Modulators – Pulse or interrupted continuous wave modulator – Pulse width modulator
Reexamination Certificate
2000-12-21
2003-03-25
Kinkead, Arnold (Department: 2817)
Modulators
Pulse or interrupted continuous wave modulator
Pulse width modulator
C375S238000, C327S172000, C377S066000, C377S094000, C377S118000
Reexamination Certificate
active
06538523
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multi-channel pulse width modulation apparatus and a down counter, and more specifically, to a multi-channel pulse width modulation apparatus having high operational reliability, and a down counter used for the multi-channel pulse width modulation apparatus.
Conventionally, in order to increase the speed of exposure processing, an image recording apparatus such as a printer or the like which exposes an image on a photosensitive material on the basis of image data, and transfers and outputs onto regular paper the image recorded on the photosensitive material by the exposure, is provided with a plurality of light emission elements such as an LED chip or an LD used for the exposure and performs exposure corresponding to a plurality of pixels at the same time by the plurality of light emission elements.
This type of image recording apparatus controls each light emission of the plurality of light emission elements by an individual pulse width modulation signal (hereinafter, referred to as a “PWM signal”), and the apparatus is generally provided with a multi-channel pulse width modulation apparatus which can generate the same number of PWM signals as that of the light emission elements at the same time.
In a multi-channel pulse width modulation apparatus provided in such an image recording apparatus, either one of the following two methods has been adopted as a setting method of a pulse output timing of each channel, as shown in FIG.
13
: a method in which each pulse of the PWM signal is started synchronously to a pixel clock showing one cycle when image recording for one pixel is carried out in a main scanning direction (hereinafter, referred to as an “edge starting output”), and a method in which each pulse is output so that a center of each pulse of the PWM signal is positioned in a vicinity of a central position between each pulse of the pixel clock (hereinafter, referred to as a “center starting output”).
In such a multi-channel pulse width modulation apparatus, there has been the problem that sometimes when PWM signals of a plurality of channels start at the same time, a large amount of current flows at the same time into a circuit for generating the PWM signals and the voltage of the power source for supplying the current becomes unstable, whereby operational reliability of the multi-channel pulse width modulation apparatus is considerably deteriorated.
With respect to a multi-channel pulse width modulation apparatus that performs edge starting output, Japanese Patent Application Laid-Open (JP-A) No. 9-23145 discloses as a technology for eliminating the aforementioned problem a technology in which the starting time of each pulse of the PWM signals is fixedly shifted between each channel. However, with respect to a multi-channel pulse width modulation apparatus that performs center starting output, there is no effective technology. In this case, the problem that operational reliability of the multi-channel pulse width modulation apparatus may be considerably deteriorated has been unavoidable.
In other words, in the case of edge starting output, simultaneous starting of the PWM signals of the plurality of channels can be avoided by fixedly shifting the starting time of the PWM signal for each channel by one reference clock, as shown in FIG.
14
A.
hence, in the case of center starting output, when the image data corresponding to each PWM signal of, for example, channels
1
,
2
and
3
is
2
,
2
and
6
, respectively, since the image data of channel
1
and channel
2
are equivalent, the start of the PWM signals of channel
1
and channel
2
will be simultaneous in an ordinary center starting output.
Therefore, when the PWM signals are generated so that the center of the pulse of the PWM signal in each channel is shifted between each channel by one standard clock, as shown in
FIG. 14B
, the start of each PWM signal of channel
1
and channel
2
is shifted by one standard clock, but the start of each PWM signal of channel
1
and channel
3
becomes simultaneous.
When this phenomenon of simultaneous start up occurs in a plurality of channels, the problem that operational reliability may be considerably deteriorated occurs.
SUMMARY OF THE INVENTION
In order to solve the above problem, a first object of the present invention is to provide a multi-channel pulse width modulation apparatus which can prevent a decline in operational reliability resulting from a simultaneous start of pulse width modulation signals, and a second object is to provide an inexpensive down counter which can be used for the multi-channel pulse width modulation apparatus.
In order to achieve the first object, a multi-channel pulse width modulation apparatus according to a first aspect of the present invention comprises: a plurality of pulse width modulation signal generators which respectively generate a pulse width modulation signal, and when a timing signal showing a shifted amount of the generation timing of the pulse width modulation signal is inputted thereto, generate a pulse width modulation signal in which the generation timing thereof is shifted corresponding to the timing signal; and a determination section that determines whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generators exceed a predetermined number and become effective at substantially the same time, and on the basis of the results of the determination, generates the timing signals so that the number of pulse width modulation signals that become effective at substantially the same time becomes no greater than the predetermined number, and outputs the timing signals to a corresponding pulse width modulation signal generation section.
According to the multi-channel pulse width modulation apparatus of the first aspect of the present invention, the pulse width modulation signals are respectively generated by the plurality of pulse width modulation signal generation sections, and when the timing signal showing the shifted amount of each generation timing is inputted, pulse width modulation signals whose generation timing is shifted corresponding to the timing signal are generated.
On the other hand, whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generation sections exceed a predetermined number and become effective at substantially the same time is determined by the determination section. On the basis of the results of the determination, the timing signal is generated so that the number of pulse width modulation signals which become effective at substantially the same time becomes no greater than the predetermined number, and is output to the corresponding pulse width modulation signal generation section. By “become effective” used herein is meant that the pulse width modulation signal “rises” when the pulse width modulation signal is generated in the positive logic, and that the pulse width modulation signal “drops” when the pulse width modulation signal is generated in the negative logic.
Accordingly, the pulse width modulation signals generated respectively by the plurality of pulse width modulation signal generation sections are generated so that the number of pulse width modulation signals that become effective at substantially the same time is no greater than the predetermined number. The predetermined number preferable has as an upper limit a value within a range in which operational reliability of the apparatus is permitted.
In this manner, according to the multi-channel pulse width modulation apparatus of the first aspect of the present invention, whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generation sections exceed a predetermined number and become effective at substantially the same time is determined, and on the basis of the results of the determination, the number of pulse width modulation signals that become effective at substantially the same time is made no greater than the predetermined num
Sugita Yukio
Toyoda Shinjiro
Toyoda Takashi
Fuji Photo Film Co. , Ltd.
Kinkead Arnold
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