Embodiment
Known image element structure has the problem of high current stress, shortens the life-span of image element structure easily.
Review, embodiments of the invention provide multiple image element structure, can improve known problem.
First kind of image element structure:
With critical voltage electric capacity between first end and gate of driving transistors, can strengthen the critical voltage of driving transistors.Can solve driving transistors because of the factors such as difference, long-time operation or environment temperature on the processing procedure, and make its operating characteristic difference to some extent, and then cause its critical voltage (ThresholdVoltage) variation.Thus, the electric current of driving transistors output then is not subject to critical voltage influences.
2. from then on the disturbing signal that amplitude equates about in the of is imported in the outside of image element structure, and disturbing signal can make the electric current (voltage) by OLED do disturbance in a fixed value by this.Therefore,, can improve because of driving transistors must continue to provide big electric current to OLED, and be in high current stress (highcurrentstress) the deterioration problem that causes, can prolong transistorized serviceable life if be used in white picture for a long time when showing.In addition, because human eye has the persistence of vision phenomenon, therefore as long as the frequency of disturbing signal is higher than the frequency of human eye institute energy identification, the display brightness of picture element almost can present a fixed value.
Second kind of image element structure:
1. use the method for shunting (SharingCurrent), can improve when the white picture of long-time demonstration, driving transistors must continue to provide big electric current to OLED, and is in high current stress (highcurrentstress) the deterioration problem that causes, and can prolong the serviceable life of TFT.
2. utilize this image element structure, the operating voltage of driving transistors is reduced.Therefore can select withstand voltage lower driving transistors for use, reduce cost.Simultaneously also can reduce power consumption.
(a) provide data signals to driving transistors, its voltage can be reduced to former
(b) in like manner, when utilizing disturbing signal that this image element structure is carried out disturbance, the voltage of disturbing signal also can be reduced to former
Elaborate embodiments of the invention below with reference to the accompanying drawings, accompanying drawing is for example understood example embodiment of the present invention, wherein same the or similar step of same numeral indication.
First embodiment
(1) image element structure explanation
Fig. 2 is the synoptic diagram according to a kind of image element structure of the first embodiment of the present invention.Please refer to Fig. 2, in the present embodiment, image element structure has used the framework of 4T2C.Image element structure 10 comprises storage capacitors Ccs, critical voltage capacitor C th, data switch transistor P1, disturbance switching transistor P2, display switch transistor P3, driving transistors P4 and OLEDD1.In the present embodiment, data switch transistor P1 is that example describes with the N channel transistor, and disturbance switching transistor P2, display switch transistor P3 and driving transistors P4 are that example describes with the P channel transistor, but the present invention is not limited to this.
The gate of data switch transistor P1 couples sweep trace GL, can receive the scanning signal.First end of data switch transistor P1 couples data line DL, can receive data signals.Second end of data switch transistor P1 couples first end of storage capacitors Ccs and second end of disturbance switching transistor P2.First end of disturbance switching transistor P2 can receive disturbing signal CSL.The gate of disturbance switching transistor P2 couples sweep trace GL.
Second end of storage capacitors Ccs couples first end of critical voltage capacitor C th and the gate of driving transistors P4.First end of driving transistors P4 couples second end of deciding voltage Vdd, critical voltage capacitor C th.Second end of driving transistors P4 couples first end of display switch transistor P3.The gate of display switch transistor P3 receives and shows controlling signal DCL.Second end of display switch transistor P3 couples the anode of OLEDD1.The negative electrode of OLEDD1 couples earth terminal.
In the present embodiment, data switch transistor P1, disturbance switching transistor P2 and display switch transistor P3 can be used as the switch use.Driving transistors P4 then is used for driving OLED D1.
In more detail, the data switching transistor P1 scanning signal that can provide according to sweep trace GL and first end that the data signals of data line DL is passed to storage capacitors Ccs is used in conducting.Disturbance switching transistor P2 can cooperate the operation of data switch transistor P1, the disturbing signal CSL of outside input is passed to first end of storage capacitors Ccs.When data switching transistor P1 ends, then conducting of disturbance switching transistor P2; Otherwise when data switching transistor P1 conducting, disturbance switching transistor P2 then ends.
Please note, in the present embodiment, because data switch transistor P1 and disturbance switching transistor P2 are respectively N channel transistor and P channel transistor, so the gate of disturbance switching transistor P2 can couple scanning and interrogate GL, and is shared with the one scan signal with data switch transistor P1.Thus, the then operation that need not additionally provide controlling signal to control disturbance switching transistor P2, but the present invention is not limited to this.In other embodiments, also can provide controlling signal to control the operation of disturbance switching transistor P2 in addition.
Driving transistors P4 can be according to the voltage of G end points driving OLED D1.Display switch transistor P3 can determine whether conducting according to showing controlling signal DCL.Whether show that controlling signal DCL inputs to the gate of display switch transistor P3, can be used as control OLEDD1 can be by the switch of electric current.When display switch transistor P3 ended, OLEDD1 can be not shinny; When display switch transistor P3 conducting, OLEDD1 can be controlled by driving transistors P4 and the brightness of sending corresponding GTG.
On the other hand, but the main critical voltage of storage drive transistor P4 of critical voltage capacitor C th.But storage capacitors Ccs is storage data line data signals that DL provides mainly.In addition, be noted that, first end of storage capacitors (C end points) more is connected with second end of disturbance switching transistor P2, the external disturbing signal CSL of first end of disturbance switching transistor P2, mainly be for data signals during a picture frame, become the data signals that has disturbing signal CSL.Disturbing signal CSL to adjust the output current of driving transistors P4, makes OLEDD1 send the brightness that will show by the gate that storage capacitors Ccs is coupled to driving transistors P4.
(2), picture element driving method
(1), the electric current by OLEDD1
:
In the above-mentioned formula (1-1),
Be oxide layer electric capacity (OxideCapacitance).
Be electron drift rate (ElectronMobility).W is channel width (ChannelWidth).L is passage length (ChannelLength).
Electric current for the driving transistors P4 that flows through.Wherein
Pressure reduction for end points S and end points G.
Critical voltage for driving transistors P4.The present embodiment hypothesis
,
, W and L be fixed value.Therefore can get following formula (1-2), wherein K is a constant.
Then, can obtain following formula (1-3) by formula (1-1).
In addition, end points S is connected to and decides voltage Vdd, and therefore the voltage of end points S can get following formula (1-4), wherein with to decide voltage Vdd identical
Voltage for end points S.
(1-4)
With formula (1-4) substitution formula (1-3), can get following formula (1-5), wherein
Voltage for end points G.
(2), critical voltage stores:
Fig. 3 is the synoptic diagram according to a kind of disturbing signal of the first embodiment of the present invention.Fig. 4 is the synoptic diagram of a kind of mode of operation of Fig. 2.Please merge with reference to Fig. 3 and Fig. 4, in the present embodiment, disturbing signal CSL does the identical disturbance (± Δ) of amplitude up and down with the ground voltage position that is as the criterion.In positive period, the voltage of disturbing signal CSL
Represent it with Vcsh; At negative cycle, the voltage of disturbing signal CSL is represented it with Vcsl, as following formula (1-6).
The dotted line representation switch is a cut-off state among Fig. 4, that is this moment, disturbance switching transistor P2 and display switch transistor P3 were cut-off state, and data switching transistor P1 is a conducting state.When
Be charged to
The time, driving transistors P4 can by (because
).This moment end points C voltage and the voltage of the data signals that provided of data line DL
Identical, as following formula (1-7).
The voltage of C end points:
(1-7)
Hold above-mentionedly, the voltage of end points G is shown in following formula (1-8).The cross-pressure of storage capacitors Ccs
Shown in following formula (1-9).
(3), disturbing signal:
Fig. 5 is the synoptic diagram of the another kind of mode of operation of Fig. 2.Among Fig. 5, the dotted line representation switch is a cut-off state, that is this moment, data switch transistor P1 was a cut-off state, and disturbance switching transistor P2 and display switch transistor P3 are conducting state.
As disturbing signal CSL during at negative cycle, can obtain following formula (1-10), this moment end points C voltage Vc such as following formula (1-11).
The potential change amount of end points C
As following formula (1-12).The potential change amount of end points G
As following formula (1-13).
Then can by following formula (1-14) push away the voltage of end points G, and by following formula (1-15) push away the electric current of the OLEDD1 that flows through.
In like manner can analogize, as disturbing signal CSL during in positive period, in the formula (1-15)
Can by
Replace, as following formula (1-15 ').
If definition
Suppose
Become through disturbance
Situation under, the electric current of the OLEDD1 that flows through is then for following formula (1-16).
Suppose
Become through disturbance
Situation under, in the formula (1-16)
Can by
Replace, as following formula (1-16 ').
(3), picture element wave mode design
Fig. 6 is the synoptic diagram according to a kind of drive waveforms of the first embodiment of the present invention.Fig. 7 is the process flow diagram according to the driving method of a kind of image element structure of the first embodiment of the present invention.Please merge with reference to Fig. 6 and Fig. 7.
Among Fig. 6, whether the scanning signal may command of sweep trace GL writes storage capacitors Ccs with the data signals of data line DL.Whether the output current that shows controlling signal DCL may command driving transistors P4 flows into OLEDD1.Disturbing signal CSL is the disturbing signal of the outside input of picture element, and this signal is with no-voltage position standard, the periodic perturbation of work ± Δ.
Can make driving transistors P4 produce the voltage signal of electric current output.T1 is that critical voltage stores and data write during this time.T2 is the data disturbance during this time.
In Fig. 7, whether data switching transistor P1 can determine conducting (step S701) according to the scanning signal.When data switch transistor P1 conducting, the data signals of data line DL can be passed to first end of storage capacitors Ccs, uses through driving transistors P4 and comes driving OLED D1(step S702), as during T1.When data switch transistor P1 by the time, see through disturbance switching transistor P2, disturbing signal CSL can be passed to first end (step S703) of storage capacitors Ccs, as during T2.
Note that when disturbing signal CSL carries out periodic disturbance that the electric current of the driving transistors P4 that flows through and the electric current of the OLEDD1 that flows through also can periodic thereupon disturbances.This practice can effectively be improved the situation of known high current stress, improves the situation of assembly deterioration, and can prolong the life-span of image element structure.Moreover, the frequency of disturbing signal CSL be higher than human eye can identification frequency the time, the brightness that human eye still can send OLEDD1 is to be a fixed value, and the situation that does not have a flicker takes place.
What deserves to be mentioned is, though image element structure and driving method thereof have been depicted a possible kenel in the foregoing description, usually know that the knowledgeable should know but have in the affiliated technical field, each manufacturer is all different for the design of image element structure and driving method thereof, and therefore application of the present invention is when being not restricted to the possible kenel of this kind.In other words, so long as when stopping to provide data signals, provide disturbing signal, be to have met spiritual place of the present invention just to image element structure to image element structure.Below know that the knowledgeable can further understand spirit of the present invention for several embodiment usually so that this area has again, and implement the present invention.
Second embodiment
(1) image element structure explanation
Fig. 8 is the synoptic diagram according to a kind of image element structure of the first embodiment of the present invention.Fig. 9 is the synoptic diagram of a kind of mode of operation of Fig. 8.Figure 10 is the synoptic diagram of the another kind of mode of operation of Fig. 8.Figure 11 is the synoptic diagram according to a kind of disturbing signal of the first embodiment of the present invention.Please merge with reference to Fig. 8~Figure 11.The image element structure 11 of Fig. 8 is similar with the image element structure of Fig. 2.Difference is that image element structure 11 more comprises shunting driving transistors P6 and diverting switch transistor P5.Image element structure 11 has used dividing technology, is the image element structure of 6T2C.
First end of shunting driving transistors P6 couples decides voltage Vdd.Second end of shunting driving transistors P6 couples second end of driving transistors P4.Diverting switch transistor P5 has first end, second end and gate.First end of diverting switch transistor P5 couples the gate of shunting driving transistors P6.Second end of diverting switch transistor P5 couples the gate of driving transistors P4.The gate of diverting switch transistor P5 can receive and show controlling signal DCL.In the present embodiment, shunting driving transistors P6 and driving transistors P4 are all the P channel transistor, and diverting switch transistor P5 and display switch transistor P3 are all the P channel transistor.
The function of the function of diverting switch transistor P5 and display switch transistor P3 is similar, can be used as switch and uses.The function of shunting driving transistors P6 and the function of driving transistors P4 are similar, can be used to driving OLED D1.When display switch transistor P3 conducting, also conducting thereupon of diverting switch transistor P5; Otherwise when display switch transistor P3 ended, diverting switch transistor P5 also can end thereupon.It should be noted that, when display switch transistor P3 and diverting switch transistor P5 conducting, the gate of shunting driving transistors P6 can obtain identical haply voltage with the gate of driving transistors P4, makes shunting driving transistors P6 have identical mode of operation with driving transistors P4.The electric current that deciding voltage Vdd provides can see through shunting driving transistors P6 and driving transistors P4 respectively and flow to OLEDD1.In other words, shunting driving transistors P6 has the shunting function, can share the electric current of the driving transistors P4 that flows through.
Image element structure 11 not only have with Fig. 2 in the similar function of image element structure 10, and the operating voltage of driving transistors P4, shunting driving transistors P6 is reduced.Driving transistors P4 and shunting driving transistors P6 can select for use withstand voltage low transistor to implement, and also can reduce power consumption simultaneously.Below provide the formula explanation to consider and examine for haveing the knack of art technology person.
(2), picture element driving method
The output current of driving transistors P4 such as formula (2-1), wherein
Be oxide layer electric capacity.W is a channel width.L is a passage length.
Here suppose
,
, W and L be fixed value.Therefore order
Above-mentioned K is a constant.
So (2-1) can be write as following formula (2-3):
With formula (2-4) substitution formula (2-3), can get formula (2-5).
Critical voltage stores: when disturbance switching transistor P2, display switch transistor P3, diverting switch transistor P5 are cut-off state with shunting driving transistors P6, data switch transistor P1 is conducting state (as shown in Figure 9).
When
Being charged to electricity arrives
The time, driving transistors P4 be cut-off state (because
).
When
The time or work as
The time (2-6)
The voltage of end points C
(2-7)
In the above-mentioned formula (2-7), m is a real number, and
Promptly suppose present embodiment
Be first embodiment
M doubly.
The voltage of end points G is
(2-8)
Then
Last cross-pressure
(2-9)
Disturbing signal: when data switching transistor P1 is a cut-off state, disturbance switching transistor P2, display switch transistor P3, diverting switch transistor P5 are conducting state (as shown in figure 10).
As disturbing signal CSL during at negative cycle.
The potential change amount of end points C such as following formula (2-12).The potential change amount of end points G such as following formula (2-13).
(2-14)
Then can push away the electric current of the driving transistors P4 that flows through
, as following formula (2-15).Flow through and shunt the electric current of driving transistors P6
, as following formula (2-16).
In like manner can analogize, as disturbing signal CSL during in positive period, in formula (2-15) and the formula (2-16)
Can by
Replace, as following formula (2-15 ') and formula (2-16 ').
If definition
。Suppose
Become through disturbance
Situation under, formula (2-15) can be rewritten as following formula (2-17), formula (2-16) can be rewritten as following formula (2-18).
Suppose
Become through disturbance
Situation under, in formula (2-17), the formula (2-18)
Can by
Replace, as following formula (2-17 '), formula (2-18 ').
Conclusion: the influence of critical voltage is offset, and can make the output current of shunting driving transistors P6 and driving transistors P4 not influenced by critical voltage variation.
Then, analyze the electric current that passes through driving transistors P4, shunting driving transistors P6 and OLEDD1.Identical at the flow through magnitude of current of OLEDD1 of this hypothesis present embodiment with first embodiment, as formula (2-19).In addition, hypothesis driven transistor P4 is identical or close with the K value of shunting driving transistors P6, as formula (2-20).
By formula (17) and formula (18), and order
In the above-mentioned formula (2-22),
,
,
Be constant.Then, can obtain following formula (2-23).
In the present embodiment, drive picture element transistor P4 with total output current that shunting drives picture element transistor P6 be (
), can get following formula (2-24), wherein
It is the output current that first embodiment drives picture element transistor P4.On the other hand,
Can be obtained by following formula (2-25), and
Can be obtained by following formula (2-26).
With formula (2-25) and formula (2-26) substitution formula (2-24), can obtain following formula (2-27).
Gained
Two values are arranged
With
When
The time:
(closing),
(not conforming to)
When
The time:
(closing),
(closing)
Therefore, satisfy simultaneously
The time,
Formula (2-29) substitution formula (2-23) formula can obtain the output current of a driving transistors of present embodiment, as following formula (2-30)
Then, order
Conclusion:
1. in the present embodiment, the required operating voltage of the gate of driving transistors P4 and shunting driving transistors is the first embodiment driving transistors P4's
2. in the present embodiment, the voltage of disturbing signal CSL is first embodiment's
Partial current is analyzed:
By formula (2-21) and formula (2-32) formula, checking formula (2-19)
Conclusion: the image element structure 11 of present embodiment uses two close driving transistorss (P4, P6), can obtain to pass through the identical size of current of OLEDD1 with first embodiment.
Transistorized power consumption analysis:
Formula (3-33) can be simplified following formula (3-33 ').
So the power consumption of driving transistors such as following formula (3-34):
Again as can be known by formula (3-34):
Conclusion: present embodiment shunting driving transistors P6 and driving transistors P4 total consumed power are less than the consumed power of the first embodiment driving transistors P4.
(3), picture element wave mode design
Please refer to Figure 11, whether the scanning signal may command of sweep trace GL writes storage capacitors Ccs with the data signals of data line DL.DL represents the signal of a dataline.Show whether controlling signal DCL may command driving transistors P4 and the output current of shunting driving transistors P4 flow into OLEDD1.Disturbing signal CSL is the disturbing signal of the outside input of picture element, and this signal is with no-voltage position standard, work ± Δ
NewPeriodic perturbation.
Can make driving transistors P4 and shunting driving transistors P4 produce the voltage signal of electric current output.T1 is that critical voltage stores and data write during this time.T2 is the data disturbance during this time.
Comprehensively above-mentioned, second embodiment not only can reach the similar effect with first embodiment, also can reduce driving transistors and the gate operating voltage of shunting driving transistors and the voltage of disturbing signal.This practice not only can effectively reduce the total power consumption of image element structure 11.Driving transistors is also comparatively loose with the specification limits of shunting driving transistors, transistorized selecting for use when helping implementing.
In addition, have the knack of the image element structure that art technology person also can change the foregoing description according to its demand.For instance, in a second embodiment, shunting driving transistors P6 and diverting switch transistor P5 can be configured in outside the picture element array, for example configurable in the frame of display.So can effectively improve the aperture opening ratio (aperturerate) of image element structure 11.
Again for example, among first embodiment, storage capacitors Ccs and inessential member.Have the knack of art technology person and can omit storage capacitors Ccs according to its demand.
In sum, when the present invention stops to provide data signals to image element structure, can provide disturbing signal to image element structure.Thus, can promote the life-span of image element structure.In addition, embodiments of the invention also have following effect:
1. critical voltage electric capacity of configuration between first end of driving transistors and gate terminal can reduce the variation of critical voltage, makes the brightness performance of picture element more stable.
2. configurable shunting driving transistors and diverting switch transistor in image element structure are used the magnitude of current of sharing driving transistors.So not only can reduce the total power consumption of image element structure.The gate operating voltage of driving transistors and shunting transistor also can be lowered, also and transistorized specification limits also can reduce transistorized selecting for use when implementing.In addition, the voltage of disturbing signal also can be lowered.
3. shunting driving transistors and diverting switch transistor are configurable outside the picture element array, use the aperture opening ratio that improves image element structure.
Though the present invention discloses as above with embodiment; right its is not in order to limit the present invention; have in the technical field under any and know the knowledgeable usually; without departing from the spirit and scope of the present invention; when doing a little change and retouching, so protection scope of the present invention is as the criterion when looking accompanying the claim person of defining.