JP2006261461A - Light-emitting element array, light-emitting element substrate, surface emitting laser, optical-scanning device, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To add a variable-capacitance element so that a stray capacitance of a wiring is approximately identical enabling a high speed driving. <P>SOLUTION: The variable-capacitance element (the variable-capacitance diode) 3 is connected to the wiring 2, and a combined capacitance of the stray capacitance of the wiring 2 and the variable-capacitance element 3 is set to be approximately identical for all the wiring. This evens out a capacitance components of the wirings of every light emitting element to even out the signal modulation characteristics of all the light emitting elements 1, and variations in signal degradation at the time of high speed modulation are reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser used as a light source, and more particularly to a surface emitting laser having a plurality of light sources on the same chip.

  FIG. 11 shows a conventional technology of a surface emitting laser constituted by a light emitting element array. FIG. 11 shows a light source arrangement and a wiring pattern example in a surface emitting laser having a 6 × 6 light source.

  In general, in order to drive a plurality of light sources arranged in a matrix within a small area, wiring is performed from the outside to the light source unit, and the light source is driven by applying a driving voltage and current to the wiring. At this time, a ground plane is formed in a planar shape substantially parallel to the wiring on the substrate as a potential plane serving as a reference for the wiring, and a return path is formed between the ground plane and the wiring. That is, a wiring pattern capable of high-speed driving with reduced deterioration of signal transmission characteristics when a high-speed signal is applied to the wiring portion is formed.

  However, as the number of light sources increases, the wiring length between the multiple light sources and their drivers and the stray capacitance of the wiring differ, causing skew in the signals between the multiple light sources and crosstalk between the wirings. Etc. occur.

  In the case of a surface emitting laser having a plurality of light sources on the same chip, the influence on the high-speed modulation characteristics due to the error of the resistance component of each element between different light source elements is not great. However, since the distance between the light sources is short and the wiring interval from the light source to the driver is also small, the effects of crosstalk, stray capacitance, parasitic capacitance, etc. become prominent. to degrade.

  As a conventional technique for solving the above-described problem, in a light emitting element array in which a plurality of light emitting elements are two-dimensionally arranged, the wiring between the light emitting element and the electrode pad is configured to have the same stray capacitance between the wirings. Thus, there is a device that suppresses density fluctuations during image formation by making the modulation characteristics of the respective light emitting elements substantially constant (see, for example, Patent Document 1).

  Further, in a light emitting element having a first electrode and a second electrode, a floating capacitance of the wiring without complicating the driving sequence for a light emitting element array in which matrix wirings two-dimensionally arranged are connected in a matrix. In addition, there is a device with a reduced electrical resistance value (see, for example, Patent Document 2).

  FIG. 12 shows a conventional image forming apparatus using an electrophotographic process. FIG. 12 shows a general configuration of an image forming apparatus such as a laser printer or a digital copying machine. Laser light emitted from a semiconductor laser unit 1001 as a light source is deflected and scanned (scanned) by a rotating polygon mirror 1002. A light spot is formed on a photoconductor 1004 that is a medium to be scanned through a scanning lens (fθ lens) 1003, and the photoconductor 1004 is exposed to form an electrostatic latent image. At this time, an image clock (pixel clock) that is phase-synchronized for each line is generated for each line based on the output signal of the photodetector 1005 and supplied to the image processing unit 1006 and the laser drive circuit 1007. In this way, the semiconductor laser unit 1001 performs the operation of the semiconductor laser via the laser driving circuit 1007 according to the image data generated by the image processing unit 1006 and the image clock whose phase is set for each line by the phase synchronization circuit 1009. By controlling the light emission time, the electrostatic latent image on the scanned medium 1004 is controlled. The phase synchronization circuit 1009 sets the modulation signal generated by the clock generation circuit 1008 to a phase synchronized with the photodetector that detects the light of the semiconductor laser deflected and scanned by the polygon mirror.

  By the way, in response to the recent demand for higher printing speed (image formation speed) and higher image quality, the polygon motor, which is a deflector, and the pixel clock, which is the reference clock for laser modulation, are increased. However, it is difficult to cope with the high speed with the conventional methods.

  Further, in the scanning optical system described above, the surface tilt of a deflector such as a polygon scanner and the variation in the distance from the rotation axis of the deflecting / reflecting surface are caused by the displacement of the scanning position of the light spot (scanning beam) that scans the surface to be scanned, Causes uneven scanning speed. This scanning position deviation and scanning speed unevenness cause image fluctuations and deteriorate image quality. Therefore, in order to obtain high quality image quality, it is necessary to correct the scanning position deviation and scanning unevenness.

  Therefore, the use of a multi-beam using a plurality of light sources can cope with high speed. In the multi-beam optical scanning method, the number of light beams that can be scanned simultaneously by the deflection of the deflector increases, so that the rotational speed of the polygon motor, which is the deflector, and the pixel clock frequency can be reduced. Formation is possible.

  As a light source constituting the multi-beam, a method of combining single beam laser chips, an LD array in which a plurality of light emitting elements are incorporated in one laser chip, a surface emitting laser, or the like is used.

  A plurality of surface-emitting lasers arranged in a grid in the x and y directions are applied to an optical scanning device in which the x and y axes of the grating are set to the horizontal scanning direction as the main scanning direction and inclined at a predetermined angle with respect to the main scanning direction. In this case, a plurality of dots can be simultaneously formed in the sub-scanning direction by a plurality of lasers, and high-speed and high-precision optical scanning is possible.

  A semiconductor laser such as an LD array constituting the multi-beam is extremely small and can be directly modulated at high speed by a driving current, so that it has been widely used as a light source for laser printers in recent years.

  However, the relationship between the drive current of the semiconductor laser and the optical output has a characteristic that varies depending on the temperature. Particularly, in the case of a surface emitting laser in which a plurality of light sources are configured on the same chip, since the distance between the light sources is short, the influence of temperature change and temperature crosstalk due to light emission and extinction appears prominently and becomes a factor of light quantity fluctuation.

JP 2002-314191 A JP 2000-12973 A

  In Patent Documents 1 and 2, since the stray capacitances of the wirings are substantially the same, useless wiring patterns such as lengthening of the short wirings are generated, and crosstalk occurs because the wirings are long.

  In addition, because the wiring length between the light emitting element and each wiring pad, the number of times the wiring is bent, the spacing between adjacent wirings, etc. are different, stray capacitance and stray capacitance of the wiring itself are likely to occur, and the wiring capacity should be substantially the same. Is extremely difficult. In particular, when a light emitting element driving driver is connected to a wiring pad to drive the light emitting element at a high speed, the modulation signal waveform becomes duller as the driving frequency increases due to variations in stray capacitance in the wiring from the wiring pad to the light emitting element. As a result, delays and variations in the rise time occur and high-speed modulation cannot be performed, and skew occurs between the light emitting elements.

The present invention has been made to solve the above problems,
SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting element array, a surface emitting laser, a light emitting element substrate, and an optical scanning device that can be driven at high speed by shortening the wiring length and making the stray capacitance between the light emitting element and the driver substantially the same And providing an image forming apparatus.

  The present invention relates to a light-emitting element array including a plurality of light-emitting elements arranged on a substrate, a wiring pad portion, and a wiring connecting the light-emitting element and the wiring pad portion on the substrate. It has the most important feature.

  According to the first aspect of the present invention, the variable capacitance element is provided in the wiring portion connecting the light source and the electrode pad, so that a light emitting element array in which the difference in stray capacitance for each wiring is reduced by the variable capacitance element can be realized. In addition, since it is possible to align the characteristics of each light emitting element without forcibly aligning the wiring length, it is possible to reduce the cost of the wiring portion. Further, by constructing the surface emitting laser as the light emitting element, it is possible to reduce the power consumption as compared with the case where a plurality of ordinary semiconductor lasers are arranged to constitute the light emitting element.

  According to the second aspect of the present invention, by changing the value of the variable capacitance element, the stray capacitance of the plurality of wirings can be made substantially the same, the difference in stray capacitance for each wiring can be reduced, and at the time of high-speed driving A light emitting element array having substantially the same characteristics can be realized.

  According to the third aspect of the present invention, it is possible to change the capacitance with a simple circuit configuration and to change the capacitance with low power consumption by configuring the variable capacitance element with a variable capacitance diode. Simplification and power saving can be realized.

  According to the fourth aspect of the present invention, the variable capacitance value is changed by changing the control voltage applied to the variable capacitance diode, so that the total capacitance with the floating capacitance due to the wiring can be made substantially the same for the plurality of wirings. The light emitting element array with high accuracy and simple control circuit can be realized by voltage value control.

  According to the fifth aspect of the present invention, since the wiring pad portions are arranged in rows on a plurality of substantially the same line, it is easy to connect the driving circuit to the wiring pad portion, the mounting cost is reduced, and the mounting time is shortened. it can.

According to the invention of claim 6, since the variable capacitance element is configured on the same substrate as the wiring connecting the light emitting element and the wiring pad portion, the capacitance variation of the variable capacitance element, the control voltage error, and the like are reduced. According to the invention of claim 7, since the variable capacitance element is configured on the driving IC substrate for driving the light emitting element array, even when the floating capacitance of the wiring changes. The light emitting element array corresponding to high speed driving with reduced difference in wiring stray capacitance on the driving IC side can be realized. According to the invention of claim 8, since the surface emitting laser is used as the light emitting element array, the array of light emitting elements is realized. And a light-emitting element array with low power consumption can be realized.

  According to the ninth aspect of the invention, by applying the above invention to an optical scanning device, it is possible to perform high-speed and high-precision optical scanning using a light-emitting element array and reducing variations in light amount and scanning position.

  According to the invention described in claim 10, by applying the above invention to an image forming apparatus, high-speed and high-precision image formation becomes possible, and image deterioration such as image density unevenness, dot position deviation, and vertical stripes is reduced. An image forming apparatus with high image quality can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1:
FIG. 1 shows a configuration of a light-emitting element array according to Example 1 of the present invention. In FIG. 1, 1 is a light emitting element, 2 is a wiring, 3 is a variable capacitance element, and 4 is a wiring pad.

  As described above, the light emitting element array includes a light emitting element disposed on a predetermined substrate, a wiring pad for connecting a control signal wiring from the drive IC to the light emitting element substrate on which the light emitting element is disposed, A wiring for transmitting a drive signal from the wiring pad to the light emitting element, and a ground layer formed in a layer different from the wiring of the light emitting element substrate. When the ground layer is arranged in the substrate in parallel with the wiring portion, there is a stray capacitance C between the wiring portion and the ground that is inversely proportional to the interval.

  In addition, when a surface emitting laser is formed by using a plurality of light emitting elements arranged on a substrate, its impedance component is about several hundreds Ω, which affects the modulation characteristics particularly at high-speed modulation. In the case of the configuration, the variation among the light emitting elements is very small, and the difference in the modulation characteristic due to the impedance of each light source hardly occurs. Therefore, in this embodiment, the influence of the impedance is ignored.

  In the light emitting element array shown in FIG. 11 (prior art), when a plurality of light emitting elements are arranged in a grid and wiring pads are arranged in a row on a substrate, wiring for connecting the wiring pad portion and the light emitting elements. When the part is designed to be as short as possible, the wiring length becomes longer as the light emitting element is near the center, and the wiring length becomes shorter as it is closer to the edge. For this reason, the wiring length is different for each light emitting element or wiring. In addition, when the light emitting elements are arranged in a grid pattern, there are various routes to the wiring pads of the wiring, so that the stray capacitance of the wiring itself takes a different value for each wiring.

  In addition, when a light emitting element is driven at a high speed, a high-speed signal of several hundreds to several tens of GHz is transmitted to the wiring part. In this case, the rise time is delayed and the signal amplitude is reduced. Furthermore, when the stray capacitance is different for each wiring, the degree of signal deterioration differs accordingly, so that the high-speed modulation characteristics in the light-emitting element array are different, so that even if the same light emission control is performed, different modulation is performed. End up.

  The present invention improves the signal transmission characteristics in the high-frequency region described above. That is, in the first embodiment of the present invention, the variable capacitance element 3 is connected to the wiring 2 as shown in FIG. In the present embodiment, the variable capacitance element 3 whose capacitance value can be changed is added, and the total capacitance of the stray capacitance of the wiring 2 and the capacitance of the variable capacitance element 3 is set to be substantially the same.

  As a result, since the capacitance component added to the wiring portion for each light emitting element becomes substantially equal, even if a high speed signal is transmitted through the wiring portion, the signal modulation characteristics in all the light emitting elements 1 are the same, and even during high speed modulation. A light emitting element array with little variation in signal deterioration can be realized.

Example 2:
2, 3 and 4 show the configuration of the second embodiment of the present invention. Example 2 (FIGS. 2, 3) is an example using a variable capacitance diode 5 as a variable capacitance element. The variable capacitance diode 5 can change its capacitance value by changing the reverse voltage value when a reverse voltage is applied to the diode.

  FIG. 4 shows the relationship between the voltage and the capacitance when the control voltage Vc is applied to the variable capacitance diode as a reverse voltage. As shown in FIG. 4, the variable capacitance diode 5 has a characteristic that the capacity increases when the reverse voltage is small, and the capacity decreases when the reverse voltage is large. Further, since no direct current flows through the variable capacitance diode 5, the power consumption is low. However, when the voltage fluctuation occurs in the control voltage Vc, the capacity fluctuates due to the voltage fluctuation, and thus a circuit that suppresses the fluctuation of the control voltage is required.

  In FIG. 2, a stray capacitance C0 and a variable capacitance diode 5 (Cc) are connected in series to the wiring pad portion 4, and a control voltage Vc is applied between both elements via a resistor R. At this time, as shown in FIG. 4, the capacitance value decreases when the reverse voltage applied to the variable capacitance diode 5, here, the control voltage with respect to the ground is high, and the capacitance value increases when the voltage is low. That is, the capacitance value of the variable capacitance diode 5 can be changed by changing the control voltage Vc.

  Therefore, the combined capacitance of the stray capacitance C0 and the variable capacitance diode Cc in the wiring portion can be made variable. When the stray capacitance is different for each wiring, the capacitance value Cc of the variable capacitance diode 5 is added to the wiring with a small stray capacitance with reference to the wiring having the largest stray capacitance, so that the combined capacitance in all the wirings Can be made substantially the same.

  The capacitance range of the variable capacitance diode is as follows. When the size of the light-emitting element substrate is about several millimeters or less and the number of light-emitting elements is several tens or less, the wiring portion (wiring pads for performing wire bonding or solder mounting from the light-emitting element to the driving IC and the like) The stray capacitance of the wiring between them becomes several pF or less. Therefore, in order to make the stray capacitances of the different wiring lengths substantially the same, it is desirable that the capacitance value of the variable capacitance diode is a capacitance value of several pF or less.

  Further, when the difference in stray capacitance is large, there is a method in which variable capacitance diodes Cc1 and Cc2 are configured in parallel as shown in FIG. 3 to realize a high capacitance value that cannot be obtained by a single diode.

Example 3:
FIG. 5 shows the configuration of Embodiment 3 of the present invention. FIG. 5 shows an embodiment in which a variable capacitance diode 5 is configured on a light emitting element substrate 6 having a light emitting element 1, wiring 2, and wiring pads 4. Changing the stray capacitance caused by the difference in wiring length and wiring width from the driving IC to the wiring pad, for example, when the driving IC is refined, by configuring the variable capacitance diode 5 on the same substrate 6 as the light emitting element 1 If the control voltage of the variable capacitance diode 5 is applied as described in the second embodiment, the total capacitance of the wiring from the driving IC to the light emitting element (floating capacitance + variable capacitance) is set to be substantially the same. it can.

  In addition, by configuring the variable capacitance diode on the same substrate as the wiring, the ground plane that serves as a reference for the stray capacitance of the wiring can be shared as the ground plane of the variable capacitance element. It is possible to realize a highly accurate variable capacitance element that reduces the above.

Example 4:
6 and 7 show the configuration of Embodiment 4 of the present invention. FIG. 6 shows a circuit configuration of this embodiment, and FIG. 7 shows a substrate configuration. 6 and 7 show an embodiment in which a variable capacitance diode 5 having a variable capacitance is formed in the drive IC 7.

  In FIG. 6, the light emitting element 1, the wiring 2a, and the wiring pad portion 4 are configured on the light emitting element substrate 8 of FIG. 7, and the wiring 2b and the driving IC portion 7 are configured on the driving IC substrate 9 of FIG. . In this embodiment, the variable capacitance diode 5 is configured in the drive IC section 7.

  When the variable capacitance diode 5 is provided in the drive IC 7 as in this embodiment, for example, a wiring for setting the variable capacitance is not necessary as compared with the case where the variable capacitance diode is provided on the light emitting element substrate. A simple substrate configuration can be realized.

  Further, even when the substrate of the light emitting element is changed and the stray capacitance of the wiring is changed, a light emitting element array compatible with high speed driving in which the difference in the stray capacitance of the wiring is reduced on the driving IC side can be realized. Note that the above light emitting element array preferably has a plurality of light sources on the same substrate.

  In general, so-called semiconductor lasers that are widely used have a configuration in which laser light is extracted horizontally from the end face of the chip substrate, and therefore it is difficult to arrange the light emitting elements in a lattice shape because of the structure of the device. On the other hand, a surface emitting laser has a structure that can extract laser light from the surface of a chip substrate, and its light emitting part can be freely arranged on the chip. There is an advantage that is easy. Further, since high-speed driving is possible with low power consumption, it is easy to realize high-speed modulation that covers a signal band by arranging many light emitting units. Therefore, by constructing a surface emitting laser using the light emitting element array of the present invention, a light emitting element array in which a plurality of light sources can be freely arranged and high speed modulation and low power consumption can be realized.

Example 5:
Next, a fifth embodiment in the case where the present invention is applied to an optical scanning device, an image forming apparatus or the like will be described. FIG. 8 shows a fifth embodiment of the optical scanning device using the pixel clock generation circuit and method.

  A printed circuit board 802 on which a drive circuit for controlling a semiconductor laser and a pixel clock generation device are formed is mounted on the rear surface of the light source unit 801 in FIG. 8, and is applied to the wall surface of the optical housing orthogonal to the optical axis by the spring described above. In contact, the inclination is adjusted by the adjusting screw 803 and the posture is maintained. The adjusting screw 803 is screwed into a protrusion formed on the wall surface of the housing. Inside the optical housing, a cylinder lens 805, a polygon motor 808 that rotates a polygon mirror, an fθ lens 806, a toroidal lens, and a folding mirror 807 are positioned and supported, respectively, and a printed circuit board 809 on which a synchronization detection sensor is mounted includes: Like the light source unit, it is mounted on the housing wall from the outside. The upper portion of the optical housing is sealed with a cover 811 and is screwed to the frame member of the image forming apparatus main body by a plurality of mounting portions 810 protruding from the wall surface.

  A multi-beam scanning device (multi-beam optical system) configured using a plurality of light sources in the present invention will be described.

  8 and 9 are block diagrams showing an embodiment of the multi-beam scanning device. In this embodiment, as shown in FIG. 9, a semiconductor laser array 702 which is a light emitting element array in which twelve light sources are arranged in a lattice shape is used, and the collimating lens is arranged in the main scanning direction with the optical axis symmetrical. As shown in FIG. 8, a plurality of beams emitted from a light source unit 801 including a semiconductor laser array are collectively scanned by a polygon mirror 808 through a cylinder lens 805, and are applied onto a photoconductor by an fθ lens 806 and a folding mirror 807. Imaged. The buffer memory in the image processing apparatus that controls the light emission signal to the light source stores the print data for one line for each light source, and is read out for each polygon mirror, and the same for multiple lines at the same time. Recording on the scanning line is performed.

  According to this embodiment, it is possible to make the high-speed modulation characteristics of the twelve light sources that perform scanning at the same time substantially the same, and it is possible to realize a high-accuracy optical scanning apparatus that reduces the density unevenness of the scanning light, the scanning position deviation, and the like.

  An embodiment of an image forming apparatus to which the present invention is applied is shown in FIG. Around the photosensitive drum 901 that is the surface to be scanned, a charging charger 902 that charges the photosensitive member to a high voltage, and a developing roller that attaches the charged toner to the electrostatic latent image recorded by the optical scanning device 900 and visualizes it. 903, a toner cartridge 904 for supplying toner to the developing roller, and a cleaning case 905 for scraping and storing toner remaining on the drum. As described above, a plurality of lines are simultaneously recorded on the photosensitive drum 901 for each surface. The recording paper is supplied from the paper supply tray 906 by the paper supply roller 907 and is sent out by the registration roller pair 908 in accordance with the recording start timing in the sub-scanning direction, and the toner is transferred by the transfer charger 906 when passing through the photosensitive drum. The image is transferred, fixed by the fixing roller 909, and discharged to the paper discharge tray 910 by the paper discharge roller 912. According to this embodiment, it is possible to prevent the occurrence of image density unevenness, dot position deviation, vertical stripe image, and the like, and an image forming apparatus capable of forming a highly accurate image with high-speed printing can be realized.

The structure of Example 1 of this invention is shown. The structure of Example 2 of this invention is shown. The modification of Example 2 of this invention is shown. The characteristic of a variable capacitance diode is shown. The structure of Example 3 of this invention is shown. The structure of Example 4 of this invention is shown. The board | substrate structure of Example 4 is shown. 1 shows an optical scanning device to which the present invention is applied. 1 shows a multi-beam scanning apparatus to which the present invention is applied. 1 shows an image forming apparatus to which the present invention is applied. The prior art of a surface emitting laser is shown. 1 shows a conventional image forming apparatus using an electrophotographic process.

Explanation of symbols

1 Light Emitting Element 2 Wiring 3 Variable Capacitance Element 4 Wiring Pad

Claims (10)

  A light-emitting element array comprising a plurality of light-emitting elements and wiring pads arranged on a substrate, and wiring that connects the light-emitting elements and wiring pads on the substrate, wherein a variable capacitance element is connected to the wiring. Light emitting element array.   2. The light emitting element array according to claim 1, wherein the total capacitance of the floating capacitance and the variable capacitance value of the wiring is made substantially the same for a plurality of wirings by setting the variable capacitance value of the variable capacitance element to a predetermined value. The light emitting element array characterized by the above-mentioned.   2. The light emitting element array according to claim 1, wherein the variable capacitance element is a variable capacitance diode.   4. The light emitting element array according to claim 3, wherein a variable capacitance value is changed by changing a control voltage applied to the variable capacitance diode, and a total capacitance of a floating capacitance and a variable capacitance value of the wiring is substantially reduced by a plurality of wirings. A light emitting element array characterized by being identical.   2. The light emitting element array according to claim 1, wherein the wiring pads are arranged in a row on a plurality of substantially identical lines.   2. The light emitting element array according to claim 1, wherein the variable capacitance element and the wiring connecting the light emitting element and a wiring pad are formed on the same substrate.   A light emitting element substrate comprising a light emitting element driving device comprising the light emitting element array according to claim 1 and a drive IC for driving the light emitting element array on a substrate, wherein a variable capacitance element is configured on the substrate. A light emitting element substrate.   A surface-emitting laser comprising a surface-emitting laser using the light-emitting element array according to claim 1.   An optical scanning device comprising the surface-emitting laser according to claim 8.   An image forming apparatus comprising the optical scanning device according to claim 9.

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