Patent Publication Number: US-9425860-B2

Title: Two wire signal transmission

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to signal transmission using conductors, and specifically to transmitting multiple signals over a minimal number of conductors. 
     BACKGROUND OF THE INVENTION 
     In many fields, a relatively large number of measurements may need to be made simultaneously, and the measurements may need to be transferred from the place of measurement to a distant location. Such transference may be difficult because of limited access between the place of measurement and the distant location. In minimally invasive medical surgery for example, the size of the access to a patient undergoing the surgery may be extremely limited, so that catheters or tools used for the surgery need to have diameters of the order of millimeters. Minimizing the number of conductors used to transfer the measurements enables the diameters of the catheters or tools to be reduced, with corresponding benefit to the patient. 
     Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides apparatus, including: 
     a first signal source generating a first signal and a second signal source generating a second signal; 
     a cross-over switch connected between the two sources so as to generate in a direct switch configuration a sum of the first and second signals and in a crossed switch configuration a difference between the first and second signals; and 
     a processor configured to receive the sum and the difference, and to recover the first signal and the second signal therefrom. 
     In a disclosed embodiment the apparatus includes a pair of conductors, respectively connected to the first signal source and to the cross-over switch, which are configured to convey therefrom the sum and the difference to the processor. 
     In a further disclosed embodiment the first and the second signals consist of analog signals. 
     In a yet further disclosed embodiment the apparatus includes a distal end of a catheter, configured for insertion into a human patient, wherein the first signal source, the second signal source, and the cross-over switch are incorporated. Typically, the first and the second signal sources respectively include first and second coils configured to generate respectively the first signal and the second signal in response to magnetic fields generated external to the distal end, and the processor is configured to determine an indication of a location and an orientation of the distal end in response to the first signal and The second signal. 
     In an alternative embodiment the processor is configured to toggle the cross-over switch between the direct switch configuration and the crossed switch configuration. 
     There is further provided, according to an embodiment of the present invention, apparatus, including: 
     a sequence of n signal sources respectively generating n signals, where n is an integer greater than one; 
     (n−1) cross-over switches, each cross-over switch being connected between a p th  signal source and a (p+1) th  signal source, where p is an integer and 1≦p&lt;n, the (n−1) cross-over switches being configured to generate n different linear combinations of the n signals; and 
     a processor configured receive the linear combinations, and to recover the n signals therefrom. 
     Typically, the processor is configured to cycle the (n−1) cross-over switches through n configurations of the switches so as to respectively generate the n different linear combinations of the n signals. 
     Respective coefficients of the n signals in the different linear combinations may be +1 or −1. 
     The apparatus may include a pair of conductors, respectively connected to a first of the n signal sources and to an (n−1) th  cross-over switch, which are configured to convey the linear combinations to the processor. 
     There is further provided, according to an embodiment of the present invention a method, including: 
     generating a first signal from a first signal source and generating a second signal from a second signal source; 
     connecting a cross-over switch between the two sources so as to generate in a direct switch configuration a sum of the first and second signals and in a crossed switch configuration a difference between the first and second signals; 
     receiving the sum and the difference; 
     and recovering the first signal and the second signal from the sum and difference. 
     The method may include providing a distal end of a catheter configured for insertion into a human patient, and incorporating the first signal source, the second signal source, and the cross-over switch into the distal end. 
     There is further provided, according an embodiment of the present invention, a method, including: 
     respectively generating n signals from a sequence of n signal sources, where n is an integer greater than one; 
     connecting each of (n−1) cross-over switches between a p th  signal source and a (p+1) th  signal source, where p is an integer and 1≦p&lt;n, the (n−1) cross-over switches being configured to generate n different linear combinations of the n signals; 
     receiving the linear combinations; and 
     recovering the n signals from the received linear combinations. 
     The present disclosure will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an invasive medical procedure using a two wire transmission system, according to an embodiment of the present invention; 
         FIG. 2  is a schematic illustration of a distal end of a catheter used in the procedure, according to an embodiment of the present invention; 
         FIG. 3A  and  FIG. 3B  are schematic circuit, diagrams illustrating a cross-over switch, according to an embodiment of the present invention; 
         FIGS. 4A, 4B, and 4C  are schematic circuit diagrams of different configurations of a circuit in the distal end of the catheter of  FIG. 2 , according to an embodiment of the present invention; and 
         FIG. 5  is a schematic circuit diagram of a sequence of multiple signal sources connected by cross-over switches, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     An embodiment of the present invention provides a method for transferring multiple signals, typically analog signals, using a minimal number of conductors. Typically, only a single pair of conductors are required to transfer the multiple signals. 
     In the case where the multiple signals comprise two signals from two signal sources, a cross-over switch having two configurations is connected between the two sources. In a “direct” configuration the switch generates a sum of the first and second signals; and in a “crossed” configuration the switch generates a difference between the first and second signals. The sum and the difference are conveyed to a processor, typically via the single pair of conductors referred to above, and the processor recovers the two signals by analysis of the received sum and difference. 
     In the case where the multiple signals comprise more than two signals from a corresponding number of signal sources, more cross--over switches are used. In general, for n signal sources (n a positive integer) (n−1) cross-over switches are connected between the n sources. Typically, the configuration of the switches is altered in sequence, so that at any one time no more than one of the switches is in the crossed configuration, providing a “local” difference between the two signals connected to the switch. For each configuration of the switches a different linear combination of the signals is generated, each linear combination comprising a signal sum with at most one signal difference. 
     The different linear combinations may be conveyed to the processor via a single pair of conductors, and the processor may recover each of the n signals by analysis of the linear combinations. 
     Embodiments of the present invention enable multiple signals to be sampled substantially simultaneously, and the signals may be transferred for subsequent recovery by a processor using a single pair of conductors. Once recovered, the processor has all of the signals available at all times, in contrast to a time multiplexing system of signal transfer, where the signals are available sequentially. 
     System Description 
     In the following description, like elements in the drawings are identified by like numerals, and the like elements are differentiated as necessary by appending a letter to the identifying numeral. 
       FIG. 1  is a schematic illustration of an invasive medical procedure using a two wire transmission system  10 , and  FIG. 2  is a schematic illustration of a distal end of a catheter used in the procedure, according to embodiments of the present invention. By way of example, system  10  is assumed to be incorporated into an apparatus  12  used for an invasive medical procedure, performed by a medical professional  14 , on a heart  16  of a human patient  18 . 
     To perform the procedure, professional  11  inserts a catheter  20  into the patient, so that a distal end  22  of the catheter enters the heart of the patient. In order to track the distal end while it is in the patient&#39;s heart, apparatus  12  comprises magnetic transmitters  24 , typically located beneath and external to the patient, in the vicinity of heart  16 . Transmitters  24  are powered and controlled by a processor  26 , which is located in an operating console  28  of apparatus  12 . The Carto® system produced by Biosense Webster, of Diamond Bar, Calif., uses such a tracking method. 
     As explained in more detail below, signals generated within distal end  22 , in response to the magnetic fields from the transmitters, are transferred back via catheter  20  to processor  26 . The processor analyzes the received signals to determine a location and an orientation of the distal end, and may present the results on a screen  30  attached to the console. The results are typically presented by incorporating an icon representing the distal end into a map of the heart. 
     Other signals generated within the distal end, examples of which are provided, below, may also be transferred back via catheter  20 , and results from analysis of the signals may be presented on screen  30 . The results derived from these signals typically include numerical, displays, and/or graphs representative of characteristics of the heart. 
       FIG. 2  schematically shows elements of distal end  22 . The distal end typically comprises one or more sensing elements used to measure characteristics of the part of heart  16  wherein distal end  22  is located. Such sensing elements may comprise, for example, a sensor measuring a force or pressure applied by the distal end to the heart, a sensor measuring a temperature of the heart, and/or an electrode measuring an electropotential of the heart. For example, U.S. Pat. No. 8,357,152 to Govari, et al., whose disclosure is incorporated herein by reference, describes a system having a sensor generating pressure-sensing signals in the distal end of a catheter. As will be apparent from the following description, signals provided by the type of sensors described above may be conveyed to processor  26  in embodiments of the present invention. 
     By way of example, distal end  22  is assumed to comprise three generally similar electrodes  50 , electrodes  52 A,  52 B, and  52 C, which may be used to measure heart electropotentials. In some embodiments electrodes  52 A,  52 B, and/or  52 C may also be used to apply radio-frequency ablation power to the heart. 
     For the measurements from the sensing elements, such as electrodes  50 , to be useful, it is typically necessary to know a location and orientation of the distal end wherein the elements are located. In order to provide the location and orientation, the distal end comprises three generally similar coils  60 , coils  60 A,  60 B, and  60 C, which are arranged, to have axes that are mutually perpendicular to each other. For clarity the figure shows the coils as having separated centers; however, the coils may be configured to have a common center in order to save space. The coils generate the signals that are received by processor  26  (and referred to above) in response to the magnetic fields from transmitters  24 . However, rather than each signal being transferred back to the processor via a respective pair of conductors for each coil  60 , in embodiments of the present invention the three coil signals are transferred back to processor  26  via a single pair of conductors  62 , conductors  62 A,  62 B, as explained below. Conductors  62  are typically enclosed in a cable  64  which is incorporated into catheter  20 . 
     In order to transfer the signals by pair of conductors  62 , coils  60  are connected to two cross-over switches  70 , switches  70 A and  70 B. Characteristics of cross-over switches  70 , used in embodiments of the present invention, are explained below. The arrangement of coils  60 , switches  70 , and conductors  62  in the distal end is herein termed circuit  80 . 
       FIG. 3A  and  FIG. 3D  are schematic circuit diagrams respectively illustrating a first “direct” configuration of a generic cross-over switch  70 , and a second “crossed-over” configuration of the switch, according to an embodiment of the present invention. Switch  70  may be in one of the two configurations, the characteristics of which are described below. Switch  70  comprises four isolated terminals T 1 , T 2 , T 3 , and T 4 . In the first configuration terminals T 1  and T 2  are connected together, and terminals T 3  and T 4  are connected together. In the second configuration terminals T 1  and T 4  are connected together, and terminals T 3  and T 2  are connected together. 
     Switch is connected to two signal sources, typically analog signal sources, respectively generating signals S 1  and S 2 . In general, expressions for S 1  and S 2  are given by equation (1)
 
S 1 =A 1 e iω     1     φ     1   ; S 2 =A 2   e   iω     2     φ     2      (1)
 
     where A 1 , A 2  are amplitudes, ω 1 , ω 2  are frequencies, and φ 1 , φ 1  are phases of the signals. 
     The signal sources generating signals S 1  and S 2  are illustrated by way of example in  FIGS. 3A and 3B  as coils. While the sources may in fact be coils, there is no requirement that this is the case, and the entities generating signals S 1  and S 2  may be any elements or combination of elements that give signals that may be represented by equation (1). 
     Signal S 1  is developed between source terminals S 1a  and S 1b ; similarly, signal. S 2  is developed between source terminals S 2a  and S 2b . The sources are connected to switch  70  as shown in the figures, i.e., source terminal. S 1b  is connected to switch terminal T 1 , source terminals S 2a  and S 2b  are respectively connected to switch terminals T 2  and T 4 ; and an output from the switched sources is taken between source terminal S 1a  and switch terminal T 3 . 
     In the first, direct, configuration of switch  70 , an output V sum  between terminals S 1a  and T 3  is a sum of the two signals, i.e.,
 
 V   sum   =S   1   +S   2    (2)
 
     In the second, crossed, configuration of switch  70 , an output v difference  between terminals S 1a  and T 3  is a sum of the first signal with a reversed polarity of the second signal, corresponding to a difference of the two signals, i.e.,
 
 V   difference   =S   1 +(− S   2 )= S   1   −S   2    (3)
 
     In embodiments of the present invention, cross-over switches  70  may be implemented by any suitable process known in the art. Such processes include, but are not limited to, producing switches as the microelectromechanical systems (MEMS) or as application specific integrated circuits (ASICs). The configuration of each switch  70 , i.e., if a specific switch  70  is in its first direct configuration or in its second crossed configuration, is under control of processor  26  which is able to toggle the switch between the two configurations. For simplicity control links to the switches from the processor, enabling the toggling, are not shown in the diagram. 
       FIGS. 4A, 4B, and 4C  are schematic circuit diagrams of different configurations of circuit  80  in distal end  22 , according to an embodiment of the present invention. As stated above, cross-over switches  70 A and  70 B are connected to coils  60 C,  60 B, and  60 A, and the connections are as shown in  FIGS. 4A, 4B, and 4C . To illustrate the equivalence of switch  70 B with generic switch  70  (shown in  FIGS. 3A and 3B ) switch  70 A is shown connected to coils  60 A and  60 B which have also been respectively labeled as sources generating signals S 1  and S 2 . As in  FIGS. 3A and 3B  the sources have terminals S 1a , S 1b , S 2a  and S 2b . 
     Switch  70 B is also equivalent to generic switch  70  having a source corresponding to coil  60 C and generating a signal S 3  connected to the switch. Coil  60 C has source terminals S 3a , S 3b  which are respectively connected to switch  70 B terminals T 4 , T 2 . 
     However, in the circuits of  FIGS. 4A, 4B, and 4C  terminal T 3  of switch  70 A is connected to switch  70 B terminal T 1 , and an output from the circuits is taken between source terminal S 1a  and switch  70 B terminal T 3 , which are respectively connected to conductors  62 A and  62 B. 
     In an embodiment of the present invention processor reconfigures circuit  80  in a cyclic manner, setting the configuration of the circuit as shown in  FIG. 4A , then in  FIG. 4B , then in  FIG. 4C , and returning to the configuration of  FIG. 4A . The periodicity of the cyclic reconfiguration is typically dependent on the characteristics of signals S 1 , S 2 , and S 3 . S 1  and S 2  are assumed to be of the form described above by equation (1); signal S 3  is assumed to be of a similar character, and to have an equation of the form:
 
S 3 =A 3 e iω     3     φ     3      (4)
 
     where A 3  is an amplitude, ω 3  is a frequency, and φ 3  is a phase of signal S 3 . 
     For example, if the frequencies ω 1 , ω 2 , ω 3  of the signals are of the order of 10 kHz, then processor  26  may set a frequency of switching between the different configurations of circuit  80  to be of the order of 1 kHz, so that a different configuration occurs approximately each millisecond. Other suitable frequencies of switching between the configurations will be apparent to those having ordinary skill in the art, and all such frequencies are assumed to be within the scope of the present invention. 
       FIG. 4A  illustrates a first configuration  82  of circuit  80 , wherein switches  70 A and  70 B are both in the direct configuration. In this case an output from conductors  62  is:
 
 V   1   =S   1   +S   2   +S   3    (5)
 
       FIG. 4B  illustrates a second configuration 84 of circuit  80 , wherein switch  70 B is in the direct configuration and switch  70 A is in the crossed configuration. In this case an output from conductors  62  is:
 
 V   2   =S   1   −S   2   +S   3    (6)
 
       FIG. 4C  illustrates a third configuration  86  of circuit  80 , wherein switch  70 B is in the crossed configuration and switch  70 A is in the direct configuration. In this case an output from conductors  62  is:
 
 V   3   =S   1   +S   2   −S   3    (7)
 
     While switching between the three configurations of circuit  80  described above, processor  26  receives values of V 1 , V 2 , and V 3 . By inspection of equations (5), (6), and (7), the following expressions for S 1 , S 2 , and S 3  may be derived: 
     
       
         
           
             
               
                 
                   
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     Processor  26  may apply, equations (8), (9), and (10), or a method equivalent to application of the equations, in order to derive values of S 1 , S 2 , and S 3  from measured values V 1 , V 2 , and V 3 . 
     The examples described above with reference to  FIGS. 2, 3A, 3B, 4A, 4B, and 4C  illustrate circuits having one cross-over switch with two signal sources connected to the switch, and two cross-over switches with three signal sources connected to the switches. However, these are particular examples, and embodiments of the present invention include circuits having n signal sources, with (n−1) cross-over switches connected between the sources, where n is any integer greater than one. 
       FIG. 5  is a schematic circuit diagram of a sequence of multiple signal sources connected by cross-over switches, according to an embodiment of the present invention. A circuit  100  comprises a sequence of n signal sources  102  sources  102 A,  102 B,  102 C, . . . ,  102 Z, which respectively generate signals S 1 , S 2 , S 3 , . . . , S n ; n is an integer equal to or greater than two. Sources  102  have respective pairs of terminals (S 1a , S 1b ), (S 2a , S 2b ), . . . , and the signals S 1 , S 2 , S 3 , . . . , S n  generated across the terminals may be represented by equations similar to equations (1) and (4). Circuit  100  provides the signals it generates to a processor, herein assumed by way of example to be processor  26 , via a pair of conductors  104 A,  104 B. 
     Circuit  100  also comprises a sequence of (n−1) cross-over switches  70 , switches  70 A,  70 B, . . . ,  70 Y. Except as described below, switches  70 A,  70 B and sources  102 A,  102 B,  102 C are connected as described above for switches  70 A,  70 B and sources  60 A,  60 B,  60 C ( FIGS. 4A, 4B, 4C ). In circuit  100  terminal S 1a  is connected to conductor  104 A, but terminal T 3  of switch  70 B is not connected to conductor  104 B. 
     Rather, terminal T 3  of switch  70 B is connected to a terminal T 1  of a succeeding switch  70  (as switch  70 A terminal T 3  is connected to switch  70 B terminal T 1 ). The pattern of connecting terminal T 3  of a given switch  70  to terminal T 1  of a succeeding switch  70  continues until a final switch  70  in the sequence of switches is reached. Terminal T 3  of the final, switch, illustrated as switch  70 Y in the figure, is connected to conductor  104 B. Thus conductor  104 A is connected to a first of the n sources  102 , and conductor  104 B is connected to the (n−1) th  switch  70 . 
     For simplicity, circuit  100  has been drawn with all switches  70  in the direct configuration. In operating the circuit, processor  26  typically begins with the circuit in this configuration. The processor then toggles each of switches  70 , between its direct and crossed configuration, in sequence, so that at any one time no more than one switch  70  is in the crossed configuration. When in its crossed configuration, the switch generates a “local” difference of the two signals connected to the switch. The toggling continues until the last switch in the sequence is reached. After the last switch has been toggled to its crossed configuration, it then reverts back to the direct configuration so that all switches  70  are again in the direct configuration shown in the figure. Processor  26  typically continues cycling the pattern of sequential toggling of the switches as long as signals S 1 , S 2 , S 3 , . . . , S n  are being measured. 
     Outputs V 1 , V 2 , V 3 , . . . , V n  developed across conductors  104  and received by processor  26 , during the sequential toggling described above, are given by the following set of equations (11), which comprise different linear combinations of signals S 1 , S 2 , S 3 , . . . , S n . 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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                             … 
                           
                           
                             1 
                           
                         
                         
                           
                             ⋮ 
                           
                           
                             ⋮ 
                           
                           
                             ⋮ 
                           
                           
                             ⋮ 
                           
                           
                             ⋱ 
                           
                           
                             ⋮ 
                           
                         
                         
                           
                             1 
                           
                           
                             1 
                           
                           
                             1 
                           
                           
                             1 
                           
                           
                             … 
                           
                           
                             
                               - 
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                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     From equation (12) an expression for signals S 1 , S 2 , S 3 , . . . , S n , is is given by:
 
 S=M   −1   ·V    (13)
 
     where M −1 is the inverse matrix of matrix M. 
     Processor  26  applies equation (13), or uses an equivalent application, to derive values for signals S 1 , S 2 , S 3 , . . . , S n  from circuit outputs V 1 , V 2 , V 3 , . . . , V n . 
     Using circuits such as those described above enables processor  26  to sample multiple signals S 1 , S 2 , S 3 , . . . , S n  substantially simultaneously, using a single pair of conductors. Thus, returning to  FIG. 2 , signals from coils  60 A,  60 B, and  60 C may be sampled simultaneously via conductors  62 A and  62 B. Furthermore, by adding cross-over switches  70  into the distal end, other signals, such as those generated by electrodes  52 , and/or those generated by sensors that may be incorporated into the distal end, such as the pressure sensor described in the above-referenced U.S. Pat. No. 8,357,152, may also be sampled via conductors  62 A and  62 B. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and suhcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.