Electricity: electrical systems and devices – Miscellaneous
Patent
1986-10-08
1988-06-21
Hix, L. T.
Electricity: electrical systems and devices
Miscellaneous
361212, 361406, H05K 710, H01R 900, H05F 300
Patent
active
047528621
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to structures for preventing portable small electronic devices and small data devices from being erroneously operated or from being broken down by static electricity.
BACKGROUND ART
Portable electronic devices such as IC cards, cameras, wristwatches, and those electronic devices that are not grounded, are prone to be erroneously operated or broken down due to the phenomenon of static electricity.
Such devices have heretofore been prevented from malfunctioning, either by erroneously operating or from breaking down, in the same manner as those electronic devices that can be usually grounded. Using a reference potential of a grounding circuit, however, the noise can be suppressed efficiently over a frequency region which is lower than that of the VHF band. Even if one point or more points are grounded, the grounding circuit is not quite effective to absorb the electromagnetic waves of large energy that are generated when the static electricity is discharged. Therefore, the noise must be suppressed in another manner.
Many examples to cope with this problem have been introduced in, for example, Electronics System, "Materials To Cope With Troubles Caused by Static Electricity" compiled by Norio Murasaki, entitled "Section 6, Countermeasures 5.6.2.3 Against Static Electricity in ECR, Electronic Circuit and Printed Board", pp. 222-224. However, many technicians are empirically aware of the fact that there is no simple method which offers sufficiently desirable effects. It has been attempted to absorb noise by extending the pattern of the ground side of the circuit board having the potential of the active side 2 or to increase the width of the pattern, or by a method taught in "Grounding of Housing", p. 84, "Practical Method of Decreasing Noise", Henry W. OTT., Bell Laboratory, U.S.A., translated by Takao Matsui. With the portable electronic devices which are not allowed to be grounded, however, noise is not emitted to the ground, and the concept of grounding cannot be pursued. In the electronic devices that cannot be grounded, a pattern of circuit board of a potential of the active side, that is formed to absorb noise, works as an antenna, and the structure connected to the potential of the active side of the metal housing to accomplish the grounding, works as an antenna. That is, with the pattern of circuit board that is not grounded or with the structure connected to the potential of the active side of the metal housing to accomplish the grounding, the electromagnetic waves are absorbed and are converted into eddy current to produce noise in the circuit network. Furthermore, under the condition where the electric charge is not discharged, the lines assuming the potential of the active side a of floated ground function to increase the difference of electric field distribution relative to the pull side. This becomes a cause of erroneous operation for field effect IC's.
As shown in FIG. 7, under such circumstances, three lines, i.e., an active side or power source line 2, an input line 4 and a pull side or ground line 3 establish an electrically important relationship. Described hereinbelow are the drawbacks that were not solved by the conventional art. For convenience of description, the high potential side of the power supply, whether positive or negative, is referred to as the active side or the power source line 2, and the low potential side is referred to as the pull side or the ground line 3.
FIG. 7 is a circuit diagram which schematically illustrates an input circuit. Here, a capacity or capacitance Ca exists between the active side 2 and the input line 4, and a capacity or capacitance Cp exists between the pull side 3 and the input line 4. The relationship Ca>Cp will be described. It is obvious that electromagnetic waves generated by static electricity or the like are simultaneously superposed as an impulse on the active side 2 and on the pull side 3 of the power source voltage. Therefore, the potential appearing on the input line 4 forms a potential on t
REFERENCES:
patent: 4557379 (1985-12-01), Lane et al.
patent: 4580193 (1986-04-01), Edwards
patent: 4617471 (1986-10-01), Suzuki
Mims, Forrest M., Engineer's Notebook, Radio Shack, 1979, pp. 105, 113.
Ochiai Hitoshi
Takahashi Akio
Adams Bruce L.
Hix L. T,.
Porterfield David
Seiko Instruments & Electronics Ltd.
Wilks Van C.
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