CN100378789C - Active Display and Pixel Driving Circuit - Google Patents

Abstract

A pixel driving circuit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, a switch circuit, a first voltage source, a second voltage source and a light emitting component. The source of the first transistor is electrically connected to the drain of the second transistor. A gate of the third transistor is electrically connected to the gate of the first transistor. The drain of the fourth transistor is electrically connected to the source of the third transistor, and the gate is electrically connected to the gate and the drain of the second transistor. The first voltage source is coupled to the sources of the second transistor and the fourth transistor. The light emitting component is coupled to the drain of the first transistor by a first electrode and is coupled to the second voltage source by a second electrode. The switch circuit is electrically connected to the drain and the gate of the third transistor.

Description

Active Display and Pixel Driving Circuit

technical field

The present invention relates to a pixel driving circuit, in particular to a pixel driving circuit capable of avoiding kink effect.

Background technique

An active organic light emitting display (AMOLED) uses organic light emitting diodes as light emitting components, and thin film transistors as switching components or driving components of the organic light emitting diodes. Organic light-emitting diode is a current control device, usually connected to the drain of the thin film transistor, so its brightness is closely related to the drain current. However, the drain current is often affected by threshold voltage shift and kink effect of thin film transistors.

Ideally, the drain current (I _D ) and the drain-source voltage (V _DS ) of a thin film transistor should be independent. But when the voltage between the drain and the source is greater than the pinched-off voltage of the channel, a depletion region will be formed at the interface between the channel and the drain so that the effective channel length is smaller than the actual channel length. When the voltage between the drain and the source is larger, the effective channel length is smaller, and because the effective channel length is inversely proportional to the drain current, the larger the voltage between the drain and the source is, the larger the drain current is. This phenomenon is called the kink effect, also known as the channel length modulation effect. The effect of the kink effect on the pixels inside the display is explained below.

Please refer to FIG. 1A , which is a pixel driving circuit of a known active organic light emitting display. The OLED 101 has a cathode connected to a reference voltage source Vss, and an anode connected to the drain of a P-channel TFT 102 . The source of the transistor 102 is connected to a display voltage source V _DD , and the gate is connected to the gate of another P-channel thin film transistor 103 . The display voltage source V _DD and the sources of the two transistors 102 and 103 are simultaneously connected to one end of a capacitor 104 , and the other end of the capacitor 104 is simultaneously connected to the gates of the transistor 102 and the transistor 103 . The gate and drain of the transistor 103 are respectively connected to the drain and source of an N-channel thin film transistor 105 . The drain of the transistor 103 is further connected to the drain of an N-channel thin film transistor 106 , and the source of the transistor 106 is connected to a data line 107 . The transistor 105 and the transistor 106 are used as switch elements, and their gates are respectively connected to the scan line 108 and the scan line 109 .

When the transistor 105 and the transistor 106 are turned on, the transistor 102 and the transistor 103 actually form a current mirror. The current I _OLED flowing through the transistor 102 and the OLED 101 is related to the data current I _DATA flowing through the transistor 103 . If the properties of the transistor 102 and the transistor 103 are similar, and the threshold voltage V _tp1 of the transistor 103 is equal to the threshold voltage V _tp2 of the transistor 102, the related parameter μ _p C _ox of the hole mobility is the same, and the gate/source of the transistor 103 The voltage V _GS1 between the gate and the source of the transistor 102 is equal to the voltage V _GS2 between the gate and the source of the transistor 102, then there is the relationship of the following formula (1):

$\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DATA</span>}}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

If the channel aspect ratio (W/L) of the transistor 102 and the transistor 103 are the same, ideally I _OLED =I _DATA .

When the transistor 105 and the transistor 106 are turned on, their equivalent circuits are shown in FIG. 1B . After the transistor 105 is turned on, the gate and the drain of the transistor 103 are short-circuited, that is, V _DS1 =V _GS1 .

Considering the kink effect, a kink-related factor λ is multiplied by the operating voltage V _DS . Assuming that the properties of the transistor 102 and the transistor 103 are similar, V _tp1 =V _tp2 and μ _p C _ox are the same. Also V _GS1 =V _GS2 , V _DS1 =V _GS1 , then the relationship between I _OLED and I _DATA is as follows:

$\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DATA</span>}}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DS</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; GS</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Therefore, even if the channel aspect ratios of the transistor 102 and the transistor 103 are the same, but V _DS2 ≠V _GS1 , then I _OLED ≠I _DATA .

Under the condition that the W/L of the transistor 102 and the transistor 103 are both 6/6, the circuit of FIG. 1B can be simulated to obtain the result of FIG. 1C , the horizontal axis is time (sec); the vertical axis is the current value (A). The broken line 110 is the current flowing through the transistor 103 , which is equivalent to the current I _DATA provided by the data line 107 ; the broken line 111 is the current I _OLED flowing through the OLED 101 . Although it is a current mirror circuit, I _OLED is still different from I _DATA , and it is indeed affected by the kink effect.

Please refer to Figure 1D, which is an I _D -V _DS curve of a low-temperature polysilicon (LTPS) P-channel metal-oxide-semiconductor field-effect transistor (PMOS), and the fraction in the icon represents W/L. Ideally, the ends of each curve should be kept horizontal, but the ends of the curves in the figure are bent upwards, which means that the p-channel mosfets have a kink effect, which increases the drain current. In addition, the shorter the physical channel length of the P-channel Mosfet, the greater the bending degree of the curve, which means the more obvious the kink effect. Incidentally, a similar phenomenon occurs in N-channel MOSFETs.

In order to reduce the kink effect of the transistor, it is usually necessary to increase the voltage of the display voltage source V _DD . As shown in Figure 1D, taking the curve of W/L=6/6 as an example, when the original operating voltage V _DS is above 2V, the transistors are all operating in the saturation region, but the slope of the curve between 2V and 4V is not zero, that is, it is affected by The influence of the kink effect. The slope of the curve between 4V and 6V is relatively close to zero, that is, the area where it is easier to control the magnitude of the transistor current. Therefore, the operating voltage V _DS of the thin film transistor needs to be increased from 2-4V to 4-6V, that is, the display voltage V _DD needs to be increased a little. But even after increasing the display voltage V _DD in the known structure, I _OLED and I _DATA are still inconsistent.

Contents of the invention

The purpose of the present invention is to provide a pixel driving circuit, which can not only avoid the kink effect, but also make the current passing through the light-emitting component consistent with the data current.

The pixel driving circuit of the present invention includes a current mirror, a switch circuit, a first voltage source, a second voltage source and a light-emitting component. The current mirror has four transistors, the source of the first transistor being electrically connected to the drain of the second transistor. The gate of the third transistor is electrically connected to the gate of the first transistor. The drain of the fourth transistor is electrically connected to the source of the third transistor, and the gate is electrically connected to the gate and drain of the second transistor. The first voltage source is coupled to sources of the second transistor and the fourth transistor. The light-emitting component has two electrodes, and a first electrode is coupled to the drain of the first transistor, and a second electrode is coupled to the second voltage source. The switch circuit is electrically connected to the drain and the gate of the third transistor.

The above switching circuit uses two scan lines and two transistors to eliminate the influence of the feed-through voltage. The light-emitting component can use organic light-emitting diodes. The voltage difference between the first voltage source and the second voltage source forms the working voltage of the pixel unit. The transistors can be amorphous silicon thin film transistors or metal oxide semiconductor field effect transistors, and are not limited to N-channel or P-channel transistors. In principle, the ratio of the channel aspect ratio of the first transistor to the channel aspect ratio of the third transistor is approximately equal to the ratio of the channel aspect ratio of the second transistor to the channel aspect ratio of the fourth transistor.

Compared with the known technology, the present invention can solve the phenomenon that the threshold voltage drift of the thin film transistor causes the panel to produce linear uneven brightness, and can compensate for the so-called channel modulation effect. In this way, the control of the current drive can be more accurate, and the power consumption of the panel can also be reduced.

Description of drawings

FIG. 1A is a pixel driving circuit of a known active organic light emitting display;

FIG. 1B is an equivalent circuit when a switching transistor of a known pixel driving circuit is turned on;

Fig. 1 C is the electric current-time curve of simulation Fig. 1 B circuit;

Fig. 1D is the I _D -V _DS curve of the P-channel metal-oxide-semiconductor field-effect transistor of the low-temperature polysilicon;

FIG. 2A is a pixel driving circuit according to the first embodiment of the present invention;

Fig. 2B is the current-time curve of the circuit of simulation Fig. 2A;

Fig. 3A is the equivalent circuit when the two transistors of the switch circuit in Fig. 2A are turned on

Fig. 3B is the equivalent circuit when the two transistors of the switch circuit in Fig. 2A are turned off;

FIG. 3C is a timing diagram of two scan lines of the switch circuit in FIG. 2A;

FIG. 4 is a pixel driving circuit according to a second embodiment of the present invention;

FIG. 5 is a pixel driving circuit according to a third embodiment of the present invention;

FIG. 6A organic electroluminescence display according to the present invention; and

FIG. 6B is an organic electroluminescence display according to another embodiment of the present invention.

Explanation of main component symbols

101 organic light-emitting diodes 26 light-emitting components

102 P-channel thin film transistor 27 Data line

103 P channel thin film transistor 28 Capacitance

104 capacitors 30 pixel drive circuit

105 N-channel thin film transistor 40 pixel drive circuit

106 N-channel thin film transistor 41 N-channel thin film transistor

107 data line 42 N-channel thin film transistor

108 scanning lines 43 N-channel thin film transistors

109 scanning lines 44 N-channel thin film transistors

20 pixel drive circuit 45 switch circuit

21 P-channel thin film transistor 451 P-channel thin film transistor

22 P-channel thin film transistor 452 P-channel thin film transistor

23 P-channel thin film transistor 50 Organic electroluminescence display

24 P-channel thin film transistor 51 Scanning drive unit

25 switch circuit 52 data drive unit

25a switch circuit 53 scan line

251 N-channel thin film transistor 54 Data line

252 N-channel thin film transistors 55 pixel units

253 scanning lines 60 organic electroluminescent display

253a scan line 61 scan line

254 scanning lines 62 data lines

63 pixel units

Detailed ways

Cooperate icon now and describe in detail the present invention " active display and pixel drive circuit thereof ", and enumerate preferred embodiment and explain as follows:

Please refer to FIG. 2A , a pixel driving circuit according to the present invention. The pixel driving circuit 20 includes at least four transistors 21 , 22 , 23 and 24 , a display voltage source V _DD and a reference voltage source V _SS , a light emitting element 26 and a switch circuit 25 . The transistors 21 , 22 , 23 and 24 all have a gate, a source, a drain and a channel, which are located between their source S and drain D, and together form a current mirror.

The current mirror is coupled to a display voltage source V _DD through the sources of transistors 22 and 24 to obtain a high voltage level. Then, the drain of the transistor 21 is coupled to an electrode of the light-emitting component 26 , and the drain and gate of the transistor 23 are connected to the switch circuit 25 . The other electrode of the light emitting element 26 is coupled to the reference voltage source V _SS to obtain a low voltage level. The voltage difference between the display voltage source V _DD and the reference voltage source V _SS forms the working voltage of the pixel unit. In this way, the data current I _DATA passing through the switch circuit 25 can pass through the current mirror to avoid the influence of the kink effect.

The current mirror structure of the present invention is explained as follows. The source of the first transistor 21 is electrically connected to the drain of the second transistor 22 . The gate of the third transistor 23 is electrically connected to the gate of the first transistor 21 . The drain of the fourth transistor 24 is electrically connected to the source of the third transistor 23 , and the gate of the fourth transistor 24 is electrically connected to the gate and drain of the second transistor 21 . Taking FIG. 2A as an example, the transistors 21 , 22 , 23 and 24 are all P-channel thin film transistors, and the reference voltage source V _SS can be grounded.

In order to achieve the purpose of the present invention, the switch circuit 25 uses two scanning lines to eliminate the influence of the feed-through voltage, because the current change caused by the feed-through voltage is an uncertain factor. The switch circuit 25 is composed of two transistors 251 and 252 and two scan lines 253 and 254 . The transistors 251 and 252 also have a gate, a source and a drain. The gate of the transistor 251 is coupled to the scan line 253 , the source is coupled to a data line 27 , and the drain is electrically connected to the drain of the transistor 23 . The gate of the transistor 252 is coupled to the scan line 254 , the source is electrically connected to the drain of the transistor 251 , and the drain is coupled to the gates of the transistor 21 and the transistor 23 .

The current-time curve in FIG. 2B can be obtained by simulating the circuit in FIG. 2A , the horizontal axis is time (sec); the vertical axis is current value (A). FIG. 2B shows that the current I _DATA provided by the data line 27 overlaps with the time-varying curve of the current I _OLED flowing through the light emitting element 26 . The simulated result is I _DATA =I _OLED , indicating that the current of the current mirror in the present invention is hardly affected by the kink effect.

Please refer to FIG. 3A , which is an equivalent circuit when the transistor 251 and the transistor 252 in FIG. 2A are turned on. When the transistor 251 and the transistor 252 are turned on by the scan line 253 and the scan line 254, the current I _OLED flowing through the light-emitting component 26 and the data current I _DATA have the following relationship (3):

$\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DATA</span>}}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; GS</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;V</span>}}_{\mathrm{<span\; class="notranslate">\; DS</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In formula (3), (W/L) ₂ and (W/L) ₄ represent the channel aspect ratios of transistors 22 and 24 respectively. V _GS2 is the gate/source voltage of transistor 22 . V _DS4 is the drain/source voltage of transistor 24 .

On the loop formed by transistors 21, 22, 23 and 24, the voltage has the relationship of the following formula (4):

V _GS2 = V _DS4 +V _GS3 -V _GS1 (4)

In formula (4), V _GS3 is the gate/source voltage of the transistor 23 . V _GS1 is the gate/source voltage of the transistor 21 . According to formulas (3) and (4), if the condition of formula (5) holds true,

$\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Then formula (6) can be obtained. In the above formula (5), (W/L) ₁ and (W/L) ₃ represent the channel aspect ratios of transistors 21 and 23 respectively,

V _GS3 = V _GS1 (6)

Then deduce formula (7), (8)

V _GS2 = V _DS4 (7)

$\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DATA</span>}}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

It can be deduced from the above formula that when the ratio of the channel aspect ratio of the transistor 21 to the channel aspect ratio of the transistor 23 is approximately equal to the ratio of the channel aspect ratio of the transistor 22 to the channel aspect ratio of the transistor 24, the flow The current I _OLED passing through the light emitting element 26 is equal to the data current I _DATA . Based on this principle, the possible approaches are as follows:

1. The channel aspect ratio of the transistor 21 is the same as that of the third transistor 23 , and the channel aspect ratio of the transistor 22 is the same as that of the transistor 24 .

2. The transistor 21 , the transistor 22 , the transistor 23 and the transistor 24 all adopt the same channel aspect ratio.

3. The transistor 21 , the transistor 22 , the transistor 23 and the transistor 24 all use the same channel length and width.

The above principles are also applicable to the following embodiments.

Please refer to FIG. 3B , which is an equivalent circuit when the transistor 251 and the transistor 252 in FIG. 2A are turned off.

A capacitor 28 is connected across the source and gate of the transistor 21, and when the transistor 251 and the transistor 252 are turned off by the scan line 253 and the scan line 254, regardless of the influence of the feed-through voltage, the voltage difference stored by the capacitor 28 is still equal to V _GS1 , so I _DATA -I _OLED is still established.

Please refer to FIG. 3C , which is a timing diagram of the scan lines 253 and 254 in FIG. 2A . Curve A represents the timing of the scan line 253 , and curve B represents the timing of the scan line 254 . The switch circuit 25 controls the on-off sequence of the two transistors 251 and 252 through the two scanning lines 253 and 254 respectively. When the pixel is active, the transistor 252 is turned off first, and then the transistor 251 is turned off; or both are turned off at the same time, which can reduce the feed-through voltage effect.

Please refer to FIG. 4 , a pixel driving circuit 30 according to a second embodiment of the present invention. The switch circuit 25 in FIG. 2A is changed to the switch circuit 25a in FIG. 4 so as to turn on or off the transistors 251 and 252 at the same time. In this embodiment, the drain of the transistor 251 and the source of the transistor 252 are both electrically connected to the drain of the transistor 23 . The gates of the transistor 251 and the transistor 252 are coupled to the same scan line 253a. The source of the transistor 251 is coupled to the data line 27 , and the drain of the transistor 252 is coupled to the gates of the transistor 21 and the transistor 23 .

Please refer to FIG. 5 , a pixel driving circuit 40 according to a third embodiment of the present invention. The difference between this embodiment and FIG. 2A is explained as follows. The current mirror is composed of N-channel thin film transistors 41 , 42 , 43 and 44 . One electrode of the light-emitting component 26 is connected to the drain of the transistor 41 , and the other electrode is connected to the display voltage source V _DD . The sources of the transistor 42 and the transistor 44 are connected to the reference voltage source V _SS or ground. The two transistors 451 and 452 of the switch circuit 45 are both P-channel thin film transistors, and are controlled by two scanning lines respectively.

To sum up, regardless of whether the four transistors of the current mirror are N-channel TFTs or P-channel TFTs, the transistors included in the switch circuit are not limited to N-channel TFTs or P-channel TFTs. In all embodiments, the gate and the source of the transistor connected to the light-emitting component are respectively connected to two ends of the capacitor, such as the transistor 21 in FIG. 2A and FIG. 4 , and the transistor 41 in FIG. 5 . The above-mentioned light-emitting component can be an organic light-emitting diode. All transistors can be amorphous silicon thin film transistors or metal oxide semiconductor field effect transistors.

Please refer to FIG. 6A, which is an organic electroluminescence display according to the present invention. The organic electroluminescent display 50 has a scan driving unit 51 connected to multiple scan lines 53 , and a data drive unit 52 connected to multiple data lines 54 . Every two scanning lines 53 and one data line 54 determine a pixel unit 55 , and the driving circuit of the pixel unit 55 may be the pixel driving circuit shown in FIG. 2A and FIG. 5 .

Referring to FIG. 6B , in the organic electroluminescent display 60 , each scan line 61 and one data line 62 define a pixel unit 63 . Each pixel unit 63 has two switching transistors, so it has two connection points with the scan line 61 , such as the pixel driving circuit 30 shown in FIG. 4 .

When the present invention compares with known technology mutually, possesses following characteristic and advantage:

1. Solve the phenomenon of linear uneven brightness of the panel due to the threshold voltage drift of the thin film transistor caused by the excimer laser heat treatment process in the low temperature polysilicon (LTPS).

2. Compensating the so-called channel length modulation will make the control of current drive more accurate.

3. The display voltage can be lowered to the voltage position where the thin film transistor operates in the saturation region, and does not need to be raised to a voltage range where the degree of kink effect is low.

4. Reducing the voltage between the display voltage and the reference voltage can reduce the power consumption on the panel.

The above detailed description is specific to the preferred embodiments of the present invention, but the above embodiments are not intended to limit the scope of the present invention, and all equivalent implementations or changes that do not depart from the technical concept of the present invention should be included in the scope of the present invention middle.

Claims (18)

1. pixel-driving circuit comprises:

One the first transistor has a grid, one source pole, a drain electrode and a raceway groove, and it is between this source electrode and this drain electrode;

One transistor seconds has a grid, one source pole, a drain electrode and a raceway groove, and it is between this source electrode and this drain electrode, and the drain electrode of this transistor seconds is electrically connected to the source electrode of this first transistor;

One the 3rd transistor has a grid, one source pole, a drain electrode and a raceway groove, and it is between this source electrode and this drain electrode, and the 3rd transistorized grid is electrically connected to the grid of this first transistor;

One the 4th transistor, have a grid, one source pole, a drain electrode and a raceway groove, it is between this source electrode and this drain electrode, and the 4th transistor drain is electrically connected to the 3rd transistorized source electrode, and the 4th transistorized grid is electrically connected to the grid and the drain electrode of this transistor seconds;

One luminescence component has one first electrode and one second electrode, and this first electrode is couple to the drain electrode of this first transistor;

One first voltage source is couple to this transistor seconds and the 4th transistorized source electrode;

One second voltage source is couple to second electrode of this luminescence component; And

One on-off circuit is electrically connected to the 3rd transistor drain and grid.

2. pixel-driving circuit as claimed in claim 1, wherein this first transistor, this transistor seconds, the 3rd transistor and the 4th transistor are the P channel thin-film transistor, and the current potential of this first voltage source is higher than the current potential of this second voltage source.

3. pixel-driving circuit as claimed in claim 2, wherein this second voltage source ground connection.

4. pixel-driving circuit as claimed in claim 1, wherein this first transistor, this transistor seconds, the 3rd transistor and the 4th transistor are the N channel thin-film transistor, and the current potential of this second voltage source is higher than the current potential of this first voltage source.

5. pixel-driving circuit as claimed in claim 4, wherein this first voltage source ground connection.

6. pixel-driving circuit as claimed in claim 1, wherein this on-off circuit comprises:

One the 5th transistor has a grid, one source pole and a drain electrode, and the 5th transistorized grid is couple to one first sweep trace, and the 5th transistor drain is electrically connected to the 3rd transistor drain, and the 5th transistorized source electrode is couple to a data line; And

One the 6th transistor, have a grid, one source pole and a drain electrode, the 6th transistorized grid is couple to one second sweep trace, the 6th transistorized source electrode is electrically connected to the 5th transistor drain, and the 6th transistor drain is couple to this first transistor and the 3rd transistorized grid.

7. pixel-driving circuit as claimed in claim 6, wherein the 5th transistor and the 6th transistor are the N channel thin-film transistor.

8. pixel-driving circuit as claimed in claim 6, wherein the 5th transistor and the 6th transistor are the P channel thin-film transistor.

9. pixel-driving circuit as claimed in claim 1, wherein this on-off circuit comprises one the 5th transistor AND gate 1 the 6th transistor, these transistors have a grid, one source pole and a drain electrode respectively, the 5th transistor drain is electrically connected with the 6th transistorized source electrode and the 3rd transistor drain, the 5th transistor AND gate the 6th transistorized grid is couple to the one scan line, the 5th transistorized source electrode is couple to a data line, and the 6th transistor drain is couple to this first transistor and the 3rd transistorized grid.

10. pixel-driving circuit as claimed in claim 9, wherein the 5th transistor and the 6th transistor are the N channel thin-film transistor.

11. pixel-driving circuit as claimed in claim 9, wherein the 5th transistor and the 6th transistor are the P channel thin-film transistor.

12. pixel-driving circuit as claimed in claim 1 also comprises an electric capacity, the two ends of this electric capacity are connected respectively between the grid and source electrode of this first transistor.

13. pixel-driving circuit as claimed in claim 1, wherein the ratio of the raceway groove length breadth ratio of this first transistor and the 3rd transistorized raceway groove length breadth ratio is substantially equal to the ratio of the raceway groove length breadth ratio and the 4th transistorized raceway groove length breadth ratio of this transistor seconds.

14. pixel-driving circuit as claimed in claim 1, wherein the raceway groove length breadth ratio of this first transistor is same as the 3rd transistorized raceway groove length breadth ratio, and the raceway groove length breadth ratio of this transistor seconds is same as the 4th transistorized raceway groove length breadth ratio.

15. pixel-driving circuit as claimed in claim 1, wherein this first transistor, this transistor seconds, the 3rd transistor and the 4th transistor have identical raceway groove length breadth ratio.

16. pixel-driving circuit as claimed in claim 1, wherein this first transistor, this transistor seconds, the 3rd transistor and the 4th transistor have identical channel length and width.

17. pixel-driving circuit as claimed in claim 1, wherein this luminescence component is an Organic Light Emitting Diode.

18. a display of organic electroluminescence comprises pixel-driving circuit as claimed in claim 1.

Images