JP2009129979A - Printed board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed board with an inexpensive configuration that prevents unwanted radiation generated from a laser driver IC as a noise source. <P>SOLUTION: An IC mounted on the printed board includes a laser element, a first circuit for driving the laser, a second circuit for driving the first circuit in a pre-stage, and a third circuit, wherein a power supply of each of the circuits and a GND terminal are internally separated from each other. The printed board includes an inductor disposed on a path from the laser element, the power supplies of the first and second circuits and a GND wiring to the third circuit, the power supply of the printed board and the GND wiring. The inductor suppresses fluctuation in high-frequency potential generated by the laser element and the operations of the first and second circuits. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a printed circuit board on which a semiconductor integrated circuit that drives a laser at high speed is mounted.

  2. Description of the Related Art Recent semiconductor integrated circuits (hereinafter referred to as ICs) have been made finer in process technology and the operation speed has been increasing year by year. By using ICs with higher operating speeds, various devices have been reduced in size and functionality.

  On the other hand, as the operation speed of the IC is increased, the high frequency noise levels of the power supply terminal, the GND terminal, and the signal terminal portion connected to the IC are increasing. High-frequency potential fluctuation propagated to the signal terminal, power supply terminal, and GND terminal of the IC propagates to the printed circuit board, cable, and metal casing on which the IC is mounted, and finally increases the radiation noise level from the device. . In order to suppress radiation noise from the equipment, countermeasures in the IC, countermeasures in the printed circuit board, cable winding method in the equipment, and measures to devise the sheet metal configuration are taken.

  In order to take measures against cable winding methods and sheet metal configurations, it often takes a great deal of time and cost to increase the cost of the equipment. It is better to apply.

  From the above background, with the main purpose of suppressing high-frequency noise generated from the IC as described above, a technique for separating the internal wiring of the IC has been proposed so far as exemplified below. Yes.

  In Patent Document 1, at least one of the power supply and reference potential wiring of at least one specific circuit is electrically separated from the power supply and / or reference potential wiring of another circuit formed on the same chip as the specific circuit. In addition, a wiring configuration inside the insulated IC is disclosed. Therefore, even if a large current flows through the specific circuit and a noise pulse is generated, the noise pulse is not transmitted to other circuits, so that a malfunction of the circuit due to the noise is not caused.

  In Patent Document 2, a power supply layer and a ground layer of a semiconductor chip are separated from a signal wiring layer, and an input-dedicated buffer, an output-dedicated buffer, and an internal logic circuit are separately provided in the power supply layer and the ground layer, respectively. Further, a wiring configuration inside the IC is disclosed. This facilitates measures on the wiring to avoid the influence of switching noise during simultaneous operation of the output buffer.

  Patent Document 3 discloses an IC having a multi-layer structure in which circuits formed by connecting elements formed on a predetermined substrate using wirings formed in a plurality of wiring layers are incorporated. Yes. In particular, the IC includes a plurality of wirings each having a layout pattern formed in each of a plurality of wiring layers and having a shape that separates a circuit portion of a noise generation source from a circuit portion that reduces noise, and the plurality of wirings. And contacts that are connected to each other. Further, the IC includes a plurality of wirings connected to each other and a constant potential wiring for connecting to a constant potential portion. As a result, the signal of a certain circuit portion in the IC is reduced from being induced as noise to other circuit portions in the IC.

  Patent Document 4 relates to an IC having a first power supply and GND wiring and a second power supply and GND wiring. According to Patent Document 4, the first power supply and the GND wiring are separated from the second power supply and the GND wiring, the first power supply and the GND wiring are connected to the output buffer circuit that operates simultaneously, and the second power supply and the GND are connected. The wiring is connected to an input / output buffer circuit other than the output buffer circuit. As described above, Patent Document 4 achieves the effect of greatly increasing the number of simultaneous operation of the output buffer circuit by separating the output buffer circuit that operates simultaneously and the power supply ground wiring of the input buffer circuit.

  Patent Document 5 relates to a semiconductor memory having a plurality of output terminals. According to Patent Document 5, the power supply line and the ground line connected to the output transistors connected to the output terminals are separated from the adjacent lines. As a result, the influence from the peripheral circuits can be reduced and the influence from other adjacent output circuits can be reduced, and in particular, a part of the power supply lines (or ground lines) arranged in parallel can be connected. As a result, the wiring width can be reduced, and the effect of suppressing an increase in area is achieved.

  Now, as the operation speed of the IC increases, the amount of noise caused by fluctuations in ground (ground) GND or power supply voltage generated during operation increases at the external output terminal section. The use operating voltage of IC tends to decrease more and more, and the noise margin also decreases. Along with this, malfunction due to noise has become a major problem. In order to solve this problem, in Patent Document 6, in the IC, peripheral power supply lines and GND lines for external output terminals or external input / output terminals, internal circuit power supply lines and GND lines for supplying power supply voltages to the internal circuits, Is divided on the pattern inside the IC. This achieves the effect that the noise generated in the former does not affect the internal circuit connected to the latter.

  Patent Document 7 relates to an IC having, as internal circuits, a circuit that generates / outputs a periodic pulse signal and a circuit that operates according to the periodic pulse signal. The IC includes an output circuit including a load unit that pulls up or pulls down an input terminal and a drive unit that drives an output terminal, and the internal circuit includes a separate power source and ground wiring, and a power source and a ground terminal, respectively. It is said. Then, a circuit having a large ratio of handling periodic pulse signals is integrated as an internal circuit, and is configured separately from the power supply system of the output circuit including the load means for pulling up or pulling down the input terminal and the driving means for driving the output terminal. Yes. Thereby, harmonic noise generated in the internal circuit is not radiated to the outside of the IC not only from the output terminal but also from the input terminal pulled up or pulled down. Therefore, according to Patent Document 7, noise can be limited to radiation only from the power supply system of the internal circuit, and an effect of reducing periodic spectrum harmonics electromagnetically radiated from the IC is achieved.

  Further, the power supply wiring and the GND wiring separated from each other inside the IC are separated by high frequency by an inductance component parasitic on the wiring portion in the semiconductor chip and a parasitic inductance component of the bonding wire connected from the semiconductor chip to the lead frame. It becomes a state. Therefore, regardless of the pattern wiring on the printed circuit board, it is possible to prevent malfunction or noise propagation.

  As described above, in order to prevent various noise interferences in the IC, a technique for separating the power supply and GND wiring for each functional block from the power supply GND wiring for other functional blocks in the IC is disclosed.

  On the other hand, even on a printed circuit board on which a plurality of ICs are mounted, problems related to noise, such as radiation noise and malfunction, by separating power wirings or GND wirings between the ICs or separating high frequency components using an inductance element or the like. A proposal has been made to solve this problem.

  Patent Documents 8 to 14 use a printed circuit board or an inductance element in which the wiring of an external power supply terminal or GND terminal of an IC is physically separated from the wiring of an external power supply terminal or GND terminal of another IC mounted on the printed circuit board. A separate printed circuit board is disclosed.

Patent Document 15 discloses a multilayer circuit board on which an IC having a plurality of power supply terminals and a GND terminal, such as an ASIC, is mounted. According to Patent Document 15, the following configuration is disclosed as providing a circuit board capable of reducing the EMI noise radiated from the circuit board while suppressing the number of bypass capacitors. That is, on the first layer, a main power supply plane and a sub power supply plane provided in an island shape through a clearance that disconnects electrical connection between the main power supply plane are provided. The main power plane and the sub power plane are formed in a layer different from the first layer, and are connected by a first power supply pattern to which a bypass capacitor is connected. Further, power supply to at least a part of the power supply terminals of the IC is performed via a second power supply pattern connected without providing a bypass capacitor between the sub power supply planes.
JP 61-1119071 A Japanese Patent Laid-Open No. 5-67682 JP-A-6-37258 JP-A-6-112320 JP 7-74259 A Japanese Patent Laid-Open No. 5-291511 Japanese Patent Laid-Open No. 9-8233 Japanese Patent Laid-Open No. 5-13909 Japanese Patent Laid-Open No. 10-41629 JP-A-10-223997 JP-A-11-233951 JP 2001-274558 A JP 2003-69169 A JP 2003-133747 A JP 2003-282811 A

  Now, as described above, ICs have been made finer in process technology and the operation speed has been increasing year by year. Therefore, in order to prevent noise generated in the internal circuit of the IC from propagating to other block circuits, the power supply wiring and the GND wiring are separated in the IC as proposed in Patent Documents 1-7. The configuration to do is becoming insufficient. In other words, there is an increasing need to take countermeasures from both sides of the internal countermeasures of the IC and the pattern wiring method of the printed board.

  On the other hand, Patent Documents 8 to 14 disclose a configuration in which a power supply pattern or a GND pattern between ICs is separated and wired using a printed circuit board on which a plurality of ICs are mounted, or separated using an inductance element or the like. Has been. According to these configurations, it is possible to suppress propagation of high-frequency potential fluctuations generated at the power supply terminals and GND terminals of the ICs separately mounted on the printed circuit board to the power supply terminals and GND terminals of other ICs. is there. However, since an IC having a plurality of functional blocks in one package has a power supply terminal and a GND terminal for each functional block, the power supply terminal or the GND terminal of the same IC has the same wiring on the printed circuit board. It will be connected. Therefore, a high-frequency potential fluctuation generated from a circuit unit that operates at high speed in the IC propagates to the power supply terminal or GND terminal of the IC via a pattern on the printed circuit board, and is connected to the circuit unit that operates at low speed in the IC. High-frequency potential fluctuations also propagate to the signal line.

  As a result, the high-frequency potential fluctuation propagated to the power supply wiring pattern, the GND wiring pattern, and the signal line pattern on the printed board propagates to the cable and the metal casing connected to the printed board as high-frequency noise. The cable becomes an antenna that radiates the propagated noise. Depending on the shape of the metal casing, it may become a noise radiation antenna. For example, when flat sheet metal is arranged in parallel at a very short distance, or when a narrow gap or the like is formed at a connection portion between a plurality of housings, it becomes an antenna.

  In the case of a device that surrounds the entire printed circuit board and cable with a BOX type metal casing, even if noise propagates to the cable, the noise is finally shielded by the BOX type metal casing. The radiation noise level from the device is easily suppressed. Moreover, the BOX type metal casing surrounding the device is configured such that each metal plate contacts at a large number of connection points, so that the radiation noise level from the device is more easily suppressed. The equipment surrounded by the BOX type metal casing is, for example, a measuring instrument such as an oscilloscope or a personal computer.

  However, in the case of a device in which it is difficult to enclose the entire device with a metal casing, the noise propagated to the cable or the like is not suppressed, resulting in a problem that the radiation noise level from the device eventually increases. .

  For example, an image forming apparatus is equipped with many parts for configuring an electrophotographic process in addition to electrical parts such as a printed circuit board and a cable, and has many user replacement parts such as a cartridge and a fixing device. A cassette is also constructed. Therefore, surrounding the entire device with a housing has a problem of reducing usability. In addition, when a printed circuit board, a cable, and the like are partially surrounded by a metal casing, there are problems that many complicated parts are formed, resulting in an increase in size and cost of the apparatus.

  Patent Document 16 divides a plurality of power supply terminals provided in one IC into a main power supply plane and a sub power supply plane that is provided in an island shape and not provided with a bypass capacitor, and supplies power to some terminals. A configuration in which power is supplied separately from a power plane is disclosed. According to the configuration, it is possible to suppress the number of bypass capacitors and to prevent leakage of common mode noise to the main power plane caused by high-speed switching operation of the IC. Further, according to Patent Document 15, a GND plane layer connected to the ground potential is formed, and the internal logic GND terminal of the ASIC is connected to a stable GND potential. For this reason, the noise leakage from the internal logic GND is not a big problem. However, when the IC operation is further speeded up and the harmonic noise reaches a noise frequency where the impedance of the GND plane cannot be ignored, the current flowing through the GND plane layer formed as a common impedance becomes a noise source. The noise frequency is, for example, about 500 MHz to 5 GHz. This causes a problem that the GND potential of the IC is not stable in the high frequency band and the EMI noise level radiated from the circuit board is increased. In order to reduce the inductance component of the GND plane, measures such as increasing the thickness of the conductive layer (generally, a 35 μm-thick copper foil) several times can be considered, but there is another problem of increasing the cost. It will occur.

  On the other hand, since the inductance component of the GND pattern is relatively large in the single-layer single-sided printed board and the double-layered double-sided printed board, the wiring impedance of the GND pattern affects even in a lower frequency band (for example, 100 MHz to 200 MHz band). It's easy to do. For this reason, the potential is not stable in a frequency band where the GND potential of the IC is lower, and the high-frequency current flowing through the GND pattern tends to cause a noise problem.

  In other words, with a single-layer single-sided printed board or a two-layer double-sided printed board, it is very difficult to construct a power plane or a GND plane that can supply a stable power supply voltage and a reference GND potential to the entire printed board. is there. For this reason, connecting the GND pattern with a solid GND configuration as close to the four-layer substrate as possible is often a noise countermeasure.

  However, when an IC that operates at a high frequency is mounted on a single-layer single-sided printed board, the effect of the inductance of the GND pattern is even greater even when trying to create a wiring pattern close to a solid GND configuration. In addition, when the GND of the printed circuit board cannot be directly connected to the ground plate of the device, the influence of the GND pattern inductance is further increased. As an example of mounting such an IC that operates at a high frequency on a single-layer single-sided printed board, there are a laser driver IC mounted on an image forming apparatus and a laser board on which the laser driver IC is mounted.

  Since a control circuit for driving a laser mounted in this image forming apparatus has been made into an IC chip, a low-cost configuration is often realized by using a single-side printed circuit board. Therefore, the influence of the inductance of the GND pattern on the laser substrate is large.

  In addition, the laser element mounted on the image forming apparatus needs to be configured with a laser scanner unit including an optical lens and the like, and a laser driver IC and a laser substrate for driving the laser element are generally laser scanners. Configured to unit. In many cases, the laser scanner unit must be configured as an independent unit in the image forming apparatus, and there is a problem in connecting the laser substrate to be mounted to the ground metal plate of the image forming apparatus main body. For example, the mechanical configuration becomes complicated, often resulting in a decrease in assemblability and service replacement workability or an increase in cost. Therefore, the laser substrate of the image forming apparatus is often not connected to the ground metal plate, and the influence of the GND pattern inductance on the noise is large.

While the laser substrate is configured as described above, with the increase in the printing speed of the image forming apparatus, the scanning speed at which the photosensitive drum is scanned with the laser is increased. As the scanning speed increases, the frequency of laser driving increases. Furthermore, in recent years, lasers have been driven at higher frequencies in order to increase the gradation of print resolution. Further, there are a single-end driving method and a differential driving method for driving the laser. Compared to the single-ended method, the differential drive method
As a result, the frequency band of the harmonic component contained in the radiation noise has become higher. When the frequency of the radiation noise component increases, the impedance value due to the pattern wiring of the printed board increases, and the GND potential of the printed board becomes more unstable. Therefore, in a single-layer single-side printed circuit board that cannot constitute a planar power supply wiring or GND wiring, such as a four-layer printed circuit board, the impedance to a relatively stable frame GND increases, and the influence on the GND terminal potential of the IC increases. It is getting bigger.

  In consideration of the size of the entire printed circuit board, the power supply terminal for the laser drive unit and the pre-driver circuit unit, the GND terminal, the power supply terminal for the I / O unit, and the GND terminal provided in the same laser driver IC are almost the same. Placed in the location. For this reason, between each power supply terminal of a laser driver IC provided with many power supply terminals and a GND terminal, the wiring impedance between each GND terminal is smaller than the impedance to the stable GND electric potential part (for example, flame | frame GND), compared with the past. Interference is likely to occur in the high frequency band. That is, high-frequency potential fluctuations generated at the power supply terminal and the GND terminal of the laser drive unit and the pre-driver circuit unit are more easily propagated to the power supply terminal and the GND terminal of the I / O unit through the pattern wiring on the printed circuit board. turn into. As a result, there arises a problem that the radiation noise level propagating to the signal input / output terminal of the I / O unit increases.

  In addition, if a single-sided single-sided printed board is changed to a two-layer double-sided printed board or a four-layered printed board in order to form a solid GND with low impedance, the cost of the printed board is greatly increased. Another problem arises.

  In order to prevent this, it is necessary to add a large number of filters on the printed circuit board or to use a ferrite core, a shield metal plate, or the like. However, such countermeasures have a problem of enormous design time and cost increase.

  The present invention has been made in view of the above-described conventional example, and can be applied to many types of printed circuit boards such as single layer, two layers, and four layers, and can suppress radiation from a noise source with an inexpensive and simple configuration. It aims at providing a simple printed circuit board. In particular, the present invention is preferably applied to a printed board on which a laser driver IC including a plurality of pairs of power supply terminals and GND terminals separated inside is mounted.

  The laser driver IC having a large number of internally separated power supply terminals and GND terminals here is an IC having a separate external connection power supply terminal / GND terminal for each type of functional block in the IC. is there.

  In order to achieve the above object, a printed circuit board on which the anode-common type laser of the present invention is mounted has the following configuration.

  A laser element; a laser element power supply connected to the anode terminal of the laser element; a first circuit for driving the laser element; a first type GND terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a type GND terminal, the second type pair terminal, and a third type pair terminal are internally separated is mounted, the power source for the laser element and the second type The wiring from the power supply terminal is the power supply for the third type power supply terminal and the printed circuit board. A first suppression means for suppressing high-frequency potential fluctuations generated by the operation of the first circuit and the operation of the second circuit, the first type GND terminal, and the first terminal on the path led to the turn High-frequency potential fluctuations generated by the operations of the first circuit and the second circuit in the path where the wiring from the two types of GND terminals is led to the third type GND terminal and the GND pattern of the printed circuit board. And a second suppression means for suppressing the above-described problem.

  Here, the second type power supply terminal, the third type power supply terminal, the second type GND terminal, and the third type GND terminal are drawn inward from the terminals of the laser driver IC, respectively. And a power supply wiring path in which the second type power supply terminal and the third type power supply terminal are pattern-connected via the first suppression means, and the second suppression means via the second suppression means. It is desirable to provide a GND wiring path in which the second type GND terminal and the third type GND terminal are pattern-connected.

  Further, in the order of proceeding clockwise around the laser driver IC, the second type GND terminal, the second type power supply terminal, the third type power supply terminal, and the third type GND terminal It is preferable that pin terminals are assigned in order, and the power supply wiring path and the GND wiring path are respectively connected to terminals of the laser driver IC without a jumper component.

  Furthermore, it is preferable that the resistor and the capacitive element that are wired to the terminal of the laser driver IC and the GND pattern are pattern-connected to the GND wiring path without a jumper component.

  The printed circuit board on which the anode common type laser of the present invention is mounted may have the following configuration.

  A laser element; a laser element power supply connected to the anode terminal of the laser element; a first circuit for driving the laser element; a first type GND terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a type GND terminal, the second type pair terminal, and a third type pair terminal are internally separated is mounted, and is a wiring from the second type power supply terminal Is routed to the third type power supply terminal and the power supply pattern of the printed circuit board First suppression means for suppressing high-frequency potential fluctuations generated by the operation of the second circuit, and wiring from the second type GND terminal are the third type GND terminal and the GND pattern of the printed circuit board. And a second suppression means for suppressing high-frequency potential fluctuations generated by the operation of the second circuit and a wiring from the laser element power source to the second type power supply terminal to the print. In the path led to the power supply pattern of the substrate, there are provided third suppression means for suppressing high-frequency potential fluctuations generated by the operation of the first circuit, and wiring from the first type GND terminal. Fourth suppression means for suppressing high-frequency potential fluctuations generated by the operation of the first circuit in a path led to two types of GND terminals or a GND pattern of the printed circuit board. Characterized in that it is kicked.

  Here, the second type power supply terminal, the third type power supply terminal, the second type GND terminal, and the third type GND terminal are respectively provided from the terminal of the laser driver IC to the inside of the laser driver IC. A power supply wiring path in which the second type power supply terminal and the third type power supply terminal are connected in a pattern through the first suppression means, and the second suppression means; It is desirable to provide a GND wiring path in which the second type GND terminal and the third type GND terminal are connected in a pattern via each other.

  Further, in the order of proceeding clockwise around the laser driver IC, the second type GND terminal, the second type power supply terminal, the third type power supply terminal, and the third type GND terminal It is preferable that pin terminals are assigned in order, and the power supply wiring path and the GND wiring path are respectively connected to terminals of the laser driver IC without a jumper component.

  Furthermore, it is desirable that the resistor and the capacitive element connected to the terminal of the laser driver IC and the GND pattern are arranged to be connected to the GND wiring path without a jumper component.

  A printed circuit board on which the cathode common type laser of the present invention is mounted has the following configuration.

  A laser element; a laser element GND connected to a cathode terminal of the laser element; a first circuit for driving the laser element; a first type power supply terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a power source terminal of the type, the second type of pair terminal, and the third type of pair terminal are internally separated is mounted, and wiring from the second type power source terminal On the path leading to the power terminal of the third type and the power pattern of the printed circuit board First suppression means for suppressing high-frequency potential fluctuations generated by the operation of the second circuit, and wiring from the second type GND terminal to the third type GND terminal and the GND pattern of the printed circuit board And the second suppression means for suppressing the high-frequency potential fluctuation generated by the operation of the second circuit and the wiring from the first type power supply terminal to the second type power supply terminal to the above In a path led to the power supply pattern of the printed circuit board, third suppression means for suppressing high-frequency potential fluctuations generated by the operation of the first circuit, and wiring from the laser element GND are the second type. Fourth suppression means for suppressing high-frequency potential fluctuations generated by the operation of the first circuit is provided in a path led from the GND terminal to the GND pattern of the printed circuit board. And features.

  Here, the second type power supply terminal, the third type power supply terminal, the second type GND terminal, and the third type GND terminal are respectively provided from the terminal of the laser driver IC to the inside of the laser driver IC. A power supply wiring path in which the second type power supply terminal and the third type power supply terminal are connected in a pattern through the first suppression means, and the second suppression means; It is desirable to provide a GND wiring path in which the second type GND terminal and the third type GND terminal are connected in a pattern via each other.

  Further, in the order of proceeding clockwise around the laser driver IC, the second type GND terminal, the second type power supply terminal, the third type power supply terminal, and the third type GND terminal It is preferable that pin terminals are assigned in order, and the power supply wiring path and the GND wiring path are respectively connected to terminals of the laser driver IC without a jumper component.

  Furthermore, it is preferable that the resistor and the capacitive element that are wired to the terminal of the laser driver IC and the GND pattern are pattern-connected to the GND wiring path without a jumper component.

  The printed circuit board on which the cathode common type laser of the present invention is mounted may have the following configuration.

  A laser element; a laser element GND connected to a cathode terminal of the laser element; a first circuit for driving the laser element; a first type power supply terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a power source terminal of the type, the second type of pair terminal, and the third type of pair terminal are internally separated is mounted, the first type power source terminal and the first type power terminal The wiring from the two types of power supply terminals is the third type power supply terminal and the power supply pad of the printed circuit board. First suppression means for suppressing high-frequency potential fluctuations generated by the operation of the first circuit and the operation of the second circuit, the laser element GND, and the second High-frequency potential fluctuations generated by the operation of the first circuit and the second circuit are caused in the path through which the wiring from the GND terminal of the type is led to the GND pattern of the third type of GND terminal and the printed circuit board. And a second restraining means for restraining.

  A ferrite bead can be considered as an aspect of the suppression means. Further, it may be an inductor formed by pattern wiring.

  Further, the pair of the first suppression means and the second suppression means may be shared by a common mode choke. Further, the pair of the third suppression means and the fourth suppression means may be shared by a common mode choke.

  Furthermore, it is desirable to have first charge storage means connected between the laser element power supply and the first type GND terminal. It is desirable to have second charge storage means connected between the second type power supply terminal and the second type GND terminal. It is desirable to have third charge storage means connected between the third type power supply terminal and the third type GND terminal.

  In addition, the typical embodiment of the said printed circuit board is a single layer single-sided printed circuit board.

  Therefore, according to the present invention, the high-frequency potential fluctuation generated by the operation of the laser driver circuit and the pre-driver of the laser driver IC with a simple configuration causes the power supply terminal and the GND terminal of the other circuits of the laser driver IC, and the entire printed circuit board. There is an effect that it is possible to suppress the propagation to.

  Thereby, it becomes possible to suppress unnecessary radiation from not only the printed circuit board but also, for example, a device including a cable and a metal housing with an inexpensive configuration.

  Hereinafter, some preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings. Laser driver ICs described in some embodiments described below are ICs incorporating a laser diode drive circuit, a laser light quantity automatic adjustment circuit, and a control circuit for transitioning each light emission state of the laser.

  First, a brief description of a laser driving device in an image forming apparatus, a control operation of a laser driver IC serving as a noise source of unnecessary radiation common to embodiments described below, and radiation noise of the laser driver IC will be described.

<Laser driving device of image forming apparatus>
In an image forming apparatus employing an electrophotographic system, the surface of an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) is uniformly charged by a charging device, and the charged photosensitive drum surface is exposed by an exposure device. An electrostatic latent image is formed. The electrostatic latent image is developed by a developing device to form a developer image, and the developer image is transferred to a transfer material such as paper by a transfer device. The developer image transferred onto the transfer material is fixed on the transfer material by a fixing device. A laser driving device is configured in the scanning optical device portion of the exposure apparatus.

  The laser driving device of the image forming apparatus will be described with reference to FIG. The laser driving device of the image forming apparatus includes a laser substrate 1, an engine controller 65, and a video controller 61. The laser substrate 1 includes a laser 13 that exposes the surface of the photosensitive drum and a laser driver IC 2 that drives the laser 13. The engine controller 65 includes a CPU 66 that performs communication with the video controller 61 and operation control of the laser driver IC 2. The video controller 61 includes a driver circuit (for example, an ASIC 62 with a built-in LVDS driver 63) for outputting image data to be transmitted to the laser driver IC2.

  Upon receiving a print command and print data from a host computer (not shown), the image forming apparatus starts and controls various actuators and motors according to a predetermined sequence. The print data transmitted from the host computer to the image forming apparatus is developed into image data used in the image forming apparatus by the video controller 61 and transmitted to the laser driver IC 2 that drives the laser 13. The laser driver IC2 is controlled by the CPU 66 in each mode of forced light emission, automatic light amount adjustment by APC (AUTO POWER CONTROL) control, and video light emission, which will be described later. When the CPU 66 is set to the video emission mode by the CPU 66, the laser driver IC2 turns on / off the emission of the laser according to the image data transmitted from the video controller 61. When the laser is emitted, the electrostatic latent image is formed on the surface of the photosensitive drum.

<Control of laser driver IC>
Next, the APC control mode of the laser will be described with reference to FIG.

  The laser 13 has temperature characteristics, and the amount of current for obtaining a constant amount of light increases as the temperature increases. Further, since the laser self-heats, a constant amount of light cannot be obtained simply by supplying a constant current, which has a significant effect on image formation.

  Therefore, in the laser drive circuit, in order to make the laser light amount during one scan of the surface of the photosensitive drum constant, a control section for monitoring the light emission amount during one scan and correcting it to a predetermined light amount is a non-image area. Provided. Then, a method is adopted in which the laser drive current amount corrected to a predetermined light quantity is kept constant during the next one scan. Therefore, a light detection element PD (photodiode) for monitoring the light emission amount of the laser is formed inside the laser 13, and a sample / hold circuit unit 33 is formed inside the laser driver IC2.

  The APC control mode of the laser 13 is set by the mode control unit 26 of the laser driver IC 2 based on the CTRL0 and CTRL1 signals (represented as laser control signals in FIG. 3) output from the CPU 66 of the engine controller 65 shown in FIG. The state transition is made to the APC control mode. In the APC control mode, the laser drive signal unit 20 outputs a signal for forced laser emission to the pre-driver unit 40 regardless of the state of the video signal (VDO, / VDO). When the APC control mode is set, the laser driver IC 2 sets the sample and hold circuit unit 33 to the sampling mode, and makes a transition to a mode for adjusting the laser light quantity while forcibly emitting the laser 13. In addition, a constant current circuit for driving the laser at a constant current is configured in the drive circuit unit of the laser 13. The constant current circuit includes a current setting amplifier 34, a current amplification transistor 43, and variable resistors RM1 and RM2 for converting a current into a voltage signal.

  When the laser is forcibly emitted, the light detection element PD converts the light emission amount of the laser into a current Ipd. In addition, since the light detection element PD is connected to the resistors RM1 and RM2 and the inverting input terminal of the light amount setting amplifier 32, the light emission amount monitor voltage V2 is determined by the set value of Ipd and the resistor (RM1 + RM2). The That is, V2 = Ipd · (RM1 + RM2).

  A reference voltage V1 for laser light quantity setting is connected to the non-inverting input terminal of the light quantity setting amplifier 32, and comparison control is performed so as to be equal to the monitor voltage V2 for the light emission quantity. Assume that the output voltage value of the light amount setting amplifier 32 in the comparison-controlled state is V3.

  A hold capacitor C5 is connected to the output terminal of the light quantity setting amplifier 32. When the sample and hold circuit unit 33 is set to the hold mode, the potential V3 is held. The hold capacitor C5 is connected to the current setting amplifier 34, and the laser is driven with a current value according to the potential V3 held by the hold capacitor C5. In this way, APC control of the laser is performed.

  Next, the video emission mode will be described. Regarding the laser video emission mode, the CPU 66 of the engine controller 65 sets the mode control unit 26 of the laser driver IC 2 to change the state. In the video emission mode, the LD drive signal unit 20 outputs an output signal in accordance with the video signals (VDO, / VDO) to the pre-driver unit 40. The transistor 41 is driven according to the output of the pre-driver 40, and the laser emits video.

<Radiation noise of laser driver IC>
Next, FIG. 5 shows how the laser driver IC generates radiation noise.

  As shown in FIG. 5, a laser driver IC 2 and a connector 11 are mounted on the laser substrate 1. The connector 11 has a signal layout input to the logic circuit I / O section 25 of the laser driver IC 2 and power sources Vcc 7 and GND 8 in a pattern layout, and is connected to the engine controller 65 by a cable 68. The GND 8 on the laser substrate 1 is not directly connected to the frame GND, and the GND pattern of the laser substrate 1 is connected to the frame GND 70 of the engine controller 65 via the cable 68.

  By driving the laser diode of the laser 13 at a high frequency (several tens to several hundreds of MHz), high frequency noise is generated in the power supply pattern of the laser driver IC 2. The high-frequency noise fluctuation propagated to the power supply terminal of the laser driver IC 2 is propagated to the power supply pattern on the laser substrate, and the high-frequency potential fluctuation is propagated to the entire portion where the power supply voltage Vcc is applied.

  Since the connector 11 is connected with a pattern for applying the power supply voltage Vcc, high-frequency noise fluctuations are radiated using the cable 68 as an antenna. Further, in the case of a single-layer single-sided printed board, since the inductance component of the GND pattern increases, the potential of the GND pattern 8 tends to be unstable.

  Therefore, the laser driver IC 2 causes a high-frequency potential fluctuation not only at the power supply terminal but also at the GND terminal, which causes radiation noise. Further, high-frequency noise propagates from the power supply or GND to the input signal terminal of the logic circuit I / O unit 25 of the laser driver IC 2 via parasitic capacitance or the like. The high frequency noise propagated to the input signal terminal propagates to the cable 68 connected to the connector 11 and is radiated using the cable 68 as an antenna to become radiation noise ranging from several hundred MHz to several GHz.

  As described in the background art, when a plurality of functional block units are configured in an IC, the power supply and GND wiring of each functional block unit are connected to the power supply and GND wiring and IC of other functional block units. If they are not wired independently of each other, malfunction due to noise interference occurs.

  Therefore, in the laser driver IC according to the present embodiment, as shown in FIG. 6, the power supply GND wirings of the LD driving unit 41 and the pre-driver 40 are wired independently from the power supply GND wirings of the other circuit units. Yes.

  FIG. 6 shows the inside of the laser driver IC 2 described with reference to FIG. 4 as a circuit block, and additionally shows a power supply terminal and a GND terminal. The power supply terminal and the GND terminal are illustrated as being roughly divided into three types of groups.

  The LD drive unit 41 is connected to the outside through an LD terminal for driving the laser 13 and an LD GND terminal (hereinafter referred to as an LDGND terminal) through which a laser drive current of several tens of mA flows. In this embodiment, an anode common type laser is shown as an example.

  The pre-driver unit 40 is a drive circuit in front of the LD driving unit, and is connected to a DRIVER-VCC terminal (hereinafter referred to as a DVCC terminal) and a DRIVER-GND terminal (hereinafter referred to as a DVSS terminal).

  The I / O circuit unit 15 includes an LD drive signal unit 20, a logic circuit I / O unit 25, and an analog circuit unit 30, and includes an I / O VCC terminal (hereinafter referred to as a VCCO terminal) and an I / O. It is connected to a GND terminal (hereinafter referred to as VSSO terminal).

  The laser driver IC described in this embodiment will be described using an example in which a terminal that outputs to the outside is not configured for convenience of description. When the laser driver IC has a terminal for outputting to the outside, the laser driver IC is internally connected to the power supply terminal VCCO and the GND terminal VSSO of the logic circuit I / O section.

  A bypass capacitor C1 is connected between Vccld that supplies power to the laser 13 and the LDGND terminal, and current is supplied to the LD drive unit 41 and the laser 13. A bypass capacitor C2 is connected between the DVCC terminal and the DVSS terminal, and current supply to the pre-driver 40 is performed. A bypass capacitor C3 is connected between the VCCO terminal and the VSSO terminal, and current is supplied to the LD drive signal unit 20, the logic circuit I / O unit 25, and the analog circuit unit 30. The analog circuit unit 30 compares the reference voltage V1 with the voltage V2 generated when the output current Ipd of the photodetector PD of the laser 13 flows through the resistors RM1 and RM2. A current corresponding to the voltage V3 held by the sample hold circuit 33 at a predetermined timing is generated by a constant current circuit composed of an operational amplifier 34 and a transistor 43. Further, the current is passed through a constant current circuit 42 composed of a current mirror circuit, and the current passed through the laser diode LD of the laser 13 is determined.

  The laser driver IC 2 includes a semiconductor chip (not shown), a lead frame, and bonding wires. The semiconductor chip and the lead frame are connected by a bonding wire 6. The power supply wiring and the GND wiring of the internal circuit of the laser driver IC 2 are connected to the power supply wiring pattern 7 and the GND wiring pattern 8 on the laser substrate 1 through a wiring portion inside the semiconductor chip, a bonding wire, and a lead frame outside the semiconductor chip. It is connected. This bonding wire is indicated by 6ld, 6ldgnd, 6dvcc, 6dvss, 6vcco, 6vsso.

  The LD drive unit 41 drives the laser 13 at high speed via the pre-driver 40 according to the video signal. When the LD driver 41 is switched at high speed, a high-frequency current i1a flows through the LD terminal and the LDGND terminal. The high-frequency current i1a flows through the bonding wires 6ld and 6ldgnd, the inductance of the wiring in the LD driving unit 41, the inductance by the pattern wiring on the laser substrate 1, and the bypass capacitor C1, and the common mode noise current i11a Noise current i12a is generated.

  Further, when the pre-driver 40 is switched at high speed, a high-frequency current i2a flows through the DVCC terminal and the DVSS terminal. The high-frequency current i2a flows through the bonding wires 6dvcc and 6dvss, the inductance of the wiring in the pre-driver 40, the inductance due to the pattern wiring on the laser substrate 2, and the bypass capacitor C2, and the common-mode noise current i21a and the noise A current i22a is generated.

  When a four-layer or two-layer printed circuit board is used, since the inductance due to the pattern wiring on the laser substrate 1 can be reduced, the noise current i11a, noise current i12a, noise current i21a, and noise current i22a are reduced. The noise level is relatively small. On the other hand, when a single-side printed circuit board is used, the noise level of the noise current i11a, the noise current i12a, the noise current i21a, and the noise current i22a increases because the inductance due to the pattern wiring on the laser substrate 1 is large.

  Propagation of the noise currents i11a and i21a to the power supply terminal VCCO and the power supply Vcc is suppressed by the high frequency impedance of the ferrite bead FB1. The noise currents i12a and i21a change to noise currents i11a and i21a in the normal mode, and flow to the frame GND 70 of the engine controller 65 via the inductance component by the pattern wiring of the laser board 1 and the cable 68 connected to the connector 11.

  Here, since the inductance due to the pattern wiring of the laser substrate 1 and the inductance of the cable 68 have relatively large values, the high-frequency noise current i21a generated from the GND terminals LDGND and DVSS and the high-frequency noise generated by the wiring inductance of the laser substrate 1 Potential fluctuation occurs at the GND terminal VSSO and propagates to the power supply terminal VCCO via the bypass capacitor C3.

  Further, there is a parasitic capacitance between the power supply wiring and the GND wiring inside the laser driver IC connected to the I / O circuit section 15 (analog circuit section 30, logic circuit section 25, LD drive signal section 20) and signal terminals. Therefore, high-frequency potential fluctuations are also propagated to the signal terminal through this parasitic capacitance. That is, high-frequency potential fluctuations propagated to the power supply terminal VCCO and the GND terminal VSSO are superimposed on the entire input / output signals of the analog circuit unit 30, the logic circuit unit 25, and the LD drive signal unit 20.

  The laser substrate according to the first embodiment is characterized in that the radiation noise generated by using the high-speed drive circuit of the laser driver IC as a noise source is suppressed by using ferrite beads. FIG. 1 is a diagram showing a connection with a laser driver IC on a laser substrate that suppresses radiation noise from the laser driver IC. In FIG. 1, the same components and signals as those already described in FIGS. 4 and 6 are denoted by the same reference numerals and reference symbols, and the description thereof is omitted.

  As shown in FIG. 1, the LDGND terminal and the DVSS terminal of the laser driver IC 2 are not directly connected to the GND pattern 8 of the laser substrate 1, but are connected to the GND pattern 8 via the ferrite bead FB2. On the other hand, the VSSO terminal of the laser driver IC 2 is directly connected to the GND pattern 8. That is, the LDGND terminal and the DVSS terminal of the laser driver IC 2 are separated from the VSSO terminal via the ferrite bead FB 2 in the high frequency band, and one VSSO terminal is directly connected to the GND pattern 8.

  Further, the laser power source Vccld and the DVCC terminal connected to the laser 13 are connected so that the power source voltage is supplied from the power source voltage Vcc7 through the ferrite bead FB1. That is, the laser power supply Vccld and the DVCC terminal are separated from the VCCO terminal in the high frequency band via the ferrite bead FB1, and one of the VCCO terminals is directly connected to the power supply voltage Vcc7.

  Next, it will be described that the ferrite beads FB2 and FB1 suppress the propagation of high frequency noise.

  The video signal transmitted to the laser substrate 1 is input to the LD drive signal unit 20 of the laser driver IC 2, and the video signal is transmitted to the pre-driver 40. The pre-driver 40 performs switching driving of the LD driving unit 41 in accordance with the transmitted video signal. The LD drive unit 41 drives the laser 13 at high speed according to the video signal. When the LD driver 41 is switched at high speed, a high-frequency current i1b flows through the LD terminal and the LDGND terminal. The high-frequency current i1b flows through the bonding wires 6ld and 6ldgnd, the inductance of the wiring in the LD driving unit 41, the inductance due to the pattern wiring on the laser substrate 1, and the bypass capacitor C1, and the common-mode noise current i11b Noise current i12b is generated.

  Further, when the pre-driver 40 is switched at a high speed, a high-frequency current i2b flows through the DVCC terminal and the DVSS terminal. The high-frequency current i2b flows through the bonding wires 6dvcc and 6dvss, the inductance of the wiring in the pre-driver 40, the inductance due to the pattern wiring on the laser substrate 1, and the bypass capacitor C2, and the common-mode noise current i21b and the noise A current i22b is generated.

  When a four-layer or two-layer printed circuit board is used, the inductance value due to the pattern wiring on the laser substrate 1 can be reduced, so that the generated noise current i11b, noise current i12b, noise current i21b, and noise The noise level of the current i22b is relatively small. On the other hand, when a single-side printed circuit board is used, since the inductance value due to the pattern wiring on the laser substrate 1 is large, the noise levels of the generated noise current i11b, noise current i12b, noise current i21b, and noise current i22b are large. Become.

  However, according to the present embodiment, the propagation of the noise current i11b generated in the power supply wiring pattern from the LD driving unit 41 to the power supply terminal VCCO and the power supply voltage Vcc is suppressed by the high frequency impedance of the ferrite bead FB1. On the other hand, the noise current i12b generated in the GND wiring pattern from the LD driving unit 41 is suppressed from being propagated to the GND terminal VSSO and the GND pattern 8 by the high frequency impedance of the ferrite bead FB2. Therefore, the high frequency noise generated by the switching operation of the LD driving unit 41 is suppressed from propagating to the I / O circuit unit 15 and the connector 11 of the laser substrate 1.

  Further, regarding the noise current i21b generated in the power supply wiring pattern from the pre-driver 40, the propagation to the power supply terminal VCCO and the power supply voltage Vcc is suppressed by the high frequency impedance of the ferrite bead FB1. Also regarding the noise current i22b generated in the GND wiring pattern from the pre-driver 40, the propagation to the GND terminal VSSO and the GND pattern 8 is suppressed by the high frequency impedance of the ferrite bead FB2. Therefore, the high frequency noise generated by the switching operation of the pre-driver 40 is suppressed from propagating to the I / O circuit unit 15 and the connector 11 of the laser substrate 1.

  That is, the noise currents i11b, i12b, i21b, i22b generated from the LD driving unit 41 and the pre-driver 40 can be enclosed in the LD driving unit 41 or the pre-driver 40. In other words, high-frequency potential fluctuations generated by the switching operation of the LD driving unit 41 and the pre-driver 40 are not propagated to the I / O circuit unit 15 of the laser substrate 1 and are formed by the LD driving unit 41 and the bypass capacitor C1. It is possible to enclose the current closed loop or the current closed loop formed by the pre-driver 40 and the bypass capacitor C2.

  However, in general, when a GND potential holds a potential that is offset from another GND potential, the GND connected to the circuit portion connected to the offset GND potential and the other circuit portion is the reference. Since there is a difference in potential, there is a risk of malfunction. In other words, it is generally considered that inserting an inductance element into the GND terminal may cause a malfunction.

  In the laser substrate 1 according to the present embodiment, the LDGND terminal of the LD driving unit 41 and the DVSS terminal of the pre-driver 40 are connected to the GND pattern 8 of the laser substrate with high impedance in the high frequency band through the ferrite bead FB2.

  On the other hand, as will be described later, in the present embodiment, the above concerns are avoided by proper connection of the bypass capacitors C1 and C2. By connecting the bypass capacitors C1 and C2, the LD driving unit 41 in which the ferrite bead FB2 is connected to the LDGND terminal, and the I / O circuit unit 15 (LD driving signal unit 20 in which the ferrite bead is not connected to the GND terminal). Also, problems such as malfunctions do not occur in the signal connection part inside the laser driver IC with the logic circuit I / O part 25 and the analog circuit part 30). As a result, high-frequency noise generated by the LD drive unit 41 and the pre-driver 40 can be enclosed in the LD drive unit 41 or the pre-driver 40. The necessity and the capacitance value of the bypass capacitors C1 and C2 are determined by the level of noise generated from the laser driver IC, the laser driving speed, the laser driving current, and the like.

  Next, the above-described high-frequency current containment will be described. FIG. 7 is a diagram schematically showing a state of high-frequency current containment according to the present embodiment.

  As shown in FIG. 7A, the instantaneous current i1b necessary for the high-speed switching operation of the LD driving unit 41 is supplied by charging and discharging repeatedly by the bypass capacitor C1. The instantaneous current i2b required for the high-speed switching operation of the pre-driver 40 is repeatedly supplied and charged by the bypass capacitor C2. On the other hand, as shown in FIG. 7B, the power consumed by the LD drive unit 41 and the pre-driver 40 is supplied from the power supply voltage Vcc7 via the ferrite beads FB1 and FB2.

  That is, the alternating current necessary for the LD driver 41 and the pre-driver 40 to operate at high speed is supplied from each bypass capacitor, and the direct current for power consumption is supplied from the power supply voltage Vcc7 via the ferrite beads FB1 and FB2. Supplied. The high-frequency noise currents i11a, i21a, i12a, i22a generated by the instantaneous current flow are blocked by the ferrite beads FB1 and FB2, and the propagation of high-frequency potential fluctuations is suppressed.

  For example, a ferrite bead having an impedance of 100Ω at 100 MHz and a direct current resistance of about 0.1 to 0.2Ω can sufficiently contain a noise source. A ferrite bead can be selected in accordance with a frequency band having a strong radiation noise level. For example, if the current consumed by the LD driving unit is 50 mA, the DC drop of the ferrite bead is 0.2Ω and the voltage drop is 0.01V. Therefore, the GND potential offset by 0.01 V compared to the GND potential of the VSSO terminal to which the I / O circuit unit 15 (analog circuit unit 30, logic circuit I / O unit 25, LD drive signal unit 20) is connected. In the above, the LD drive unit 41 and the pre-driver 40 operate. However, since the power supply voltage Vcc is about 3.3V to 5V, there is no problem in normal operation.

  Further, when the current consumption of the laser driver IC2 is large, it is sufficient to select one having a smaller DC resistance. Further, the capacitance value of the bypass capacitor C1 is determined according to the switching frequency and the drive current value of the LD drive unit 41. The capacitance value of the bypass capacitor C2 is determined according to the switching frequency and drive current value of the pre-driver 40. Usually, a chip ceramic capacitor having a small impedance in the MHz band is used. Further, since the ferrite bead FB1 is also formed in the Vccld that supplies power to the laser 13, the VCCOd is also supplied with the voltage of the power supply Vccld supplied to the laser 13 due to a voltage drop corresponding to the DC resistance of the ferrite bead. The potential is slightly lower than the power supply voltage at the terminal.

  However, in the present invention, since the GND potential and the power supply voltage connected to the laser driver IC2 are only slightly offset according to the consumption current, there is no problem in normal operation.

  In FIG. 1, the diodes D1 and D2 configured in both directions are added as an ESD countermeasure between the LDGND terminal and the DVSS terminal and the VSSO terminal separated in the high frequency band. Normally, this is provided in the laser driver IC 2, but it may be possible to further improve the ESD tolerance by additionally configuring the laser driver IC outside.

  Next, a specific example of pattern wiring in this embodiment will be described together with the pin assignment of the laser driver IC2. FIG. 2A is a diagram schematically illustrating a specific pattern layout for the connection circuit of the laser substrate 1 that suppresses radiation noise from the laser driver IC shown in FIG. FIG. 2B shows pin assignments of terminals provided in the laser driver IC2.

  As shown in FIG. 1, the laser driver IC 2 includes a GND terminal LDGND for the LD drive unit 41, a power supply terminal DVCC and a GND terminal DVSS for the pre-driver 40, an I / O circuit unit 15 (LD drive signal unit 20). , A common power supply terminal VCCO and a common GND terminal VSSO for the logic circuit I / O unit 25 and the analog circuit unit 30).

  The wiring pattern connected to the LDGND terminal of the LD driving unit 41 and the DVSS terminal of the pre-driver 40 is P2g, the wiring pattern connected to the VSSO terminal of the I / O circuit unit 15 is P3g, the power supplied to the laser 13 and the pre-driver A wiring pattern connected to the DVCC terminal of the driver 40 is shown as P2v, and a pattern connected to the VCCO of the I / O circuit unit 15 is shown as P3v.

  The GND wiring patterns P2g and P3g are separated in the high frequency band by the ferrite bead FB2. The power supply wiring patterns P2v and P3v are separated in the high frequency band by the ferrite beads FB1. Further, the bypass capacitors C1, C2, and C3 are disposed in the vicinity of the circuit block that supplies the instantaneous current, and each power supply and the GND terminal are pin-assigned to the laser driver IC so that the proximity arrangement is possible. Note that RM1 and RM2 are variable resistors and are used for variable adjustment of the laser light quantity. A check pad 14 is used when checking the operation of the laser substrate 1.

  Since the laser substrate 1 of the present embodiment is mainly applied to a single-layer single-sided printed circuit board, the ferrite beads FB1 and FB2 need to be mounted at positions that do not overlap with the package of the laser driver IC2.

  Therefore, the laser driver IC 2 of this embodiment uses the LDGND terminal and the DVSS terminal as adjacent pin assignments, and further uses the DVSS terminal and the DVCC terminal as adjacent pin assignments. In addition, each pin assignment is devised so that the wiring pattern in which the DVCC terminal and the VCCO terminal are connected directly under the laser driver IC2 and the wiring pattern in which the DVSS terminal and the VSSO terminal are connected directly under the laser driver IC2 do not intersect. Is done.

  As a result, the DVSS terminal and the VSSO terminal are separated and wired by the ferrite bead FB2, the DVCC terminal and the VCCO terminal are separated and wired by the ferrite bead FB1, and a circuit block for supplying an instantaneous current to the bypass capacitors C1, C2, and C3. It is possible to use a jumper-less single-layer printed circuit board. Furthermore, since the separation wiring is made possible without a jumper, a laser substrate capable of suppressing radiation noise without increasing the substrate area while using the portion immediately below the laser driver IC 2 for the power supply / GND pattern wiring is provided. It becomes possible.

  As described above, according to the present embodiment, the GND terminal LDGND of the LD driving unit 41, the GND terminal DVSS of the pre-driver, and the I / O circuit unit 15 (LD driving signal unit 20, logic circuit I / O unit 25, analog In a printed circuit board on which a laser driver IC is internally separated from the GND terminal for the circuit unit 30), an inductance element is provided between the LDGND terminal / DVSS terminal and the VSSO terminal and between the power supply Vccld / DVCC terminal and the VCCO terminal. By adding each, impedance separation in a high frequency band is performed. As a result, the high-frequency potential fluctuation generated at the GND terminal LDGND for the LD driver 41 and the GND terminal DVSS for the pre-driver is caused by the power supply of the laser substrate 1 via the pattern on the laser substrate 1 on which the laser driver IC 2 is mounted. Propagation to the pattern, the GND pattern, the signal line pattern, and the entire printed circuit board can be suppressed.

  In other words, according to the embodiment described above, it is possible to realize a configuration capable of suppressing radiation from a device including a laser substrate, a cable, and a metal housing only by adding several ferrite beads.

  Conventionally, the GND pattern of the printed circuit board is formed in a solid shape in as wide a space as possible to take measures against radiation noise. However, according to the present embodiment, the GND pattern area of the printed circuit board is almost independent. In addition, it is possible to take measures against radiation noise of the laser driver IC. As a result, it has become possible to implement measures using a single-sided single-sided printed circuit board compared to the conventional practice of using a double-sided double-sided printed circuit board as a countermeasure against radiation noise. Is possible.

  In addition, it is possible to reduce the shielding member for preventing radiation noise and the like provided in a device including a laser substrate on which the laser driver IC is mounted.

  The laser substrate according to the second embodiment is characterized in that the radiation noise generated by using the high-speed drive circuit of the laser driver IC as a noise source is suppressed by using ferrite beads. FIG. 8 is a diagram showing a connection with a laser driver IC on a laser substrate that suppresses radiation noise from the laser driver IC. In FIG. 8, the same components and signals as those already described in FIGS. 1 to 7 are denoted by the same reference numerals and reference symbols, and the description thereof is omitted.

  In the first embodiment, the power supply terminals of the LD drive unit 41 and the pre-driver 40 are combined and separated by the ferrite bead FB1, and the configuration in which the LD drive unit 41 and the GND terminal of the pre-driver 40 are combined and separated by the ferrite bead FB2 is described. Went. In the second embodiment, each power supply terminal and the GND terminal of the LD driving unit 41 and the pre-driver 40 are independently separated from the power supply terminal and the GND terminal of the I / O circuit unit 15 by four ferrite beads. FIG. 8 is a diagram showing a laser substrate that suppresses radiation noise from an IC using four ferrite beads. FIG. 9 is a diagram schematically illustrating a specific pattern layout of the connection circuit of the laser substrate 1 that suppresses radiation noise from the laser driver IC shown in FIG.

  The laser substrate according to the second embodiment includes the GND terminal LDGND of the LD driving unit 41, the GND terminal DVSS of the pre-driver 40, and the I / O circuit unit 15 (LD driving signal unit 20, logic circuit) configured in the laser driver IC2. The GND terminals VSSO of the I / O unit 25 and the analog circuit unit 30) are respectively connected via ferrite beads. Further, the power supply voltage Vccld supplied to the laser 13, the power supply terminal DVCC of the pre-driver, and the power supply terminal VCCO of the I / O circuit unit 15 are also connected through ferrite beads. Since a large current of a high frequency and several tens of mA flows in the LD drive unit 41 and a slight instantaneous current of a high frequency flows in the pre-driver, especially when the noise level of the LD drive unit is large, as in this embodiment By connecting the power source GND terminal of the LD driver 41 and the pre-driver 40, it is possible to further suppress noise.

  FIG. 8 will be described. The LDGND terminal of the LD drive unit 41 is not directly connected to the DVSS terminal of the pre-driver 40 but is connected via the ferrite bead FB4. The DVSS terminal of the pre-driver 40 is not directly connected to the VSSO terminal of the I / O circuit unit 15, but is connected via the ferrite bead FB2. On the other hand, the VSSO terminal of the I / O circuit unit 15 is connected to the GND pattern 8 as it is.

  That is, the DVSS terminal of the pre-driver 40 is separated from the VSSO terminal via the ferrite bead FB2 in the high frequency band, and the LDGND terminal is further separated from the DVSS terminal via the ferrite bead FB4 in the high frequency band. One VSSO terminal is directly connected to the GND pattern 8.

  The laser power supply Vccld is connected from the power supply terminal VCCO of the I / O circuit unit 15 via ferrite beads FB1 and FB3. The power supply terminal DVCC of the pre-driver 40 is connected so that a power supply voltage is supplied via the ferrite bead FB1.

  That is, Vccld for supplying power to the laser 13 is separated from the DVCC terminal in the high frequency band via the ferrite beads FB1 and FB3, and the DVCC terminal is separated from the DVCC terminal in the high frequency band via the ferrite bead FB1. One VCCO terminal is directly connected to the power supply voltage Vcc7.

  That is, the DVCC terminal of the pre-driver 40 is separated from the VCCO terminal via the ferrite bead FB1 in the high frequency band, and Vccld that supplies power to the laser 13 is further separated from the DVCC terminal via the ferrite bead FB3 in the high frequency band. Is done. One VCCO terminal is directly connected to the power supply voltage Vcc7.

  Next, it will be described that the four ferrite beads suppress the propagation of high frequency noise.

  The LD drive unit 41 drives the laser 13 at high speed via the pre-driver 40 according to the video signal. When the LD driver 41 is switched at high speed, a high-frequency current i1c flows through the LD terminal and the LDGND terminal. The high-frequency current i1c flows through the bonding wires 6ld and 6ldgnd, the inductance of the wiring in the LD driving unit 41, the inductance by the pattern wiring on the laser substrate 1, and the bypass capacitor C1, and the common mode noise current i11c A noise current i12c is generated.

  Further, when the pre-driver 40 is switched at high speed, a high-frequency current i2c flows through the DVCC terminal and the DVSS terminal. The high-frequency current i2c flows through the bonding wires 6dvcc and 6dvss, the inductance of the wiring in the pre-driver 40, the inductance due to the pattern wiring on the laser substrate 1, and the bypass capacitor C2, and the common-mode noise current i21c and the noise A current i22c is generated.

  When a four-layer or two-layer printed circuit board is used, the inductance value due to the pattern wiring on the laser substrate 1 can be reduced, so that the generated noise current i11c, noise current i12c, noise current i21c, and noise The noise level of the current i22c is relatively small. On the other hand, when a single-side printed circuit board is used, since the inductance value due to the pattern wiring on the laser substrate 1 is large, the noise levels of the generated noise current i11c, noise current i12c, noise current i21c, and noise current i22c are large. Become.

  However, according to the present embodiment, the propagation of the noise current i11c generated in the power supply wiring pattern from the LD driving unit 41 to the power supply terminal DVCC is suppressed by the high frequency impedance of the ferrite bead FB3. On the other hand, the propagation of the noise current i12c generated in the GND wiring pattern from the LD driving unit 41 to the GND terminal DVSS is suppressed by the high frequency impedance of the ferrite bead FB4. Therefore, the high frequency noise generated by the switching operation of the LD driving unit 41 is suppressed from propagating to the pre-driver 40, the I / O circuit unit 15 and the connector 11 of the laser substrate 1.

  Further, the noise current i21c generated in the power supply wiring pattern from the pre-driver 40 is suppressed from propagating to the power supply terminal VCCO and the power supply voltage Vcc due to the high frequency impedance of the ferrite bead FB1. On the other hand, the noise current i22c generated in the GND wiring pattern from the pre-driver 40 is suppressed from being propagated to the GND terminal VSSO and the GND pattern 8 by the high frequency impedance of the ferrite bead FB2. Therefore, high-frequency noise generated by the switching operation of the pre-driver 40 is suppressed from propagating to the LD driving unit 41, the I / O circuit unit 15 and the connector 11 of the laser substrate 1.

  That is, the noise currents i11b, i12b, i21b, i22b generated from the LD driving unit 41 and the pre-driver 40 can be enclosed in the LD driving unit 41 or the pre-driver 40. In other words, the high-frequency potential fluctuation generated by the switching operation of the LD driving unit 41 and the pre-driver 40 does not propagate to the I / O circuit 15 of the laser substrate 1, and the current formed by the LD driving unit 41 and the bypass capacitor C1. It is possible to enclose in a closed loop and in a current closed loop formed by the pre-driver 40 and the bypass capacitor C2.

  However, in general, when a GND potential holds a potential that is offset from another GND potential, the GND connected to the circuit portion connected to the offset GND potential and the other circuit portion is the reference. Since there is a difference in potential, there is a risk of malfunction. However, as described in the first embodiment, in the present embodiment, the above concern is avoided by proper connection of the bypass capacitors C1 and C2. By connecting the bypass capacitors C1 and C2, the LD driving unit 41 in which the ferrite bead FB2 is connected to the LDGND terminal, the analog circuit unit 30 in which the ferrite bead is not connected to the GND terminal, and the logic circuit I / O unit 25. Even in the signal connection part inside the IC with the LD drive signal part 20, problems such as malfunction do not occur. As a result, high-frequency noise generated by the LD drive unit 41 and the pre-driver 40 can be enclosed in the LD drive unit 41 or the pre-driver 40.

  Next, a specific example of pattern wiring in this embodiment will be described together with the pin assignment of the laser driver IC2. FIG. 9A is a diagram schematically illustrating a specific pattern layout for the connection circuit of the laser substrate 1 that suppresses radiation noise from the laser driver IC shown in FIG. FIG. 9B shows pin assignments of terminals provided in the laser driver IC2.

  As shown in FIG. 8, the laser driver IC 2 includes a GND terminal LDGND for the LD driving unit 41, a power supply terminal DVCC and a GND terminal DVSS for the pre-driver 40, an I / O circuit unit 15 (LD driving signal unit 20). , Logic circuit I / O unit 25, analog circuit unit 30) and common power supply terminal VCCO and common GND terminal VSSO.

  The wiring pattern connected to the LDGND terminal of the LD driving unit 41 is P1g, the wiring pattern connected to the DVSS terminal of the pre-driver 40 is P2g, the wiring pattern connected to the VSSO terminal of the I / O circuit unit 15 is P3g, and the laser A wiring pattern connected to the power source supplied to 13 is indicated as P1v, a wiring pattern connected to the DVCC terminal of the pre-driver 40 is indicated as P2v, and a pattern connected to the VCCO of the I / O circuit unit 15 is indicated as P3v.

  The GND wiring patterns P1g and P2g are separated in the high frequency band by the ferrite beads FB4. The power supply GND wiring patterns P2g and P3g are separated in the high frequency band by the ferrite bead FB2. The power supply wiring patterns P1v and P2v are separated in the high frequency band by the ferrite beads FB3. The power supply wiring patterns P2v and P3v are separated in the high frequency band by the ferrite beads FB1. Further, the bypass capacitors C1, C2, and C3 are disposed in the vicinity of the circuit block that supplies the instantaneous current, and each power supply and the GND terminal are pin-assigned to the laser driver IC so that the proximity arrangement is possible.

  Since the laser substrate 1 of this embodiment uses a single-layer single-sided printed board, the ferrite beads FB1, FB2, FB3, and FB4 need to be mounted at positions that do not overlap with the package of the laser driver IC2.

  Therefore, the laser driver IC 2 of this embodiment uses the LDGND terminal and the DVSS terminal as adjacent pin assignments, and further uses the DVSS terminal and the DVCC terminal as adjacent pin assignments. In addition, each pin assignment is devised so that the wiring pattern in which the DVCC terminal and the VCCO terminal are connected directly under the laser driver IC2 and the wiring pattern in which the DVSS terminal and the VSSO terminal are connected directly under the laser driver IC2 do not intersect. Is done.

  As a result, the LDGND terminal and the DVSS terminal are separated and wired by the ferrite bead FB4, the DVSS terminal and the VSSO terminal are separated and wired by the ferrite bead FB2, and the power supply Vccld and the DVCC terminal of the laser 13 are separated by the ferrite bead FB3. Separating the DVCC terminal and the VCCO terminal with the ferrite bead FB1, and disposing the bypass capacitors C1, C2, and C3 in the vicinity of the circuit block that supplies the instantaneous current is a single layer without jumper components. This is easily possible using a single-sided printed circuit board. Furthermore, since the above-described separation wiring is possible without using a jumper while using the portion directly under the laser driver IC 2 for the pattern wiring of the power supply GND, a laser substrate capable of suppressing radiation noise without increasing the substrate area is provided. Is possible.

  As described above, according to the present embodiment, the GND terminal LDGND of the LD driving unit, the GND terminal DVSS of the pre-driver and the I / O circuit unit 15 (LD driving signal unit 20, logic circuit I / O unit 25, analog circuit) Part 30) in a printed circuit board on which a laser driver IC is internally separated from the GND terminal, between the LDGND terminal and the DVSS terminal, between the DVSS terminal and the VSSO terminal, between the power supply Vccld and the DVCC terminal, By adding an inductance element between the DVCC terminal and the VCCO terminal, impedance separation in the high frequency band is performed. As a result, high-frequency potential fluctuations generated at the power source terminal / GND terminal for the LD driving unit and the power source terminal / GND terminal for the pre-driver are caused by the pattern on the printed circuit board on which the laser driver IC is mounted. Propagation to the power supply pattern, the GND pattern, the signal line pattern, and the entire printed board can be suppressed.

  That is, according to the embodiment described above, it is possible to realize a configuration capable of suppressing radiation from a device including a printed circuit board, a cable, and a metal housing only by adding several ferrite beads.

  Conventionally, the GND pattern of the printed circuit board is formed in a solid shape in as wide a space as possible to take measures against radiation noise. However, according to the present embodiment, the GND pattern area of the printed circuit board is almost independent. In addition, it is possible to take measures against radiation noise of the IC. As a result, it has become possible to implement a countermeasure that has conventionally been performed using a two-layer double-sided printed board as a countermeasure against radiation noise, using a single-layered single-sided printed board, thereby reducing costs.

  In addition, it is possible to reduce the shielding member for preventing radiation noise and the like provided in a device including a laser substrate on which an IC is mounted.

  Needless to say, the same effect can be obtained by changing the ferrite beads FB1 and FB2 used in this embodiment to the common mode choke. It goes without saying that the same effect can be obtained by changing the ferrite beads FB3 and FB4 to the common mode choke.

  The laser substrate according to the third embodiment is an example in which the configuration for suppressing the radiation noise of the anode / common one-beam laser driver IC described in the second embodiment is applied to the anode / common two-beam laser driver IC. . The third embodiment is also characterized in that radiation noise generated using a high-speed drive circuit as a noise source is suppressed by using ferrite beads. FIG. 10 shows a specific example of pattern wiring in this embodiment. Since the contents relating to the laser operation are the same as those of the anode / common type 1-beam laser driver described in the first and second embodiments, the description thereof will be omitted, and the pattern layout of the third embodiment described below will be described.

  FIG. 10A is a diagram schematically illustrating a specific pattern layout for the connection circuit of the laser substrate 1 that suppresses radiation noise from the laser driver IC of the present embodiment. FIG. 10B shows pin assignments of terminals provided in the laser driver IC2.

  In the one-beam laser driver, the number of terminals for setting the mode is two (2 bits), whereas the two-beam laser driver is three (3 bits), and each mode transition of the two-beam laser is performed by the CPU. Controlled by In the laser driver IC 2c, terminals LD1 and LD2 for laser connection and GND connection terminals LD1GND and LD2GND for the LD driver 41 are configured for two channels. Also, connection terminals CH1 and CH2 of the sample hold capacitor, terminals R5 and R6 for connecting a constant current setting resistor, terminals RM1 and RM2 for connecting a PD current detection resistor, a data signal input terminal DATA1, and For / DATA1, / DATA2, and / DATA2, two channels are also configured. The other terminals (PD, DVCC, DVSS, VCCO, VSSO) are configured one by one in the same manner as the one-beam laser driver IC described in the first and second embodiments.

  The wiring pattern connected to the LDGND terminal of the LD driving unit 41 is P1g, the wiring pattern connected to the DVSS terminal of the pre-driver 40 is P2g, the wiring pattern connected to the VSSO terminal of the I / O circuit unit 15 is P3g, and the laser A wiring pattern connected to the power supply Vccld supplied to 13 is indicated as P1v, a wiring pattern connected to the DVCC terminal of the pre-driver 40 is indicated as P2v, and a pattern connected to the VCCO of the I / O circuit unit 15 is indicated as P3v.

  The GND wiring patterns P1g and P2g are separated in the high frequency band by the ferrite beads FB4. The GND wiring patterns P2g and P3g are separated in the high frequency band by the ferrite bead FB2. The power supply wiring patterns P1v and P2v are separated in the high frequency band by the ferrite beads FB3. The power supply wiring patterns P2v and P3v are separated in the high frequency band by the ferrite beads FB1. Further, the bypass capacitors C1, C2, and C3 are arranged in the vicinity of the circuit block that supplies the instantaneous current, and each power supply and the GND terminal are pin-assigned to the laser driver IC 2c so that the proximity arrangement is possible.

  Since the laser substrate 1c of the present embodiment uses a single-layer single-sided printed board, the ferrite beads FB1, FB2, FB3, and FB4 need to be mounted at positions that do not overlap with the package of the laser driver IC 2c.

  Therefore, the laser driver IC 2c of this embodiment uses the LD1GND terminal and the DVSS terminal as adjacent pin assignments, and further sets the DVSS terminal and the DVCC terminal as adjacent pin assignments. Further, the LD1 terminal and the LD2 terminal are pin-assigned adjacent to both sides of the PD terminal, the LD1GND terminal is adjacent to the LD1 terminal, and the LD2GND terminal is adjacent to the LD2 terminal. Each pin assignment is devised so that the wiring pattern in which the DVCC terminal and the VCCO terminal are connected directly under the laser driver IC 2c and the wiring pattern in which the DVSS terminal and the VSSO terminal are connected directly under the laser driver IC 2c do not intersect. Is done. Components that require GND connection to the wiring pattern side in which the DVSS terminal and the VSSO terminal are connected directly below the laser driver IC 2c (terminals for connecting the sample hold capacitor connection terminals CH1 and CH2 and a constant current setting resistor) R5 and R6, and terminals RM1 and RM2 for connecting PD current detection resistors can be arranged without jumpers, and the RS1 terminal, RS2 terminal, CH1 terminal, CH2 terminal, RM1 terminal, and RM2 terminal are pin-assigned.

  As a result, the LD1GND terminal and the DVSS terminal are separated and wired by the ferrite bead FB4, the DVSS terminal and the VSSO terminal are separated and wired by the ferrite bead FB2, and the power supply Vccld and the DVCC terminal of the laser 13 are separated by the ferrite bead FB3. Separating the DVCC terminal and the VCCO terminal with the ferrite bead FB1, and disposing the bypass capacitors C1, C2, and C3 in the vicinity of the circuit block that supplies the instantaneous current is a single layer without jumper components. This is easily possible using a single-sided printed circuit board. Furthermore, since the above-described separation wiring is made possible without using a jumper while using the portion directly below the laser driver IC 2 for the power supply / GND pattern wiring, a laser substrate capable of suppressing radiation noise without increasing the substrate area is provided. It becomes possible.

  As described above, according to the present embodiment, the GND terminal LDGND of the LD driving unit, the GND terminal DVSS of the pre-driver and the I / O circuit unit 15 (LD driving signal unit 20, logic circuit I / O unit 25, analog circuit) 30) In the printed circuit board on which the laser driver IC is internally separated from the GND terminal, between the LD1GND terminal and the DVSS terminal, between the LD2GND terminal and the DVSS terminal, and between the DVSS terminal and the VSSO terminal. Inductance elements are added between the power supply Vccld and the DVCC terminal, and between the DVCC terminal and the VCCO terminal, respectively, thereby performing impedance separation in the high frequency band. As a result, high-frequency potential fluctuations generated at the power source terminal / GND terminal for the LD driving unit and the power source terminal / GND terminal for the pre-driver are caused by the pattern on the printed circuit board on which the laser driver IC is mounted. Propagation to the power supply pattern, the GND pattern, the signal line pattern, and the entire printed circuit board can be suppressed.

  That is, according to the embodiment described above, it is possible to realize a configuration capable of suppressing radiation from a device including a printed circuit board, a cable, and a metal housing only by adding several ferrite beads.

  Conventionally, the GND pattern of the printed circuit board is formed in a solid shape in as wide a space as possible to take measures against radiation noise. However, according to the present embodiment, the GND pattern area of the printed circuit board is almost independent. In addition, it is possible to take measures against radiation noise of the IC. As a result, it has become possible to implement a countermeasure that has conventionally been performed using a two-layer double-sided printed board as a countermeasure against radiation noise, using a single-layered single-sided printed board, thereby reducing costs.

  In addition, it is possible to reduce the shielding member for preventing radiation noise and the like provided in a device including a laser substrate on which an IC is mounted.

  The laser substrate according to the fourth embodiment is an example in which the configuration for suppressing the radiation noise of the anode / common two-beam laser driver IC described in the third embodiment is applied to the cathode / common two-beam laser driver IC. . The fourth embodiment is also characterized in that radiation noise generated using a high-speed drive circuit as a noise source is suppressed by using ferrite beads. FIG. 11 shows a specific example of pattern wiring in this embodiment. Since the contents related to the laser operation are the same as those of the anode / common type 1-beam laser driver described in the first and second embodiments, the description thereof will be omitted, and the pattern layout of the fourth embodiment described below will be described.

  FIG. 11A is a diagram schematically illustrating a specific pattern layout for the connection circuit of the laser substrate 1 that suppresses radiation noise from the laser driver IC of the present embodiment. FIG. 11B shows pin assignments of terminals provided in the laser driver IC2.

  Similar to the anode / common type two-beam laser driver IC described in the third embodiment, the mode setting terminal is three (3 bits), and each mode transition of the two-beam laser is controlled by the CPU. . The laser driver IC 2d includes two channels of laser connection terminals LD1 and LD2 and power supply connection terminals LD1VCC and LD2VCC for the LD driver 41. The cathode common type laser driver IC has a laser drive current direction as viewed from the IC opposite to that of the anode common type laser driver IC. Therefore, a power supply terminal is connected to the LD drive unit. In the anode / common type laser driver IC, the LD current is drawn, whereas in the cathode / common type laser driver IC, the current flows.

Also, connection terminals CH1 and CH2 of the sample hold capacitor, terminals R5 and R6 for connecting a constant current setting resistor, terminals RM1 and RM2 for connecting a PD current detection resistor, a data signal input terminal DATA1, and For / DATA1, / DATA2, and / DATA2, two channels are also configured. The other terminals (PD, DVCC, DVSS, VCCO, VSSO) are configured one by one in the same manner as the one-beam laser driver IC described in the first and second embodiments.
In the anode / common type laser driver IC, the PD current flows into the laser driver IC, whereas in the cathode / common type laser driver IC, the PD current flows out of the laser driver IC. Therefore, the cathode common type laser driver IC configured in the present embodiment incorporates a current mirror circuit and performs inversion in the PD current direction. Accordingly, the terminals RM1 and RM2 for connecting the PD current detection resistor are connected to the GND pattern in the same manner as the anode / common type laser driver.

  As described above, the power supply terminal LDVCC is connected to the LD drive unit 41. The wiring pattern connected to the LDVCC terminal is P1v, the wiring pattern connected to the DVCC terminal of the pre-driver 40 is P2v, the pattern connected to the VCCO of the I / O circuit unit 15 is P3v, and the GND is connected to the laser 13. A wiring pattern is indicated as P1g, a wiring pattern connected to the DVSS terminal of the pre-driver 40 is indicated as P2g, and a wiring pattern connected to the VSSO terminal of the I / O circuit unit 15 is indicated as P3g.

  The GND wiring patterns P1g and P2g are separated in the high frequency band by the ferrite beads FB4. The GND wiring patterns P2g and P3g are separated in the high frequency band by the ferrite bead FB2. The power supply wiring patterns P1v and P2v are separated in the high frequency band by the ferrite beads FB3. The power supply wiring patterns P2v and P3v are separated in the high frequency band by the ferrite beads FB1. Further, the bypass capacitors C1, C2, and C3 are disposed in the vicinity of the circuit block that supplies the instantaneous current, and each power supply and the GND terminal are pin-assigned to the laser driver IC 2d so that the proximity arrangement is possible.

  Since the laser substrate 1d of this embodiment uses a single-layer single-sided printed circuit board, the ferrite beads FB1, FB2, FB3, and FB4 need to be mounted at positions that do not overlap with the package of the laser driver IC 2d.

  Therefore, the laser driver IC 2d of this embodiment uses the LD1VCC terminal and the DVCC terminal as adjacent pin assignments, and further sets the DVCC terminal and the DVSS terminal as adjacent pin assignments. Further, the LD1 terminal and the LD2 terminal are pin-assigned adjacent to both sides of the PD terminal, the LD1VCC terminal is adjacent to the LD1 terminal, and the LD2VCC terminal is adjacent to the LD2 terminal. Each pin assignment is devised so that the wiring pattern in which the DVCC terminal and the VCCO terminal are connected directly under the laser driver IC 2d and the wiring pattern in which the DVSS terminal and the VSSO terminal are connected directly under the laser driver IC 2d do not intersect. Is done. Components that require GND connection to the wiring pattern side in which the DVSS terminal and the VSSO terminal are directly connected to the laser driver IC 2d (terminals for connecting the sample hold capacitor connection terminals CH1 and CH2 and a constant current setting resistor) R5 and R6, and terminals RM1 and RM2 for connecting PD current detection resistors can be arranged without jumpers, and the RS1 terminal, RS2 terminal, CH1 terminal, CH2 terminal, RM1 terminal, and RM2 terminal are pin-assigned.

  As a result, the GND wiring pattern connected to the laser 13 and the DVSS terminal are separated by the ferrite beads FB4, the DVSS terminal and the VSSO terminal are separated by the ferrite beads FB2, and the LD1VCC terminal and the DVCC terminal are ferrite beads. Separation wiring by FB3, separation of DVCC terminal and VCCO terminal by ferrite bead FB1, and placement of bypass capacitors C1, C2 and C3 in the vicinity of the circuit block for supplying instantaneous current are jumper parts-free. This can be easily achieved using a single-layer single-sided printed circuit board. Furthermore, since the above-described separation wiring is made possible without using a jumper while using the portion directly below the laser driver IC 2 for the power supply / GND pattern wiring, a laser substrate capable of suppressing radiation noise without increasing the substrate area is provided. It becomes possible.

  As described above, according to the present embodiment, the power supply terminals LD1VCC and LD2VCC of the LD drive unit, the power supply terminal DVCC of the pre-driver, and the I / O circuit unit 15 (the LD drive signal unit 20, the logic circuit I / O unit 25, In a printed circuit board on which a laser driver IC is internally separated from the GND terminal for the analog circuit section 30), between the LD1VCC terminal and the DVCC terminal, between the LD2VCC terminal and the DVCC terminal, and between the DVCC terminal and the VCCO terminal Inductance elements are respectively added between the GND wiring pattern connected to the laser 13 and the DVSS terminal, and between the DVSS terminal and the VSSO terminal, thereby performing impedance separation in the high frequency band. As a result, high-frequency potential fluctuations generated at the power source terminal / GND terminal for the LD driving unit and the power source terminal / GND terminal for the pre-driver are caused by the pattern on the printed circuit board on which the laser driver IC is mounted. Propagation to the power supply pattern, the GND pattern, the signal line pattern, and the entire printed circuit board can be suppressed.

  That is, according to the embodiment described above, it is possible to realize a configuration capable of suppressing radiation from a device including a printed circuit board, a cable, and a metal housing only by adding several ferrite beads.

  Conventionally, the GND pattern of the printed circuit board is formed in a solid shape in as wide a space as possible to take measures against radiation noise. However, according to the present embodiment, the GND pattern area of the printed circuit board is almost independent. In addition, it is possible to take measures against radiation noise of the IC. As a result, it has become possible to implement a countermeasure that has conventionally been performed using a two-layer double-sided printed board as a countermeasure against radiation noise, using a single-layered single-sided printed board, thereby reducing costs.

  In addition, it is possible to reduce the shielding member for preventing radiation noise and the like provided in a device including a laser substrate on which an IC is mounted.

  In the fourth embodiment, similarly to the second embodiment, the power source terminals and the GND terminals of the LD driving unit 41 and the pre-driver 40 are independently connected to four ferrites from the power source terminal and the GND terminal of the I / O circuit unit 15. As described in the first embodiment, the power supply terminals of the LD driving unit 41 and the pre-driver 40 are combined and separated by one of the ferrite beads FB1, and the LD driving unit 41 and the pre-driver are also described. For example, the 40 GND terminals may be combined and separated by one ferrite bead FB2.

  A fifth embodiment of the present invention will be described.

  In the fifth embodiment, instead of the ferrite beads FB1, FB2, FB3, and FB4 described in the first to fourth embodiments, the inductance by the pattern wiring is used and the high-speed drive circuit of the laser driver IC is generated as a noise source. It is characterized by suppressing radiation noise. When the noise component of the high-speed drive circuit is relatively small, each power supply terminal and GND terminal can be separated and wired in a high-frequency band by using a pattern inductance instead of a ferrite bead.

  FIG. 12 illustrates the form of this example on the laser substrate on which the anode / common type 1-beam laser driver IC described in Example 2 is mounted. Similarly to FIG. 12, the laser substrate on which the laser driver IC described in the third to fourth embodiments is mounted also includes an inductance component by pattern wiring instead of the ferrite beads FB1, FB2, FB3, and FB4. Since the configuration method of the inductance component by the pattern wiring is the same, the illustration is omitted. In addition, the contents relating to the laser operation and the configuration for high-frequency separation are only differences in the suppression effect, and thus description thereof is omitted.

  According to the present embodiment, although the noise suppressing effect is lower than that of the first to third embodiments, the GND terminal LDGND of the LD driving unit, the GND terminal DVSS of the pre-driver, and the I / O circuit unit 15 (LD driving signal 15 Unit 20, logic circuit I / O unit 25, analog circuit unit 30) on a printed circuit board mounted with a laser driver IC internally separated, between LDGND terminal and DVSS terminal, DVSS terminal and VSSO Impedance separation in the high frequency band is performed by interposing inductance components formed by pattern wiring between the terminals, between the power supply Vccld and the DVCC terminal, and between the DVCC terminal and the VCCO terminal. As a result, high-frequency potential fluctuations generated at the power source terminal / GND terminal for the LD driving unit and the power source terminal / GND terminal for the pre-driver are caused by the pattern on the printed circuit board on which the laser driver IC is mounted. Propagation to the power supply pattern, the GND pattern, the signal line pattern, and the entire printed circuit board can be suppressed.

  According to the present embodiment, although the noise suppression effect is lower than that of the fourth embodiment, the power supply terminals LD1VCC and LD2VCC of the LD drive unit, the power supply terminal DVCC of the pre-driver, and the I / O circuit unit 15 (LD drive signal unit 20). In the printed circuit board on which the laser driver IC is internally separated from the GND terminal for the logic circuit I / O unit 25 and the analog circuit unit 30), between the LD1VCC terminal and the DVCC terminal, and between the LD2VCC terminal and the DVCC terminal Inductance components formed by the pattern wiring are interposed between the DVCC terminal and the VCCO terminal, between the GND wiring pattern and the DVSS terminal connected to the laser 13, and between the DVSS terminal and the VSSO terminal. Impedance separation in the band is performed. As a result, high-frequency potential fluctuations generated at the power source terminal / GND terminal for the LD driving unit and the power source terminal / GND terminal for the pre-driver are caused by the pattern on the printed circuit board on which the laser driver IC is mounted. Propagation to the power supply pattern, the GND pattern, the signal line pattern, and the entire printed circuit board can be suppressed.

It is a figure which shows the mode of the laser driver IC on the laser substrate which suppresses the radiation noise according to Example 1 of this invention, and its connection. It is a figure which shows an example of the pattern wiring of the laser substrate according to Example 1 of this invention. 1 is a diagram illustrating a laser driving device of an image forming apparatus and a system connection configuration thereof. It is a figure which shows the internal block circuit of a laser driver IC. It is a figure which shows a mode that the noise of a laser driver IC propagates in an apparatus. It is a figure which shows a mode that the noise of a laser driver IC propagates the inside of a laser substrate. It is a figure which shows typically the mode of the containment of the high frequency current according to the Example of this invention. It is a figure which shows the mode of the laser driver IC on the laser substrate which suppresses the radiation noise according to Example 2 of this invention, and its connection. It is a figure which shows an example of the pattern wiring of the laser substrate according to Example 2 of invention. It is a figure which shows an example of the pattern wiring of the laser substrate according to Example 3 of invention. It is a figure which shows an example of the pattern wiring of the laser substrate according to Example 4 of invention. It is a figure which shows an example of the pattern wiring of the laser substrate according to Example 5 of invention.

Explanation of symbols

1 Laser substrate 2 Laser driver IC
7 Power supply 8 GND pattern 11 Connector 13 Laser element 15 I / O circuit unit 20 LD drive signal unit 25 Logic circuit I / O unit 30 Analog circuit unit 40 Pre-driver 41 LD drive unit FB1, FB2, FB3, FB4 Ferrite beads C1, C2, C3 capacitors

Claims (21)

A laser element; a laser element power supply connected to the anode terminal of the laser element; a first circuit for driving the laser element; a first type GND terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a seed GND terminal, the second type pair terminal, and the third type pair terminal are internally separated is mounted;
The operation of the first circuit and the second circuit are connected to a path through which the wiring from the power supply for the laser element and the second type power supply terminal is led to the power supply pattern of the third type power supply terminal and the printed circuit board. First suppression means for suppressing high-frequency potential fluctuations generated by the operation of the circuit;
The wiring from the first type GND terminal and the second type GND terminal is routed to the third type GND terminal and the GND pattern of the printed circuit board. A printed circuit board comprising: a second suppression unit configured to suppress a high-frequency potential fluctuation generated by the operation of the circuit.   The second type power supply terminal, the third type power supply terminal, the second type GND terminal, and the third type GND terminal are respectively drawn from the laser driver IC terminal to the inside of the laser driver IC. A pattern wiring is provided, and a power supply wiring path in which the second type power supply terminal and the third type power supply terminal are pattern-connected via the first suppression means, and via the second suppression means The printed circuit board according to claim 1, further comprising a GND wiring path in which the second type GND terminal and the third type GND terminal are pattern-connected.   In the order of proceeding clockwise around the laser driver IC, the second type GND terminal, the second type power supply terminal, the third type power supply terminal, and the third type GND terminal are arranged in this order. 3. The printed circuit board according to claim 2, wherein a terminal is assigned, and the power supply wiring path and the GND wiring path are pattern-connected to terminals of the laser driver IC without a jumper component.   4. The printed circuit board according to claim 3, wherein the resistor or the capacitive element connected to the terminal of the laser driver IC and the GND pattern is pattern-connected to the GND wiring path without a jumper component. A laser element; a laser element power supply connected to the anode terminal of the laser element; a first circuit for driving the laser element; a first type GND terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a seed GND terminal, the second type pair terminal, and the third type pair terminal are internally separated is mounted;
A second circuit that suppresses high-frequency potential fluctuations caused by the operation of the second circuit in a path through which the wiring from the second type power supply terminal is led to the third type power supply terminal and the power supply pattern of the printed circuit board. 1 suppression means;
The second type GND terminal suppresses high-frequency potential fluctuations generated by the operation of the second circuit in the path leading to the third type GND terminal and the GND pattern of the printed circuit board. Two suppression means;
A third circuit that suppresses high-frequency potential fluctuations generated by the operation of the first circuit in a path through which the wiring from the laser element power supply is led to the second type power supply terminal or the power supply pattern of the printed circuit board. Suppression means;
The first type GND terminal suppresses high-frequency potential fluctuations generated by the operation of the first circuit in the path leading from the second type GND terminal to the GND pattern of the printed circuit board. 4. A printed circuit board, comprising: 4 suppression means.   The second type power supply terminal, the third type power supply terminal, the second type GND terminal, and the third type GND terminal are respectively drawn from the laser driver IC terminal to the inside of the laser driver IC. A pattern wiring is provided, and a power supply wiring path in which the second type power supply terminal and the third type power supply terminal are pattern-connected via the first suppression means, and via the second suppression means 6. The printed circuit board according to claim 5, further comprising a GND wiring path in which the second type GND terminal and the third type GND terminal are pattern-connected.   In the order of proceeding clockwise around the laser driver IC, the second type GND terminal, the second type power supply terminal, the third type power supply terminal, and the third type GND terminal are arranged in this order. 7. The printed circuit board according to claim 6, wherein a terminal is assigned, and the power supply wiring path and the GND wiring path are respectively connected to terminals of the laser driver IC without a jumper component.   8. The printed circuit board according to claim 7, wherein the resistor or the capacitive element connected to the terminal of the laser driver IC and the GND pattern is pattern-connected to the GND wiring path without a jumper component. A laser element; a laser element GND connected to a cathode terminal of the laser element; a first circuit for driving the laser element; a first type power supply terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a seed power source terminal, the second type pair terminal, and the third type pair terminal are internally separated is mounted,
A second circuit that suppresses high-frequency potential fluctuations caused by the operation of the second circuit in a path through which the wiring from the second type power supply terminal is led to the third type power supply terminal and the power supply pattern of the printed circuit board. 1 suppression means;
The second type GND terminal suppresses high-frequency potential fluctuations generated by the operation of the second circuit in the path leading to the third type GND terminal and the GND pattern of the printed circuit board. Two suppression means;
A first circuit that suppresses a high-frequency potential fluctuation caused by the operation of the first circuit in a path through which the wiring from the first type power supply terminal is led to the second type power supply terminal to the power supply pattern of the printed circuit board. 3 suppression means;
A fourth path that suppresses high-frequency potential fluctuations generated by the operation of the first circuit in a path through which the wiring from the laser element GND is led to the second type GND terminal to the GND pattern of the printed circuit board. A printed circuit board characterized by comprising suppression means.   The second type power supply terminal, the third type power supply terminal, the second type GND terminal, and the third type GND terminal are respectively drawn from the laser driver IC terminal to the inside of the laser driver IC. A pattern wiring is provided, and a power supply wiring path in which the second type power supply terminal and the third type power supply terminal are pattern-connected via the first suppression means, and via the second suppression means The printed circuit board according to claim 9, further comprising a GND wiring path in which the second type GND terminal and the third type GND terminal are pattern-connected.   In the order of proceeding clockwise around the laser driver IC, the second type GND terminal, the second type power supply terminal, the third type power supply terminal, and the third type GND terminal are arranged in this order. 11. The printed circuit board according to claim 10, wherein a terminal is assigned, and the power supply wiring path and the GND wiring path are respectively connected to terminals of the laser driver IC without a jumper component.   12. The printed circuit board according to claim 11, wherein the resistor and the capacitive element connected to the terminal of the laser driver IC and the GND pattern are connected to the GND wiring path without a jumper component. A laser element; a laser element GND connected to a cathode terminal of the laser element; a first circuit for driving the laser element; a first type power supply terminal connected to the first circuit; A second circuit for driving the circuit in the previous stage, a second type pair terminal of a second type power supply terminal and a second type GND terminal connected to the second circuit, and the first and second types The third circuit different from the second circuit, a third type power supply terminal connected to the third circuit, and a third type pair terminal of a third type GND terminal, A printed circuit board on which a laser driver IC in which a seed power supply terminal, the second type pair terminal and the third type pair terminal are internally separated is mounted;
The operation of the first circuit and the second circuit are connected to a path through which wiring from the first type power supply terminal and the second type power supply terminal is led to the third type power supply terminal and the power supply pattern of the printed circuit board. First suppression means for suppressing high-frequency potential fluctuations generated by the operation of the circuit of 2;
The wiring from the laser element GND and the second type GND terminal is routed to the third type GND terminal and the GND pattern of the printed circuit board in the path of the first circuit and the second circuit. A printed circuit board comprising: a second suppression unit configured to suppress a high-frequency potential fluctuation generated by the operation.   The printed circuit board according to claim 1, wherein the suppressing means is a ferrite bead.   The printed circuit board according to claim 1, wherein the suppression unit is an inductor formed by pattern wiring.   The printed circuit board according to claim 1, wherein the pair of the first suppression unit and the second suppression unit is also used as a common mode choke.   The printed circuit board according to any one of claims 5 to 13, wherein the pair of the third suppression unit and the fourth suppression unit is also used as a common mode choke.   18. The printed circuit board according to claim 1, further comprising first charge storage means connected between the laser element power supply and the first type GND terminal.   19. The printed circuit board according to claim 1, further comprising second charge storage means connected between the second type power supply terminal and the second type GND terminal. .   20. The printed circuit board according to claim 1, further comprising third charge storage means connected between the third type power supply terminal and the third type GND terminal. .   21. The printed circuit board according to claim 1, wherein the printed circuit board is a single-layer single-sided printed circuit board.

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