JP4281240B2 - Self-scanning light emitting element array and driving method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-scanning light-emitting element array, and more particularly to a self-scanning light-emitting element array capable of simultaneously lighting two thyristors on one chip and a driving method thereof.
[0002]
[Prior art]
A write head (optical write head) of an optical printer is a light source for exposing a photosensitive drum to light, and has a light emitting element array. FIG. 1 shows a principle diagram of an optical printer having an optical writing head. A photoconductive material (photosensitive member) such as amorphous Si is formed on the surface of the cylindrical photosensitive drum 5. This drum rotates at the speed of printing. The surface of the photosensitive drum of the rotating drum is uniformly charged by the charger 6. Then, the optical writing head 7 irradiates the photosensitive member with the light of the dot image to be printed, neutralizes the charging where the light hits, and forms a latent image. Subsequently, the developing unit 8 applies toner to the photoconductor according to the charged state on the photoconductor. Then, the toner is transferred onto the paper 14 sent from the cassette 12 by the transfer device 10. The sheet is heated and fixed by the fixing device 16 and sent to the stacker 18. On the other hand, the drum that has been transferred is neutralized by the erasing lamp 20 over the entire surface, and the remaining toner is removed by the cleaner 22.
[0003]
The structure of the optical writing head 7 is shown in FIG. The optical writing head is composed of a light emitting element array 24 and an erecting equal-magnification optical system, for example, a rod lens array 26, and the focal point of the lens is formed on the photosensitive drum 5.
[0004]
The present inventors have paid attention to a three-terminal light-emitting thyristor having a pnpn structure as a component of a self-scanning light-emitting element array, and have already applied for patents (Japanese Patent Application Laid-Open Nos. 1-238962 and 2-14584). JP-A-2-92650, JP-A-2-92651), and as a light source for an optical printer, it is easy to mount, the light-emitting element pitch can be made fine, and a compact self-scanning light-emitting element array can be produced. showed that.
[0005]
Furthermore, the present inventors have proposed a self-scanning light-emitting element array having a structure in which a transfer thyristor array is used as a shift portion and separated from a light-emitting thyristor array that is a light-emitting portion (Japanese Patent Laid-Open No. 2-263668).
[0006]
A circuit example of a conventional self-scanning light emitting element array is shown in FIG. Shift units (thyristors T ₀ , T ₁ , T ₂ ,...) Driven by the two-phase clock pulses φ1, φ2 and light emitting units (thyristors L ₀ , L ₁ , L ₂ ,. ). Diodes D ₀ , D ₁ , D ₂ ,... Are used to electrically connect the gates of the transfer unit thyristors. V _GK is a power supply (usually +5 V), and is connected to the gate electrodes G ₀ , G ₁ , G ₂ ,... Of each transfer unit thyristor via a load resistance R _L. The gate electrode of the transfer unit thyristor is also connected to the gate electrode of the light emitting unit thyristor. A start pulse φ _S is applied to the gate electrode of the transfer unit thyristor T ₀ , transfer clock pulses φ 1 and φ 2 are applied alternately to the anode electrode of the transfer unit thyristor, and writing is performed on the anode electrode of the light emitting unit thyristor. signal phi _I is added.
[0007]
Note in the figure, is 10 phi _I line, 12 V _GK line 14 is φ1 line 16 represents the φ2 line. Further, R1, R2, R _I is, .phi.1 line, .phi.2 line, current limiting resistor inserted phi _I line, R _S represents a current limiting resistor for the start pulse.
[0008]
Now, when the n-th shift unit thyristor T _n is on, when the write signal phi _I and H, the light emitting unit thyristors L _n are turned on corresponding to the selectively shifting unit thyristor T _n. This is because the gates of the thyristor T _n and the thyristor L _n are directly connected to each other and have the same potential. When the thyristor T _n is on, the gate potential of the light emitting unit thyristor L _n is almost the substrate potential. This is because the potential becomes low. The light emitting unit thyristor having the next lowest potential is the gate of the thyristor L _{n + 1} and has a value about 1 V higher than the voltage drop of the coupling diode D _n . In this state, when the write signal φ _I line is pulled up to an H voltage (for example, +5 V), the thyristor L _n having the lowest gate potential is turned on earliest. Once turned on, the anode voltage of the thyristor L _n, is fixed at approximately 1V of the forward voltage of the pn junction. Since the anodes of all the thyristors of the light emitting section are directly connected to the φ _I line 10, the thyristor L _{n + 1} having the next highest gate potential disappears because the potential difference between the gate and the anode disappears. For this reason, in a conventional self-scanning light emitting element array, only one thyristor can be turned on simultaneously per φ _I line.
[0009]
[Problems to be solved by the invention]
In order to increase the printing speed of the optical printer, it is necessary to increase the exposure energy on the photosensitive drum. Since the exposure energy is the product of the light output of the thyristor (having the power factor dimension) and the exposure time, in order to increase the exposure energy, it is necessary to increase the light output or to increase the exposure time.
[0010]
In order to increase the optical output, if the thyristor has the same structure, the current is increased. However, since the device life is affected, the current cannot be increased unnecessarily. For example, it is known that the speed of the electromigration that determines the life of the Al wiring is proportional to the 1.6 to the fourth power of the current. If the current is increased, the life may be dramatically shortened.
[0011]
On the other hand, to increase the exposure time, it is necessary to increase the number of thyristors that can emit light simultaneously. However, a problem in the conventional art, it is necessary to increase the number of phi _I line to increase the number of thyristors capable of emitting light at the same time, in this way, phi _I line increase only element area and, that the takeout terminal increases There was a point. An increase in the element area results in an increase in chip cost, and an increase in the number of extraction terminals causes an assembly cost and a complicated drive circuit.
[0012]
An object of the present invention is to provide a self-scanning light-emitting element array capable of simultaneously lighting two thyristors while keeping the number of φ _I lines at one.
[0013]
[Means for Solving the Problems]
The first aspect of the present invention is a self-scanning light emitting element array. In the present invention, a number of three-terminal transfer elements whose threshold voltage or threshold current can be electrically controlled from the outside are arranged one-dimensionally to control the threshold voltage or threshold current of adjacent transfer elements. The control electrodes are connected to each other by electrical means having a unidirectional voltage or current, and a two-phase clock is externally applied to one of the remaining two electrodes of each of the one-dimensionally arranged transfer elements. Two clock pulse lines for supplying pulses every other element are provided, and when a certain transfer element is turned on by a clock pulse of one phase, the threshold voltage or threshold of the transfer element in the vicinity of the transfer element is set. The threshold current for the light emission is changed by changing the threshold current through the electrical means and turning on the adjacent transfer element of the certain transfer element by the clock pulse of the other phase. Are arranged in a one-dimensional manner, and each control electrode of the transfer element is connected to a corresponding control electrode of the light-emitting element. In the self-scanning light emitting element array in which one write signal line for applying a write signal for light emission is provided on one of the remaining two electrodes, one of the remaining two electrodes of each light emitting element is connected via a resistor. And connected to the write signal line.
[0014]
The value of the resistance is selected so that the adjacent light emitting element does not emit light when the current passed through one light emitting element, and the adjacent light emitting element emits light simultaneously when a double current flows.
[0015]
The three-terminal transfer element and the three-terminal light-emitting element are each composed of a three-terminal light-emitting thyristor having a pnpn structure. In this case, the resistance is
(1) A resistor formed on the uppermost protective film of the pnpn structure,
(2) a resistor formed on one of the remaining two electrodes of the light emitting element;
(3) The contact resistance between one of the remaining two electrodes of the light emitting element formed on the semiconductor layer by adjusting the impurity concentration of the semiconductor layer which is the uppermost layer of the pnpn structure so,
Or
(4) It can be formed by a parasitic resistance of a light emitting thyristor which is the light emitting element.
[0016]
The second aspect of the present invention is a method for driving a self-scanning light emitting element array. According to this method, when the transfer element is turned on, the write signal applied to one electrode of the light emitting element connected to the control electrode of the transfer element is transmitted to one light emitting element. Control is performed when the lamp is turned on and when two adjacent light-emitting elements are turned on simultaneously.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 4 shows an equivalent circuit diagram of an embodiment of the self-scanning light emitting element array of the present invention. Basically, it is almost the same as the circuit of FIG. 3, and therefore the same components as those of FIG. 3 are denoted by the same reference numerals or symbols as those of FIG.
[0018]
According to the present embodiment, in the circuit of FIG. 3, the resistor _RA having an appropriate value is provided between the φ _I line and the anode terminal of the light emitting unit thyristor.
[0019]
In the self-scanning light-emitting element array having such a configuration, when the shift unit thyristor T _n is turned on, an example of the IV characteristic of the light-emitting unit thyristor L _n to which the gate is connected to the thyristor T _n. This is indicated by a solid line in FIG. In FIG. 5, the horizontal axis represents current and the vertical axis represents voltage. Since the shift unit thyristor T _n is on, the light emitting unit thyristor L _n has the same linear IV characteristics as a simple diode. That is, the forward rise voltage of approximately 1V, the resistance value of the slope of the line resistance R _A (hereinafter, R _A is may show a resistance value) corresponds to, in this figure, a 50 [Omega. On the other hand, the gate of the thyristor L _{n + 1 on} the right side of the light emitting unit thyristor L _n is applied with a voltage that is higher by the voltage drop (about 1 V) of the coupling diode D _n , so that the φ _I line is (2 + α) V. It cannot be turned on unless voltage is applied. If the thyristor L _{n + 1 is} to be turned on simultaneously with the thyristor L _n , the current is increased, and the voltage of φ _I only needs to exceed the ON voltage (threshold voltage) of the thyristor L _{n + 1} . At this time, the IV characteristic curve changes from a solid line to a broken line in FIG.
[0020]
Now, in the case of R _A = 0, that is, in the case of the circuit of FIG. 3, if the internal resistance of the thyristor is ignored, the IV characteristic curve becomes horizontal and the threshold of the thyristor L _{n + 1} no matter how much current flows. The voltage cannot be exceeded. This is the reason why only one thyristor can be turned on per φ _I line in the conventional self-scanning light emitting element array.
[0021]
In the circuit of FIG. 4, the resistance value R _A is selected so that the adjacent thyristor does not light up when a current flows through one thyristor, and the adjacent thyristor also lights up when a double current flows. . That is, when the current is trying to light the thyristor is I _L,
[0022]
[Expression 1]
V _D + R _A × I _L <V _{th (n + 1)} <V _D + R _A × 2I _L
However,
V _{th (n + 1)} is the threshold voltage of the thyristor L _{n + 1} , and V _D is the rising voltage of the pn junction of the thyristor.
Solving for _RA ,
[0023]
[Expression 2]
(V _{th (n + 1)} −V _D ) / I _L > + R _A > (V _{th (n + 1)} −V _D ) / 2I _L
For example, if V _{th (n + 1)} = 2.1V, I _L = 15 mA, V _D = 1V,
73.3Ω> R _A > 36.7Ω
It becomes.
[0024]
FIG. 6 shows a first example in which the resistor _RA having such a value is formed in a three-terminal light-emitting thyristor having a pnpn structure. (A) is a top view, (b) is the sectional view on the AA 'line of (a).
[0025]
In the three-terminal light-emitting thyristor, an n-type semiconductor substrate 161, a p-type semiconductor layer 162, an n-type semiconductor layer 163, and a p-type semiconductor layer 164 are sequentially stacked on an n-type semiconductor substrate 160. On the protective film 150, a φ _I line (Al wiring) 120, an Al wiring 119 to the anode electrode 112 of the light emitting unit thyristor, and an Al wiring 130 to the gate electrode 132 are provided. The resistor _RA is formed by a thin film resistor 140 made of CrSiO cermet provided on the protective film 150 between the Al wiring 120 and the Al wiring 119. Here, CrSiO cermet is used as the resistor, but other cermets (AuSiO, AgSiO, etc.) may be used, and a metal film such as Ni, Cr, NiCr, W, Pt, Pd is used as the resistor. Also good.
[0026]
A common back electrode 100 is provided on the back surface of the n-type semiconductor substrate 160.
[0027]
FIG. 7 shows another configuration example of the resistor _RA . (A) is a top view, (b) is the BB 'sectional view taken on the line of (a). In this example, the resistor _RA is configured by inserting a Ni resistor 113 between the Al wiring 119 and the anode electrode 112. Here too, the same material as that of the resistor can be used.
[0028]
Further, the resistor _RA can be formed by adjusting the impurity concentration of the anode layer 164 and adjusting the contact resistance with the anode electrode 112. The resistor _RA may be realized by a parasitic resistance of a thyristor when it is turned on.
[0029]
It should be noted that in the example of FIG. 7, the Al wiring 119 to the anode electrode is directly connected to the φ _I wiring 120.
[0030]
FIG. 8 shows an example of a driving circuit for the φ _I line of the self-scanning light emitting element array of the above embodiment. This drive circuit includes an inverter, a MOSFET, and current limiting resistors R _Ia and R _Ib . V _Ia and V _Ib are control terminals, and V _I is an output terminal.
[0031]
When the control terminal V _{Ia is set} to H level, the output terminal is connected to + V _DD via the resistor R _Ia . Furthermore, control when a terminal V _Ib to the H level, the resistance R _Ia and the resistor R _Ib is connected in parallel, the resistance R _Ia, current idea to the same resistance value of R _Ib phi _I is doubled.
[0032]
Therefore, according to this drive circuit, to turn on one thyristor, the control terminal V _{Ia is set} to the H level, and to turn on two adjacent thyristors simultaneously, the control terminals V _Ia and V _Ib are simultaneously turned on. It becomes H level.
[0033]
FIG. 9 shows another example of the φ _I line driving circuit including two current sources J _a and J _b and switches SW _a and SW _b connected to the outputs of the respective current sources. Each switch is controlled to be opened / closed by control terminals V _Ia and V _Ib . That is, the switch is closed when the control terminal is at the H level.
[0034]
By the control terminal V _Ia to H level, the current of the current source J _a flows to the switch SW _a is closed phi _I terminal. Further, when the control terminal V _{Ib is set} to H level, current flows from the current sources J _a and J _b . If the current of each current source is the same, twice the current flows through the φ _I terminal.
[0035]
Therefore, according to this drive circuit, as in the drive circuit of FIG. 8, in order to turn on one thyristor, the control terminal V _{Ia is set} to H level and two adjacent thyristors are turned on simultaneously. The control terminals V _Ia and V _Ib are simultaneously set to the H level.
[0036]
Next, an example of a method for driving the self-scanning light-emitting element array in FIG. 4 will be described using the drive circuit as described above. A self-scanning light-emitting element array having a resolution of 1200 dpi is used.
[0037]
In this driving method, when a high resolution (high image quality) output is desired, drawing is performed at 1200 dpi. On the other hand, even at a low resolution, drawing is performed at 600 dpi. That is, two adjacent thyristors are connected. It shall be turned on sequentially at the same time.
[0038]
FIG. 10A shows a drive waveform when drawing at a high resolution of 1200 dpi, and FIG. 10B shows a drive waveform when drawing at a low resolution of 600 dpi.
[0039]
In FIG. 10A, the control terminal V _Ia is set to the H level in correspondence with the clock pulses φ1 and φ2, respectively. On the other hand, the control terminal V _Ib is kept at the L level. Accordingly, the light emitting unit thyristors in FIG. 4 are sequentially turned on one by one. According to this driving method, rendering is performed at a resolution of 1200 dpi. However, in this method, since one thyristor is sequentially turned on, the exposure time does not change even if the resolution is lowered. Therefore, since the exposure amount does not change, the printing speed hardly changes.
[0040]
In FIG. 10B, the control terminals V _Ia and V _Ib are set to the H level at the same timing so as to correspond to the two continuous clock pulses φ1 and φ2, respectively. As a result, the two thyristors are sequentially turned on simultaneously. According to this driving method, drawing is performed with a resolution of 600 dpi. However, since the exposure time can be doubled compared to the driving method of FIG. 10A, the printing speed can be doubled.
[0041]
Another example of the method for driving the self-scanning light emitting element array of FIG. 4 will be described. With this driving method, the exposure amount can be doubled without reducing the resolution. An example of the drive waveform is shown in FIG.
[0042]
In the self-scanning light-emitting element array of FIG. 4, when the control terminal V _{Ia is set} to H level with the n-th thyristor of the shift unit turned on, the thyristor L _n of the light-emitting unit is turned on. Further, when the control terminal V _{Ib is set} to H level while the control terminal V _Ia is at H level, the thyristor L _{n + 1} is also turned on at the same time. In the figure, the dot sequence A indicates that the thyristor L _n is lit when the control terminal V _Ia is at the H level by hatching with a circle. Further, the case where the thyristor L _{n + 1} is also turned on at the same time when the control terminal V _Ib becomes H level is indicated by hatching in the circle of the point sequence B. Since the point in point sequence B is the (n + 1) th point, it is shifted to the right.
[0043]
After one line is drawn, the exposure amount of each dot is determined by how many two dots arranged in the vertical direction in the point sequences A and B are lit. A white circle (no exposure) when 0, a hatched circle (1 unit of exposure) when it is 1, and a black circle (2 units of exposure) when 2 (dot sequence C). According to this, the head where the black circles are arranged is a hatched circle in which the exposure amount is always halved.
[0044]
With this driving method, the exposure amount can be doubled without reducing the resolution. However, if this driving method is used, the exposure amount of the first dot of the drawing line is half that of the other dots. However, since the electrophotographic method is often thicker than the original image depending on the pattern, it is possible to perform exposure more faithful to the original image by suppressing the exposure amount at the head. If necessary, the exposure amount of the last dot of the drawing line can be halved.
[0045]
【The invention's effect】
According to the present invention, it is possible to provide a self-scanning light emitting element array capable of simultaneously lighting two thyristors while keeping the number of φ _I lines at one. Therefore, since the exposure time can be increased, the amount of exposure on the photosensitive drum increases, and as a result, the printing speed of the optical printer device can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of an optical printer including an optical writing head.
FIG. 2 is a diagram showing a structure of an optical writing head.
FIG. 3 is an equivalent circuit diagram of a self-scanning light emitting element array having a structure in which a shift unit and a light emitting unit are separated.
FIG. 4 is an equivalent circuit diagram of an embodiment of the self-scanning light emitting element array of the present invention.
FIG. 5 is a diagram illustrating IV characteristics of a light emitting unit thyristor.
FIG. 6 is a diagram showing a first example in which a resistor _RA is formed in a three-terminal light-emitting thyristor having a pnpn structure.
FIG. 7 is a diagram illustrating a second example in which a resistor _RA is formed in a three-terminal light-emitting thyristor having a pnpn structure.
FIG. 8 is a diagram illustrating a first example of a φ _I line driving circuit;
FIG. 9 is a diagram illustrating a second example of a φ _I line driving circuit.
FIG. 10 is a waveform diagram showing a first example of a driving method.
FIG. 11 is a waveform diagram showing a second example of a driving method.
[Explanation of symbols]
10 φ _I line 12 V _GK line 14 φ 1 line 16 φ 2 line 112 Anode electrode 119 Al wiring 120 φ _I line 130 Al wiring 132 Gate electrode 150 Protective film 160 n-type semiconductor substrate 162 p-type semiconductor layer 163 n-type semiconductor layer 164 p Type semiconductor layer

Claims (13)

A plurality of three-terminal transfer elements having a gate electrode, an anode electrode, and a cathode electrode, in which a threshold voltage or a threshold current can be electrically controlled from the outside, are arranged one-dimensionally,
The gate electrodes that control the threshold voltage or threshold current of adjacent transfer elements are connected to each other with diodes interposed so that diodes having a unidirectional voltage or current are connected in series ,
Two clocks for supplying either one of the two-phase clock pulses from the outside to one of the anode electrode and the cathode electrode of each transfer element connected to each other by the diode Provided a pulse line,
When a transfer element is turned on by a clock pulse of one phase, the transfer element connected to the transfer element via the diode and having a threshold voltage or a threshold current changed by the diode is transferred to the other phase. by the clock pulse to Rio down,
A plurality of three-terminal light emitting elements having a gate electrode, an anode electrode, and a cathode electrode whose threshold voltage or threshold current for light emission can be electrically controlled from the outside are one-dimensionally associated with each of the transfer elements. Array
Connecting each gate electrode of the transfer element to the gate electrode of the light emitting element corresponding to the transfer element ;
In the self-scanning light-emitting element array in which one write signal line for applying a write signal for light emission is provided on one of the anode electrode or the cathode electrode of each light-emitting element,
One of the anode electrode or cathode electrode of each light emitting element is connected to the write signal line through a resistor,
The resistance value corresponds to a transfer element in which a threshold voltage or a threshold current is changed through a diode, although a light-emitting element corresponding to a transfer element that is on emits light when a current flows through one light-emitting element. The self-scanning light-emitting element array is selected so that the light-emitting element that emits light does not emit light and the light-emitting element emits light at the same time when a current of twice is passed . The three-terminal transfer element and the 3-terminal light emitting element, a self-scanning light-emitting array of claim 1, wherein a formed of three-terminal light-emitting thyristor of pnpn structure. 3. The self-scanning light-emitting element array according to claim 2 , wherein the resistor is formed of a resistor formed on the uppermost protective film of the pnpn structure. The resistor, the anode electrode or cathode self-scanning light-emitting array according to claim 1, characterized in that from one of the formed on the electrode resistance of the electrode of the light emitting element. The resistor is a self-scanning light-emitting element array according to claim 3 or 4, wherein the formed of cermet. 6. The self-scanning light-emitting element array according to claim 5 , wherein the cermet is CrSiO, AuSiO, or AgSiO. The resistor is a self-scanning light-emitting element array according to claim 3 or 4 wherein a made of a metal film. 8. The self-scanning light emitting element array according to claim 7 , wherein the metal film is made of Ni, Cr, NiCr, W, Pt or Pd. The resistor adjusts the impurity concentration of the semiconductor layer which is the uppermost layer of the pnpn structure, and is formed between the anode electrode and the cathode electrode of the light emitting element formed on the semiconductor layer. 3. The self-scanning light-emitting element array according to claim 2 , wherein the self-scanning light-emitting element array is formed by contact resistance. 3. The self-scanning light emitting element array according to claim 2 , wherein the resistor is formed by a parasitic resistance of a light emitting thyristor that is the light emitting element. A method of driving a self-scanning light-emitting element array of claim 1, when the transfer element is turned on, the anode electrode or the cathode of the light emitting element in which the gate electrode is connected to the gate electrode of the transfer element A self-scanning light-emitting element characterized by controlling a current of an address signal applied to one of the electrodes when one light-emitting element is turned on and when two adjacent light-emitting elements are turned on simultaneously Array drive method. 12. The method of driving a self-scanning light-emitting element array according to claim 11 , wherein the write signal is controlled so as to reduce a resolution when the two adjacent light-emitting elements are turned on simultaneously. 12. The method of driving a self-scanning light-emitting element array according to claim 11 , wherein when the two adjacent light-emitting elements are turned on simultaneously, the write signal is controlled for each of the two-phase clock pulses.

Images