Abstract:
An adapter allows the interconnection of a sensor originating from one manufacturer to be coupled with conventionally incompatible monitors originating from other manufacturers to form a properly functioning pulse oximetry system. The adapter matches a sensor driver in a monitor to the current requirements and light source configuration of a sensor. The adapter also matches a sensor&#39;s light detector signal level to the dynamic range requirements of a monitor preamplifier. Further, the adapter provides compatible sensor calibration, sensor type and security information to a monitor. The adapter may have a self-contained power source or it may derive power from the monitor, allowing both passive and active adapter components. The adapter is particular suited as an adapter cable, replacing a conventional patient cable or sensor cable as the interconnection between a sensor to a monitor in a pulse oximetry system.

Description:
RELATED APPLICATION 
       [0001]    This is a continuation application based on application Ser. No. 11/341,999, filed Jan. 27, 2006, now U.S. Pat. No. 7,844,313, which is a continuation of application Ser. No. 10/624,446, filed Jul. 22, 2003, now U.S. Pat. No. 6,993,371, which is a continuation of application Ser. No. 09/982,453, filed Oct. 17, 2001, now U.S. Pat. No. 6,597,933, which is a divisional of application Ser. No. 09/404,060, filed Sep. 23, 1999, now U.S. Pat. No. 6,349,228, which is a continuation of application Ser. No. 09/021,957, filed on Feb. 11, 1998, now U.S. Pat. No. 5,995,855, the entirety of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Oximetry is the measurement of the oxygen status of blood. Early detection of low blood oxygen is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of oxygen supply. A pulse oximetry system consists of a sensor attached to a patient, a monitor, and a cable connecting the sensor and monitor. 
         [0003]    Conventionally, a pulse oximetry sensor has both red and infrared LED emitters and a photodiode detector. The sensor is typically attached to an adult patient&#39;s finger or an infant patient&#39;s foot. For a finger, the sensor is configured so that the emitters project light through the fingernail and into the blood vessels and capillaries underneath. The photodiode is positioned at the finger tip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues. 
         [0004]    The pulse oximetry monitor determines oxygen saturation by computing the differential absorption by arterial blood of the two wavelengths emitted by the sensor. The monitor alternately activates the sensor LED emitters and reads the resulting current generated by the photodiode detector. This current is proportional to the intensity of the detected light. A ratio of detected red and infrared intensities is calculated by the monitor, and an arterial oxygen saturation value is empirically determined based on the ratio obtained. The monitor contains circuitry for controlling the sensor, processing sensor signals and displaying a patient&#39;s oxygen saturation, heart rate and plethysmographic waveform. A pulse oximetry monitor is described in U.S. Pat. No. 5,632,272 assigned to the assignee of the present invention. 
         [0005]    The patient cable provides conductors between a first connector at one end, which mates to the sensor, and a second connector at the other end which mates to the monitor. The conductors relay the drive currents from the monitor to the sensor emitters and the photodiode detector signals from the sensor to the monitor. 
       SUMMARY OF THE INVENTION 
       [0006]    A drawback to conventional pulse oximetry systems is the lack of standardization of the sensor and the monitor. Unless the sensor and the monitor are manufactured by the same company, it is unlikely that these two components can be connected as a functioning pulse oximetry system. This incompatibility is mainly due to physical configuration and signal parameter differences among both the sensors and the monitors. Sensors differ primarily with respect to the configuration, drive requirements and wavelength of the LEDs. Sensors also differ in the configuration and value of coding and calibration resistors used to identify, for example, sensor type or LED wavelength. Monitors differ primarily with respect to the configuration and current limit of the LED driver; the amount of preamplifier gain applied to the photodiode detector signal; and the method of reading and interpreting sensor coding and calibration resistors. Further, the physical interface between sensors and monitors, such as connector types and pinouts, is also variable. Sensor and monitor variations among various pulse oximetry systems are discussed in detail below with respect to  FIGS. 1 through 3 . 
         [0007]      FIG. 1  depicts one type of sensor  100  and a corresponding monitor  150  for one type of pulse oximetry system. For this particular sensor  100 , the red LED  110  and infrared LED  120  are connected back-to-back and in parallel. That is, the anode  112  of the red LED  110  is connected to the cathode  124  of the infrared LED  120  and the anode  122  of the infrared LED  120  is connected to the cathode  114  of the red LED  110 . Also for this sensor  100 , the photodiode detector  130  is configured so that the photodiode leads  102 ,  104  are not in common with either of the LED leads  106 ,  108 . 
         [0008]    As shown in  FIG. 1 , the sensor  100  is also configured with a coding resistor  140  in parallel with the LEDs  110 ,  120 . The coding resistor  140  is provided as an indicator that can be read by the monitor  150 , as described in pending U.S. patent application Ser. No. 08/478,493, filed Jun. 7, 1995 and assigned to the assignee of the present application. The resistor  140  is used, for example, to indicate the type of sensor  100 . In other words, the value of the coding resistor  140  can be selected to indicate that the sensor  100  is an adult probe, a pediatric probe, a neonatal probe, a disposable probe or a reusable probe. The coding resistor  140  is also utilized for security purposes. In other words, the value of the coding resistor  140  is used to indicate that the sensor  100  is from an authorized sensor supplier. This permits control over safety and performance concerns which arise with unauthorized sensors. In addition, the coding resistor  140  is used to indicate physical characteristics of the sensor  100 , such as the wavelengths of the LEDs  110 ,  120 . 
         [0009]    Also shown in  FIG. 1  is a portion of a monitor  150  that is compatible with the sensor described above. The monitor  150  has drive circuitry that includes a pair of current drivers  162 ,  164  and a switching circuit  170 . The monitor  150  also has a signal conditioner, which includes an input buffer  195  that conditions the output of the sensor photodiode  130 . In addition, the monitor has a low-voltage source  164  and corresponding reference resistor  194  that read the sensor coding resistor  140 . 
         [0010]    Each current driver  162 ,  164  provides one of the LEDs  110 ,  120  with a predetermined activation current as controlled by the switching circuit  170 . The switching circuit  170 , functionally, is a double-pole, triple throw (2P3T) switch. A first switch  172  connects to a first LED lead  106  and a second switch  174  connects to a second LED lead  108 . The first switch  172  has a first position  181  connected to the red LED driver  162 ; a second position  182  connected to a reference resistor  194  and a buffer  195 ; and a third position  183  connected to ground  168 . The second switch  174  has a first position  181  connected to ground  168 ; a second position  182  connected to a low-voltage source  192 ; and a third position  183  connected to the infrared LED driver  164 . 
         [0011]    During a particular time interval, the switching circuit  170  causes the first switch  172  to connect the red LED driver  162  to the red LED anode  112  and simultaneously causes the second switch  174  to connect the ground  168  to the red LED cathode  114 . As a result, a forward current is established in the red LED  110 , which is activated to emit light. During another particular time interval, the switching circuit  170  causes the first switch  172  to connect the ground  168  to the infrared LED cathode  124  and simultaneously causes the second switch  174  to connect the infrared LED driver  164  to the infrared LED anode  122 . As a result, a forward current is established in the infrared LED, which is activated to emit light. This cycle is repeated to cause the sensor to alternately emit red and infrared light. These alternating light pulses result in currents in the photodiode detector  130 , which are input to a monitor buffer  166  and multiplexed  197  into an analog-to-digital converter (ADC)  199 . The digitized outputs from the ADC  199 , representing detected intensities, are then processed by the monitor  150  and displayed as oxygen status. 
         [0012]    During a monitor initialization interval, the switching circuit  170  causes the first and second switches  172 ,  174  to be in a second position  182 . This isolates the LED leads  106 ,  108  from the drivers  162 ,  164  and ground  168 . Further, the low-voltage source  192  is connected to one LED lead  108  and the reference resistor  194  is connected to the other LED lead  106 . As a result, a voltage is established across the parallel combination of the coding resistor  140  and the LEDs  110 ,  120 . If this voltage is less than the forward voltage of the forward biased infrared LED  120 , then, because the red LED  110  is reverse biased, neither LED  110 ,  120  conducts significant current. In such a scenario, the current that passes through the parallel combination of the red LED  110 , infrared LED  120 , and coding resistor  140  is approximately equal to the current through the coding resistor  140 . Thus, the equivalent circuit is the low-voltage source  192  across the series combination of the coding resistor  140  and the reference resistor  194 . The resistance of the coding resistor  140  is then easily determined via Ohms Law from the voltage across the reference resistor  194 , which is read as a digitized value from the ADC  199 . 
         [0013]      FIG. 2  depicts another type of sensor  200  and corresponding monitor  250  for a conventional pulse oximetry system. This pulse oximetry system is described in U.S. Pat. No. 4,621,643 to New Jr. et al., issued Nov. 11, 1986. The sensor  200  of  FIG. 2  is similar to that of  FIG. 1  in that it comprises a red LED  210  and an infrared LED  220 . However, in this sensor  200 , the LEDs  210 ,  220  are in a common cathode, three-wire configuration. That is, the cathode  214  of the red LED  210  is connected to the cathode  224  of the infrared LED  220  and a common input lead  208 . Also, the anode  212  of the red LED  210  and the anode  222  of the infrared LED  220  have separate input leads  202 ,  204 . The photodiode detector  230  shown in  FIG. 2  functions in much the same way as the detector  130  shown in  FIG. 1  but shares one input lead  208  with the sensor LEDs  210 ,  220 . As shown in  FIG. 2 , the sensor  200  also has a calibration resistor  240  with one separate input lead  206  and one lead  208  in common with the LEDs  210 ,  220  and photodiode  230 . This resistor  240  is encoded to correspond to the measured wavelength combination of the red LED  210  and infrared LED  220 . 
         [0014]    Also shown in  FIG. 2  is a portion of a monitor  250  that is compatible with the depicted sensor  200 . The monitor  250  has LED drive circuitry  260  which activates the LEDs  210 ,  220  one at time with a predetermined drive current independently applied to each of the LED anodes  212 ,  222 . The monitor  250  also has a signal conditioner, including amplification and filtration circuitry  270  that conditions the input current from the detector  230 , which is multiplexed  282  into a successive-approximation analog-to-digital converter (ADC)  284  comprising a comparator  285  and digital-to-analog converter (DAC)  286 . A microprocessor  288  then reads the digitized detector signal for analysis. The monitor  250  reads the calibration resistor  240  by passing a predetermined current from a current source  290  through the resistor  240 . The microprocessor  288  reads the resulting voltage across the resistor  240 , which is passed through the multiplexer  282  and ADC  284 . The microprocessor  288  then computes the resistor value per Ohm&#39;s Law. 
         [0015]      FIG. 3  illustrates yet another type of sensor  300  and corresponding monitor  350 . This configuration is similar to those of  FIGS. 1 and 2  in that the sensor  300  has a red LED  310 , an infrared LED  320  and a photodiode detector  330 . The configuration of the LEDs  310 ,  320  and the corresponding LED driver  360 , however, differ from those previously described. The LED driver  360  has a voltage source  362 , a red LED current sink  364  and an infrared LED current sink  367 . The LEDs  310 ,  320  are arranged in a three-wire, common-anode configuration. That is, the red LED anode  312  and the infrared LED anode  322  have a common anode lead  302 , the red LED cathode  314  has one separate lead  304  and the infrared LED cathode  324  has another separate lead  305 . The voltage source output  352  connects to the common anode lead  302 , the red LED current sink input  354  connects to the red LED cathode lead  304 , and the infrared LED current sink input  355  connects to the infrared LED cathode lead  305 . 
         [0016]    The current sinks  364 ,  367  control the drive current through each LED  310 ,  320 . The voltage source  362  has sufficient output capability to supply this drive current to each LED  310 ,  320  individually. Each current sink  364 ,  367  is a grounded emitter transistor  365 ,  368  having a bias resistor  366 ,  369  and a base control input  372 ,  374  that switches each transistor  365 ,  368  on and off. The bias resistor value and voltage of the base control input determine the amount of LED drive current. In operation, the red and infrared LEDs  310 ,  320  are alternately activated by pulsed control signals alternately applied to the base control inputs  372 ,  374 . 
         [0017]    The detector portion of the sensor  300  of  FIG. 3  also differs from those in the previously miniature described sensors in that a gain resistor  340  is connected to the photodiode  330 . When connected to the corresponding monitor  350 , the gain resistor  340  provides feedback, which adjusts the gain of a monitor preamplifier within the signal conditioner portion  380  of the monitor  350 , which reduces the preamplifier dynamic range requirements. For example, if the sensor  300  is configured for neo-natal patients, where the sensor site is of relatively narrow thickness and the skin relatively transparent, the gain can be correspondingly low. However, if the sensor  300  is configured for adult patients, with a relatively thick and opaque sensor site, such as a finger, the gain can be correspondingly higher to compensate for lower detected intensities. 
         [0018]      FIGS. 1 through 3  are examples of just some of the functional variations between sensors and monitors in pulse oximetry systems. These functional variations thwart the use of different sensors on different monitors. There are other sensor and monitor variations not described above. For example, a sensor may have LEDs with a three-wire common-anode configuration, as depicted in  FIG. 7  below. There are also other potential mismatches between sensors and monitors. For example, the LED drive current supplied by a particular monitor may be either too high or too low for the LEDs on an incompatible sensor. 
         [0019]    Besides the functional variations described above, physical variations between sensors and monitors may prevent interconnection to form a pulse oximetry system. For example, sensors have a variety of connectors. These connectors may vary from subminiature D-type connectors to flex-circuit edge connectors to name a few. Similar connector variations exist on the monitor. Further, some pulse oximetry systems require a separate patient cable, which mates to the sensor at one end and the monitor at the other end to span the distance between patient and monitor. In other systems, the sensor incorporates a cable that plugs directly into a monitor. Another physical variation is the pinouts at both the sensor connector and monitor connector. That is, there are potential differences between what signals are assigned to what connector pins. 
         [0020]    A conventional adapter cable can sometimes be used to interconnect two dissimilar devices. The connector at one end of the adapter cable is configured to mate with one device and the connector at the other end of the cable is configured to mate with the second device. The cable wires can be cross-connected as necessary to account for pinout differences. A conventional adapter cable, however, is of little use in interconnecting various sensors to various pulse oximetry monitors. As described above, although the sensors have similar components that perform similar functions, the incompatibilities are more than connector and pinout related. In particular, a conventional adapter cable is incapable of correcting for the signal mismatches between sensors and monitors. 
         [0021]    Although it is perhaps possible to design sensors that accommodate a variety of monitors, such sensors would be, for the most part, commercially impractical. For one, pulse oximetry sensors can be either reusable or disposable. In the case of disposable sensors, cost per sensor is critical. Even for reusable sensors, cost and complexity are important design factors. A universal sensor having integrated adapter components could be significantly more expensive than the sensors described in  FIGS. 1 through 3 . A sensor adapter according to the present invention solves many of the problems associated with both sensor and monitor compatibility and the need to avoid sensor complexity. 
         [0022]    One aspect of the present invention is an adapter that provides an interconnection between a pulse oximetry sensor and a monitor. The sensor has a light source and a light detector, and the monitor has a driver and a signal conditioner. The adapter comprises a plurality of signal paths. The signal paths are detachably connected to either the monitor, the sensor or both. A first signal path is in communication with the driver and the light source. A second signal path is in communication with the light detector and the signal conditioner. The adapter also comprises an adapter element that is connected to at least one of the signal paths. The adapter element modifies a characteristic of at least one of the signal paths so that the sensor and the monitor are jointly operable to measure oxygen status. In one embodiment, where the monitor has an information element detector in communication with at least one of the signal paths, the adapter element conveys information about the sensor that is compatible with the information element detector. In another embodiment, the adapter element is connected to the first signal path and matches the light source configuration with the driver configuration. In yet another embodiment, the adapter element is connected to the first signal path and matches the drive requirements of the light source with the drive capabilities of the driver. In an additional embodiment, the adapter element is connected to the second signal path and provides gain for a detector signal. 
         [0023]    Another aspect of the present invention is a sensor adapter comprising a sensor having a light source and a light detector and comprising a plurality of signal paths. The signal paths are detachably connected to a monitor. A first signal path communicates a drive signal from the monitor to the light source. A second signal path communicates an intensity signal from the light detector to the monitor. The sensor adapter also comprises an adapter element in communication with at least one of the signal paths. The adapter element creates a compatibility signal that allows the sensor and the monitor to be jointly operable as a pulse oximetry system. In one embodiment, the sensor adapter comprises an active component. The active component generates a predetermined signal level applied to the first signal path that conveys information regarding a compatible sensor. In another embodiment of the sensor adapter, the light source has a conductive portion with a predetermined equivalent resistance that conveys information regarding a compatible sensor. Advantageously, the conductive portion may be an LED encapsulant or incorporated within the semiconductor material of an LED. In yet another embodiment, the sensor adapter further comprises a translator that senses a sensor information element and communicates equivalent information to the monitor. 
         [0024]    Yet another aspect of the present invention is a method of connecting an incompatible sensor to a monitor. The method comprises the step of adapting a signal in communication with either the sensor, the monitor or both so that the sensor and the monitor are jointly operable as a pulse oximetry system. In one embodiment, the adapting step comprises the steps of sensing a drive signal and switching the drive signal to a particular one of a plurality of light source leads in response to the drive signal. Advantageously, the switching step may connect a two-wire driver to a three-wire light source or may connect a three-wire driver to a two-wire light source, either connection being made through a multiple-pole, multiple-throw switch. In another embodiment, the adapting step comprises adjusting a drive signal from the monitor to match the drive requirements of a light source in the sensor. In yet another embodiment, the adapting step comprises providing a feedback signal to the monitor. The amount of the feedback determines the gain applied within the monitor to a light detector signal from the sensor. In an additional embodiment, the adapting step comprises generating an information signal to an information element detector that corresponds to information from a compatible sensor. In another embodiment, the adapting step comprises translating an information signal from a sensor into a translated information signal that is read by an information element detector and corresponds to a compatible sensor. 
         [0025]    A further aspect of the present invention is a sensor adapter for operably interconnecting an incompatible sensor to a monitor in a pulse oximetry system comprising an interconnect means for providing a signal path between the sensor and the monitor. The sensor adapter also comprises an adapter means for creating a compatible signal on the signal path. In one embodiment, the adapter means comprises a configuration means for routing a drive signal from the monitor so as to correspond to a light source in the sensor. In another embodiment, the adapter means comprises a limit means for changing the amount of a drive signal from the monitor so as to correspond to a light source in the sensor. In yet another embodiment, the adapter means comprises a gain means for modifying the amplitude of a detector signal from the sensor. In an additional embodiment, the adapter means comprises an information means for providing a signal to an information element detector that corresponds to a compatible sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The present invention is described in detail below in connection with the following drawing figures in which: 
           [0027]      FIG. 1  is a schematic diagram representing a sensor and corresponding monitor interface circuitry; 
           [0028]      FIG. 2  is a schematic diagram representing another prior art sensor and corresponding monitor interface circuitry; 
           [0029]      FIG. 3  is a schematic diagram representing yet another prior art sensor and corresponding monitor interface circuitry; 
           [0030]      FIG. 4  is a block diagram of a sensor adapter according to the present invention; 
           [0031]      FIG. 5  is an illustration of various physical embodiments of a sensor adapter in relation to a sensor and a monitor; 
           [0032]      FIG. 6  is a block diagram of a drive configuration adapter portion of the sensor adapter for a monitor with three-wire, common-anode drivers to a sensor with two-wire, back-to-back LEDs; 
           [0033]      FIG. 7  is a block diagram of a drive configuration adapter portion of the sensor adapter for a monitor with two-wire, back-to-back LED drivers to a sensor with three-wire, common-anode LEDs; 
           [0034]      FIG. 8  is a block diagram of a drive limit adapter portion of the sensor adapter illustrating a drive current gain; 
           [0035]      FIG. 9  is a block diagram of a drive limit adapter portion of the sensor adapter illustrating a drive current reduction; 
           [0036]      FIG. 10  is a block diagram illustrating the active gain adapter portion of the sensor adapter; 
           [0037]      FIG. 11  is a schematic of an embodiment of the information generator adapter portion of the sensor adapter featuring an adapter information element; 
           [0038]      FIG. 12  is a schematic of another embodiment of the information generator adapter portion of the sensor adapter; 
           [0039]      FIG. 13  is a schematic of yet another embodiment of the information generator adapter portion of the sensor adapter; 
           [0040]      FIG. 14  is a schematic diagram of the information translation adapter portion of the sensor adapter; 
           [0041]      FIG. 15  is a block diagram of a universal sensor adapter embodiment of the sensor adapter; 
           [0042]      FIG. 16  is an illustration of a universal adapter cable embodiment of the universal sensor adapter; 
           [0043]      FIG. 17  is a block diagram of the configuration adapter portion of the universal sensor adapter; and 
           [0044]      FIG. 18  is a schematic diagram of the driver test and sensor test portions of the configuration adapter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0045]      FIG. 4  shows a functional block diagram of a sensor adapter  400  for interconnecting a sensor  402  to an incompatible monitor  404  in a pulse oximetry system. Interconnecting the monitor light source driver  410  with the sensor light source  412  are a light source configuration  414  adapter and a drive limit  418  adapter. The light source configuration  414  element adapts the light source driver  410  to the particular configuration of the sensor light source  412 , such as two-wire, back-to-back LEDs, three-wire, common-anode LEDs and three-wire, common-cathode LEDs. The drive limit  418  element increases or decreases the current of the light source driver  410  to adapt to the requirements of the sensor light source  412 . 
         [0046]    Also shown in  FIG. 4  is an active gain  434  element, which adapts the sensor light detector  432  to the monitor signal conditioner  430 . Active gain  434  sets the amount of amplification of the signal from the sensor light detector  432  that occurs in the monitor signal conditioner  430 . Active gain  434  may also provide preamplification of the light detector signal before input to the monitor  404 . 
         [0047]      FIG. 4  further shows a monitor information element detector  450  that is interconnected with an information generator  458  and information translator  454 . The information generator  458  simulates an information element  452  on the sensor to provide the monitor information element detector  450  with information regarding, for example, sensor type, origin or light source calibration. The information translator  454  reads a sensor information element  452  and provides the equivalent information to the monitor information element detector  450 , adapting to the configuration and value expected by the monitor  404 . 
         [0048]    As shown in  FIG. 4 , the sensor adapter  400  has a power supply  470 . As such, the functions of the sensor adapter  400  as described above can be performed with both active and passive components. In one embodiment, the power supply  470  has an internal power source  472 , such as a lithium-ion battery. In another embodiment, the power supply  470  uses an external power source. The external power source may be, for example, one or more d.c. voltages available from a monitor output  474 . Alternatively, the external power source may be derived from the light source driver  410 , which supplies pulsed power to the sensor light source  412 . A fraction of this pulsed power can be routed by a tap  478  to the power supply  470 , where it is a.c.-to-d.c. converted. Regardless of the power source, the power supply  470  may also include d.c.-to-d.c. conversion, filtering and voltage regulation to provide suitable voltage levels and power conditioning for the active components of the sensor adapter  400 , as is well-known in the art. 
         [0049]      FIG. 5  illustrates embodiments of the pulse oximetry sensor adapter according to the present invention. In one embodiment, the sensor adapter is configured as a connector block  510  that has a first connector  512  on one end that is attachable directly to a monitor  502  by plugging into a monitor connector  504  and a second connector  514  on the other end that accepts a cable connector  522 . The components of the sensor adapter are mounted to a small substrate  515 , and may be, for example, surface-mount devices soldered on one or both sides of a circuit board or flex-circuit. The substrate  515  is electrically interconnected to the connectors  512 ,  514 . This interconnection may be done with conductors  516 , such as individual wires, flex-circuit traces or ribbon cable soldered to both the substrate  515  and the connectors  512 ,  514 . Alternatively, the substrate  515 , might be directly attached to both connectors  512 ,  514 . The substrate  515 , conductors  516  and portions of the connectors  512 ,  514  are encapsulated by insulating material that forms the connector block body  518 . One will recognize other possibilities for mounting and interconnecting the adapter components within the connector block  510 . 
         [0050]      FIG. 5  illustrates another embodiment of the sensor adapter where the adapter is configured as an adapter cable  520  that also serves the function and substitutes for a conventional patient cable or sensor cable. In this embodiment, the sensor adapter can be alternatively incorporated into a first end portion  530  of the cable  520 , which would attach proximate to the monitor  502 ; a second end portion  540  of the cable  520 , which would attach proximate to the sensor  506 ; or the cable body  522 , as, for example, an attached molded cable block  550 . Whether incorporated into the first end portion  530 , second end portion  540  or the cable body  522 , the adapter components are mounted to a substrate  515 , as described. 
         [0051]    If the sensor adapter is incorporated into the first end portion  530  or the second end portion  540 , the substrate  515  with the adapter components is interconnected between the cable connector  522 ,  542  and the wiring within the cable body  522 . If the sensor adapter is incorporated into the cable body  522 , the substrate  515  is interconnected with the wiring within the cable body  522 . Regardless, the substrate  515  is interconnected as described above with respect to the connector block  510 . The substrate  515 , connector  522 ,  542  and interconnection are then encapsulated to form a connector body  532 ,  542  or cable block body  552 , also as described above. 
         [0052]    As shown in  FIG. 5 , the sensor adapter may also be incorporated into the sensor  506 . This, however, increases the cost of the sensor, which may be particularly critical for disposable sensors. For this embodiment, the adapter components can be mounted on a substrate  515 , as described above. In turn, the substrate  515  can be mounted to the sensor  506 , for example, by attaching and electrically interconnecting the substrate  515  to a flex circuit portion of the sensor  506 . Alternatively, the adapter components can be mounted directly to the flex circuit portion of the sensor  506  or incorporated within particular sensor components, as with a conductive LED layer or encapsulant to form a coding or calibration resistor, as described below. 
         [0053]      FIG. 6  shows an embodiment of the light source configuration portion  414  of the sensor adapter. The light source portion  412  of the sensor is shown with a red LED  110  and infrared LED  120  in a back-to-back configuration. The light source driver portion  410  of the monitor is shown with a voltage source  362  and two current sinks  364 ,  367 . This driver was described above with respect to  FIG. 3  in connection with a common-anode LED sensor. Thus, the embodiment of the light source configuration element  414  shown in  FIG. 6  adapts a three-wire common-anode driver to a two-wire, back-to-back LED light source. The discussion below is equally applicable to a sensor where the positions of the red LED  110  and the infrared LED  120  are swapped and, correspondingly, that of the red LED current sink  364  and infrared LED current sink  367  are swapped from that shown in  FIG. 6 . 
         [0054]    As shown in  FIG. 6 , the adapter  414  has a double-pole, double-throw (DPDT) switch  610 . A first switch pole  612  is connected to a first lead  106  of the sensor LEDs  110 ,  120 . A second switch pole  614  is connected to a second lead  108  of the sensor LEDs  110 ,  120 . In a first position  616  (depicted), the switch  610  connects the red LED anode  112  to the voltage source  362  and the red LED cathode  114  to the red LED current sink  364 . In a second position  618  (not depicted), the switch  610  connects the infrared LED anode  122  to the voltage source  362  and the infrared LED cathode  124  to the infrared LED current sink  367 . In this manner, the voltage source  362  is alternately switched between LED anodes  112 ,  122  and the appropriate current sink  364 ,  367  is alternately switched to the appropriate LED cathode  114 ,  124 , alternately activating each of the LEDs  110 , 120 . 
         [0055]    As illustrated in  FIG. 6 , the adapter also has a drive sense  620  that controls the switch  610 . The drive sense  620  has a tap  652 ,  654 ,  655  on each of the monitor driver leads  352 ,  354 ,  355 , which allows the drive sense  620  to determine which of the current sink transistors  365 ,  368  is biased to a conducting state. The drive sense  620  then sets the switch position accordingly. One will recognize many ways to implement the drive sense  620 . For example, the output of a differential amplifier could control the switch  610 , where the amplifier input is a resistor connected between the voltage source  362  and the red LED current sink  364 . The amplifier could detect the voltage drop as current flows in the resistor when the red LED current sink  364  is in a conducting state, and actuate the switch  610  to the first position accordingly. When no voltage drop is detected, the switch  610  would return to the second position. 
         [0056]    The switch  610  is implemented with active components, such as multiple FET transistors connected in a DPDT configuration and having a control voltage applied to the FET gates to control conduction through the FET channels, as is well-known in the art. One will also recognize that a number of FET transistor configurations are equivalent to the DPDT configuration shown in  FIG. 6 . 
         [0057]      FIG. 7  shows another embodiment of the light source configuration portion  414  of the sensor adapter. The light source portion  412  of the sensor is shown with a red LED  310  and infrared LED  320  in a three-wire, common-anode configuration. The light source driver portion  410  of the monitor is shown with two drivers  162 ,  164  and a DPDT switch  170 . This driver was described above with respect to  FIG. 1  in connection with a back-to-back LED sensor. Thus, the embodiment of the light source configuration element  414  shown in  FIG. 7  adapts a two-wire, back-to-back LED driver  410  with a three-wire, common-anode LED light source  412 . 
         [0058]    As shown in  FIG. 7 , the adapter has a triple-pole, double-throw (3PDT) switch  710 . A first switch pole  712  is connected to a first lead  302  of the sensor LEDs  310 ,  320 . A second switch pole  714  is connected to a second lead  304  of the LEDs  310 ,  320 . A third switch pole  718  is connected to a third lead  305  of the LEDs  310 ,  320 . The adapter switch first position  722  corresponds to the driver switch first position  181 , as depicted in  FIG. 7 . The adapter switch second position  728  corresponds to the driver switch third position  183 . When the driver switch  170  is in the second position  182 , the adapter switch  710  can be in either position  722 ,  728 . In the first position  722 , the adapter switch  710  connects the red LED anode  312  to a first monitor lead  156 , when that lead  156  is connected to the red LED current source  162 . In this first position  722 , the switch  710  also connects the red LED cathode  314  to a second monitor lead  158 , when that lead  158  is connected to ground  168 . In this first position  722 , the infrared LED cathode  324  is disconnected. In a second position  728 , the adapter switch  710  connects the infrared LED anode  322  to the monitor second lead  158 , when that lead  158  is connected to the infrared LED current source  164 . In this second position  728 , the adapter switch  710  also connects the infrared LED cathode  324  to the first monitor lead  156 , when that lead  156  is connected to ground  168 . In this second position  728 , the red LED cathode  314  is disconnected. In this manner, the red LED current source  162  is driving the red LED  310  alternately as the infrared LED current source  164  is driving the infrared LED  320 . 
         [0059]    As illustrated in  FIG. 7 , the light source configuration portion  414  of the sensor adapter also has a drive sense  730  that controls the positions of the adapter switch  710 . The drive sense  730  has a tap  756 ,  758  on each of the driver leads  156 ,  158  that allow the drive sense  730  to determine the position of the driver switch  170 . The drive sense  730  then sets the sensor switch position accordingly. One will recognize many ways to implement the drive sense  730 . For example, a differential amplifier could detect the polarity of the taps  756 ,  758 , the amplifier output controlling the positions of the adapter switch  710 . For example, the amplifier could detect that the polarity of the first monitor lead  156  is positive with respect to the second monitor lead  158 , indicating the driver switch  170  is in the first position  181 . The amplifier output would then actuate the adapter switch  710  to the first position  722 . As discussed above with respect to  FIG. 6 , the switch is implemented with active components, for example, FET transistors. Also, as discussed above, one will also recognize that a number of FET transistor configurations would be equivalent to the 3PDT configuration shown in  FIG. 7 . 
         [0060]      FIG. 8  shows an embodiment of the drive limit portion  418  of the sensor adapter. In this embodiment, the drive limit adapter  418  provides increased drive current through the sensor light source  410 . For purposes of illustration, the sensor light source  410  shown in  FIG. 8  is a three-wire, common-anode LED configuration as described above with respect to  FIG. 3 . Also for purposes of illustration, the monitor light source driver  412  is configured to drive a three-wire, common-anode LED configuration, also as described above with respect to  FIG. 3 . It is assumed, however, that the sensor LEDs  310 ,  320  require an increased drive current over what the driver  412  provides. The drive limit adapter portion  418 , therefore, provides an adapter red LED current sink  810  in parallel with the monitor red LED current sink  364  and an adapter infrared LED current sink  820  in parallel with the monitor infrared LED current sink  367 . A drive sense  830  similar to the one described above with respect to  FIG. 6  controls the adapter current sinks  810 ,  820 . That is, the drive sense  830  has a tap  852 ,  854 ,  855  on each of the driver leads  352 ,  354 ,  355  that allow the drive sense  830  to determine which of the monitor current sinks  364 ,  367  are biased to a conducting state. The drive sense  830  then biases the corresponding adapter current sink  810 ,  820  to a conducting state. The bias resistors  812 ,  822  and the bias voltage applied by the drive sense control outputs  832 ,  834  determine the current through the adapter current sinks  810 ,  820 . The current through the red LED  310  is the sum of the current through the corresponding adapter red LED current sink  810  and the monitor red current sink  364 . Likewise, the current through the infrared LED  320  is the sum of the current through the corresponding adapter infrared LED current sink  820  and the monitor infrared current sink  367 . 
         [0061]      FIG. 9  shows another embodiment of the drive limit portion  418  of the sensor adapter. In this embodiment, the drive limit adapter  418  provides for decreased drive current through the sensor light source  410 . For purposes of illustration, the sensor light source  410  and the monitor driver  412  are shown the same as described above with respect to  FIG. 8 . For this embodiment, however, it is assumed that the sensor LEDs  310 ,  320  require a reduced drive current from what the driver  412  provides. The drive limit adapter  418 , therefore, provides a red LED shunt  910  and an infrared LED shunt  920 . Each shunt  910 ,  920  allows an amount of current to bypass a particular LED  310 ,  320 , as determined by the resistance value of the shunt  910 ,  920 . The current through the red LED  310  is the difference between the current drawn by the red LED current sink  364  and the current bypassed through the red LED shunt  910 . Likewise, the current through the infrared LED  320  is the difference between the current drawn by the infrared LED current sink  367  and the current bypassed through the infrared LED shunt  920 . 
         [0062]      FIG. 10  depicts an embodiment of the active gain portion  434  of the sensor adapter. Active gain  434  adapts the light detector portion  432  of the sensor to the signal conditioner portion  430  of the monitor. One function of the active gain adapter  434  is to provide a resistor  1080  in the feedback path  356  of a preamplifier  380 , for monitors which require this feature to control dynamic range, as described above with respect to  FIG. 3 . The value, R gain , of the resistor  1080  determines the gain of the preamplifier  380 . As illustrated in  FIG. 10 , another function of the active gain adapter  434  is to adjust the signal level of the photodiode  130 . This function also adapts the dynamic range of the monitor preamplifier  380  to a particular sensor type or application. A variable gain amplifier  1010  adjusts the detected signal level from the photodiode  130 . The amplifier inputs  1012 ,  1014  are connected to the photodiode output leads  102 ,  104 . The amplifier output  1018  drives the preamplifier input  358 . A single-pole, double-throw (SPDT) gain switch  1060  selects one of two feedback resistors  1072 ,  1074 . The selected resistor value, R high  or R low , determines the amplifier gain. 
         [0063]    The gain switch  1060  is controlled by a comparator  1020  in combination with a peak detector  1030  and a reference  1040 . The peak detector  1030  has an input  1032  connected to the output  1018  of the amplifier  1010 . The peak detector  1030  measures the amplified difference between detector dark current and detector signal current. This difference at the peak detector output  1034  is compared  1020  to a reference output  1042 . If the peak signal level is below the reference value, the comparator output  1022  actuates the gain switch  1060  to select the high gain resistor  1072 . If the peak signal level is above the reference value, the comparator output  1022  actuates the gain switch  1060  to select the low gain resistor  1074 . Hysteresis or integration of the peak detector output, for example, can be used to stabilize the amplifier gain settings, as is well-known in the art. Also, one will recognize that a bank of N resistors and single-pole, N-throw switch can be used to provide multiple gain settings for the amplifier  1010 , as determined by multiple reference outputs from the reference source  1040 . 
         [0064]      FIG. 11  illustrates an embodiment of the information generator portion  458  of the sensor adapter. An information element  1110  is located in the sensor adapter to substitute for an equivalent sensor information element. The information element  1110  connects via conductors  1120  to the information element detector portion  450  of the monitor  404 , which senses the information content of the information element  1110 . The information element  1110  may have series connections  1130  or parallel connections  1140  to outputs  424  of the sensor  402 . 
         [0065]    As an example, the sensor adapter could be an adapter cable having a coding or calibration resistor mounted as described above with respect to  FIG. 5 . In particular, as illustrated with the monitor  250  of  FIG. 2 , the adapter cable could have an information element that is a calibration resistor, which connects between the monitor leads  256 ,  258 . Similarly, as illustrated with the monitor  150  of  FIG. 1 , the adapter cable could have an information element that is a coding resistor, which connects between the monitor leads  156 ,  158 . In this manner, a sensor without a coding or calibration resistor would properly function when attached with the adapter cable to a monitor that requires such a resistor. 
         [0066]    As illustrated in  FIG. 1 , an equivalent substitute for a calibration or coding resistor can also be located on the sensor itself in the form of leakage resistance built into the sensor. In one embodiment, the red LED  110  and infrared LED  120  can be encapsulated with a material having some conductance so as to form an equivalent resistance equal to the desired value of the coding resistor  140 . In another embodiment, the semiconductor material of the red LED  110 , the infrared LED  120  or both can be fabricated with some conductance to form an equivalent resistance equal to the desired value of the coding resistor  140 . 
         [0067]      FIG. 12  illustrates another embodiment of the information generator portion  458  of the sensor adapter. The information generator  458  has a DPDT adapter switch  1210 , an adapter resistor  1220  and a low-voltage detector  1230 . The adapter switch  1210  has a first position  1242  that connects the sensor LED leads  106 ,  108  to the monitor output leads  156 ,  158 . The adapter switch  1210  has a second position  1244  that connects the adapter resistor  1220  across the output leads  156 ,  158 . The low-voltage detector  1230  has an input  1232  that can be connected to the low-voltage output lead  158 . The low-voltage detector  1230  has an output that controls the adapter switch  1210 . 
         [0068]    As illustrated in  FIG. 12 , the operation of the information generator  458  is illustrated with respect to the monitor  150 , described above with respect to  FIG. 1 . In its first position  1242 , the adapter switch  1210  connects the two leads of the sensor LEDs  106 ,  108  to the two monitor output leads  156 ,  158 . The adapter switch first position  1242  corresponds to the monitor switching circuit first position  181  and third position  183 , at which the LED drivers  162 ,  164  alternately activate the LEDs  110 ,  120 . 
         [0069]    As shown in  FIG. 12  and described above with respect to  FIG. 1 , during calibration, the switching circuit  170  is set to a second position  182  which isolates the monitor output leads  156 ,  158  from the drivers  162 ,  164  and ground  168 . During this calibration period, a combination of a low-voltage source  192  and a reference resistor  194  are connected to the output leads  156 ,  158  to determine the value of a sensor coding resistor. The low voltage detector  1230  senses the low voltage on the output leads  156  and actuates the adapter switch  1210  to its second position  1244 . With the adapter switch  1210  in the second position  1244 , the adapter resistor  1220  is connected between to the low-voltage source  192  and the reference resistor  194 . As a result, the monitor reads the value of the adapter resistor  1220 , which is a predetermined resistance equivalent to the value of a coding resistor required by the monitor  150  for proper operation. In this manner, the information generator  458  adapts a sensor  100  without a coding resistor  140  to the monitor  150 . 
         [0070]      FIG. 13  illustrates yet another embodiment of the information generator portion  458  of the sensor adapter. The information generator  458  comprises a fixed voltage source  1310  connected to the output lead  156  of the reference resistor  194 . The voltage source  1310  has a bias voltage input  1312  and, bias resistors  1314 , which divide the voltage between the bias voltage input  1312  and the input  1315  of the buffer amplifier  1316 . The output  1317  of the amplifier  1316  is connected to the anode of an isolation diode  1318 , the cathode of which is connected to the output lead  156 . While the LEDs  110 ,  120  are driven, the isolation diode  1318  is back biased by the red LED driver  162  or by the combination of the infrared LED driver  164  and the infrared LED  120  voltage drop, effectively isolating the fixed voltage source  1310  from the output lead  156 . 
         [0071]    During the initialization interval described above, the monitor  150  is expecting to read a coding resistor of value 
         [0000]        R   c   =R   ref ·[( V   low   /V   adc )−1],
 
         [0072]    where R ref  is the resistance of the monitor reference resistor  194 , V low  is the output voltage of the low-voltage source  192  and V adc  is the voltage measured at the buffer input  196  and also output to the ADC  199 . The LEDs  110 ,  120  are not conducting during the calibration period because the red LED  110  is back biased and the low-voltage source  192  provides insufficient forward voltage to the infrared LED  120  for conduction to occur. Because the sensor  100  does not have a coding resistor, the low-voltage source  192  is effectively isolated from the output lead  156  and reference resistor  194 . During this period, the isolation diode  1318  is forward biased by the amplifier  1317 . As a result, the voltage at the amplifier output  1317 , ignoring the diode voltage drop, appears across the reference resistor  194 . If the predetermined value of the voltage source is 
         [0000]        V=V   low   ·[R   ref /( R   c   +R   ref )], 
         [0073]    The voltage at the buffer input  196  is the same as if the sensor had a coding resistor of value, R c , as can be seen by substituting V for V adc  in the equation for R c  above. Thus, the fixed voltage source provides equivalent information to the monitor  150  as if the sensor  100  had a coding resistor. One will recognize that other voltage source configurations are possible. Further, an equivalent current source can be connected to the output lead  156  to simulate a sensor coding resistor. The predetermined value of that current source is: 
         [0000]        I=I   low /( R   c   +R   ref ) 
         [0074]    This current flows through the reference resistor  194  such that the voltage read by the monitor, V adc  at the ADC  199 , is the same as given above for the voltage source embodiment. 
         [0075]      FIG. 14  illustrates an embodiment of the information translator portion  454  of the sensor adapter. The information translator  454  reads a sensor information element  452  and provides an equivalent value, i.e. a translated value providing the same information, to the information element detector portion  450  of a monitor  404 . The translator  454  has an information element reader  1410  that determines the sensor information, e.g. sensor type, manufacturer, calibration data, or security code from a sensor information element  452 . The translator  454  also has an information element array  1420 . The array  1420  is a predetermined set of different information elements that correspond to the possible sensors that the monitor  404  accepts. At least one information element is selected from the array  1420  and connected to the information element detector  450 , as determined by a switching circuit  1430 . The information element reader  1410  controls the state of the switching circuit  1430 . In this manner, the information element reader  1410  can determine the sensor information element value, select an equivalent value from the information element array  1420 , and actuate the switching circuit  1430 , thereby connecting the corresponding element or elements from the array  1420  to the monitor information element detector  450 . 
         [0076]      FIG. 15  shows an embodiment of a sensor adapter which incorporates a combination of the adapter elements described above in addition to other elements described in detail below to create a universal adapter  1500 . In general, the universal adapter  1500  allows one sensor  1502  from a variety of possible sensors to be connected to one monitor  1504  from a variety of possible monitors to create a pulse oximetry system. The universal adapter  1500  has a first connector adapter  1510 , a monitor selector  1520 , a first switch  1530  and a number of adapter elements  1540 . These components allow the universal adapter  1500  to sense the electrical characteristics of the monitor  1504 , such as the drive configuration and drive levels, and to select the necessary adapter elements  1540  accordingly. The universal adapter  1500  also has a second connector adapter  1560 , a sensor selector  1570 , and a second switch  1580 . These components allow the universal adapter to sense the electrical characteristics of the sensor  1502 , such as LED configuration and information element presence and to select the necessary adapter elements  1540  accordingly. 
         [0077]      FIG. 16  further illustrates the universal adapter  1500  described above with respect to  FIG. 15 . The universal adapter  1500  is shown as a sensor adapter cable  1600  having generic connectors  1610 ,  1620  at either end of the cable  1600 . Attached to the cable and electrically connected to the cable wiring is an molded cable block  550  as described above with respect to  FIG. 5 . The cable block contains the adapter components  1520 ,  1530 ,  1540 ,  1570 ,  1580  shown in  FIG. 15 . 
         [0078]    As illustrated in  FIG. 16 , a first connector adapter  1510  is a conventional adapter cable having a connector  1630  at one end which mates with the generic connector  1620  of the sensor adapter cable  1600 . A connector  1640  at the other end of the connector adapter  1510  is the specific connector which mates with a particular monitor connector  1650 . The cable wiring of the connector adapter  1510  is cross-wired between the end connectors  1630 ,  1640  as necessary to match the predetermined pinouts of the connector  1620  of the sensor adapter cable  1600  to the pinouts of the connector  1650  of the monitor  1504 . In this manner, the first connector adapter  1510  accommodates a variety of physical connectors and pinouts of various monitors  1504 . 
         [0079]    Likewise, a second connector adapter  1560  is a conventional adapter cable having a connector  1660  at one end which mates with the generic connector  1610  of the sensor adapter cable  1600 . A connector  1670  at the other end of the connector adapter  1560  is the specific connector  1670  which mates with a particular sensor connector  1680 . The cable wiring of the connector adapter  1560  is cross-wired between the end connectors  1660 ,  1670  as necessary to match the predetermined pinouts of the connector  1610  of the sensor adapter cable  1500  to the pinouts of the connector  1680  of the sensor  1502 . In this manner, the second connector adapter  1560  accommodates a variety of physical connectors and pinouts of various sensors  1502 . The sensor adapter cable  1600 , as described above, is advantageously of a single design having generic connectors  1610 ,  1620  with predetermined signal pinouts that mate with each of a family of specific adapter cables  1510 ,  1560  manufactured to match specific sensors  1502  and specific monitors  1504 . 
         [0080]    As illustrated in  FIG. 15 , the signal lines  1532  between the first switch  1530  and the connector adapter  1510  have branches  1522  to the monitor selector  1520 . Because the pinouts of the universal adapter  1500  are predetermined, it is known which of these signal lines  1532  correspond to particular monitor leads  1512 . Thus, the monitor selector  1520  tests these signal lines  1532  to determine the signal characteristics of an attached monitor  1504 , as described in more detail below with respect to  FIG. 17 . Once the signal characteristics for the monitor  1504  are determined, the output  1524  of the monitor selector  1520  controls the first switch  1530  to connect the signal lines  1532  to corresponding adapter element  1540 . 
         [0081]    Likewise, the signal lines  1582  between the second switch  1580  and the connector adapter  1560  have branches  1572  to the sensor selector  1570 . Because the pinouts of the universal adapter  1500  are predetermined, it is known which of these signal lines  1582  correspond to particular sensor leads  1562 . Thus, the sensor selector  1570  tests these signal lines  1582  to determine the signal characteristics of an attached sensor  1502 , as described in more detail below with respect to  FIG. 17 . Once the signal characteristics for the sensor  1502  are determined, the output  1574  of the sensor selector  1570  controls the second switch  1580  to connect the signal lines  1582  to corresponding ones of the adapter elements  1540 . 
         [0082]      FIG. 17  illustrates an embodiment for a configuration portion  1700  of the universal adapter  1500  that matches the monitor driver  1704  to the sensor LEDs  1702 . This configuration portion  1700  has a driver test  1710  and a switch control  1712 . The driver test  1710  senses the driver configuration from the monitor signal lines  1532  and provides an output  1714  to the switch control  1712 . The switch control  1712  has inputs from the driver test output  1714  and the LED test output  1724  and provides a control output  1718  that causes a first bi-directional switch  1530  to connect the monitor driver  1704  to the corresponding adapter elements  1731 - 1737 . That is, the first switch is equivalent to a bi-directional one-line to seven-line multiplexer. 
         [0083]    The configuration portion  1700  also has an LED test  1720 . The LED test  1720  senses the LED configuration from the sensor signal lines  1582  and provides an output  1724  to the switch control  1712 . The switch control  1712  has inputs from the LED test output  1724  and the driver test output  1714  and provides a control output  1728  that causes a second bi-directional switch  1580  to connect the sensor LEDs  1702  to the corresponding adapter elements  1731 - 1737 . The second switch  1580  is equivalent to the first switch  1530 . The adapter elements comprise adapters  1732 - 1737  for all six combinations of drivers and incompatible sensor configurations. In addition, there is a “straight-through” adapter  1731  for the case of matching drivers and sensor LEDs, e.g. back-to-back driver  1704  and back-to-back LEDs  1702 . 
         [0084]    As illustrated in  FIG. 17 , it is assumed that a monitor  1504  has three possible drivers  1704 . That is, an attached monitor will have circuitry for driving either back-to-back LEDs, common-anode LEDs or common-cathode LEDs. Thus, the configuration adapter  1700  has three signal lines  1532  from the monitor driver  1704 . For example, as illustrated in  FIG. 6 , a common-anode driver  410  has three leads  352 ,  354 ,  355  that correspond to the three signal lines  1532 . As illustrated in  FIG. 7  as another example, a back-to-back driver  410  has two leads  156 ,  158  which would correspond to two of the three signal lines  1532 , leaving one of the three signal lines  1532  unused. 
         [0085]      FIG. 18  illustrates an embodiment of the driver test  1710 . The driver test  1710  looks at the three signal lines  1532  to determine the driver configuration. The drive test circuit  1710  shown has three differential amplifiers  1810 ,  1820 ,  1830 , each with inputs across a unique pair of the three signal lines  1532 . That is, a first amplifier  1810  senses a signal on a first pair of signal lines  1802 ,  1804 , a second amplifier  1820  senses a signal on a second pair of signal lines  1802 ,  1805 , and a third amplifier  1830  senses a signal on a third pair of signal lines  1804 ,  1805 . 
         [0086]    If a monitor driver is configured for back-to-back LEDs, then, as illustrated in  FIG. 7 , the equivalent to driver leads  156 ,  158  are wired to correspond to signal lines  1802 ,  1804  shown in  FIG. 18 , respectively, and signal line  1805  is disconnected. The first amplifier  1810  would sense a voltage of alternating polarity corresponding to red LED and infrared LED drive signals, and the second amplifier  1820  and third amplifier  1830  would sense nothing. Hence, an alternating output voltage from only the first amplifier  1810  would indicate to the switch control  1712  in  FIG. 17  that the driver  1704  is configured for back-to-back LEDs. 
         [0087]    As illustrated in  FIG. 18 , by contrast, if the monitor driver is configured for common-anode LEDs, then, as illustrated in  FIG. 6 , the equivalent to driver leads  352 ,  354 ,  355  are wired to correspond to signal lines  1802 ,  1804 ,  1805 , shown in  FIG. 18 , respectively. The first amplifier  1810  would sense a unipolar voltage corresponding to the red LED drive signal. The second amplifier  1820  would sense a unipolar voltage corresponding to the infrared LED drive signal. The third amplifier  1830  would sense nothing. Hence, alternating output voltages from the first amplifier  1810  and the second amplifier  1820  would indicate to the switch control  1712  in  FIG. 17  that the driver  1704  is configured for common-cathode LEDs. By comparison, if the monitor driver is configured for common cathode LEDs, a different two of the amplifiers  1810 ,  1820 ,  1830  would sense similar voltages as in the common-anode case. Thus, the outputs of the amplifiers  1810 ,  1820 ,  1830  provide sufficient information to the first switch control  1712  in  FIG. 17  to determine the driver configuration. 
         [0088]    As illustrated in  FIG. 17 , it is assumed that a sensor  1502  has three possible LED configurations  1702 . That is, an attached sensor will have either back-to-back LEDs, common-anode LEDs or common-cathode LEDs. Thus, the configuration adapter  1700  has three signal lines  1582  from the sensor LEDs  1702 . For example, as illustrated in  FIG. 6 , a back-to-back LED sensor  412  has two leads  106 ,  108  that correspond to two of the three signal lines  1582 , leaving one of the three signal lines  1582  unused. As illustrated in  FIG. 7  as another example, a common-anode sensor  412  has three leads  302 ,  304 ,  305  that correspond to the three signal lines  1582 . 
         [0089]      FIG. 18  illustrates an embodiment of the LED test  1720 . The LED test  1720  looks at the three signal lines  1582  to determine the sensor configuration. The LED test circuit  1720  shown has a voltage source  1850  and two differential amplifiers  1860 ,  1870  that provide a return path for the voltage source  1850 . To test the sensor LED configuration, a switch  1880  alternately connects the voltage source  1850  to each of the three signal lines  1582  and, at the same time, connects the differential amplifiers  1860 ,  1870  to the remaining two signal lines  1582 . For example, in a first position  1882  (depicted), the output of the voltage source  1850  is connected to a first signal line  1806 , the input of the first amplifier  1860  is connected to a second signal line  1808 , and the input of the second amplifier  1870  is connected to a third signal line  1809 . 
         [0090]    If a sensor has back-to-back LEDs, then, as illustrated in  FIG. 6 , the equivalent to sensor leads  106 ,  108  are wired to correspond to signal lines  1806 ,  1808  shown in  FIG. 18 , respectively, and signal line  1809  is disconnected. In the first switch position  1882 , the voltage source  1850  drives the red LED and current is detected by the first amplifier  1860 . In the second position  1884 , the voltage source  1850  drives the infrared LED and current is detected by the first amplifier  1860 . In the third switch position  1886 , the voltage source  1850  drives the disconnected line  1809  and no current is detected by either amplifier  1860 ,  1870 . Hence, a voltage output from the first amplifier  1860  at the first and second switch positions  1882 ,  1884 , with no amplifier output at the third switch position  1886 , indicates that the sensor has back-to-back LEDs. 
         [0091]    As illustrated in  FIG. 18 , by contrast, if the sensor is configured for common-anode LEDs, then, as illustrated in  FIG. 7 , the equivalent to driver leads  302 ,  304 ,  305  are wired to correspond to signal lines  1806 ,  1808 ,  1809 , shown in  FIG. 18 , respectively. In the first switch position  1882 , the voltage source  1850  drives the anodes of both LEDs, but a current path is only provided by the input to the first amplifier  1860 , which produces a corresponding output. In the second and third switch positions  1884 ,  1886  the voltage source  1850  back biases both LEDs and no current is detected by either amplifier  1860 ,  1870 . Hence, a voltage output from the first amplifier  1860  at the first switch position  1882 , with no amplifier outputs at the second and third switch positions  1884 ,  1886 , indicates that the sensor has common-anode LEDs. By comparison, if the sensor has common-cathode LEDs, in the first switch position  1882 , the voltage source  1850  would back-bias the diodes and no current would be detected by either amplifier  1860 ,  1870 . In the second and third positions  1884 ,  1886 , current would be detected by the first and second amplifiers  1860 ,  1870 , respectively. Thus, the outputs of the amplifiers  1860 ,  1870  provide sufficient information to the second switch control  1722  in  FIG. 17  to determine the sensor LED configuration. 
         [0092]    As illustrated in  FIG. 17 , the switch control  1712  could be a simple state machine. After the LED test  1720  cycles through the three positions of the switch  1880  shown in  FIG. 18 , and after the driver test  1710  senses driver activation, the switch control  1712  would latch the first and second bi-direction switches  1530 ,  1580  to connect the appropriate adapter element to the signal lines  1532 ,  1582 . For example, if back-to-back LEDs  1702  were detected and a common-anode driver  1704  was detected, the bi-directional switches  1530 ,  1580  would connect the three signal lines  1532 ,  1582  to the common-anode (CA) to back-to-back (BB) adapter element  1734 . The CA to BB adapter element is described above with respect to  FIG. 6 . 
         [0093]    As illustrated in  FIG. 15 , a simplified embodiment of the universal adapter  1500  is possible if the sensor  1502  is of a known configuration. For example, a sensor manufacturer may wish to provide a universal adapter  1500  between their particular sensors and most or all pulse oximetry monitors. In that case, there would be fewer combinations of adapter elements  1540  and the first switch  1530  and second switch  1580  would be simpler accordingly. For example, as illustrated in  FIG. 17 , if it is known that the sensor  1502  has back-to-back LEDs  1702 , then only the “straight-through”  1731 , “CA to BB”  1734  and “CC to BB”  1736  adapter elements are required. Correspondingly, the first switch  1530  and second switch  1580  would be equivalent to bi-directional one-line to three-line multiplexers, rather than the more complex one-line to seven-line multiplexers shown. 
         [0094]    One would appreciate that testing and switching circuitry, such as shown in  FIG. 17 , is also applicable to embodiments of, for example, drive limit portions and information translator portions of the universal adapter  1500  shown in  FIG. 15 . Further, one will recognized that portions of the sensor adapter shown in  FIGS. 4 and 15  could be implemented with microcontroller or microprocessor circuitry and associated firmware rather than in hardwired circuitry. Also, particular adapter elements might be selected manually, such as with hand-actuated switches, rather than through automatic sensing of the sensor and monitor configurations as described above. As another alternative to automatic sensing of the sensor and monitor configurations, particular connector adapters  1560 ,  1510  could contain coding elements that function as indicators of the corresponding sensor  1502  or monitor  1504  configurations. 
         [0095]    The pulse oximetry sensor adapter has been disclosed in detail in connection with the preferred embodiments of the present invention. These embodiments are disclosed by way of examples only and are not to limit the scope of the present invention, which is defined by the claims that follow. One in the art will appreciate many variations and modifications within the scope of this invention.