U.S. patent application number 15/750852 was filed with the patent office on 2020-03-19 for pixel driving circuit for oled display device and oled display device.
This patent application is currently assigned to Shenzhen China Star Optoelectronics Semiconductor Display Technology Co., Ltd.. The applicant listed for this patent is Shenzhen China Star Optoelectronics Semiconductor Display Technology Co., Ltd.. Invention is credited to Yuying CAI.
Application Number | 20200090583 15/750852 |
Document ID | / |
Family ID | 60645436 |
Filed Date | 2020-03-19 |
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United States Patent
Application |
20200090583 |
Kind Code |
A1 |
CAI; Yuying |
March 19, 2020 |
PIXEL DRIVING CIRCUIT FOR OLED DISPLAY DEVICE AND OLED DISPLAY
DEVICE
Abstract
A pixel driving circuit of OLED display device and an OLED
display device having the pixel driving circuit are disclosed. The
pixel driving circuit adopts a 4T1C pixel structure such that when
turning on or turning off, the OLED display device detects the
threshold voltage of the driving thin-film transistor, and
compensating the threshold voltage being detected into the driving
current of the organic light-emitting diode when operates normally
such that the present invention is capable of eliminating an
affection of the threshold voltage of the driving thin-film
transistor to the driving current of the organic light-emitting
diode so as to improve the quality of the display image of the OLED
display device.
Inventors: |
CAI; Yuying; (Shenzhen,
Guangdong, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shenzhen China Star Optoelectronics Semiconductor Display
Technology Co., Ltd. |
Shenzhen, Guangdong |
|
CN |
|
|
Assignee: |
Shenzhen China Star Optoelectronics
Semiconductor Display Technology Co., Ltd.
Shenzhen, Guangdong
CN
|
Family ID: |
60645436 |
Appl. No.: |
15/750852 |
Filed: |
September 27, 2017 |
PCT Filed: |
September 27, 2017 |
PCT NO: |
PCT/CN2017/103563 |
371 Date: |
February 7, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G 2320/045 20130101;
G09G 3/3225 20130101; G09G 2300/0819 20130101; G09G 2330/12
20130101; G09G 2310/0216 20130101; H01L 27/3265 20130101; H01L
27/3276 20130101; G09G 2310/0264 20130101 |
International
Class: |
G09G 3/3225 20060101
G09G003/3225; H01L 27/32 20060101 H01L027/32 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 2017 |
CN |
201710709578.8 |
Claims
1. A pixel driving circuit for OLED display device, comprising: a
first thin-film transistor, wherein a gate electrode of the first
thin-film transistor T1 is electrically connected to a first node,
and a source electrode of the first thin-film transistor is
electrically connected to a second node; a second thin-film
transistor, wherein a gate electrode of the second thin-film
transistor receives a second scanning signal, and a drain electrode
of the second thin-film transistor is electrically connected to the
first node; a third thin-film transistor, wherein a gate electrode
of the third thin-film transistor receives a third scanning signal,
a drain electrode of the third thin-film transistor is connected to
a drain electrode of the first thin-film transistor, and a source
electrode of the third thin-film transistor is electrically
connected to a direct-current power positive electrode; a fourth
thin-film transistor, wherein a gate electrode of the fourth
thin-film transistor receives the first scanning signal, and a
drain electrode of the fourth thin-film transistor is electrically
connected to the second node; a capacitor, wherein one terminal of
the capacitor is electrically connected to the first node, and the
other terminal of the capacitor is electrically connected to the
second node; an organic light-emitting diode, an anode of the
organic light-emitting diode is electrically connected to the
second node, and a cathode of the organic light-emitting diode is
electrically connected to a direct-current power negative
electrode; when the organic light-emitting diode display device is
turned off or turned on, the source electrode of the second
thin-film transistor receives a first data signal, the source
electrode of the fourth thin-film transistor receives an
initialization signal or a threshold voltage detector, the
threshold voltage detector is used for detecting a threshold
voltage of the first thin-film transistor, and generating a
threshold voltage signal; when the organic light-emitting diode
display device operates normally, the source electrode of the
second thin-film transistor receives a second data signal formed by
the threshold voltage signal and an original data signal, and the
source electrode of the fourth thin-film transistor receives the
initialization signal; and wherein each of the initialization
signal and the first data signal has a constant low voltage level,
and the original data signal has a pulse high voltage level.
2. The pixel driving circuit according to claim 1, wherein when the
organic light-emitting diode display device is turned off or turned
on, the pixel driving circuit executes a reset operation and a
threshold voltage detection operation.
3. The pixel driving circuit according to claim 2, wherein in the
reset operation, each of the first scanning signal, the second
scanning signal and the third scanning signal is at a high voltage
level, and the source electrode of the fourth thin-film transistor
receives the initialization signal.
4. The pixel driving circuit according to claim 3, wherein in the
threshold voltage detection operation, each of the first scanning
signal, the second scanning signal, and the third scanning signal
is at a high voltage level, and the source electrode of the fourth
thin-film transistor receives the threshold voltage detector.
5. The pixel driving circuit according to claim 1, wherein when the
organic light-emitting diode display device displays normally, the
pixel driving circuit executes a reset operation, a threshold
voltage detection operation, a threshold voltage compensation
operation and a driving emitting operation.
6. The pixel driving circuit according to claim 5, wherein in the
reset operation, each of the first scanning signal and the second
scanning signal is at a high voltage level, the third scanning
signal is at a low voltage level, the second data signal is a sum
of the reference signal having a low voltage level and the
threshold voltage signal.
7. The pixel driving circuit according to claim 6, wherein in the
threshold voltage detection operation, the firs scanning signal is
at low voltage level, each of the second scanning signal and the
third scanning signal is at a high voltage level, and the second
data signal is a sum of the reference signal having the low voltage
level and the threshold voltage signal.
8. The pixel driving circuit according to claim 7, wherein in the
threshold voltage compensation operation, each of the first
scanning signal and the third scanning signal is at a low voltage
level, the second scanning signal is at a high voltage level, and
the second data signal is a sum of the displaying data signal
having a high voltage level and the threshold voltage signal.
9. The pixel driving circuit according to claim 8, wherein in the
driving emitting operation, each of the first scanning signal and
the second scanning signal is at a low voltage level, the third
scanning signal is at a high voltage level, and the second data
signal is a sum of the reference signal having a low voltage level
and the threshold voltage signal.
10. An OLED display device, wherein the display device includes a
pixel driving circuit as claimed in claim 1.
11. The OLED display device according to claim 10, wherein when the
OLED display device is turned off or turned on, the pixel driving
circuit executes a reset operation and a threshold voltage
detection operation; wherein in the reset operation, each of the
first scanning signal, the second scanning signal and the third
scanning signal is at a high voltage level, and the source
electrode of the fourth thin-film transistor receives the
initialization signal; wherein in the threshold voltage detection
operation, each of the first scanning signal, the second scanning
signal, and the third scanning signal is at a high voltage level,
and the source electrode of the fourth thin-film transistor
receives the threshold voltage detector.
12. The OLED display device according to claim 10, wherein when the
OLED display device displays normally, the pixel driving circuit
executes a reset operation, a threshold voltage detection
operation, a threshold voltage compensation operation and a driving
emitting operation; wherein in the reset operation, each of the
first scanning signal and the second scanning signal is at a high
voltage level, the third scanning signal is at a low voltage level,
the second data signal is a sum of the reference signal having a
low voltage level and the threshold voltage signal; wherein in the
threshold voltage detection operation, the first scanning signal is
at low voltage level, each of the second scanning signal and the
third scanning signal is at a high voltage level, and the second
data signal is a sum of the reference signal having the low voltage
level and the threshold voltage signal; wherein in the threshold
voltage detection operation, the firs scanning signal is at low
voltage level, each of the second scanning signal and the third
scanning signal is at a high voltage level, and the second data
signal is a sum of the reference signal having the low voltage
level and the threshold voltage signal; and wherein in the driving
emitting operation, each of the first scanning signal and the
second scanning signal is at a low voltage level, the third
scanning signal is at a high voltage level, and the second data
signal is a sum of the reference signal having a low voltage level
and the threshold voltage signal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a display technology field,
and more particularly to a pixel driving circuit for OLED display
device and OLED display device.
2. Description of Related Art
[0002] Recently, an Organic Light-Emitting Diode (OLED) display
device has become a hot and emerging flat display device at home
and abroad. The reason is that an OLED display device has features
of self-luminous, wide viewing angle, short response time, high
luminous efficiency, wide color gamut, low operating voltage, thin
thickness, capable of producing large-size and flexible display
device and the simple process. Besides, the OLED display further
has a low cost potential.
[0003] In an OLED display device, a thin-film transistor (TFT) is
adopted to cooperate with a capacitor to store a signal to control
a brightness grayscale level of the OLED display device. In order
to achieve a constant current driving purpose, each pixel at least
requires two TFTs and one storage capacitor, that is, a 2T1C mode.
FIG. 1 is a circuit diagram of a pixel driving circuit of a
conventional OLED display device. With reference to FIG. 1, the
driving circuit of the conventional OLED display device includes
two thin-film transistors (TFT) and one capacitor. Specifically,
including one switching TFT Ti, a driving TFT T2 and one storage
capacitor Cst. A driving current of the OLED is controlled by the
driving TFT T2, and the magnitude of the driving current is:
I.sub.OLED=k(V.sub.gs-V.sub.th).sup.2, wherein k is intrinsic
conductance factor of the driving TFT T2, and is decided by the
characteristic of the driving TFT T2 itself, V.sub.th is a
threshold voltage of the TFT T2, V.sub.gs is a voltage between a
gate electrode and a source electrode of the TFT T2. Because of the
long time operation, the threshold voltage V.sub.th of the driving
TFT T2 will generate a drift, the driving current of the OLED will
change such that the OLED display device will occur a bad display
so as to affect the quality of the display image.
SUMMARY OF THE INVENTION
[0004] In order to solve the above technology problem, the purpose
of the present invention is to provide a pixel driving circuit and
an OLED display device capable of eliminating an affection of the
threshold voltage of the driving thin-film transistor to the
driving current of the organic light-emitting diode.
[0005] According to an aspect of the present invention, providing a
pixel driving circuit for OLED display device, comprising: a first
thin-film transistor, wherein a gate electrode of the first
thin-film transistor T1 is electrically connected to a first node,
and a source electrode of the first thin-film transistor is
electrically connected to a second node; a second thin-film
transistor, wherein a gate electrode of the second thin-film
transistor receives a second scanning signal, and a drain electrode
of the second thin-film transistor is electrically connected to the
first node; a third thin-film transistor, wherein a gate electrode
of the third thin-film transistor receives a third scanning signal,
a drain electrode of the third thin-film transistor is connected to
a drain electrode of the first thin-film transistor, and a source
electrode of the third thin-film transistor is electrically
connected to a direct-current power positive electrode; a fourth
thin-film transistor, wherein a gate electrode of the fourth
thin-film transistor receives the first scanning signal, and a
drain electrode of the fourth thin-film transistor is electrically
connected to the second node; a capacitor, wherein one terminal of
the capacitor is electrically connected to the first node, and the
other terminal of the capacitor is electrically connected to the
second node; an organic light-emitting diode, an anode of the
organic light-emitting diode is electrically connected to the
second node, and a cathode of the organic light-emitting diode is
electrically connected to a direct-current power negative
electrode; when the organic light-emitting diode display device is
turned off or turned on, the source electrode of the second
thin-film transistor receives a first data signal, the source
electrode of the fourth thin-film transistor receives an
initialization signal or a threshold voltage detector, the
threshold voltage detector is used for detecting a threshold
voltage of the first thin-film transistor, and generating a
threshold voltage signal; when the organic light-emitting diode
display device operates normally, the source electrode of the
second thin-film transistor receives a second data signal formed by
the threshold voltage signal and an original data signal, and the
source electrode of the fourth thin-film transistor receives the
initialization signal; and wherein each of the initialization
signal and the first data signal has a constant low voltage level,
and the original data signal has a pulse high voltage level.
[0006] Furthermore, when the organic light-emitting diode display
device is turned off or turned on, the pixel driving circuit
executes a reset operation and a threshold voltage detection
operation.
[0007] Furthermore, in the reset operation, each of the first
scanning signal, the second scanning signal and the third scanning
signal is at a high voltage level, and the source electrode of the
fourth thin-film transistor receives the initialization signal.
[0008] Furthermore, in the threshold voltage detection operation,
each of the first scanning signal, the second scanning signal, and
the third scanning signal is at a high voltage level, and the
source electrode of the fourth thin-film transistor receives the
threshold voltage detector.
[0009] Furthermore, when the organic light-emitting diode display
device displays normally, the pixel driving circuit executes a
reset operation, a threshold voltage detection operation, a
threshold voltage compensation operation and a driving emitting
operation.
[0010] Furthermore, in the reset operation, each of the first
scanning signal and the second scanning signal is at a high voltage
level, the third scanning signal is at a low voltage level, the
second data signal is a sum of the reference signal having a low
voltage level and the threshold voltage signal.
[0011] Furthermore, in the threshold voltage detection operation,
the firs scanning signal is at low voltage level, each of the
second scanning signal and the third scanning signal is at a high
voltage level, and the second data signal is a sum of the reference
signal having the low voltage level and the threshold voltage
signal.
[0012] Furthermore, in the threshold voltage compensation
operation, each of the first scanning signal and the third scanning
signal is at a low voltage level, the second scanning signal is at
a high voltage level, and the second data signal is a sum of the
displaying data signal having a high voltage level and the
threshold voltage signal.
[0013] Furthermore, in the driving emitting operation, each of the
first scanning signal and the second scanning signal is at a low
voltage level, the third scanning signal is at a high voltage
level, and the second data signal is a sum of the reference signal
having a low voltage level and the threshold voltage signal.
[0014] According to another aspect of the present invention, the
present invention also provides an OLED display device, including
the pixel driving circuit described above.
[0015] The beneficial effect of the present invention: the OLED
display device of the present invention detect the threshold
voltage of the driving thin-film transistor when turning on or
turning off, and compensating the threshold voltage being detected
into the driving current of the organic light-emitting diode when
operates normally such that the present invention is capable of
eliminating an affection of the threshold voltage of the driving
thin-film transistor to the driving current of the organic
light-emitting diode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Through following to combine figures to describe in detail,
the above, the other purposes, the features and benefits of the
exemplary embodiment of the present disclosure will become clearer,
wherein:
[0017] FIG. 1 is a circuit diagram of a pixel driving circuit of a
conventional OLED display device;
[0018] FIG. 2 is a schematic diagram of an organic light-emitting
diode display device according to an embodiment of the present
invention;
[0019] FIG. 3 is an equivalent circuit diagram of a pixel structure
of an organic light-emitting diode display device according to an
embodiment of the present invention;
[0020] FIG. 4 is a timing diagram of each operation stage of the
pixel driving circuit when turning on or off according to an
embodiment of the present invention;
[0021] FIG. 5A and FIG. 5B are operation process diagrams of the
pixel driving circuit when turning on or turning off according to
an embodiment of the present invention;
[0022] FIG. 6 is a timing diagram of each operation stage when the
pixel driving circuit displays normally; and
[0023] FIG. 7A to FIG. 7D are operation process diagrams of the
pixel driving circuit when displaying normally according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The following content combines with the drawings and the
embodiment for describing the present invention in detail. However,
many other forms can be used to implement the present invention.
Besides, the present invention should not be interpreted to be
limit in the specific embodiment described here. On the contrary,
the embodiments provided here are used for explaining the operation
principle and practical application such that person skilled in the
art can under various embodiments of the present invention and
various modification suitable for specific applications.
[0025] In the figures, in order to illustrate the devices clearly,
thickness of the layers and regions are enlarged. A same numeral in
the entire specification and figures represents a same device.
[0026] FIG. 2 is a schematic diagram of an organic light-emitting
diode display device according to an embodiment of the present
invention.
[0027] With reference to FIG. 2, the organic light-emitting diode
display device includes: a display panel 100, a scanning driver 200
and a data driver 300. It should be noted that the organic
light-emitting diode display device according to the present
invention can also include the other suitable devices such as a
timing controller that controls the scanning driver 200 and the
data driver 300 and a power voltage generator for providing a power
positive voltage and a power negative voltage.
[0028] Specifically, the display panel 100 includes: multiple
pixels PX arranged as a matrix, N scanning lines G.sub.1 to
G.sub.N, M data lines D.sub.1 to D.sub.M. The scanning driver 200
is connected to the scanning lines G.sub.1 to G.sub.N, and drives
the scanning lines G.sub.1 to G.sub.N. The data driver 300 is
connected to the data lines D.sub.1 to D.sub.M, and drives the data
lines D.sub.1 to D.sub.M.
[0029] The scanning driver 200 can provide one or more scanning
signals to each pixel PX, and will be illustrated later. The data
driver 300 can provide data signal to each pixel PX, and will be
illustrated later.
[0030] Each pixel includes a pixel driving circuit. The following
content will describe the pixel driving circuit (that is, the pixel
structure of pixel PX) according to an embodiment of the present
invention in detail.
[0031] FIG. 3 is an equivalent circuit diagram of a pixel structure
of an organic light-emitting diode display device according to an
embodiment of the present invention.
[0032] With reference to FIG. 3, each pixel PX of the organic
light-emitting diode display device according to an embodiment of
the present invention has a 4T1C pixel structure. The 4T1C pixel
structure includes an organic light-emitting diode OLED, a first
thin-film transistor T 1, a second thin-film transistor T2, a third
thin-film transistor T3, a fourth thin-film transistor T4 and a
capacitor C.
[0033] A gate electrode of the first thin-film transistor T1 is
electrically connected to a first node "a", and a source electrode
of the first thin-film transistor T1 is electrically connected to a
second node "b".
[0034] A gate electrode of the second thin-film transistor T2
receives a second scanning signal Scan2, and a drain electrode of
the second thin-film transistor T2 is electrically connected to the
first node "a".
[0035] A gate electrode of the third thin-film transistor T3
receives a third scanning signal Scan3, and a drain electrode of
the third thin-film transistor T3 is connected to a drain electrode
of the first thin-film transistor T1, and a source electrode of the
third thin-film transistor T3 is electrically connected to a
direct-current power positive electrode Vdd.
[0036] A gate electrode of the fourth thin-film transistor T4
receives the first scanning signal Scan1, and a drain electrode of
the fourth thin-film transistor T4 is electrically connected to the
second node "b".
[0037] One terminal of the capacitor C is electrically connected to
the first node "a", and the other terminal of the capacitor C is
electrically connected to the second node "b".
[0038] An anode of the organic light-emitting diode OLED is
electrically connected to the second node "b", and a cathode of the
organic light-emitting diode OLED is electrically connected to a
direct-current power negative electrode Vss.
[0039] Wherein, the first thin-film transistor T1 is a driving
thin-film transistor.
[0040] When the organic light-emitting diode display device is
turned off or turned on (or in a preset period after turning off or
turning on), the source electrode of the second thin-film
transistor T2 receives a first data signal DATA1, the source
electrode of the fourth thin-film transistor T4 receives an
initialization signal INI or a threshold voltage detector 400. The
threshold voltage detector 400 is used for detecting a threshold
voltage Vth of the first thin-film transistor T1, and generating a
threshold voltage signal. The specific working process will be
described below.
[0041] When the organic light-emitting diode display device
operates normally (that is, a period after turning on (or a preset
time after turning on) to turning off), the source electrode of the
second thin-film transistor T2 receives a second data signal DATA2
formed by the threshold voltage signal and an original data signal,
and the source electrode of the fourth thin-film transistor T4
receives the initialization signal INI.
[0042] In the present embodiment, the initialization signal INI and
the first data signal DATA1 has a constant low voltage level, and
the original data signal has a unit pulse high voltage level.
[0043] Specifically, the first thin-film transistor T1, the second
thin-film transistor T2, the third thin-film transistor T3, and the
fourth thin-film transistor T4 are all low temperature polysilicon
thin-film transistors, oxide semiconductor thin-film trans.
[0044] The first scanning signal Scan1, the second scanning signal
Scan2, the third scanning signal Scan3, the initialization signal
INI, the first data signal DATA1 and the original data signal are
all generated through an external timing controller (not
shown).
[0045] The following will illustrate the operation principle when
the pixel driving circuit is turned on or turned off according to
an embodiment of the present invention in detail. In the present
embodiment, the pixel driving circuit adopting the 4T1C pixel
structure according to an embodiment of the present invention
execute a reset operation (that is, a reset stage) and a threshold
voltage detection operation (that is, a threshold voltage detection
stage). FIG. 4 is a timing diagram of each operation stage of the
pixel driving circuit when turning on or off according to an
embodiment of the present invention. FIG. 5A and FIG. 5B are
operation process diagrams of the pixel driving circuit when
turning on or turning off according to an embodiment of the present
invention.
[0046] In a reset stage, with reference to FIG. 4 and FIG. 5A, each
of the first scanning signal Scan1, the second scanning signal
Scan2 and the third scanning signal Scan3 is at a high voltage
level. The first data signal DATA1 is at a low voltage level VA,
the source electrode of the fourth thin-film transistor T4 receives
the initialization signal INI. The initialization signal INI is at
a low voltage level Vini. At this time, the third thin-film
transistor T3, the second thin-film transistor T2 and the fourth
thin-film transistor T4 are all turned on. The voltage at the first
node "a" Va=VA, the voltage at the second node "b" Vb=Vini. Setting
Vini=VA in order to finish the initialization.
[0047] In the threshold voltage detection stage, with reference to
FIG. 4 and FIG. 5B, each of the first scanning signal Scan1, the
second scanning signal Scan2 and the third scanning signal Scan3 is
at a high voltage level. The first data signal DATA1 is at a low
voltage level VA. The source electrode of the fourth thin-film
transistor T4 receives the threshold voltage detector 400. At this
time, the third thin-film transistor T3, the second thin-film
transistor T2 and the fourth thin-film transistor T4 are all turned
on. The voltage at the first node "a" Va=VA, the voltage at the
second node "b" Vb=VA-Vth so that the voltage sensed by the
threshold voltage detector 400 is VA-Vth. Wherein Vth is a
threshold voltage of the first thin-film transistor T1.
Furthermore, through an internal calculation of the threshold
voltage detector 400 such as using the voltage VA to subtract the
voltage sensed by the threshold voltage detector 400 in order to
obtain the threshold voltage Vth. Then, the threshold voltage
detector 400 feedback the threshold voltage Vth being obtained to
the original signal in order to overlap with the original data
signal to form the second data signal DATA2. The specific process
is described below.
[0048] The flowing will describe the operation principle when the
pixel driving circuit displays normally according to an embodiment
of the present invention, in the present embodiment, the pixel
driving circuit adopting the 4T1C pixel structure in the present
embodiment of the present invention executes a reset operation
(reset stage), a threshold voltage detection operation (threshold
voltage detection stage), a threshold voltage compensation
operation (that is, a threshold voltage compensation stage) and a
driving emitting operation (that is, a driving emitting stage).
FIG. 6 is a timing diagram of each operation stage when the pixel
driving circuit displays normally. FIG. 7A to FIG. 7D are operation
process diagrams of the pixel driving circuit when displaying
normally according to an embodiment of the present invention. In
FIG. 7A to FIG. 7D, a cross symbol (X) on the thin-film transistor
represents that the thin-film transistor is under an off state.
[0049] In the reset stage, with reference to FIG. 6 and FIG. 7A,
each of the first scanning signal Scan1 and the second scanning
signal Scan2 is at a high voltage level, the third scanning signal
Scan3 is at a low voltage level, the second data signal DATA2 is a
sum of the reference signal Vref having a low voltage level and the
threshold voltage signal Vth, and the source electrode of the
fourth thin-film transistor T4 receives the initialization signal
INI. At this time, the third thin-film transistor T3 is turned off,
the second thin-film transistor T2 and the fourth thin-film
transistor T4 are turned on. The constant low voltage level of the
initialization signal INI is inputted to the second node "b" (that
is, the source electrode of the first thin-film transistor T1)
through the fourth thin-film transistor T4. The second data signal
DATA2 is inputted to the first node "a" (that is the gate electrode
of the first thin-film transistor T1) through the third thin-film
transistor T3 in order to initialize the gate electrode and the
source electrode of the first thin-film transistor T1 to empty a
remaining data. The first thin-film transistor T1 is turned off,
and the organic light-emitting diode OLED does not emit a
light.
[0050] In the reset stage:
Vg=Va=Vref+Vth
Vs=Vb=Vini
[0051] wherein, Vg represents a gate voltage of the first thin-film
transistor T1, Va represents a voltage at the first node "a", Vs
represent a source voltage of the first thin-film transistor T1, Vb
represents a voltage of the second node "b", Vini represent the
constant low voltage of the initialization signal INI.
[0052] In the threshold voltage detection stage, with reference to
FIG. 6 and FIG. 7B, the firs scanning signal Scan1 is at low
voltage level, each of the second scanning signal Scan2 and the
third scanning signal Scan3 is at a high voltage level. The second
data signal DATA2 is a sum of the reference signal Vref having a
low voltage level and the threshold voltage signal Vth. At this
time, the second thin-film transistor T2 and the third thin-film
transistor T3 are turned on, and the fourth thin-film T4 is turned
off. The gate electrode of the first thin-film transistor T1, that
is the first node "a", is inputted with the second data signal
DATA2 formed by a sum of the reference signal Vref having the low
voltage level and the threshold voltage Vth, and the voltage level
at the source voltage of the first thin-film transistor T1, that is
the second node "b" becomes Vref.
[0053] In the threshold voltage detection stage:
Vg=Va=Vref+Vth
Vs=Vb=Vref
[0054] In the threshold voltage compensation stage, with reference
to FIG. 6 and FIG. 7C, each of the first scanning signal Scan1 and
the third scanning signal Scan3 is at a low voltage level, the
second scanning signal Scan2 is at a high voltage level. The second
data signal DATA2 is a sum of the displaying data signal Vdata
having high voltage level and the threshold voltage signal Vth. At
this time, the third thin-film transistor T3 and the fourth
thin-film transistor T4 are turned off, the second thin-film
transistor T2 is turned on, the second data signal DATA2 inputs the
sum of the displaying data signal Vdata having the high voltage
level and the threshold voltage Vth to the first node "a" (that is,
the gate electrode of the first thin-film transistor T1) and the
capacitor C. The voltage level of the source electrode of the first
thin-film transistor T1 (that is, the second node "b") becomes
Vref+.DELTA.V. Wherein the .DELTA.V is an affection of the
displaying data signal Vdata having the high voltage level to the
voltage level of the source electrode of the first thin-film
transistor T1, and is unrelated to the threshold voltage Vth of the
first thin-film transistor.
[0055] In the threshold voltage compensation stage:
Vg=Va=Vdata+Vth
Vs=Vb=Vref+.DELTA.V
[0056] By this way, a difference value between the gate voltage Vg
and the source voltage Vs of the first thin-film transistor T1
is:
Vgs=Vg-Vs=Vdata+Vth-Vref-.DELTA.V
[0057] In the driving emitting stage, with reference to FIG. 6 and
FIG. 7D, each of the first scanning signal Scan1 and the second
scanning signal Scan2 is at a low voltage level, the third scanning
signal Scan3 is at a high voltage level. The second data signal
DATA2 is a sum of the reference signal Vref having a low voltage
level and the threshold voltage signal Vth. At this time, the
second thin-film transistor T2 to the fourth thin-film transistor
T4 are all turned off. Because of the storage function of the
capacitor C, the voltage difference Vgs between the gate voltage Vg
(that is the first node "a") and the source voltage Vs (that is the
second node "b") of the first thin-film transistor T1 is
unchanged.
[0058] Furthermore, the current I flowing through the organic
light-emitting diode OLED can be represented as:
I=K(Vgs-Vth).sup.2=K(Vdata-Vref-.DELTA.V+Vth-Vth).sup.2=K(Vdata-Vref-.DE-
LTA.V).sup.2
[0059] Wherein, K represents an intrinsic conductance factor of the
first thin-film transistor T1, and is decided by the characteristic
of the first thin-film transistor itself.
[0060] Accordingly, in the express of the current I flowing through
the organic light-emitting diode OLED, the current I is unrelated
to the threshold voltage Vth of the first thin-film transistor T1
such that the bad display generated by the drift of the threshold
voltage Vth of the first thin-film transistor T1 is eliminated.
[0061] The above embodiments of the present invention are only
exemplary, however, the present invention is not limited. The
person skilled in the art can understand: without exceeding the
principle and spirit of the present invention, the above
embodiments can be changed in form and detail.
* * * * *