JP3513455B2 - Electronics - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital clock circuit mounted on a signal transmission side printed wiring board and a signal reception side printed wiring board having a ground conductor. Electronic equipment connected on a conductive equipment housing by a cable including a signal wiring and a ground wiring. 2. Description of the Related Art Conventionally, printed wiring boards have been used in various electronic devices such as electric devices such as cameras and video cameras. In recent years, the functions of the various electronic devices described above have been advanced. In recent years, the printed circuit boards are divided into a plurality of parts, and the printed circuit boards are connected by cables to transmit signals. As described above, a digital clock circuit is mounted, and a signal transmission side printed wiring board and a signal reception side printed wiring board having a ground conductor are connected by a cable including signal wiring for signal transmission and ground wiring. In the configuration where the connection is made on the conductive equipment case, if the impedance characteristics of each connected printed wiring board and the signal line of the cable are different, reflection of the electric signal occurs due to the impedance characteristic mismatch, which is the radiation noise. This may cause generation or disturbance of the signal waveform. [0004] In order to solve this problem, various techniques have been conventionally proposed. For example, Japanese Patent Application Laid-Open No. 5-276
Japanese Patent Publication No. 97 discloses a configuration in which the impedance characteristic of a signal line of a cable, the load impedance of a transistor, and the receiving end impedance of a substrate are matched to reduce radiation noise. This technique aims to reduce radiation noise by matching the impedance of a signal line. However, in a mode in which a signal is transmitted by connecting a cable between two printed wiring boards on a conductive casing, the current flowing through the signal line is smaller than the current flowing through the signal line. The current flowing through the ground wiring may be a major cause of radiation noise. The characteristics of the current flowing through the ground wiring are determined by the impedance characteristics determined by the relationship between the ground wiring and the housing. However, the shape of the ground conductor of the printed wiring board and the shape of the ground conductor of the cable are greatly different. In addition, the impedance characteristics of the wiring board and the cable differ greatly, and the junction between the printed wiring board and the cable becomes a mismatch point of the impedance characteristics, the current flowing through the ground conductor is reflected, and the resonance peak of radiation noise caused by this is There is a possibility that a problem in terms of standards or practicality may occur. An object of the present invention is to provide a form in which a signal is transmitted between a signal transmission side printed wiring board and a signal reception side printed wiring board by a cable on a conductive equipment housing (ground), and a signal flowing through a ground conductor of the cable is provided. It is an object of the present invention to reduce radiated noise generated by reflection at a junction between a printed wiring board and a conductor of a cable, where a current is a mismatch point of impedance characteristics. According to the present invention, there is provided a signal transmitting side printed wiring board having a digital clock circuit, a signal conductor and a ground conductor, and a signal receiving circuit. In an electronic device in which a side printed wiring board is connected on a conductive device housing by a cable including a signal conductor and a ground conductor for signal transmission, a ground conductor of the cable determined by a correlation with the conductive device housing Where μ is the magnetic permeability and ε is the dielectric constant.
And the impedance characteristics determined by √ (μ / ε)
Determined by √ (μ / ε) of the ground conductor of the signal receiving side printed wiring board determined by the correlation with the conductive device housing
Impedance balance to balance impedance characteristics
Means, the impedance balancing means comprising:
And a high dielectric member disposed between the conductive device housing and
And the impedance of the high-dielectric-constant member
A configuration that adjusts the dance characteristics is adopted. Here, a mechanism for preventing noise emission in a mode in which a signal is transmitted by connecting a printed wiring board to which the present invention is applied with a cable will be considered. According to the present invention, there is provided a cable for connecting printed wiring boards such that the impedance characteristic between the ground of the printed wiring board and the conductive casing substantially matches the impedance characteristic between the cable ground and the conductive casing. By devising the distance between the printed circuit board and the conductive housing, reflection occurring at the junction between the ground of the printed wiring board and the cable ground is reduced, and radiation noise caused by the reflection is reduced. In general, when transmission lines having impedance characteristics different from those of Z0 and Z1 are connected, a part of an incident wave is reflected at a connection point of the transmission lines. At this time, the reflectance Γ is given by: ## EQU1 ## [Equation 1] represents the relationship between the reflectivity け る at which the current flowing from the conductor 1 to the conductor 2 at the junction of the signal line 1 having the impedance characteristic Z1 and the signal line 2 having the impedance characteristic Z2 and the impedance characteristic. The reflected wave generated at the junction of the transmission lines as described above is combined with the incident wave to become a standing wave, which causes radiation noise. Therefore, by configuring the reflectivity to be zero, that is, to satisfy Z1 = Z2 in [Equation 1], it is possible to reduce radiation noise caused by signal reflection. In general, impedance characteristics of a ground conductor of a printed wiring board and a ground conductor of a cable are as follows.
It is determined according to the positional relationship between each conductor and the conductive housing. Therefore, in the present invention, the impedance characteristic is adjusted by changing the state of either the ground conductor of the printed wiring board and the ground conductor of the cable, or both of the conductive housings, and the radiated noise caused by signal reflection is adjusted. To reduce. Hereinafter, embodiments of the present invention as described above will be described in detail with reference to the accompanying drawings. [First Embodiment] FIG. 1 shows an example of the internal structure of an electronic apparatus employing the present invention. In the configuration shown in FIG. 1, a signal transmission side printed wiring board 110 and a signal reception side printed wiring board 120 are arranged on a housing 101 made of a conductive member via a suitable spacer, and a cable ( The ground conductor 138 and the signal conductor 139) are connected to perform signal transmission. The ground conductor 112 of the signal transmission-side printed wiring board 110 and the ground conductor 123 of the signal reception-side printed wiring board 120 are placed on the surface or layer of each wiring board via appropriate spacers (supposed to be insulating materials). And the ground conductor 138 of the cable connects the ground conductors of both wiring boards to each other.
Here, the cables (the ground conductor 138 and the signal conductor 139) are pair cables. In the present embodiment, the impedance between the ground conductor 112 of the signal transmission-side printed wiring board 110, the ground conductor 138 of the cable, the ground conductor 123 of the signal reception-side printed wiring board 120, and the housing 101 made of a conductive member is determined. For matching, the high dielectric member A is inserted between the cable (the ground conductor 138 and the signal conductor 139) and the housing. Here, the signal transmission side printed wiring board 110
Ground conductor 112 and cable ground conductor 1
38 and the impedance between the ground conductor 123 of the signal-receiving-side printed wiring board 120 and the housing 101 made of a conductive member are Z0PCB1GND, Z0CableGND, and Z0PCB2GN, respectively.
Assuming that D, in the present embodiment, the value of each impedance Z0PCB1GND, Z0CableGND, and Z0PCB2GND is given by inserting the high dielectric member A between the cable and the housing. [0024] [Equation 2] indicates that the impedance characteristics of the ground conductor of the signal transmission side printed wiring board, the ground conductor of the cable, and the ground conductor of the signal reception side printed wiring board are equal. As a result, the printed wiring board 11 on the signal transmission side
It is possible to reduce reflection at each connection point of the ground conductor 112 of No. 0, the ground conductor 138 of the cable, and the ground conductor 123 of the printed wiring board 120 on the signal receiving side, thereby reducing radiated noise caused by the reflection. Usually, the impedance Z0 of the conductor is expressed by using the magnetic permeability μ and the dielectric constant ε. Can be represented by And, in general,
Because the ground conductor of the cable is elongated,
The impedance is higher than the impedance between the ground conductor of the printed wiring board and the housing. Therefore, by arranging the high dielectric member A near the cable ground and increasing ε in [Equation 3], the ground conductor 138 of the cable and the casing 10
The impedance characteristic Z0CableGND between the two can be reduced, impedance characteristics close to the above [Equation 2] can be realized, and radiation noise caused by signal reflection can be reduced. Thus, in this embodiment,
By inserting the high dielectric constant member A, the impedance of the ground conductor 138 of the cable is reduced, and the impedance is balanced with the impedance of the wiring boards 110 and 120 on the transmission side and the reception side. Signal reflection at a connection point between the conductor 138 and the ground conductors 112 and 123 of the transmission-side and reception-side wiring boards 110 and 120 can be suppressed, and radiation noise due to the reflection can be reduced. As the high dielectric constant member A, a member formed of a sheet or a block of an appropriate size from various materials which are usually used as a dielectric material for a capacitor or the like can be used. [Second Embodiment] FIG. 2 shows a different embodiment of the present invention. 2, the cable (ground conductor 13) between the signal transmission side printed wiring board 110 and the signal reception side printed wiring board 120 is almost the same as in FIG.
8, the signal conductor 139) is connected for signal transmission. FIG. 2 shows an example of a configuration in which a large high-dielectric-constant member as shown in FIG. 1 cannot be arranged in consideration of an arrangement space for other components (not shown) on the housing 101. Here, it is assumed that a space for arranging the high dielectric member is not provided between the ground conductor of the cable and the housing, and a small high dielectric member B must be used. In the present embodiment, the impedance Z0CableGND between the cable ground conductor 138 and the housing 101 is reduced by making the cable ground conductor 138 thicker, for example, as thick as possible than the signal conductor 139. I'm lowering. Thereby, the state of [Equation 2] can be realized. In this way, even if a large high-permittivity member as shown in FIG. 1 cannot be arranged in consideration of the arrangement space for other parts (not shown), the thickness of the cable ground conductor 138 is not limited. Is adjusted, the impedance Z0CableGND between the ground conductor 138 of the cable and the housing 101 is lowered, and the wiring board 1 on the transmission side and the reception side is reduced.
By balancing with the impedances of the cables 10 and 120, the unbalance is eliminated and the ground conductor 13 of the cable is removed.
Signal reflection at the connection point between the ground conductors 112 and 123 of the wiring boards 110 and 120 on the transmission side and the reception side can be suppressed, and radiation noise due to the reflection can be reduced. [Third Embodiment] FIG. 3 shows a different embodiment of the present invention. Also in the configuration of FIG. 3, the signal transmission side printed wiring board 110 and the signal reception side printed wiring board 120 are connected by cables (ground conductors D and signal conductors E) to transmit a signal, similarly to FIGS. It is. In the present embodiment, the cable ground conductor 13 is used in order to obtain the state of [Equation 2] similar to the first embodiment.
8 and the cable signal conductor 139 are brought close to a housing made of the conductive member 101. As described in the second embodiment, the impedance of the cable ground conductor becomes larger than that of the printed wiring board ground conductor if the distance from the housing 101 made of a conductive member is equal. Here, the relationship between the impedance of the wire and the distance from the conductive casing is approximately: It can be shown that [Equation 4] represents the relationship between the height d, the conductor radius a, and the impedance characteristic when there is a conductor having a radius a at the position of the height d parallel to the ideal ground. Therefore, the ground conductor D of the cable
Is bent as shown in FIG.
By reducing the distance between 1 and the ground conductor D of the cable, it is possible to lower the impedance Z0 of the cable ground conductor D, thereby obtaining the state of [Equation 2]. As described above, in the present embodiment,
By bending the ground conductor of the cable to reduce the distance between the housing 101 made of a conductive member and the ground conductor D of the cable, the impedance Z0CableGND between the ground conductor 138 of the cable and the housing 101 is reduced.
By lowering the impedance and balancing the impedances of the transmitting and receiving wiring boards 110 and 120, the unbalance is eliminated, and the ground conductor 138 of the cable and the ground conductor 11 of the transmitting and receiving wiring boards 110 and 120 are eliminated.
It is possible to suppress signal reflection at the connection point between 2, 2 and 123, and reduce radiation noise caused by this reflection. [Fourth Embodiment] FIG. 4 shows a different embodiment of the present invention. The configuration of FIG.
Signals are transmitted between the signal transmission side printed wiring board 110 and the signal reception side printed wiring board 120 by cables (ground conductors 138 and signal conductors 139) in substantially the same manner as in FIG. The present embodiment is designed not only to realize [Equation 2] as described in the first embodiment, but also to realize the signal conductor 116 and the signal conductor 116 on the signal transmission side printed wiring board 110. The purpose of the present invention is to prevent disturbance of the signal waveform passing through the signal line conductor 139 of the cable and the signal conductor 127 on the signal receiving side printed wiring board 120. That is, in this embodiment, the signal conductor 116 on the signal transmission side printed wiring board 110, the signal line conductor 139 of the cable, and the signal reception side printed wiring board 1
When the impedance characteristics of the signal conductor 127 on 20 are Z0PCB1Sig, Z0CableSig, and Z0PCB2Sig, respectively,
By adjusting the width and the like of the signal conductor on the printed wiring board, The configuration is such that As described above, in the present embodiment, not only the ground conductor but also the signal conductor, that is, the signal conductor of the cable and the signal conductor of the wiring board are adjusted so that the impedance imbalance is reduced. Thereby, signal reflection at connection points between the signal conductors 116 and 127 and the ground conductors 112 and 123 of the wiring boards 110 and 120 on the transmission side and the reception side are suppressed,
Radiation noise caused by this reflection can be reduced. [Fifth Embodiment] FIG. 5 shows a different embodiment of the present invention. Also in the configuration of FIG. 5, a cable (ground conductor 1) is connected between the signal transmission side printed wiring board 110 and the signal reception side printed wiring board 120 in substantially the same manner as in FIGS.
38, a signal conductor 139). In the third embodiment, the cable is brought close to the housing made of a conductive member in order to match the impedance characteristics of the ground conductor with the wiring board and the cable. , The impedance of the cable signal conductor 139 also decreases. Therefore, in this embodiment, the signal conductor G
And a coaxial cable comprising a ground conductor F,
By bringing the cable closer to the housing 101 made of a conductive member, the impedance characteristics of the outer cover ground conductor F of the coaxial cable are reduced. In the present embodiment, since the impedance of the signal conductor G of the coaxial cable is determined by the outer cover ground conductor F of the coaxial cable surrounding it,
The problem that the impedance of the cable signal conductor 139 is affected as in the third embodiment without changing can be avoided. As described above, according to the present invention,
A digital clock circuit is mounted, and a signal transmission side printed wiring board and a signal reception side printed wiring board having a signal conductor and a ground conductor are mounted on a conductive device housing by a cable including a signal conductor and a ground conductor for signal transmission. In the electronic device connected by the above , when μ is a magnetic permeability and ε is a dielectric constant, グ ラ ウ ン ド (μ / ε) of a ground conductor of the cable determined by a correlation with the conductive device case.
The grounding of the printed wiring board on the signal receiving side, which is determined by the impedance characteristic determined and the correlation with the conductive device housing.
And the impedance characteristic determined by √ (μ / ε)
And impedance balancing means for balancing the impedance.
Dance balance means is provided between the cable and the conductive device housing.
The high dielectric constant member is disposed between the high dielectric constant members.
The impedance characteristic is adjusted by the dielectric constant of the dielectric member.
Because it uses a formation, and a ground conductor of the cable, suppress signal reflection at the junction between the ground conductors of the signal transmitting-side printed wiring board to signal receiving-side printed wiring board, the radiation noise due to the signal reflection Can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows, as a first embodiment of the present invention, a configuration in which a signal is transmitted by a cable between a signal transmission side printed wiring board and a signal reception side printed wiring board on a conductive device housing. It is the perspective view shown. FIG. 2 is a perspective view showing, as a second embodiment of the present invention, a configuration in which a signal is transmitted by a cable between a signal transmission side printed wiring board and a signal reception side printed wiring board on a conductive device housing. FIG. 3 is a perspective view showing, as a third embodiment of the present invention, a configuration in which a signal is transmitted by a cable between a signal transmission side printed wiring board and a signal reception side printed wiring board on a conductive device housing. FIG. 4 is a perspective view showing, as a fourth embodiment of the present invention, a configuration in which a signal is transmitted by a cable between a signal transmission side printed wiring board and a signal reception side printed wiring board on a conductive device housing. FIG. 5 is a perspective view showing a configuration for transmitting a signal between a signal transmission side printed wiring board and a signal reception side printed wiring board on a conductive device housing by a coaxial cable as a fifth embodiment of the present invention. . DESCRIPTION OF SYMBOLS 101 Housing 110 made of conductive member Signal transmission side printed wiring board 120 Signal reception side printed wiring board 112 Ground conductor 123 of signal transmission side printed wiring board Ground conductor 114 of signal reception side printed wiring board Signal transmission Circuit 125 Signal receiving circuit 116 Signal conductor 127 of signal transmission side printed wiring board Signal conductor 138 of signal reception side printed wiring board Ground conductor 139 of cable Signal conductor A of cable High dielectric member B High dielectric member with limited shape D Ground conductor of cable E Signal conductor of cable F Ground conductor of coaxial cable G Signal conductor of coaxial cable

Continuation of front page (56) References JP-A-10-208791 (JP, A) JP-A-11-298182 (JP, A) JP-A-8-320747 (JP, A) JP-A-2000-22762 (JP, A A) JP-A-3-259597 (JP, A) JP-A-5-22628 (JP, A) JP-A-63-82102 (JP, A) JP-A-11-177189 (JP, A) JP-A-6 JP-A-53702 (JP, A) JP-A-4-109701 (JP, A) JP-A-5-335436 (JP, A) JP-A-1-216677 (JP, A) JP-A-2001-168235 (JP, A) U.S. Pat. No. 5,746,695 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 7/14 H05K 3/36 H05K 9/00 G06F 1 / 00 G06F 1/18 G06F 3/00 G09G 1/00 H04B 15/02 H04N 5/00 H04N 5/66

Claims (1)

(57) [Claim 1] A digital clock circuit is mounted, and a signal transmission side printed wiring board and a signal reception side printed wiring board having a signal conductor and a ground conductor are connected to a signal for signal transmission. In an electronic device connected on a conductive device housing by a cable including a conductor and a ground conductor , μ is a permeability and ε is a dielectric constant of a ground conductor of the cable determined by a correlation with the conductive device housing. When
Inpi defined by √ (μ / ε) and the impedance characteristic which is determined by, the ground conductor of the signal receiving-side printed wiring board which is determined by the correlation between the conductive device enclosure √ (μ / ε) in
Impedance balance means to balance the
The impedance balancing means is connected to the cable and the conductor.
Structured by a high dielectric constant member
Impedance is determined by the dielectric constant of the high dielectric member.
An electronic device characterized by adjusting characteristics .