Inductive filter and method of reducing vibration sensitivity

A filter according to a present invention embodiment reduces the effects of microphonic behavior in a communications network. The filter passes a network signal, while filtering out unwanted voiceband leakage (e.g., emissions of plaintext voice signals) due to microphonic behavior of the network equipment. The filter employs inductive units each including at least two inductive elements connected in series and arranged to cancel current within the inductive elements induced by vibrations and/or sound pressure (or acoustic) waves in the surrounding environment, thereby reducing extraneous signals produced within the filter (e.g., signals produced from microphonic behavior that may be in the form of perceivable voice or audio, noise, etc.). The filter reduces the extraneous signals in active and passive modes, and prevents compromise of secure or sensitive information (e.g., in the form of perceivable voice or audio) due to microphonic behavior of filter elements.

BACKGROUND

1. Technical Field

The present invention embodiments pertain to reduction of extraneous signals within electrical elements. In particular, the present invention embodiments pertain to electrical filters with one or more inductive units each including at least two inductive elements connected in series and arranged to cancel current within the inductive elements induced by vibrations and/or sound pressure (or acoustic) waves, thereby reducing extraneous signals (e.g., signals produced from microphonic behavior, noise, etc.).

2. Discussion of Related Art

In secured facilities, modern networked digital telephone systems (e.g., Voice over Internet Protocol (VoIP) systems) eliminate many of the security concerns with older telephony systems. This is primarily due to the potential to encrypt the voice transmission “end-to-end” beginning at the handset of the telephone device. Although the intentional, packetized voice signal is protected by encryption, limitations of the VoIP equipment design may result in measurable unintended emissions of the original unencrypted (or plaintext) analog voice signal onto a computer network cable. Since almost any inductive component in a telecommunications or computer networking device may exhibit microphonic behavior (e.g., emissions of the conveyed signal) in response to acoustic vibrations, unintended voiceband emissions of plaintext may be present on a network interface when a call is not in progress, or even during the interval equipment is powered down.

Accordingly, telephony equipment intended for installation in secured facilities is tested for immunity to this potential security breach by exposing the equipment to test tones (at voice frequencies from a loudspeaker and at calibrated sound pressure levels), and measuring the electrical signal level present at the corresponding frequency on a network interface cable. In the event of a testing failure, the equipment may be redesigned to pass the test, thereby significantly increasing the costs and complexity of the equipment.

In the event electronic circuitry is utilized to correct the deficiencies, certain circuit elements may be susceptible to microphonic behavior (e.g., emissions of the plaintext or conveyed signal that may be in the form of perceivable voice or audio), thereby producing extraneous signals (e.g., signals produced from microphonic behavior, noise, etc.). A source of these extraneous signals (e.g., voice or audio signals produced from microphonic behavior, noise, etc.) in electronic circuits includes vibration present in the operating environment. For example, mechanical vibration and sound pressure (or acoustic) waves may initiate microphonic behavior and produce the extraneous signals in a circuit exposed to those items. Ferrous core inductors or coils are among circuit elements that are most sensitive to vibration and sound pressure waves. These stimuli may excite vibration of inductor windings with respect to the fixed core, and induce an unwanted alternating current (representing the extraneous signals (e.g., audio or electrical noise)) in the coil with the same frequency as the inducing vibration force. Although the inductor windings may be encapsulated in a rigid compound (e.g., epoxy resin) to prevent movement of the windings relative to the core, this construction is often not available “off the shelf”, or is more costly to produce.

SUMMARY

According to the present invention embodiments, a filter reduces the effects of microphonic behavior in a communications network. The filter passes a network signal, preferably including digitized voice signals, while filtering out unwanted voiceband leakage (e.g., emissions of plaintext voice signals) due to microphonic behavior of the network equipment. The filter employs inductive units each including at least two inductive elements connected in series and arranged to cancel current within the inductive elements induced by vibrations and/or sound pressure (or acoustic) waves in the surrounding environment, thereby reducing extraneous signals produced within the filter (e.g., signals produced from microphonic behavior that may be in the form of perceivable voice or audio, noise, etc.). The filter reduces the extraneous signals in an active mode when processing signals between the network and network equipment, thereby providing a passed network signal substantially unaltered. In addition, the filter reduces the extraneous signals in a passive mode (e.g., in the absence of signals between the network and network equipment). Accordingly, the filter prevents compromise of secure or sensitive information (e.g., in the form of perceivable voice or audio) due to microphonic behavior of filter elements, and maintains security. The filter is preferably disposed external of network equipment and within a network link. However, the filter may alternatively be disposed within network equipment (e.g., retrofitted within the equipment, included within the equipment design, etc.).

The present invention embodiments provide several advantages. For example, an embodiment of the present invention may be inserted in a network link or within network equipment to be easily retrofitted for an existing equipment design. In this manner, a non-compliant equipment design may be corrected without redesigning the equipment. The present invention embodiment is simpler and lower in cost relative to other retrofit solutions (e.g., an optoisolator or a redesign of the equipment), and consumes no power. Further, the present invention embodiment provides effective isolation of voiceband leakage, including both common-mode and differential leakage. Moreover, the present invention embodiment supports communications channels that employ simultaneous signaling in both directions on wire pairs (e.g., 1000Base-T Ethernet, etc.). In addition, the present invention embodiment reduces extraneous signals (e.g., signals produced from microphonic behavior that may be in the form of perceivable voice or audio, noise, etc.) in both active and passive modes, thereby preventing compromise of secure or sensitive information due to microphonic behavior and maintaining security.

The above and still further features and advantages of the present invention embodiments will become apparent upon consideration of the following detailed description of example embodiments thereof, particularly when taken in conjunction with the accompanying drawings wherein like reference numerals in the various figures are utilized to designate like components.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Digital telephone systems (e.g., Voice over Internet Protocol (VoIP) systems) eliminate many security concerns due to the ability to encrypt a voice transmission. Although the packetized voice signal is protected by encryption, limitations of the equipment design may result in measurable unintended emissions of the original unencrypted (or plaintext) analog voice signal onto a computer network cable. Since almost any inductive component in a telecommunications or computer networking device may exhibit microphonic behavior (e.g., emissions of the conveyed signal) in response to acoustic vibrations, unintended voiceband emissions of plaintext may be present on a network interface when a call is not in progress, or even during the interval equipment is powered down. For example, plaintext or unencrypted voice or speech signals conveyed by a user into a communications device (e.g., handset, etc.) of the digital telephone system may be reproduced by inductive components due to microphonic behavior of those components, even though the voice signals are eventually encrypted for transmission.

The present invention embodiments reduce the effects of microphonic behavior in a communications network as illustrated inFIG. 1. Specifically, a communications device10is coupled to a network access connector20via a network link15. The communications device is preferably a telephone handset configured to communicate voice or audio signals over a digital telephone system or network. Network access connector20may be implemented by any conventional data access port connector, and provides access to the digital telephone system. An isolation filter unit30according to an embodiment of the present invention is disposed between communications device10and network access connector20to process signals therebetween, and includes a device connector33and a network connector35. The device and network connectors may be implemented by any conventional data or other port connectors. Device connector33couples the isolation filter unit to communications device10via a cable25, while network connector35couples the isolation filter unit to network access device20via a cable27. Cables25,27may be implemented by any conventional or other network cable. Alternatively, isolation filter unit30may be disposed within communications device10.

Referring toFIG. 2, the network signal (e.g., VoIP signal) has a greater frequency than the voiceband, thereby enabling the voiceband and network signals to be isolated. Isolation filter unit30includes an isolation filter (e.g., filter60,70,80) as described below and coupled between connectors33,35, to remove or filter the voiceband leakage (e.g., emissions of plaintext voice signals) due to microphonic behavior of inductive elements of communications device10. In other words, the isolation filter blocks signals (e.g., in the approximate range of 200 Hz-8 kHz) in the voiceband frequency range, while passing the network signal. The design of the isolation filter preferably includes one or more capacitive components (e.g., capacitors, etc.) and one or more inductive components (e.g., inductors, etc.), and may further include additional circuit components (e.g., resistive components, etc.). In order to reduce introduction of extraneous signals (e.g., signals produced from microphonic behavior that may be in the form of perceivable voice or audio, noise, etc.) due to vibrations and/or sound pressure (or acoustic) waves in the surrounding environment, the inductive components in the design of the isolation filter are implemented by inductive units each including at least two inductive elements (e.g., inductors, etc.) arranged to cancel current within the inductive elements induced by the vibrations and/or sound pressure (or acoustic) waves as described below. The isolation filter reduces the extraneous signals in an active mode when processing signals between the digital telephone system and communications device10, thereby providing a passed network signal substantially unaltered. In addition, the isolation filter reduces the extraneous signals in a passive mode (e.g., in the absence of signals between the network and network equipment). Accordingly, the isolation filter prevents compromise of secure or sensitive information (e.g., in the form of perceivable voice or audio) due to microphonic behavior of isolation filter elements, and maintains security. For example, plaintext or unencrypted voice or speech signals conveyed by a user into communications device10may be reproduced by inductive components due to microphonic behavior of those components (e.g., the voice signals being incident on inductive components in the vicinity of the communications device), even though the voice signals may be encrypted. The reproduced signals are typically perceivable and may be susceptible to interception. The inductive units of the isolation filter are configured to reduce the effect of microphonic behavior in both passive and active modes, thereby preventing compromise of the voice signals.

An isolation filter according to an embodiment of the present invention is illustrated inFIG. 3. In particular, isolation filter60includes one or more stages32, depending upon the desired filter complexity for an application. Each stage32includes conductors31,37,39, a capacitor34, and an inductive unit40. Conductor39is disposed between and coupled to conductors31and37. Capacitor34is disposed along conductor31, while inductive unit40is disposed along conductor39and coupled to capacitor34. The inductive unit is coupled to conductors31,37at the junctions of conductors31,39and conductors37,39(each located beyond capacitor34). Subsequent stages32are each appended to an immediately preceding stage and extend from the junctions of conductors31,39and conductors37,39of the prior stage.

A source of extraneous signals (e.g., voice or audio signals produced from microphonic behavior, noise, etc.) in electronic circuits includes vibration present in the operating environment. For example, mechanical vibration and sound pressure waves may produce the extraneous signals in a circuit exposed to those items. Ferrous core inductors or coils are among circuit elements that are most sensitive to vibration and sound pressure waves. These stimuli may excite vibration of inductor windings with respect to the fixed core, and induce an unwanted alternating current (representing the extraneous signals (e.g., audio or electrical noise)) in the coil with the same frequency as the inducing vibration force.

In order to significantly reduce the extraneous signals (e.g., voice or audio signals produced from microphonic behavior, noise, etc.) induced in an inductive element, isolation filter60employs inductive unit40as illustrated inFIG. 4. In particular, the inductive unit represents a corresponding inductive component in the design of isolation filter60, and includes inductive elements42,44. Inductive element42includes a substantially cylindrical core43with a coil or windings41disposed about core43(e.g., in a direction D1as viewed inFIG. 4). Inductive element44similarly includes substantially cylindrical core43and a coil or windings45. By way of example only, windings45are disposed about core43in the same direction (e.g., direction D2as viewed inFIG. 4) that windings41are disposed about core43of inductive element42. Inductive elements42,44are directly connected in series with their axes substantially parallel and arranged with a signal path (e.g., a ‘U’-shaped path, etc.) directing currents induced by vibration and/or sound pressure (or acoustic) waves to flow toward each other (e.g., between the inductive elements) and effectively cancel, thereby removing the extraneous signals as described below. The series arrangement of inductive elements42,44enable the combined inductance to match the desired inductance of inductive unit40. In other words, each inductive element42,44includes an inductance equal to one-half the desired inductance for inductive unit40(e.g., each inductive element includes an inductance of n/2 Henrys, where n Henrys is the desired inductance for inductive unit40).

Isolation filter60is generally implemented in the form of a multi-pole passive high-pass filter inserted into each signal-bearing wire pair. The filter design is preferably tuned to the characteristic impedance of the network cable employed (e.g., cables25,27ofFIG. 1). The corner frequency of isolation filter60is designed to be below that of the network signal (and above the voiceband signal) to enable the isolation filter to block the voiceband signals (including the voiceband leakage due to microphonic behavior of the communications device) and pass the network signal unaltered. The complexity (e.g., number of poles) of isolation filter60and the characteristics of the filter components (e.g., inductance, capacitance, etc.) may be of any desired values suitable to provide the desired attenuation in the voiceband.

Referring toFIG. 5, inductive unit40is exposed to acoustic or sound waves47from an acoustic wave or vibration source49(e.g., human voice, audio speaker, etc.). The wavelength, λ, of an acoustic or sound wave is expressed by the following equation:
λ=c/f,
where f is the frequency of the acoustic wave, and c is the speed of sound in the medium through which the wave travels. For example, the speed of sound in air at 25° C. is approximately 346.65 meters/second. Accordingly, the approximate wavelength of acoustic or sound waves in air at various audible frequencies based on the above equation is shown in Table I.

TABLE IWAVELENGTH OF SOUND WAVES AT VARIOUSFREQUENCIES IN AIR (25° C.)FrequencyWavelength100Hz3.4665m500Hz69.33cm1,000Hz34.67cm5,000Hz6.93cm10,000Hz3.467cm
The wavelength of sound or acoustic waves in air within the audible frequency band (of Table I) is significantly greater than the dimensions and spacing of typical surface mount inductor components (e.g., on the order of 1 centimeter or less).

Further, the speed of sound in the FR4 fiberglass material used in the construction of printed circuit boards (PCBs) is approximately 3620 meters/second. Thus, the approximate wavelengths of the vibration waves induced in a PCB on which inductive elements42,44are mounted based on the above equation is shown in Table II.

TABLE IIWAVELENGTH OF SOUND WAVES AT VARIOUSFREQUENCIES IN FR4 FIBERGLASS (25° C.)FrequencyWavelength100Hz36.2m500Hz7.24m1,000Hz3.62m5,000Hz72.4cm10,000Hz36.2cm

Accordingly, the wavelength of the induced vibrations in the PCB substrate on which inductive elements42,44are mounted are at least an order of magnitude greater than the separation distance between those inductive elements. If the mounting separation between inductive elements42,44is sufficiently small in relation to the distance to the vibration or acoustic wave source49, these inductive elements are exposed to substantially similar vibration forces (e.g., in amplitude, frequency and phase).

The effect of the arrangement of inductive elements42,44to reduce extraneous signals is illustrated inFIG. 6A. Specifically, an intentional signal current, Is, flows through inductive unit40. This current is derived from the signals provided to isolation filter unit30from communications device10and network access connector20(FIG. 1). The intentional current signal flows through inductive element42followed by inductive element44, and experiences a net inductance of the combined inductances of the inductive elements. Extraneous signal current i1is induced in inductive element42by incident vibration or acoustic waves47(e.g., audio or voice signals conveyed by a user to communications device10, etc.), while extraneous signal current i2is induced in inductive element44by those incident waves. Extraneous signal currents i1, i2induced in inductive elements42,44are substantially similar in frequency, amplitude and phase, but opposing in direction due to the arrangement of coils41,45and routing of the signal flow. This enables the extraneous signal currents to effectively cancel, thereby removing the vibration-induced extraneous signals in inductive unit40, and enhancing the signal passed by the isolation filter. In addition, each inductive unit40of isolation filter60reduces the effect of microphonic behavior in both passive and active modes, thereby preventing compromise of any sensitive information in incident waves47.

Referring toFIG. 6B, inductive elements42,44are mounted on a substrate22(e.g., Printed Circuit Board (PCB), etc.) with their axes in substantially parallel relation, and are connected on an upper substrate surface with a signal path directing currents induced in those inductive elements to effectively cancel, thereby reducing extraneous signals as described above. Alternatively, inductive elements42,44may be disposed on opposing surfaces of substrate22as illustrated inFIG. 6C. In this case, inductive elements42,44are respectively disposed on the upper and lower surfaces of substrate22with a signal path directing currents induced in those inductive elements to effectively cancel, thereby reducing extraneous signals as described above.

Inductive unit40may include any quantity of inductive elements, where the inductive elements may include the same or opposing winding directions and are arranged with a signal path that directs the induced currents to collectively cancel. An alternative arrangement of inductive elements42,44within inductive unit40is illustrated, by way of example only, inFIG. 6D. Specifically, inductive elements42,44are substantially similar to the inductive elements described above. In this case, inductive element44includes windings45disposed about core43(FIG. 4) in a direction opposite to the direction windings41are disposed about core43of inductive element42. Accordingly, extraneous signal currents i1, i2respectively induced in inductive elements42,44due to incident vibration and/or sound pressure (or acoustic waves) flow in opposite directions. The inductive elements are connected in series and arranged with a signal path (e.g., a substantially linear path, etc.) directing the induced currents to flow toward each other (e.g., between the inductive elements) and effectively cancel, thereby removing the extraneous signals.

Yet another arrangement of inductive elements42,44within inductive unit40is illustrated, by way of example only, inFIG. 6E. Specifically, inductive elements42,44are substantially similar to the inductive elements described above. In this case, inductive element44includes windings45disposed about core43(FIG. 4) in a direction opposite to the direction windings41are disposed about core43of inductive element42. Accordingly, extraneous signal currents i1, i2respectively induced in inductive elements42,44due to incident vibration and/or sound pressure (or acoustic waves) flow in opposite directions. The inductive elements are connected in series and arranged with a signal path (e.g., a ‘Z’—shaped path, etc.) directing the induced currents to flow toward each other (e.g., between the inductive elements) and effectively cancel, thereby removing the extraneous signals.

An embodiment of the isolation filter for a balanced signal wire pair is illustrated inFIG. 7. Specifically, the design of isolation filter70is substantially symmetric, and includes one or more stages52, depending upon the desired filter complexity for an application. Each stage52includes conductors31,37,39, capacitors34,36and inductive units40a,40b. Conductor39is disposed between and coupled to conductors31and37. Capacitor34is disposed along conductor31, while inductive unit40ais disposed along conductor39. Inductive unit40ais coupled to capacitor34, and disposed between a junction of conductors31,39(located beyond capacitor34) and a ground potential. Similarly, capacitor36is disposed along conductor37, while inductive unit40bis disposed along conductor39. Inductive unit40bis coupled to capacitor36, and disposed between a junction of conductors37,39(located beyond capacitor36) and the ground potential. The ground potential is coupled to conductor39at a junction located between inductive units40a,40b. Subsequent stages52are each appended to an immediately preceding stage, and extend from: the junction of conductors31,39; the junction of conductors37,39; and the junction between inductive units40a,40b.

In order to increase the filter immunity to vibration (and/or sound pressure or acoustic wave) induced extraneous signals (e.g., signals produced from microphonic behavior that may be in the form of perceivable voice or audio, noise, etc.), inductive units40a,40bmay include any of the current-canceling arrangements described above. In particular, each inductive element40a,40bis substantially similar to inductive unit40described above, and includes inductive elements42,44. Inductive element42includes substantially cylindrical core43with coil or windings41disposed about core43. Inductive element44similarly includes substantially cylindrical core43and coil or windings45; however, windings45may be disposed about core43in the same or opposite direction relative to the direction that windings41are disposed about core43of inductive element42. Inductors42,44are directly connected in series to enable the combined inductance to match the desired inductance of the respective inductive unit40a,40b(e.g., each inductive element includes an inductance of n/2 Henrys, where n Henrys is the desired inductance for inductive unit40a,40b).

Inductive elements42,44of each respective inductive unit40a,40bare mounted on a substrate (e.g., Printed Circuit Board (PCB), etc.) with a signal path to effectively cancel the induced extraneous signal currents as described above. Basically, extraneous signal current is induced in each of inductive elements42,44by incident vibration or acoustic waves. The extraneous signal current induced in inductive elements42,44are substantially similar in frequency, amplitude and phase, but opposing in direction due to the arrangement of coils41,45and routing of the signal flow. This enables the extraneous signal currents to effectively cancel, thereby removing the vibration-induced extraneous signals in inductive units40a,40band enhancing the signal passed by the isolation filter. In addition, inductive units40a,40bof isolation filter70reduce the effect of microphonic behavior in both passive and active modes, thereby preventing compromise of any sensitive information in the incident vibration or acoustic waves.

Isolation filter70is generally implemented in the form of a multi-pole passive high-pass filter inserted into each signal-bearing wire pair. The filter design is preferably tuned to the characteristic impedance of the network cable employed (e.g., cables25,27ofFIG. 1). The corner frequency of isolation filter70is designed to be below that of the network signal (and above the voiceband signal) to enable the isolation filter to block the voiceband signals (including the voiceband leakage due to microphonic behavior of the communications device) and pass the network signal unaltered. The complexity (e.g., number of poles) of isolation filter70and the characteristics of the filter components (e.g., inductance, capacitance, etc.) may be of any desired values suitable to provide the desired attenuation in the voiceband.

An example embodiment of the isolation filter for a particular networking application is illustrated inFIG. 8. Initially, isolation filter80may be employed within isolation filter unit30and between communications device10and network access connector20(FIG. 1). Isolation filter80includes isolation filters70a,70b. Each isolation filter70a,70bis similar to isolation filter70for balanced signal wire pairs described above forFIG. 7, and corresponds to respective transmission (e.g., from communications device10to network access connector20(and the digital telephone system)) and reception (e.g., from network access connector20(and the digital telephone system) to communications device10) operations. Specifically, isolation filter80is coupled between device connector33and network connector35of isolation filter unit30. By way of example only, connectors33,35include a series of pins1-8, where isolation filter70afor the transmission operation is coupled to pins1and2of the connectors, while isolation filter70bis for the reception operation and is coupled to pins3and6of the connectors. However, the connectors may each include any quantity of pins, where the isolation filters70a,70bmay be utilized for signals for any desired operations and be coupled to any quantity of any desired connector pins.

Isolation filter70aincludes conductors51,53,55,57, capacitors34a,34b,36a,36band inductive units40a,40b. Isolation filter70aprocesses signals for the communications device transmission operation (e.g., from communications device10to network access connector20), thereby processing signals traveling from device connector33toward network connector35. Conductor51is coupled to pin1of each connector33,35, while conductor53is coupled to pin2of each of those connectors. A capacitor34ais disposed along conductor51toward device connector33, while inductive unit40ais disposed along conductor55. Inductive unit40ais disposed between a junction of conductors51,55(located beyond capacitor34a) and a ground potential. Capacitor34bis disposed along conductor51subsequent inductive unit40atoward network connector35. Inductive unit40ais thus coupled to capacitors34a,34b.

Similarly, a capacitor36ais disposed along conductor53toward device connector33, while inductive unit40bis disposed along conductor57. Inductive unit40bis disposed between a junction of conductors53,57(located beyond capacitor36a) and a ground potential. Capacitor36bis disposed along conductor53subsequent inductive unit40btoward network connector35. Inductive unit40bis thus coupled to capacitors36a,36b.

Isolation filter70bis substantially similar to isolation filter70aand includes conductors61,63,65,67, capacitors34a,34b,36a,36band inductive units40a,40b. Isolation filter70bprocesses signals for the communications device reception operation (e.g., signals from network access connector20to communications device10), thereby processing signals traveling from network connector35toward device connector33. Conductor61is coupled to pin3of each connector33,35, while conductor63is coupled to pin6of each of those connectors. A capacitor34ais disposed along conductor61toward network connector35, while inductive unit40ais disposed along conductor65. Inductive unit40ais disposed between a junction of conductors61,65(located beyond capacitor34a) and a ground potential. Capacitor34bis disposed along conductor61subsequent inductive unit40atoward device connector33. Inductive unit40bis thus coupled to capacitors34a,34b.

Similarly, a capacitor36ais disposed along conductor63toward network connector35, while inductive unit40bis disposed along conductor67. Inductive unit40bis disposed between a junction of conductors63,67(located beyond capacitor36a) and a ground potential. Capacitor36bis disposed along conductor63subsequent inductive unit40btoward device connector33. Inductive unit40bis thus coupled to capacitors36a,36b.

In order to increase the filter immunity to vibration (and/or sound pressure or acoustic wave) induced extraneous signals (e.g., signals produced from microphonic behavior that may be in the form of perceivable voice or audio, noise, etc.), inductive units40a,40bof isolation filters70a,70beach preferably include the current-canceling arrangement described above forFIG. 6A. However, the inductive units of isolation filters70a,70bmay alternatively include any of the current-canceling arrangements described above. In particular, each inductive element40a,40bis substantially similar to inductive unit40described above, and includes inductive elements42,44. Inductive element42includes substantially cylindrical core43with coil or windings41disposed about core43. Inductive element44similarly includes substantially cylindrical core43and coil or windings45disposed about core43in the same direction relative to the direction that windings41are disposed about core43of inductive element42. Inductors42,44are directly connected in series to enable the combined inductance to match the desired inductance of the respective inductive unit40a,40b(e.g., each inductive element includes an inductance of n/2 Henrys, where n Henrys is the desired inductance for inductive unit40a,40b).

Inductive elements42,44of each respective inductive unit40a,40bare mounted on a substrate (e.g., Printed Circuit Board (PCB), etc.) with a signal path to effectively cancel the induced extraneous signal currents as described above. Basically, extraneous signal current is induced in each of inductive elements42,44by incident vibration or acoustic waves. The extraneous signal current induced in inductive elements42,44are substantially similar in frequency, amplitude and phase, but opposing in direction due to the arrangement of coils41,45and routing of the signal flow. This enables the extraneous signal currents to effectively cancel, thereby removing the vibration-induced extraneous signals in inductive units40a,40b, and enhancing the signal passed by the isolation filter. In addition, inductive units40a,40bof isolation filter80reduce the effect of microphonic behavior in both passive and active modes, thereby preventing compromise of any sensitive information in the incident vibration or acoustic waves.

Isolation filter80is generally implemented in the form of a multi-pole passive high-pass filter inserted into each signal-bearing wire pair. The filter design is preferably tuned to the characteristic impedance of the network cable employed (e.g., cables25,27ofFIG. 1). The corner frequency of isolation filter80is designed to be below that of the network signal (and above the voiceband signal) to enable the isolation filter to block the voiceband signals (including the voiceband leakage due to microphonic behavior of the communications device) and pass the network signal unaltered.

The complexity (e.g., number of poles) of isolation filter80and the characteristics of the filter components (e.g., inductance, capacitance, etc.) may be of any desired values suitable to provide the desired attenuation in the voiceband. By way of example only, capacitors34a,34b,36a,36beach include a capacitance of approximately 27 nanoFarads, while inductive units40a,40beach include an inductance of approximately 94 microHenrys (where each inductive element42,44includes an inductance of approximately 47 microHenrys). Isolation filter80(e.g., and filters70a,70b) accommodates 100Base-T Ethernet, and provides a corner frequency of approximately 80 kHz to 100 kHz (e.g., well below the Ethernet signal), thereby allowing the network signal to be passed without alteration. A third order isolation filter (e.g., of the forms shown inFIGS. 7-8(e.g., filters70,70a,70b)) inserted into both the transmit and receive signal pairs provides approximately 40 dB of attenuation at 8 kHz (e.g., the upper range of the voiceband).

It will be appreciated that the embodiments described above and illustrated in the drawings represent only a few of the many ways of implementing an inductive filter and method of reducing vibration sensitivity.

The present invention embodiments may be utilized in any types of circuits or filters (e.g., high-pass, low-pass, band-pass, etc.) including inductive or other components with coils or other items susceptible to motion from external sources and inducing any extraneous signals (e.g., audio, noise, voice, data, etc.). The present invention embodiments may be employed for any types of network or other signals, and may be configured to provide filtering for any desired frequencies or frequency ranges. The present invention embodiments may reduce any unwanted, unintentional or extraneous signals (e.g., audio, noise, voice, data, etc.) induced from any external or surrounding conditions exciting motion in inductive or other circuit element coils or windings (e.g., vibrations, sounds, motion of the circuit, air flow or wind, etc.).

The isolation filter unit may include any quantity of isolation filters, where any quantity of isolation filter units may be employed within a network or other link in any desired fashion. The isolation filter may include any quantity of poles (e.g., any desired complexity, etc.), and be configured for any suitable frequencies or frequency ranges. The isolation filter may include any quantity of stages, where each stage may include any quantity of inductive components, capacitive components and/or resistive components. The stages may be connected or appended to each other at any locations and in any desired fashion.

The isolation filter may include any quantity of any conventional or other circuit components (e.g., inductors, capacitors, resistors, etc.) arranged in any desired fashion (e.g., parallel, series, etc.) to filter signals. The capacitive components or capacitors may be implemented by any quantity of any conventional or other capacitive devices (e.g., capacitors or other elements providing capacitance, etc.) including any desired capacitance and arranged in any desired fashion (e.g., series, parallel, etc.). The resistive components or resistors may be implemented by any quantity of any conventional or other resistive devices (e.g., resistors or other elements providing resistance, etc.) including any desired resistance and arranged in any desired fashion (e.g., series, parallel, etc.).

The inductive unit may be of any quantity and be arranged in the isolation filter in any desired fashion (e.g., series, parallel, etc.). The inductive unit may include any desired signal flow path suitable to direct currents induced in the inductive elements in opposing directions and effectively cancel (e.g., U-shape, Z-shape, L-shape, V-shape, parallel, non-parallel etc.). The inductive unit may include any quantity of inductive elements arranged in any desired fashion (e.g., serial, parallel, directly or indirectly coupled, etc.) providing the desired inductance and with a signal flow path canceling the induced extraneous signal currents, where the signal flow path enables at least two inductive elements to provide opposing directions for the induced signal flow to collectively cancel the currents induced in all of the inductive elements. For example, the inductive unit may include two or more inductive elements with the same or different winding direction. The quantity of inductive elements with each winding direction may be the same or different, where the inductive elements with different winding directions may be arranged in any fashion (e.g., interleaved, groups with the same winding direction, etc.), and the inductances may be selected to induce currents that are directed by the signal flow path to effectively cancel. By way of example only, the inductive unit may include three inductive elements with a first winding direction and one inductive element with the opposing winding direction, where the inductances are selected to enable the current induced in the one inductive element with the opposing winding direction to cancel the currents induced in the remaining inductive elements.

The inductive elements may be implemented by any quantity of any conventional or other inductive devices (e.g., inductors or other elements providing inductance, etc.) including any desired inductance and arranged in any desired fashion (e.g., series, parallel, directly or indirectly coupled, etc.). The inductive elements may be mounted in any fashion or arrangement on any surfaces of any suitable substrate (e.g., PCB, etc.). The inductive element cores may be of any quantity, shape or size, arranged in any desired fashion, and may be constructed of any suitable materials. The inductive element coil or windings may be of any quantity, shape or size, arranged in any desired fashion, may be wound about the core in any desired direction and any quantity of times, and may be constructed of any suitable materials. The direction of the windings of the inductive elements within the inductive unit may be in any direction and be selected in accordance with the signal flow path to effectively cancel the induced currents.

The communications device may be implemented by any conventional or other communications device (e.g., handset, cellular device, etc.). The network access connector may be of any quantity, and may be implemented by any conventional or other connector or access port. The cables may be implemented by any quantity of any conventional or other cables, may be of any shape or size, and may be constructed of any suitable materials. The conductors may be implemented by any quantity of any conventional or other conductors, may be of any shape or size, and may be constructed of any suitable conducting materials. The device and network connectors may be implemented by any quantity of any conventional or other connectors, and may each include any quantity of pins. The pins may be utilized for any desired signals. The connectors (and isolation filter unit) may be disposed external or internal of the communications device and/or network access connector in any desired fashion.

The present invention embodiments may be employed for any suitable communications or other network (digital telephone or other system, LAN, WAN, Internet, Intranet, VPN, etc.). The isolation filter of the present invention embodiments may be utilized for any desired applications (e.g., and within or external of any devices or circuits) to reduce any types of extraneous signals from external conditions exciting coils or other items of circuit components. In addition, the isolation filter unit may include one or more of any of the filters described above (e.g., either individually or in any desired combinations), where each filter may include any quantity of stages.

It is to be understood that the terms “top”, “bottom”, “front”, “rear”, “side”, “height”, “length”, “width”, “upper”, “lower”, “vertical” and the like are used herein merely to describe points of reference and do not limit the present invention embodiments to any particular orientation or configuration.

From the foregoing description, it will be appreciated that the invention makes available a novel inductive filter and method of reducing vibration sensitivity, wherein a filter includes one or more inductive units each including at least two inductive elements and a signal flow path providing opposing flow direction to effectively cancel extraneous signal currents induced by vibrations and/or sound pressure (or acoustic) waves, thereby reducing the extraneous signals.

Having described preferred embodiments of a new and improved inductive filter and method of reducing vibration sensitivity, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined by the appended claims.