JP2001166844A - Clock frequency transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a clock frequency transmission system capable of reducing EMI noises as much as possible. SOLUTION: In the case of transmitting clock frequency from an oscillation circuit 1 to plural function block circuits 3 in the clock frequency transmission system built in an electronic circuit, a clock frequency signal having only a reference frequency and not including a higher harmonic component or including little higher harmonic component is transmitted from the oscillation circuit 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a clock frequency transmission system, and more particularly, to a clock frequency transmission system capable of reducing EMI (electromagnetic wave) noise.

[0002]

2. Description of the Related Art To operate an electronic circuit, a basic clock is usually required. This basic clock is usually circulated in the circuit as it is. The clock is a rectangular wave, and its frequency component includes components from a low frequency to a high frequency. Therefore, the transmission of the clock may cause a problem that the wiring between the circuits becomes an antenna, and a harmonic component generated by Nobushige Samejima from the clock enters another circuit.

[0003] Generally, the point of EMI countermeasures for equipment is:
The purpose is to reduce harmonic components of a clock signal required for circuit operation. Accordingly, at present, a spread spectrum clock signal focused on this clock signal has been used as a countermeasure.

[0004]

In the operation of a logic circuit, a clock signal is required as described above. From the oscillation circuit to the functional block circuit, it is sufficient that only the frequency component of the clock can be transmitted. It need not be a clock signal containing waves. In particular, a clock line from an oscillation circuit or a clock line to another substrate is often relatively long, which is a major cause of unnecessary radiation.

[0005] The present invention has been made in view of such a problem, and an object of the present invention is to provide a clock frequency transmission system capable of reducing EMI noise as much as possible.

[0006]

(1) The invention according to claim 1 is a clock frequency transmission system in an electronic circuit, wherein the clock frequency is transmitted from an oscillation circuit to a plurality of functional block circuits. The oscillator circuit transmits a clock frequency signal containing only a fundamental frequency and containing no or less harmonic components.

[0007] With this configuration, it is possible to make the transmission waveform propagating between the functional block circuits hardly contain a harmonic component, so that EMI noise can be reduced as much as possible.

(2) The invention according to claim 2 is a clock frequency transmission system between circuit boards in a device, wherein the clock frequency is transmitted from the oscillation circuit to a plurality of circuit boards. It is characterized by transmitting a clock frequency signal containing only a fundamental frequency and containing no or few harmonic components.

With this configuration, it is possible to make the transmission waveform propagating between the circuit boards hardly contain any harmonic components, so that EMI noise can be reduced as much as possible.

(3) A third aspect of the present invention is characterized in that a sine wave or a cosine wave is used as a signal wave containing only the fundamental frequency and containing no or few harmonic components.
According to this configuration, by using a sine wave or a cosine wave as the transmission waveform, it is possible to propagate a waveform having almost only the frequency component.

(4) The invention according to claim 4 is characterized in that the transmission of the clock frequency uses a differential circuit. With this configuration, only the frequency signal component can be transmitted.

(5) The invention according to claim 5 is characterized in that in transmitting the clock frequency, a reference voltage required for generating a rectangular wave is supplied in pairs with a sine wave or a cosine wave. With this configuration, a rectangular wave can be obtained using the transmitted signal in the functional block circuit or the circuit board that has been received using the pair of signals whose waveforms have been transmitted.

(6) The invention according to claim 6 is characterized in that in transmitting the clock frequency, a reference voltage required for generating a rectangular wave is generated in the functional block circuit. With this configuration, a rectangular wave can be obtained from the clock frequency signal using the reference voltage generated in the function block circuit.

(7) According to a seventh aspect of the present invention, in transmitting the clock frequency, a reference voltage required for generating a rectangular wave is generated in the circuit board. With this configuration, using the reference voltage generated in the circuit board,
A rectangular wave can be obtained from the clock frequency signal.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The figure shows a configuration in a certain electronic circuit. In the figure, 1 is an oscillation circuit for outputting a sine wave or a cosine wave of a specific frequency, 2 is a transmission line for transmitting the output of the oscillation circuit 1, and 3 is a functional block circuit connected to the transmission line 2. . As each functional block circuit 3, for example, an ASIC circuit is used. Reference numeral 4 denotes a waveform shaping circuit provided at the input stage of each functional block circuit 3. The waveform shaping circuit 4 converts the input sine wave or cosine wave into a rectangular clock.

To transmit a sine wave or a cosine wave,
Switching circuits such as logic circuits are not feasible and require analog circuits. Therefore, the oscillation circuit 1
To the transmission line 2 are realized by analog circuits. The operation of the system configured as described above will be described below.

The oscillation circuit 1 outputs a sine wave or cosine wave clock frequency signal of a specific frequency. The clock frequency signal is input to each functional block circuit 3 via the transmission line 2. According to the present invention, up to the entrance of each functional block circuit 3, since the sine wave or the cosine wave hardly contains the harmonic component, the harmonic does not diverge to the outside. Therefore, according to the present invention, it is possible to make the transmission waveform propagating between the functional block circuits hardly contain the higher harmonic components, so that the EMI noise can be reduced as much as possible.

The sine wave or cosine wave arriving at each functional block 3 is converted by the waveform shaping circuit 4 into a rectangular clock. Hereinafter, each functional block 3 operates as a logic circuit so as to realize each function using the basic clock. According to the present invention, since the transmission line 2 does not include harmonics, the transmission line 2 does not become an antenna and does not hinder the operation of each functional block 3.

In the above embodiment, the operation in each electronic circuit has been described, but the present invention is not limited to this. For example, the present invention can be similarly applied to a case where a basic clock is input to a plurality of circuit boards in a device. That is, an oscillating circuit that oscillates a sine wave or a cosine wave is provided at a specific place, and the output of the oscillating circuit is supplied to each circuit board via a transmission line to provide a clock frequency signal. An analog sine wave or cosine wave rides on the transmission line and is input to each circuit board. In each circuit board, a waveform shaping circuit for converting a sine wave or a cosine wave into a digital clock is provided at the input stage. By doing so, it is possible to make the transmission waveform propagating between the circuit boards hardly contain a harmonic component, so that EMI noise can be reduced as much as possible.

In the above-described embodiment, a sine wave or a cosine wave is used as a signal wave having only the fundamental frequency and containing no or little harmonic component. In this way, it is possible to propagate a waveform of almost only the frequency component.

FIG. 2 is a diagram showing a first transmission method of the present invention. 1 are denoted by the same reference numerals.
In this example, a sine wave or a cosine wave is put on the transmission line 2 via the analog buffer amplifier 10. By receiving the sine wave or the cosine wave by the buffer amplifier, the output impedance can be reduced and the noise characteristics can be improved.

At the same time, the reference voltage is transmitted via the signal line 11. Reference numeral 12 denotes a reference voltage generation circuit for generating a reference voltage. In this example, a reference voltage is generated using a Zener diode D. By transmitting the reference voltage from one place, it is not necessary to generate the reference voltage independently in another function block circuit or circuit board, and the circuit configuration is simplified. At the same time, since all the reference voltages used in each circuit are common, almost the same clock (clock having the same duty ratio) can be generated as the reference clock, which is convenient. It is preferable that the reference voltage is also transmitted via the buffer amplifier in terms of noise resistance.

Reference numeral 13 denotes a comparator which generates a rectangular clock by comparing the clock frequency signal with a reference voltage. FIG. 3 is a time chart showing the operation of the first transmission method, showing the operation of the comparator. By comparing the clock frequency signal as shown in (a) with the reference voltage TH, a voltage comparator operation is performed such that when the clock frequency signal is higher than the reference voltage, the voltage comparator signal becomes "H" level. As a result, a basic clock (rectangular wave) as shown in (b) can be obtained.

FIG. 4 is an explanatory diagram of a second transmission method according to the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals.
In this embodiment, when a sine wave is transmitted as a clock frequency signal, a cosine wave having a phase 180 ° different from that of the sine wave is transmitted as a pair.

The sine wave is transmitted to the transmission line 2 via the buffer amplifier 10, and the cosine wave is
, And is transmitted to the transmission line 5 through a cosine wave. Thus, both signals are transmitted in pairs. By performing differential transmission in this way, a stable output that is resistant to noise can be obtained.

FIG. 5 is a time chart showing the operation of the second transmission method according to the present invention. Here, in (a), f
1 is a sine wave and f2 is a cosine wave. If the comparator 13 of the input receiving unit is operated so as to be at “H” level only when f1> f2, a rectangular clock as shown in FIG.

According to this structure, a rectangular wave can be obtained by using a pair of signals transmitted in a waveform and using a signal transmitted in the received functional block circuit or the circuit board. According to this embodiment, since signals are differentially transmitted, a stable output that is resistant to noise can be obtained.

FIG. 6 is a diagram showing a third transmission method according to the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals.
In this method, the clock frequency signal and the reference voltage are transmitted in the method shown in FIG. 2, but only the clock frequency signal is transmitted, and the reference voltage is generated on each comparator side.

The input sine wave or cosine wave is sent to the transmission line 2 via the analog buffer 10. The transmission line 2 propagates a sine wave or a cosine wave. The comparator 13 compares the input sine wave or cosine wave with the reference voltage generated by the reference voltage generation circuit 15.
Here, the reference voltage generation circuit is configured using a Zener diode D.

FIG. 7 is a time chart showing the operation of the third transmission method according to the present invention. (A) is a sine wave or a cosine wave, and TH is a reference voltage. Comparator 13
An "H" level is output when the input signal is higher than the reference voltage TH. According to this method, it is necessary to provide a reference voltage generating circuit on the circuit side receiving the sine wave or the cosine wave, that is, in the functional block circuit or the circuit board, but the number of transmission lines is reduced accordingly.

According to this embodiment, a rectangular wave can be obtained from a clock frequency signal using a reference voltage generated in a functional block circuit or a circuit board. FIG. 8 is a diagram showing a fourth transmission method of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. This embodiment uses a zero level as a reference voltage.

The sine wave or cosine wave is sent to the transmission line 2 via the analog buffer 10. This clock frequency signal enters one input of the comparator 13 after being terminated by the capacitor C and the resistor R. The other input of the comparator 13 is grounded.

In the system configured as described above,
The sine wave or cosine wave transmitted through the transmission line enters the comparator 13. Since the other end of the comparator 13 is grounded, the input clock frequency signal is compared with the zero level.

FIG. 9 is a time chart showing the operation of the fourth transmission method according to the present invention. When a sine wave or a cosine wave as shown in FIG.
This input signal is compared with the zero level. Then, when it is larger than the zero level, it outputs the “H” level. As a result, a rectangular wave as shown in (b) is output.

[0035]

As described above, according to the present invention, the following effects can be obtained. (1) According to the first aspect of the invention, when transmitting a clock frequency from an oscillation circuit to a plurality of functional block circuits, a clock frequency signal containing only a fundamental frequency and containing no or little harmonic component is transmitted from the oscillation circuit. , It is possible to make the transmission waveform propagating between the functional block circuits hardly contain harmonic components.
MI noise can be reduced as much as possible.

(2) According to the second aspect of the present invention, when transmitting the clock frequency from the oscillation circuit to the plurality of circuit boards, the oscillation circuit outputs only the fundamental frequency and does not contain any harmonic component. By transmitting the frequency signal, it is possible to make the transmission waveform propagating between the circuit boards hardly contain a harmonic component, so that EMI noise can be reduced as much as possible.

(3) According to the third aspect of the present invention, a sine wave or a cosine wave is used as a signal wave containing only the fundamental frequency and containing no or few harmonic components.
By using a sine wave or a cosine wave as a transmission waveform, it is possible to propagate a waveform having almost only the frequency component.

(4) According to the invention of the fourth aspect, by using a differential circuit for transmitting the clock frequency, noise resistance can be improved and a stable output can be obtained.

(5) According to the fifth aspect of the invention, in transmitting the clock frequency, the reference voltage required for generating the rectangular wave is supplied as a pair with the sine wave or the cosine wave, so that the transmitted signal of the pair is transmitted. A rectangular wave can be obtained by using the transmitted signal in the functional block circuit or the circuit board received by using.

(6) According to the sixth aspect of the present invention, a reference voltage required for generating a rectangular wave is generated in the functional block circuit, so that a clock is generated using the reference voltage generated in the functional block circuit. A rectangular wave can be obtained from the frequency signal.

(7) According to the seventh aspect of the present invention, the reference voltage required for generating the rectangular wave is generated in the circuit board, and the clock frequency signal is generated using the reference voltage generated in the circuit board. Can obtain a square wave.

As described above, according to the present invention, it is possible to provide a clock frequency transmission system capable of reducing EMI noise as much as possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a first transmission method of the present invention.

FIG. 3 is a time chart showing an operation of the first transmission method of the present invention.

FIG. 4 is a diagram illustrating a second transmission method of the present invention.

FIG. 5 is a time chart showing the operation of the second transmission method of the present invention.

FIG. 6 is a diagram illustrating a third transmission method of the present invention.

FIG. 7 is a time chart showing the operation of the third transmission method of the present invention.

FIG. 8 is a diagram illustrating a fourth transmission method of the present invention.

FIG. 9 is a time chart showing the operation of the fourth transmission method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 oscillation circuit 2 transmission line 3 each functional block circuit 4 waveform shaping circuit

Claims (7)

[Claims] 1. A clock frequency transmission system in an electronic circuit, wherein when transmitting a clock frequency from an oscillation circuit to a plurality of functional block circuits, the oscillation circuit only includes a fundamental frequency and does not include a harmonic component. A clock frequency transmission system for transmitting a small number of clock frequency signals. 2. A system for transmitting a clock frequency between circuit boards in a device, wherein when the oscillator circuit transmits a clock frequency to a plurality of circuit boards, the oscillator circuit includes only a fundamental frequency and a harmonic component. A clock frequency transmission system for transmitting a clock signal with little or no clock frequency. 3. The clock frequency transmission system according to claim 1, wherein a sine wave or a cosine wave is used as the signal wave having only the fundamental frequency and containing no or few harmonic components. 4. The clock frequency transmission system according to claim 1, wherein the transmission of the clock frequency uses a differential circuit. 5. The clock frequency transmission system according to claim 1, wherein in transmitting the clock frequency, a reference voltage required for generating a rectangular wave is supplied in pairs with a sine wave or a cosine wave. . 6. The clock frequency transmission system according to claim 1, wherein in transmitting the clock frequency, a reference voltage required for generating a rectangular wave is generated in the functional block circuit. 7. The clock frequency transmission system according to claim 2, wherein in transmitting the clock frequency, a reference voltage required for generating a rectangular wave is generated in the circuit board.