Method and apparatus for electromagnetic shielding and electrostatic discharge protection

• US 6,058,000 A
• Filed: 04/12/1995
• Issued: 05/02/2000
• Est. Priority Date: 07/31/1990
• Status: Expired due to Term

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Harris, David A., Hanson, George E., Koenck, Steven E., Durbin, Dennis A., Davis, Patrick H.
• Primary Examiner(s): Jackson, Stephen W.
• Application Number:
  US08/419,664
• Time in Patent Office: 1,847 Days
• Field of Search: 361/111, 361/56, 361/91, 361/118, 361/119, 361/113, 361/818, 307/91
• US Class Current: 361/113
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 1/1632 External expansion units, e.g. docking stations
• CPC Class Codes: G06F 1/1656 Details related to functional adaptations of the enclosure, e.g. to provide protection against EMI, shock, water, or to host detachable peripherals like a mouse or removable expansions units like PCMCIA cards, or to provide access to internal components for maintenance or to removable storage supports like CDs or DVDs, or to mechanically mount accessories mounting of accessories to a computer display G06F1/1607; display hoods G06F1/1603; cooling arrangements for portable computers G06F1/203
• CPC Class Codes: G06F 1/28 Supervision thereof, e.g. detecting power-supply failure by out of limits supervision
• CPC Class Codes: G06K 17/0022 arrangements or provisious for transferring data to distant stations, e.g. from a sensing device "transfer between computer elements G06F13/00 "; data-transmission H04L
• CPC Class Codes: G06K 7/10574 Multiple sources
• CPC Class Codes: G06K 7/10584 Source control
• CPC Class Codes: G06K 7/10702 Particularities of propagating elements, e.g. lenses, mirrors G06K7/10831 takes precedence
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10811 Focalisation
• CPC Class Codes: G06K 7/10841 Particularities of the light-sensitive elements semiconductor devices H01L
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03
• CPC Class Codes: G06K 7/10881 constructional details of hand-held scanners
• CPC Class Codes: G06K 7/12 using a selected wavelength, e.g. to sense red marks and ignore blue marks
• CPC Class Codes: H01Q 1/242 specially adapted for hand-held use
• CPC Class Codes: H01Q 1/50 Structural association of antennas with earthing switches, lead-in devices or lightning protectors
• CPC Class Codes: H01Q 1/526 Electromagnetic shields
• CPC Class Codes: H04B 2001/3894 Waterproofing of transmission device
• CPC Class Codes: H05K 1/0233 Filters, inductors or a magnetic substance

Abstract

The present invention provides protection from electromagnetic interference and electrostatic discharge. The invention teaches a shielding conductor surface enclosure, an interior shielding conductor plane, a contact conductor from the shielding conductor plane and the shielding conductor surface enclosure, a path for electromagnetic signals to pass through a shielding conductor plane, a filter network, and an electrostatic voltage clamp. Protection is provided by filtering the incoming signals, electrically coupling the signals of an undesired bandwidth to a shield barrier, and electrically coupling signals of an undesired voltage to a shield barrier. The shield surface is physically differentiated from the ground plane surface.

Claims

1. An apparatus for providing protection from electromagnetic interference, comprising:

(a) a shielding conductor surface enclosure;

(b) a shielding conductor plane interior to said shielding conductor surface enclosure;

(c) means for providing electrical continuity between said shielding conductor surface enclosure and said shielding conductor plane;

(d) at least one aperture in said shielding conductor plane for providing passage of electrical signals through said shielding conductor plane;

(e) an electrical path through each of said at least one aperture in said shielding conductor plane; and

(f) frequency based signal separation means connected between said shielding conductor plane and said electrical path for separating electrical signals present on said electrical path wherein frequency components within a predetermined range of frequencies are electrically connected to said shielding conductor plane such that said shielding conductor plane and said shielding conductor surface appear as a completely enclosed and continuous conductor surface to the frequency components within the predetermined range of frequencies.

2. The apparatus according to claim 1, wherein said shielding conductor surface enclosure and shielding conductor plane are composed of magnetic and electrically conductive material.

3. The apparatus according to claim 1, wherein said shielding conductor plane is incorporated within a circuit board.

4. The apparatus according to claim 1, wherein said frequency based signal separation means includes a filter network.

5. The apparatus according to claim 4, wherein said filter network comprises:

(a) a first inductor

(b) a second inductor electrically connected in series at an electrical node with said first inductor; and

(c) a shunting capacitor electrically connected at the electrical node with said inductors.

6. A method for protecting a data terminal from electromagnetic interference and electrostatic discharge comprising:

(a) filtering electrical data signals present within the data terminal such that the electrical signals are separated into multiple frequency ranges;

(b) electrically coupling the electrical data signals within a first frequency range to a shielding surface such that the shielding surface appears as a continuous shielding surface;

(c) passing the electrical data signals within a second frequency range through the shielding surface; and

(d) electrically coupling the electrical signals of an electrostatic potential greater than a predetermined electrostatic potential to the shielding surface.

7. In an electronic device having a housing and an electronic circuit disposed within the housing, an apparatus for preventing undesirable electromagnetic signals from penetrating the housing and interfering with the electronic circuit while allowing a desirable signal to pass through the housing and couple with the electronic circuit, comprising:

a conductor surface coincident with an interior surface of the housing for shielding the electronic circuit from the undesirable electromagnetic signals, said conductor surface exhibiting a shielding effectiveness and having an aperture for allowing the desirable signal to pass therethrough; and

a filter operatively connected between the electronic circuit and said conductor surface wherein signals having frequency components characteristic of the desirable signal are coupled by the filter to the electronic circuit and signals having frequency components characteristic of the undesirable electromagnetic signals are coupled by the filter to said conductor surface, thereby increasing the shielding effectiveness of said conductor surface against the undesirable electromagnetic signals.

8. An apparatus as claimed in claim 7, wherein said filter is a low pass filter.

9. An apparatus as claimed in claim 7, wherein said filter is a high pass filter.

10. An apparatus as claimed in claim 7 wherein said filter is a band pass filter.

11. An apparatus as claimed in claim 7 wherein said filter is a band reject filter.

12. An apparatus as claimed in claim 7, wherein said filter comprises first and second inductors each having first and second terminals, respectively, the second terminal of said first inductor and the first terminal of said second inductor being connected at a node, the first terminal of said first inductor receiving the desirable signal, and the second terminal of said second inductor being coupled to the electronic circuit;

and a capacitor connected between the node and said conductor surface.

13. In an electronic device having a housing and an electronic circuit disposed within the housing, an apparatus for preventing undesirable electromagnetic signals emanating from a transmission line disposed within the housing from interfering with the electronic circuit, comprising:

a first conductor having a surface coincident with an interior surface of the housing for shielding the electronic circuit from the undesirable electromagnetic signals;

a second conductor disposed within the housing, said second conductor being generally planar and having an upper surface and a lower surface, the circuit being disposed above the upper surface and the transmission line being disposed below the lower surface; and

a shield contact for connecting said first conductor to said second conductor thereby providing shielding continuity between said first and second conductors by enclosing a volume containing the electronic circuit and excluding the transmission line such that the electronic circuit is shielded from the undesirable electromagnetic signals emanating from the transmission line.

14. A circuit board for preventing undesirable electromagnetic signals emanating from a transmission line from interfering with an electronic circuit disposed on a surface of the circuit board, comprising:

a first conductor being disposed between the electronic circuit and the transmission line and having an aperture through which a desired signal transmitted via the transmission line may pass for coupling with the electronic circuit, said first conductor providing a surface for shielding the electronic circuit from the undesirable electromagnetic signals emanating from the transmission line; and

a second conductor disposed on said circuit board for providing a return current path for the desired signal separate from said first conductor wherein said first conductor and said second conductor are connected at a single point.

15. A circuit board as claimed in claim 14, wherein the transmission line is disposed between said first conductor and said second conductor.

16. An apparatus for providing protection from electromagnetic interference, comprising:

first means for providing electromagnetic shielding, said first electromagnetic shielding means having an aperture formed thereon for providing passage of desired electrical signals therethrough;

second means for providing electromagnetic shielding, said second electromagnetic shielding means at least partially enclosing said first electromagnetic shielding means wherein said first electromagnetic shielding means separates an interior region of said second electromagnetic means into at least first and second interior regions of said second electromagnetic shielding means; and

means for coupling electrical signals of a first range of frequencies to said first means for providing electromagnetic shielding and for allowing electrical signals of a second range of frequencies to pass through the aperture from the first interior region to the second interior region.

17. An apparatus as claimed in claim 16, said first and second electromagnetic shielding means being electrically coupled.

18. An apparatus as claimed in claim 16, said first electromagnetic shielding means being integrated within a means for mounting an electrical component.

19. An apparatus as claimed in claim 16, further comprising means for limiting electrical signals passing through said aperture to a predetermined voltage level.

20. An apparatus as claimed in claim 16, said coupling means including means for providing electrical reactance.

21. An apparatus, comprising:

means, capable of enclosing a circuit, for providing electromagnetic shielding of the circuit, said electromagnetic shielding means having an aperture for allowing a transmission line external to said electromagnetic shielding means to couple with the circuit; and

means for coupling signals on the transmission line of a first frequency to said electromagnetic shielding means while allowing signals on the transmission line of a second frequency to pass through the aperture to the electronic circuit such that the shielding effectiveness of said electromagnetic shielding means is increased for signals of the first frequency.

22. An apparatus as claimed in claim 21, further comprising means for limiting signals on the transmission line passing through the aperture to a predetermined voltage level.