The present disclosure relates to a field of a transistor-based pixel circuit, in particular to a pixel compensation circuit.
In a transistor-based pixel circuit, a driving transistor serves as a core transistor to provide a driving current for an organic light-emitting diode (OLED) to light up each pixel. The magnitude of current directly determines brightness of the pixel. However, during an operation of the pixel circuit, a threshold voltage of the driving transistor will drift due to a long-term operation of the transistor under a gate voltage, which affects stability of the driving current. Although many existing compensation circuits compensate for the threshold voltage of the driving transistor, most of them may only compensate for an enhancement-mode (positive threshold voltage) driving transistor due to structural limitations, and the driving transistor is very likely to be in a depleted state (negative threshold voltage), and thus this type of compensation circuit is quite limited.
In addition, a turn-on voltage of the organic light-emitting diode (OLED) will also have a tendency to increase as operation time increases, which means that under the same driving current condition, the brightness of the organic light-emitting diode will decrease as operation time increase. There are few compensation circuits for this problem in the prior art.
In view of above-mentioned problems, the present disclosure intends to provide a circuit capable of simultaneously having a compensation function for a positive and negative threshold voltage and a compensation function for an OLED current attenuation.
An embodiment of the present disclosure provides a pixel compensation circuit comprising a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a first capacitor, a second capacitor and an organic light-emitting diode, each of the first transistor to the sixth transistor comprising a drain, a source and a gate, wherein a drain of the first transistor is coupled to an output terminal of a reference voltage, a source of the first transistor is coupled to a first node, and a gate of the first transistor is coupled to an output terminal of a first control signal; a drain of the second transistor is coupled to the first node, a source of the second transistor is coupled to a third node, and a gate of the second transistor is coupled to an output terminal of a third control signal; a drain of the third transistor is coupled to an output terminal of a data voltage, a source of the third transistor is coupled to the third node, and a gate of the third transistor is coupled to an output terminal of a second control signal; a drain of the fourth transistor is coupled to a second node, a source of the fourth transistor is coupled to a fourth node, and a gate of the fourth transistor is coupled to the output terminal of the third control signal; a drain of the fifth transistor is coupled to the third node, a source of the fifth transistor is coupled to the fourth node, and a gate of the fifth transistor is coupled to the output terminal of the first control signal; a drain of the sixth transistor is coupled to an output terminal of a supply voltage, a source of the sixth transistor is coupled to the second node, and a gate of the sixth transistor is coupled to the first node; a terminal of the first capacitor is coupled to the second node, and another terminal of the first capacitor is coupled to the supply voltage or ground; a terminal of the second capacitor is coupled to the second node, and another terminal of the second capacitor is coupled to the third node; and an anode of the organic light-emitting diode is coupled to the fourth node, and a cathode of the organic light-emitting diode is coupled to the ground.
In some embodiments, a combination of the first control signal, the second control signal, and the third control signal sequentially corresponds to a threshold voltage compensation phase, a data input phase, and a light-emitting phase.
In some embodiments, in the threshold voltage compensation phase, the first control signal is at a high level, the second control signal is at a low level, and the third control signal is at a low level.
In some embodiments, in the data input phase, the first control signal is at a low level, the second control signal is at a high level, and the third control signal is at a low level.
In some embodiments, in the light-emitting phase, the first control signal is retained at a low level, the second control signal is at a low level, and the third control signal is at a high level.
In some embodiments, the first control signal and the second control signal are both line scanning signals, and the first control signal and the second control signal are multiplexed signals.
In some embodiments, each of the first to the sixth transistors is a thin film transistor.
In some embodiments, the thin film transistors are made of amorphous indium gallium zinc oxide material.
Based on above technical solutions, it may be known that the present disclosure has at least the following beneficial effects: the pixel compensation circuit proposed in the present disclosure realizes a compensation for the threshold voltage of the driving transistor, regardless whether the threshold voltage is positive or negative; and it also realizes a compensation for the current attenuation of the organic light-emitting diode.
In order to make an objective, a technical solution and an advantage of the present disclosure clearer, a technical solution of the present disclosure will be clearly and completely described below. Obviously, the embodiments described are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure described, all other embodiments obtained by those of ordinary skills in the art without creative work shall fall within the protection scope of the present disclosure.
Unless otherwise defined, technical terms or scientific terms used in the present disclosure should have usual meanings understood by those of ordinary skills in the art to which the present disclosure pertains.
A drain of the first transistor T1 is coupled to an output terminal of a reference voltage VREF, a source of the first transistor T1 is coupled to a first node A, and a gate of the first transistor T1 is coupled to an output terminal of a first control signal Sn-1.
A drain of the second transistor T2 is coupled to the first node A, a source of the second transistor T2 is coupled to a third node C, and a gate of the second transistor T2 is coupled to a third control signal EM.
A drain of the third transistor T3 is coupled to an output terminal of a data voltage VDATA, a source of the third transistor T3 is coupled to the third node C, and a gate of the third transistor T3 is coupled to an output terminal of a second control signal Sn.
A drain of the fourth transistor T4 is coupled to a second node B, a source of the fourth transistor T4 is coupled to a fourth node D, and a gate of the fourth transistor T4 is coupled to the output terminal of the third control signal EM.
A drain of the fifth transistor T5 is coupled to the third node C, a source of the fifth transistor T5 is coupled to the fourth node D, and a gate of the fifth transistor T5 is coupled to the output terminal of the first control signal Sn-1.
A drain of the sixth transistor T6 is coupled to an output terminal of a supply voltage VDD, a source of the sixth transistor T6 is coupled to the second node B, and a gate of the sixth transistor T6 is coupled to the first node A.
A terminal of the first capacitor C1 is coupled to the second node B, and another terminal is coupled to the supply voltage VDD. In other embodiments, the another terminal of C1 may also be coupled to ground, and the same effect may also be achieved.
A terminal of the second capacitor C2 is coupled to the second node B, and another terminal is coupled to the third node C.
An anode of the organic light-emitting diode OLED is coupled to the fourth node D, and a cathode is coupled to the ground.
Through the pixel compensation circuit in the embodiment, the threshold voltage of the driving transistor may be compensated, regardless whether the threshold voltage is positive or negative, and the current attenuation of the organic light-emitting diode may also be compensated. At the same time, the number of control signals is small and waveforms are simple. It is easy to use Gate Driver on Array (GOA) technology to realize a high-resolution and narrow border display.
According to some embodiments, each of the first transistor T1 to the sixth transistor T6 is a thin film transistor (TFT), preferably a n-type amorphous indium gallium zinc oxide (a-IGZO) thin film transistor. In an embodiment, the first transistor T1 to the fifth transistor T5 serve as switching transistors, and the sixth transistor T6 serves as a driving transistor.
An operating principle of the pixel compensation circuit in the embodiment of the present disclosure will be described below with reference to the accompanying drawings.
As shown in
Further referring to
In this phase, a source following structure is composed of the supply voltage VDD, the sixth transistor T6, the fourth transistor T4 and the organic light-emitting diode OLED. The gate voltage of the sixth transistor T6 is constant, and the source of the sixth transistor T6 is charged by the supply voltage VDD. As a result, a detection of the threshold voltage Vth6 of the sixth transistor T6, that is, the driving transistor, is completed, regardless whether the threshold voltage Vth6 is positive or negative.
As shown in
Further referring to
in which C1 and C2 are capacitance values of the first capacitor and the second capacitor, respectively.
At the same time, a voltage (VC2) across the second capacitor C2 changes to:
As shown in
Further referring to
IOLED in this phase may be obtained as:
in which μ, Cox, and
represent the mobility of the sixth transistor T6, the unit-area gate dielectric capacitance, and the ratio of channel width to length, respectively.
It may be seen that the luminous current IOLED of the organic light-emitting diode OLED finally obtained in the embodiment of the present disclosure is irrelevant with respect to the threshold voltage Vth6 of the sixth transistor T6, indicating that a threshold voltage drift of the sixth transistor T6 serving as the driving transistor, hardly affects the luminous current. The embodiment realizes the compensation of the threshold voltage of the driving transistor, and at the same time, the current IOLED is also positively correlated with VOLED_TH, indicating that when the turn-on voltage VOLED_TH of the organic light-emitting diode OLED increases with operating time of the organic light-emitting diode OLED, the current flows through the organic light-emitting diode OLED will also increase. Therefore, the embodiments of the present disclosure may provide additional driving current to compensate for the problem that the brightness of the organic light-emitting diode OLED will decrease as operating time increases.
According to some embodiments, the first control signal Sn-1 and the second control signal Sn are both line scanning signals, and they are multiplexed signals. Therefore, in the embodiment of the present disclosure, only two additional signals (line scanning signal and EM) are needed to achieve the above effect, and as shown in
Specific embodiments described above further describe a purpose, a technical solution and a beneficial effect of the present disclosure in detail. It should be understood that above descriptions are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Within spirit and principle of the present disclosure, any modification, equivalent replacement, improvement, and the like, shall be included in the protection scope of the present disclosure.
Number | Date | Country | Kind |
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201810627356.6 | Jun 2018 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2018/098339 | 8/2/2018 | WO | 00 |