U.S. patent application number 14/550651 was filed with the patent office on 2015-03-19 for display device and driving method thereof.
The applicant listed for this patent is SAMSUNG DISPLAY CO., LTD.. Invention is credited to Choon-Yul OH, Myoung-Hwan YOO.
Application Number | 20150077414 14/550651 |
Document ID | / |
Family ID | 44476113 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150077414 |
Kind Code |
A1 |
YOO; Myoung-Hwan ; et
al. |
March 19, 2015 |
DISPLAY DEVICE AND DRIVING METHOD THEREOF
Abstract
A display device includes a display unit including a plurality
of scan lines, a plurality of data lines to which a plurality of
compensation data signals are transmitted, a plurality of light
emitting signal lines, and a plurality of pixels respectively
connected to the plurality of scan lines, the plurality of data
lines, and the plurality of light emitting signal lines, and a data
driver generating a data voltage corresponding to a image data
signal, and converting the data voltage to the compensation data
signal. The data driver includes a compensator generating the
compensation data signal in accordance with a feedback voltage. The
feedback voltage is determined by a degree of deterioration
associated with each pixel, and increases with an increasing
deterioration degree of the pixel.
Inventors: |
YOO; Myoung-Hwan;
(Yongin-City, KR) ; OH; Choon-Yul; (Yongin-City,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG DISPLAY CO., LTD. |
Yongin-City |
|
KR |
|
|
Family ID: |
44476113 |
Appl. No.: |
14/550651 |
Filed: |
November 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12929802 |
Feb 16, 2011 |
8896585 |
|
|
14550651 |
|
|
|
|
Current U.S.
Class: |
345/212 |
Current CPC
Class: |
G09G 2320/0295 20130101;
G09G 3/3275 20130101; G09G 2300/043 20130101; G09G 2300/0861
20130101; G09G 2320/043 20130101 |
Class at
Publication: |
345/212 |
International
Class: |
G09G 3/32 20060101
G09G003/32 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2010 |
KR |
10-2010-0015379 |
Claims
1.-15. (canceled)
16. A display device, comprising: a display unit including a
plurality of scan lines to which a plurality of scan signals are
transmitted, a plurality of data lines to which a plurality of
compensation data signals are transmitted, a plurality of light
emitting signal lines to which a plurality of light emitting
signals are transmitted, and a plurality of pixels respectively
connected to the plurality of scan lines, the plurality of data
lines, and the plurality of light emitting signal lines; and a data
driver configured to generate a data voltage corresponding to an
image data signal and to convert the data voltage into a
compensation data signal, wherein the data driver includes a
compensator configured to receive a feedback voltage from each
pixel according to a compensation control signal generated in
accordance with the scan signal, the compensation control signal
being supplied to the compensator and the plurality of pixels, the
compensation data signal being determined in accordance with the
feedback voltage.
17. The display device as claimed in claim 16, wherein the
compensation control signal is generated in synchronization with
the scan signal.
18. The display device as claimed in claim 16, wherein: the
feedback voltage corresponds to the degree of deterioration of the
pixel; and the compensation control signal is generated from the
scan signal with a predetermined phase delay.
19. The display device as claimed in claim 18, wherein each of the
plurality of pixels comprises: a switching transistor having a
source terminal connected to the data line and a gate terminal
connected to the scan line; a driving transistor having a source
terminal receiving a first power source voltage and a gate terminal
connected to a drain terminal of the switching transistor; a
capacitor having a first end connected to the source terminal of
the driving transistor and a second end connected between the gate
terminal of the driving transistor; a light emission control
transistor having a gate terminal connected to the light emitting
signal line and a source terminal connected to the drain terminal
of the driving transistor; an organic light emitting diode (OLED)
having an anode connected to the drain terminal of the light
emission control transistor and a cathode receiving a second power
source voltage; and a threshold voltage compensation transistor
having a gate terminal receiving the compensation control signal, a
drain terminal connected to the drain terminal of the driving
transistor, and a source terminal connected to the source terminal
of the switching transistor.
20. The display device as claimed in claim 19, wherein the
compensator comprises: a deterioration detector detecting a voltage
at both ends of the organic light emitting diode as the feedback
voltage according to the compensation control signal; and a
compensation data voltage generator calculating the variation
amount of the feedback voltage and generating the compensation data
signal by compensating the data voltage by the amount of the
calculated feedback voltage.
21. The display device as claimed in claim 20, wherein the
compensator further comprises a switch transmitting the
compensation data signal to the pixel according to a load signal
that instructs transmission of the compensation data signal to the
plurality of data lines.
22. The display device as claimed in claim 20, wherein the
deterioration detector comprises: an analog digital converter
transmitting the feedback voltage to the compensation data voltage
generator; and a switch transmitting the feedback voltage to the
analog digital converter according to the compensation control
signal.
23. A driving method of a display device including a plurality of
scan lines to which a plurality of scan signals are transmitted, a
plurality of data lines to which a plurality of compensation data
signals are transmitted, a plurality of light emitting signal lines
to which a plurality of light emitting signals are transmitted, and
a plurality of pixels respectively connected to the plurality of
scan lines, the plurality of data lines, and the plurality of light
emitting signal lines, the driving method comprising: generating a
data voltage corresponding to an image data signal; outputting a
feedback voltage from each of the plurality of pixels according to
a compensation control signal generated in accordance with the scan
signal; detecting the feedback voltage from each of the plurality
of pixels according to the compensation control signal; and
compensating the data voltage in accordance with the feedback
voltage.
24. The driving method as claimed in claim 23, wherein: the
feedback voltage corresponds to the degree of deterioration of the
pixel; and the compensation control signal is generated from the
scan signal with a predetermined phase delay.
25. The driving method as claimed in claim 24, wherein detecting
the feedback voltage comprises: applying the data voltage to each
of the plurality of pixels; transmitting a current corresponding to
the data voltage to an organic light emitting diode according to
the light emission control signal; and generating a voltage at both
ends of the organic light emitting diode with the feedback
voltage.
26. The driving method as claimed in claim 24, further comprising
transmitting the compensation data signal to the pixel is in
accordance with a load signal that instructs transmission of the
compensation data signal to the plurality of data lines.
27. The method as claimed in claim 23, wherein the compensation
control signal is generated in synchronization with the scan
signal.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application based on pending
application Ser. No. 12/929,802, filed Feb. 16, 2011, the entire
contents of which is hereby incorporated by reference.
BACKGROUND
[0002] 1. Field
[0003] Embodiments relate to a display device and a driving method
thereof. More particularly, embodiments relate to an organic light
emitting diode (OLED) display and a driving method thereof.
[0004] 2. Description of the Related Art
[0005] A display device includes a display panel formed of a
plurality of pixels arranged in a matrix format. A display panel
may include a plurality of scan lines formed in a row direction and
a plurality of data lines formed in a column line. The plurality of
scan lines and the plurality of data lines are arranged to cross
each other. Each of the plurality of pixels is driven by a scan
signal and a data signal transmitted from respectively
corresponding scan and data lines.
[0006] The display device is classified into a passive matrix (PM)
light emitting display device and an active matrix (AM) light
emitting display device depending on the method of driving the
pixels. In view of resolution, contrast, and response time, the
trend is towards the AM display devices in which respective unit
pixels are selectively turned on or off.
[0007] The display device is used as a display unit for a personal
computer, a portable phone, a PDA, and other mobile information
devices, or as a monitor for various kinds of information systems.
A liquid crystal panel-based LCD, an organic light emitting diode
(OLED) display, a plasma panel-based PDP, etc., are well known.
Various kinds of emissive display devices, which have lower weight
and volume than CRTs, have been recently developed. Particularly,
organic light emitting diode (OLED) displays have come to the
forefront, due to their excellent emissive efficiency, luminance,
and viewing angle, and short response time.
[0008] Each pixel of the OLED display includes an OLED and a
driving transistor for driving the OLED. However, the current
flowing in the OLED is changed due to changes in the threshold
voltage of the driving transistor. In order to solve this problem,
the threshold voltage of the driving transistor is calculated to
compensate a data voltage with the calculated threshold voltage.
However, the threshold voltage cannot be accurately calculated,
resulting in inconsistent luminance of the OLED.
[0009] The above information disclosed in this Background section
is only for enhancement of understanding of the background of the
invention and therefore it may contain information that does not
form the prior art that is already known in this country to a
person of ordinary skill in the art.
SUMMARY
[0010] Embodiments are therefore directed to a display device and
driving method thereof, which substantially overcome one or more of
the problems due to the limitations and disadvantages of the
related art.
[0011] It is therefore a feature of an embodiment to provide a
display device that can constantly maintain luminance of an organic
light emitting diode, and a driving method thereof.
[0012] A display device according to an exemplary embodiment
includes a display unit and a data driver. The display unit
includes a plurality of scan lines to which a plurality of scan
signals are transmitted, a plurality of data lines to which a
plurality of compensation data signals are transmitted, a plurality
of light emitting signal lines to which a plurality of light
emitting signals are transmitted, and a plurality of pixels
respectively connected to the plurality of scan lines, the
plurality of data lines, and the plurality of light emitting signal
lines. The data driver generates a data voltage corresponding to an
image data signal, and converting the data voltage to the
compensation data signal. The data driver includes a compensator
configured to generate an additive voltage by adding a
predetermined first power source voltage to the data voltage,
receive a feedback voltage corresponding to a threshold voltage of
a driving transistor of each pixel according to a compensation
control signal generated by synchronization with the scan signal,
and generate a difference between the additive voltage and the
feedback voltage as the compensation data signal.
[0013] The compensator may include an additive voltage generator
configured to generate the additive voltage by adding the data
voltage and the first power source voltage, a compensation data
voltage generator configured to generate the compensation data
signal by performing subtraction between the additive voltage and
the feedback voltage, a first switch transmitting the feedback
voltage to the compensation data voltage generator according to the
compensation control signal; and a second switch transmitting the
compensation data signal to the pixel according to a load signal
that instructs transmission of the compensation data signal to the
plurality of data lines. The compensation data voltage generator
may include a non-inversion terminal receiving the additive
voltage, an inversion terminal receiving the feedback voltage, and
an output terminal connected to the data line.
[0014] Each of the plurality of pixels may includes a switch
transistor having a source terminal connected to the data line and
a gate line connected to the scan line, a driving transistor having
a source terminal receiving the first power source voltage and a
gate terminal connected to a drain terminal of the switching
transistor, a capacitor having a first end connected to the source
terminal of the driving transistor and a second end connected
between the gate terminals of the driving transistor, a light
emission control transistor having a gate terminal connected to the
light emitting signal line and a source terminal connected to the
drain of the driving transistor, an organic light emitting diode
(OLED) having an anode connected to the drain terminal of the light
emission control transistor and a cathode receiving a second power
source voltage, and a threshold voltage compensation transistor
having a gate terminal receiving the compensation control signal, a
drain terminal connected to the drain terminal of the driving
transistor, and a source terminal connected to the source terminal
of the switching transistor.
[0015] A driving method according to another exemplary embodiment
is provided to a display device including a plurality of scan lines
to which a plurality of scan signals are transmitted, a plurality
of data lines to which a plurality of compensation data signals are
transmitted, a plurality of light emitting signal lines to which a
plurality of light emitting signals are transmitted, and a
plurality of pixels respectively connected to the plurality of scan
lines, the plurality of data lines, and the plurality of light
emitting signal lines. The driving method includes generating a
data voltage corresponding to an image data signal, generating an
additive voltage by adding a predetermined power source voltage to
the data voltage, receiving a feedback voltage corresponding to a
threshold voltage of a driving transistor of each of the plurality
of pixels according to a compensation control signal generated by
synchronization with the scan signal, and generating a difference
between the additive voltage and the feedback voltage and
transmitting the difference as a compensation data signal to the
plurality of data lines. The feedback voltage may equal a
difference between the power source voltage and the threshold
voltage of the driving transistor.
[0016] A display device according to another exemplary embodiment
includes a display unit and a data driver. The display unit
includes a plurality of scan lines to which a plurality of scan
signals are transmitted, a plurality of data lines to which a
plurality of compensation data signals are transmitted, a plurality
of light emitting signal lines to which a plurality of light
emitting signals are transmitted, and a plurality of pixels
respectively connected to the plurality of scan lines, the
plurality of data lines, and the plurality of light emitting signal
lines. The data driver is configured to generate a data voltage
corresponding to an image data signal and converts the data voltage
to the compensation data signal. The data driver includes a
compensator configured to detect a feedback voltage corresponding
to the degree of deterioration of the pixel according to a
compensation control signal generated from the scan signal with a
predetermined phase delay and to compensate the data voltage by
calculating the variation amount of the feedback voltage.
[0017] Each of the plurality of pixels may include a switching
transistor having a source terminal connected to the data line and
a gate terminal connected to the scan line, a driving transistor
having a source terminal receiving a first power source voltage and
a gate terminal connected to a drain terminal of the switching
transistor, a capacitor having a first end connected to the source
terminal of the driving transistor and a second end connected
between the gate terminal of the driving transistor, a light
emission control transistor having a gate terminal connected to the
light emitting signal line and a source terminal connected to the
drain terminal of the driving transistor; an organic light emitting
diode (OLED) having an anode connected to the drain terminal of the
light emission control transistor and a cathode receiving a second
power source voltage, and a threshold voltage compensation
transistor having a gate terminal receiving the compensation
control signal, a drain terminal connected to the drain terminal of
the driving transistor, and a source terminal connected to the
source terminal of the switching transistor.
[0018] The compensator may include a deterioration detector
detecting a voltage at both ends of the organic light emitting
diode as the feedback voltage according to the compensation control
signal, and a compensation data voltage generator configured to
calculate the variation amount of the feedback voltage and generate
the compensation data signal by compensating the data voltage by
the amount of the calculated feedback voltage.
[0019] The compensator may further include a switch transmitting
the compensation data signal to the pixel according to a load
signal that instructs transmission of the compensation data signal
to the plurality of data lines. The deterioration detector may
include an analog digital converter transmitting the feedback
voltage to the compensation data voltage generator, and a switch
transmitting the feedback voltage to the analog digital converter
according to the compensation control signal.
[0020] A driving method according to another exemplary embodiment
is a provided to a display device including a plurality of scan
lines to which a plurality of scan signals are transmitted, a
plurality of data lines to which a plurality of compensation data
signals are transmitted, a plurality of light emitting signal lines
to which a plurality of light emitting signals are transmitted, and
a plurality of pixels respectively connected to the plurality of
scan lines, the plurality of data lines, and the plurality of light
emitting signal lines. The driving method includes generating a
data voltage corresponding to an image data signal, detecting a
feedback voltage corresponding to the degree of deterioration of
the pixel according to a compensation control signal generated from
the scan signal with a predetermined phase delay, and compensating
the data voltage by calculating the variation amount of the
feedback voltage.
[0021] Detecting the feedback voltage may include applying the data
voltage to each of the plurality of pixels, transmitting a current
corresponding to the data voltage to an organic light emitting
diode according to the light emission control signal, and
generating a voltage at both ends of the organic light emitting
diode with the feedback voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other features and advantages will become more
apparent to those of ordinary skill in the art by describing in
detail exemplary embodiments with reference to the attached
drawings, in which:
[0023] FIG. 1 illustrates a display device according to an
exemplary embodiment.
[0024] FIG. 2 illustrates an equivalent circuit diagram of a
compensator and a pixel according to a first exemplary
embodiment.
[0025] FIG. 3 illustrates a waveform diagram of a driving method of
the display device according to the first exemplary embodiment.
[0026] FIG. 4 illustrates an equivalent circuit diagram of a
compensator and a pixel according to a second exemplary
embodiment.
[0027] FIG. 5 illustrates a waveform diagram of a driving method of
a display device according to the second exemplary embodiment.
DETAILED DESCRIPTION
[0028] Korean Patent Application No. 10-2010-0015379, filed on Feb.
19, 2010, in the Korean Intellectual Property Office, and entitled:
"Display Device and Driving Method Thereof," is incorporated by
reference herein in its entirety.
[0029] In the following detailed description, only certain
exemplary embodiments of the present invention have been shown and
described, simply by way of illustration. As those skilled in the
art would realize, the described embodiments may be modified in
various different ways, all without departing from the spirit or
scope of the present invention. Accordingly, the drawings and
description are to be regarded as illustrative in nature and not
restrictive. Like reference numerals designate like elements
throughout the specification.
[0030] Throughout this specification and the claims that follow,
when it is described that an element is "coupled" to another
element, the element may be "directly coupled" to the other element
or "electrically coupled" to the other element through a third
element. In addition, unless explicitly described to the contrary,
the word "comprise" and variations such as "comprises" or
"comprising" will be understood to imply the inclusion of stated
elements but not the exclusion of any other elements.
[0031] FIG. 1 illustrates a display device according to an
exemplary embodiment. Referring to FIG. 1, a display device
according may include a display unit 100, a scan driver 200, a data
driver 300, a light emission driver 400, and a controller 500.
[0032] The display unit 100 includes a plurality of signal lines
S1-Sn, D1-Dm, and E1-En, and a plurality of pixels PX connected to
the signal lines and arranged in a matrix format. The signal lines
S1-Sn, D1-Dm, and E1-En include a plurality of scan lines S1-Sn
transmitting scan signals SS1-SSn, a plurality of data lines D1-Dm
transmitting a compensation data voltage Vdata_c, and a plurality
of light emitting signal lines E1-En transmitting light emitting
signals EM1-EMn. The scan lines S1-Sn and the light emitting signal
lines E1-En extend substantially in a row direction and
substantially parallel with each other, and the data lines D1-Dm
extend substantially in a column direction and substantially
parallel with each other.
[0033] The scan driver 200 is connected to the signal lines S1-Sn
of the display unit 100, and sequentially applies the scan signals
SS1-SSn to the scan lines S1-Sn according to a scan control signal
CONT1. The plurality of scan signals SS1-SSn are formed of a
combination of a scan ON voltage Von turning on a switching
transistor M2 of each pixel PX (FIG. 2) and a scan OFF voltage
turning off the switching transistor M2. If the switching
transistor M2 is formed as a p-channel field effect transistor, the
scan ON voltage is a low voltage and the scan OFF voltage is a high
voltage.
[0034] The data driver 300 is connected to the data lines D1-Dm of
the display unit 100, generates a data voltage Vdata corresponding
to image data signals DR, DG, and DB input from the controller 500
according to a data control signal CONT2, converts the data voltage
Vdata to a compensation data voltage Vdata_c compensated for a
threshold voltage Vth of a driving transistor M1 of each pixel PX,
and applies the compensation data voltage Vdata_c to the data lines
D1-Dm.
[0035] The data driver 300 includes a compensator 310 that
generates the compensation data voltage Vdata_c in accordance with
a feedback voltage Vfb. The feedback voltage Vfb is determined by a
voltage between an anode and a cathode of the organic light
emitting diode OLED when a current I.sub.OLED flows thereto, and
increases with an increasing deterioration degree of the organic
light emitting diode OLED. The feedback voltage Vfb is used to
compensate the data voltage Vdata.
[0036] The light emission driver 400 is connected to the light
emitting signal lines E1-En of the display unit 100, and
sequentially applies the plurality of light emitting signals
EM1-EMn to the light emitting signal lines E1-En according to a
light emission control signal CONT3. The plurality of light
emitting signals EM1-EMn are formed of a combination of a gate ON
voltage Von turning on a light emission control transistor M3 of
each pixel PX and a gate OFF voltage turning off the light emission
control transistor M3. If the light emission control transistor M3
is formed as a p-channel field effect transistor, the gate ON
voltage Von and the gate OFF voltage Voff are respectively a low
voltage and a high voltage.
[0037] The controller 500 receives an input signal IS, a horizontal
synchronization signal Hsync, a vertical synchronization signal
Vsync, and a main clock signal MCLK from an external source to
generate the image data signals DR, DG, and DB, the scan control
signal CONT1, the data control signal CONT2, and the light emission
control signal CONT3. The scan control signal CONT1 includes a scan
start signal STV that instructs the start of scanning and at least
one clock signal controlling the scan start signal STV and an
output cycle of the gate ON voltage. The scan control signal CONT1
may further include an output enable signal OE that limits the
duration of the gate ON voltage Von. The data control signal CONT2
includes a horizontal synchronization start signal STH that informs
the start of transmission of the image data signals DR, DG, and DB
of pixels PX in one row to the data driver 300, and a load signal
LOAD that instructs application of a compensation data voltage
Vdata_c to the data lines D1-Dm.
[0038] The light emission control signal CONT3 includes a
synchronization signal that instructs the start of scanning of the
gate ON voltage Von with respect to the light emitting signal lines
E1-En and at least one clock signal that controls an output of the
gate ON voltage Von. The light emission control signal CONT3 may
further include a signal that limits the duration of the gate ON
voltage Von.
[0039] FIG. 2 illustrates an equivalent circuit diagram of a
compensator 310a and the pixel PX according to a first exemplary
embodiment. Referring to FIG. 2, the compensator 310a may include
an additive voltage generator 312, a compensation data voltage
generator 314, and switches SW1 and SW2. The pixel PX includes an
organic light emitting diode OLED, a driving transistor M1, a
capacitor Cst, the switching transistor M2, a light emission
control transistor M3, and a threshold voltage compensation
transistor M4.
[0040] The additive voltage Va is the sum of the data voltage Vdata
and a predetermined power source voltage VDD. The compensator
receives a feedback voltage Vfb corresponding to the threshold
voltage Vth of the driving transistor M1 of each pixel PX according
to a compensation control signal CCS_1, and generates a
compensation data voltage Vdata_c corresponding to a voltage
difference between the additive voltage Va and the feedback voltage
Vfb. The data control signal CONT2 according to the first exemplary
embodiment includes the compensation control signal CCS_1 for
compensation of the threshold voltage Vth of the driving transistor
M1 of each pixel PX. The compensation control signal CCS_1 includes
a low-level pulse signal generated in synchronization with a
low-level pulse of the scan signal.
[0041] While the compensator 310a illustrated in FIG. 2 includes
one subtractor AD connected to the data line D1 for ease of
explanation, multiple subtractors AD may be provided and
respectively connected to the plurality of data lines D1-Dm. Each
of the subtractors AD may sequentially receive a feedback voltage
Vfb from the plurality of pixels PX respectively connected to the
plurality of data lines D1-Dm. In addition, the pixel PX of FIG. 2
is an example of a pixel connected to the scan line S1 and the data
line D1.
[0042] The additive voltage generator 312 receives the data voltage
Vdata corresponding to the image data signals DR, DG, and DB, and
adds the data voltage Vdata and the power source voltage VDD to
generate the additive voltage Va.
[0043] The compensation data voltage generator 314 includes the
subtractor AD. The subtractor AD receives the additive voltage Va
through a non-inversion terminal (+) and receives the feedback
voltage Vfb through an inversion terminal (-). The subtractor AD
generates a compensation data voltage Vdata_c corresponding to a
difference between the additive voltage Va and the feedback voltage
Vfb.
[0044] The switch SW1 includes a first end connected to the
inversion terminal (-) of the subtractor AD and a second end
connected to a source terminal of the switching transistor M2 of
the pixel PX. The switch SW1 is turned on/off according to the
compensation control signal CCS_1. The switch SW2 includes a first
end connected to an output terminal of the subtractor AD and a
second end connected to the source terminal of the switching
transistor M2 of the pixel PX. The switch SW2 is turned on/off
according to the load signal LOAD.
[0045] For example, the switch SW1 is turned on when the
compensation control signal CCS_1 is low and turned off when the
compensation control signal CCS_1 is high. In addition, the switch
SW2 is turned on when the load signal LOAD is low and turned off
when the load signal LOAD is high.
[0046] The driving transistor M1 of the pixel PX includes a source
terminal receiving the power source voltage VDD and a drain
terminal connected to a source terminal of the light emitting
transistor M3. The switching transistor M2 includes a gate terminal
receiving the scan signal SS1, a drain terminal connected to the
source terminal of the driving transistor M1, and a source terminal
connected to the data line D1. The capacitor Cst is connected
between the source terminal and the gate terminal of the driving
transistor M1. The capacitor Cst charges a data voltage applied to
the gate terminal of the driving transistor M1 and maintains the
charge of the data voltage when the switching transistor M2 is
turned off.
[0047] The light emission control transistor M3 of the pixel PX
includes a gate terminal receiving a light emitting signal EM1 and
a drain terminal connected to an anode of the organic light
emitting diode OLED. The light emission control transistor M3 is
selectively turned on according to the light emitting signal EM1 to
supply a current I.sub.OLED flowing in the driving transistor M1 to
the organic light emitting diode OLED.
[0048] The threshold voltage compensation transistor M4 of the
pixel PX includes a gate terminal receiving the compensation
control signal CCS_1, a drain terminal connected to the drain
terminal of the driving transistor M1, and a source terminal
connected to the source terminal of the switching transistor M2.
The threshold voltage compensation transistor M4 is selectively
turned on by the compensation control signal CCS_1 to transmit the
feedback voltage Vfb at the drain terminal of the driving
transistor M1 to the compensator 310a when the driving transistor
M1 is diode-connected. That is, the feedback voltage Vfb
corresponds to a voltage difference between the power source
voltage VDD and the threshold voltage Vth of the driving transistor
M1.
[0049] The organic light emitting diode OLED of the pixel PX
includes a cathode receiving the power source voltage VDD. The
intensity of light emitted from the organic light emitting diode
OLED varies depending upon the current I.sub.OLED supplied from the
driving transistor M1 through the light emission control transistor
M3 so as to display an image.
[0050] The organic light emitting diode OLED may emit light of one
of primary colors. The primary colors may be three primary colors,
e.g., red, green, and blue, and a desired color may be expressed by
a spatial or temporal sum of the three primary colors. Some of the
organic light emitting elements OLED may emit white light to
increase luminance. Alternatively, the organic light emitting
elements OLED at all of the pixels PX may emit white light. In this
case, some of the pixels PX may further include a color filter (not
shown) for converting the white light output from the organic light
emitting element OLED into any one of the primary colors.
[0051] The driving transistor M1, the switching transistor M2, the
light emission control transistor M3, and the threshold voltage
compensation transistor M4 are illustrated in FIG. 2 as all being
p-channel field effect transistors (FET). However, at least one of
the driving transistor M1, the switching transistor M2, the light
emission control transistor M3, and the threshold voltage
compensation transistor M4 may be an n-channel FET. In addition,
interconnections between the driving transistor M1, the switching
transistor M2, the light emission control transistor M3, the
threshold voltage compensation transistor M4, the capacitor Cst,
and the organic light emitting diode OLED may be changed. The pixel
PX shown in FIG. 2 is merely an example, and pixels having a
different structure may be used instead.
[0052] FIG. 3 illustrates a waveform diagram of a driving method of
the display device according to the first exemplary embodiment.
Referring to FIG. 3, the image data signals DR, DG, and DB are
transmitted, and the data driver 300 generates the data voltage
Vdata corresponding to the image data signals DR, DG, and DB.
[0053] The additive voltage generator 312 generates the additive
voltage Va by adding the power source voltage VDD to the data
voltage Vdata. The additive voltage Va is transmitted to the
non-inversion terminal (+) of the subtractor AD. In this state,
when the scan signal SS1 becomes low at a time point P1, the
compensation control signal CCS_1 becomes low. Then, the switching
transistor M2 is turned on by the scan signal SS1 and the threshold
voltage compensation transistor M4 is turned on by the compensation
control signal CCS_1. Thus, the gate terminal and the drain
terminal of the driving transistor M1 are connected. Accordingly, a
feedback voltage Vfb is generated at the drain terminal of the
driving transistor M1. In this case, the feedback voltage Vfb
corresponds to a voltage obtained by subtracting the threshold
voltage Vth of the driving transistor M1 from the power source
voltage VDD. Since the switch SW1 is in the turn-on state by the
compensation control signal CCS_1, the feedback voltage Vfb is
transmitted to the inversion terminal (-) of the subtractor AD. The
subtractor AD subtracts the feedback voltage Vfb from the additive
voltage Va to output the compensation data voltage Vdata_c. The
compensation data voltage Vdata_c is obtained as given in Equation
1.
Vdata.sub.--c=Va-Vfb=(VDD+Vdata)-(VDD-Vth)=Vdata+Vth (Equation
1)
[0054] That is, the compensation data voltage Vdata_c equals the
sum of the data voltage Vdata and the threshold voltage Vth of the
driving transistor M1. At a time point P2, the load signal LOAD
becomes low and then the switch SW2 is turned on. Since the
switching transistor M2 is turned-on, the compensation data voltage
Vdata_c is transmitted to the gate terminal of the driving
transistor M1 through the switching transistor M2. Here, the
current I.sub.OLED flowing in the driving transistor M1 is defined
as given in Equation 2.
I.sub.OLED=k*(Vgs-Vth).sup.2 (Equation 2)
[0055] Here, Vgs denotes a voltage difference between the voltage
at the gate terminal and the voltage at the source terminal of the
driving transistor M1, and equals (Vdata+Vth)-VDD when Equation 1
is used, and k is a constant. When this value is applied to
Equation 2, the current I.sub.OLED flowing in the driving
transistor M1 is as given in Equation 3.
I.sub.OLED=k*(Vdata-VDD).sup.2 (Equation 3)
[0056] This means that the current I.sub.OLED flowing in the
driving transistor M1 is not influenced by the threshold voltage
Vth. Accordingly, variation of the intensity of the current
I.sub.OLED flowing to the driving transistor M1 due to the
threshold voltage Vth can be prevented. That is, luminance of the
organic light emitting diode OLED may be constantly maintained by
offsetting the threshold voltage Vth of the driving transistor M1
according to the first exemplary embodiment.
[0057] FIG. 4 illustrates an equivalent circuit diagram of a
compensator 310b and the pixel PX according to a second exemplary
embodiment of the present invention. The pixel PX in FIG. 4 is the
same as the pixel PX in FIG. 2, and the description will not be
repeated. However, unlike the threshold voltage compensation
transistor M4 of FIG. 2, a threshold voltage compensation
transistor M4 in FIG. 4 is selectively turned on by a compensation
control signal CCS_2 instead of a compensation control signal
CSS_1. The compensation control signal CCS_2 according to the
second exemplary embodiment includes a low-level pulse signal
generated from the scan signal with a predetermined phase delay,
e.g., a delay equal to one scan pulse. Referring to FIG. 4, the
compensator 310b according to the second exemplary embodiment
includes a deterioration detector 316, a compensation data voltage
generator 318, and a switch SW4.
[0058] The deterioration detector 316 transmits a feedback voltage
Vfb that corresponds to the deterioration degree of an organic
light emitting diode OLED to the compensation data voltage
generator 318 according to the compensation control signal CCS_2.
The feedback voltage Vfb according to the second exemplary
embodiment is determined by a voltage between an anode and a
cathode of the organic light emitting diode OLED when a current
I.sub.OLED flows thereto, and increases as the deterioration degree
of the organic light emitting diode OLED increases.
[0059] The deterioration detector 316 includes an analog digital
converter A/D and a switch SW3. The analog digital converter A/D
transmits the feedback voltage Vfb to the compensation data voltage
generator 318. The switch SW3 includes a first end connected to the
analog digital converter A/D and a second end connected to a source
of the switching transistor M2, and is turned on/off according to
the compensation control signal CCS_2. For example, the switch SW3
according to the second exemplary embodiment is turned on when the
compensation control signal CCS_2 is low and turned off when the
compensation control signal CCS_2 is high. Here, the compensation
control signal CCS_2 according to the second exemplary embodiment
of the present invention includes a low-level pulse signal
generated from the scan signal with a predetermined phase
delay.
[0060] The compensation data voltage generator 318 calculates the
variation amount of the feedback voltage Vfb detected from the
deterioration detector 316 and generates the compensation data
voltage Vdata_c by compensating a data voltage Vdata as much as the
varied amount of the feedback voltage Vfb. The compensation data
voltage generator 318 compensates the data voltage Vdata depending
on the variation of the feedback voltage Vfb to generate the
compensation data voltage Vdata_c. The compensation data voltage
generator 318 determines the degree of compensation of the data
voltage Vdata according to the variation of the feedback voltage
Vfb. In this case, the relationship between the variation of the
feedback voltage Vfb and the degree of the compensation of the data
voltage Vdata may be stored in a lookup table acquired through
experimental methods.
[0061] In further detail, since an increase of the feedback voltage
Vfb implies deterioration of the organic light emitting diode OLED,
much more current should flow in the organic light emitting diode
OLED for light emission with luminance set in the initial state. In
addition, when the driving transistor M1 is a P-type transistor,
deterioration of the organic light emitting diode OLED may be
compensated by appropriately decreasing the data voltage Vdata. In
this case, the lookup table stores the degree of compensation of
the data voltage Vdata according to the variation of the feedback
voltage Vfb. The variation of the feedback voltage Vfb implies a
difference between a previously measured feedback voltage Vfb and a
current feedback voltage Vfb when the feedback voltage Vfb
generated according to the current flowing in the organic light
emitting diode OLED is measured with a predetermined time gap.
[0062] The switch SW4 includes a first end connected to the
compensation data voltage generator 318 and a second end connected
to the data line D1. The switch SW4 is turned on/off according to
the load signal LOAD. For example, the switch SW4 of the present
exemplary embodiment is turned on when the load signal LOAD is low
and turned off when the load signal LOAD is high.
[0063] FIG. 5 illustrates a waveform diagram of a driving method of
the display device according to the second exemplary embodiment.
Referring to FIG. 5, when image data signals DR, DG, and DB are
transmitted, the data driver 300 generates a data voltage Vdata
corresponding to the image data signals DR, DG, and DB.
[0064] When the scan signal SS1 becomes low at a time point P11,
the switching transistor M2 is turned on and the data voltage Vdata
is transmitted to a gate terminal of the driving transistor M1.
When the scan signal SS1 becomes high at a time point P12, the
switching transistor M2 is turned off and the light emission
control signal EM1 becomes low. Then, the light emission control
transistor M3 is turned on and a current I.sub.OLED flows in the
driving transistor M1.
[0065] The current I.sub.OLED is supplied to the organic light
emitting diode OLED through the light emission control transistor
M3 such that the organic light emitting diode OLED emits light. In
this case, the feedback voltage Vfb at both sides of the organic
light emitting diode OLED varies according to the degree of
deterioration of the organic light emitting diode OLED. The
feedback voltage Vfb is increased as the degree of the
deterioration of the organic light emitting diode OLED is
increased.
[0066] When the compensation control signal CSS_2 becomes low at
the time point P12, the threshold voltage compensation transistor
M4 and the switch SW3 are turned on. Then, the feedback voltage Vfb
is transmitted to the analog digital converter A/D. The feedback
voltage Vfb transmitted through the analog digital converter A/D is
transmitted to the compensation data voltage generator 318. The
compensation data voltage generator 318 calculates the variation
amount of the feedback voltage Vfb, and compensates the data
voltage Vdata according to the calculated variation amount to
generate the compensation data voltage Vdata_c. That is, luminance
of the organic light emitting diode OLED may be constantly
maintained by detecting and compensating deterioration of the
organic light emitting diode OLED according to the second exemplary
embodiment.
[0067] <Description of Symbols>
[0068] Display unit 100, scan driver 200, data driver 300,
controller 400, light emission driver 400, scan lines S1-Sn, data
lines D1-Dm, scan signals SS1-SSn, switching transistor M2, pixel
PX, light emitting signal lines E1-En, light emitting signals
EM1-EMn, input signal IS, horizontal synchronization signal Hsync,
vertical synchronization signal Vsync, main clock signal MCLK,
image data signals DR, DG, DB, gate ON voltage Von, scan control
signal CONT1, data control signal CONT2, light emission control
signal CONT3, compensators 310, 310a, 310b, subtractor AD, additive
voltage generator 312, gate OFF voltage Voff, compensation data
voltage generator 314, deterioration detector 316, compensation
data voltage generator 318, switches SW1, SW2, SW3, SW4, analog
digital converter A/D, driving transistor M1, light emission
control transistor M3, threshold voltage compensation transistor
M4, capacitor CST, organic light emitting diode OLED.
[0069] Exemplary embodiments have been disclosed herein, and
although specific terms are employed, they are used and are to be
interpreted in a generic and descriptive sense only and not for
purpose of limitation. Accordingly, it will be understood by those
of ordinary skill in the art that various changes in form and
details may be made without departing from the spirit and scope of
the present invention as set forth in the following claims.
* * * * *