TWI421837B - A driver circuit and a pixel circuit with the driver circuit - Google Patents

Description

Driving circuit and pixel circuit having the same

The present invention relates to a driving circuit and a pixel circuit having the same, and particularly to a driving circuit capable of improving a threshold voltage drift effect and aging of a light emitting element, and a pixel circuit having the driving circuit.

The brightness of an organic light emitting diode (OLED) is proportional to its driving current I _OLED . At present, when the OLED is applied to a display system, the connection with the corresponding driving circuit still has the following problems: First, the critical voltage of the transistor in the driving circuit may cause drift phenomenon due to the variation of the process, resulting in a drift phenomenon. The driving current of the OLED is unstable, which in turn causes the brightness of the OLED to be unstable. The second is that the OLED is prone to gradual increase in the luminous efficiency due to the aging of the OLED due to aging of the material or long-time operation. Because the rise of the across voltage will affect the attenuation of the driving current of the OLED, and the attenuation of the driving current will cause the brightness of the OLED to decay. In addition, in today's technology, the design of the pixel compensation circuit mostly uses too many transistors, which will cause the aperture ratio in the pixel to be attenuated or even too low. Therefore, it is necessary to find a kind of effective threshold voltage for the transistor. The driving current decay caused by drift and OLED aging makes the OLED brightness stable, and at the same time, the pixel aperture ratio must be maintained by using a simplified circuit design.

Therefore, an object of the present invention is to provide a pixel circuit comprising: a light emitting unit having a first end and a second end; and a driving circuit comprising: a first transistor having a first end a second end, and a control end that determines whether the first end and the second end are conductive; a capacitor; a first switch having a first end and a second end; and a second switch having a first end and a second end; wherein the first end of the light emitting unit receives a first power voltage and the second end of the first transistor receives a second power voltage, the first end of the first switch The first end of the first switch is electrically connected to the first end of the first transistor, and the second end of the first switch is electrically connected to the control end of the first transistor, and the first switch receives a first control signal to determine the first The first end of the transistor and the control end are electrically connected, and the first end of the second switch is electrically connected to the second end of the light emitting unit, and the second end of the second switch is opposite to the first transistor One end is electrically connected, and the second switch receives a second control signal to determine the The second end of the unit is electrically connected to the first end of the first transistor, one end of the capacitor is electrically connected to the control end of the first transistor, and the other end of the capacitor receives a data voltage, and according to the first A switch and an on state of the second switch to control a driving current of one of the light emitting units.

In addition, the present invention further provides a driving circuit for controlling a light emitting unit having a first end and a second end, comprising: a first transistor having a first end, a second end, and a Decide a control end of the first end and the second end; a capacitor; a first switch having a first end and a second end; and a second switch having a first end and a second end An illuminating unit having a first end and a second end; and a driving circuit comprising: a first transistor having a first end and a second end, and a determining the first end and the first a second terminal is a conductive terminal; a capacitor; a first switch having a first end and a second end; and a second switch having a first end and a second end; wherein the light emitting unit The first end receives a first power voltage and the second end of the first transistor receives a second power voltage, and the first end of the first switch is electrically connected to the first end of the first transistor, the first The second end of the switch is electrically connected to the control end of the first transistor, and the first switch receives a first control signal to determine whether the first end of the first transistor and the control end are electrically connected, and the The first end of the second switch is electrically connected to the second end of the light emitting unit, and the second end of the second switch is The first end of the first transistor is electrically connected, and the second switch receives a second control signal to determine whether the second end of the light emitting unit is electrically connected to the first end of the first transistor. The control terminal of the first transistor is electrically connected, and the other end of the capacitor receives a data voltage, and controls the driving current of one of the light emitting units according to the conduction states of the first switch and the second switch.

In addition, the present invention further provides a pixel circuit comprising: An illuminating unit having a first end and a second end; and a driving circuit comprising: a first transistor having a first end and a second end, and a determining the first end and the second end a control terminal that is turned on; a capacitor; a first switch having a first end and a second end; a second switch having a first end and a second end; and a third switch having a first One end and a second end; wherein the first end of the light emitting unit receives a first power voltage and the second end of the first transistor receives a second power voltage, the first end of the first switch The first end of the first transistor is electrically connected, the second end of the first switch is electrically connected to the control end of the first transistor, and the first switch receives a first control signal to determine the first transistor The first end and the control end are electrically connected, and the first end of the second switch is electrically connected to the second end of the light emitting unit, the second end of the second switch and the first end of the first transistor Electrically connected, and the second switch receives a second control signal to determine the second end of the light emitting unit Whether the first end of the first transistor is electrically connected, the first end of the third switch receives a data voltage, and the second end of the third switch and the first end of the second switch, the first of the light emitting unit The second switch is electrically connected, and the third switch receives a third control signal to determine whether the first end and the second end of the third switch are electrically connected, and one end of the capacitor is electrically connected to the control end of the first transistor, and The other end of the capacitor receives a data voltage and controls a driving current of one of the light emitting units according to an on state of the first switch.

In addition, the present invention further provides a driving circuit for controlling a light emitting unit having a first end and a second end, comprising: a first transistor having a first end, a second end, and a a control end that determines whether the first end and the second end are conductive; a capacitor; a first switch having a first end and a second end; and a second switch having a first end and a second end And a third switch having a first end and a second end; wherein the first end of the light emitting unit receives a first power voltage and the second end of the first transistor receives a second power voltage The first end of the first switch is electrically connected to the first end of the first transistor, the second end of the first switch is electrically connected to the control end of the first transistor, and the first switch receives a first Controlling a signal to determine whether the first end of the first transistor and the control end are electrically connected, and the first end of the second switch is electrically connected to the second end of the light emitting unit, and the second end of the second switch Electrically connected to the first end of the first transistor, and the second switch receives a second control a signal to determine whether the second end of the light emitting unit is electrically connected to the first end of the first transistor, the first end of the third switch receives a data voltage, and the second end of the third switch The first end of the second switch is electrically connected to the second end of the light emitting unit, and the third switch receives a third control signal to determine whether the first end and the second end of the third switch are electrically connected, and the one end of the capacitor is The control terminal of the first transistor is electrically connected, and the other end of the capacitor receives a data voltage, and controls a driving current of one of the light emitting units according to an on state of the first switch.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention.

Before the present invention is described in detail, it is noted that in the following description, similar elements are denoted by the same reference numerals.

First preferred embodiment

There are a plurality of pixels in a panel, and there are different numbers of columns depending on the resolution. For example, a panel of 1920×1080 resolution has 1080 columns, and each column has 1920 pixels. The pixel circuits in the same column are the data voltages corresponding to the data input in the same period. Therefore, this embodiment is a pixel pixel in the Nth column of a panel.

Referring to FIG. 1 , a first preferred embodiment of the present invention includes: a light emitting unit 1 and a driving circuit 2, wherein the driving circuit 2 includes: a first transistor 21, a first switch, and a second switch. And a capacitor 24, in the embodiment, the light-emitting unit 1 is an organic light-emitting diode (OLED), and the first switch and the second switch are respectively a second transistor 22 and a third transistor 23. In the following description, the above-mentioned transistors are all described in the form of N-type thin film transistors, but in the present invention, all of the P-type thin film transistors, N-type metal oxide semiconductors, and P-type metal oxide semiconductors are available. It is simply modified and implemented accordingly, so it is not limited to N-type thin film transistors.

Each of the transistors 21, 22, 23 has a first end, a second end, and a control end for determining whether the first end and the second end are conductive. The light emitting unit has a first end electrically connected to a first power voltage V _DD and a second end electrically connected to the first end of the third transistor 23, and the first end of the first transistor 21 The second end of the second transistor 22 is electrically connected to the second end of the second transistor 22, and the second end of the first transistor 21 is electrically connected to a second power voltage V _SS , the first The control terminals of the second transistor 22 are electrically connected to the first end of the second transistor 22 and the one end of the capacitor 24. The control terminals of the second and third transistors 22 and 23 respectively receive a first control signal and a first The second control signal, the other end of the capacitor 24 is electrically connected to a data voltage V _DATA .

It should be noted that, since the second and third transistors 22 and 23 are all N-type thin film transistors, when the first and second control signals are high, the corresponding second, The first end and the second end of the third transistor 22, 23 are in an on state; and when the first and second control signals are at a low level, the second and third transistors 22, 23 are corresponding One end and the second end are non-conductive. If the transistors are implemented in a P-type transistor, the relationship between the potential state of the control signal and the corresponding P-type transistor is inverse.

The operation mode of the pixel circuit of this embodiment is as follows: Referring to FIG. 1 and FIG. 2 together, first, the first and second control signals are all set to a high potential, and therefore, the second and third transistors 22, 23 All of the first transistor 21 and the voltage at the control terminal thereof are V _DD - V _OLED , and the V _{OLED is} the first of the light-emitting unit 1 (ie, an organic light-emitting diode) The voltage across the terminal and the second terminal is such that the voltage difference across the capacitor 24 is V _DATA -( V _DD - V _OLED ), and V _{DATA is} the data voltage.

When the capacitor 24 is charged to V _DATA -( V _DD - V _OLED ), the pixel circuit will operate in a compensation mode, at which time the second control signal is set to a low potential, so that the third transistor 23 is not turned on. , so that the capacitor 2421 begins to discharge through the first transistor until the voltage of the control terminal 21 of the first transistor is discharged to V _SS + V _{TH 1} when (V _{TH 1} for the first transistor 21 of the voltage threshold The first transistor 21 is switched to a non-conducting state. At this time, the voltage difference between the capacitors 24 is V _DATA -( V _SS + V _{TH 1} ), and then the first control signal is set to a low potential. The second transistor 22 is made non-conducting. Therefore, the capacitor 24 has a voltage difference between the two terminals because the voltage difference is maintained at V _DATA -( V _SS + V _{TH 1} ), so the capacitor 24 in the pixel circuit The terminal voltage can be kept constant, that is, the voltages at the two terminals of the pixel circuits in the Nth column remain unchanged.

Then, the second and first control signals corresponding to the N+1th column pixel circuit are sequentially set to a low potential, so that the voltage difference between the two ends of the capacitor 24 can be kept fixed, and so on, until the last column of pixel circuits The voltage difference across the capacitor 24 remains fixed.

Then, the pixel circuit operates in a light emitting mode, a second control signal in each pixel circuit row is set to the high potential simultaneously, so that the crystal 23 corresponding to the third electrically conductive, and a data voltage emission but also increases a voltage △ V At this time, the control terminal voltage of the first transistor 21 is V _SS + V _{TH 1} + Δ V . Therefore, the driving current I _OLED of the light-emitting unit 1 is calculated according to the following equation: I _OLED = K ( V _GS - V _{TH 1} ) ² = K ( V _SS + V _{TH 1} + Δ V - V _SS - V _{TH 1} ) ² ∴ I _OLED = K (Δ V ) ² ..... ( F .1)

From the above equation, the square drive of the light emitting unit 1 and the emission current I _OLED voltage proportional relationship, therefore, the light emitting unit of a driving current I _OLED of the first transistor and the threshold voltage V _{TH 1} 21 independent, Therefore, the influence of the threshold voltage V _{TH 1} on the driving current I _OLED after the first transistor 21 is mutated due to a difference in process or long-term operation thereof can be avoided. Further, in the present circuit, since only three transistors are used, the aperture ratio of the pixel can be greatly improved.

Second preferred embodiment

Referring to FIG. 3, the second preferred embodiment is different from the first preferred embodiment in that a third switch is added in the embodiment, which is the same as the first and second switches 22 and 23. In this embodiment, The third switch is implemented by a fourth transistor 25, wherein the fourth transistor 25 is also an N-type thin film transistor, but is not limited thereto.

The fourth transistor 25 has a first end electrically connected to one end of the capacitor 24, a second end electrically connected to a second end of the light emitting unit 1 and a first end of the third transistor 23, and A control terminal that receives and determines whether the first end and the second end are conductive according to a third control signal.

In this embodiment, before the pixel circuit operates in the compensation mode, a debug mode is first executed as follows: when a pixel circuit having the third switch operates in the debug mode, the first and second control signals are set. For the low potential, the third control signal is set to a high potential. Therefore, the second and third transistors 22 and 23 are in a non-conducting state, and the fourth transistor 25 is in a conducting state. At this time, when the fourth electrode is When the first end of the crystal 25 receives a data voltage (when the data voltage is an input reference voltage value V _REF ), in other words, when the pixel circuit operates in the debug mode, a reference voltage is input first. The value V _{REF is applied} to the fourth transistor 25 to detect the light-emitting unit. At this time, the voltage across the light-emitting unit 1 is V _DD - V _REF , and at this time, according to the voltage across the light-emitting unit 1 The driving current I _{REAL of} the light-emitting unit 1 can be calculated, and then a current decay rate can be calculated according to the ideal driving current I _{IDEAL of} the light-emitting unit 1 as follows:

Where α is the current decay rate.

Therefore, when the driving unit 1 is attenuated due to factors such as aging of materials or excessive use time, the current attenuation rate can be compensated by the above-mentioned current attenuation rate, and the compensation method is as follows: for example, the illuminating is assumed The brightness decay rate of the unit 1 is 0.6, and the driving current correction formula of the light-emitting unit 1 is as follows:

among them, For the corrected drive current.

The equation (F .1), with the square of the light emission drive current is a voltage proportional relationship, therefore, the equation (F .3) can be modified as follows:

Because Δ V = V _peak - V _DATA , and Δ V ^* = V _peak - V _DATA ^* , where V _{peak is} the sum of the data voltage V _DATA plus the illuminating voltage Δ V .

Therefore, the equation (F .4) can be modified as follows:

Therefore, the illumination unit 1 is operated in the debug mode, and the drive current attenuation phenomenon caused by factors such as aging of the material is obtained, and the correction formula of the data voltage is used. Therefore, the illumination unit can be avoided by the embodiment. Attenuation of the driving current caused by aging causes a phenomenon in which the luminance of the light-emitting unit 1 is simultaneously attenuated.

Finally, the third control signal is set to a low potential, so that the fourth transistor 25 is not turned on, and then the data voltage is input and the first and second control signals are set to be high, so that the pixel circuit is like the first In a preferred embodiment, the compensation mode and the illumination mode are sequentially performed to drive the illumination unit 1.

In summary, the design of the present invention can effectively avoid the critical voltage drift effect of the transistor caused by process variation or long use time, so that the pixel circuit does not affect the luminous efficiency due to the threshold voltage drift effect. At the same time, the driving current decay caused by the aging phenomenon of the organic light emitting diode can be effectively avoided, thereby causing the phenomenon that the light emitting brightness is attenuated. In addition, the design of the present invention is quite simple, and three to four transistors can be used to achieve the above purpose. Therefore, the aperture ratio is not greatly affected, so the object of the present invention can be achieved.

However, the above is only the preferred embodiment of the present invention, when not The scope of the invention is to be construed as being limited by the scope of the invention and the scope of the invention.

1‧‧‧Lighting unit

2‧‧‧Drive circuit

21‧‧‧First transistor

22‧‧‧Second transistor

23‧‧‧ Third transistor

24‧‧‧ Capacitance

25‧‧‧ Fourth transistor

1 is a circuit diagram of a first preferred embodiment of the present invention; FIG. 2 is a timing diagram of the first preferred embodiment; and FIG. 3 is a circuit diagram of a first preferred embodiment of the present invention.

1‧‧‧Lighting unit

2‧‧‧Drive circuit

21‧‧‧First transistor

22‧‧‧Second transistor

23‧‧‧ Third transistor

24‧‧‧ Capacitance

Claims (23)

A pixel circuit includes: a light emitting unit having a first end and a second end; and a driving circuit comprising: a first transistor having a first end, a second end, and a determining a first end and a second end of the control end; a capacitor; a first switch having a first end and a second end; a second switch having a first end and a second end; The third switch has a first end and a second end; wherein the first end of the light emitting unit receives a first power voltage and the second end of the first transistor receives a second power voltage, the first The first end of the switch is electrically connected to the first end of the first transistor, the second end of the first switch is electrically connected to the control end of the first transistor, and the first switch receives a first control signal, Determining whether the first end of the first transistor and the control end are electrically connected, and the first end of the second switch is electrically connected to the second end of the light emitting unit, and the second end of the second switch a first end of a transistor is electrically connected, and the second switch receives a second control signal to determine The second end of the third switch is electrically connected to the first end of the first transistor, the first end of the third switch receives a data voltage, and the second end of the third switch and the second switch One end of the light emitting unit is electrically connected to the second end of the light emitting unit, and the third switch receives a third control signal to determine whether the first end and the second end of the third switch are electrically connected, and one end of the capacitor and the first end The control end of the crystal is electrically connected, and the electric The other end of the capacitor receives a data voltage and controls the driving current of one of the light emitting units according to the conduction state of the first switch. According to the pixel circuit of claim 1, in a debug mode, wherein the first, second, and third control signals are respectively set when the pixel circuit operates in the debug mode. The first switch and the second switch are not turned on, the third switch is turned on, and then a reference voltage is transmitted to the second end of the light emitting unit. According to the pixel circuit of claim 2, the pixel circuit operates in a compensation mode and an illumination mode, wherein the first, second, and third controls are respectively set when the pixel circuit operates in the compensation mode. a signal, the first switch is turned on and the second and third switches are not turned on until the control terminal voltage of the first transistor is discharged to the second power voltage plus a threshold voltage value; when the pixel circuit operates In the illuminating mode, the first, second, and third control signals are respectively set, so that the first and third switches are not turned on and the second switch is turned on, and the data voltage is increased by a illuminating voltage to control the illuminating. The drive current of the unit is proportional to the square of the illuminating voltage. The pixel circuit of claim 3, operating in a compensation mode, further comprising setting the control terminal voltage of the first transistor to the second power voltage plus a threshold voltage value The first control signal makes the first switch non-conductive. The pixel circuit of claim 1, wherein the first switch comprises a first end, a second end, and a control end a second transistor, wherein the first end and the second end of the second transistor are respectively electrically connected to the first end and the control end of the first transistor, and the control end of the second transistor is configured to receive the first control signal . The pixel circuit of claim 1, wherein the second switch comprises a third transistor having a first end, a second end, and a control end, the first of the third transistors The second end is electrically connected to the second end of the light emitting unit and the first end of the first transistor, and the control end of the third transistor is configured to receive the second control signal. The pixel circuit of claim 1, wherein the third switch comprises a fourth transistor having a first end, a second end, and a control end, the first of the fourth transistors The second end is electrically connected to the data voltage and the second end of the light emitting unit, and the control end of the fourth transistor is configured to receive the third control signal. The pixel circuit of claim 1, wherein the light emitting unit is an organic light emitting diode. The pixel circuit of claim 1, wherein the first transistor is an N-type thin film transistor. The pixel circuit of claim 1, wherein the first transistor is a P-type film transistor. The pixel circuit of claim 1, wherein the first transistor is an N-type metal oxide semiconductor. The pixel circuit of claim 1, wherein the first transistor is a P-type metal oxide semiconductor. a driving circuit for controlling a first end and a second end The light-emitting unit includes: a first transistor having a first end, a second end, and a control end determining whether the first end and the second end are conductive; a capacitor; a first switch having a first end and a second end; a second switch having a first end and a second end; and a third switch having a first end and a second end; wherein the light emitting unit is Receiving a first power voltage at one end and receiving a second power voltage at a second end of the first transistor, the first end of the first switch is electrically connected to the first end of the first transistor, the first switch The second end is electrically connected to the control end of the first transistor, and the first switch receives a first control signal to determine whether the first end of the first transistor and the control end are electrically connected, and the first The first end of the second switch is electrically connected to the second end of the light emitting unit, the second end of the second switch is electrically connected to the first end of the first transistor, and the second switch receives a second control signal. Determining whether the second end of the light emitting unit is electrically connected to the first end of the first transistor, The first end of the third switch receives a data voltage, and the second end of the third switch is electrically connected to the first end of the second switch and the second end of the light emitting unit, and the third switch receives a third control signal Determining whether the first end and the second end of the third switch are electrically connected, one end of the capacitor is electrically connected to the control end of the first transistor, and the other end of the capacitor receives a data voltage, and according to the first The on state of the switch controls the driving current of one of the light emitting units. According to the driving circuit described in claim 13 of the patent application, in a debugging mode The operation, wherein when the driving circuit operates in the debugging mode, the first, second, and third control signals are respectively set, so that the first and second switches are not turned on, the third switch is turned on, and then A reference voltage is transmitted to the second end of the lighting unit. The driving circuit according to claim 14 is operated in a compensation mode and an illumination mode, wherein when the driving circuit operates in the compensation mode, the first, second, and third control signals are respectively set. The first switch is turned on and the second and third switches are not turned on until the control terminal voltage of the first transistor is discharged to the second power voltage plus a threshold voltage value; when the driving circuit operates in the light emitting mode The first, second, and third control signals are respectively set, so that the first and third switches are not turned on and the second switch is turned on, and the data voltage is increased by a light-emitting voltage to control driving of the light-emitting unit. The current is proportional to the square of the illuminating voltage. The driving circuit according to claim 15 of the invention, operating in a compensation mode, further comprising: setting the first voltage of the first transistor to the second power voltage plus a threshold voltage value A control signal causes the first switch to be non-conducting. The driving circuit of claim 13, wherein the first switch comprises a second transistor having a first end, a second end, and a control end, the first of the second transistors, The second end is electrically connected to the first end and the control end of the first transistor, and the control end of the second transistor is configured to receive the first control signal. The driving circuit of claim 13, wherein the second switch comprises a third transistor having a first end, a second end, and a control end, the first of the third transistors, The second end is electrically connected to the second end of the light emitting unit and the first end of the first transistor, and the control end of the third transistor is configured to receive the second control signal. The driving circuit of claim 13, wherein the third switch comprises a fourth transistor having a first end, a second end, and a control end, the first of the fourth transistors, The second end is electrically connected to the data voltage and the second end of the light emitting unit, and the control end of the fourth transistor is configured to receive the third control signal. The driving circuit of claim 13, wherein the first transistor is an N-type thin film transistor. The driving circuit of claim 13, wherein the first transistor is a P-type thin film transistor. The driving circuit of claim 13, wherein the first transistor is an N-type metal oxide semiconductor. The driving circuit of claim 13, wherein the first transistor is a P-type metal oxide semiconductor.