Pixel circuit and micro-light emitting diode panel using the same

Abstract

A pixel circuit and a micro-LED panel using the same, the pixel circuit comprising: a first transistor having a first end, receiving a first data voltage, a second end, and a control end, receiving a first control signal, the first transistor being controlled to be turned on or off by the first control signal; a second transistor having both a driving function and a switching function, the second transistor having a first end coupled to an operating voltage, a second end, and a control end coupled to the second end of the first transistor; a first capacitor having a first end coupled to the control end and a second end of the second transistor; a pulse width modulation control circuit coupled to the second end of the first capacitor; and a micro-LED coupled to the second end of the second transistor, the second transistor driving the micro-LED, and the second transistor controlling whether current is allowed to flow through the micro-LED, wherein the PWM control circuit controls the micro-LED to emit light multiple times and end light multiple times within a frame by controlling the second transistor.

Description

Technical Field

[0001] The present invention relates to a pixel circuit and a micro-light emitting diode (MICRO-LED) panel using the pixel circuit. Background Art

[0002] Micro LEDs are extremely small, energy-efficient, and offer high brightness. Their penetration in AR applications can reach up to 80%. Beyond AR, micro LEDs are also well-suited for automotive applications and displays larger than 100 inches (such as billboards and TVs).

[0003] Current micro-LED pixel circuits utilize pulse-width modulation (PWM) control circuits, with a switching transistor connected in series with the micro-LED's drive current path to control the light-emission duration. This switching transistor consumes additional power. Furthermore, due to the high drive current of the micro-LED, the switching transistor must be larger to reduce heat generation. However, this larger switching transistor consumes more circuit area.

[0004] Due to circuit operation limitations, current pixel circuits can only emit light once within a frame, which limits the use of micro-LEDs.

[0005] Therefore, there is a need for a pixel circuit and a micro-LED panel using the same, which can reduce power consumption and circuit area. Summary of the Invention

[0006] According to one aspect of the present disclosure, a pixel circuit is proposed, comprising: a first transistor having a first end receiving a first data voltage, a second end, and a control end receiving a first control signal, the first transistor being turned on or off by the first control signal; a second transistor having both a driving function and a switching function, the second transistor having a first end coupled to an operating voltage, a second end, and a control end coupled to the second end of the first transistor; a first capacitor having a first end coupled to the control end of the second transistor and a second end; a pulse width modulation (PWM) control circuit coupled to the second end of the first capacitor; and a micro-LED coupled to the second end of the second transistor, the second transistor driving the micro-LED and controlling whether a current flows through the micro-LED, wherein the PWM control circuit controls the second transistor to control the micro-LED to emit light multiple times and to stop emitting light multiple times within a frame.

[0007] According to another aspect of the present disclosure, a micro LED panel is provided, comprising: a pixel circuit array including a plurality of pixel circuits as described above; and a driving circuit coupled to the pixel circuit array, the driving circuit driving the pixel circuit array to emit light.

[0008] In order to better understand the above and other aspects of the present invention, the following embodiments are specifically described in detail with reference to the accompanying drawings: BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. 1 shows a circuit structure diagram of a pixel circuit according to an embodiment of the present invention.

[0010] Figure 2 FIG. 1 shows a circuit structure diagram of a pixel circuit according to an embodiment of the present invention.

[0011] Figure 3 A signal waveform diagram of a pixel circuit according to an embodiment of the present disclosure is shown.

[0012] Figures 4A to 4C The data writing phase, the light emitting phase and the light emitting end phase of the pixel circuit according to one embodiment of the present disclosure are respectively shown.

[0013] Figure 5 A schematic diagram showing the structure of a pixel circuit with compensation function according to an embodiment of the present disclosure.

[0014] Figure 6 A schematic diagram showing the structure of a pixel circuit with compensation function according to an embodiment of the present disclosure.

[0015] Figure 7 A functional block diagram of a micro LED panel according to an embodiment of the present disclosure is shown.

[0016] Description of reference numerals:

[0017] 100: Pixel circuit

[0018] T1~T7:Transistors

[0019] C1~C2:Capacitors

[0020] 110: PWM control circuit

[0021] D: Micro LED

[0022] 700: Micro LED Panel

[0023] 710: Pixel circuit array

[0024] 720: Driving circuit DETAILED DESCRIPTION

[0025] The technical terms used in this specification are based on customary terms in the technical field. If some terms are explained or defined in this specification, the interpretation of these terms shall be based on the explanations or definitions in this specification. Each embodiment of the present disclosure has one or more technical features. Under the premise of possible implementation, those skilled in the art may selectively implement some or all of the technical features in any embodiment, or selectively combine some or all of the technical features in these embodiments.

[0026] Please refer to Figure 1 , which shows a circuit architecture diagram of a pixel circuit according to an embodiment of the present invention. The pixel circuit 100 according to an embodiment of the present invention includes: a first transistor T1, a second transistor T2, a first capacitor C1, a PWM control circuit 110, and a micro-LED D.

[0027] The first transistor T1 has a first terminal receiving a first data voltage Data_PAM (Pulse-Amplitude Modulation, PAM); a second terminal coupled to the second transistor T2; and a control terminal receiving a first control signal S1. The first transistor T1 is turned on or off by the first control signal S1.

[0028] The second transistor T2 can have both a driving function and a switching function. That is, the second transistor T2 can drive the micro-LED D (driving function), and the second transistor T2 can control whether to allow a current I LED The second transistor T2 has a first terminal coupled to an operating voltage VDD, a second terminal coupled to the micro LED D, and a control terminal coupled to the first transistor T1 and the first capacitor C1.

[0029] The first capacitor C1 has: a first terminal coupled to the control terminal of the second transistor T2; and a second terminal coupled to the PWM control circuit 110. The first capacitor C1 is a coupling capacitor.

[0030] The PWM control circuit 110 is coupled to the first capacitor C1 and can control the light emission and light emission termination of the micro LED D by controlling the second transistor T2.

[0031] The micro LED D is coupled to the second transistor T2 and driven by the second transistor T2 to emit light.

[0032] Please refer to Figure 2 , which shows a circuit structure diagram of a pixel circuit according to an embodiment of the present invention. Figure 2In the embodiment, the PWM control circuit 110 includes a third transistor T3, a fourth transistor T4, a fifth transistor T5, and a second capacitor C2.

[0033] The third transistor T3 has a first terminal coupled to a first reference voltage V L a second terminal coupled to the first capacitor C1; and a control terminal coupled to the second capacitor C2. The coupling point between the second transistor T2 and the first capacitor C1 is referred to as a first node N1. The coupling point between the third transistor T3 and the second capacitor C2 is referred to as a second node N2.

[0034] The fourth transistor T4 has a first terminal coupled to a second reference voltage V H A second terminal coupled to the first capacitor C1; and a control terminal receiving a second control signal S2. The coupling point between the third transistor T3, the fourth transistor T4 and the first capacitor C1 is called a third node N3. The second reference voltage V H Higher than the first reference voltage V L .

[0035] The fifth transistor T5 comprises: a first terminal receiving a second data voltage Data_PWM; a second terminal coupled to the second capacitor C2; and a control terminal receiving the first control signal S1.

[0036] The second capacitor C2 has: a first terminal coupled to the control terminal of the third transistor T3; and a second terminal receiving a third control signal Sweep.

[0037] Figure 3 The signal waveform diagram of the pixel circuit according to one embodiment of the present disclosure is shown. Figure 3 As shown, when the first control signal S1 is enabled, it represents the start of a frame. In one embodiment of the present disclosure, the third control signal Sweep is, for example but not limited to, a triangular wave signal. In other possible embodiments of the present disclosure, the third control signal Sweep may have other waveforms, which are all within the scope of the present disclosure. In one embodiment of the present disclosure, the second control signal S2 and the third control signal Sweep can be enabled multiple times within one frame time. The enabling of the third control signal Sweep refers to rising from the lowest point to the highest point. When the second control signal S2 is enabled, the second transistor T2 can be turned on to drive the micro light-emitting diode D to emit light. When the micro light-emitting diode D emits light, when the third control signal Sweep rises to a reference potential, the second transistor T2 can be turned off to end the light emission of the micro light-emitting diode D.

[0038] In one embodiment of the present disclosure, the pixel circuit has three operation phases: data writing phase, light emitting phase and light emitting end phase. Figures 4A to 4C , respectively showing the data writing stage, the light emitting stage and the light emitting end stage of the pixel circuit according to an embodiment of the present disclosure.

[0039] like Figure 4A As shown, when the pixel circuit is in the data writing phase, the first control signal S1 is enabled, the first transistor T1 is turned on, and the first data voltage Data_PAM is written to the first node N1 (N1=V Data_PAM ); and, the fifth transistor T5 is turned on, and the second data voltage Data_PWM is written to the second node N2 (N2 = V Data_PWM ). By designing the first reference voltage V L The voltage value can make V Data_PWM With V L The voltage difference is higher than the critical voltage V of the third transistor T3 TH_T3 , so that the third transistor T3 is turned on ((V Data_PWM -V L )>V TH_T3 ). In addition, V Data_PAM With V ANO The voltage difference (anode voltage of the micro LED D) is less than the critical voltage V of the second transistor T2. TH_T2 , so that the second transistor T2 is turned off ((V Data_PAM -V ANO ) <V TH_T2 ). Therefore, during the data writing phase, the second transistor is turned off.

[0040] like Figure 4B As shown, when the pixel circuit is in the light-emitting stage, the third control signal Sweep has a voltage drop ΔV Sweep , this voltage drop ΔV Sweep The voltage of the second node N2 is coupled to the second node N2 through the second capacitor C2, so that the voltage of the second node N2 becomes V Data_PAM -ΔV Sweep Since the voltage of the second node N2 changes, the third transistor T3 is turned off, that is, (V Data_PWM -ΔV Sweep -V L ) <V TH_T3 Since the second control signal S2 is enabled, the fourth transistor T4 is turned on, and thus the voltage of the third node N3 changes to a positive voltage (V H -V L ), this positive voltage change (V H -V L ) is coupled to the first node N1 through the first capacitor C1, so that the voltage of the first node N1 becomes ((V Data_PAM -V ANO +(VH -V L ))>V TH_T2 ), so the second transistor T2 becomes conductive. The conductive second transistor T2 can output a driving current I LED To drive the micro light emitting diode D to emit light.

[0041] like Figure 4C As shown, when the pixel circuit is in the end stage of light emission, when the third control signal Sweep rises to a reference potential ΔV Sweep_rise When the voltage change is applied, it will be coupled to the second node N2 through the second capacitor C2, so that the voltage of the second node N2 becomes V Data_PAM -ΔV Sweep +ΔV Sweep_rise Since the voltage of the second node N2 changes, the third transistor T3 becomes conductive, that is, (V Data_PWM -ΔV Sweep +ΔV Sweep_rise -V L )>V TH_T3 Since the second control signal S2 is disabled, the fourth transistor T4 is turned off, and thus the voltage of the third node N3 changes to a negative voltage (V L –V H ), this negative voltage change (V L –V H ) is coupled to the first node N1 through the first capacitor C1, so that the voltage of the first node N1 becomes ((V Data_PAM -V ANO +(V H -V L )+(V L –V H )=(V Data_PAM -V ANO ) <V TH_T2 Therefore, the second transistor T2 is turned off. Since the second transistor T2 is turned off, the micro light emitting diode D stops emitting light.

[0042] From the above description, it can be seen that in one embodiment of the present disclosure, if the second control signal S2 and the third control signal Sweep are enabled multiple times within one frame time, the micro LED D can emit light multiple times. Figure 3 Only one frame is displayed, but the waveforms of other frames can also be displayed in the same way. Figure 3 shown.

[0043] Figure 5 The structure diagram of the pixel circuit with compensation function according to one embodiment of the present disclosure is shown. Figure 5 As shown, compared with Figure 2 The pixel circuit 200, Figure 5The pixel circuit 500 further includes a sixth transistor T6. The sixth transistor T6 has: a first terminal coupled to the coupling point between the second transistor T2 and the micro-LED D; a second terminal outputting a sensed voltage V Sensing ; and a control end, receiving the first control signal S1.

[0044] Figure 5 The pixel circuit 500 has the function of sensing the current of the second transistor T2 to compensate for the threshold voltage deviation and the on-current deviation of the second transistor T2. The details are as follows.

[0045] During the current sensing of the second transistor T2, the third transistor T3, the fourth transistor T4 and the micro-LED D are all turned off. The first control signal S1 is enabled to turn on the sixth transistor T6. At this time, the first transistor T1 and the second transistor T2 are both turned on. The current of the second transistor T2 (sensing current I Sensing ) can flow to the compensation circuit 510 through the sixth transistor T6. In one embodiment of the present disclosure, by writing different first data voltages Ddata_PAM to the control terminal of the second transistor T2, a voltage-current (VI) curve of the second transistor T2 is obtained. In response to the voltage-current (VI) curve of the second transistor T2, the compensation circuit 510 can output a first compensation voltage ΔV External_compensation1 That is, after compensation, when driving the micro light emitting diode D, the first data voltage input to the first transistor T1 becomes: V Ddata_PAM +V External_compensation1 That is, the first data voltage Ddata_PAM can be compensated.

[0046] Figure 6 The structure diagram of the pixel circuit with compensation function according to one embodiment of the present disclosure is shown. Figure 6 As shown, compared with Figure 5 The pixel circuit 500, Figure 6 The pixel circuit 600 further includes a seventh transistor T7. The seventh transistor T7 has a first terminal coupled to the third node N3, a second terminal coupled to the sixth transistor T6, and a control terminal receiving the first control signal S1.

[0047] Figure 6 The pixel circuit 600 has the function of sensing the current of the third transistor T3 to compensate for the threshold voltage deviation and the on-current deviation of the third transistor T3. The details are as follows.

[0048] During the current sensing of the third transistor T3, the second transistor T2, the fourth transistor T4 and the micro-LED D are all turned off. The first control signal S1 is enabled to turn on the seventh transistor T7. At this time, the third transistor T3 and the sixth transistor T6 are both turned on. The current of the third transistor T3 (sensing current I Sensing ) can flow to the compensation circuit 510 through the seventh transistor T7 and the sixth transistor T6. In one embodiment of the present disclosure, by writing a different second data voltage Ddata_PWM to the fifth transistor T5, a voltage-current (VI) curve of the third transistor T3 is obtained. In response to the voltage-current (VI) curve of the third transistor T3, the compensation circuit 510 can output a second compensation voltage ΔV External_compensation2 That is, after compensation, when driving the micro light emitting diode D, the second data voltage input to the fifth transistor T5 becomes: V Ddata_PWM +V External_compensation2 That is, the second data voltage Ddata_PWM can be compensated.

[0049] Figure 7 The following is a functional block diagram of a micro-LED panel according to an embodiment of the present disclosure. The micro-LED panel 700 includes a pixel circuit array 710 and a driving circuit 720. The pixel circuit array 710 includes a plurality of pixel circuits as described in the above-described embodiments. The pixel circuit array 710 is coupled to the driving circuit 720 to be driven by the driving circuit 720 and emit light. The driving circuit 720 sends a first control signal S1, a second control signal S2, a third control signal Sweep, a first data voltage Data_PAM, and a second data voltage Data_PWM to the pixel circuit array 710 to drive the pixel circuit array 710 to emit light. The details of the pixel circuit array 710 and the driving circuit 720 have been described above and will not be repeated here.

[0050] As described above, in the embodiment of the present disclosure, by allowing the driving transistor to have both driving and switching functions, the pixel circuit does not need a large-sized switching transistor, thereby saving circuit area and reducing power consumption.

[0051] As described above, in the embodiment of the present disclosure, the pixel circuit can emit light multiple times within one frame, so that the micro light emitting diode can be used for better purposes.

[0052] As described above, in the embodiments of the present disclosure, the pixel circuit can compensate for the threshold voltage deviation and on-current deviation of the internal transistors to enhance and improve the performance of the pixel circuit.

[0053] In summary, although the present invention has been disclosed above with reference to the embodiments, these are not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A pixel circuit comprising: A first transistor having: a first terminal receiving a first data voltage; a second terminal; and a control terminal receiving a first control signal, wherein the first transistor is controlled to be turned on or off by the first control signal; a second transistor having both a driving function and a switching function, the second transistor comprising: a first terminal coupled to an operating voltage; a second terminal; and a control terminal coupled to the second terminal of the first transistor; a first capacitor having: a first terminal coupled to the control terminal of the second transistor; and a second end; a pulse width modulation control circuit coupled to the second end of the first capacitor; and a micro light emitting diode coupled to the second end of the second transistor, the second transistor driving the micro light emitting diode, and the second transistor controlling whether a current flows through the micro light emitting diode; The pulse width modulation control circuit controls the second transistor to control the micro light emitting diode to emit light multiple times and end the light emission multiple times within one frame. The pulse width modulation control circuit includes: a third transistor having: a first terminal coupled to a first reference voltage; a second terminal coupled to the first capacitor; and a control terminal, wherein a coupling point between the second transistor and the first capacitor is a first node; a fourth transistor having: a first terminal coupled to a second reference voltage; a second terminal coupled to the first capacitor; and a control terminal receiving a second control signal, the second reference voltage being higher than the first reference voltage; a fifth transistor having: a first terminal receiving a second data voltage; a second terminal; and a control terminal receiving the first control signal; and A second capacitor has: a first terminal coupled to the control terminal of the third transistor and the second terminal of the fifth transistor; and a second terminal receiving a third control signal; A coupling point between the third transistor and the second capacitor is a second node, A coupling point among the third transistor, the fourth transistor and the first capacitor is a third node.

2. The pixel circuit according to claim 1, wherein: When the first control signal is enabled, it indicates the start of the frame; The third control signal is a triangle wave signal; In the frame, the second control signal and the third control signal are enabled multiple times; When the second control signal is enabled, the second transistor is turned on to drive the micro light emitting diode to emit light; as well as When the micro light emitting diode emits light, when the third control signal rises to a reference potential, the second transistor is turned off to terminate the light emitting of the micro light emitting diode.

3. The pixel circuit according to claim 2, wherein: When the pixel circuit is in a data writing stage, the first control signal is enabled, the first transistor is turned on to write the first data voltage to the first node, the fifth transistor is turned on to write the second data voltage to the second node, the voltage difference between the second data voltage and the first reference voltage is higher than a critical voltage of the third transistor so that the third transistor is turned on, and the voltage difference between the first data voltage and an anode voltage of the micro-light-emitting diode is less than a critical voltage of the second transistor so that the second transistor is turned off.

4. The pixel circuit according to claim 3, wherein: When the pixel circuit is in a light emitting stage, The third control signal has a voltage drop. The voltage drop of the third control signal is coupled to the second node through the second capacitor to turn off the third transistor. The second control signal is enabled to turn on the fourth transistor, and A positive voltage change of the third node is coupled to the first node through the first capacitor to turn on the second transistor to drive the micro light emitting diode to emit light.

5. The pixel circuit according to claim 4, wherein: When the pixel circuit is in a light-emitting end stage, When the third control signal rises to a reference potential, a rising voltage change of the third control signal is coupled to the second node through the second capacitor to turn on the third transistor. The second control signal is disabled to turn off the fourth transistor. A negative voltage change occurs at the third node. The negative voltage change is coupled to the first node through the first capacitor to turn off the second transistor and stop the micro LED from emitting light.

6. The pixel circuit as claimed in claim 5 , further comprising a sixth transistor having: a first terminal coupled to a coupling point between the second transistor and the micro-LED; a second terminal outputting a sensed voltage; and a control terminal receiving the first control signal. When sensing a current of the second transistor, the third transistor, the fourth transistor, and the micro-LED are turned off, the first control signal is enabled to turn on the sixth transistor, and the first transistor and the second transistor are both turned on. The current of the second transistor flows through the sixth transistor to a compensation circuit. By writing different first data voltages to the control terminal of the second transistor, the compensation circuit compensates the first data voltage with a first compensation voltage.

7. The pixel circuit according to claim 6, further comprising: a seventh transistor having: a first terminal coupled to the third node; a second terminal coupled to the sixth transistor; and a control terminal, receiving the first control signal, When sensing a current of the third transistor, the second transistor, the fourth transistor, and the micro-LED are turned off, the first control signal is enabled to turn on the seventh transistor, and the third transistor and the sixth transistor are both turned on. The current of the third transistor flows to the compensation circuit through the seventh transistor and the sixth transistor. By writing a different second data voltage into the fifth transistor, the compensation circuit compensates the second data voltage with a second compensation voltage.

8. A micro-light emitting diode panel, comprising: A pixel circuit array comprising a plurality of pixel circuits according to claim 1; as well as A driving circuit is coupled to the pixel circuit array, and drives the pixel circuit array to emit light.

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