JPH04296579A - Driving of light-emitting element array - Google Patents

Abstract

PURPOSE:To make the life of a light-emitting element long by allowing the light-emitting element for increasing luminescent intensity to emit light for a longer time than does the other light-emitting elements. CONSTITUTION:The luminescent state of a light-emitting element T (1) is transferred to a light-emitting element (2) to cause the latter to emit light with a transfer clock pulse phi2 set to a high level while the light-emitting element T (1) is left luminescent. Almost at the same time, a transfer clock pulse phi1 is set to a low level and thereby the light-emitting element T (2) is turned OFF. Next, the transfer clock pulse phi1 is set to a high level while the light- emitting element T (2) remains luminescent and thereby the luminescent state of the light-emitting T (2) is transferred to the light-emitting element T (3) to cause the light-emitting element T (3) to emit light. Immediately after that, the pulse phi2 becomes low level and the light-emitting element T (2) is turned OFF. Thus the luminescent intensity is increased at light-emitting elements up to the one (3328) sequentially using the clock pulses phiI1, phi12 for luminescent intensity modulation. Subsequently, the light-emitting elements T (1) to T (3328) last longer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a light emitting element array formed by integrating a large number of light emitting elements on the same substrate, and particularly to extending the life of this light emitting element array.

0002

2. Description of the Related Art A light emitting element array in which a large number of light emitting elements are integrated on the same substrate is used in combination with a driving IC as a writing light source for an optical printer or the like. The present inventors have focused on a light emitting thyristor having a PNPN structure as a component of a light emitting element array, and have already filed a patent application (Japanese Patent Laid-Open No. 1-238962
JP-A-2-14584, JP-A-2-92650, JP-A-2-92651), it is easy to implement as a light source for an optical printer, the light emitting element pitch can be made fine, and a compact light emitting device can be produced. We showed what we can do.

As an example of these inventions made by the present inventors, FIG. 4 shows a light emitting element array capable of self-scanning by two-phase clock drive using potential coupling by diodes, as shown in Japanese Patent Laid-Open No. 2-14584. show. Both φ1 and φ2 are transfer clock pulses in which the ratio of high level time to low level time (duty ratio) is approximately 1:1, and VGK is a power supply (usually 5V). T(1)~T(
5) is a light emitting thyristor used as a light emitting element, D1
-D5 are potential coupling diodes, and G1-G5 are gate electrodes of light-emitting thyristors T(1)-T(5). RL is the load resistance of the gate electrode and limits the current to the gate electrode.

[0004] The operation will be briefly explained. First, when the voltage of the transfer clock pulse φ2 is high level, the light emitting thyristor T
Assume that (2) is in the on state (light emitting state). At this time, the potential of the gate electrode G2 goes from 5V of VGK to almost 0V.
decreases to . The effect of this potential drop is the diode D2
is transmitted to the gate electrode G3, setting its potential to about 1V. However, since the diode D1 is in a reverse bias state, the potential is not connected to the gate electrode G1, and the potential of the gate electrode G1 remains at 5V. The on-potential of a light-emitting thyristor is the gate electrode potential + diffusion potential (
1V), the high level voltage of the next transfer clock pulse φ1 is approximately 2V (light emitting thyristor T(
If the voltage is set to be at least 4 V (the voltage required to turn on the light emitting thyristor T(3)) and below approximately 4V (the voltage required to turn on the light emitting thyristor T(5)), the light emitting thyristor T(3) will turn on.
Only one light-emitting thyristor can be turned on, and the other light-emitting thyristors can remain off. Therefore, the light emission state is transferred using two transfer clock pulses.

FIG. 5 shows an example in which the light emitting element array of FIG. 4 is formed on the same semiconductor substrate. A PNPN structure of GaAs is formed on an N-type GaAs substrate, and the structure shown in FIG. 5 is formed by a method such as photoetching.

[0006] In order to write an image on the photosensitive drum of an optical printer (sensitize it), it is necessary to apply energy above a certain minimum energy to the photosensitive drum. The energy given to the photosensitive drum is given by the product of the light emission time of the light emitting element corresponding to the position where an image is to be written and the light emission intensity of this element. Therefore, in order to use the light emitting element array of FIG. 4 as a light source for an optical printer, it is necessary not only to transfer the light emitting points but also to modulate the light emission intensity. ing.

FIG. 6 shows a simplified method of driving a light emitting element array for modulating the light emission intensity of the light emitting elements, as disclosed in Japanese Patent Application Laid-Open No. 1-238962. Figure 6
The circuit is the same as that in FIG. 4 except that the clock lines that provide the emission intensity modulation clock pulses (current pulses) φI1 and φI2 are connected to the clock lines that provide the transfer clock pulses φ1 and φ2, respectively. . The transfer clock pulses φ1 and φ2 both have a ratio of high level time to low level time (duty ratio) of approximately 1:1, and are substantially inverse pulses to each other. The clock pulses φI1 and φI2 for light emission intensity modulation are at a high level only when the light emitting element corresponding to the position where an image is to be written is in the light emitting state (the current value is determined by the product of the light emission time and the light emission intensity at this time). , is set to be at least the minimum energy for writing an image on the photosensitive drum)
. As a result, a current is applied to the corresponding clock line, the light emitting intensity of the light emitting element corresponding to the position where an image is to be written increases, and the minimum energy can be applied to the photosensitive drum.

[0008]

However, when the above method increases the light emission intensity of the light emitting element corresponding to the position where an image is to be written, the amount of current flowing through the light emitting element also increases. It is known that the life of a light emitting element decreases at an accelerating rate as the amount of current flowing through the element increases, and particularly when a large current flows, the life of a light emitting element decreases significantly. Therefore, if the emission intensity is modulated using the method disclosed in Japanese Patent Application Laid-Open No. 1-238962, the life of the light emitting element will be shortened.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving a light emitting element array that can modulate the emission intensity of the light emitting elements without shortening the life of the light emitting elements.

0010

[Means for Solving the Problems] In order to solve the above object, the method for driving a light emitting element array of the present invention sets the light emitting time of the light emitting elements whose emission intensity is to be increased to be longer than the light emitting time of other light emitting elements. It was designed to be long. That is, the light emitting element of the present invention having a gate electrode for controlling a threshold voltage or a threshold current, and an anode electrode to which an external voltage or an external current is applied can be one-dimensionally, two-dimensionally or three-dimensionally A network wiring is formed by connecting the gate electrode of each of the light emitting elements to the gate electrode of at least one light emitting element located near the light emitting element through electrical means, and the light emitting elements A plurality of clock lines each individually applying a first group of clock pulses, which are signals for transferring the light emission state of the light emitting element to other light emitting elements, are connected to the anode electrode of each of the light emitting elements, one by one; A method for driving a light emitting element array includes connecting a current source that supplies a second group of clock pulses, which are signals for increasing the light emission intensity of the light emitting elements, to each of the clock lines.

The first group of clock pulses transfers the high level to the other first group of clock pulses while their high level times overlap each other by a small amount of time, and the light emitting elements whose light emission intensity is to be increased are brought into a light emitting state. The high-level time of the first group of clock pulses is approximately the same length no matter which light-emitting element whose emission intensity should be increased emits light, and the light-emitting elements whose emission intensity does not increase are in the light-emitting state. The high-level time of the first group of clock pulses when emitting light is approximately the same length no matter which light emitting element is emitted without increasing the emitted light intensity,
The high level time of the first group of clock pulses when the light emitting elements that increase the light emission intensity are brought into the light emitting state is the high level time of the first group of clock pulses when the light emitting elements that do not increase the light emission intensity are brought into the light emitting state. The clock pulses of the second group are at a high level only when the corresponding clock pulses of the first group are at a high level and increase the light emission intensity of the light emitting element that is emitting light at that time. It is characterized by becoming.

In other words, the conventional transfer clock pulse is
The light emitting element that increases the emission intensity and the light emitting element that does not increase the emission intensity both emit light for the same amount of time (the high level times and the low level times are all the same length), but in the present invention, The transfer clock pulse is controlled so that the light emission time of the light emitting element that increases the light emission intensity is longer than the light emission time of the light emitting element that does not increase the light emission intensity. At the same time, the light emission intensity modulation clock pulse becomes high level only when the corresponding transfer clock pulse is high level and increases the light emission intensity of the light emitting element that is emitting light at that time.

In the present invention, the minimum number of clock lines to which transfer clock pulses are individually applied is sufficient for the transfer operation of the light emitting state.
The number may be greater than the minimum number required for the light emitting state transfer operation. Further, the product of the time for increasing the emission intensity and the emission intensity at that time is set to be equal to or greater than the minimum energy for writing an image on the photosensitive drum. Furthermore, the present invention can also be applied to a light emitting element array formed by arranging switch elements and light emitting elements together. Further, the number of current sources that supply the second clock pulses may be the same as the number of clock lines, and each may be connected one-to-one, or there may be only one current source and that source may be connected to all clock lines. may be commonly connected.

[0014]

[Operation] According to the present invention, the light emitting time of the light emitting element that increases the light emission intensity is significantly longer than that of the conventional method, so when the above-mentioned minimum energy is applied to the photosensitive drum, the light emitting element increases the light emission intensity The light emission intensity can be made much weaker than before. In other words, since the current when the clock pulse (current pulse) for light emission intensity modulation is at a high level can be reduced, the amount of current flowing through the light emitting element that increases the light emission intensity can be reduced, thereby extending the life of the light emitting element. It can extend its lifespan.

[0015]

[Example] The following is an example of the present invention in Figs. 1 and 2.
This will be explained with reference to FIG.

FIG. 1 is a diagram showing a first embodiment of the present invention, and part (A) shows the case where the above-mentioned light emitting element array is used as a light source for an optical printer. Since the resolution of the optical printer is 400 DPI (dots per inch), approximately 3,300 light emitting elements are arranged one-dimensionally in one line (approximately 21 cm) on the short side of an A4 sheet. In this case, 26 light emitting element arrays each having 128 light emitting elements arranged one-dimensionally are connected in series to form a one-dimensional light emitting element array consisting of 3328 light emitting elements, as shown in FIG. 6(A). The circuit configuration is the same.

Part (B) is a diagram illustrating a method for driving a light emitting element array according to the present invention for self-scanning the circuit in (A).

Transfer clock pulses φ1, φ2 and emission intensity modulation clock pulse φI shown in FIG. 1(B)
1, a block diagram for obtaining φI2 is shown in FIG. First, image information is stored in one line memory (
1). This image information is transferred from the 1-line memory to a light emission intensity modulation element number counter (2), which calculates the number of light emitting elements that increase the light emission intensity per line.

Based on this calculation result, the time allocated to one line, and the high level time of the transfer clock pulse (
In this example, the minimum time for operating the light emitting element array is 0.1 μs [S. Ohns et al.
Extended Abstract of the
22nd Conference on Solid
State Device and Material
s, Sendai 1990, pp. 801-804], the high level time of the clock pulse for transfer when the light emitting elements that increase the luminous intensity are put into the light emitting state (one light emitting element transfers an image to the photosensitive drum). write time) is calculated in the light emission intensity modulation element number counter.

In this example, the time allotted to one line is 1.28 msec, and the number of light emitting elements for increasing the light emission intensity for this one line is 166 (normal blackening rate (
5%)). Then, the high level time of the transfer clock pulses φ1 and φ2 when setting the light emitting elements to the light emitting state to increase the light emission intensity is (1.28 ms-
0.1 μs×3300)÷166=5.7 μs. This is approximately 1 times longer than the high level time of the conventional transfer clock pulse (1.28 ms ÷ 3300 = 0.39 μs).
That's five times as long.

The above calculation result (4) using the emission intensity modulation element number counter and the image information from the 1-line memory (3)
is sent to the transfer clock pulse generator. The transfer clock pulse generator has a high level time of 5.7 μs when a light emitting element that increases the light emission intensity is set to a light emitting state, and a high level time of 5.7 μs when a light emitting element that does not increase the light emitting intensity is set to a light emitting state. Generate transfer clock pulses φ1 and φ2 with a duration of 0.1 μsec (Figure 1 shows transfer clock pulses φ1 and φ2 that increase the emission intensity of light emitting elements T(2) and T(7)). ). The transfer clock pulses φ1 and φ2 are sent to the memory for correcting variations in light emission intensity (5), the clock pulse generator for light emission intensity modulation (6), and the light emitting element array (7).

[0022] One memory for correcting light emission intensity variations is one.
It stores variations in the light emission intensity of each light emitting element, and is used for fine adjustment of the high level current value of the clock pulse for light emission intensity modulation.

Signal from the light emission intensity modulation element number counter (
8), Signal from memory for correcting light emission intensity variation (9)
By taking in the signal (6) from the transfer clock pulse generator and the transfer clock pulse generator, the emission intensity modulation clock pulse generator generates emission intensity modulation clock pulses φI1 and φI2. FIG. 1 shows a clock pulse for light emission intensity modulation in which φI2 and φI1 are at a high level only when the light emitting elements T(2) and T(7) are emitting light, respectively. These light emission intensity modulation clock pulses φI1, φI2
is sent to the light emitting element array (10). By the means described above, the transfer clock pulse and the emission intensity modulation clock pulse shown in FIG. 1(B) can be obtained.

Next, the pulse of FIG. 1(A) is generated by the pulse of FIG. 1(B).
) operation is explained. First, the start pulse φS is set to a low level (approximately 0 V), and at the same time the transfer clock pulse φ1 is set to a high level (approximately 2 to 4 V), causing the light emitting element T(1) to emit light. Immediately after that, the start pulse φ
S is returned to high level.

Next, in order to transfer the light emitting state of the light emitting element T(1) to the light emitting element T(2), the transfer clock pulse φ2 is set to a high level (with the light emitting element T(1) still emitting light). (about 2 to about 4 V). Then, the light emitting element T(2
) emits light. Immediately thereafter, clock pulse φ1 for transfer
is set to low level, so the light emitting element T(1) is turned off (at this time, the transfer clock pulse φ1 is 0.1μ
s was at a high level). After the light emitting element T(2) emits light, and at approximately the same time, the light emission intensity modulation clock pulse φI2 is set to a high level. Then, the current flowing to the light emitting element T(2) increases, and the light emitting element T(2) increases the light emission intensity.

Next, in order to transfer the light emitting state of the light emitting element T(2) to the light emitting element T(3), the transfer clock pulse φ1 is set to a high level (with the light emitting element T(2) still emitting light). (about 2 to about 4 V). Then, the light emitting element T(3
) emits light. Immediately thereafter, clock pulse φ2 for transfer
becomes a low level, and the light emitting element T(2) is turned off (at this time, the transfer clock pulse φ2 was at a high level for 5.7 μs). Light emitting elements T(3), T(4),
T(5) and T(6) each emit light for 0.1 μs each and transfer the light emitting state to the next light emitting element. The light emitting element T(7) emits light for 5.7 μs, during which time the light emission intensity modulation clock pulse φI1 is set to a high level. Thereafter, the light emitting state is transferred to the light emitting element T (3328), but in the meantime, the light emitting intensity of 166 light emitting elements including the light emitting elements T (2) and T (7) is changed by the light emitting intensity modulation clock pulse φ.
It is increased by I1 and φI2.

In the above process, the product of the light emission intensity of the light emitting element whose light emission intensity has been increased and the time during which the light emission intensity is increased becomes the minimum value for exposing the photosensitive drum of the optical printer. The above emission intensity is adjusted accordingly. These 166 light-emitting elements write images, but the current value flowing through them can be suppressed to about one-fifteenth of the conventional value. Therefore, the life of these light emitting elements is extended, and the life of the entire light emitting element array is extended.

[0028] In the above embodiment, a case was shown in which the emission intensity of 166 light emitting elements was increased. However, if the number of elements that increase the light emission intensity is doubled (332), for example, the high level time of the corresponding transfer clock pulse is halved, so the light emission intensity must be doubled. In other words, the number of light emitting elements that increase the light emission intensity per line must be controlled so that the light emission intensity and light emission time are always equal to or higher than the above-mentioned minimum energy.

Further, in the above embodiment, the number of light emitting elements in the light emitting state in one line was one.
The present invention is not necessarily limited to this. For example, 128
In a one-dimensional light emitting element array consisting of 3328 light emitting elements in which 26 light emitting elements are connected in series, each light emitting element array consisting of 128 light emitting elements is one light emitting element array. Alternatively, each of the 26 light emitting elements may be in a light emitting state, and the light emitting states of these 26 light emitting elements may be transferred. In this case, 128 elements have 1
．． Since 28 msec is allocated, if the blackening rate is calculated as 5% in the same way as in the above-mentioned embodiment, image writing can be performed with one-eighteenth the current amount of the conventional method.

FIG. 3 is a diagram showing a second embodiment of the present invention, in which a light emitting element array is used as a light source for an optical printer, as in FIG. 1. The circuit in the upper half of the part (A) consists of the light emitting elements T(1) to T(
4) is replaced with switch elements S(1) to S(3328) to further increase the number. The gate electrode of each switch element is connected to the gate electrode of one light emitting element that is paired with the switch element. As a result, each light emitting element is in a light emitting state if the corresponding switch element is in an on state. Furthermore, a current source that supplies a common clock pulse φI for modulating the emission intensity is connected to the anode electrode of this light emitting element.

The transfer clock pulses φ1 and φ2 are pulses generated by exactly the same procedure as in FIG. 1(B), and their waveforms are also the same as in FIG. 1(B). In this case, only the light emitting elements T(2) and T(7) can increase the emission intensity. The light emission intensity modulation clock pulse φI is at a high level only when either of the light emitting elements T(2) and T(7) is emitting light.

The operation is exactly the same as the first embodiment shown in FIG. The difference from the first embodiment is that there is only one type of clock pulse for light emission intensity modulation, and the clock pulse φI for light emission intensity modulation in this case is different from the one for light emission intensity modulation in the first embodiment. Clock pulse φI1, φI2
The waveform is a superimposition of the waveforms of . In this embodiment as well, the light emission intensity is controlled by the number of light emitting elements that increase the light emission intensity. It is also possible to increase the number of light emitting elements in a light emitting state.

In the first and second embodiments described above, the number of clock lines is two, but the present invention is not limited to this, and the number of clock lines is three. It is also possible to carry out more than one book. Also,
In the above description, the clock pulse was of a two-phase drive type with high level and low level, but it can also be applied to a three-phase drive type clock pulse. Further, the coupling portion of each light emitting element is not limited to a diode, but may be an electrical coupling means such as a transistor or a resistor. Furthermore, the light-emitting element array to which the present invention can be applied is not limited to the light-emitting element array in which light-emitting elements are arranged one-dimensionally as described above, but also in light-emitting element arrays in which light-emitting elements are arranged two-dimensionally or three-dimensionally. It may be.

[0034]

According to the present invention, the life of each light emitting element constituting the light emitting element array is extended, so that the long-term reliability of equipment using the light emitting element array can be increased.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of a method for driving a light emitting element array of the present invention.

FIG. 2 is a block diagram for obtaining the clock pulse shown in FIG. 1(B).

FIG. 3 is a diagram showing a second embodiment of the method for driving a light emitting element array of the present invention.

FIG. 4 is a diagram showing a method for driving a light emitting element array proposed in Japanese Patent Application Laid-Open No. 2-14584.

FIG. 5 is a schematic partial cross-sectional structure diagram of the light emitting element array shown in FIG. 4;

FIG. 6 is a diagram showing a driving method that is a simplified version of the driving method for a light emitting element array proposed in Japanese Patent Application Laid-Open No. 1-238962.

[Explanation of symbols]

T(1) Light emitting element T(2) Light emitting element T(3) Light emitting element T(4) Light emitting element T(5) Light emitting element D1 Coupling diode D2 Coupling diode D3 Coupling diode D4 Coupling diode D5 Coupling diode φ1 Transfer clock pulse φ2
Transfer clock pulse φI1 Clock pulse for emission intensity modulation φI2 Clock pulse for emission intensity modulation φI Clock pulse for emission intensity modulation φS Start pulse

Claims (6)

[Claims] Claim 1: A light-emitting element having a gate electrode for controlling a threshold voltage or a threshold current, and an anode electrode to which an external voltage or an external current is applied, one-dimensionally, two-dimensionally, or three-dimensionally. A network wiring is formed by arranging a large number of the light emitting elements and connecting the gate electrode of each of the light emitting elements to the gate electrode of at least one light emitting element located near the light emitting element through electrical means. A plurality of clock lines for individually applying the first group of clock pulses, which are signals for transferring the light emission state to other light emitting elements, are connected one by one to the anode electrode of each light emitting element. In the method for driving a light emitting element array, a current source supplying a second group of clock pulses, which is a signal for increasing the light emission intensity of the elements, is connected to each of the clock lines, wherein the first group of clock pulses are mutually connected to each other. The high level of the first group of clock pulses when the high level is transferred to another first group of clock pulses while overlapping the high level time by a small amount of time, and the light emitting element whose emission intensity is to be increased is brought into a light emitting state. The time is approximately the same length no matter which light emitting element whose light emission intensity is to be increased is emitted, and the high level time of the first group of clock pulses when the light emitting element whose emission intensity is not to be increased is brought into a light emitting state. is approximately the same length when any light emitting element whose emission intensity is not to be increased emits light, and the high level time of the first group of clock pulses when the light emitting element whose emission intensity is to be increased is brought into a light emitting state is , the clock pulses of the second group are sufficiently longer than the high level time of the first group of clock pulses when the light emitting element that does not increase the light emission intensity is brought into the light emitting state, and the clock pulses of the second group are sufficiently long when the corresponding first group of clock pulses are high level. 1. A method for driving a light emitting element array, characterized in that the light emitting element array is at a high level and becomes a high level only when increasing the emission intensity of a light emitting element that is emitting light at that time. [Claim 2] A set consisting of one switch element and one light emitting element each having a gate electrode for controlling a threshold voltage or a threshold current and an anode electrode to which an external voltage or external current is applied is arranged in one dimension. The gate electrode of each of the above-mentioned switch elements is connected to the gate electrode of at least one switch element located near the above-mentioned switch element, and each of the above-mentioned switch elements is arranged in a large number in a two-dimensional or three-dimensional manner. connecting with the gate electrode of the light emitting element through electrical means to form a network wiring;
A plurality of clock lines each individually applying a first group of clock pulses, which are signals for transferring the on-state of the switch element and the light-emission state of the light-emitting element to other sets of switch elements and light-emitting elements, respectively. , a second signal which is connected to the anode electrode of each of the switch elements one by one and is a signal for increasing the light emission intensity of the light emitting element.
In a method for driving a light emitting element array in which a current source supplying a group of clock pulses is connected to the anode electrode of each light emitting element, the clock pulses of the first group are arranged such that the high level time of the clock pulses overlaps each other by a small amount of time. The high level time of the first group of clock pulses when the high level is transferred to another first group of clock pulses and the light emitting element whose emission intensity is to be increased is brought into a light emitting state is determined by which light emission whose emission intensity is to be increased. Even when the elements are made to emit light, they all have approximately the same length. They all have approximately the same length even when emitting light, and the high level time of the first group of clock pulses when the light emitting elements whose emission intensity is to be increased are set to emit light is the time when the light emitting elements whose emission intensity is not to be increased are emitted. The clock pulses of the second group are sufficiently longer than the high level time of the first group of clock pulses when the corresponding light emitting element is in the light emitting state, and the light emitting element of the light emitting element is emitting light. A method for driving a light emitting element array, characterized in that the level is set to a high level only when the intensity is increased. 3. The high level time of the first group of clock pulses when the light emitting elements whose light emission intensity is to be increased is brought into a light emitting state is a maximum time determined by the number of the light emitting elements whose light emission intensity is to be increased; 3. The method of driving a light emitting element array according to claim 1, wherein the time is less than that but sufficiently close to that. 4. The product of the light emission intensity of the light emitting element when the light emission intensity is increased and the time during which this light emission intensity is increased is a minimum value for exposing a photosensitive drum of an optical printer,
4. The method of driving a light emitting element array according to claim 1, wherein the light emitting intensity is determined to be a value that is greater than or equal to and sufficiently close to that value. 5. The number of clock pulses constituting the second group of clock pulses is one, and a current source supplying this clock pulse is commonly connected to all the clock lines. Or the method for driving a light emitting element array according to 4. 6. The number of clock pulses constituting the second group of clock pulses is one, and a current source supplying this clock pulse is commonly connected to all the light emitting elements. Or the method for driving a light emitting element array according to 4.