JP2002124732A - Device for driving light emitting element and image forming device provided with the driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To offer a device for driving a light emitting element which can restrain radiation noise caused by a common mode current, and to offer an image forming device using that driving device. SOLUTION: A single image signal S is processed into a complementary pair of differential signal by a differential circuit 1. A light emitting element LD is driven by an output signal SO generated in a light emitting element driving circuit 2 based on that pair of differential signals. A common mode choke filter CH1 for removing common mode components of the pair of differential signals selectively is inserted between the differential circuit 1 and the light emitting element driving circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a light emitting element such as a semiconductor laser used as a recording light source of an image forming apparatus, and more particularly to a reduction in common noise.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a configuration of a conventional light emitting element driving device. This will be described below with reference to FIG.

Conventionally, in a light emitting element driving device for driving a light emitting element, a single image signal S is converted by a differential circuit 1 into a pair of complementary differential signals S + and S−, The light-emitting element L is transmitted and converted into an output signal SO.
A method of driving D is used.

In this system, a set of complementary differential signals S
By constructing the + and S- transmission lines so as to be equal in length and close to each other, the signal currents are exactly in opposite phases at all places and at all frequencies on the transmission line, and the magnetic fields cancel each other out. This has the effect of greatly reducing the occurrence of normal mode noise.

Here, the normal mode noise has a property that is approximately proportional to the loop area (= l * d) formed by the normal mode current path, and consideration is given to making the two-line distance (d) close. As long as the line length "l" becomes redundant, unnecessary radiation noise is not significantly increased.

Therefore, among various units constituting the image forming apparatus, the units are separated from other units and substrates mainly by restrictions such as optical adjustment and are arranged at relatively distant positions via cables and the like. A substrate provided with a light-emitting element having many components has a degree of freedom in arrangement.

FIG. 6 is a block diagram showing a configuration of a conventional light emitting element driving device using a light emitting element. Hereinafter, differences from the configuration of FIG. 5 will be described.

The difference from the light emitting element driving apparatus of FIG. 5 is that a pair of complementary differential signals S + and S− are respectively converted to a pair of complementary differential output signals SO + and SO− for driving the light emitting element. This is the point of conversion and use for driving the light emitting element.

This configuration is a logical operation signal required when processing a single pair of differential signals S + and S− obtained by processing a single image signal S into a single output signal again to drive a light emitting element. In order to prevent the light emitting element drive signal waveform from deviating from the original image signal waveform due to processing or the like, the differential signals S + and S- are directly converted into a complementary pair of differential output signals SO + and SO for driving the light emitting element. To-. Here, since the differential output signals SO + and SO− are for driving the light emitting element, they have a larger current component than the differential signals S + and S−.

[0010]

However, when the frequency of the image information signal is increased due to the demand for higher speed of the image forming apparatus, for example, when the rise and fall of the signal become steep, the phase shift of the differential signal is caused. Is increased, and a problem of deterioration of common mode noise due to an increase in common mode current, which has not been much of a problem in the past, occurs.

The intensity of the normal mode noise is approximately proportional to the frequency, while the intensity of the common mode noise is proportional to the square of the frequency. Another problem is that it becomes difficult.

Further, since the intensity of the common mode noise is substantially proportional to the length of the path through which the common mode current flows, it is not allowed to make the signal transmission path to the substrate having the light emitting element redundant. There is a problem that the degree of freedom of arrangement of the substrate having the light emitting element is lost, and the product form of the image forming apparatus is greatly restricted.

In addition, in the light emitting element driving device shown in FIG. 6, since the differential output signals S + and S− for driving the light emitting element are relatively large currents, the amount of common mode current generated due to the phase shift. And the intensity of common mode noise also increases.

The present invention has been made under such circumstances, and an object of the present invention is to provide a light emitting element driving device capable of suppressing radiation noise caused by a common mode current, and an image forming apparatus using the same. Things.

[0015]

In order to achieve the above object, according to the present invention, a light emitting element driving device is configured as in the following (1) to (7), and an image forming apparatus is configured in the following (8). Configure as follows.

(1) A light emitting element, a differential circuit for processing a single signal into a complementary pair of differential signals, and an output signal generated based on the set of differential signals, And a common mode component removing means provided between the differential circuit and the light emitting device drive circuit for selectively removing a common mode component of the set of differential signals. Light emitting element driving device provided with the same.

(2) In the light emitting device driving device according to the above (1), the common mode component removing means is formed on the transmission line of the pair of differential signals, and has a low level with respect to a normal mode current component. A light emitting element driving device that becomes impedance and has high impedance with respect to a common mode current component.

(3) In the light emitting device driving device according to the above (1), the common mode component removing means is a common mode choke filter.

(4) A light emitting element, a differential circuit for processing a single signal into a complementary pair of differential signals, and generating a differential output signal based on the differential signal set A light emitting element driving circuit for driving the light emitting element; and a common mode provided between the light emitting element driving circuit and the light emitting element, for selectively removing a common mode component of the set of differential output signals. A light emitting element driving device comprising: a component removing unit.

(5) In the light emitting device driving device according to the above (4), the common mode component removing means is formed on the transmission line of the pair of differential output signals, and is provided for a normal mode current component. A light emitting element driving device which has a low impedance and a high impedance with respect to a common mode current component.

(6) In the light emitting element driving device according to the above (4), the common mode component removing means is a common mode choke filter.

(7) A light emitting element, a differential circuit for processing a single signal into a complementary pair of differential signals, and generating a set of differential output signals based on the one set of differential signals And a light-emitting element driving circuit for driving the light-emitting element, and a common mode choke filter provided between the differential circuit and the light-emitting element driving circuit and between the light-emitting element driving circuit and the light-emitting element. Light emitting element driving device provided with the same.

(8) An image forming apparatus comprising the light emitting element driving device according to any one of (1) to (7), wherein the light emitting element is a light emitting element for image recording.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples of a light emitting element driving device.

[0025]

(Embodiment 1) FIG. 1 is a block diagram showing the configuration of a "light emitting element driving device" according to Embodiment 1. Hereinafter, description will be made with reference to FIG. The same parts as those in FIG. 5 are denoted by the same reference numerals. Only the differences from the conventional example will be described.

The light emitting element driving device shown in FIG. 1 is different from the conventional light emitting element driving device shown in FIG. 5 in that a set of differential signals S +, A common mode choke filter (also called a common mode choke coil) CH1 for removing a common mode component of S− is inserted.

FIG. 2 and FIG. 3 are diagrams showing differential signals S + and S− whose phases are slightly shifted, and a common mode current component schematically represented by a combination thereof. FIG. 2 shows a common mode choke. FIG. 3 shows a waveform when the filter CH1 is not mounted, and FIG. 3 shows a waveform when the common mode choke filter CH1 is inserted. This will be described below with reference to FIGS.

In FIG. 2, since the differential signals S + and S− are slightly out of phase, the common mode current component flowing in the two lines in phase increases. Therefore, as shown in FIG. 1, the common mode choke filter CH1 has a low impedance with respect to a reverse-phase current, that is, a normal mode current, and has a very high impedance with respect to an in-phase current, that is, a common mode current. 3, the phase shift can be corrected while the rounding of the waveform is minimized, as shown in FIG. 3, and the common mode current can be reduced.

The position where the common mode choke coil CH1 is inserted is set as close as possible to the differential circuit 1 for generating the differential signal, and the phase shift of the differential signal is corrected at the root, so that the light emitting element driving circuit can be inserted. A common mode current is prevented from flowing on up to two differential signal transmission lines.

As described above, according to this embodiment,
It is possible to reduce a common mode current that may be generated due to a phase shift between the differential signals, and to suppress radiated common mode noise.

(Embodiment 2) FIG. 4 is a block diagram showing the configuration of a "light emitting element driving device" according to Embodiment 2. Less than,
This will be described with reference to FIG. The same parts as those in the conventional example 2 shown in FIG. 6 are denoted by the same reference numerals.

Only the differences from the first embodiment will be described. The difference from the light emitting element driving device of the first embodiment is that a common mode choke filter CH2 for selectively removing a common mode component from a set of complementary differential output signals SO + and SO− connected to the light emitting element LD is provided. The point is to provide. With this configuration, generation of a common mode current due to a phase shift between the differential output signals SO + and SO− is reduced.

As described above, according to this embodiment,
It is possible to reduce a large common mode current that can be generated due to a phase shift between the differential output signals for driving the light emitting elements, and to suppress generation of common mode noise. further,
Even if the distance between the light emitting element drive circuit 2 and the light emitting element LD is increased, the radiation intensity of the common mode noise is reduced as compared with the related art, so that the degree of freedom in the arrangement of the light emitting elements can be given.

Here, in addition to the configuration shown in the second embodiment, it is also possible to add the configuration of the first embodiment, that is, a configuration in which a common mode choke filter CH1 is inserted for the differential signals S + and S−. Obviously, it is more effective in reducing common mode noise.

[0035]

As described above, according to the present invention,
The radiation noise due to the common mode current can be suppressed.

More specifically, according to the first to third, seventh, and eighth aspects of the present invention, it is possible to reduce the common mode current that can be generated due to the phase shift between the differential signals and to suppress the occurrence of common mode noise. Thus, when used in an image forming apparatus, it is possible to increase the printing speed, and to secure a degree of freedom in arranging a substrate having a light emitting element for optical adjustment or the like.

According to the present invention, a large common mode current which can be generated due to a phase shift between the differential output signals for driving the light emitting element can be reduced, and the common mode noise can be reduced. When used in an image forming apparatus, the printing speed can be increased while maintaining the reproducibility of image information.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first embodiment.

FIG. 2 is a diagram showing a current waveform when a common mode choke filter is not mounted.

FIG. 3 is a diagram showing a current waveform when a common mode choke filter is mounted.

FIG. 4 is a block diagram illustrating a configuration of a second embodiment.

FIG. 5 is a block diagram showing a configuration of a conventional example 1.

FIG. 6 is a block diagram showing a configuration of a conventional example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Differential circuit 2 Light emitting element drive circuit LD Light emitting element CHl Common mode choke filter

Claims (8)

[Claims] 1. A light emitting device, a differential circuit for processing a single signal into a complementary pair of differential signals, and an output signal generated based on the one set of differential signals, A light emitting element driving circuit for driving; and a common mode component removing means provided between the differential circuit and the light emitting element driving circuit, for selectively removing a common mode component of the set of differential signals. A light-emitting element driving device, characterized in that: 2. The light emitting element driving device according to claim 1, wherein said common mode component removing means is provided on a transmission line of said pair of differential signals, and has a low impedance with respect to a normal mode current component. A light emitting element driving device having a high impedance with respect to a common mode current component. 3. The light emitting device driving device according to claim 1, wherein said common mode component removing means is a common mode choke filter. 4. A light emitting element, a differential circuit for processing a single signal into a complementary pair of differential signals, and generating a set of differential output signals based on said one set of differential signals. A light emitting element driving circuit for driving the light emitting element; and a common mode component provided between the light emitting element driving circuit and the light emitting element, for selectively removing a common mode component of the set of differential output signals. A light emitting element driving device comprising: a removing unit. 5. The light emitting element driving device according to claim 4, wherein said common mode component removing means is provided on a transmission line of said pair of differential output signals, and has a low impedance with respect to a normal mode current component. And a high-impedance element having high impedance with respect to a common mode current component. 6. The light emitting element driving device according to claim 4, wherein said common mode component removing means is a common mode choke filter. 7. A light emitting element, a differential circuit for processing a single signal into a complementary pair of differential signals, and a differential output signal based on the differential signal. A light emitting element driving circuit that drives the light emitting element, and a common mode choke filter provided between the differential circuit and the light emitting element driving circuit and between the light emitting element driving circuit and the light emitting element. A light-emitting element driving device, characterized in that: 8. An image forming apparatus comprising the light emitting element driving device according to claim 1, wherein the light emitting element is a light emitting element for image recording.