AU2017101007A4 - Low Cost Galvanic Isolator with Improved High Voltage Performance for Coaxial Distribution Networks - Google Patents

Abstract

Abstract: A galvanic isolator comprising internal insulating structures which improve manufacturability and high voltage performance, RF shields made from sheet metal which reduce cost, and capacitors which improve high voltage surge tolerance. Figure 3b 306 305 303 Figure 3a Figure 3b

Description

1 2017101007 26 Jul 2017

Low Cost Galvanic Isolator with Improved High Voltage Performance for Coaxial Distribution Networks.

FIELD OF THE INVENTION

[0001] The present invention relates generally to novel structures, component arrangements and assembly methods which reduce the cost of Galvanic Isolators, simplify assembly methods, increase reproducibility and improve high voltage performance. The invention has been developed primarily for use as a galvanic isolator in coaxial communication distribution networks and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

[0002] As the world’s demand for entertainment and information content increases, new means of distributing this content are being developed. Cable TV (CATV) networks have been deployed since the 1980’s and are an example of a telecommunication network that was built to offer subscribers a significantly increased range of content. Coaxial cable has traditionally been used for such distribution networks because it has relatively low cost and because it simplifies connection to network devices and customers premises. Network coaxial cables consist of outer plastic insulation, a conductive outer sheath, a low loss insulator and central conductor. Although original CATV networks were entirely made from coaxial cables, modern networks often employ a so called Hybrid Fibre Coax (HFC) structure where connectivity is provided using optical fibres for the core network and coaxial cables for connection to customer's premises.

[0003] Although the content capacity of CATV networks has previously met subscriber’s requirements, there is a growing demand for subscriber customised content, for example in the form of streaming video on demand and other internet related sources of information or entertainment content. As a result, network operators are under increased pressure to make use of the full bandwidth capacities of their networks and/or to increase their network bandwidth capacities by upgrading network elements.

[0004] In typical installation scenarios, a Tap is installed on the network coaxial cable as it passes a user’s premises and a drop cable is run from the tap into the user’s building. This connection unusually terminates inside the building at a network element such as a set-top-box (STB) which decodes network signals and connects to user devices such as TVs or computer network devices.

[0005] When an electrically conductive cable enters a user’s premises there is an inherent risk that small voltage differences at each end of the cable can cause dangerous currents to flow along the cable. This may occur, for example, if the network coax cable in the street is connected to the neutral connection of the power grid and the power distribution system uses Main Earthed Neutral (MEN) connection schemes inside the premises. In this case, if a building has a high resistance power neutral connection, the neutral return current for the premises can 2 2017101007 26 Μ 2017 potentially flow along the coax cable via set top box connection, thereby creating the risk of overload and fire. For this reason, network operators typically install galvanic isolators.

[0006] There is also a risk that cables entering some premises can convey dangerous voltages as a result of power grid faults or transient lightning surges. In this case, a galvanic isolator is designed to withstand dangerous voltages and limit the current flowing into the user's premises.

[0007] A galvanic isolator is therefore a device which permits the passage of high frequency information-containing signals through the device and blocks the passage of low frequency current from mains frequency power systems and current surges such as produced from lightning strikes.

[0008] Figure 1 shows a circuit schematic of one type of conventional galvanic isolator. In this design, isolator functionality is split into two stages: a signal coupling stage and a filtering stage. Referring to Figure 1, components C1, C2 and T1 form the signal coupling stage. The values of the components are chosen to allow the passage of high frequency signals carrying data, for example above 5MHz, and block the flow of current from 50-60Hz power mains and surges, for example, surges induced by lightning strikes.

[0009] An unavoidable aspect of any isolator’s design is the need to break ground conductor continuity in order to introduce an isolating component between incoming and outgoing signal port grounds. This causes signals passing through an isolator to ‘leak’ out and appear as a differential signal between ground connections of the isolator ports, thereby potentially generating interference in radio frequency bands. This same mechanism also allows signals to leak into the distribution network at each isolator resulting in impaired network performance.

[0010] To lessen the effect of this problem, isolators employ a filtering stage which attenuates signals leaving or entering the network at the isolator. Referring to Figure 1, components C3,C4 and T2 are an example of a conventional filter which attenuates these signals.

[0011] In order to obtain the best performance, it is preferable for isolators to physically separate the signal coupling stage from the filtering stage by enclosing each of them in separate shielded enclosures.

[0012] Figure 2a shows an exploded isometric view of a conventional isolator case comprising main housing 200, upper and lower lids 201, and signal port connectors 202. Figure 2b provides an additional top isometric view of a conventional isolator housing 200 showing a first shielded chamber 203 comprising a central partition 204 and an access hole 205 which allows signals to be coupled to and from this chamber. Figure 2c provides a further bottom isometric view of the conventional isolator housing 200 showing a second shielded chamber 206 and an alternative view of the central partition 204 and access hole 205. Figure 2d provides a cross section view of the conventional isolator housing 200 demonstrating a characteristic Ή” shape formed by first and second shielded chambers 203 and 206 and central partition 204. Finally, Figure 2e shows a cross section view of a conventional isolator comprising signal 3 2017101007 26 Μ 2017 coupling circuit board assembly 207 and filter circuit board assembly 208 mounted in shielded chambers 203 and 206 and coupled together by cable 209 which passes through access hole 205.

[0013] Referring to Figures 2a-e, housing 200 and lids 201 are conventionally made by a die casting process utilising metals such as zinc or aluminium. Conventionally, the primary advantage of this design is believed to be that it provides excellent RF (Radio Frequency) screening because of the effective EMF (Electromagnetic Field) shield formed by the lack of joins or seams in the housing and hence the tight electrical bonding of each conductive surface. Additionally, die cast cases are able to be easily sealed to form environmentally robust enclosures which are resistant to moisture and contaminants.

[0014] Despite these advantages, the use of die cast enclosures creates significant problems for isolator manufacturers. Network operators place great importance on lowering equipment costs and die cast housings are relatively expensive, particularly when made from zinc. For example, in conventional isolators the die cast case can represent as much as 50% of the overall product cost. Furthermore, the considerable weight of the die cast housings significantly increases shipping costs and creates mounting difficulties, particularly in plastic wall boxes.

[0015] Accordingly, the inventor has realised that there is a need for a new isolator architecture which reduces cost and weight of isolator enclosures, without compromising RF screening performance of EMF shielding.

[0016] From a different perspective, conventional isolators generally have difficulty meeting the high voltage immunity requirements specified by network operators. For example, some network operators specify that isolators need to withstand surges caused by lightning strikes which can have magnitudes of 7000 volts. The difficulty facing designers of isolators is that there is a need for RF circuitry to be surrounded by extensive metallic shields and these metallic surfaces present a large surface area susceptible to forming electrical breakdown paths.

[0017] Accordingly, the inventor has realised that there is at least a need for an improved isolator structure which provides greater high voltage isolation between internal circuitry and the surrounding EMF shield.

[0018] From yet another perspective, conventional isolators often have poor immunity to repeated high voltage surges. For example, it is often observed that isolators will fail when subjected to repeated high voltage surges, even though the surges are below the DC voltage rating of the isolator’s components.

[0019] Accordingly, there is a need to overcome this source of failure and provide a means of improving HV surge tolerance.

[0020] The discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain prior art problems by the inventor and, moreover, any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the 4 2017101007 26 Μ 2017 material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.

SUMMARY OF THE INVENTION

[0021] It is an object of the present invention to provide a method and apparatus, which alleviates at least one disadvantage associated with related art arrangements as discussed herein.

[0022] According to a first aspect, the present invention provides a galvanic isolator comprising an improved enclosure which lowers cost and weight by eliminating the need for expensive die cast enclosures and allowing the use of thin preformed metal sheets.

[0023] According to a second aspect, the invention provides a galvanic isolator comprising internal insulating trays which increase the breakdown voltage between signal circuitry and the isolator’s metallic RF screen by providing an insulating barrier for discharges.

[0024] According to a third aspect, the invention provides a galvanic isolator comprising capacitors with improved tolerance to repeated high voltage surges.

[0025] According to a fourth aspect, the present invention provides a galvanic isolator comprising non-conventional capacitors with improved high voltage surge tolerance.

[0026] According to a further aspect, the present invention provides methods of assembly of a galvanic isolator which achieve the noted aspects of the invention.

[0027] It is therefore an object of the preferred embodiments described herein to overcome or alleviate at least one of the above noted drawbacks of conventional systems or to at least provide a useful alternative to conventional systems.

[0028] In one form the present invention provides a galvanic isolator comprising a metallic shield wherein said shield comprises folded sheet metal which forms; a substantially-planar central panel; and a plurality of side panels operatively connected to said central panel; wherein said metallic shield is electrically connected to at least one of the isolator’s signal ports at said central panel and said side panels are bent so that they are substantially perpendicular to said central panel.

[0029] In another form the present invention provides a galvanic isolator adapted for high voltage tolerance and simplified manufacturing comprising: a first electrically insulating tray; a second electrically insulating tray; a metallic shield comprised of folded sheet metal; wherein said first insulating tray is coupled to a first surface of said metallic shield and said second insulating tray is coupled to a second surface of said metallic shield, wherein said first and second surfaces are located on opposite sides of the same portion of said metal shield.

[0030] In yet another form the present invention provides a galvanic isolator adapted for high voltage impulse tolerance comprising ceramic capacitors wherein said capacitors are: coupled from a first signal port to a second signal port of said isolator, and 5 2017101007 26 Μ 2017 comprised of ceramic material with relative permittivity less than 4000.

[0031] In still another form the present invention provides a method of assembling a galvanic isolator comprising the steps of: mounting a first coaxial connector onto a PCB assembly of signal coupling components; mounting said PCB assembly into a first of two generally opposed insulating trays; bending one or more panels of a contiguous plurality of panels around the first tray to partially form a first EMF shield for the first tray; connecting one end of a coaxial cable to electrical contacts of the PCB assembly; feeding the other end of the coaxial cable through an aperture of said first insulating tray which is coincident with an aperture in one of the plurality of contiguous panels and said second insulating tray; bending one or more further panels of the contiguous plurality of panels around the first tray so as to enclose the first tray within a formed first EMF shield for the first tray; fitting electrical components to recesses disposed in the second insulating tray; connecting the other end of the coaxial cable to the fitted electrical components in the second insulating tray; bending one or more further panels of the contiguous plurality of panels around the second tray so as to enclose the second tray within a formed second EMF shield for the second tray.

[0032] Preferably, the contiguous plurality of panels comprises one of:

an integral sheet of conductive material for forming both first and second EMF shields; or, separate sheets of conductive material for forming the first and second EMF shields, respectively.

[0033] In still another form the present invention provides a galvanic isolator comprising one or a combination of: a metallic shield formed from a folded metal sheet and having a surface comprising contiguous panels wherein boundaries formed between the contiguous panels are aligned substantially parallel to the paths that induced RF currents would form in a metallic shield with a continuous and/or electrically uninterrupted surface; separate insulating trays adapted for housing a signal coupling stage and a filtering stage, respectively; and at least one capacitor coupled from a first signal port of the isolator to a second signal port of the isolator wherein the at least one capacitor comprises dielectric material with a relative permittivity less than 4000.

[0034] In embodiments, the folded metal sheet of the galvanic isolator is preferably less than 0.5mm thick and most preferably less than 0.25mm thick. Furthermore, the folded metal sheet preferably comprises steel. 6 2017101007 26 Μ 2017 [0035] Preferably, the folded metal sheet further comprises a corrosion resistant, solderable coating such as tin. The folded metal sheet is also preferably manufactured by a stamping process.

[0036] Preferably, the insulating trays are manufactured by injection moulding.

[0037] In preferred embodiments the capacitors comprise Y5P class ceramic material.

[0038] These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. Accordingly, further scope of applicability of embodiments of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure herein will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Further disclosure, objects, advantages and aspects of preferred and other embodiments of the present invention may be better understood by those skilled in the relevant art by reference to the following description of embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the disclosure herein, and in which:

Figure 1 is a schematic diagram of a conventional galvanic isolator;

Figures 2a to 2e are isometric views of conventional isolators showing features and overall structure;

Figures 3a and 3b are exploded views of an insulating tray covered by a folded metallic shield according to a preferred embodiment of the present invention;

Figures 4a to 4e are exploded isometric views of an isolator comprising two insulating trays and two folded sheet metal shields according to preferred embodiments of the present invention;

Figure 4f shows a fully assembled structure comprising the elements shown in Figures 4a-e;

Figures 5a to 5c are isometric drawings summarising a method of assembly of a galvanic isolator according to a preferred embodiment of the present invention;

Figures 6a and 6b are isometric views of a metal shield in accordance with preferred embodiments, which is comprised of a single piece of sheet metal which offers improvements in cost and assembly processes;

Figures 7a to 7c show a preferred assembly process for a galvanic isolator including a metal shield comprising a single piece of sheet metal.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0040] Preferred embodiments of the present invention will now be described in relation to the drawings. Where possible, equivalent numbers have been used to identify the same 7 2017101007 26 Μ 2017 element in each drawing or sub-drawing. Terms such as “upper” and “lower” or “top” and “bottom” are intended to aid description of the drawings as shown and are not meant to restrict the scope of the invention. In particular, a galvanic isolator is a bidirectional device, meaning that signals flow simultaneously in different directions through the isolator. Hence terms relating to “input” and “output” are used to describe certain features of embodiments of the present invention and are not meant to restrict the scope of the invention.

[0041] The term “galvanic isolator” refers to a device, comprising at least two coaxial isolator ports, which permits the passage of high frequency information-containing signals through the device and blocks the passage of low frequency current from mains frequency power systems and transient voltage surges.

[0042] The term “isolator port" refers to the coaxial electrical interface point where a cable is coupled to a galvanic isolator.

[0043] The term “grounded port” refers to the isolator port where there is a low voltage DC resistance of less than 1 ohm between the outer conductor of the coaxial connector located at this port and the isolator's metallic RF shield.

[0044] The term “isolated port” refers to an isolator port where there is a low voltage DC resistance of greater than about 1 Megaohm between the outer conductor of the coaxial connector located at this port and the isolator's metallic RF shield.

[0045] The term “signal path” refers to the passage of electromagnetic energy coupled from one isolator port, through isolator circuitry, to another isolator port in the form of differential voltages and corresponding currents which flow according to these voltages.

[0046] The term “tray” refers to a physical structure which is shaped to accept, support and surround, or partially surround, portions of isolator circuitry.

[0047] The term “RF shielding” may be herein used synonymously for the term “EMF shielding” but without limitation to the term.

[0048] From a first perspective, a preferred embodiment of the present invention provides a galvanic isolator comprising: a grounded port, an electrically insulating tray, and a metallic shield comprising folded sheet metal wherein: said metallic shield comprises a substantially planar central panel said central panel is bounded by panels bent substantially perpendicular to said central panel, said central panel is electrically coupled to the ground connection of said grounded port of the isolator, and said insulating tray is enclosed within said metal shield.

[0049] Contrary to conventional belief, the inventor has realised that the RF shielding requirements of galvanic isolators can be met using folded sheet metal instead of die cast metal enclosures providing the fold lines and individual shield panels are arranged so that RF currents 2017101007 26 Μ 2017 8 in the shield are not interrupted by panel boundaries. This can be achieved if the panel boundaries are aligned substantially parallel to the path shield current would take if there were no shield panel boundaries.

[0050] Figure 3a shows one view of a preferred embodiment of the present invention. Metal shield 301 is manufactured to comprise multiple panels 302 which join central panel 303 along fold lines 305. Central panel 303 comprises an aperture to receive coaxial connector 304 which provides the point of connection for the grounded port of the isolator. In this way, connector 304 is electrically bonded to the central panel of the metal shield 301.

[0051] Preferably metal shield 301 is manufactured from a low cost metal with high strength and stiffness so the sheet can be reduced to a minimal thickness to save cost. Preferably the metal sheet is made from steel with a thickness less than 0.5mm. Most preferably the sheet thickness is 0.2mm. In order to prevent corrosion and to assist solderability, the sheet preferably comprises tin plated steel. Because this material is available with high quality and low cost as a result of its widespread use in the food industry, the inventor has realised this is a preferred option for lowering the cost of RF shields used in galvanic isolators but it is to be noted that the invention is not limited to this specific material, only.

[0052] Preferably, metal shield 301 is manufactured with a low cost process such as stamping. During shield manufacture some panels 306 are preferably bent in a substantially perpendicular orientation to adjacent panels to provide stiffness and contact area for other panels after assembly. However, in order to minimise metal shield volume and shipping costs prior to assembly, it is advantageous to leave other panels 302 in the same planar orientation as central panel 303. During isolator manufacture metal shield 301 is preferably bent along fold lines 305 either by hand or by machine to form the metal shield for the isolator. In order to assist hand assembly, features such as perforations or indentations are preferably arranged along fold lines 305 to concentrate bending forces and improve bend alignment accuracy.

[0053] Figure 3b provides a different perspective of the same assembly showing metal shield 301, insulating tray 307 and the rear side of connector 304. Preferably tray 307 is made from a low cost thermoplastic material such as polypropylene, ABS, polyethylene or similar materials. The function of this tray includes: to house isolator circuitry which is immediately coupled to the grounded connector 304, to provide an insulating barrier between this circuitry and metal shield 301 to increase the high voltage tolerance of the isolator to provide a rigid structure around which the metal shield can easily be bent into the desired shape.

[0054] Tray 307 preferably has a lid made of the same insulating material as the tray. This is not shown in Figure 3b to avoid obscuring other details. The lid may be a separate piece or may be attached to the tray by features such as living hinges. 9 2017101007 26 Jul 2017 [0055] Tray 307 may also include retention features on its surface which clip into or around corresponding features of the metal shield to hold the shield in place against the surfaces after it is bent around the tray.

[0056] In normal operation, components carrying RF signals in an isolator can couple energy to the nearby metal shield resulting in induced currents which flow across the surface. These currents travel across the shield along the shortest path toward the grounded isolator port. The conventional belief held by isolator designers is that the metal shield needs to have a continuous surface to allow these currents to flow freely and minimise leakage from the shield. The inventor has realised that non-continuous shield panels can be used provided the boundaries of panels are aligned in parallel with prevailing current paths. Non-continuous shielding allows the use of sheet metal for the shield, which provides a significant cost saving.

[0057] Referring to Figure 3b, dashed arrows 308 represent the direction of induced currents flowing across the inner surface of the metal shield 301 toward connector 304. According to embodiments of the present invention, the panels 302 of the metal shield 301 are arranged to avoid any surface discontinuities along the prevailing paths of surface currents. This maximises the effectiveness of the metal shield and prevents localised disturbances which can lead to leakage of RF energy through the shield and to variations in shield ground impedance.

[0058] From another perspective, a preferred embodiment of the present invention provides a galvanic isolator comprising a first electrically insulating tray surrounded by a metallic shield comprised of folded sheet metal, said tray coupled to a first surface of said metallic shield and a second insulating tray coupled to a second surface of said metallic shield, wherein said first and second surfaces are located on opposite sides of a portion of said metal shield.

[0059] Figure 4a provides an exploded view of two trays according to a preferred embodiment of the present invention. The metal shield of the isolator is not shown in this diagram to avoid obscuring key features in this description. It is shown in place in Figures 4c and 4d which follow. By accommodating isolator circuitry in insulating trays, the inventor has realised that an isolator's tolerance of high voltages appearing between the isolator’s ports can be increased. Preferably, components associated with coupling signals through the isolator are housed in one tray and components associated with filtering unwanted common mode signals at isolator ports are housed in the other tray.

[0060] Grounded connector 404 is coupled to a wall of grounded port tray 411 which provides mechanical support. The active and ground connections of connector 404 are coupled to conductors on printed circuit board 405 which contains signal coupling components 406. Tray 411 also comprises an aperture 407 which allows signals to be carried to and from circuitry contained in the tray through a cable (not shown for simplicity). Apart from this aperture, the bottom surface of tray 411 is preferably a continuous layer of plastic which provides high voltage insulation between the tray's circuitry and the isolator’s metal shield (shown in later figures). For example, indicative dimensions of tray 411 are: 60mm long, 40mm wide and 20mm tail with 10 2017101007 26 Μ 2017 a wall thickness of 1-2mm. As noted previously, tray 411 preferably comprises a low cost thermoplastic material and is made by an injection moulding process, [0061 j Still referring to Figure 4a, isolated port tray 421 is preferably positioned in an inverted manner underneath tray 411 such that the closed faces of each tray are adjacent to each other and the open faces of each tray is oriented in opposite directions. Isolated tray 421 preferably has the same outer surface dimensions as tray 411 so they stack neatly on top of each other. These trays preferably have retaining features on adjacent surfaces which lock the trays together when assembled. Tray 421 is also preferably made of low cost thermoplastic material. Tray 421 also has an aperture 427 positioned adjacent to aperture 407 in tray 411 to allow a cable to pass from one tray to the other carrying signals between circuitry contained in each tray.

[0062] According to a preferred aspect of the invention, tray 421 comprises apertures 423 in its closed surface 422 which allow components housed within tray 421 to connect to the isolator’s metal shield which passes across surface 422 between tray 411 and tray 421 as shown in Figures 4c and 4d. The advantage of providing connection from these components to the metal shield at this point is that the net ground impedance between these components and main ground at the isolator’s grounded port is minimised. This maximises RF performance by minimising parasitic inductances which can reduce bandwidth.

[0063] Figure 4b shows trays 411 and 421 from the opposite perspective. Isolated port connector 424 is mounted in a feature of tray 421 which is designed to receive and mechanically support it. Unlike the grounded port tray 411, the isolated port tray 421 preferably does not contain a printed circuit board. Instead isolated port tray 421 comprises support structures 428 which hold components captive at prescribed locations and in prescribed orientations. These support structures are made of the same material as the tray and are formed by the same manufacturing process that makes the tray, preferably by injection moulding. By holding the components in this manner, they can be soldered to the cable as it passes by them on its path from tray 411 to the isolated connector 424 in tray 421. The advantage of this approach is that the cost of the isolator is reduced because no PCB is needed to provide connectivity and the components have minimal parasitic impedances in their connections which improves RF performance.

[0064] Figure 4c shows an additional exploded isometric view of trays 411 and 421 with metal shield 401, corresponding to shield 301 in Figure 3, fitted to tray 411. In the fully assembled form, the metal shield 401 surrounding tray 411 is in contact with the adjacent surface of tray 421, This allows the metal shield to provide multiple functions: it provides electromagnetic screening for components contained in tray 411 it provides a low inductance current path for grounded components in tray 411 to the isolator’s grounded port connector, and it simultaneously provides a low inductance current path for grounded components in tray 421 to the isolator's grounded port connector. 11 2017101007 26 Μ 2017 [0065] To facilitate connection to the metal shield for components, tray 421 preferably comprises apertures 423 which expose portions of the shield surface so that connections can be made. Preferably, connection is made by soldering.

[0066] Referring to Figure 4e, preferred embodiments of the present invention additionally comprises a second metallic shield 427 which is preferably made of the same material as shield 401, and is preferably made using the same manufacturing process as shield 401, preferably by stamping. Shield 427 has multiple panels 428 which are joined along fold lines 429.

[0067] Figure 4f shows a fully assembled structure comprising the elements shown in Figures 4a-e. Shield 427 is fitted to the outer surface of tray 421 and is preferably joined to shield 401 surrounding tray 411 by means of screws, locking tabs or other features designed to provide both mechanical and electrical connection. In this way, the isolator made according to embodiments of the present invention provides an outer RF shield around all internal components.

[0068] Referring to Figure 4e, the inventor has realised that an additional improvement can be achieved in another embodiment if the two separate elements of the isolator’s folded metal shield 401 and 427, as described above, are combined to form a single metallic shield component. By combining the two separate shield parts, the following advantages are provided: • the net manufacturing cost of the shield is lowered, • the isolator assembly process is simplified, and • the electrical bonding between shield elements is optimised because they are a continuous conductive part.

[0069] Figures 6a and 6b show metal shield 601 fitted to insulating plastic tray 611. Metal shield 601 is manufactured to comprise multiple panels 602 which join central panel 603 along fold lines 605. Central panel 603 comprises an aperture to receive coaxial connector 604 which provides the point of connection for the grounded port of the isolator. In this way, connector 604 is electrically bonded to the central panel of the metal shield 601.

Shield 601 further comprises panels 627 and 628 which correspond to equivalent features of shield 427 in Figure 4e.

[0070] Shield 601 is preferably manufactured by a process such as stamping. This process forms apertures in the shield, including perforations to aid bending of panels, and also bends certain features of the shield into predefined orientations.

[0071] Preferably the shield is bent to fit around plastic insulating trays during product assembly. Referring to Figures 7a-c, plastic insulating trays 711 and 721 are fitted to opposite sides of a single panel of metal shield 701. The shield is then bent to form a conductive surface surrounding trays 711 and 721, using the rigid surface of these trays to assist bending of the shield along predefined fold lines.

[0072] From another perspective, a preferred embodiment of the present invention provides a method of assembly for a galvanic isolator. Referring to Figures 5a-c, a preferred embodiment of the assembly process proceeds as follows: 12 2017101007 26 Μ 2017 [0073] Step 1: coupling components 501 comprising capacitors and ferrite transformers are mounted on PCB 502 using conventional means; [0074] Step 2: the assembled PCB 502 is mounted in insulating tray 511 and is preferably held in place by plastic tabs or latches or by screws; [0075] Step 3: a coaxial connector 503 is mounted into a retaining feature of tray 511 and is connected to contacts on PCB 502. Preferably at this time a coaxial cable 505 (not shown) is also connected to contacts on PCB 502 and one or more ferrite beads are fitted around the cable by sliding them over the loose end (not shown). The loose end of the cable is then fed through aperture 507. A plastic lid 508 (not shown) is then fitted to the top of tray 511 to cover PCB components. This lid may be part of tray 511 as a panel supported by a living hinge.

[0076] Step 4: metal shield 541 is fitted to tray 511 by passing connector 503 through an aperture in the shield and bending the shield panels around the surfaces of tray 511. The metal shield is preferably held in place in its bent position by features on tray 511. Connector 503 is preferably pulled against the surface of shield 541 using screws to form an electrical contact.

[0077] Step 5: tray 521 is fitted to the surface of shield 541 on the opposite side as tray 511 and is held in place by latching features. Components 535 are fitted to recesses in tray 521 which hold them in predefined orientations.

[0078] Step 6: isolated connector 564 is mounted into tray 521 and held in place by retention features of the tray. Coaxial cable 505 (not shown) coming from tray 511 is then connected to connector 564 and to components 535 fitted to tray 521. A plastic lid 518 (not shown) is then fitted to tray 521 in a similar fashion to the way lid 508 is fitted to tray 511.

[0079] Step 7: metal shield 581 is then fitted to plastic tray 521 and bent over its surfaces. Screws are preferably used to bond shields 541 and 581 together in areas where they overlap. As noted above, the metallic shields may be formed from a single or an integral sheet of metallic material to construct the first and second metallic shields.

[0080] Within the scope of embodiments of the invention, a method of assembling a galvanic isolator may be provided comprising the steps of: mounting a PCB assembly of signal coupling components to a first insulating tray; retaining a first coaxial connector within the first insulating tray and connecting same to electrical contacts of the PCB assembly; connecting one end of a coaxial cable to the electrical contacts of the PCB assembly and feeding the other end of the coaxial cable through an aperture of the PCB assembly; fitting a lid to the first insulating tray; forming a first metallic shield comprising a contiguous plurality of panels around the first insulating tray by passing the retained coaxial connector through an aperture in a panel of the metallic shield and bending further panels of the metallic shield to enclose the first insulating tray within the first metallic shield; fitting a second insulating tray to a surface of the formed first metallic shield such that the first and second insulating trays are in opposed positions with respect to each other; 13 2017101007 26 Μ 2017 fitting electrical components to recesses disposed in the second insulating tray; retaining an isolated second coaxial connector within the second insulating tray; electrically connecting the other end of the coaxial cable through apertures of the second insulating tray and the first metallic shield corresponding to the aperture of the PCB assembly to both the isolated second coaxial connector and the electrical components fitted to recesses in the second insulating tray; fitting a lid to the second insulating tray; forming a second metallic shield from the contiguous plurality of panels around the second insulating tray by passing the isolated second coaxial connector through an aperture in a panel of the metallic shield and bending further panels of the contiguous plurality of panels to enclose the second insulating tray within the second metallic shield wherein the contiguous plurality of panels are formed from an integral sheet of metallic material to construct the first and second metallic shields.

[0081] Another embodiment encompassing manufacture of a galvanic isolator includes a method of assembling a galvanic isolator comprising the steps of: mounting a first coaxial connector onto a PCB assembly of signal coupling components; fitting a first metallic shield comprising a contiguous plurality of panels between a first and second plastic insulating tray;

connecting one end of a coaxial cable to the electrical contacts of the PCB assembly; mounting said PCB assembly into a first insulating tray; feeding the other end of the coaxial cable through an aperture of said first insulating tray which is coincident with an aperture in said metal shield and said second insulating tray; forming an enclosing metallic shield comprising a contiguous plurality of panels around the first and second insulating trays by bending further panels of the metallic shield to enclose the first and second insulating trays within the first metallic shield; fitting electrical components to recesses disposed in the second insulating tray; retaining an isolated second coaxial connector within the second insulating tray; electrically connecting the other end of the coaxial cable to both the isolated second coaxial connector and the electrical components fitted to recesses in the second insulating tray; connecting at least two points on the metal shield to form one or more conductive paths for current to flow around said insulating plastic trays.

[0082] Preferably, the contiguous plurality of panels is formed from an integral sheet of metallic material to construct the first and enclosing metallic shields.

[0083] From another perspective, a preferred embodiment of the present invention provides a galvanic isolator with improved high voltage impulse tolerance. The inventor has found that high voltage ceramic capacitors that are conventionally used in isolators can fail if subjected to repeated high voltage surges. The inventor believes the failure mechanism is a combination of thermal shock and piezoceramic fluctuations which cause insulating 2017101007 26 Μ 2017 14 encapsulation to delaminate from the ceramic. The effect of this phenomenon is that capacitors with voltage ratings in excess of the applied surge can fail when subjected to repeated surges less than this value. For example capacitors which can tolerate 9kV DC will fail when subjected to multiple 7kV impulses with standard pulse shapes of 10/700 microseconds. The inventor has discovered that the problem is particularly severe for ceramic capacitors used in conventional isolators which have high relative permittivities, for example greater than 15,000 as is the case with capacitor materials such as Y5V.

[0084] The inventor has found that the failure problem can be substantially reduced by using capacitors with lower permittivities for example less than 4000, as is the case with capacitor materials such as Y5P.

[0085] A preferred embodiment of the present invention therefore provides a galvanic isolator with improved surge voltage tolerance comprising ceramic capacitors having relative permittivities less than 4000.

[0086] As noted above, while this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations, uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[0087] “Comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.” Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

Claims (5)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   1. A galvanic isolator comprising a metallic shield wherein said shield comprises folded sheet metal which forms; a substantially-pianar central panel; and a plurality of side panels operatively connected to said central panel; wherein said metallic shield is electrically connected to at least one of the isolator’s signal ports at said central panel and said side panels are bent so that they are substantially perpendicular to said central panel.
2. 2. A galvanic isolator adapted for high voltage tolerance and simplified manufacturing comprising: a first electrically insulating tray; a second electrically insulating tray; a metallic shield comprised of folded sheet metal; wherein said first insulating tray is coupled to a first surface of said metallic shield and said second insulating tray is coupled to a second surface of said metallic shield, wherein said first and second surfaces are located on opposite sides of the same portion of said metal shield.
3. 3. A galvanic isolator adapted for high voltage impulse tolerance comprising ceramic capacitors wherein said capacitors are: coupled from a first signal port to a second signal port of said isolator, and comprised of ceramic material with relative permittivity less than 4000.
4. 4. A method of assembling a galvanic isolator comprising the steps of: mounting a first coaxial connector onto a PCB assembly of signal coupling components; mounting said PCB assembly into a first of two generally opposed insulating trays; bending one or more panels of a contiguous plurality of panels around the first tray to partially form a first EMF shield for the first tray; connecting one end of a coaxial cable to electrical contacts of the PCB assembly; feeding the other end of the coaxial cable through an aperture of said first insulating tray which is coincident with an aperture in one of the plurality of contiguous panels and said second insulating tray; bending one or more further panels of the contiguous plurality of panels around the first tray so as to enclose the first tray within a formed first EMF shield for the first tray; fitting electrical components to recesses disposed in the second insulating tray; connecting the other end of the coaxial cable to the fitted electrical components in the second insulating tray; bending one or more further panels of the contiguous plurality of panels around the second tray so as to enclose the second tray within a formed second EMF shield for the second tray.
5. 5. A galvanic isolator comprising one or a combination of: a metallic shield formed from a folded metal sheet and having a surface comprising contiguous panels wherein boundaries formed between the contiguous panels are aligned substantially parallel to the paths that induced RF currents would form in a metallic shield with a continuous and/or electrically uninterrupted surface; separate insulating trays adapted for housing a signal coupling stage and a filtering stage, respectively; and at least one capacitor coupled from a first signal port of the isolator to a second signal port of the isolator wherein the at least one capacitor comprises dielectric material with a relative permittivity less than 4000.