Abstract:
A device and method for reducing crosstalk between wires is provided. The method includes spatially separating first and second sets of wires. A device is disposed relative to the first and second sets of wires to maintain the spatial separation. The method also comprises coupling pins to the first and second sets of wires. Additionally, the method includes covering the device with a connector housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 11/900,853, filed on Sep. 13, 2007, which is a divisional of U.S. application Ser. No. 11/540,376 filed on Sep. 29, 2006, now U.S. Pat. No. 7,476,131. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to electronic devices, such as medical devices, and more particularly to reducing crosstalk in such devices. 
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Medical devices such as those used for monitoring a patient&#39;s vital sign or other physiologic variable, are commonly comprised of a patient-contacting signal transducer and a monitor that connects to the transducer, processes the signals, and provides information to the caregiver. Typically, the transducer is connected to the monitor with and interface cable that includes wires for conducting electrical signals. 
     An ideal cable and connector assembly for use in such medical devices would be immune to noise interference from external sources as well as crosstalk between wires within the cable and connector assembly. In reality, however, the manufacturing process of a cable and connector assembly includes steps that make the wires within a cable and connector assembly vulnerable to noise, such as capacitive and inductive crosstalk, wherein electrical signals in one wire or pair of wires may interfere or create noise on a nearby wire. The crosstalk may be detrimental to the operation of a medical device. For example, in pulse oximetry, the crosstalk can result in inaccurate readings of SpO 2  values. 
     Cables are generally manufactured to limit the amount of external noise and inductive and capacitive crosstalk that can occur between wires. For example, the cables are bundled together with an electrically insulating protective coating and a conductive shield mesh to protect against environmental noise sources. Additionally, the cables may be made up of twisted wire pairs, commonly referred to as twisted pairs. As their name suggests, the twisted pairs are a pair of wires twisted together in a manner that results in each wire becoming exposed to the same or similar amounts noise elements such that the noise can be nearly or completely canceled out. A twisted pair may be surrounded by an electrically grounded conductive mesh shield to help eliminate noise interference from other wires within the cable bundle. Twisted pairs having the conductive mesh shield are referred to as shielded twisted pairs, while twisted pairs without the conductive mesh are referred to as unshielded twisted pairs. The cables used in medical devices such as pulse oximetry systems are commonly constructed with one or both types of twisted pairs, where multiple sets of wires are combined into a cable bundle. Electrical crosstalk can occur when signal wires electrically contact one another (a “short”), or come into close proximity to adjacent conductors. 
     In order to connect the wires to connector pins, the cable bundle must be stripped and the wires untwisted. Thus, in this section of the cables, the wires are unprotected and vulnerable to crosstalk interference. Furthermore, after the wires have been connected to connector pins and the pins are placed in a connector housing, even if the wires are initially pushed apart and spatially separated, additional handling and processing may push the wires together and increase the likelihood of crosstalk. 
     SUMMARY 
     Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
     In accordance with one aspect of the present invention, there is provided a medical device cable. In the examples used herein, the medical device is a pulse oximeter. The pulse oximeter cable comprises a first pair of wires, a second pair of wires and an insulative piece configured to maintain spatial separation between the first and second pairs of wires. Additionally, the cable comprises a connector housing formed over the insulative piece. 
     In accordance with another aspect of the present invention, there is provided a method of manufacturing an electrical cable comprising spatially separating a first set of wires from a second set of wires and disposing a device relative to the first and second sets of wires to maintain the spatial separation and coupling pins to the first and second sets of wires. Additionally, the method comprises covering the device with a connector housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain exemplary embodiments are described in the following detailed description and in reference to the drawings in which: 
         FIG. 1  illustrates an exemplary pulse oximetry system in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  illustrates a pulse oximetry cable in accordance with an embodiment of the present invention; 
         FIG. 3  illustrates an insulative material with slots through which wires pass in accordance with an exemplary embodiment of the present invention; 
         FIG. 4  illustrates an insulative piece between wires in accordance with an alternative exemplary embodiment of the present invention; 
         FIG. 5  illustrates an electrically grounded conductive object between wires in accordance with an alternative exemplary embodiment of the present invention; 
         FIG. 6  illustrates an insulative block with pads and traces configured to spatially separate wires in accordance with an alternative exemplary embodiment of the present invention; 
         FIG. 7  illustrates placing an epoxy material on and in between wires in accordance with an alternative exemplary embodiment of the present invention; 
         FIG. 8  illustrates a cross-sectional view of the material of  FIG. 7 ; 
         FIG. 9  illustrates a printed circuit board configured to spatially separate wires in accordance with an alternative exemplary embodiment of the present invention; 
         FIG. 10  illustrates an alternative embodiment for using a printed circuit board in accordance with an alternative exemplary embodiment of the present invention; 
         FIG. 11  illustrates top view of the printed circuit board of  FIG. 10 ; 
         FIG. 12  illustrates a view of the bottom of the printed circuit board of  FIG. 10 ; and 
         FIG. 13  is a flow chart depicting a technique for reducing crosstalk in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Turning initially to  FIG. 1 , an exemplary medical device, such as a pulse oximetry system, is illustrated and generally designated by the reference numeral  10 . Pulse oximetry systems, such as system  10 , calculate various physiological parameters by detecting electromagnetic radiation (light) that is scattered and absorbed by blood perfused tissue. The pulse oximeter system  10  has a main unit  12  which houses hardware and software configured to calculate various physiological parameters. The main unit  12  has a display  14  for displaying the calculated physiological parameters, such as oxygen saturation or pulse rate, to a caregiver or patient. The pulse oximetry system  10  also has a sensor unit  16 , which may take various forms. As shown in  FIG. 1 , the sensor unit  16  may be configured to fit over a digit of a patient or a user. The sensor unit  16  is connected to the main unit  12  via a cable  18 . The cable  18  may be coupled to main unit  12  using a connector housing  20 . It is at the interface between the cable  18  and the pins  34  (shown in  FIG. 2 ) of the connector housing  20  where noise interference in the form of crosstalk is most likely to occur. 
     A more detailed illustration of the cable  18  is shown in  FIG. 2 . Specifically, the cable  18  is shown having an outer jacket  22 . The outer jacket  22  is a polymeric material jacket to hold the cable bundle together and to protect the wires from environmental factors. Under the outer jacket  22 , the cable  18  has an outer shield  24  which may be configured to prevent electromagnetic interference from external sources. The outer shield  24  may be made up any type of shielding material, such as a metallic mesh, for example. 
     The cable  18 , as shown in  FIG. 2 , has both emitter wires  26  and detector wires  28 . Both the emitter wires  26  and the detector wires  28  are twisted pair wires. The wire pairs are twisted so that each wire is similarly exposed to any potential electromagnetic interference that reaches the wires. Because each of the wires is exposed to similar levels of interference, the interference can be reduced through circuit designs that cancel such common-mode signals. 
     The emitter wires  26  may comprise an unshielded twisted pair and the detector wires  28  may comprise a shielded twisted pair. As can be seen in  FIG. 2 , the detector wires  28  have a jacket  30 , such as a polymeric coating for example, and an inner shield  32  similar to the outer shield  24  of the cable  18 . The detector wires  28  are shielded electrically to prevent potential crosstalk from the emitter wires  26 , as well as interference from environmental factors. Both the emitter wires  26  and the detector wires  28  are individually connected to respective pins  34  of a connector housing, such as connector housing  20 . 
     During the manufacturing process, the outer jacket  22  is stripped from the cable  18 , and the coating  30  of the detector wires  28  is stripped from the detector wires  28 . The emitter wires  26  and detector wires  28  are then untwisted to facilitate connection of the emitter wires  26  and detector wires  28  to their respective pins  34 . The detector wires  28 , however, become vulnerable to a variety of noise-inducing influences, including inductive and capacitive crosstalk from the emitter wires  26  when they are unshielded and untwisted. 
     Initially, during the manufacturing process, the emitter wires  26  and the detector wires  28  are separated. The wires may be pulled apart by a worker or a machine may push a tool in between the pairs of wires to separate them. Unfortunately, after this initial separation, little may be done to maintain the separation of the wires. 
     Although workers may understand their specific role in the manufacturing process, they may not fully appreciate the importance of maintaining the separation between the wires and may fail to take precautions to maintain the separation of the wires. As such, the cables may be tossed into bins for transportation to different workstations, and the cables may be handled and manipulated by multiple workers and machines before the cables are fully assembled and ready for operation. In the bins, the cables may be compacted together or get tangled together. While being handled and manipulated by workers and machines, the wires may be pushed together. Therefore, at the end of the manufacturing process, there is a risk that the wires will no longer be separated, resulting in an increased susceptibility to crosstalk in the fully assembled cables. 
     To address this concern, an insulative material  36 , as illustrated in  FIG. 3 , may be used to maintain spatial separation between the emitter wires  26  and detector wires  28  in order to prevent crosstalk. The insulative material  36  may be a silicon rubber, polymer, or other electrically non-conductive material. The insulative material  36  may have apertures  38 , such as slots, through which the emitter wires  26  and detector wires  28  are passed during the manufacturing process. The wires may be coupled to the pins before or after being passed through the apertures  38 . The apertures  38  of the insulative material  36  help ensure that the emitter wires  26  and detector wires  28  remain separated throughout the manufacturing process to prevent crosstalk. 
     After the emitter wires  26  and detector wires  28  have been positioned in the apertures  38 , the insulative material  36  and a portion of the pins  34  and the wires  26  and  28  are encapsulated by the connector housing  20 . An over-molding process (such as insert, injection, or transfer molding), or other means, may be implemented to form the connector housing  20 . The connector housing  20  is formed over the insulative piece  36  so that the insulative piece  36  can continue to prevent the emitter and detector wires from moving closer to each other during the encapsulation process. By preserving the spatial separation, the insulative piece  36  helps the detector wires  28  to be less susceptible to crosstalk interference from the emitter wires  26 . 
     In another embodiment, as illustrated in  FIG. 4 , an insulative piece  40 , such as a piece of silicon rubber, polymer or other electrically non-conductive material, may be wedged or coupled between the emitter wires  26  and detector wires  28  to prevent electrical crosstalk. The insulative piece  40  is wedged or coupled between the emitter wires  26  and detector wires  28  by directing the wires into open ended apertures  42  located on opposite sides of the insulative piece  40 . The insulative piece  40  is installed prior to the encapsulation process and prevents the emitter wires  26  and the detector wires  28  from moving into closer proximity of each other during the encapsulation process or handling prior during the manufacturing process. The encapsulation process forms the connector housing  20  over the insulative piece  40 , as described above. 
     Alternatively, as illustrated in  FIG. 5 , a conductive object  50 , such as a piece of copper, positioned between the emitter wires  26  and detector wires  28  can help reduce or eliminate crosstalk. The conductive object  50  is electrically grounded via the wire  52 . The wire  52  may be formed by aggregating the wire mesh of the outer shield  24  to form a single wire, or comprise a separate drain or ground wire. The conductive object  50  is positioned between the emitter wires  26  and detector wires  28 . It should be understood that the conductive object  50  may be implemented alone or in conjunction with insulative embodiments described herein. Specifically, for example, the conductive object  50  may be supported by the insulative material  36  of  FIG. 3 . The connector housing  20  would then be formed over the both conductive object  50  and the insulative material  36 . 
     Turning to  FIG. 6 , yet another embodiment includes an insulative piece  60  with solder pads  62  and traces  64  and  66 . The insulative piece  60  may be a resin glass composition, a polymer capable of withstanding the temperatures used in soldering, or other suitable material. As illustrated, the insulative piece  60  has solder pads  62  on one side to connect the emitter wires  26  and detector wires  28  to the insulative piece  60 . The solder pads  62  are connected to electrically conductive traces  64  and  66  that run on the front side and backside of the insulative piece  60 , respectively. Specifically, the traces  64 , which are coupled to the detector wires  28 , run on a front side of the insulative piece  60 , while the traces  66 , which are coupled to the emitter wires  26 , run on a backside of the piece  60 . Thus, the insulative piece  60  spatially separates the emitter traces  26  from the detector traces  28  to prevent crosstalk from occurring. Once the wires and pins are coupled to the insulative piece, the connector housing  20  may be formed over the insulative piece  60  through the encapsulation process. 
     Alternatively, an insulative material  70 , such as epoxy resin or silicone, for example, may be used to maintain spatial separation of the detector wires  28  and the emitter wires  26 , as illustrated in  FIG. 7 . The material  70  may be placed on and in between the wires  26  and  28  after the external coating has been removed and the wires  26  and  28  have been separated from each other. The material  70  may initially be a two-part gel that cures and hardens as the two parts interact. Once cured, the material  70  holds the wires in place to prevent the wires from coming into proximity of each other during the manufacturing process. 
     A cross-sectional view of the material  70  is illustrated in  FIG. 8 . As can be seen, the detector wires  28  are spatially separated from the emitter wires  26 . The material  70  has a high dielectric constant to reduce capacitive effects, and, therefore, the emitter wires  26  and the detector wires are spatially and electrically isolated. The connector housing  20  may be formed over the material  70  through the encapsulation process after the material  70  has cured. 
     In another embodiment, a printed circuit board (PCB)  72  may also be used to maintain spatial separation between the emitter wires  26  and detector wires  28 , as shown in  FIG. 9 . The PCB  72  may be a multi-layer PCB with solder pads or holes (not shown) for coupling the wires to the PCB  72 . The solder pads or holes for coupling the emitter wires  26  to the PCB  72  may be located remotely from the solder pads or holes for coupling the detector wires  28  to the PCB  72 . Vias and traces in and on the PCB  72  connect the emitter wires  26  and detector wires  28  to the proper pins. The connector housing  20  may be formed over the PCB  72 . 
     An alternative embodiment using a PCB to prevent crosstalk is shown in  FIG. 10 . Specifically,  FIG. 10  shows a side view of a PCB  74  positioned between a top layer and a bottom layer of pins  34 . The PCB  74  is a two surface circuit board having traces, pads, and connection points for the connector pins  34  on both surfaces of the PCB  74 . As can be seen by further referring to  FIGS. 11 and 12 , the detector contacts  76   a - b  are physically remote from the emitter contacts  78   a - b . In addition, the inner shield wire  32  is soldered on the top surface  80  of the PCB  74  while the detector wires  28  are soldered on the bottom surface  82  of the PCB  74 . The location of the detector wires  28  provide spatial separation from the emitter wires  26 . The PCB  74  additionally shields the detector contacts  76   a - b  and emitter contacts  78   a - b  from the memory chip contacts. The inner shield  32  is routed by trace  84  to a contact pad  90  which may be conductively coupled to a pin  6  (not shown) of a connector. The connector housing  20  may be formed over the PCB  74 . Wires  26  and  28  emanating from cable  18  may be kept short in length to prevent cross-talk. Use of the PCB provides an easier substrate to terminate the wires to during the manufacturing process than terminating the wires to the pins directly. 
     Turning to  FIG. 13 , a technique to prevent crosstalk in pulse oximetry cables in accordance with an exemplary embodiment of the present invention is illustrated as a flow chart and generally designated by the reference numeral  100 . The technique  100  begins by stripping a cable, as indicated at block  102 . The cable may be any cable used in medical devices, such as those used in pulse oximeters and may include multiple wires which are also stripped. Once stripped, the wires are vulnerable to potential noise-inducing influences, such as crosstalk from the other wires of the cable. Therefore, the stripping of the wires should be performed with the goal of preserving as much of the shield on the wires as possible. 
     After the wires are stripped, the wires are spatially separated from each other, as indicated at block  104 . Specifically, sets of twisted pairs are separated from each other. The spatial separation of the wires may be done by a person or by a machine. Because the twisting of the wires is a noise cancellation technique, effort should be made to keep the pairs of wires twisted, insofar as it is practicable. 
     The spatial separation between the sets of wires is maintained by coupling or inserting a device between the sets of wires, as indicated at block  106 . Specifically, the spatial separation may be maintained by implementing one of the embodiments described above, such as using a PCB to physically separate the emitter wires  26  from the detector wires  28 , for example, or inserting an insulative object between the pairs of wires. The use of one of the above mentioned exemplary embodiments, or other device, precludes the pushing of the separated wires into closer proximity of each other during the over-molding process or other processing and handling that may occur during manufacture. 
     Connector pins are electrically coupled to the wires, as indicated by block  108 . The connector pins may be connected to the wires either directly by soldering the wires to the pins or indirectly via traces on a PCB, as described above, depending on the particular embodiment being implemented. By physically separating the wires and preserving that separation, crosstalk between wires is greatly reduced, or eliminated. The elimination of crosstalk may increase the accuracy of the medical devices. 
     The techniques described herein for maintaining spatial separation of the signal wires during the cable termination process to reduce cross-talk have applicability in patient monitoring applications beyond pulse oximetry. With respect to devices that utilize photo-emitters and photo-detectors as described herein, such techniques can be utilized in devices intended to monitor other blood constituents such as carboxyhemoglobin, methemoglobin, total hemoglobin content, glucose, pH, water content and others. Reducing signal cross-talk is also of importance in bio-impedance measurements for evaluating physiologic variables such as tissue hydration, cardiac output or blood pressure. 
     The step of creating a cabling connector may not be restricted to over-molding processes. Pre-molded connector housing components may be assembled to contain the pins and cable. During assembly, wires may come into close proximity that results in cross-talk (noise). The techniques described above may be used to reduce the likelihood of this occurring by ensuring proper spatial separation during the assembly process. 
     Additionally, it should be understood, that although the figures and the associated discussion describe embodiments wherein the cable  18  comprises twisted pair wires, the techniques disclosed herein may be applicable to any type of cable. Indeed, the techniques disclosed herein may be implemented with a coaxial cable, for example. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.