AU2016100894B4 - Galvanic isolator for coaxial distribution networks - Google Patents

Abstract

The invention provides at least one galvanic isolator, a galvanic isolator filter structure and a method of manufacturing a galvanic isolator product. According to one embodiment of present invention, the galvanic isolator, having a signal input and a signal output, comprises a signal transformer coupled to an inductive element which is part of a T-section filter. According to another embodiment, the galvanic isolator filter structure formed from a length of coaxial cable inserted through apertures in a plurality of ferrite cores wherein: said ferrite cores are positioned within respective voids formed in a printed circuit board dimensioned to receive said ferrite cores; said coaxial cable is positioned against the surface of said printed circuit board; and the outer conductor of said coaxial cable is conductively bonded to the surface of said printed circuit board. L2 C 2ue Figure 4A

Description

2016100894 08 Aug 2017

Galvanic Isolator for Coaxial Distribution Networks RELATED APPLICATIONS

[0001 ] This application claims priority to Australian Provisional Patent Application No. 2015902323 in the name of Shaun Joseph Cunningham, which was filed on 18 June 2015, entitled “Galvanic Isolator for Coaxial Distribution Networks” and to Australian Provisional Patent Application No.2016902123 in the name of Shaun Joseph Cunningham, which was filed on 1 June 2016, entitled “Low Cost Galvanic Isolator with Improved High Voltage Performance for Coaxial Distribution Networks” and the specifications thereof are incorporated herein by reference in their entirety and for all purposes.

FIELD OF INVENTION

[0002] The present invention relates generally to galvanic isolators for use in coaxial distribution networks and the like. Circuit topologies, component structures and assembly methods are presented which enable improved operational performance, simplified assembly, increased reproducibility and lower manufacturing costs.

[0003] It will be convenient to hereinafter describe the invention with specific reference to galvanic isolation in coaxial communication distribution networks, however it should be appreciated that the present invention is not necessarily limited to that application, only.

BACKGROUND ART

[0004] 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 2016100894 08 Aug 2017 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.

[0005] 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.

[0006] 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 usually 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.

[0007] 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 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.

[0008] There is also a risk that cables entering a premise 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.

[0009] 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. 2016100894 08 Aug 2017 [0010] 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 may cause 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 may also allow signals to leak into the distribution network at each isolator resulting in impaired network performance.

[0011] To lessen the effect of this problem, isolators employ a filtering stage which attenuates signals leaving or entering the network at the isolator. 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] Conventionally such enclosures are made by a die casting process utilising metals such as zinc or aluminium. The primary advantage of this design is believed to be that it provides excellent RF screening because of the lack of joins or seams in the housing and hence the tight electrical bonding of each conductive surface.

[0013] 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. Aluminium enclosures have lower weight, however they are more problematic and more costly to cast than zinc, and are covered by a dense oxide layer which makes electrical contact unreliable.

[0014] Metallic isolator enclosures in general also increase the risk of electric shock to users and field technicians because they expose the electric potential of the connected coaxial cable to touch across their exposed surface. Diecast enclosures also do not facilitate means of providing adequate environmental sealing and generally require the use of sealing compounds such as adhesives which are problematic to apply in manufacture. 2016100894 08 Aug 2017 [0015] Accordingly, the inventor has realised that there is a need for a new isolator architecture which reduces cost and weight of isolator enclosures, is able to provide outer insulation, and facilitates environmental sealing, without compromising RF screening performance.

[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 for electrical breakdown paths to reach.

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

[0018] From yet another perspective, conventional isolators often have poor immunity to repeated high voltage surges. For example, it is often observed that isolator 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 the source of failure and provide a means of improving HV surge tolerance.

[0020] Various other issues associated with conventional isolator design, construction and operation are discussed and described in greater detail hereinbelow and with reference to several of the accompanying drawings.

[0021] Figure 1 shows the circuit architecture of a simple conventional galvanic isolator. The isolator is comprised of two coaxial connectors, J1 and J2, and two capacitors C1 and C2. The capacitance value of these capacitors is chosen to be high enough that it presents a low series impedance and minimum attenuation for high frequency RF signals, typically in the range 1 to 1000MHz, but low enough so that it presents a high series impedance at mains power frequencies, typically 50 to 60Hz. Typical values for these capacitors in conventional isolators are in the range 1 to 10nF. 2016100894 08 Aug 2017 [0022] However, there is a fundamental problem with isolators which use this circuit topology: although the impedance of these series capacitors is very low at the high frequency end of the signal frequency range (e.g. 0.016 ohms at 1GHz), it is quite significant at the low end of the signal range (e.g. 16 ohms at 1 MHz). This means that at low frequencies, the signal current causes a significant proportion of the signal voltage to appear across capacitor C2. This creates a so-called common mode component of the signal which is coupled through the isolator ports to the outer shield conductors of connected coaxial cables. This means a proportion of the signal power at low frequencies is potentially radiated from the isolator as electromagnetic interference, with the connected coaxial cables acting as an antenna. Because of fundamental laws of symmetry, this also means that RF energy coupled into the isolator’s coaxial cables from external sources will create voltages across C2 and cause electromagnetic interference to leak into the distribution network. Both scenarios are highly undesirable for users and network operators.

[0023] To overcome these problems, designers of conventional isolators have used more complex circuits as shown in Figure 2A. In this circuit, signals enter the isolator at coaxial connector J1 and are coupled to transformer T1 through capacitors C1 and C2. Transformer T1 is configured as an inverting transmission line transformer. In this circuit, a significant signal voltage is still induced across grounded capacitor C2 at low frequencies, however this voltage is not directly coupled to the other isolator port and is instead attenuated by the capacitive divider formed by the inter-winding capacitance of transformer T1 (shown symbolically as Cp) and capacitor C3. For typical component values, this capacitive divider will provide around -60dB of attenuation at low signal frequencies. The central feature of these conventional circuits is that grounded capacitor C3 is deliberately closely coupled to transformer T1, without any intervening impedances, to form a capacitive divider with the inter-winding capacitance Cp of T1.

[0024] Having passed through T1, RF signals then pass through transformer T2, which is configured as a common mode choke. This transformer does not present any significant impedance to differential signals passing through its windings, but forms a so-called “Pi-section” low pass filter together with C3 and C4, which attenuates common mode signals induced between the ground connections of the isolator ports. Figure 2B 2016100894 08 Aug 2017 shows the circuit topology of the equivalent Pi-section low pass filter wherein signals first encounter a shunt capacitance to ground.

[0025] In practice, conventional isolators may use more than one common mode choke filtering stage to provide the degree of attenuation required for common mode signals.

[0026] A central requirement for all isolators is that they need to withstand high voltages which appear differentially across the isolator’s ground connections. Specifications for voltage rating of isolators typically stipulate that there will be no breakdown when the isolator is subjected to 3kV mains frequency AC or 7kV lightning surges. This necessitates the use of high voltage capacitors at each point in the isolator.

[0027] Normally, surface mount capacitors are preferred in high frequency circuits because they intrinsically have low parasitic inductance. High voltage surface mount capacitors are generally unsuitable in isolators because they are relatively expensive compared to radial leaded equivalent capacitors. For example a surface mount 2.2nF 6kV capacitor is approximately five times the cost of an equivalent radial capacitor. In addition, because surface mount capacitors are generally not encapsulated, there is a need to apply encapsulation after assembly onto a circuit board which increases manufacturing costs.

[0028] Therefore, as a result of considerable pressure to minimise cost, isolator manufacturers use radially leaded capacitors. However, the parasitic inductance of the leads of these capacitors introduces significant impedances into the isolator circuit which degrade its high frequency performance. This is currently a prominent problem because coaxial network operators want to increase network bandwidths by increasing the upper operational frequency limit of all network elements, including isolators. For example, CATV operators used to specify an upper frequency limit of 750MHz for network elements, but now wish to extend this to 1200MHz. The current use of high voltage radial capacitors limits isolator bandwidth to around 800MHz. In excess of that frequency, conventional isolator insertion loss increases dramatically which is unacceptable to network operators. Accordingly, there is a need for a galvanic isolator with improved insertion loss at frequencies above 800MHz. 2016100894 08 Aug 2017 [0029] The high frequency transmission characteristics of isolators are largely determined by the arrangement of circuit elements, notably capacitors. It is important for isolators to maintain transmission impedance which matches the characteristic impedance of the coaxial cable network, which typically is 75 ohms. Current construction practices for isolators involve hand assembly of mostly radial components in an ad-hoc random orientation. In this situation, component orientation and lead length, and hence RF characteristics, are poorly controlled. This creates poor circuit reproducibility and degrades return loss, which is a measure of how well the isolator matches the impedance of the connected cables and passes RF signals through without degradation. Accordingly there is a need for improved devices and assembly methods which optimise RF characteristics and signal transmission performance of galvanic isolators.

[0030] Figure 6 is a representation of a disk capacitor with radial leads wherein a central ceramic disk 600 is encapsulated in an insulating material 601. On high voltage capacitors, for example capacitors having an operating voltage in excess of 1000 volts, the encapsulating material is deliberately extended onto the leads 602 to prevent breakdown near the capacitor edges. Capacitor leads 603 extend from the centre of the disk and are generally bent in a parallel form to facilitate insertion through mounting holes in printed circuit boards.

[0031 ] A typical value for lead inductance for high voltage radial capacitors is around 0.5nH per mm. This equates to 3 ohms of reactance per mm of lead length at 1GHz. If the total parasitic reactance becomes comparable to the characteristic impedance of the signal transmission circuit, e.g. 75 ohms, it becomes extremely difficult to obtain good RF transmission characteristics such as low insertion loss and good return loss. It is therefore very important to minimise capacitor lead length.

[0032] When leaded capacitors are mounted on conventional printed circuit boards, they are mounted on one side of the PCB with their leads extending through holes to the other side where they are soldered to circuit pads. Typically the capacitor’s leads are bent after insertion through the PCB holes to allow the PCB assembly to be turned upside down without the capacitors falling out while the leads are soldered. When this happens, the capacitors tend to fall downwards away from the circuit board and it is very difficult to control the length of the capacitor lead between the capacitor and the PCB circuit pad. Hence in conventional mounting schemes it is difficult to control the parasitic impedances 2016100894 08 Aug 2017 of high voltage capacitors in high frequency circuits. Accordingly there is a need for improved devices and assembly methods which accurately control parasitic inductance of capacitors.

[0033] From a different perspective, poor control of component placement creates the possibility that capacitors can rest against the metallic enclosure of the isolator or against adjacent capacitors. When this happens, the high voltage tolerance of these capacitors is significantly degraded. For example, the plastic coating on a 6kV capacitor may only be rated to withstand 1kV. The 6kV rating of a capacitor may therefore be reduced to only 1kV if it rests against a nearby metal structure. Similarly, because the high voltage side of one radial capacitor naturally faces the low voltage side of an adjacent parallel capacitor, the voltage tolerance of the capacitor pair may be reduced if the capacitors touch each other. Accordingly, there is a need for an improved component placement technique which guarantees the ability of the isolator to withstand high voltages.

[0034] Figure 3A shows a conventional isolator, including inductors L1 to L4 which represent the total parasitic inductance associated with leads of capacitors C1 to C4. These are shown as single inductances in this diagram for simplicity, but in reality, half of these inductance values are associated with each of the two capacitor leads.

[0035] The signal transmission characteristics of conventional isolators, in particular insertion loss, are known to degrade significantly in the region of 750MHz. The inventor has realised that the main cause for this degradation is a parasitic series resonance predominantly caused by the series combination of Cp and parasitic inductances L1 to L3. Figure 3B shows the simulated performance of a simplified conventional isolator, including excess insertion loss 400 around 750MHz caused by this parasitic series resonance.

[0036] Conventional isolators use small RF transformers wound around ferrite cores typically with a volume of only 10-20 cubic millimetres. The parasitic capacitance Cp of the transformer is largely determined by wire insulation and the length of the wire wound around the transformer core. It is not practical to reduce the core size further and all transformers have a similar Cp value, around 3 pF. 2016100894 08 Aug 2017 [0037] Capacitors C1 to C4 need to tolerate the maximum voltage rating of the isolator and are physically large. The total lead inductance for radial high voltage capacitors commonly used in isolators is around 15nH.

[0038] The reactances of these parasitic elements combine to create a series resonance around 750MHz in conventional isolators. This resonance couples energy out of the signal path and causes increased insertion loss at the resonant frequency, as shown in Figure 4c. Accordingly, there is a need for improved isolator circuit architectures which avoid parasitic resonances and improve insertion loss characteristics.

[0039] From a different perspective, again referring to Figure 2, in conventional isolators, the low inter-winding capacitance of T1 forms a capacitive voltage divider with the parallel combination of C1 and C2. This causes voltages applied between isolator ports to be concentrated across the windings of transformer T1. The voltage rating of these transformers is generally determined by the thickness of the insulating coating on the winding wire and is typically in the range 100 to 500 volts. Isolators are generally specified to provide isolation to voltages much higher than this, for example 3kVAC or 7 kV transient surges. Exposure to these voltages will cause the an arc to form between the windings ofT 1 until such time as capacitors C1 and C2 charge to the applied voltage. Arcing of this nature can degrade the RF characteristics of this transformer and could potentially lead to transformer and isolator failure.

[0040] Accordingly, there is a need for improved isolator circuit structures which eliminate the possibility of component degradation in the presence of high voltages.

[0041] The discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain related 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 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. 2016100894 08 Aug 2017

SUMMARY OF INVENTION

[0042] In view of the foregoing, it is an object of the present invention to overcome or alleviate at least one disadvantage associated with related art arrangements, or at least provide a useful alternative.

[0043] In one form, the present invention provides a galvanic isolator adapted for a coaxial cable network, said galvanic isolator comprising: a first isolator port coupled to a signal transformer by a plurality of capacitive elements configured to provide an electrically isolating barrier for low frequency currents; and, a common mode filter stage coupled to said signal transformer, said common mode filter stage comprising at least one further capacitive element connected with at least two series inductive elements to form a T-section, wherein the inductive elements comprise ferrite cores in the form of beads with apertures adapted to pass a coaxial cable therethrough which couples signals from the signal transformer to a second isolator port.

[0044] In another form, the present invention provides a method of manufacturing a galvanic isolator product including isolator circuitry, the method comprising the steps of: accommodating a first isolator port coupled to a signal transformer by a plurality of capacitive elements configured to provide an electrically isolating barrier for low frequency currents on a tray formed from an insulating material; fitting a plurality of ferrite beads at intervals to a coaxial cable having an exposed outer conductor and exposed inner conductor at its ends to form a common mode choke assembly; positioning the common mode choke assembly onto a printed circuit board with at least one aperture for accommodating the ferrite beads and pads for contacting the exposed outer conductor and exposed inner conductor, respectively, of the coaxial cable such that the coaxial cable is substantially coplanar with the printed circuit board; 2016100894 08 Aug 2017 soldering the exposed outer and inner conductors of the coaxial cable to the pads to provide electrical contact for the coaxial cable to couple signals from the signal transformer to a second isolator port; forming a shield enclosure from metallic sheet material around the tray to create an RF shield for the isolator circuitry.

[0045] According to a first aspect of the present invention there is provided a galvanic isolator having a signal input and a signal output, the galvanic isolator comprising a signal transformer with a T-section filter stage having a series inductive element coupled to said signal transformer.

[0046] The galvanic isolator T-section filter stage may be part of a common mode signal filter. The T-section filter may comprise at least one inductive element in the form of a ferrite material effective to damp parasitic resonances and improve insertion loss. Preferably the permeability of the ferrite is predominantly lossy above 10MHz. The T-section filter may comprise a coaxial cable arranged to pass through apertures in one or more ferrite cores.

[0047] According to another aspect of the present invention there is provided a galvanic isolator filter structure formed from a length of coaxial cable inserted through apertures in a plurality of ferrite cores wherein: said ferrite cores are positioned within respective voids formed in a printed circuit board dimensioned to receive said ferrite cores; said coaxial cable is positioned against the surface of said printed circuit board; and the outer conductor of said coaxial cable is conductively bonded to the surface of said printed circuit board.

[0048] Preferably the coaxial cable does not have an outer insulating coating and is soldered to said circuit board.

[0049] Those skilled in the art will recognise that the filter structure formed from coaxial cable and ferrite cores may be readily incorporated in the galvanic isolator hereinbefore described. 2016100894 08 Aug 2017 [0050] According to another aspect of the present invention there is provided a galvanic isolator comprising circuitry contained within a metallic shield enclosure constructed from folded sheet metal to form a RF shield.

[0051] The shield enclosure may be situated within an outer plastic case which provides environmental sealing and/or protection. Selected components of the circuitry may be conductively bonded (e.g. soldered) to features formed on the surface of said shield enclosure.

[0052] The shield enclosure may contain features which are produced by a stamping process. The metallic shield enclosure may be made from tin plated steel, brass or galvanised steel less than approximately 1 millimetre in thickness.

[0053] The galvanic isolator shield enclosure may include raised features which provide means of locating components on the surface of the shield. The shield enclosure may further comprise tab features which provide a means of soldering or attaching the shield to other structures.

[0054] Those skilled in the art will recognise that the shield enclosure may be readily employed to contain the galvanic isolator circuitry and/or filter structure formed from coaxial cable and ferrite cores, hereinbefore described.

[0055] According to another aspect of the present invention there is provided a method of manufacturing a galvanic isolator product comprising accommodating isolator circuitry on a tray formed from an insulating material, and forming a shield enclosure from metallic sheet material around the tray to create an RF shield for the isolator circuitry.

[0056] The method may additionally include accommodating the shield enclosure within an outer plastic case to provide environmental sealing and/or protection.

[0057] According to aspects of the present invention a galvanic isolator comprising an improved enclosure enables lower cost and weight by eliminating the need for expensive die cast enclosures through the use of thin preformed metal sheets. 2016100894 08 Aug 2017 [0058] According to aspects of the present invention a galvanic isolator comprising internal insulating trays enables increased breakdown voltage between signal circuitry and the isolator’s metallic RF screen by providing an insulating barrier for discharges.

[0059] These and other aspects, features and advantages of the invention and its various embodiments will be apparent from the description contained in this specification as a whole, including the following detailed disclosure and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] 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 simplistic conventional galvanic isolator;

Figures 2A and 2B are schematic diagrams of a conventional galvanic isolator with reduced electromagnetic leakage at low frequencies and a simplified representation of a Pi-section low pass filter;

Figures 3A is a schematic diagram of a conventional galvanic isolator with reduced electromagnetic leakage at low frequencies showing parasitic inductances of capacitors;

Figure 3B is a plot of indicative insertion loss of a conventional galvanic isolator equivalent to the circuit of Figure 3A;

Figures 4A and 4B are a schematic diagram of an embodiment of the present invention and a simplified representation of a T-section low pass filter;

Figure 4C is a plot of indicative insertion loss of an embodiment of the present invention showing a significant improvement compared to a conventional galvanic isolator;

Figure 5 is a schematic diagram of a galvanic isolator incorporating a surge arrestor according to another embodiment of the present invention; 2016100894 08 Aug 2017

Figure 6 is an isometric drawing of a conventional radial leaded high voltage capacitor;

Figure 7 is an isometric drawing of a high voltage radial leaded capacitor as may be used in embodiments of the present invention;

Figures 8A to 8E are isometric drawings of an insulating mounting structure for high voltage capacitors as may be used in embodiments of the present invention;

Figure 9A is an equivalent circuit diagram of an embodiment of the present invention;

Figure 9B is a circuit diagram of a preferred arrangement of capacitors according to an embodiment of the present invention, including parasitic inductances;

Figure 9C is an isometric drawing of an insulating mounting structure for high voltage capacitors which has controlled signal transmission characteristics at high frequencies as may be used in embodiments of the present invention;

Figures 10A to 10F are a set of isometric drawings indicating an assembly method for insulating mounting structures and high voltage capacitors as may be used in embodiments of the present invention;

Figures 11A to 11F are a set of isometric drawings indicating an alternative assembly method for insulating mounting structures and high voltage capacitors as may be used in embodiments of the present invention;

Figure 12 is a flow chart summary of possible methods of assembly according to embodiments of the present invention;

Figures 13A to 13F are isometric drawings illustrating assembly of a circuit structure to implement a common mode filter according to an embodiment of the present invention;

Figures 14A and 14B are isometric views of a metallic shield structure in an open and closed form according to an embodiment of the present invention; 2016100894 08 Aug 2017

Figures 15A to 15H are a series of isometric drawings which indicate a method of assembly of a galvanic isolator according to an embodiment of the present invention;

Figures 16A and 16B are front and rear isometric views illustrating formation of a sheet metal RF shield for a galvanic isolator according to embodiments of the present invention; and

Figures 17A to 17F are exploded isometric views of an isolator comprising two insulating trays and two folded sheet metal shields according to embodiments of the present invention.

DETAILED DESCRIPTION

[0061] Features and aspects of the present invention may be better understood from the following detailed description of related art and embodiments with reference to the drawings. 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 may become apparent to those skilled in the art from this detailed description.

[0062] In the description throughout this specification, 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 the present invention and are not meant to restrict the scope of the invention.

[0063] At high frequencies, linear circuit elements often need to be treated as complex arrangements of resistance and reactance. For example, capacitors and inductors may possess frequency dependent capacitive, resistive and inductive qualities. For the purpose of clarity in the following description and claims, the following definitions are provided.

[0064] The term “capacitive element” refers to one or more discrete capacitors connected to provide a single capacitance, or to a purposely crafted circuit structure, 2016100894 08 Aug 2017 whose reactance at 1 KHz is predominantly capacitive. Similarly, the term “inductive element” refers to one or more discrete inductors connected to provide a single inductance, or to a purposely crafted circuit structure, whose reactance at 1 KHz is predominantly inductive.

[0065] 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.

[0066] The term “isolator port” refers to the coaxial electrical interface point where a cable is coupled to a galvanic isolator.

[0067] 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.

[0068] The term “signal transformer” refers to a transformer comprising two or more wires wound around a ferromagnetic core as a parallel group of wires wherein signals passing through the transformer are electromagnetically coupled from one winding to the other.

[0069] The term “common mode signal” refers to electromagnetic energy in the form of voltage which appears between the outer conductors of isolator ports, and the corresponding current which flows according to this voltage.

[0070] The term “tray” refers to a physical structure which is shaped to accept and surround, or partially surround, portions of isolator circuitry.

[0071] Additional definitions and a guide to interpreting the present specification are provided toward the end of the detailed description.

[0072] From a first perspective, the present invention provides a galvanic isolator comprising a first isolator port coupled to a plurality of capacitive elements configured to provide an electrically isolating barrier for low frequencies, a transformer coupled to said 2016100894 08 Aug 2017 capacitive elements and a T-section common mode filter stage coupled to said transformer.

[0073] The inventor has realised that the poor insertion loss characteristics of conventional isolators can be significantly improved by the use of a T-section common mode filter stage instead of a Pi-section common mode filter stage coupled to the signal transformer T1. Figure 4A provides a circuit schematic of a preferred embodiment of the present invention. In this preferred embodiment, signals are coupled from a first isolator port J1, through capacitors C1 and C2 and their associated parasitic inductances L1 and L2, to inverting transmission line transformer T1 and then to a transformer T3. T3 forms the series inductive element of a T section filter which attenuates common mode signals produced by isolator circuitry. Figure 4B shows the generic form of a so-called T-section low pass filter stage comprising capacitive element C3 and inductive elements LT2 and LT3. T2 and T3 can also be conveniently referred to as common mode chokes.

[0074] Preferably common mode chokes T3, T2 and any additional common mode chokes, are provided by ferrite cores fitted to a coaxial cable which couples signals from transformer T1 to one or more second isolator port(s) J2. Preferably the ferrite cores are cylindrical tubes or “beads” with round apertures slightly bigger than the diameter of the coaxial cable they are fitted onto. For example, the coaxial cable is preferably a so called “086” industry standard cable with an outside diameter of 0.086 of an inch (or 2.2mm) or RG179 with an outside diameter of 2.5mm. The ferrite bead preferably has an aperture diameter of around 2.5 to 3mm, an external diameter of between 5 and 10mm and a length of between 5 and 20mm.

[0075] A key feature of this aspect of preferred embodiments of the present invention is the type of ferrite material used for common mode choke T3. Preferably, the ferrite material used for this choke is one whose complex permeability provides a predominantly lossy or resistive characteristic at the resonant frequency of Cp and L3. Preferably the ferrite material is predominantly lossy above 10MHz. Because T3 induces a resistive series impedance between Cp and inductors L1 to L3, the Q of the series resonance is significantly lowered and the impact of the series resonance on insertion loss is substantially reduced. Figure 4C shows an indicative simulation of the insertion loss of a conventional isolator, depicted as curve 400, and an improved isolator, depicted as curve 401, according to a preferred embodiment of the present invention. 2016100894 08 Aug 2017 [0076] From another perspective, an embodiment of the present invention provides a galvanic isolator comprising a signal coupling transformer and a gaseous discharge device coupled to said signal coupling transformer.

[0077] Referring to Figure 5, a preferred embodiment of the present invention comprises a signal coupling transformer T1 and a gaseous discharge device S1 coupled to said signal coupling transformer.

[0078] The gaseous discharge device comprises a plurality of electrodes and gas at a specific pressure contained in a sealed chamber. When the voltage across the gaseous discharge device reaches its so-called striking voltage, a low impedance arc discharge is formed and the voltage across the gaseous discharge device collapses close to zero volts.

[0079] As noted in the foregoing description, it is important to minimise the interwinding capacitance of T1 in order to prevent common mode RF signal leakage. The inventor has realised that a gaseous discharge device is able to provide protection for the transformer by limiting the maximum voltage that can be induced between its windings. Furthermore the gaseous discharge device can do this without significantly increasing the net capacitance appearing across the transformer’s windings. For example gaseous discharge devices are available in small device packages measuring less than 50 cubic millimetres which have less than 1pF capacitance and a striking voltage of 140 volts. In a preferred embodiment of the present invention, a gaseous discharge device is connected between the ends of the transformer windings which are closely coupled to the outer coaxial shield conductor of the isolator ports 501, 502.

[0080] From another perspective, an embodiment of the present invention provides a galvanic isolator comprising mounting structures for high voltage disk capacitors having radial leads wherein parasitic lead inductances are minimised, manufacturing assembly processes are simplified and tolerance to high voltage is increased.

[0081] A preferred embodiment of the present invention comprises an insulating holder formed to receive a plurality of radial capacitors. Referring to Figure 8A, the insulating holder 800 preferably comprises a base section 802 and perpendicular partitions 801. The base section preferably includes recesses 803 intended to receive and contain leads of radial capacitors. The perpendicular partitions 801 are intended to 2016100894 08 Aug 2017 provide physical support for capacitors and to prevent adjacent capacitors from coming into contact with each other. By providing a controlled mounting arrangement for radial capacitors, the present invention provides improved RF circuit characteristics and guaranteed high voltage tolerance.

[0082] The insulating holder is preferably made from low cost plastic and is manufactured using injection molding techniques. By way of example, the dimensions of each partition 801 (or 1001 as shown in figure 10a) may be 12 x 12 x 1mm and the dimensions of the base section may be 12 x 30 x 1mm.

[0083] With reference to Figure 8B, the opposite side of the base section to the partitions comprises protrusions 804 and 805 which allow the holder to be located and retained on a printed circuit board using detent features.

[0084] With reference to Figure 8C, radial capacitors 806 are mounted between partitions of the holder 800 so that their leads are located by recesses in the base section 807 prior to soldering to the PCB. Prior to mounting in the insulating holder 800 the capacitor leads are preferably bent by approximately 90 degrees so that they are parallel to the surface of the PCB. An example of a radial capacitor with leads bent in this manner is shown in Figure 7. Preferably, the bends 701 are as close to the end of the capacitor encapsulation 702 as possible.

[0085] With reference to Figure 8D, this embodiment of the invention further comprises printed circuit board apertures 809 and 810 which match the protrusions 804 and 805 on the base section of the holder. The PCB preferably also includes conductive pads 811 which are aligned to the capacitor leads when mounted in the insulation holder. With reference to Figure 8E, capacitors are preferably connected to the conductive pads 811 using solder. Key advantages of this means of mounting capacitors are: capacitor connections are confined to a single side of the PCB which helps manage high voltage insulation requirements, capacitor lead lengths and parasitic inductances are minimised, and; it is easy to control and inspect the quality of the soldered connections to improve reproducibility.

[0086] Optionally, adhesive can be applied after capacitors have been mounted to improve mechanical robustness. In this case, adhesive is applied along the top of the insulating partitions and runs down between the partitions and capacitors. 2016100894 08 Aug 2017 [0087] From another perspective, an embodiment of the present invention provides a galvanic isolator comprising mounting structures for high voltage disk capacitors having radial leads wherein a plurality of capacitors is configured to optimise the passage of RF signals through said capacitors.

[0088] Figure 9A, shows a simplified circuit diagram of an embodiment of the present invention wherein RF signals flow through capacitors C1 and C2 and their respective parasitic lead inductances L1 and L2.

[0089] A preferred embodiment of the present invention comprises a plurality of capacitors connected in parallel to form capacitors C1 and C2. For example C1 and C2 may be provided by a parallel combination of C1a and C1b and C2a and C2b respectively, as shown in Figure 9B. The advantage of this arrangement is that the net parasitic inductance of C1 and C2 is lowered because parasitic lead inductances L1a1 to L2b2 are arranged in parallel pairs. For two capacitors in parallel, the net parasitic inductance is therefore halved.

[0090] Another key advantage of this circuit feature is that the capacitors are deliberately arranged to maximise capacitance between C1 and C2 at the midpoint of the components, shown as Ca and Cb in Figure 9B. Introducing balanced capacitance at this point assists in tuning the return loss characteristics of this portion of the RF signal path and the overall galvanic isolator. A preferred embodiment of the present invention comprises four capacitors C1a, C1b, C2a and C2b arranged with C1a and C1b located in the two central positions of the insulating holder and C2a and C2b located in the outermost positions of the insulating holder, as shown in Figure 9C.

[0091] Other embodiments of the present invention may include more than 4 capacitors. For example if a fifth capacitor is used, it may be located between C1a and C1b to further increase the midpoint capacitances of the capacitor group. This may prove advantageous in achieving good return loss. Embodiments of the invention therefore contemplate a plurality of capacitors mounted in an insulating holder and arranged in an interleaved manner to create inter-component capacitance.

[0092] From a related perspective, the present invention may be embodied in a method of manufacturing a galvanic isolator, including the operations of: mounting an insulating holder onto a printed circuit board; 2016100894 08 Aug 2017 fitting capacitors into said insulating holder; and soldering the leads of said capacitors to conductive pads on the surface of said printed circuit board.

[0093] Various intermediate stages of the manufacturing process according to this embodiment are shown in Figures 10A-10F. Insulating holder 1001, according to preferred aspects of the present invention, is mounted onto printed circuit board 1002 to form assembly 1003. A plurality of capacitors 1004 are then inserted into assembly 1003 to form assembly 1005. Solder is applied 1007 to capacitor leads to create circuit connectivity and produce the completed assembly 1006.

[0094] From a related perspective, the present invention may be embodied in an alternative method of manufacture of a galvanic isolator, including the operations of: inserting capacitors into an insulating holder; mounting said insulating holder onto a printed circuit board; and soldering the leads of said capacitors to conductive pads on the surface of said printed circuit board.

[0095] Various intermediate stages of this manufacturing process are shown in Figures 11A-11F. A plurality of capacitors 1102 is inserted into an insulating holder 1101 according to other preferred aspects of the present invention, to form assembly 1103. This assembly is mounted onto printed circuit board 1104 to form assembly 1105. Solder is applied 1107 to capacitor leads to create circuit connectivity and produce the completed assembly 1106.

[0096] Figure 12 provides a summary of the methods of manufacture according to the above alternative embodiments of the present invention.

[0097] From yet another perspective the present invention may be embodied by a galvanic isolator comprising a common mode filter wherein: the filter is formed from ferrite beads fitted to a length of coaxial cable; the ferrite beads are located within apertures in a printed circuit board; and the coaxial cable is soldered to the surface of the printed circuit board adjacent to the apertures. 2016100894 08 Aug 2017 [0098] Various intermediate stages of production of this embodiment are shown in Figures 13A-13F. Coaxial cable 1302 is cut to a prescribed length and its ends are prepared for termination by exposing a short length of the inner conductor 1303. Preferably this coaxial cable is one which does not have a plastic outer sheath and has an outer coaxial conductor which can be soldered. For example a semi-rigid coaxial cable with tin soaked outer conductor is preferably used. A plurality of ferrite beads 1301 are fitted onto said coaxial cable to form assembly 1304. Circuit board 1305 comprises contact pads 1306 on its surface which are used for connection to the filter and apertures 1311. Assembly 1304 is positioned onto PCB 1305 so that the ferrite beads 1301 are located within apertures 1311 of the PCB and the coaxial cable outer conductor is in contact with the pads 1306 on the surface of the PCB. Figure 13E is an isometric side view showing an example of the alignment of the coaxial cable, ferrite bead and PCB according to a preferred embodiment of the present invention. Finally solder is used to attach the outer coaxial conductor to pads in the circuit board 1309 and to attach the inner conductor to other pads 1310.

[0099] Key advantages of this preferred aspect of the present invention may include: connections to the coaxial cable have very low parasitic inductance and hence improved RF performance, and assembly procedures are simplified because the coaxial cable is arranged in a planar form which can be connected very quickly.

[00100] From yet another perspective, the present invention may be embodied in a galvanic isolator comprising an inner metallic shield surrounded by an outer plastic case, said internal metallic shield comprising metal less than 1 millimetre thick and comprising features formed by a stamping process.

[00101] Referring to Figure 14A, a preferred embodiment of the present invention comprises a metal shield structure 1400 which is made from thin metal. For reasons of cost, strength and weight, preferably this shield structure is made from tin plated steel, however any solderable metal such as brass or zinc galvanised steel may be used. Preferably the metal shield is between about 1 and about 0.1 millimetres thick, but is most preferably between about 0.2 and about 0.4 millimetres thick. Apertures 1402 are made in the shield to accommodate components such as isolator ports. Mounting guides 1403 are formed on the shield by bending portions which protrude from the surface. These guides allow circuit boards and other components of the isolator to be aligned 2016100894 08 Aug 2017 with features of the shield. The shield also includes solder tabs 1404 which are used to attach the shield to printed circuit boards or other shield panels by soldering or mechanical means such as bending. Preferably the physical structure of the metal shield is formed using a stamping process.

[00102] The metal shield is preferably assembled by folding the panels of the shield 1401 to form a box structure as shown in Figure 14B.

[00103] The key advantage of this shield assembly is that it uses relatively little metallic materials which lowers cost and weight and it is produced using a manufacturing method which is well suited to high volume production.

[00104] From another perspective, the present invention may be embodied in a method of assembly of a galvanic isolator comprising an inner metallic shield and an outer plastic case comprising the steps of: folding a patterned metal sheet to form a box structure; inserting printed circuit board assemblies into said box structure; inserting metallic shield partitions into said box structure; and inserting said box structure into a plastic case.

[00105] Referring to Figures 15A-15H, a metallic box 1500 is formed from a piece of sheet metal, preferably tin plate steel. PCB assemblies 1501 are inserted into said box in direction A1 preferably with the aid of guides 1505. A metallic partition 1502 is then inserted into the box in direction A2 to provide separate shield enclosures. Preferably this partition is also made from the same thin metal sheet used to make the box. A metal panel 1503 is then attached to the open end of the box to form a closed shield structure. Preferably metal tabs 1504 on the shield box protrude through holes in the metal panel 1503 and are bent to retain the panel.

[00106] Preferably at least one of these tabs is soldered to the panel. Figure 15E provides a close up view of the tabs.

[00107] Figure 15F is a view of the assembled metal box from the opposite side to Figure 15E. A plastic case 1505 is fitted over the metal box in direction A3. Finally a plastic panel 1506 is fitted in direction A4 to complete the plastic case. The advantage 2016100894 08 Aug 2017 of this assembly method is that cost and weight of the galvanic isolator are reduced compared to conventional isolators.

[00108] From a related perspective an embodiment of the present invention may provide a galvanic isolator comprising: a grounded port; an electrically insulating tray; and a metallic shield comprising folded sheet metal; wherein the metallic shield comprises a substantially planar central panel, the central panel is bounded by panels bent substantially perpendicular to said central panel, the central panel is electrically coupled to the ground connection of said grounded port of the isolator, and the insulating tray is enclosed within said metal shield.

[00109] Figure 16A shows one view of a preferred embodiment of the present invention. Metal shield 1601 is manufactured to comprise multiple panels 1602 which join central panel 1603 along fold lines 1605. Central panel 1603 comprises an aperture to receive coaxial connector 1604 which provides the point of connection for the grounded port of the isolator. In this way, connector 1604 is electrically bonded to the central panel 1603 of the metal shield 1601.

[00110] Preferably metal shield 1601 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 about 0.5mm. Most preferably the sheet thickness is about 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 an attractive option for lowering the cost of RF shields used in galvanic isolators.

[00111] Preferably, metal shield 1601 is manufactured with a low cost process such as stamping. During shield manufacture some panels 1606 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 1602 in the same planar orientation as central panel 1603. During isolator manufacture metal shield 1601 is preferably bent along fold lines 1605 either by hand or by machine to form the metal shield for the isolator. In order to assist hand assembly, features such as 2016100894 08 Aug 2017 perforations or indentations are preferably arranged along fold lines 1605 to concentrate bending forces and improve bend alignment accuracy.

[00112] Figure 16B provides a different perspective of the same assembly showing metal shield 1601, insulating tray 1607 and the rear side of connector 1604. Preferably tray 1607 is made from a low cost thermoplastic material such as polypropylene, ABS, polyethylene or similar materials. The primary functions of this tray are: • to house isolator circuitry which is immediately coupled to the grounded connector 1604; • to provide an insulating barrier between this circuitry and metal shield 1601 to increase the high voltage tolerance of the isolator; and • to provide a rigid structure around which the metal shield can easily be bent into the desired shape.

[00113] Tray 1607 preferably has a lid made of the same insulating material as the tray. This is not shown in Figure 16B 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.

[00114] Tray 1607 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.

[00115] In normal operation, components carrying RF signals in an isolator can couple energy to the nearby metal shield resulting in 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.

[00116] Referring to Figure 16B, dashed arrows 1608 represent the direction of induced currents flowing across the inner surface of the metal shield 1601 toward connector 1604. According to embodiments of the present invention, the panels 1602 of the metal shield 1601 are arranged to avoid any surface discontinuities along the 2016100894 08 Aug 2017 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.

[00117] As with the embodiment of Figure 15, a plastic case may be fitted to the outside of the isolator enclosure, if desired.

[00118] From a another perspective, an 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, the tray being coupled to a first surface of the metallic shield and a second insulating tray being coupled to a second surface of the metallic shield, wherein the first and second surfaces are located on opposite sides of a portion of the metal shield.

[00119] Figure 17A 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 17C and 17D 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.

[00120] Grounded connector 1704 is coupled to a wall of grounded port tray 1711 which provides mechanical support. The active and ground connections of connector 1704 are coupled to conductors on printed circuit board 1705 which contains signal coupling components 1706. Tray 1711 also comprises an aperture 1707 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 1711 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 1711 are: 60mm long, 40mm wide and 20mm tall with a wall thickness of 1-2mm. As noted previously, tray 1711 preferably comprises a low cost thermoplastic material and is made by an injection moulding process. 2016100894 08 Aug 2017 [00121] Still referring to Figure 17A, isolated port tray 1721 is preferably positioned in an inverted manner underneath tray 1711 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 1721 preferably has the same outer surface dimensions as tray 1711 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 1721 is also preferably made of low cost thermoplastic material. Tray 1721 also has an aperture 1727 positioned adjacent to aperture 1707 in tray 1711 to allow a cable to pass from one tray to the other carrying signals between circuitry contained in each tray.

[00122] According to a key aspect of this embodiment, tray 1721 comprises apertures 1723 in its closed surface 1722 which allow components housed within tray 1721 to connect to the isolator’s metal shield which passes across surface 1722 between tray 1711 and tray 1721 as shown in Figures 17C and 17D. 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.

[00123] Figure 17B shows trays 1711 and 1721 from the opposite perspective. Isolated port connector 1724 is mounted in a feature of tray 1721 which is designed to receive and mechanically support it. Unlike the grounded port tray, the isolated port tray 1721 preferably does not contain a printed circuit board. Instead tray 1721 comprises support structures 1728 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 1711 to the isolated connector 1724 in tray 1721. The advantage of this approach is that the cost of the isolator is reduced because no RGB is needed to provide connectivity and the components have minimal parasitic impedances in their connections which improves RF performance.

[00124] Figure 17C shows an additional exploded isometric view of trays 1711 and 1721 with metal shield 1701, corresponding to shield 1601 in Figure 16A, fitted to tray 1711. In the fully assembled form, the metal shield 1701 surrounding tray 1711 is in 2016100894 08 Aug 2017 contact with the adjacent surface of tray 1721. This allows the metal shield to provide multiple functions, for example: • electromagnetic screening for components contained in tray 1711; • a low inductance current path for grounded components in tray 1711 to the isolator’s grounded port connector; and • simultaneously providing a low inductance current path for grounded components in tray 1721 to the isolator’s grounded port connector.

[00125] To facilitate connection to the metal shield for components, tray 1721 preferably comprises apertures 1723 which expose portions of the shield surface so that connections can be made. Preferably, connection is made by soldering.

[00126] Referring to Figure 17E, these embodiments of the present invention may additionally comprise a second metallic shield 1727 which is preferably made of the same material as shield 1701, and is preferably made using the same manufacturing process as shield 1701, preferably by stamping. Shield 1727 has multiple panels 1728 which are joined along fold lines 1729.

[00127] Figure 17F shows a fully assembled structure comprising the elements shown in Figures 17A-17E. Shield 1727 is fitted to the outer surface of tray 1721 and is preferably joined to shield 1701 surrounding tray 1711 by means of screws, locking tabs or other features designed to provide both mechanical and electrical connection. In this way, an isolator made according to embodiments of the present invention is able to provide an outer RF shield around all internal components.

[00128] 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.

[00129] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless 2016100894 08 Aug 2017 otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

The following sections I - III provide a guide to interpreting the present specification. I. Terms [00130] The term “product” means any machine, manufacture and/or composition of matter, unless expressly specified otherwise.

[00131] The term “process” means any process, algorithm, method or the like, unless expressly specified otherwise.

[00132] Each process (whether called a method, algorithm or otherwise) inherently includes one or more steps, and therefore all references to a “step” or “steps” of a process have an inherent antecedent basis in the mere recitation of the term ‘process’ or a like term. Accordingly, any reference in a claim to a ‘step’ or ‘steps’ of a process has sufficient antecedent basis.

[00133] The term “invention” and the like mean “the one or more inventions disclosed in this specification”, unless expressly specified otherwise.

[00134] The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, “certain embodiments”, “one embodiment”, “another embodiment” and the like mean “one or more (but not all) embodiments of the disclosed invention(s)”, unless expressly specified otherwise.

[00135] The term “variation” of an invention means an embodiment of the invention, unless expressly specified otherwise.

[00136] A reference to “another embodiment” in describing an embodiment does not imply that the referenced embodiment is mutually exclusive with another embodiment (e.g., an embodiment described before the referenced embodiment), unless expressly specified otherwise. 2016100894 08 Aug 2017 [00137] The terms “including”, “comprising” and variations thereof mean “including but not limited to”, unless expressly specified otherwise.

[00138] The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise.

[00139] The term “plurality” means “two or more”, unless expressly specified otherwise.

[00140] The term “herein” means “in the present specification, including anything which may be incorporated by reference”, unless expressly specified otherwise.

[00141] The phrase “at least one of, when such phrase modifies a plurality of things (such as an enumerated list of things), means any combination of one or more of those things, unless expressly specified otherwise. For example, the phrase “at least one of a widget, a car and a wheel” means either (i) a widget, (ii) a car, (iii) a wheel, (iv) a widget and a car, (v) a widget and a wheel, (vi) a car and a wheel, or (vii) a widget, a car and a wheel. The phrase “at least one of”, when such phrase modifies a plurality of things, does not mean “one of each of the plurality of things.

[00142] Numerical terms such as “one”, “two”, etc. when used as cardinal numbers to indicate quantity of something (e.g., one widget, two widgets), mean the quantity indicated by that numerical term, but do not mean at least the quantity indicated by that numerical term. For example, the phrase “one widget” does not mean “at least one widget”, and therefore the phrase “one widgef does not cover, e.g., two widgets.

[00143] The phrase “based on” does not mean “based only on”, unless expressly specified otherwise. In other words, the phrase “based on” describes both “based only on” and “based at least on”. The phrase “based at least on” is equivalent to the phrase “based at least in part on”.

[00144] The term “represent” and like terms are not exclusive, unless expressly specified otherwise. For example, the term “represents” do not mean “represents only”, unless expressly specified otherwise. In other words, the phrase “the data represents a credit card number” describes both “the data represents only a credit card number” and “the data represents a credit card number and the data also represents something else”. 2016100894 08 Aug 2017 [00145] The term “whereby” is used herein only to precede a clause or other set of words that express only the intended result, objective or consequence of something that is previously and explicitly recited. Thus, when the term “whereby” is used in a claim, the clause or other words that the term “whereby” modifies do not establish specific further limitations of the claim or otherwise restricts the meaning or scope of the claim.

[00146] The term “e.g.” and like terms mean “for example”, and thus does not limit the term or phrase it explains. For example, in the sentence “the computer sends data (e.g., instructions, a data structure) over the Internet”, the term “e.g.” explains that “instructions” are an example of “data” that the computer may send over the Internet, and also explains that “a data structure” is an example of “data” that the computer may send over the Internet. However, both “instructions” and “a data structure” are merely examples of “data”, and other things besides “instructions” and “a data structure” can be “data”.

[00147] The term “i.e.” and like terms mean “that is”, and thus limits the term or phrase it explains. For example, in the sentence “the computer sends data (i.e., instructions) over the Internet”, the term “i.e.” explains that “instructions” are the “data” that the computer sends over the Internet.

[00148] Any given numerical range shall include whole and fractions of numbers within the range. For example, the range “1 to 10” shall be interpreted to specifically include whole numbers between 1 and 10 (e.g., 2, 3, 4,. .. 9) and non-whole numbers (e.g., 1.1, I. 2, . . . 1.9). II. Forms of Sentences [00149] Where a limitation of a first claim would cover one of a feature as well as more than one of a feature (e.g., a limitation such as “at least one widget” covers one widget as well as more than one widget), and where in a second claim that depends on the first claim, the second claim uses a definite article “the” to refer to the limitation (e.g., “the widget”), this does not imply that the first claim covers only one of the feature, and this does not imply that the second claim covers only one of the feature (e.g., “the widget” can cover both one widget and more than one widget). 2016100894 08 Aug 2017 [00150] When an ordinal number (such as “first”, “second", “third” and so on) is used as an adjective before a term, that ordinal number is used (unless expressly specified otherwise) merely to indicate a particular feature, such as to distinguish that particular feature from another feature that is described by the same term or by a similar term. For example, a “first widget” may be so named merely to distinguish it from, e.g., a “second widget”. Thus, the mere usage of the ordinal numbers “first” and “second” before the term “widget” does not indicate any other relationship between the two widgets, and likewise does not indicate any other characteristics of either or both widgets. For example, the mere usage of the ordinal numbers “first” and “second” before the term “widget” (1) does not indicate that either widget comes before or after any other in order or location; (2) does not indicate that either widget occurs or acts before or after any other in time; and (3) does not indicate that either widget ranks above or below any other, as in importance or quality. In addition, the mere usage of ordinal numbers does not define a numerical limit to the features identified with the ordinal numbers. For example, the mere usage of the ordinal numbers “first” and “second” before the term “widget” does not indicate that there must be no more than two widgets.

[00151] When a single device or article is described herein, more than one device/article (whether or not they cooperate) may alternatively be used in place of the single device/article that is described. Accordingly, the functionality that is described as being possessed by a device may alternatively be possessed by more than one device/article (whether or not they cooperate).

[00152] Similarly, where more than one device or article is described herein (whether or not they cooperate), a single device/article may alternatively be used in place of the more than one device or article that is described. For example, a plurality of computer-based devices may be substituted with a single computer-based device. Accordingly, the various functionality that is described as being possessed by more than one device or article may alternatively be possessed by a single device/article.

[00153] The functionality and/or the features of a single device that is described may be alternatively embodied by one or more other devices which are described but are not explicitly described as having such functionality/features. Thus, other embodiments need not include the described device itself, but rather can include the one or more other devices which would, in those other embodiments, have such functionality/features. 2016100894 08 Aug 2017 III. Disclosed Examples and Terminology Are Not Limiting [00154] Neither the Title nor the Abstract in this specification is intended to be taken as limiting in any way as the scope of the disclosed invention(s). The title and headings of sections provided in the specification are for convenience only, and are not to be taken as limiting the disclosure in any way.

[00155] Numerous embodiments are described in the present application, and are presented for illustrative purposes only. The described embodiments are not, and are not intended to be, limiting in any sense. The presently disclosed invention(s) are widely applicable to numerous embodiments, as is readily apparent from the disclosure. One of ordinary skill in the art will recognize that the disclosed invention(s) may be practiced with various modifications and alterations. Although particular features of the disclosed invention(s) may be described with reference to one or more particular embodiments and/or drawings, it should be understood that such features are not limited to usage in the one or more particular embodiments or drawings with reference to which they are described, unless expressly specified otherwise.

[00156] The present disclosure is not a literal description of all embodiments of the invention(s). Also, the present disclosure is not a listing of features of the invention(s) which must be present in all embodiments.

[00157] Devices that are described as in communication with each other need not be in continuous communication with each other, unless expressly specified otherwise. On the contrary, such devices need only transmit to each other as necessary or desirable, and may actually refrain from exchanging data most of the time. For example, a machine in communication with another machine via the Internet may not transmit data to the other machine for long period of time (e.g. weeks at a time). In addition, devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries.

[00158] A description of an embodiment with several components or features does not imply that all or even any of such components/features are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the present invention(s). Unless otherwise specified explicitly, no component/feature is essential or required. 2016100894 08 Aug 2017 [00159] Although process steps, algorithms or the like may be described in a particular sequential order, such processes may be configured to work in different orders. In other words, any sequence or order of steps that may be explicitly described does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order practical. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modifications thereto, does not imply that the illustrated process or any of its steps are necessary to the invention(s), and does not imply that the illustrated process is preferred.

[00160] Although a process may be described as including a plurality of steps, that does not imply that all or any of the steps are preferred, essential or required. Various other embodiments within the scope of the described invention(s) include other processes that omit some or all of the described steps. Unless otherwise specified explicitly, no step is essential or required.

[00161] Although a product may be described as including a plurality of components, aspects, qualities, characteristics and/or features, that does not indicate that any or all of the plurality are preferred, essential or required. Various other embodiments within the scope of the described invention(s) include other products that omit some or all of the described plurality.

[00162] An enumerated list of items (which may or may not be numbered) does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. Likewise, an enumerated list of items (which may or may not be numbered) does not imply that any or all of the items are comprehensive of any category, unless expressly specified otherwise. For example, the enumerated list “a computer, a laptop, a PDA” does not imply that any or all of the three items of that list are mutually exclusive and does not imply that any or all of the three items of that list are comprehensive of any category. 2016100894 08 Aug 2017 [00163] An enumerated list of items (which may or may not be numbered) does not imply that any or all of the items are equivalent to each other or readily substituted for each other.

[00164] All embodiments are illustrative, and do not imply that the invention or any embodiments were made or performed, as the case may be. 34

Claims (5)

1. A galvanic isolator adapted for a coaxial cable network, said galvanic isolator comprising: a first isolator port coupled to a signal transformer by a plurality of capacitive elements configured to provide an electrically isolating barrier for low frequency currents; and, a common mode filter stage coupled to said signal transformer, said common mode filter stage comprising at least one further capacitive element connected with at least two series inductive elements to form a T-section, wherein the inductive elements comprise ferrite cores in the form of beads with apertures adapted to pass a coaxial cable therethrough which couples signals from the signal transformer to a second isolator port.

2. A galvanic isolator as claimed in claim 1 further comprising a RF shield structure enclosing the electrically isolating barrier and common mode filter stage and formed by stamped foldable metal panels having apertures for accommodating and electrically connecting to the isolator ports.

3. A galvanic isolator as claimed in claim 1 or 2 wherein: at least one of the ferrite cores in the form of beads are positioned within respective voids formed in a printed circuit board dimensioned to receive said ferrite cores; said coaxial cable is positioned against the surface of said printed circuit board; and, the outer conductor of said coaxial cable is conductively bonded to the surface of said printed circuit board.

4. A method of manufacturing a galvanic isolator product including isolator circuitry, the method comprising the steps of: accommodating a first isolator port coupled to a signal transformer by a plurality of capacitive elements configured to provide an electrically isolating barrier for low frequency currents on a tray formed from an insulating material; fitting a plurality of ferrite beads at intervals to a coaxial cable having an exposed outer conductor and exposed inner conductor at its ends to form a common mode choke assembly; positioning the common mode choke assembly onto a printed circuit board with at least one aperture for accommodating the ferrite beads and pads for contacting the exposed outer conductor and exposed inner conductor, respectively, of the coaxial cable such that the coaxial cable is substantially coplanar with the printed circuit board; soldering the exposed outer and inner conductors of the coaxial cable to the pads to provide electrical contact for the coaxial cable to couple signals from the signal transformer to a second isolator port; forming a shield enclosure from metallic sheet material around the tray to create an RF shield for the isolator circuitry.

5. A method as claimed in claim 4, wherein the step of forming a shield enclosure comprises one or a combination of soldering and folding panels of the metallic sheet material to form a box structure.