Abstract:
A dual mode regulator provides power to a tower mounted low noise amplifier (LNA) and operates in either one of two modes. The dual mode regulator comprises a microcontroller that controls the amplifier and two regulators to operate in an Antenna Interface Standards Group (AISG) mode when the microcontroller is detecting AISG protocol information or in a current window alarm (CWA) mode when the microcontroller is not receiving AISG protocol information. In the CWA mode the total current to the two regulators and associated circuitry is maintained at a constant amplitude. Further in the CWA mode, the microcontroller is able to generate an alarm signal and deactivate the amplifier when it detects improper operation by the amplifier. In the AISG mode, a single regulator is used and the other regulator is de-activated by the microcontroller.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    Example embodiments generally relate to a regulator and a method for operating same and particularly, but not exclusively to a dual mode regulator for an amplifier. 
         [0003]    2. Description of the Related Art 
         [0004]    Amplifiers that are part of equipment used at base stations to amplify signals received by and/or transmitted to power equipment to remotely control the orientation of one or more antennas positioned at a tower of a base station. Many of these amplifiers are mounted at the top of a tower of a base station and are thus referred to as Tower Mounted Amplifiers (TMA). TMAs operate in accordance with a certain standard called the Current Window Alarm (CWA) mode. The CWA mode of operation, which is a legacy mode of operation, is still used in many base station towers. In the CWA mode, the regulators for the amplifiers used at the base station are required to operate for a range of input voltages provided by the base station equipment while providing a constant DC current (having a defined amplitude) to the amplifiers. Further, the regulators are to monitor the current used by the amplifiers and enter an alarm mode if such current becomes appreciably greater than the defined constant amplitude level. Moreover, while in the alarm mode, the regulators are required to sink an alarm current by changing the duty cycle of the PWM pulses applied to a current load to achieve a desired DC current amplitude. That is, the regulators are able to intentionally sink large currents being provided by the base station to generate this alarm signal. Linear regulators are used in these CWA systems because linear regulators are able to provide a constant current for a range of input voltages. However, these linear regulators achieve this feature by simply dissipating the additional current they need to meet the constant current requirement or the large current they need to generate the alarm signal through resistive loads. As such these CWA legacy systems are very inefficient as they waste relatively large amounts of energy to meet their operational requirements. 
         [0005]    The switching regulator is widely used for its high energy efficient operation. These regulators operate in accordance with the Antenna Interface Standards Group (AISG), which allows exchange of messages (formatted as per a certain recognized protocol) between the base station equipment and the TMAs that remotely control the electrical tilt of antennas mounted at the top of base station towers. AISG messages are exchanged in a virtually continuous fashion between tower mounted equipment and other base station equipment. In addition to the switching regulators being energy efficient (relative to the linear regulators), there is no requirement for generating an energy wasting alarm signal such as the alarm signal required by base stations still operating in accordance with the CWA mode. In the AISG base stations, a message informing of an alarm condition is simply used to inform the base station of the occurrence of an alarm. 
         [0006]    Unfortunately, many communication systems still use antenna systems that still adhere to the CWA approach. However the need and desire for AISG type approach is clear. 
       SUMMARY 
       [0007]    At least one example embodiment relates to a dual mode regulator for an amplifier. In one example embodiment, the dual mode regulator for an amplifier comprises a microcontroller, a first regulator for driving the amplifier, a variable dummy current load (VDCL) controlled by the microcontroller, and a second regulator for driving the variable current dummy load. The respective inputs of the regulators form a main path that is coupled to a power source with the main path carrying a total current that is applied to the regulators and the first regulator provides an operating current to the amplifier. 
         [0008]    In a first mode of operation, the microcontroller controls the VDCL and amplifier to maintain a constant total current and the microcontroller generates an alarm signal upon detecting an alarm based on amplitudes of the total current or the operating current of the amplifier or both. In a second mode of operation, the microcontroller de-activates the VDCL. 
         [0009]    At least one example embodiment relates to a method for operating a dual mode regulator for an amplifier, the method comprises determining whether the dual mode regulator system is to operate in a first mode or a second mode; operating the dual mode regulator system in one of the first and second modes and activating the amplifier where the system is operated based on a protocol signal received by the system; and entering into an alarm mode and de-activating the amplifier when the system detects an alarm condition. The terms “activate” or “activating” refers to a component, device or circuit being provided the proper amount of energy and signals to be able to operate in a manner for which such component, device or circuit was designed. Conversely, the terms “de-activate” or “de-activating” refers to a component, device or circuit not able to operate at all, or not able to operate in the manner for which it was designed even when the proper power and signals are provided to such component, device or circuit, or both. 
         [0010]    In example embodiments of the dual mode regulator for an amplifier and a method for operating a dual mode regulator for an amplifier, the first mode is a CWA mode and the second mode is an AISG mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The following are drawings of some of the exemplary embodiments of this disclosure. Other aspects, features, implementations and benefits of these and other embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.  FIGS. 1-2  represent non-limiting, example embodiments as described herein. 
           [0012]      FIG. 1  illustrates a dual regulator system according to an example embodiment; 
           [0013]      FIG. 2  illustrates a method of operation of a dual regulator system according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are illustrated. Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but on the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the claims. Like numbers refer to like elements throughout the description of the figures. 
         [0015]    As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). It will be further understood that the term “path” as used herein refers to any electrically conductive medium that allows conduction of electrical current from one point to another point of a circuit or system. A path is used to conduct current between any two points of a circuit or between any two electrical components of a circuit (without any intervening components). A path may be used to conduct control signals; such a path is referred to as a “control path.” Control signals as used herein are signals that directly cause a desired result when applied to a specific point in a circuit or system. 
         [0016]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and unless so defined herein will not be interpreted in an idealized or overly formal sense. 
         [0017]    Referring to  FIG. 1 , an embodiment of the dual mode regulator for an amplifier is shown coupled to a Low Noise Amplifier (LNA)  108 . It will be readily understood that the amplifier  108  is not limited to an LNA, but may be other types of amplifiers that can be used by other embodiments of the dual mode regulator. For ease of description, suppose the amplifier is a TMA that is part of circuitry used to control antenna equipment (not shown), and in particular to control the tilting angle (or other orientations) of one or more antennas positioned at the top of the tower of a base station. The base station may, for example, be part of a communication network or system. A protocol comprising various commands or instructions sent to circuitry associated with controlling the orientation (e.g., tilt angle) of one or more antennas at the top of the base station tower (not shown) is referred to as the AISG protocol. 
         [0018]      FIG. 1  shows microcontroller  102  having, at one of its input/output (I/O) ports on path  116 , signals representing information that is part of the AISG protocol. It should be understood that microcontroller  102  can be implemented as a computer, a microprocessor, a microcomputer, a server or any well known computing machine that is able to process information based on received signals and a set of executable commands (e.g., a computer program). Although not shown, it is understood that microcontroller  102  has a reset input which causes the microcontroller to restart its operation as dictated by its stored program as will be discussed herein. The base station or the communication network provides on main path  140  a DC (Direct Current) voltage having a certain range (e.g., 10 volts to 30 volts DC). The provided DC voltage has an associated total current (I T ) on main path  140 . Part of the total current I T  is carried by path  120  to a first regulator  104  and another part of I T  is carried by path  122  to a second regulator  110 . A current sensor  114  is positioned with respect to path  140  to measure or sense the total current I T  flowing through path  140 . The current sensor  114  can any one of well known circuits or devices (or both) used to sense the amplitude of a current flowing though a electric current conducting medium such as a wire or a metallic land on a printed circuit board. Various integrated circuit current sensors (e.g., AD8217) are available and can be used as a component in the dual mode regulator disclosed herein. The current sensor  114  or the microcontroller  102  (or the combination of both the microcontroller  102  and the current sensor  114 ) may contain the circuitry that provides the value (i.e., amplitude) of the sensed current onto path  118  in a format that can be understood or ascertained by microcontroller  114 . The microcontroller may then process the sensed current information in accordance with commands or executions (e.g., a computer program) stored therein. 
         [0019]    In the example embodiment of  FIG. 1 , the first regulator  104  is a switching regulator (also referred to as a switcher) and the second regulator  110  is a linear regulator. Switching regulator  104  LNA  108  via path  124 A, controllable switch  106  and path  124 B. The current from switching regulator  104  flows through path  124 A, controllable switch  106  (when in a closed state) and path  124 B to LNA  108 , is hereinafter referred to as the input current of the amplifier (e.g., LNA  108 ). When the input current of LNA  108  has a value that falls within a defined acceptable current range, LNA  108  is deemed to be operating properly and the input current is referred to as the operating current. The input current of LNA  108  is sensed by current sensor  138  and the sensing information is provided to microcontroller  102  via path  128 . Current sensor  138  may be similar to or the same type as current sensor  114 . Current sensor  138  is positioned with respect to path  124 B to sense the input current and thus provides to the microcontroller  102 —via path  128 —the value of the amplitude of the input current of the amplifier  108  in a format recognizable to microcontroller  102 . 
         [0020]    Microcontroller  102  thus senses the total current on main path  140  and the input current of amplifier  108  when controllable switch  106  is in a closed state. Microcontroller  102  controls the operation of switch  106  via control path  126 , and controls pulse width modulator (PWM)  136  via control path  130 . When controllable switch  106  is in an open state, no current flows from switching regulator  104  to amplifier  108 ; in such a case, the amplifier  108  is said to be de-activated. Thus, the microcontroller can de-activate the amplifier  108  by causing switch  106  to open. On the other hand when switch  106  is in a closed state, current flows from switching regulator  104  to path  124 A through switch  106  and onto LNA  108  via path  124 B as previously described. Thus microcontroller  102  is able to activate or de-activate LNA  108  by closing or opening switch  106  respectively. Switch  106  can be implemented in well known fashion through the use of integrated circuits or through the use of discrete semiconductor components such as transistors. In sum, switch  106  is able to allow current used by LNA  108  (provided by switching regulator  104 ) to flow to LNA  108  causing LNA to be activated and to operate properly when it is using a current that is equal to an operating current. 
         [0021]    In other embodiments, microcontroller  102  can de-activate or activate LNA  108  directly; that is, LNA  108  can be designed with a control input (not shown) coupled to microcontroller  102  to allow the microcontroller  102  to activate or de-activate LNA  108  and switch  106  is replaced by a conductive path directly coupled to paths  124 A and  124 B. In yet another embodiment, again paths  124 A and  124 B are directly coupled to each other where switch  106  is part of LNA  108  and can be controlled by microcontroller  102  to activate or de-activate amplifier  108 . LNA  108  is said to be activated when it is operating in the manner for which it was designed. That is, when LNA  108  is able to amplify signals applied to its signal input (not shown) and is being provided an input current, the amplifier is said to be activated. When the input current value is within the defined acceptable current range, the amplifier is activated and is operating properly. 
         [0022]    Pulse width modulator (PWM)  136  is designed to generate pulse width modulated signals on path  134  based on control signals it receives from microcontroller  102  via control path  130 . Thus the VDCL  112  is a microcontroller controlled circuit or system or both capable of varying the resistance presented to the second regulator  110  based on control signals applied to the control input of the VDCL from the microcontroller. The pulses on path  134  are received by variable dummy current load (VDCL)  112  which provides a load (preferably a resistive load) to second regulator (preferably a linear regulator)  110 . By controlling the duty cycle of the pulses generated by PWM  136 , the microcontroller is able to change the resistance that the VDCL  112  presents to regulator  110 . That is, VDCL  112  is a circuit whose input resistance as seen from the output of regulator  110  can be changed based on the control signals (e.g., PWM signals) present on path  131 . The PWM signals on path  132  are based on the particular control signals being generated on control path  130  by microcontroller  102 . In another embodiment, a filter (preferably a low pass filter) is positioned between PWM  136  and VDCL  112  to filter the PWM pulses and output a filtered PWM signal that changes the input resistance of VDCL  112  as seen from the output of second regulator  110 . VDCL  112  thus presents a certain varying load to regulator  110  to cause the output current of second regulator  110  (i.e., current on path  132 ) to change. Thus, any change in the load presented by VDCL  112  to regulator  110  will cause a certain amount of change in the current on path  132 , which will accordingly cause a change in the input current to regulator  110  on path  122 . In this manner, the microcontroller will be able to increase or decrease the amount of current flowing though path  122  and ultimately the amount of total current flowing through main path  140 . 
         [0023]    It should be noted that the VDCL  112  and PWM  136  are well known circuits that can be implemented in many ways. For example VDCL  112  can be designed with transistors (and also capacitors and resistors) that are biased at a certain biasing point to cause them to sink a certain amount of current. The amount of current sunk by the VDCL can change (increase or decrease) depending on the duty cycle or other characteristics of the PWM signal (filtered or unfiltered) on path  134 . The VDCL  112  is designed to have at least one control input which is coupled to an output of PWM  136  that generates pulse width signals to vary the voltage presented by VDCL  112  to the second regulator  110  thus varying the current from linear regulator  110  to VDCL  112 . The PWM can be implemented with transistors, off-the-shelf integrated circuits, or other semiconductor circuit or components. It will be understood that microcontroller  102  can control VDCL  112  to present an open circuit to linear regulator  110 . When linear regulator  110  is not coupled directly or indirectly to any other load it will have no current at its output; that is there will be no current on path  132 . In such a case, linear regulator  110  is de-activated. Similarly, when microcontroller  102  controls switch  106  to be in an open state, there is no current flow on paths  124 A or  124 B and with switching regulator  104  not driving any other load (other than LNA  108 —now no longer coupled to switching regulator  104 ) there is no current on path  124  and thus on path  120 . As such the switching regulator is de-activated. By having the ability to activate or de-activate switching regulator  104 , LNA  108 , and linear regulator  110 , the microcontroller  102  is able to operate the example embodiment of the dual mode regulator of  FIG. 1  in accordance with an example embodiment of a method of operation as shown in  FIG. 2 . 
         [0024]    Referring now to  FIG. 2 , an example embodiment of a method of operation of the dual mode regulator system  200  is shown. In step  202 , the microcontroller  102  is reset and thus starts to execute its stored commands (i.e., stored program). It should be understood that during reset and immediately thereafter, microcontroller  102  de-activates LNA  108  through the switch  106 . 
         [0025]    In step  204  microcontroller  102  monitors (continuously or continually or both in alternate fashion) its AISG I/O port to determine whether there are AISG protocol signals (i.e., AISG messages) on path  116 . If AISG protocol signals are present the method of this example embodiment moves to step  232  wherein the microcontroller  102  operates the dual mode regulator in an AISG mode. If, however, there are no protocol signals detected by microcontroller  102  on path  116 , the method of this example embodiment moves to step  206  wherein the microcontroller operates in a CWA mode. 
       AISG Mode of Operation 
       [0026]    In step  232 —referring temporarily to  FIG. 1 —microcontroller  102  activates LNA  108  by generating a control signal onto path  126  to cause controllable switch  106  to be in a closed state thus allowing LNA  108  to present a load to regulator  124  and to therefore operate and sink operating current via path  124 B as needed. LNA  108  is thus activated. After activating LNA  108 , the method of this example embodiment moves to step  234  wherein microcontroller  102  adjusts VDCL so as to present a relatively high resistive load to linear regulator  110  thus effectively maintaining linear regulator  110  and VDCL  112  in a de-activated state. It should be noted that in the AISG mode, the microcontroller is able to send and receive AISG protocol messages via at least path  116  connected to an I/O port of the microcontroller  102 . The AISG protocol messages (e.g., AISG protocol signals) may be from base station equipment, such as an antenna or antenna system that is part of a communication network to which the base station belongs. Further the amplifier  108  mounted at the top of the base station may be part of the antenna system. 
         [0027]    In step  236 , microcontroller  102  senses the input current of LNA  108  (i.e., current on path  124 B) using information it receives from current sensor  138  via path  128 . The microcontroller  102  may sense the input current continuously, continually or both in alternate fashion. In step  238 , microcontroller  102  determines whether the current value of path  124 B (i.e., LNA current) is within acceptable range. Depending on the voltage applied onto total path  140  and the nominal operating current of LNA  108 , the input current of LNA  108  will have a nominal value plus and minus an acceptable tolerance. The tolerance value is typically expressed as a percentage of the nominal value and is usually defined by the operators of the base station within which the dual mode regulator is operating. For example, if the nominal operating current of the LNA is 60 mA (milliamps) for a certain input voltage range of 20V to 28V, and the tolerance is 30% (i.e., 30% of 60 mA), then the acceptable operating range is 42 mA-78 mA. If the input current to LNA  108  is deemed acceptable (i.e., input current to LNA  108  is within the defined acceptable operating range) the method of this example embodiment moves to step  242  where microcontroller  102  checks for power reset. If no power reset has been received, the microcontroller  102  continues to monitor the input current of LNA  108 . If there is a power reset detected at step  242 , microcontroller  102  returns to the initial power up reset step  202  via step  246  as shown. Returning to step  238 , if the input current value of LNA  108  does not fall within the defined acceptable range, the method of this example embodiment deactivates LNA  108  (step  240 ), sends an AISG error message over its output port (not shown) indicating a non-operable amplifier (i.e., LNA  108  not operating properly) and returns to the initial power up reset step  202  of this method via step  246 . It should be noted that the terms “nominal operating current” or “operating current” as they relate to a component, device or circuit refer to a particular current value which when applied to such device, component or circuit allows the circuit to operate in a certain acceptable manner for which the circuit, component or device is designed. 
         [0028]    Still referring to  FIG. 2 , returning to step  204  of the method of this example embodiment, if the microcontroller  102  does not detect any AISG signaling on path  116 , the method of this example embodiment moves to step  206  and enters into the CWA mode of operation. 
       CWA Mode of Operation 
       [0029]    In step  206 , microcontroller  102  activates LNA  108  by causing controllable switch  106  to be in a closed state thus allowing LNA  108  to have the current it needs—from switching regulator  104 —to operate properly. Further, microcontroller  102  activates VDCL  112  so that a load is presented to the output of linear regulator  110  allowing current to flow on path  132  to the load presented by VDCL  112 . As a result of both linear regulator  110  and LNA  108  being activated, there exist currents on paths  120  and  122  respectively. The sum of these currents is total current I T  on main path  140 . 
         [0030]    A first requirement of the CWA mode is that the regulator for the amplifier of a base station be able to operate at a constant current (having an amplitude defined by operators of the base station, for example) for a particular range of input voltage being provided to regulator by a power supply source of the base station. From the standpoint of the power supply source of the base station, the regulator for amplifier  108  is the example dual mode regulator embodiment of  FIG. 1  and the current being supplied to that regulator is I T . Therefore, to meet the first requirement of the CWA mode, I T  is to remain constant (at a defined amplitude) for a range of input voltages from a power source of the base station. For example, say the input voltage range from the base station is 10V-30V DC. Further, say the communication system, of which the base station is a part, requires a constant regulator current of 100 mA. Thus, for the example embodiment of a dual mode regulator of  FIG. 1 , I T  is to be maintained at a value of 100 mA+/−a tolerance value. The tolerance value may be, for example, 20% of the nominal value or 20 mA for the case being discussed. Thus, the acceptable range for I T  for this example is 80 mA to 120 mA. Continuing with the example being discussed, say for a 10V input voltage to the dual mode regulator  100  of  FIG. 1 , I T  is 100 mA and this current would be totally used by switching regulator  104 . For a 30V input to the dual mode regulator, switching regulator would consume 33 mA; that is, there would be current of 33 mA on path  120 . Because I T  is to be maintained at 100 mA, microcontroller  102  would sense I T  and upon detecting the 33 mA value microcontroller would adjust the resistive load presented by VDCL  112  to linear regulator  110  to cause the current on path  122  to be equal to 67 mA so that I T  is maintained at the 100 mA requirement. 
         [0031]    Thus, in step  208 , microcontroller  102  senses the input current to LNA  108 . The value of the current sensed on path  124 B falling within the acceptable range for the operating current of the LNA indicates that the LNA is operating properly; this is determined in step  210 . However, if in step  210  the input current of the LNA  108  does not fall within an acceptable range, the method of this example embodiment enters the alarm state (the second requirement of the CWA mode) and moves to step  222 . 
       A. Alarm State 
       [0032]    In step  222  microcontroller  102  de-activates LNA  108  by causing controllable switch  106  to be in an open state. Microcontroller  102  temporarily de-activates VDCL  112  and thus linear regulator  110 . Microcontroller  102  achieves the deactivation of VDCL  112  (and thus linear regulator  110 ) by adjusting the resistance VDCL  112  so that a relatively very high resistance (effectively an open circuit) is seen by linear regulator  110 . In step  224 , as part of the second requirement of the CWA mode, microcontroller activates VDCL  112  to increase the current being sunk on path  122  through the linear regulator  110  to a defined alarm current value. Because the LNA  108  is de-activated (thus no current on path  120 ), the total current I T  on path  140  is thus the alarm current. The alarm current value is typically defined by the operators of the base station of which the dual regulator  100  is a part. The alarm current value is typically much higher than the constant current value that appears on path  140  during proper operation of the dual mode regulator. The value of the alarm is typically defined by the base station operator. For example, the amplitude of the alarm current can be 200 mA or 250 mA for a case where the total current is 100 mA The base station or communication network equipment is able to detect the alarm current as it appears on path  140 . Microcontroller  102  will continue to cause the alarm signal to occur until the dual mode regulator receives a power reset signal. The occurrence of an alarm signal is usually an indication that the dual mode regulator is no longer operational and should be replaced. Upon receipt of a power reset signal, the dual mode regulator returns to step  202  via step  228  and continues operation accordingly. 
         [0033]    Returning to step  210 , if the LNA sensed current value falls within an acceptable range, the method of this example embodiment moves to step  212  where microcontroller  102  generates control signals on path  130  to generate the proper pulse width modulated signals on path  134 . In this manner the resistive load seen by linear regulator  110  is adjusted so that the current on path  132  is adjusted and thus the current on path  122  is also adjusted allowing the total current I T  on path  140  to be continuously or continually (or both in an alternate manner) to be at a value that falls within an acceptable range of the defined constant total current value. In step  214  the microcontroller  102  senses the total current on path  140  and in step  216  confirms that the value of the total current I T  on path  140  does fall within the acceptable range and does remain constant within that range. If the value of I T  does not fall within the acceptable range or does not remain within such range, the method of this example embodiment moves to the Alarm state, viz., to step  222  and proceeds accordingly as described above. If, however, I T  does remain constant within the acceptable range, the method of this example embodiment moves to step  218  where microcontroller controls the VDCL  112  to ensure that the total current I T  remains constantly within the acceptable range. In step  220 , microcontroller  102  checks whether the dual mode regulator is still in the CWA mode. The microcontroller does this by monitoring (continually, continuously or both in alternate fashion) its I/O port connected to path  116 . If there are no AISG protocol signals on path  116 , the dual mode regulator remains in the CWA mode and the method of this example embodiment returns to step  208  and proceeds accordingly. If, however, AISG protocol signals are detected by microcontroller  102 , the method of this example embodiment moves to step  234  thus returning to the AISG mode of operation. Thus, in the first mode of operation (e.g., CWA mode), the microcontroller causes an alert signal to occur upon detecting an improper total current amplitude on the main path  140 , or an improper current amplitude on the first regulator ( 104 ) path  120  or an improper current amplitude on the main path and the first regulator path. 
         [0034]    The foregoing Detailed Description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention. 
         [0035]    Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.