JP2000227776A - Current control type light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a luminance control making light emitting elements emit light with prescribed luminance at high speed by shortening the delay time of the switching of a constant current source. SOLUTION: A first transistor(Tr) 45 controls the switching between a constant current source 42 and a light emitting element 41 and a second Tr 46 controls the switching between a constant voltage source 44 and the constant current source 42. When a selection signal is inputted from a line control circuit to a gate 45a and the Tr 45 is turned on by the selection signal, the output of the constant current source 42 is conducted o the light emitting element 41. Moreover, the inversion signal of the selection signal from the line control circuit is inputted to a gate 46a via an inverter 47. The input of the first Tr 45 and the input of the second Tr 46 are in a reversal relation each other and when the transistor of one side is turned on, the transistor of other side is made to be turned off complementarily and the output terminal (e) point of the constant current source 42 is made to be always in a conductive state and, thus, a time delay posterior to the changeover between transistors is not present and a prescribed current is made to be instantly conducted to the light emitting element 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-controlled light-emitting device which performs high-precision, high-speed display control using a current-controlled light-emitting element and is driven at a low voltage.

[0002]

2. Description of the Related Art An example of a brightness control method used in a display using a current control type light emitting element according to the prior art is described below. FIG. 8 is a drawing showing a configuration of a display using a current control type light-emitting element having m × n pixels. 8, 101 is a display panel, 102 is a brightness control circuit, and 103 is a line control circuit. The display panel 101 has a plurality of display pixels in an array, and controls the light emission of each pixel to display an image on the entire display. The luminance control circuit 102 is a circuit that controls the luminance of each pixel, and controls the light emission luminance of each pixel. The line control circuit 103 scans the pixels line by line, activates the pixels line by line, and selectively inputs the output of the luminance control circuit. In progressive scanning, scanning is performed sequentially line by line. In interlaced scanning, interlaced scanning is performed line by line, and scanning is performed separately for odd-numbered frame scanning and even-numbered frame scanning.

[0005] A pixel circuit is provided for each display pixel of the display panel 101. FIG. 9 shows the configuration of the pixel circuit. Each pixel circuit is composed of a current control type light emitting element 111 composed of a cold electron emission emitter or a phosphor, a constant current source transistor 112, and a switching transistor 113, and a gate terminal 114 of the constant current source transistor 112 and a switching terminal. Transistor 113
Are connected to the outputs of the luminance control circuit 102 and the line control circuit 103, respectively.

FIG. 10 shows a simple block diagram of the brightness control circuit 102. In the luminance control circuit 102, when the luminance input signal is rewritten in the horizontal direction by one line into the shift register 121, the respective data are latched by the latch circuit 122 and the lines selected by scanning as one line data of Y1 to Yn. Is output to each pixel. Y1 in FIG.
To Yn correspond to Y1 to Yn in FIG. 8, and a voltage corresponding to the luminance signal is output from Y1 to Yn, respectively.
Are connected to the gate terminal 114 of the constant current source transistor 112 of each pixel, and the outputs X1 to Xm of the line control circuit 103 are connected to the gate terminal 115 of the switching transistor 113 of each pixel. As shown in FIG. 9, the constant current source transistor 112 and the switching transistor 113
6, 117.

[0005] A procedure for producing an image of one frame in a display using the above-mentioned conventional current control type light emitting element will be described. As an example, the case of progressive scanning will be described. First, in FIG. 8, a high-level voltage is applied to X1 of the line control circuit 103, and the display panel 101
The first line at the top left of is selected. After securing the transistor switching period for line selection, the luminance control circuit 102 transmits the luminance data of each pixel on the first line to Y1.
To Yn, and the light emitting element 1 of each pixel on the first line
11 is supplied with a corresponding voltage signal among Y1 to Yn, and emits light at a predetermined luminance. During this time, the lines after the second line are not selected, that is, in the off state. Next, the X1 output of the line control circuit 103 goes low,
When the output is switched to the high level, the first line is not selected and the second line is selected. The second line performs the same brightness control as the first line during the selection period,
Each pixel in the second line emits light. By repeating this operation up to the m-th line, one image is created.

[0006]

According to the above-described conventional brightness control method for a display using a cold electron emission current control type light emitting element, as shown in FIG. 9, a constant current source transistor 112 and a switching transistor. Since the parasitic capacitances 116 and 117 occur in each of the 113,
The constant current source transistor 112 has a problem in that the proper constant current source operation cannot be performed unless the potentials at points d and e in the circuit are charged to a predetermined operating point potential in consideration of the parasitic capacitance. . That is, even when the pixel is selected by the line selection, a predetermined voltage is applied to the light emitting element 111 of the pixel, and there is a problem that a delay time occurs until the pixel emits light with desired luminance.

The manner in which a light emission delay time occurs in the light emitting element 111 of a pixel will be described with reference to FIG. FIG. 11 shows the constant current source characteristics of the constant current source transistor 112 and the light emitting element 111.
FIG. 4 is a diagram showing a relationship of current characteristics of the present invention. In the steady state of light emission of the light emitting element 111, the point e in FIG. 9 operates at the operating point 131 indicated by a circle in FIG. 11, but when the switching transistor 113 is turned off, the point e in FIG. The conduction current moves to 132 near the origin as shown by the mark x in FIG. The next selection period comes,
Even if the luminance signal is given to the light emitting element 111, the current at the point e once moved to 132 near the origin does not immediately return to the steady light emission state, and a delay time occurs. This delay time is
The current value of the constant current source transistor 112 and the parasitic capacitance 11
6, 117 nsec to several μse, depending on the size of
c. There is little problem if the control method is such that the pixel selection period can be secured so long that the delay time can be ignored. Since it is necessary to apply a constant voltage and finely control the pulse width of the voltage applied to the gate terminal 115 of the switching transistor 113 in accordance with the image signal, there is little time margin in the selection period, and the effect of the delay time cannot be ignored. This causes a problem that the light emission luminance cannot be controlled properly.

The present invention has been made in view of the above problems, and has been made in consideration of the above problem.
It is an object of the present invention to provide a current control type light emitting device capable of realizing luminance control for causing a light emitting element to emit light at a predetermined luminance at high speed by shortening a delay time of constant current source switching caused by a parasitic capacitance in one of the selection circuits. .

[0009]

In order to achieve the above object, a current control type light emitting device according to the present invention comprises, for each pixel, a current control type light emitting element and a constant for controlling the light emission luminance of the current control type light emitting element. A current source transistor, a constant voltage source, and a switch unit for selecting whether to connect the output current of the constant current source transistor to the current control type light emitting element or the constant voltage source, and the switch unit Selecting the current control type light emitting element during the element selection period of the current control type light emitting element, selecting the constant voltage source during periods other than the element selection period, and complementing the selection of the current control type light emitting element and the constant voltage source. And the constant current source transistor is always connected to one of the current control type light emitting element and the constant voltage source.

With the above configuration, the constant current source transistor is always connected to either the light emitting element or the constant voltage source and operates as a constant current source, so that the potential of the output terminal can be controlled in a desired range. Switching delay time is eliminated, and a desired light emitting element current can be conducted to the light emitting element immediately after the start of the light emitting element selection period.

Next, the switch section has, as a first configuration, a first transistor having one end connected to the output end of the constant current source transistor and the other end connected to the current control type light emitting element. A second terminal having one end connected to the output terminal of the constant current source transistor and the other end connected to the constant voltage source;
A transistor selection signal of the current control type light emitting element is input to a gate of the first transistor,
It is preferable that an inverted signal of the element selection signal is input to a gate of the second transistor.

According to the above configuration, in the switch section, when one of the first transistor and the second transistor is turned on complementarily, the other is turned off, the two transistors are turned on and off, and either the light emitting element or the constant voltage source is turned off. Either one is reliably connected to the constant current source.

Next, the switch section has, as a second configuration, a first transistor having one end connected to the output end of the constant current source transistor and the other end connected to the current control type light emitting element. A second terminal having one end connected to the output terminal of the constant current source transistor and the other end connected to the constant voltage source;
A transistor selection signal of the current control type light emitting element is input to a gate of the first transistor,
The potential of the output terminal of the constant current source transistor whose one end of the second transistor is connected to the gate of the second transistor is changed from the potential at which the constant current source transistor can operate in a saturation region to the second potential. It is preferable to input a voltage signal for controlling one transistor to a potential that can be completely turned on when the element selection signal is input.

According to the above configuration, the potential at the output terminal of the constant current source transistor can be kept within a certain range. The potential range is such that the constant current source transistor operates in the saturation region, and a current of a predetermined value is output as the output current. This is a range in which the switching of the first transistor can be normally performed, the normal on / off of the light emitting element can be performed, and the current of a predetermined value can be supplied to the light emitting element without delay time. it can. Since it is not necessary to have a circuit for generating an inversion signal in each pixel, the circuit configuration can be simplified.

Preferably, the voltage input to the gate of the second transistor is in the range of 30% to 70% of the voltage of the element selection signal of the current control type light emitting element input to the gate of the first transistor. It is assumed that

[0016] The relative value of the element selection signal is used to easily calculate Vs.
Can be selected.

More preferably, the voltage input to the gate of the second transistor is 50% of the voltage of the element selection signal of the current control type light emitting element input to the gate of the first transistor. I do.

The relative value of the element selection signal is used to easily calculate Vs
Can be selected, and stable operation can be expected with respect to fluctuations in element characteristics due to changes in environmental conditions such as temperature.

In the second configuration of the switch section of the present invention,
If the voltage input to the gate of the second transistor is within this range, the light emitting element can be normally turned on and off normally,
In addition, a current of a predetermined value can be supplied to the light emitting element without delay time.

Next, in the current-type light-emission control device of the present invention, the constant current source transistor controls the duty of a signal applied to the gate of the first transistor, thereby controlling the light emission luminance of the current-control light-emitting element. Preferably, it is

According to the above configuration, the present invention can be applied to a current control type light emitting device in which the switching of the light emitting element is duty-controlled, and the current of the light emitting element turns on / off following the high speed switching. It is possible to cope with the gradual brightness control.

The gate signal of the constant current source transistor is changed from a start point of a horizontal synchronization signal indicating the start of the selection period of the current control type light emitting element to a start point of the horizontal synchronization signal indicating the end of the selection period. Until the horizontal synchronizing signal indicating the end of the selection period from the start time of the horizontal synchronizing signal indicating the start of the next selection period, and repeatedly switching between the on level and the off level. Drive.

According to the above configuration, by setting the ON period of the constant current source transistor from the start of the horizontal synchronizing signal for instructing the start of the selection period, the ON period becomes longer than that in which only the effective pixel area is turned ON. A longer control time can be secured. Further, the constant current source transistor is turned off at the start of the horizontal synchronizing signal for instructing the end of the selection period, and no current flows during the non-selection period, so that power consumption can be reduced.

[0024]

(Embodiment 1) Hereinafter, an embodiment of a current control type light emitting device according to claims 1 and 2 of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a display to which the current control type light emitting device according to the first embodiment of the present invention is applied. In FIG. 1, reference numeral 1 denotes a display panel having m × n pixels with m scanning lines and n signal lines. The numerical values of m and n can be changed according to the standard. For example, m = 480 and n = 640. Reference numeral 2 denotes a luminance control circuit, 3 denotes a line control circuit, and 4 denotes a pixel circuit for forming each pixel. The first embodiment can be applied to any of the interlaced scanning and the progressive scanning as the scanning method. Here, it is assumed that progressive scanning is performed, and the description focuses on the operation of each pixel during a line selection period and a line non-selection period.

The scanning method for selecting each pixel circuit 4 and supplying a luminance signal is the same as the conventional progressive method.
In accordance with the line selection signals X (1) to X (m), the line control circuit 3 sequentially selects each line, and outputs the luminance signals Y (1) to Y (n) for each pixel circuit 4 of the selected line to the luminance control circuit. 2 and output to the pixel circuit 4 within a predetermined period. The pixel circuit 4 receives the supplied luminance signals Y (1) to Y (1).
Light emission of luminance according to Y (n) is performed. All lines X
When scanning for (1) to X (m) is completed, one frame image is formed on the display 1.

FIG. 2 shows the configuration of the pixel circuit 4. As shown in FIG. 2, each pixel circuit 4 includes a voltage source 40, a current control type light emitting element 41, a constant current source transistor 42, a switch unit 43, and a constant voltage source 44.

The voltage source 40 supplies a voltage to the current control type light emitting element 41.

The light emitting element 41 is, for example, a current-controlled light emitting element that emits cold electrons.

The constant current source transistor 42 has a gate 42
A luminance signal corresponding to each signal line is input from a luminance control circuit 2 to a, and switching control of a current input corresponding to the luminance signal to the current control type light emitting element 41 is performed.

The switch unit 43 includes a first switching transistor 45 and a second switching transistor 4.
6. The inverter 47 is provided. The first switching transistor 45 is connected to the gate 45 a by the line control circuit 3.
When a selection signal corresponding to each line is input from the switch, and the signal is turned on by the selection signal, the output of the constant current source transistor 42 is conducted to the light emitting element 41. The inverted signal of the selection signal corresponding to each line is input to the gate 46 a of the second switching transistor 46 from the line control circuit 3 via the inverter 47 via the inverter 47. That is, the input of the first switching transistor 45 and the input of the second switching transistor 46 are in an inverting relationship, and if one is complementarily on, the other is off and the selection signal from the line control circuit 3 is input. When the first switching transistor 45 is turned on, the second switching transistor 46 is turned off, and there is no selection signal from the line control circuit 3 (that is, during the line non-selection period) (that is, during the line non-selection period). , The first switching transistor 45 is turned off, and the second switching transistor 46
Is on. The second switching transistor 46 switches between the output terminal of the constant current source transistor 42 and the constant voltage source 44. That is,
The state of the output terminal e of the constant current source transistor 42 in FIG. 2 is in a conductive state in which a predetermined current flows through the first switching transistor 45 during the line selection period, and the second switching state during the line non-selection period. The transistor 46 and the constant voltage source 44 are in a state in which a constant potential is applied, and neither of them is in the cutoff state, and the operation transition after switching between the two can be completed in a short time. Thus, by the operation of the switch unit 43,
In both the line selection period and the non-selection period, the constant current source transistor 42 is always connected to either the light emitting element 41 or the constant voltage source 44.

FIG. 3 shows the state of the output terminal e of the constant current source transistor 42 shown in FIG. 2 during the line selection period and the non-selection period. The graph shown by the solid line in FIG. 3 is the light emitting element current of the current control type light emitting device of the present invention. Also in the line non-selection period, the constant potential of the constant voltage source 44 is supplied to the output terminal e of the constant current source transistor 42 of FIG. 2 via the second switching transistor 46. When the switching circuit 46 is turned off and the first switching transistor 45 is turned on and switching is performed, the light emitting element 4 is immediately turned on.
It can be seen from FIG. 1 that the light emitting element current for the luminance signal rises. The delay period in this case is shown as t1. On the other hand, the light emitting element current of the conventional light emitting device not using the current control type light emitting device of the present invention is shown by a dotted line. In the conventional device, the constant current source transistor 42 is cut off during the line non-selection period. Therefore, a parasitic capacitance component occurs as shown in FIG. 10 in the description of the related art. Charging is required, and a time delay occurs in the rise of the current. The delay period in this case is t2
It is illustrated. As is clear from FIG. 3, when the delay time t2 increases, the operation of the device during the selection period T is affected. It can be seen that in the current control type light emitting device of the present invention, such an influence is small and reduced.

Finally, a procedure for displaying an image for one frame will be described.

The luminance input signal is input to the shift register in the luminance control circuit 2, and when one line is input, the output to each pixel is latched and output to Y1 to n. In this case, it is assumed that the luminance input signal has been converted in advance into a value to be given to the gate of the constant current source transistor. Next, only X1 is high level (selected) by the line control circuit 3.
A signal is output, and a current flows through the light emitting element of each pixel on the first line to emit light at a predetermined luminance. When the selection period of one line ends, the outputs of all the line control circuits 3 including X1 once become low level (unselected). Then, the shift register in the brightness control circuit 2 is latched when all the brightness signals of the second line are input and output to Y1 to Yn. Immediately thereafter, a high level (selection) signal is output only from X2 by the line control circuit 3, and the second line emits light. These operations are repeated up to the m-th line to complete an image for one frame.

(Embodiment 2) Hereinafter, claim 1 of the present invention,
Embodiments of the current-controlled light-emitting devices described in 3, 4, and 5 will be described with reference to the drawings.

The schematic configuration of the current control type light emitting device of the second embodiment is the same as the device configuration of FIG. 1 described in the first embodiment, but the pixel circuit 4 of the current control type light emitting device shown in the first embodiment. And a pixel circuit 4a having a different configuration from that of FIG. Parts other than the pixel circuit 4a may be the same as those described in the first embodiment, and thus the description thereof will not be repeated here, and the description will focus on the pixel circuit 4a.

FIG. 4 shows the configuration of the pixel circuit 4a of the current control type light emitting device of the second embodiment. The same components as those in FIG. 2 are denoted by the same reference numerals. As shown in FIG. 4, the pixel circuit 4a includes a current control type light emitting element 41, a constant current source transistor 42, a switch 43a, a constant voltage source 4
4 is provided. Except for the switch 43a, the power supply 40,
A current control type light emitting element 41, a constant current source transistor 42,
The constant voltage source 44 is the same as that shown in FIG. 2 of the first embodiment.
The same applies to the input and output of the signal, and a description thereof will be omitted as appropriate.

The switch section 43a includes a first transistor 45, a second transistor 46, and a voltage source Vs48. The voltage source Vs48 is connected to the gate of the second transistor 46, and provides a voltage signal for controlling the potential of the output terminal of the constant current source transistor within a certain range.
The output voltage from the constant voltage source 44 is controlled by the gate signal of the second transistor 46 from the voltage source Vs48, and the potential at the output point e of the constant current source transistor 42 is controlled within a predetermined range. In other words, the potential of the point e is maintained at a certain potential or more even in the line non-selection period, and the light emitting element 41 is immediately switched to the line selection period.
Thus, the rise of the light emitting element current with respect to the luminance signal is enabled.

FIG. 5 is a diagram for explaining the theoretical range of the voltage source Vs48 for the normal operation of the current control type light emitting device. The vertical axis represents the current I1 of the first transistor 45, and the horizontal axis represents the gate voltage Vb of the first transistor 45. V
The first transistor 45 switches around b = Vs.
When the voltage source Vs48 becomes higher, the gate voltage at which the first transistor 45 is turned on becomes higher. When the voltage source Vs48 becomes too high, the first transistor 45 becomes higher at the high level voltage supplied to Vb as shown by the current characteristic 51. 45
Is in a state where switching cannot be performed completely. Therefore, as shown by the current characteristic 52, it can be seen that the upper limit is the voltage signal Vs that gives the potential at the point e at which the first transistor 45 can be completely turned on when the element selection signal is input.

On the other hand, considering the lower limit, the effect of the present invention, that is, the effect of immediately applying a predetermined current to the light emitting element 41 when switching to the line selection period is sufficiently exhibited. Preferably, a potential for completely turning on the constant current source transistor is applied. That is, the lower limit is a potential at which the constant current source transistor 42 can operate in the saturation region. As shown in the current characteristic 53 of FIG. 5, when the voltage Vs is excessively lowered, the potential at the point e also decreases, and when the constant current source transistor 42 is turned on, it operates sufficiently in the saturation region (completely turned on). Since a high potential cannot be obtained, the device operates in a non-saturation region, and a rated constant current cannot be initially obtained. Therefore, as shown by the current characteristic 54 in FIG. 5, the lower limit is the voltage signal Vs that gives the potential that the constant current source transistor 42 can operate in the saturation region to the point e.

As described above, the range of the voltage signal Vs applied to the gate of the second transistor 46 of the switch section 43a, the potential of the output terminal e of the constant current source transistor 42, the constant current source transistor 42 operates in the saturation region. The voltage signal is controlled so as to control the potential from a high potential to a potential at which the first transistor 45 can be completely turned on when the element selection signal is input.

The value of Vs may be accurately designed so as to be within the above range. Here, the value of Vs is a relative value based on the voltage of the element selection signal input to the gate of the first transistor 45. Here is an example of the decision. The range of Vs varies depending on actual variations in element characteristics, parasitic capacitance, temperature characteristics, and the like. However, if the range is 30% to 70% of the element selection signal, the first transistor 45 is completely switched. , Constant current source transistor 4
Normally, 2 is a transistor that operates in a saturation region at a small voltage. Therefore, if it is smaller than the selected Vs, the range condition of the Vs is satisfied. More preferably, if it is 50% of the element selection signal, the device can be highly stable against changes in environmental conditions such as temperature.

The procedure for displaying an image for one frame may be the same as the method described in the embodiment, and a description thereof will be omitted.

(Embodiment 3) Hereinafter, an embodiment of a current control type light emitting device according to claim 6 of the present invention will be described with reference to the drawings. In the third embodiment, a signal given to the gate of the first transistor is duty-controlled to control the light emission luminance of the current control type light emitting element.

In the pixel circuit shown in FIG. 2 or FIG. 4, the output of the line control circuit 3 is applied to the gate terminal 42a of the constant current source transistor 42, and the output of the luminance control circuit 2 is applied to the gate terminal 45a of the first transistor 45. Connecting. FIG. 6 shows an example of the luminance control circuit 2 in this case. As shown in FIG. 6, the luminance control circuit 2 includes a shift register 21, a latch 22, a sawtooth generator 23, and a comparator 24. The comparator 24 is provided with 24 (1) to 24 (n) corresponding to the respective signal line outputs Y1 to Yn. One of the input signals to be compared is a latched luminance input signal, and the other is a sawtooth wave generator 23. Is a sawtooth wave supplied from. In this case, the luminance input is not the value converted for the gate voltage of the constant current source transistor 42 but the luminance signal itself, and is latched when the luminance signal for one line is input. The sawtooth generator 23 rises from the zero scale of the luminance signal at the same time as the start of the line and generates a level exceeding the full scale of the luminance signal over one line, and the same from the zero level again at the start of the next line. It is a kind of counter that repeats a pattern. The output of the sawtooth generator 23 is connected to the inverting input terminal of the comparator 24, and is compared with the luminance signal of each pixel. As a result, a high level (active) is output to Y1 to n only during a period corresponding to the luminance signal.

First, a high-level (selection) signal is output only to X1 of the line control circuit 3, and after a period for allowing the constant current source transistor to enter the constant current source operation, the signal is input to the shift register for one line. The thus-obtained first-line luminance signal is latched, and the sawtooth generator starts counting up.
Thus, each pixel on the first line starts emitting light only during a period corresponding to the luminance level. When one line period ends, X1
Becomes low level (non-selection), subsequently, only X2 goes high (selection), and after a period of time sufficient for the constant current source transistor to enter the constant current source operation, the second line input to the shift register , And the sawtooth generator starts counting up from zero scale. That is, each pixel of the second line emits light by the same processing as that of the first line. By repeating this operation up to the m-th line, an image for one frame is completed.

As described above, the duty ratio of the signal applied to the gate of the first transistor is controlled by the constant current source transistor to control the light emission luminance of the current control type light emitting element.

(Embodiment 4) Next, an embodiment of a current control type light emitting device according to claim 7 of the present invention will be described with reference to the drawings. In the fourth embodiment, the on-period of the constant current source transistor is set from the start of the horizontal synchronization signal instructing the start of the selection period, and the duty control time is secured longer than that in which only the effective pixel area is turned on. is there. Further, the constant current source transistor is turned off at the start of the horizontal synchronization signal instructing the end of the selection period,
When it is not during the selection period, unnecessary current does not flow and power consumption is reduced.

In the fourth embodiment, the gate terminal 42a of the constant current source transistor 42 of the pixel circuit shown in FIGS.
By controlling the signal output of the line control circuit 3 to be applied to the control signal. FIG. 7 shows an outline of a line selection signal output of the line control circuit 3. FIG. 7A is a timing chart of a signal applied to the gate terminal 42a of the constant current source transistor 42 by the line control circuit 3 according to the fourth embodiment, and FIG. 7B is a line chart according to the conventional method without using the present invention. 5 is a timing chart of a signal from a control circuit.

In FIG. 7A, the upper part is a horizontal synchronizing signal. For example, in the case of the NTSC system, a pulse of about 5 μsec is intermittently given. The middle row is the first line X
1 is the timing of the line selection signal given to
This is the timing of the line selection signal given to the second line X2. The third and subsequent components are omitted.

In the fourth embodiment, as shown in FIG. 7A, the level is set to the high level in accordance with the start of the horizontal synchronization signal for instructing the start of the line selection period. For this reason, the period for duty control can be extended.

In particular, by combining with the configuration shown in the first, second, and third embodiments of the present invention, it becomes possible to apply a predetermined current to the light emitting element 41 immediately when the line selection signal becomes high. On the other hand, as shown in FIG. 7B, when the invention described in claim 7 of the present invention is not used, the period during which the line selection signal is high is shorter than that of the method of the present invention, and thus the duty control is performed. The time required for this is short.

Next, as shown in FIG. 7A, in the configuration of the fourth embodiment, the line selection signal is set to a low level in synchronization with the start of the horizontal synchronizing signal indicating the end of the line selection period, and the constant current The source transistor 42 is off. Therefore, unnecessary current does not flow during periods other than the line selection period, which is effective in reducing power consumption.

Further, when the horizontal synchronizing signal for instructing the start of the next line selection period is started, the level is switched to the high level, and the operation without delay is ensured in the next line selection period.

In the description of each of the above embodiments, m = 4
Although 80 and n = 640, it is needless to say that the present invention can be used with other values of m and n.

[0056]

According to the current control type light emitting device of the first and second aspects of the present invention, the constant current source transistor is always connected to either the light emitting element 41 or the constant voltage source, and the constant current source As a result, it is possible to control the potential of the output terminal within a desired range, eliminate a switching delay time, and immediately conduct a desired light emitting element current to the light emitting element at the start of the light emitting element selection period. Can be.

According to the current control type light emitting device according to the third, fourth, and fifth aspects of the present invention, the same operation as that of the second aspect can be performed, and a circuit for generating an inverted signal in each pixel is required. Since there is no circuit, the circuit configuration is simplified.

According to the current control type light emitting device of the sixth aspect of the present invention, the present invention can be applied to the current control type light emitting device which performs duty control of the switching of the light emitting element of the present invention. In this case, since the current of the light-emitting element can be turned on / off by following the operation, there is an effect that it is possible to cope with small-scale brightness control.

According to the current control type light emitting device of the seventh aspect of the present invention, the period during which the duty control is performed with the start time of the line selection signal as the start time of the horizontal synchronizing signal can be extended. After the pixel selection period ends,
By turning off the constant current source transistor 42 until the next selection period approaches, power consumption can be saved.

[0060]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a display to which a current-controlled light-emitting device according to a first embodiment of the present invention is applied.

FIG. 2 is a diagram showing a configuration of a pixel circuit 4 according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a state of a constant current source transistor 42 in a line selection period and a non-selection period according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a pixel circuit 4 of FIG. 1 according to a second embodiment of the present invention;

FIG. 5 is a diagram for explaining a theoretical range of a voltage source Vs48 for a normal operation of the current control type light emitting device according to the second embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration example of a brightness control circuit 2 according to a third embodiment of the present invention.

FIG. 7 is a diagram schematically illustrating a line selection signal output of a line control circuit 3 according to a fourth embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a display using light-emitting elements having m × n pixels.

FIG. 9 is a diagram showing a configuration of a pixel circuit of a display using a conventional light-emitting element.

FIG. 10 is a simplified block diagram of a conventional luminance control circuit 102;

FIG. 11 is a diagram showing a relationship between a constant current source characteristic of a conventional constant current source transistor 112 and a current characteristic of a light emitting element 111;

[Description of Signs] 1 display panel 2 brightness control circuit 3 line control circuit 4 pixel circuit 21 shift register 22 latch 23 sawtooth generator 24 comparator 40 voltage source 41 current control type light emitting element 42 constant current source transistor 43, 43a switch Unit 44 constant voltage source 45 first switching transistor 46 second switching transistor 47 inverter 48 voltage source Vs 51 to 54 current characteristics

Claims (7)

[Claims] In a current control type light emitting device, a current control type light emitting element, a constant current source transistor for controlling light emission luminance of the current control type light emitting element, a constant voltage source, and a constant current source are provided for each pixel. A switch unit for selecting whether to connect the output current of the transistor to the current control type light emitting element or to the constant voltage source, wherein the switch unit is configured to control the current during an element selection period of the current control type light emitting element. Select a control type light emitting element, select the constant voltage source other than the element selection period, complementarily switch the selection of the current control type light emitting element and the constant voltage source,
The current control type light emitting device, wherein the constant current source transistor is always connected to one of the current control type light emitting element and the constant voltage source. A first transistor having one end connected to an output terminal of the constant current source transistor and the other end connected to the current control type light emitting element; and one end connected to the constant current source transistor. A second transistor connected to the output end of the second transistor and the other end connected to the constant voltage source,
The current control type light emission according to claim 1, wherein an element selection signal of the current control type light emitting element is input to a gate of the first transistor, and an inverted signal of the element selection signal is input to a gate of the second transistor. apparatus. 3. A first transistor having one end connected to the output terminal of the constant current source transistor, the other end connected to the current control type light emitting element, and one end connected to the constant current source transistor. A second transistor connected to the output end of the second transistor and the other end connected to the constant voltage source,
An element selection signal of the current control type light emitting element is input to a gate of the first transistor, and an output of the constant current source transistor having one end of the second transistor connected to a gate of the second transistor. A voltage signal for controlling the potential at the end to be in a range from a potential at which the constant current source transistor can operate in a saturation region to a potential at which the first transistor can be completely turned on when the element selection signal is input is input. The current control type light emitting device according to claim 1. Preferably, a voltage input to a gate of the second transistor is 30% to 70% of a voltage of an element selection signal of the current control type light emitting element input to a gate of the first transistor. The current-controlled light-emitting device according to claim 3, wherein 5. The voltage input to a gate of the second transistor is more preferably 50% of a voltage of an element selection signal of the current control type light emitting element input to a gate of the first transistor. The current control type light emitting device according to claim 3. 6. The constant current source transistor according to claim 1, wherein a duty ratio of a signal applied to the gate of the first transistor is controlled to control light emission luminance of the current control type light emitting element. Item 2. The current control type light emitting device according to item 1. 7. A gate signal of the constant current source transistor is changed from a start point of a horizontal synchronization signal indicating the start of a selection period of the current control type light emitting element to a start of a horizontal synchronization signal indicating the end of the selection period. The on-level until the point in time, the off-level from the start of the horizontal synchronization signal instructing the end of the selection period to the start of the horizontal synchronization signal instructing the start of the next selection period, The current control type light emitting device according to any one of claims 1 to 6, which is driven repeatedly.