) one by one, so the light-emitting time of the pixels on each column/row is limited by the scanning frequency of the display and The number of scanning lines is not suitable for large-screen and high-resolution displays. The active matrix display forms an independent pixel circuit in each pixel, and each pixel circuit includes a storage capacitor, an organic light-emitting diode light-emitting element, and two thin-film transistors (thin-film transistor, TFT), so as to use the pixel circuit to Adjusting the magnitude of the drive current of the organic light-emitting diode light-emitting component, so even under the requirements of large screen and high resolution, it can still provide a stable drive current for each pixel, and improve the brightness uniformity of the display.

Please refer to FIG. 1 , which is a schematic diagram of an active matrix organic light emitting display panel 10 in the prior art. The organic light emitting display panel 10 includes a data line DL, a scan line GL, and a pixel circuit 100 . The pixel circuit 100 includes an organic light emitting diode 110, a storage capacitor 120, thin film transistors 130 and 140, and voltage sources Vcc and Vss. The gate of the thin film transistor 130 is coupled to the scan line GL, and the drain thereof is coupled to the data line DL. The gate of the TFT 140 is coupled to the source of the TFT 130 , and the drain thereof is coupled to the voltage source Vcc. The storage capacitor 120 is coupled between the source of the TFT 130 and the ground potential, and the OLED 110 is coupled between the source of the TFT 140 and the voltage source Vss. When the pixel circuit 10 intends to display an image, it first transmits a signal through the scanning line GL to turn on (make it conductive) the thin film transistor 130, at this time, the storage capacitor 120 can be coupled to the data line DL through the thin film transistor 130, and the data line DL transmits The incoming current can charge the storage capacitor 120 , and store the gate voltage required to turn on the TFT 140 into the storage capacitor 120 . After the TFT 140 is turned on, a current I _OLED flows through the OLED 110 , and the brightness displayed by the OLED 110 is related to the magnitude of I _OLED . The current I _OLED can be expressed by the following formula:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; OX</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; GS</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Wherein, μ represents the electron mobility, Cox represents the gate capacitance per unit area of the thin film transistor 140 (gate oxide capacitance per unit area), W represents the channel width of the thin film transistor 140, L represents the channel length of the thin film transistor 140, V _TH represents the thin film transistor 140 The threshold voltage (threshold voltage), and V _GS represents the voltage difference between the gate and the source of the thin film transistor 140 . The grayscale value of the image displayed by the OLED 110 is determined by the magnitude of the current I _OLED , and V _CS relative to the magnitude of the current I OLED depends on the charge stored in the storage capacitor 120 . When the organic light emitting diode 110 displays a low-gray-scale image below a gray-scale reference value, the current I _OLED required to drive the pixel circuit 100 is extremely small, and the required V _GS is also very small. The current value of capacitor 120 is also very low. In the case of low current, the storage capacitor 120 cannot be effectively charged to provide the required V _GS voltage difference, which affects the performance of the pixel circuit 100 in displaying grayscale images. Therefore, when the active matrix organic light emitting display panel in the prior art displays low-grayscale images, the picture quality is not good.

Contents of the invention

The present invention provides a driving method for an active matrix organic light emitting diode display, which includes judging whether the grayscale value of a pixel circuit on a scanning line to display an image is lower than a grayscale reference value; if the pixel circuit intends to display The grayscale value of the image is lower than the grayscale reference value, and the number of pixel circuits on the scanning line whose grayscale value of the image to be displayed is lower than the grayscale reference value is greater than a threshold value, then input a pre-charging current to the pixel circuit; and After inputting the pre-charging current to the pixel circuit, input the signal corresponding to the display image to the pixel circuit.

The present invention also provides an active matrix organic light emitting diode display, which includes: a plurality of data lines for transmitting data signals; a plurality of scanning lines for transmitting control signals; a plurality of pixel circuits, each of which is coupled Connected to the corresponding data lines and scan lines; a source drive circuit, which includes a data line drive circuit, used to generate a drive current related to a pixel circuit to display an image; a current source, used for a data The data line is pre-charged before the line transmits the driving current generated by the data line driving circuit; and a switch, coupled between the current source and the data line, is used to establish or cut off the electrical connection between the current source and the data line; a timing sequence The data control circuit is used to control the source drive circuit and the gate drive circuit according to the video and timing data; and a grayscale circuit is used to control the source drive according to the grayscale value of the image to be displayed by the pixel circuit on the data line circuit switch.

The beneficial effects of the present invention are: the present invention can improve the poor display quality caused by insufficient charging when the active matrix organic light-emitting display panel in the prior art displays gray-scale images, and it can be used without affecting the normal image. Improved display quality in case of I/O.

Description of drawings

FIG. 1 is a schematic diagram of a pixel circuit of an active matrix organic light emitting display panel in the prior art.

FIG. 2 is a schematic diagram of an active matrix organic light emitting display panel in the present invention.

FIG. 3 is a schematic diagram of a data line driving circuit in the present invention.

FIG. 4 is a schematic diagram of a gray scale circuit in the present invention.

FIG. 5 is a flowchart of the operation of the gray scale circuit in FIG. 4 .

FIG. 6 is a timing diagram of the active matrix organic light emitting display panel in FIG. 2 in operation.

22 Source Driver 24 Gate Driver

26 Control Circuit 28 Timing Data Control Circuit

30 Gray scale circuit 31 Data line drive circuit

32 Shift register circuit 33 Data latch circuit

34 Digital/Analog Converter 35 Output Buffer

36 Voltage/current conversion circuit I _pre pre-charge current source

110. OLED Organic Light Emitting Diode

120. Cs storage capacitor

500-570 steps

40, 60, 80 Judgment circuit

Vcc, Vss Voltage source

SW _r , SW _g , SW _b switch

47, 67, 87 Line buffers

48, 68, 88 Gray scale counter

49, 69, 89 Switch counter

50, 70, 90 JK flip-flop

41-43, 61-63, 81-83 storage unit

44-46, 64-66, 84-86 Comparator

DL, DL _r , DL _g , DL _b data lines

GL, GL ₁ -GL _n scan line

130, 140, TFT1, TFT2 Thin film transistor

100, Pr ₁ , Pr ₂ , Pr _n , Pg ₁ , Pb ₁ pixel circuit

10, 20 Active Matrix Organic Light Emitting Display Panel

Detailed ways

Please refer to FIG. 2 , which is a schematic diagram of an active matrix organic light emitting display panel 20 in the present invention. The organic light emitting display panel 20 includes data lines DL _r , DL _g , DL _b , scan lines GL ₁ -GL _n , pixel circuits Pr ₁ -Pr _n , Pg ₁ -Pg _n , Pb ₁ -Pb _n , source drivers (source driver) 22, a gate driver (gate driver) 24, and a control circuit 26. Each pixel circuit includes an organic light emitting diode OLED, a storage capacitor Cs, thin film transistors TFT1 and TFT2, and voltage sources Vcc and Vss. The gate of the thin film transistor TFT1 of each pixel circuit is coupled to the corresponding scan line, and the drain thereof is coupled to the corresponding data line DL. The gate of the thin film transistor TFT2 of each pixel circuit is coupled to the source of the corresponding thin film transistor TFT1 , and its drain is coupled to the voltage source Vcc. The storage capacitor Cs of each pixel circuit is coupled between the source of the corresponding thin film transistor TFT1 and the ground potential, and the organic light emitting diode OLED is coupled between the source of the corresponding thin film transistor TFT2 and the voltage source Vss.

The control circuit 26 is coupled to the source driver 22 and the gate driver 24 and includes a timing data control circuit 28 and a gray scale circuit 30 . The timing data control circuit 28 receives the timing signal V _gate and the data signal V _source of the image to be displayed on the active matrix organic light-emitting display panel 20 within a frame period, and generates according to the timing signal V _gate and the data signal V _source The control signals are sent to the gate driver 24 and the source driver 22 so that the active matrix organic light emitting display panel 20 can correctly display images. The gray scale circuit 30 is used to generate switch control signals V _r , V _g , V _b according to the gray scale value of the image to be displayed on the active matrix organic light emitting display panel 20 within one frame period. The operation of the timing data control circuit 28 and the grayscale circuit 30 will be further described in detail later.

The source driver 22 includes a data line driver circuit 31 , a precharge current source I _pre , and switches SW _r , SW _g , SW _b . Please refer to FIG. 3 , which is an enlarged schematic diagram of the data line driving circuit 31 in the present invention. The data line driving circuit 31 includes a shift register circuit (shift register) 32, a data latch circuit (latch circuit) 33, a digital/analog converter (digital to analog converter, DAC) 34, an output buffer (output buffer) 35, and a voltage/current conversion circuit 36. The shift register circuit 32 temporarily stores the digital data of the image to be displayed sent from the sequential data control circuit 28 and performs shift processing. After receiving the digital image data of the entire scanning line, the multiple The digital image data is stored in the data latch circuit 33 . The DAC 34 receives the digital voltage signal output by the data latch circuit 33 and converts the digital voltage signal into an analog voltage signal. The output buffer 35 is used to stabilize the analog voltage signal, and output the received analog voltage signal to the voltage-current conversion circuit 36 to generate driving currents I _r , I _g , and I _b corresponding to the data of the image to be displayed.

Under normal circumstances, the active matrix organic light emitting display panel 20 turns on the thin film transistor TFT1 in the pixel circuit through the gate driver 24 coupled to the scanning lines GL ₁ -GL _n according to the timing signal V _gate transmitted from the control circuit 26, The driving currents I _r , I _g , and I _b corresponding to the data signal V _source of the image to be displayed are transmitted to the storage capacitor Cs in the corresponding pixel circuit through the data line, and the voltage difference generated after the storage capacitor Cs is charged To turn on the thin film transistor TFT2 in the pixel circuit, and control the magnitude of the current flowing through the corresponding organic light emitting diode OLED, so that the pixel circuit can achieve different gray scale display effects.

However, when a pixel circuit displays a low-gray-scale image below a gray-scale reference value, the charging current required by the storage capacitor Cs is very small, and it is not easy to charge the storage capacitor Cs to the required voltage within the operating time. value. At this time, the active matrix organic light emitting display panel 20 of the present invention can firstly charge the pixel circuits that are to display images with low grayscale values through the pre-charging current source Ipre. Assuming that the active matrix organic light-emitting display panel 20 judges (the judging method of the present invention will be further described later) that the pixel circuit Pr ₁ must be precharged, the thin film transistor TFT1 of the pixel circuit Pr ₁ is first turned on by the gate driver 24, and then the The grayscale circuit 30 generates a switch control signal V _r to turn on (short circuit) the switch SW _r , so that the pixel circuit Pr ₁ can be electrically connected to the pre-charging current source I _pre , and the pre-charging current source I _pre can first charge the pixel circuit Pr The storage capacitor Cs of ₁ is precharged, and finally the driving current I _r generated by the data line driving circuit 31 of the source driver 22 corresponding to the image to be displayed by the pixel circuit Pr ₁ will be transmitted to the pixel circuit Pr ₁ through the data line DL _r Storage capacitor Cs. In this way, even if the value of the driving current I _r is small, since the storage capacitor Cs of the pixel circuit Pr ₁ has been pre-charged to a certain level by the pre-charge current source I _pre , the storage capacitor Cs of the pixel circuit Pr ₁ can be easily charged during the operation time. It is charged to the required voltage value, which can effectively improve the image quality of the pixel circuit Pr ₁ when displaying low-grayscale images.

Please refer to FIG. 4 . FIG. 4 is a schematic diagram of the grayscale circuit 30 in the present invention. FIG. 4 further illustrates the precharging method of the active matrix organic light emitting display panel 20 . The grayscale circuit 30 includes judgment circuits 40 , 60 , and 80 . The judging circuits 40, 60, 80 judge whether pre-charging needs to be performed according to the image data signal V _source to be displayed by the active matrix organic light emitting display panel 20 within one frame period, and then generate switch control signals V _r and V _g according to the judging result. , V _b . The judgment circuit 40 includes storage units 41, 42, 43, comparators 44, 45, 46, a line buffer (line buffer) 47, a gray scale counter 48, a switch counter 49, and a JK flip flop (JK flip flop) ) 50; the judging circuit 60 includes storage units 61, 62, 63, comparators 64, 65, 66, a line buffer 67, a grayscale counter 68, a switch counter 69, and a JK flip-flop 70; judging circuit 80 It includes storage units 81 , 82 , 83 , comparators 84 , 85 , 86 , a line buffer 87 , a grayscale counter 88 , a switch counter 89 , and a JK flip-flop 90 . Storage units 41, 61 and 81 respectively store an R gray-scale reference value, a G gray-scale reference value, and a B gray-scale reference value; storage units 42, 62 and 82 respectively store a R gray-scale critical value, a G gray scale critical value, and a B gray scale critical value; storage units 43 , 63 and 83 respectively store an R switch reference value, a G switch reference value, and a B switch reference value. The grayscale reference value and the grayscale threshold value can be set to different values according to the requirements. When the grayscale value of the image to be displayed by a pixel circuit is lower than the grayscale reference value, the image to be displayed by the pixel circuit is defined as low grayscale Image; when the number of pixel circuits displaying low-grayscale images in a scan line exceeds the gray-scale threshold, it means that the pixel circuits of this scan line need to be pre-charged at this time; the switch reference value corresponds to the pixels that need to be scanned for this scan line The time it takes for the circuit to charge.

Please refer to FIG. 5, the flowchart of FIG. 5 illustrates the operation of the grayscale circuit 30 in the present invention, which includes the following steps:

Step 500: Store the data signals of all pixel circuits related to a scanning line to display images into the line buffer;

Step 510: Determine whether the grayscale value of the data signal of a pixel circuit is smaller than a grayscale reference value; if the grayscale value of the data signal of the pixel circuit is smaller than the grayscale reference value, perform step 520; if the grayscale value of the data signal of the pixel circuit is If the scale value is not less than the gray scale reference value, go to step 530;

Step 520: increase a gray-scale count value of a gray-scale counter;

Step 530: Determine whether the gray scale count value is greater than a gray scale critical value; if the gray scale count value is greater than the gray scale critical value, perform step 540; if the gray scale count value is not greater than the gray scale critical value, perform step 570;

Step 540: Generate a switch control signal, and increase a switch count value of a switch counter;

Step 550: Determine whether the switch count value is less than a switch reference value; if the switch count value is less than a switch reference value, perform step 560; if the switch count value is not less than the switch reference value, perform step 570;

Step 560: Outputting the switch control signal; and

Step 570: end.

Taking the scanning line _GL1 as an example, in step 500, the control circuit 26 of the active matrix organic light emitting display panel ₂₀ first stores the R data signal related to the red image in the line according to the data signal of the image to be displayed on the scanning line GL1. The buffer 47 stores the G data signal related to the green image into the line buffer 67 , and stores the B data signal related to the blue image into the line buffer 87 . In step 510, the grayscale circuit 30 judges the relationship between the R data signal stored in the line buffer 47 and the R grayscale reference value stored in the storage unit 41, and judges the G data signal stored in the line buffer 67. The magnitude relationship between the G grayscale reference value stored in the storage unit 61 and the magnitude relationship between the B data signal stored in the line buffer 87 and the B grayscale reference value stored in the storage unit 81 are determined. Taking the R data signal of the scanning line _GL1 as an example, when the R data signal of the scanning line _GL1 is smaller than the R grayscale reference value stored in the storage unit 41, the judgment circuit 40 of the grayscale circuit 30 will increase the grayscale in step 520. If the gray-scale count value of the level counter 48 is obtained, then step 530 is executed; if the R data signal of the scanning line GL ₁ is not less than the R gray-scale reference value, the judging circuit 40 directly executes step 530 . In step 530, the judging circuit 40 judges whether the gray-scale count value of the gray-scale counter 48 is greater than an R gray-scale critical value stored in the storage unit 42; if the gray-scale count value is greater than the R gray-scale critical value, it means that the scanning line The number of pixel circuits that GL ₁ intends to display a low-gray-scale red image is large enough. At this time, the judgment circuit 40 will execute step 540 to generate a switch control signal V _r , and increase the switch count value of the switch counter 49; if the gray-scale count value If it is not greater than the R gray scale critical value, the judging circuit 40 will execute step 570 . Finally in step 550, if the switch count value of the switch counter 49 is less than a R switch reference value stored in the storage unit 43, the judging circuit 40 will output the switch control signal V _r in step 560 to turn on the switch of the source driver 22 SW _r , at this moment, the current source I _pre is electrically connected to the data line DL _r , so that the current source I _pre can provide the current required for precharging the data line DL _r .

Similarly, when the judging circuits 60 and 80 of the grayscale circuit 30 also respectively perform the aforementioned steps for the G data signal and the B data signal of the scanning line _GL1 : when the G data signal of the scanning line _GL1 is smaller than the G grayscale reference value, the grayscale count value of the grayscale counter 68 is greater than a G grayscale critical value stored in the storage unit 62, and the switch count value of the switch counter 69 is smaller than a G switch reference stored in the storage unit 63 value, the judgment circuit 60 will output the switch control signal V _g in step 560 to turn on the switch SW _g of the source driver 22. At this time, the pre-charging current source I _pre will be electrically connected to the data line DL _g , thus pre-charging The current source I _pre can provide the current required for precharging the data line DL _g ; when the B data signal of the scanning line GL ₁ is smaller than the B gray-scale reference value stored in the storage unit 81, the gray-scale count value of the gray-scale counter 88 is greater than When a B gray scale critical value stored in the storage unit 82, and the switch count value of the switch counter 89 is less than a B switch reference value stored in the storage unit 83, the judgment circuit 80 will output the switch control signal V in step 560 _b to turn on the switch SW _b of the source driver 22, at this time the pre-charging current source I _pre will be electrically connected to the data line DL _b , so that the pre-charging current source I _pre can provide the current required for pre-charging the data line DL _b .

Therefore, the present invention can improve the poor display quality caused by insufficient charging when the active matrix organic light emitting display panel in the prior art displays gray scale images.

Please refer to FIG. 6 , which is a timing diagram of the active matrix organic light emitting display panel 20 in operation. In FIG. 6 , the waveform D _in represents the image input signal input to a scan line, and the waveform D _out represents the image output signal of the scan line. When the waveform D _in has a high potential, it means that image data is being input to the data lines DL ₁ -DL _r at this time; and when the waveform D _out has a high potential, it means that the data lines DL ₁ -DL _r are outputting image data at this time . A blanking period Tb ₁ -Tb _m is included between image input/output, and the operation of the gray scale circuit 30 shown in the flow chart of FIG. 5 is carried out during the blanking period. Therefore, the driving method of the present invention does not affect the input/output of normal images, and can improve display quality.

The above specific embodiments are only used to illustrate the present invention, but not to limit the present invention.

Claims (3)

1. the driving method of an active matrix organic LED display is characterized in that, comprises the following step:

(a) judge on the display panel that an image element circuit on the one scan line desires the GTG value of show image and whether be lower than a GTG reference value;

(b) be lower than the GTG reference value if image element circuit is desired the GTG value of show image, and the image element circuit number that the GTG value of desire show image is lower than the GTG reference value on the sweep trace is then imported a pre-charge current to image element circuit greater than a critical value; And

(c) in the input pre-charge current to image element circuit, input with respect to the signal of show image to image element circuit.

2. driving method as claimed in claim 1 is characterized in that other comprises:

Calculate in a picture, calculate the number of times of sweep trace desire charging.

3. driving method as claimed in claim 1 is characterized in that, imports a pre-charge current to image element circuit to be: couple the current source of image element circuit and one source pole driving circuit, to import a pre-charge current to image element circuit.

Images