JPS5939168A - Modulation circuit of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the quality of an intermediate tone picture, by producing a dot picture proportional to the picture density with an analog video signal, in performing picture recording with a laser printer. CONSTITUTION:A signal DVS and an AVS are multiplied when the binary video signal DVS is applied based on a bias decided with an output of a monitor signal processing circuit 21, and a semiconductor laser is modulated with a drive current corresponding to the binary video signal DVS. While the analog video signal is applied, the clock ASC and the signal AVS are multiplied based on the bias decided with the addition between the output of the processing circuit 21 and a generated voltage E of a power supply 22, and the laser 31 is modulated with a drive current having a level proportional to the picture density with the signal AVS and the same time width with the clock ASC. Thus, the intermediate tone picture with good quality without raster pattern is produced on a photoreceptor drum.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates generally to semiconductor laser modulation circuits used in laser printers, and more particularly to circuits for improving the generation of halftone images by laser printer traps.

Conventionally, laser printers using xerography were thought to be incapable of recording black-and-white binary images; however, the use of semiconductor lasers as the light source for laser printers has begun. (Since then, it has become easier to modulate light intensity, so it has become possible to record images with halftones in addition to the above-mentioned black and white binary images.

However, when the above-mentioned one-shot recording is performed by a laser printer using such a semiconductor laser, an unnecessary line pattern called a Lascoba pattern often appears in the middle of the image. In addition, this raster pattern may be uneven due to vibration or other reasons (if such a raster pattern appears, the quality of the recorded image will be significantly impaired). The future challenge for laser printers that use semiconductor lasers is how to prevent the occurrence of such problems and obtain high-quality halftone images.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a semiconductor laser modulation circuit that can prevent the generation of raster patterns and allow a laser printer to record high-quality halftone images.

That is, this invention separates an image into points using the principle of the halftone method, and records the area of these points so that they are thick in proportion to the image production, so that a high-quality intermediate sub-image can be obtained. Focusing on the fact that no raster pattern appears, the first modulator receives a binary video signal or an analog video signal sampling clock, and the second modulator receives an analog video signal. By using the semiconductor laser with the output of this 4L'tn device, especially when inputting an analog video signal, a set of points with different effective spot shapes in proportion to the image density of the valleys is created. A latent image is formed on a photoreceptor drum as a high-quality halftone image without a raster pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser modulation circuit according to the present invention will be described in detail below according to an embodiment shown in the accompanying drawings.

Fig. 1 shows a schematic configuration of a laser printer using a semiconductor laser modulation circuit according to the present invention.1-0 As shown in Fig. 1, 300 laser light sources emit a built-in semiconductor laser such as a laser diode. The laser beam passes through a lens system (not shown) to a rotating polygon mirror 40.
The light is reflected there and reaches the scanning Fθ lens 50. However, the rotating polygon mirror 40 is connected to a motor 41 and is configured to rotate in the direction of arrow F2 in the figure. The laser beam that has passed through the Fθ lens 50 reaches a photosensitive drum 70 whose surface is coated with a photoreceptor, where an electrostatic latent image is formed. , scanning is performed in the direction of arrow F1 in the figure as the rotating polygon mirror 400 rotates. Further, a portion of the laser beam is reflected by a mirror 61 placed at an appropriate position near the photosensitive drum 70, and is configured to be incident on a monitor circuit 60 having a built-in light receiving element such as a photodiode.

On the other hand, the laser light source 3() and the monitor circuit 60 are connected to a modulation circuit 20 according to the present invention, and the modulation circuit 20 further converts the manually input video signal S into a command to be described later on the video signal VS. The signal is connected to a video signal processing circuit 10 which divides the signal into a binary video signal 1) VS and an analog video signal AVS, and performs predetermined processing on each of these signals, which will be described later.

Next, the structure of one embodiment of the modulation circuit 20 is shown in FIG. 2, and its functions will be explained.

This modulation circuit 20 adjusts the level of the monitor signal MS applied from the monitor circuit 60 as appropriate, and then samples and holds 1 based on an SOS (start of scan detector) signal indicating the start of scanning of the video signal VS.
- Monitor signal processing circuit 21, j that performs processing such as
9r The power supply 22 that generates the IJF voltage E, the selection signal SS applied from the video signal processing circuit 10 (the logic level becomes 1H'' level only during the time when the video signal vS input to the video signal processing circuit 10 is the analog video signal AVS) An analog switch 23 that is turned on only for the time that the signal (signal) is at the logic level "H"; and a sum that adds the output of the monitor signal processing circuit 21 and the voltage E when the analog switch 23 is turned on. Arithmetic circuit 24
, and when the selection signal SS is at the logic level "l", the output of the human-powered monitor signal processing circuit 21 is selected and output, and when it is at the "H" level, the output of the summation circuit 24 of the B input is output. A bias setting section which also serves as a selector 25 for selective output, an operational amplifier 26 and a transistor 'l
'lt, depending on the selector 250 output 1 - that is, the output SO of the bias setting section, the transistor TR,
The collector emitter current is set and stabilized by setting the collector emitter current and stabilizing it. The clock ASC for the binary video signal DVS or the analog video signal No. 4g the 7 Furinog is configured with a modulation section, and the collector emitter current of the transistor TR8 set by the current control section is used as the bias current of the modulation section. The semiconductor laser 31 built in the laser light source 30 is modulated by the output DS multiplied by the analog video signal AVS and the analog video signal AVS.

This operation mode is shown in FIG. 3 and will be explained in more detail with reference to a time chart. As shown in Figure (b), a video signal S containing the SO8in number and a command signal is input for each scanning line.However, if the internal medicine of this video signal S is a binary video? , analog video, or a mixture of binary video and analog video as shown in the figure, etc., differs for each scanning line signal, and usually these are determined by the above command signal. The video signal content for each scanning line is shown. That is, the command signal is composed of a synchronization beat formed by 9 fixed bits, a video signal identification signal, an analog video signal start address, an analog video signal end address, etc. There is.

Therefore, if the input video signal VS is the third
Assuming that the signal is in the state shown in FIG. 3(c), the video signal processing circuit 10 outputs the aforementioned selection signal SS based on the contents of the command signal (see FIG. 3(d)). The digital video signal DVS and the analog video signal AVS are separated, and each of these separated signals is subjected to predetermined processing as shown in FIGS. 3(f) and (g), respectively. That is, when the video signal is a binary video, the internal medicine of the binary video is output as is as the binary video signal DVS (Fig. 3<1).
(See Figure 3 (g) to maintain this level at a predetermined level), and when the video signal is analog video, it is based on the video clock instead of the binary video signal DVS. Analog video signal sample link clock ASC formed by
(see FIG. 3(f)) and JJAi! based on the analog pixel shown in FIG. 3(c) as a 7 analog video signal AVS as shown in FIG. 3(c). Outputs the analog signal (de,iatal/analog conversion) (Figure 3 (g)
reference).

Note that such a video signal processing circuit 1o can be constructed as appropriate using already well-known techniques, and illustration of this detailed construction, etc., is omitted.

Now, the modulation circuit 20 collects the monitor signal MS based on the above-mentioned SOS signal, and the video signal processing circuit 1o also collects the binary video ID No. d UV which has been subjected to the above-mentioned processing.
S (or analog video signal sampling clock ASC) and analog video signal AV8 are added to the sampled monitor signal MS.
Based on this, 7Q Jjr constant modulation operation is started.

In other words, during the time when the two-channel video signal DV8 is applied, the signal DVS and the No. 8 AVS are adjusted based on the bias determined by the output of the monitor signal processing circuit 21 (see FIG. 3(, )). The added binary video signal E7 modulates the semiconductor laser 31 with a dynamic current (see Fig. 3 (h)), which corresponds directly to the contents of No. DV8, and the analog Video signal AV8
During the time period during which the voltage is applied, -
The clock ASC and No. 14 AVS are connected to each other, and the clock ASC and No. 14 AVS have a level proportional to the image density indicated by the applied analog video signal AVS, and the separate analog video signal sampling pulse ASC The semiconductor laser 31 is modulated with a drive current (see FIG. 3(h)) having the same time width. As a result, the photosensitive drum 70
(See FIG. 1), a horizontal image is formed in the manner shown in 314210), and especially when modulating an analog video signal, it is generated as a high-quality mid-view image without a raster pattern.

Note that, as in this embodiment circuit shown in FIGS. 1 and 2, the output stability of the semiconductor laser 31 can be stabilized by monitoring the actual optical output of the semiconductor laser 31 and determining the bias during the above modulation. Of course, it is effective for achieving A.
However, the transformation circuit according to the present invention is not necessarily limited to such a configuration.In other words, the bias level necessary for the modulation operation using a binary video signal and the bias level necessary for the modulation operation using an analog video signal is not necessarily limited to such a configuration. It is also possible to have a configuration in which the bias levels are set empirically using appropriate power supply circuits, and these are selectively used by the above-mentioned selection SS, or even have equivalent functions. Other configurations may also be adopted if necessary.

Further, the configuration of the multiplier in the above-mentioned modulation section is also arbitrary, and any other configuration may be used as long as an equivalent function can be obtained.

As explained above, the modulation circuit of the semiconductor laser according to the present invention effectively generates a halftone image proportional to the image error p:+,I shown by the analog video signal and is free from raster patterns. This has the excellent effect of printing a high quality intermediate word image.

In addition, even when a binary video signal and an analog video signal are mixed in the video signal for -scanning lines, the modulation operation is automatically switched in response to each of these signals. This is especially effective when printing information and photo information at the same time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of a laser printer using a semiconductor laser modulation circuit according to the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the configuration of the modulation circuit.
FIG. 3 is a time chart showing an example of the operation of the embodiment circuit shown in FIG.

Claims (2)

[Claims] (1) A bias setting section for selectively determining different first and second bias levels depending on whether the input video signal, binary video signal or analog video signal is input; a first modulator that receives the binary video signal and modulates the semiconductor laser based on the bias level of vJ1; and a second modulator that receives the analog video signal and modulates the semiconductor laser based on the second bias level. 1. A semiconductor laser modulation circuit, characterized in that a multiplier is configured with a modulation section, and a semiconductor laser is modulated by the output of the +1+n multiplier. (2) The bias setting unit is configured to set the bias setting unit to the first and second bias settings based on a monitor signal of the optical output of the semiconductor laser.
2. A semiconductor laser modulation circuit according to claim 1, wherein the bias level is formed and the formed bias level is selected based on a command signal of the video signal.