JP2003271259A - Clock transmission device and image-forming device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely suppress EMI noise in a clock transmission device 61 that divides a clock CLK1 into a clock CLK2 with a frequency divider 14, and transmits it so as to suppress the EMI noise for sharing the clock CLK1 without frequency fluctuations between devices 11, 21. <P>SOLUTION: A frequency dividing ratio of the frequency divider 14 is made to be variable and is set with a setting circuit 19, and the information on the frequency dividing ratio is also transmitted to a multiplying circuit 22. Accordingly, even if the spectrum of EMI noise emitted from a clock transmission channel 16 differs from a designed value, the EMI noise level of the clock transmission channel 16 in a state in which circuits are actually connected and the clock CLK1 is in transit is measured, and the frequency dividing ratio is adjusted so that a favorable spectrum is obtained, thereby permitting to surely suppress the EMI noise. In addition, the frequency dividing ratio can be easily adjusted. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EMI countermeasure for a device that transmits a clock for common use between circuits, and more particularly to a clock whose frequency fluctuation is not allowed, and moreover, such a frequency fluctuation. The present invention relates to an image forming apparatus that uses a clock that is not allowed.

[0002]

2. Description of the Related Art In recent years, the frequency of a clock generated by a crystal oscillator or the like has become high, and EMI (Electromagnetic Inte
rference) is needed. And EMI
As for noise, some measures can be taken against the circuit board with a shield plate, etc., but if the clock transmission line is routed to use a common clock between the circuits separated from each other, However, it is not easy to take sufficient measures due to leakage from the gap of the shield housing.

Particularly, in an image forming apparatus such as a copying machine or a facsimile machine, the reference clock of the CCD for reading the original image is often structurally arranged over a plurality of substrates, and the frequency itself is relatively large. Since the cost is high, there are frequent cases where EMI becomes a problem.

On the other hand, the EMI noise level is a value obtained by integrating the electromagnetic wave received by the antenna for each frequency component for a predetermined time. Therefore, in the conventional EMI countermeasure, the frequency of the clock is constantly changed to be specified. A spread spectrum technique is used to suppress the radiation noise at the frequency of. The EMI countermeasure by the spread spectrum is described in USP. 5,488,627.

However, although such a conventional technique can be applied to a circuit such as a microprocessor that allows a certain degree of fluctuation in the clock frequency, the image forming apparatus described above has a frequency fluctuation. There is a problem that it is not allowed and cannot be applied.

That is, for example, if the clock frequency changes during reading, the charge accumulation time differs depending on the read area, resulting in uneven density. Further, if the timings are not exactly matched, such as between the polygon mirror and the CCD, the formed image will be distorted or uneven.

Therefore, in another conventional technique for solving such a problem, the clock frequency in the clock transmission line is restored by dividing the clock to be transmitted on the transmitting side and multiplying it by the receiving side to restore the clock. Has been proposed to reduce the EMI noise level.

[0008]

However, in the prior art as described above, the situation of routing in the circuit-mounted device,
Depending on environmental conditions such as temperature and individual differences in equipment,
There is a problem that the spectrum of EMI noise does not always match the design value in mass production.
That is, there is a problem that the EMI noise cannot be surely suppressed at the set transmission clock frequency.

An object of the present invention is to provide a clock transmission device capable of reliably suppressing EMI noise and an image forming apparatus using the same.

[0010]

A clock transmission device of the present invention is provided on a transmission side in a device for transmitting a first clock having no frequency fluctuation so that the first clock is commonly used between circuits. And a dividing circuit with variable dividing ratio,
A clock transmission line for transmitting a second clock obtained by dividing the first clock by the frequency dividing circuit, and a frequency division ratio information transmission line for transmitting information on a frequency division ratio in the frequency dividing circuit. When,
A multiplying circuit which is provided on the receiving side and restores the second clock from the clock transmission line to the first clock by using the information of the division ratio from the division ratio information transmission line. Is characterized by.

According to the above arrangement, when taking measures against EMI noise in the clocks routed to match the timing between the circuits, it is necessary to exactly match the timing between the circuits as in the image forming apparatus. However, in an application where the method of suppressing EMI noise due to spread spectrum that causes frequency fluctuation cannot be used, the clock is frequency-divided and transmitted from the transmission side by the frequency dividing circuit,
On the receiving side, by recovering the clock with a multiplication circuit,
The frequency of the clock transmitted through the clock transmission line is reduced,
The EMI noise on the clock transmission line is suppressed.

Then, the frequency division ratio in the frequency division circuit is made variable, and the information of the frequency division ratio is transmitted through the frequency division ratio information transmission line. Therefore, even if the spectrum of the EMI noise emitted from the clock transmission line is different from the design value due to the conditions of routing in the circuit-equipped equipment and the environmental conditions such as temperature, it is possible to actually connect the circuits. The EMI noise can be surely suppressed by measuring the EMI noise level of the clock transmission line in the state where the clock is transmitted and adjusting the frequency division ratio so as to obtain a preferable spectrum.

Further, even if the frequency division ratio is arbitrarily adjusted, the information of the frequency division ratio is transmitted to each frequency multiplication circuit via the frequency division ratio information transmission line, so that it is not necessary to set the frequency division circuit. Can be This makes it possible to easily adjust the division ratio when transmitting a clock from one transmitting circuit to many receiving circuits.

Further, in the clock transmission device of the present invention, the frequency division ratio is set in units of two.

According to the above configuration, since the harmonic components of the rectangular wave clock appear in odd orders, the harmonic components of the second clock obtained by frequency division are different from the first clock of the fundamental wave. The frequencies are different, and the spectrum of EMI noise can be spread.

Furthermore, in the clock transmission device of the present invention, the frequency dividers and the frequency dividers in the frequency multipliers are configured so that they can be switched stepwise to the frequency division ratio of the factorial unit of 2. And

According to the above arrangement, the frequency divider in the frequency dividing circuit and the frequency multiplying circuit can be constituted by only the binary counter, and the constitution can be simplified.

Further, the clock transmission device of the present invention is characterized by further comprising a frequency division ratio setting circuit for changing the frequency division ratio of the frequency division circuit while the on-board equipment is not operating.

According to the above configuration, when it is determined that the device in which the clock transmission device is mounted is not operating,
The frequency division ratio setting circuit changes the frequency division ratio of the frequency division circuit.

Therefore, with respect to the second clock, the EMI noise can be suppressed by the same method as the spread spectrum, and the EMI noise level represented by the integrated value of the electromagnetic waves of each frequency over a predetermined time can be expressed as The stability of the first clock supplied to each circuit can be suppressed without lowering.

Furthermore, in the clock transmission device of the present invention, when transmitting the first clock to a plurality of circuits, the receiving side circuit is grouped into one or a plurality, and the transmitting side frequency dividing circuit is provided for each group. And transmitting the second clocks having different frequency division ratios.

With the above arrangement, the EMI noise level of the entire circuit sharing the first clock can be lowered. Further, it is possible to set an optimum frequency division ratio according to the environment for each circuit on the receiving side.

An image forming apparatus of the present invention is characterized by using any one of the above clock transmission devices.

According to the above arrangement, the image forming apparatus must strictly match the timing, such as between the polygon mirror and the image reading element, and uses the spread spectrum technique as a countermeasure for EMI. Since a circuit that cannot do so is mounted, the above method is particularly effective as a countermeasure against EMI.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing an electrical configuration of a clock transmission device 1 according to the first embodiment of the present invention.
The clock transmission device 1 includes the polygon mirror and CC.
In order to share the clock CLK1 generated by the clock oscillation circuit 12 and having no frequency fluctuation between the devices 11 and 21 of the respective units of the image forming apparatus whose timings need to be exactly matched, such as with D. Used.

On the device 11 side, which is the transmitting side, the clock CLK1 generated by the clock oscillation circuit 12 is generated.
Are directly supplied to the device 11 via the buffer 13. Further, the clock CLK1 is frequency-divided by the frequency divider 14 into the clock CLK2 at the frequency division ratio N, and then output from the transmission buffer 15 to the clock transmission line 16.

Correspondingly, the receiving side is generally provided with the device 21 and a multiplication circuit 22 for restoring the clock CLK1 from the clock CLK2. The multiplier circuit 22 includes a VCO (voltage controlled oscillator) 2
3, a frequency divider 24, a phase comparator 25, and a loop filter 26 are included in a normal phase-locked loop circuit. The clock CLK1 generated by the VCO is frequency-divided by the frequency division ratio N in the frequency divider 24 and applied to the phase comparator 25. The phase comparator 25 is
The clock CLK2 from the clock transmission line 16 input via the reception buffer 27 and the frequency-divided signal of the clock CLK1 divided by the frequency divider 24 are compared with each other to correspond to the phase difference between them. The generated error signal is output to the loop filter 26. The loop filter 26 smoothes the error signal from the phase comparator 25 into a DC voltage and supplies it to the VCO 23.

Therefore, the recovered clock CLK1 from the VCO 23 has a frequency N times that of the clock CLK2 from the clock transmission line 16 and the clock CL
It becomes a signal whose phase is synchronized with K2, and thereby becomes a signal whose phase is synchronized with the same frequency as the clock CLK1 generated by the clock oscillation circuit 12 (actually, the clock transmission line 16 and the frequency dividers 14, 24). It is difficult to completely compensate the delay of the clock oscillation circuit 12 and the phase of the output of the clock oscillation circuit 12 and the output of the VCO 23, but
In many cases, the purpose of transmitting the clock can be achieved only by regulating the fluctuations of both by the PLL and matching the frequencies. In this way, the frequency of the clock CLK2 passing through the clock transmission line 16 can be reduced and EMI noise can be suppressed. The clock CLK1 restored by the multiplication circuit 22 is supplied to the device 21 via the buffer 28.

It should be noted that, in the present invention, the frequency divider 1
The frequency division ratio N of 4 and 24 is variable, and the frequency divider 1
The information of the frequency division ratio N in 4 is output from the transmission buffer 17 to the frequency division ratio information transmission line 18, and the information of the frequency division ratio N received by the reception buffer 29 is set in the frequency divider 24. Is. Regarding the frequency divider 14 on the transmission side, the frequency division ratio N
A setting circuit 19 for setting the frequency division ratio is provided, and the frequency divider 14 performs frequency division at the set frequency division ratio N, and information of the frequency division ratio N is transmitted to the frequency division ratio information transmission line 18. It is transmitted to the frequency divider 24 via the same, and the same frequency division ratio N is used on the receiving side.

From the setting circuit 19, while measuring the actual EMI noise spectrum, the dividing ratio N is adjusted so as to obtain the most preferable spectrum. Therefore, even if the spectrum of the EMI noise emitted from the clock transmission line 16 is different from the design value due to the circumstances of the routing inside the circuit-equipped device and the environmental conditions such as temperature, the EMI noise is surely suppressed. can do.

Further, even if the dividing ratio N is arbitrarily adjusted,
Since the information of the frequency division ratio N is transmitted to the frequency multiplication circuit 22 via the frequency division ratio information transmission line 18, it is not necessary to set the frequency multiplication circuit 22. Accordingly, when transmitting the common clock CLK1 from one transmitting circuit to many receiving circuits, the division ratio N can be easily adjusted.

The clock CLK1 does not have to have the same frequency, corresponding to the difference in clock frequency of the devices 11 and 21 of each part on the transmitting side and the receiving side, and one frequency is a predetermined frequency of the other frequency. It suffices that they are doubled and the phases match (or fluctuations in the phase difference are suppressed).

FIG. 2 shows the second embodiment of the present invention.
The explanation is based on the following.

FIG. 2 is a block diagram showing an electrical configuration of the clock transmission device 31 according to the second embodiment of the present invention. The clock transmission device 31 is similar to the clock transmission device 1 described above, and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that in this clock transmission device 31, the frequency division ratio N of the frequency divider 32 on the transmission side and the frequency divider 34 of the multiplication circuit 33 on the reception side is set in units of two. .

Therefore, since the harmonic component of the clock CLK2a of the rectangular wave transmitted through the clock transmission line 16 appears in an odd order, the harmonic component of the clock CLK2a is converted into the fundamental wave by such a configuration. EM with a frequency different from the frequency of a certain clock CLK1
The spectrum of I noise can be spread.

FIG. 3 shows the third embodiment of the present invention.
The explanation is based on the following.

FIG. 3 is a block diagram showing the electrical configuration of the clock transmission device 41 of the third embodiment of the present invention. The clock transmission device 41 is similar to the clock transmission device 31 described above, and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that in the clock transmission device 41, the frequency divider 42 on the transmission side and the frequency divider 44 of the multiplication circuit 43 on the reception side are constituted by binary counters. Correspondingly, each tap of the binary counter is That is, selectors 45 and 46 for selecting the frequency-divided signal extracted from are provided.

The selector 45 outputs the frequency-divided signal extracted from each tap of the binary counter of the frequency divider 42,
In response to the frequency division ratio N set by the setting circuit 49,
Alternatively, it is selected and output as the clock CLK2a. The information of the division ratio N from the setting circuit 49 is also transmitted to the selector 46 via the transmission buffer 17, the division ratio information transmission line 18 and the reception buffer 29, and the selector 46 is a binary of the divider 44. The frequency-divided signal taken out from each tap of the counter is selectively selected and supplied to the phase comparator 25.

Therefore, similarly to the frequency dividers 32 and 34, the frequency division ratios N of the frequency dividers 42 and 44 are set in the unit of factorial of 2, and the frequency dividers 42 and 44 are only binary counters. Can be configured, and the configuration can be simplified.

FIG. 4 shows the fourth embodiment of the present invention.
The explanation is based on the following.

FIG. 4 is a block diagram showing an electrical configuration of a clock transmission device 51 according to the fourth embodiment of the present invention. The clock transmission device 51 is similar to the above-described clock transmission device 41, and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that in the clock transmission device 51, the device 52 on the reception side operates using the clock CLK1 from the multiplication circuit 53 and transmits a signal indicating the operation / non-operation to the setting circuit 59, When the setting circuit 59 determines that the device 52 is not operating, it changes the frequency division ratio N to change the frequency of the clock CLK2a.

In order to transmit the enable signal indicating the operation / non-operation from the device 52, the transmission buffer 5
6, enable signal transmission path 57 and reception buffer 58
Is provided, and the phase comparator 5 in the multiplication circuit 53 is provided.
5 responds to the enable signal to stop the phase comparison operation during the frequency change.

Therefore, with respect to the clock CLK2a in the clock transmission line 16, EMI noise can be suppressed by a method similar to the above-described spread spectrum, and is represented by an integrated value of electromagnetic waves of each frequency over a predetermined time. The EMI noise level can be suppressed without lowering the stability of the clock CLK1 supplied to the device 52.

FIG. 5 shows the fifth embodiment of the present invention.
The explanation is based on the following.

FIG. 5 is a block diagram showing an electrical configuration of a clock transmission device 61 according to the fifth embodiment of the present invention. The clock transmission device 61 is similar to the clock transmission device 41 described above. It should be noted that in the clock transmission device 61, the receiving side circuits are grouped into one or a plurality of groups, and mutually different clocks are transmitted to these respective circuits. Note that in FIG. 6, for simplification of the drawing, there are two groups, and the receiving side circuit 6 is provided in each group.
The number 2 is provided one by one, and the configurations corresponding to the two are denoted by the same reference numerals with suffixes a and b.

Therefore, the frequency-divided signals extracted from the taps of the binary counter of the frequency divider 42 on the transmission side are commonly supplied to the selectors 45a and 45b.
45b selects the frequency-divided signal corresponding to the frequency division ratios N different from each other set by the setting circuit 69, and outputs the clock CLK.
2a and CLK2b are output. The clock CLK
2a and CLK2b are transmission buffers 15a and 15b, clock transmission lines 16a and 16b, and a reception buffer 27.
It is given to the multiplication circuits 43a and 43b via a and 27b. Further, the information of the frequency division ratio N in the setting circuit 69 includes the transmission buffers 17a and 17b, the frequency division ratio information transmission line 18a,
It is given to the frequency multiplying circuits 43a and 43b via 18b and the receiving buffers 29a and 29b.

In this way, the clocks CLK1a and CLK1b are restored in the frequency multiplication circuits 43a and 43b and supplied to the devices 21a and 21b. The clock CLK1
The frequencies of a and CLK1b may be the same, or different from each other as described above, and in order to match the timing between the devices 11; 21a and 21b, the phases thereof match each other. (Or, the fluctuation of the phase difference is suppressed).

With this configuration, the EMI noise level of the entire circuit sharing the clock CLK1 can be lowered. In addition, the circuits 62a on the receiving side,
It is possible to set an optimum frequency division ratio according to the environment for each 62b.

Clock transmission device 1, 31, 4 of the present invention
When the clock CLK1 is shared as described above, the reference numerals 1, 51 and 61 are required to exactly match the timing of the clock CLK1. Therefore, the image forming apparatus that cannot use the spread spectrum method for EMI countermeasures. Is particularly effective.

[0051]

As described above, according to the clock transmission apparatus of the present invention, when the clocks routed to match the timing between the circuits are subjected to EMI noise countermeasures, the clocks transmitted between the circuits as in the image forming apparatus. In applications where it is necessary to exactly match the timings of the above and the method of spread spectrum that causes frequency fluctuation cannot be used, the clock is frequency-divided and transmitted from the transmission side, and is multiplied and restored at the reception side. At the same time, the frequency division ratio is made variable, and information on the frequency division ratio is also transmitted.

Therefore, the frequency of the clock transmitted through the clock transmission line is lowered, and the E on the clock transmission line is reduced.
It is possible to suppress MI noise, and even if the spectrum of EMI noise emitted from the clock transmission line is different from the design value due to the conditions of routing inside the circuit-equipped device and environmental conditions such as temperature, The EM noise level of the clock transmission line is measured in a state where the circuits are actually connected and clocks are transmitted, and the frequency division ratio is adjusted to obtain a preferable spectrum.
It is possible to reliably suppress I noise.

Further, even if the frequency division ratio is arbitrarily adjusted, the information of the frequency division ratio is transmitted to each frequency multiplication circuit through the frequency division ratio information transmission line, so that setting in the frequency multiplication circuit is unnecessary. Can be This makes it possible to easily adjust the division ratio when transmitting a clock from one transmitting circuit to many receiving circuits.

Further, in the clock transmission device of the present invention, the frequency division ratio is set in the unit of factorial of 2, as described above.

Therefore, since the harmonic component of the rectangular wave clock appears in an odd order, the harmonic component of the clock obtained by frequency division has a frequency different from that of the fundamental wave clock.
The spectrum of EMI noise can be spread.

Furthermore, in the clock transmission device of the present invention, as described above, the frequency divider can be stepwise switched to the frequency division ratio of the factorial unit of 2.

Therefore, the frequency divider in the frequency dividing circuit and the frequency multiplying circuit can be configured by only the binary counter, and the configuration can be simplified.

Further, as described above, the clock transmission device of the present invention changes the frequency division ratio while the on-board equipment is not operating.

Therefore, for the transmitted clock,
The EMI noise can be suppressed by the same method as the spread spectrum, and the EMI noise level represented by the integrated value of the electromagnetic waves of each frequency over a predetermined time can be set to the stability of the clock of the fundamental wave supplied to each circuit. Without lowering
Can be suppressed.

Furthermore, in the clock transmission device of the present invention, as described above, when transmitting a clock to a plurality of circuits, the receiving side circuits are grouped into one or a plurality of groups,
The frequency dividing circuit on the transmission side transmits clocks having different frequency division ratios for each group.

Therefore, the EMI noise level of the entire circuit sharing the clock can be lowered. Further, it is possible to set an optimum frequency division ratio according to the environment for each circuit on the receiving side.

Further, the image forming apparatus of the present invention uses any one of the above clock transmission devices as described above.

Therefore, in the image forming apparatus, it is necessary to exactly match the timing, such as between the polygon mirror and the image reading element, and a circuit in which the spread spectrum technique cannot be used as an EMI countermeasure. Is installed and is particularly effective.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a clock transmission device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of a clock transmission device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing an electrical configuration of a clock transmission device according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing an electrical configuration of a clock transmission device according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing an electrical configuration of a clock transmission device according to a fifth embodiment of the present invention.

[Explanation of symbols]

1, 31, 41, 51, 61 Clock transmission device 11, 21, 21a, 21b, 52 Device 12 Clock oscillation circuit 13, 28, 28a, 28b Buffer 14, 24, 32, 34, 42, 44 Frequency divider 15, 15a, 15b, 17, 17a, 17b, 56
Transmission buffer 16, 16a, 16b Clock transmission line 18, 18a, 18b Dividing ratio information transmission line 19, 49, 59, 69 Setting circuit 22, 33, 43, 43a, 43b, 53 Multiplying circuit 23 VCO 25, 55 Phase comparison Device 26 loop filter 27, 27a, 27b, 29, 29a, 29b, 58
Reception buffers 45, 46, 45a, 45b Selector 57 Enable signal transmission paths 62a, 62b Reception side circuit CLK1 clock (first clock) CLK2, CLK2a, CLK2b clock (second)
Clock)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuuki Kai             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Kiyoshi Inoue             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Yoshiomi Hamano             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Akihiko Taniguchi             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Koichi Tsunoda             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Hikaru Tamagaki             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 5B079 BA20 BC06 CC20 DD03                 5J106 AA04 BB04 CC01 CC21 CC41                       CC53 KK22

Claims (6)

[Claims] 1. An apparatus for transmitting a first clock having no frequency fluctuation for common use between circuits, wherein a frequency dividing circuit provided on the transmission side and having a variable division ratio, A clock transmission line for transmitting a second clock obtained by dividing the first clock by the frequency dividing circuit, and a frequency division ratio information transmission line for transmitting information on a frequency division ratio in the frequency dividing circuit. And a multiplication circuit which is provided on the reception side and restores the second clock from the clock transmission line to the first clock by using the frequency division ratio information from the frequency division ratio information transmission line. A clock transmission device comprising: 2. The clock transmission device according to claim 1, wherein the division ratio is set in units of factorials of two. 3. The clock transmission according to claim 2, wherein the frequency dividers and the frequency dividers in the frequency multiplication circuit are configured to be capable of switching in stages to the frequency division ratio of the factorial unit of 2. apparatus. 4. The clock transmission according to claim 1, further comprising a frequency division ratio setting circuit that changes a frequency division ratio of the frequency division circuit while the onboard equipment is not operating. apparatus. 5. When transmitting the first clock to a plurality of circuits, the receiving side circuits are grouped into one or a plurality, and the transmitting side frequency dividing circuits have different frequency division ratios for each group. The clock transmission device according to claim 1, wherein the clock transmission device transmits two clocks. 6. An image forming apparatus using the clock transmission device according to any one of claims 1 to 5.