U.S. patent application number 11/979668 was filed with the patent office on 2008-04-10 for luminance control method and luminance control circuit for organic el display.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Masutaka Inoue, Shigeo Kinoshita, Yukio Mori, Haruhiko Murata, Susumu Tanase, Atsuhiro Yamashita.
Application Number | 20080084433 11/979668 |
Document ID | / |
Family ID | 26625384 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080084433 |
Kind Code |
A1 |
Mori; Yukio ; et
al. |
April 10, 2008 |
Luminance control method and luminance control circuit for organic
EL display
Abstract
A luminance control method for an organic EL display comprises a
first step of calculating a luminance accumulation value for each
screen on the basis of a video input signal, and a second step of
controlling the amplitude of the video input signal on the basis of
the luminance accumulation value calculated in the first step and
feeding to the organic EL display the video signal whose amplitude
has been controlled.
Inventors: |
Mori; Yukio; (Hirakata City,
JP) ; Tanase; Susumu; (Kadoma City, JP) ;
Yamashita; Atsuhiro; (Osaka City, JP) ; Inoue;
Masutaka; (Neyagawa City, JP) ; Kinoshita;
Shigeo; (Higashiosaka City, JP) ; Murata;
Haruhiko; (Suita City, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
Osaka
JP
|
Family ID: |
26625384 |
Appl. No.: |
11/979668 |
Filed: |
November 7, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10500374 |
Oct 28, 2004 |
7304654 |
|
|
PCT/JP02/13728 |
Dec 26, 2002 |
|
|
|
11979668 |
Nov 7, 2007 |
|
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Current U.S.
Class: |
345/690 |
Current CPC
Class: |
G09G 5/04 20130101; G09G
2330/021 20130101; G09G 2320/0242 20130101; G09G 3/3208 20130101;
G09G 2360/16 20130101; G09G 2320/0238 20130101; G06F 3/147
20130101 |
Class at
Publication: |
345/690 |
International
Class: |
G09G 5/10 20060101
G09G005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2001 |
JP |
2001-400238 |
Mar 28, 2002 |
JP |
2002-91796 |
Claims
1-11. (canceled)
12. In a portable telephone set comprising a camera having an
automatic exposure control function and an organic
electroluminescence display, a portable telephone set characterized
by comprising: judgment means for judging peripheral brightness on
the basis of exposure control information relating to the camera;
and display luminance control means for controlling the display
luminance of the organic electroluminescence display on the basis
of the peripheral brightness judged by the judgment means.
13. The portable telephone set according to claim 12, characterized
in that the display luminance control means controls the display
luminance of the organic electroluminescence display such that the
display luminance of the organic electroluminescence display is
reduced when the peripheral brightness judged by the judgment means
is low, while being increased when the peripheral brightness judged
by the judgment means is high.
14. The portable telephone set according to claim 12, characterized
in that the exposure control information relating to the camera is
one selected from exposure time information and AGC gain
information.
15. In a portable telephone set comprising an organic
electroluminescence display, a portable telephone set characterized
by comprising: detection means for detecting the direction of a
display surface of the organic electroluminescence display; and
display luminance control means for controlling the display
luminance of the organic electroluminescence display on the basis
of the direction of the display surface of the organic
electroluminescence display which is detected by the detection
means.
16. The portable telephone set according to claim 15, characterized
in that the display luminance control means controls the display
luminance of the organic electroluminescence display such that the
display luminance of the organic electroluminescence display is
increased when the display surface of the organic
electroluminescence display is directed upward, while being reduced
when the display surface of the organic electroluminescence display
is directed downward.
Description
RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. application Ser.
No. 10/500,374, filed Oct. 28, 2004, which is a 371 of
PCT/JP02/13728, filed Dec. 26, 2002, claiming priority of Japanese
Application Nos. 2001-400238, filed Dec. 28, 2001, and 2002-91796,
filed Mar. 28, 2002, the entire contents of each of which are
hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a luminance control method
and a luminance control circuit for an organic electroluminescence
(EL) display and a portable telephone set comprising the organic EL
display.
BACKGROUND ART
[0003] Examples of organic EL displays include passive-type ones
having a simple matrix structure and active-type ones using a TFT
(Thin Film Transistor).
[0004] FIG. 1 illustrates the basic pixel structure of the active
type organic EL display.
[0005] A circuit corresponding to one pixel in the active type
organic EL display comprises a switching TFT 101, a capacitor 102,
a driving TFT 103, and an organic EL element 104.
[0006] A display signal Data(Vin) is applied to the drain of the
switching TFT 101 through a display signal line 111. A selection
signal SCAN is applied to the base of the switching TFT 101 through
a selection signal line 112. The switching TFT 101 has its source
connected to the base of the driving TFT 103 and grounded through
the capacitor 102.
[0007] A driving power supply voltage Vdd is applied to the drain
of the driving TFT 103 through a power supply line 113. The driving
TFT 103 has its source connected to the anode of the organic EL
element 104. The cathode of the organic EL element 104 is
grounded.
[0008] The switching TFT 101 is subjected to ON/OFF control by the
selection signal SCAN. The capacitor 102 is charged by the display
signal Data(Vin) fed through the switching TFT 101 when the
switching TFT 101 is turned on. The capacitor 102 holds a charging
voltage when the switching TFT 101 is turned off. The driving TFT
103 supplies to the organic EL element 104 a current corresponding
to the voltage, held in the capacitor 102, which is applied to the
base thereof.
[0009] FIG. 2 illustrates the relationship between the display
signal Data(Vin) and a light-emitting luminance (a driving current)
of the organic EL element 104 in the basic pixel structure shown in
FIG. 1.
[0010] In FIG. 2, RefW and RefB respectively indicate a white-side
reference voltage for defining a light-emitting luminance
corresponding to the white level of an input signal and a
black-side reference voltage for defining a light-emitting
luminance corresponding to the black level of the input signal.
[0011] In the above-mentioned active type organic EL display, a
large current flows through the organic EL element 104 with respect
to an image which is bright on the whole screen. When the large
current flows through the organic EL element 104, power consumption
is increased. When the large current continues to flow through the
organic EL element 104, the degradation of the performance thereof
is advanced.
[0012] Therefore, a technique for detecting the current flowing
into the cathode of the organic EL element 104, and controlling the
power supply voltage Vdd of the organic EL element 104 in response
to the value of the detected current, thereby reducing the power
supply voltage to reduce a driving current when the overall screen
is bright, for example, has been developed (see
JP-A-2000-267628).
[0013] The control of the power supply voltage by the
above-mentioned prior art is feedback control for controlling the
power supply voltage Vdd of the organic EL element 104 in response
to the value of the detected current. In the case of the feedback
control, when the brightness of a video is rapidly changed, for
example, excessive control easily occurs. In the case, a luminance
varies in a short period, which is so-called "hunting".
[0014] An object of the present invention is to provide a luminance
control method and a luminance control circuit for an organic EL
display capable of achieving power saving as well as restraining
the degradation in the performance of an organic EL element and
capable of preventing "hunting" from occurring.
[0015] Another object of the present invention is to provide a
portable telephone set capable of changing the display luminance of
an organic EL display depending on peripheral brightness.
[0016] A further object of the present invention is to provide a
portable telephone set capable of changing the display luminance of
an organic EL display depending on the direction of a portable
telephone set.
DISCLOSURE OF INVENTION
[0017] A luminance control method for an organic EL display
according to the present invention is characterized by comprising a
first step of calculating a luminance accumulation value for each
screen on the basis of a video input signal; and a second step of
controlling the amplitude of the video input signal on the basis of
the luminance accumulation value calculated in the first step, and
feeding to the organic EL display the video signal whose amplitude
has been controlled and in that in the second step, the amplitude
of the video input signal is controlled, when the luminance
accumulation value calculated in the first step exceeds a
predetermined value, such that the larger the difference between
the luminance accumulated value and the predetermined value is, the
smaller the amplitude of the video input signal becomes.
[0018] When the video input signal is a digital video signal, a
reference voltage supplied to a digital-to-analog (DA) converter
for converting the digital video input signal into an analog video
signal is controlled on the basis of the luminance accumulation
value calculated in the first step, to control the amplitude of the
video input signal in the second step.
[0019] The reference voltage supplied to the digital-to-analog
converter includes a black-side reference voltage for defining a
light-emitting luminance corresponding to the black level of the
input signal and a white-side reference voltage for defining a
light-emitting luminance corresponding to the white level of the
input signal, and in the second step, the white-side reference
voltage is controlled on the basis of the luminance accumulation
value calculated in the first step.
[0020] A luminance control circuit for an organic EL display
according to the present invention is characterized by comprising a
digital-to-analog converter for converting a digital video input
signal into an analog video output signal on the basis of
input/output characteristics defined by a given reference voltage,
and feeding the analog video output signal to the organic EL
display; and a reference voltage control circuit for controlling
the reference voltage supplied to the digital-to-analog converter
on the basis of the digital video input signal, and in that the
reference voltage control circuit comprises a luminance
accumulation value calculation circuit for calculating a luminance
accumulation value for each screen on the basis of the digital
video input signal, and a voltage control circuit for controlling
the reference voltage supplied to the digital-to-analog converter
on the basis of the luminance accumulation value calculated by the
luminance accumulation value calculation circuit the reference
voltage supplied to the digital-to-analog converter includes a
black-side reference voltage for defining a light-emitting
luminance corresponding to the black level of the input signal and
a white-side reference voltage for defining a light-emitting
luminance corresponding to the white level of the input signal, and
the voltage control circuit controls, when the luminance
accumulation value calculated by the luminance accumulation value
calculation circuit exceeds a predetermined value, the white-side
reference voltage such that the larger the difference between the
luminance accumulation value and the predetermined value is, the
lower the light-emitting luminance corresponding to the white level
of the input signal becomes.
[0021] The voltage control circuit comprises a gain calculation
circuit for calculating a gain for controlling the white-side
reference voltage on the basis of the luminance accumulation value
calculated by the luminance accumulation value calculation circuit,
and a control circuit for controlling the white-side reference
voltage on the basis of the gain calculated by the gain calculation
circuit.
[0022] The gain calculation circuit has such input/output
characteristics that a gain to be outputted is set to a constant
value when the inputted luminance accumulation value is not more
than a predetermined value, and the larger the inputted luminance
accumulation value is, the smaller the gain to be outputted is made
when the inputted luminance accumulation value exceeds the
predetermined value, and the control circuit controls the
white-side reference voltage such that the smaller the gain is, the
lower the light-emitting luminance corresponding to the white level
of the input signal becomes.
[0023] The voltage control circuit comprises a gain calculation
circuit for calculating a first gain for controlling the white-side
reference voltage on the basis of the luminance accumulation value
calculated by the luminance accumulation value calculation circuit,
a multiplication circuit for multiplying the first gain calculated
by the gain calculation circuit by a second gain given from the
exterior, and a control circuit for controlling the white-side
reference voltage on the basis of a third gain which is the result
of the multiplication by the multiplication circuit.
[0024] The gain calculation circuit has such input/output
characteristics that a gain to be outputted is set to a constant
value when the inputted luminance accumulation value is not more
than a predetermined value, and the larger the inputted luminance
accumulation value is, the smaller the gain to be outputted is made
when the inputted luminance accumulation value exceeds the
predetermined value, and the control circuit controls the
white-side reference voltage such that the smaller the third gain
is, the lower the light-emitting luminance corresponding to the
white level of the input signal becomes.
[0025] In a portable telephone set comprising a camera having an
automatic exposure control function and an organic EL display, a
first portable telephone set according to the present invention is
characterized by comprising judgment means for judging peripheral
brightness on the basis of exposure control information relating to
the camera, and display luminance control means for controlling the
display luminance of the organic EL display on the basis of the
peripheral brightness judged by the judgment means.
[0026] The display luminance control means controls the display
luminance of the organic EL display such that the display luminance
of the organic EL display is reduced when the peripheral brightness
judged by the judgment means is low, while being increased when the
peripheral brightness judged by the judgment means is high.
[0027] The exposure control information relating to the camera is
one selected from exposure time information and AGC gain
information.
[0028] In a portable telephone set comprising an organic EL
display, a second portable telephone set according to the present
invention is characterized by comprising detection means for
detecting the direction of a display surface of the organic EL
display; and display luminance control means for controlling the
display luminance of the organic EL display on the basis of the
direction of the display surface of the organic EL display which is
detected by the detection means.
[0029] The display luminance control means controls the display
luminance of the organic EL display such that the display luminance
of the organic EL display is increased when the display surface of
the organic EL display is directed upward, while being reduced when
the display surface of the organic EL display is directed
downward.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is a circuit diagram showing the basic pixel
structure of an active type organic EL display.
[0031] FIG. 2 is a graph showing the relationship between a display
signal Data(Vin) and a light-emitting luminance (a driving current)
of an organic EL element in the basic pixel structure shown in FIG.
1.
[0032] FIG. 3 illustrates the configuration of a luminance control
circuit for an organic EL display according to a first embodiment
of the present invention.
[0033] FIGS. 4(a) and 4(b) are graphs showing examples of the
input/output characteristics of a gain calculation circuit 14.
[0034] FIG. 5 is a circuit diagram showing a reference voltage
control circuit corresponding to R.
[0035] FIG. 6 is a graph showing the input/output characteristics
of a DAC 2.
[0036] FIG. 7 illustrates the configuration of a luminance control
circuit for an organic EL display according to a second embodiment
of the present invention.
[0037] FIG. 8 is a graph showing an example of the setting of the
input/output characteristics of each of gain correction circuits
61, 62, and 63.
[0038] FIG. 9 is a block diagram showing the schematic
configuration of a portable telephone set according to a third
embodiment of the present invention.
[0039] FIG. 10 is a block diagram showing the configuration of a
luminance control circuit provided in a timing control IC 213 shown
in FIG. 9, and an MPU 209 for controlling a luminance for the whole
screen and its peripheral device.
[0040] FIG. 11 is a block diagram showing the schematic
configuration of a portable telephone set according to a fourth
embodiment of the present invention.
[0041] FIG. 12 is a block diagram showing the configuration of a
luminance control circuit provided in a timing control IC 213 shown
in FIG. 11, and an MPU 209 for controlling a luminance for the
whole screen and its peripheral device.
BEST MODE FOR CARRYING OUT THE INVENTION
[0042] Referring now to FIGS. 3 to 10, embodiments of the present
invention will be described.
[1] DESCRIPTION OF FIRST EMBODIMENT
[0043] FIG. 3 illustrates the configuration of a luminance control
circuit for an organic EL display according to a first embodiment
of the present invention.
[0044] The luminance control circuit for the organic EL display
comprises a reference voltage control circuit 1 and a DAC
(Digital-to-Analog Converter) 2. Digital video input signals R _in,
G _in, and B _in are fed to the reference voltage control circuit 1
and are fed to the DAC 2. The reference voltage control circuit 1
controls a reference voltage supplied to the DAC 2. The reference
voltage supplied to the DAC 2 includes black-side reference
voltages R _RefB, G _RefB, and B _RefB (generically referred to as
a RefB) and white-side reference voltages R _RefW, G _RefW, and B
_RefW (generically referred to as RefW), respectively, with respect
to colors R (Red), G (Green), and B (Blue).
[0045] The black-side reference voltage RefB is a reference voltage
for defining a light-emitting luminance corresponding to the black
level of an input signal, and is fixed in the present embodiment.
The white-side reference voltage RefW is a reference voltage for
defining a light-emitting luminance corresponding to the white
level of an input signal, and is controlled by the reference
voltage control circuit 1 in the present embodiment.
[0046] The DAC 2 respectively converts the digital video input
signals R _in, G _in, and B _in into analog video output signals R
_out, G _out, and B _out on the basis of input/output
characteristics defined by the black-side reference voltage RefB
and the white-side reference voltage RefW' which are fed from the
reference voltage control circuit 1. The analog video output
signals R _out, G _out, and B _out obtained by the DAC 2 are fed to
the organic EL display 3. The analog video output signals R _out, G
_out, and B _out correspond to the display signal Data (Vin) shown
in FIG. 1.
[0047] The reference voltage control circuit 1 comprises a
luminance signal generation circuit (Y generation circuit) 11, a
luminance accumulation circuit 12, an LPF (Low-Pass Filter) 13, a
gain calculation circuit 14, a reference voltage control circuit
(Ref voltage control circuit) 15, and a plurality of DACs 16 to
21.
[0048] The luminance signal generation circuit 11 generates a
luminance signal Y on the basis of the digital video input signals
R _in, G _in, and B _in. The luminance accumulation circuit 12
calculates a luminance accumulation value for each frame on the
basis of the luminance signal Y generated by the luminance signal
generation circuit 11. The LPF 13 smoothes in the time direction
the luminance accumulation value for each frame calculated by the
luminance accumulation circuit 12. Although the LPF 13 is provided
to slowly change a gain Gain, described later, with a rapid change
in brightness, it may be omitted.
[0049] The gain calculation circuit 14 calculates the gain Gain for
controlling the white-side reference voltage RefW depending on the
luminance accumulation value for each frame obtained from the LPF
13. FIGS. 4 (a) and 4 (b) respectively illustrate examples of
input/output characteristics of the gain calculation circuit 14,
that is, the characteristics of a gain against a luminance
accumulation value for each frame.
[0050] In the characteristics shown in FIG. 4 (a), the gain is 1.00
when the luminance accumulation value for each frame is 0 to a, and
gradually decreases when the luminance accumulation value for each
frame exceeds a. In the characteristics shown in FIG. 4 (b), the
gain is 1.00 when the luminance accumulation value for each frame
is 0 to b, gently decreases when the luminance accumulation value
for each frame is b to c, and somewhat rapidly decreases when the
luminance accumulation value for each frame exceeds c.
[0051] The reference voltage control circuit 15 generates
white-side reference voltages R _RefW', G _RefW', and B _RefW'
after control for the colors R, G and B on the basis of the
black-side reference voltages R _RefB, G _RefB, and B _RefB
previously set for the colors R, G, and B, the white-side reference
voltages R _RefW, G _RefW, and B _RefW previously set for the
colors R, G, and B, and the gain Gain calculated by the gain
calculation circuit 14.
[0052] Each of the black-side reference voltages R _RefB, G _RefB,
B _RefB and each of the white-side reference voltages R _RefW, G
RefW, B _RefW are respectively fed as digital signals.
[0053] Although the reference voltage control circuit 15 includes
reference voltage control circuits respectively corresponding to
the colors R, G, and B, their respective configurations are the
same. Therefore, description is herein made of the reference
voltage control circuit corresponding to the color R.
[0054] FIG. 5 illustrates the reference voltage control circuit
corresponding to the color R.
[0055] The reference voltage control circuit comprises a subtracter
31, a multiplier 32, and a subtracter 33.
[0056] The subtracter 31 operates the difference (R _RefB-R _RefW)
between the black-side reference voltage R _RefB corresponding to
the color R and the white-side reference voltage R _RefW
corresponding to the color R. The multiplier 32 multiplies an
output of the subtracter 31 (R _RefB-R _RefW) by the gain Gain. The
subtracter 33 subtracts an output of the multiplier 32
(Gain.times.(R _RefB-R _RefW)) from the black-side reference
voltage R _RefB, to calculate a white-side reference voltage R
_RefW' after control.
[0057] When the gain is 1.00, the white-side reference voltage R
_RefW' after control is equal to the white-side reference voltage R
_RefW. The smaller the gain Gain becomes, that is, the larger the
luminance accumulation value for each frame becomes, the larger the
white-side reference voltage R _RefW' after control becomes, to
come closer to the black-side reference voltage R _RefB. That is,
the larger the luminance accumulation value for each frame becomes,
the lower a light-emitting luminance (a driving current),
corresponding to the white level of an input signal, of the organic
EL element becomes.
[0058] The black-side reference voltages R _RefB, G _RefB, B _RefB
are respectively converted into analog signals by DACs 16, 17, and
18, and are fed to the DAC 2. The white-side reference voltages R
_RefW', G _RefW', B _RefW' after control are respectively converted
into analog signals by the DACs 19, 20, and 21, and are fed to the
DAC 2.
[0059] FIG. 6 illustrates the input/output characteristics of the
DAC 2.
[0060] In FIG. 6, RefW'1 indicates a white-side reference voltage
(=a white-side reference voltage RefW) supplied to the DAC 2 when
the luminance accumulation value is small (in the case of a dark
video). RefW'3 indicates a white-side reference voltage supplied to
the DAC 2 when the luminance accumulation value is large (in the
case of a bright video). RefW'2 indicates a white-side reference
voltage supplied to the DAC 2 when the luminance accumulation value
is an intermediate value (in the case of a video with intermediate
brightness).
[0061] When the white-side reference voltage supplied to the DAC 2
is RefW'1, the input/output characteristics of the DAC 2 are
characteristics indicated by a straight line L1. In this case, when
an input signal which changes from a black level to a white level
is periodically inputted to the DAC 2, an output waveform as
indicated by a curved line S1 is obtained.
[0062] When the white-side reference voltage supplied to the DAC 2
is RefW'3, the input/output characteristics of the DAC 2 are
characteristics indicated by a straight line L3. In this case, when
an input signal which changes from a black level to a white level
is periodically inputted to the DAC 2, an output waveform as
indicated by a curved line S3 is obtained.
[0063] When the white-side reference voltage supplied to the DAC 2
is RefW'2, the input/output characteristics of the DAC 2 are
characteristics indicated by a straight line L2. In this case, when
an input signal which changes from a black level to a white level
is periodically inputted to the DAC 2, an output waveform as
indicated by a curved line S2 is obtained.
[0064] That is, it is found by controlling the white-side reference
voltage depending on the luminance accumulation value for each
frame that the amplitude of the output signal of the DAC 2 is
controlled.
[0065] In the above-mentioned embodiment, when the input video is a
bright video, the amplitude of a video input signal (display
signal) is reduced, thereby reducing the driving current for the
organic EL element. Since the amplitude of the video input signal
is controlled by controlling a reference voltage at the time of
digital-to-analog conversion, the gray scale is not reduced.
[0066] Since the amplitude of the video input signal (display
signal) is controlled by feed forward control, no "hunching"
occurs.
[2] DESCRIPTION OF SECOND EMBODIMENT
[0067] FIG. 7 illustrates the configuration of a luminance control
circuit for an organic EL display according to a second embodiment
of the present invention. In FIG. 7, the same components as those
shown in FIG. 3 are assigned the same reference numerals and hence,
the description thereof is not repeated.
[0068] The luminance control circuit for the organic EL display
according to the second embodiment differs from the luminance
control circuit for the organic EL display according to the first
embodiment in the following points.
[0069] (1) A multiplier 41 for controlling a luminance for the
whole screen from the exterior is provided in a reference voltage
control circuit 1.
[0070] (2) Multipliers 51, 52, and 53 for allowing white balance
control are provided in the reference voltage control circuit
1.
[0071] (3) The characteristics of a light-emitting luminance
corresponding to a display signal differ for colors R, G, and B, so
that gain correction circuits 61, 62, and 63 for correcting a gain
Gain are provided for the colors R, G, and B.
[0072] The differences will be described in more detail.
[0073] The gain Gain calculated by a gain calculation circuit 14 is
inputted to the multiplier 41. A whole luminance control signal W
_Gain for controlling the luminance for the whole screen from the
exterior is fed to the multiplier 41. By controlling the signal W
_Gain given to the multiplier 41, it is possible to make the screen
bright when the display is used in a bright place and to make the
screen dark after an elapse of a predetermined time period.
[0074] An output of the multiplier 41 is fed to each of the
multipliers 51, 52, and 53. Arbitrary gains R _Gain, G _Gain, B
Gain are respectively fed for the colors R, G, and B to the
multipliers 51, 52, and 53. Since the gains R _Gain, G _Gain, B
_Gain respectively given to the multipliers 51, 52, and 53 can be
individually controlled, white balance control can be made.
[0075] Outputs of the multipliers 51, 52, and 53 are respectively
given to the corresponding gain correction circuits 61, 62, and 63.
Each of the gain correction circuits 61, 62, and 63 sets
input/output characteristics, as indicated by straight lines K1 and
K2 shown in FIG. 8, for example, thereby correcting the inputted
gain.
[0076] In a reference voltage control circuit 15, white-side
reference voltages are corrected for the colors R, G, and B using
the gains, respectively given from the gain correction circuits 61,
62, and 63, corresponding to the colors R, G, and B.
[3] DESCRIPTION OF THIRD EMBODIMENT
[0077] FIG. 9 illustrates the schematic configuration of a portable
telephone set.
[0078] An MPU (Microprocessor Unit) 209 carries out the overall
control of the portable telephone set. An antenna 201 transmits and
receives electric waves. A transmitting/receiving unit 202 receives
the electric waves, and transmits the contents of the receiving to
the MPU 209. Further, the transmitting/receiving unit 202 transmits
a transmission signal outputted from the MPU 209 with the
transmission signal on the electric waves.
[0079] A microphone 203 feeds an audio signal to the MPU 209. A
speaker 204 outputs as an audio the audio signal outputted from the
MPU 209. A first camera 205 is a camera mounted on a front surface
of the main body of the portable telephone set provided with an
organic EL display 214, and sends to the MPU 209 a video which it
has picked up. A second camera 206 is a camera mounted on a rear
surface of the main body of the portable telephone set, and sends
to the MPU 209 a video which it has picked up. At the time of an
imaging mode, the video picked up by the camera 205 or 206 is
displayed on the organic EL display 214 in place of the content of
the display at the time of a normal mode.
[0080] An operation unit 208 is provided in the main body of the
portable telephone set, and comprises various buttons 221 and
various switches 222, as shown in FIG. 10. A timer 211 is used for
luminance control, described later.
[0081] A flash memory 210 stores data to be stored even when the
power is turned off. A graphics memory 212 stores image data to be
displayed on the display. Image data is written into a
predetermined address in the graphics memory 212 on the basis of
image data outputted from the MPU 209 and a writing control signal.
Pixel data representing a corresponding pixel is outputted at the
timing of scanning in conformity with a display period of the
organic EL display 214 from the graphics memory 212.
[0082] A timing control IC 213 feeds image data and a driving
signal to the organic EL display 214, and displays a video on the
organic EL display 214. The timing control IC 213 comprises a
luminance control circuit.
[0083] FIG. 10 illustrates the configuration of the luminance
control circuit provided in the timing control IC 213, and the MPU
209 for controlling a luminance for the whole screen and its
peripheral device.
[0084] In FIG. 10, the same components as those shown in FIG. 3 are
assigned the same reference numerals and hence, the description
thereof is not repeated. The luminance control circuit shown in
FIG. 10 is approximately the same as the luminance control circuit
shown in FIG. 3 except that a multiplier 41 for controlling a
luminance for the whole screen (a display luminance) is provided in
a reference voltage control circuit 1. An whole luminance control
signal W _Gain given to the multiplier 41 is generated by the MPU
209.
[0085] The various buttons 208 and the various switches 222 which
are provided in the operation unit 208 are connected to the MPU
209. The MPU 209 comprises the timer 211. The cameras 205 and 206
are connected to the MPU 209. Each of the cameras 205 and 206 has
an automatic exposure control function. In this example, exposure
time information is sent to the MPU 209 from the first camera 205
mounted on the front surface of the main body of the portable
telephone set.
[0086] The MPU 209 estimates peripheral brightness under current
environments in which the portable telephone set is used on the
basis of the exposure time information from the first camera 205,
to generate the whole luminance control signal W _Gain. The whole
luminance control signal W _Gain takes a value between 2.0 and 0.5,
for example.
[0087] Specifically, when the exposure time is long, that is, the
peripheral brightness is low, the whole luminance control signal W
_Gain is reduced. As a result, a gain outputted from the multiplier
41 becomes smaller than a gain calculated by the gain calculation
circuit 14, and a white-side reference voltage R _Refw' after
control becomes high, so that the display luminance becomes low.
Conversely, when the exposure time is short, that is, the
peripheral brightness is high, the whole luminance control signal W
_Gain is increased. As a result, the gain outputted from the
multiplier 41 becomes larger than the gain calculated by the gain
calculation circuit 14, and the white-side reference voltage R
_Refw' after control becomes low, so that the display luminance
becomes high.
[0088] The above-mentioned control may be carried out using AGC
gain information relating to the first camera 205 in place of the
exposure time information relating to the first camera 205. In this
case, when the AGC gain is large, it is judged that the peripheral
brightness is low, to reduce the whole luminance control signal W
_Gain. Conversely, when the AGC gain is small, it is judged that
the peripheral brightness is high, to increase the whole luminance
control signal W _Gain.
[0089] The MPU 209 reduces, when the various buttons 221 or the
various switches 222 which are provided in the operation unit 208
are operated, the whole luminance control signal W _Gain is
reduced, to increase the display luminance. When a predetermined
time period has elapsed, the whole luminance control signal W _Gain
is increased, to reduce the display luminance.
[0090] It is judged using the timer 211 whether or not a
predetermined time period has elapsed. Specifically, the timer 211
is reset when the buttons 221 or the switches 222 are operated, to
automatically start measurement of time. The luminance for the
screen is controlled depending on the time measured by the timer
211. When not less than the predetermined time period has elapsed,
the display luminance is reduced by half.
[4] DESCRIPTION OF FOURTH EMBODIMENT
[0091] FIG. 11 illustrates the schematic configuration of a
portable telephone set. In FIG. 11, the same components as those
shown in FIG. 9 are assigned the same reference numerals and hence,
the description thereof is not repeated.
[0092] The portable telephone set differs from the portable
telephone set shown in FIG. 9 in that a direction sensor 207 for
sensing the direction (upward, downward, sideward, etc.) of a
display surface of an organic EL display 214 is provided. In the
portable telephone set, display luminance control based on exposure
time information from a first camera 205 is not carried out.
[0093] FIG. 12 illustrates the configuration of a luminance control
circuit provided in a timing control IC 213, and an MPU 209 for
controlling a luminance for the whole screen and its peripheral
device.
[0094] In FIG. 12, the same components as those shown in FIG. 3 are
assigned the same reference numerals and hence, the description
thereof is not repeated. Although the luminance control circuit
shown in FIG. 12 is approximately the same as the luminance control
circuit shown in FIG. 3, it differs from the luminance control
circuit shown in FIG. 3 in that a multiplier 41 for controlling a
luminance for the whole screen (a display luminance) is provided in
a reference voltage control circuit 1. A whole luminance control
signal W _Gain given to the multiplier 41 is generated by the MPU
209.
[0095] Various buttons 221 and various switches 222 which are
provided in an operation unit 208 are connected to the MPU 209. The
MPU 209 comprises a timer 211. The direction sensor 207 is
connected to the MPU 209.
[0096] The MPU 209 estimates the direction (upward, downward,
sideward, etc.) of the display surface of the organic EL display
214 on the basis of a detection signal of the direction sensor 207,
to generate a whole luminance control signal W _Gain. The whole
luminance control signal W _Gain takes a value between 2.0 and 0.5,
for example.
[0097] Specifically, as the display surface of the organic EL
display 214 is directed upward, the whole luminance control signal
W _Gain is reduced, thereby making the display luminance higher.
The whole luminance control signal W _Gain is controlled to a small
value when the display surface of the organic EL display is
directed upward, is controlled to a large value when the display
surface of the organic EL display 214 is directed downward, and is
controlled to an intermediate value when the display surface of the
organic EL display 214 is directed sideward.
[0098] Furthermore, the MPU 209 reduces the whole luminance control
signal W _Gain when the various buttons 221 or the various switches
222 which are provided in the operation unit 208 are operated, as
in the above-mentioned third embodiment, thereby making the display
luminance higher. When a predetermined time period has elapsed, the
whole luminance control signal W _Gain is increased, thereby
reducing the display luminance.
[0099] The direction (upward, downward, sideward, etc.) of the
display surface of the organic EL display 214 may be detected from
the exposure times and the AGC gains of two cameras 205 and
206.
[0100] That is, when the display surface of the organic EL display
214 is directed upward, the possibility that a front surface of the
main body of the portable telephone set is brighter than a rear
surface thereof is high. Therefore, it is considered that the
exposure time of the first camera 205 attached to the front surface
of the main body of the portable telephone set is shorter than the
exposure time of the second camera 206 attached to the rear surface
of the main body of the portable telephone set (the AGC gain
thereof is reduced when the exposure times are the same).
[0101] Conversely, when the display surface of the organic EL
display 214 is directed downward, the possibility that the rear
surface of the main body of the portable telephone set is brighter
than the front surface thereof is high. Therefore, it is considered
that the exposure time of the second camera 206 attached to the
rear surface of the main body of the portable telephone set is
shorter than the exposure time of the first camera 205 attached to
the front surface of the main body of the portable telephone set
(the AGC gain thereof is reduced when the exposure times are the
same).
[0102] Therefore, the direction of the display surface of the
organic EL display 214 can be judged by the exposure times and the
AGC gains of the two cameras 205 and 206.
* * * * *