Abstract:
A multi-mode bidirectional communications device including a diplexer having a high-pass filter, a low-pass filter, and a notch filter selectively coupled to the low-pass filter. The notch-filter is selectively coupled to the low-pass filter in response to an indicium of a desired spectral region.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This patent application claims the benefit of U.S. Provisional Application serial No. 60/305,193, filed Jul. 13, 2001, which is incorporated herein by reference in its entirety, and U.S. Provisional Application serial No. 60/327,529, filed Oct. 2, 2001, which is also incorporated herein by reference in its entirety. This patent application is related to simultaneously filed U.S. Patent Application No. ______, filed ______ (Attorney Docket No. PU010147) entitled MULTI-MODE BIDIRECTIONAL COMMUNICATIONS DEVICE INCLUDING A DIPLEXER HAVING SWITCHABLE LOW PASS FILTERS; and U.S. Patent Application No. ______, filed ______ (Attorney Docket No. PU010223) entitled MULTI-MODE DOWNSTREAM SIGNAL PROCESSING IN A BI-DIRECTIONAL COMMUNICATIONS DEVICE, both of which are incorporated herein by reference in their entireties. 
     
    
     
       FIELD OF INVENTION  
         [0002]    The present invention relates to diplexers. More particularly, the invention relates to a single diplexer suitable for use in multiple standard systems such as both the North American and European DOCSIS standards.  
         BACKGROUND OF INVENTION  
         [0003]    Bi-directional communication devices, such as cable modems, have been designed to specifically operate under a single standard, such as the North American Data Over Cable Service Interface Specifications (DOCSIS) or the European DOCSIS standards. The European version of the North American DOCSIS standard was not available when DOCSIS was first proposed to European customers. Many European cable operators started deploying the North American DOCSIS standard. They now express the need to change to a European DOCSIS-compliant system.  
           [0004]    There are three main differences between a European DOCSIS cable modem and a North American DOCSIS cable modem. First, a diplexer within the cable modem has a different cross over point in the European and North American systems, since the forward (downstream) and the return (upstream) data channel bandwidths on the coax cable are slightly different. This difference in diplexer crossover point is realized by different high pass filter and low pass filter cutoff frequencies between the European and North American systems. Second, the forward data channel is 8 MHz wide for European DOCSIS, while in the North American DOCSIS the forward data channel is 6 MHz wide. This requires a different surface acoustic wave (SAW) filter to maximize performance when additional channels are located next to the desired channel without any guard band. Third, the forward data channel for the European DOCSIS uses a different forward error correction (FEC) scheme than is used in the North American DOCSIS. Providing a single cable modem that could operate under both the North American and European standard systems would reduce the costs for the manufacturers, re-sellers, and renters by economy of scale.  
         SUMMARY OF INVENTION  
         [0005]    The disadvantages heretofore associated with the prior art, are overcome by a multi-mode bi-directional communications device including a diplexer having a high-pass filter, a low-pass filter, and a notch filter selectively coupled to the low-pass filter. The notch-filter is selectively coupled to the low-pass filter in response to an indicium of a desired spectral region.  
           [0006]    A method of passing bi-directional communications signals of differing modes through a diplexer having a high-pass filter coupled between a first and a second signal port, a first low-pass filter selectively coupled to a notch filter, the low-pass filter coupled between the first and a third signal port, is also provided. In particular, the method includes receiving downstream signals at the first signal port and filtering the received downstream signals using the high-pass filter. The filtered downstream signals are then communicated to the second signal port. Furthermore, the method includes receiving upstream signals at the third signal port; selectively coupling the notch filter to the low-pass filter for filtering the received upstream signals in response to a desired communications mode, and sending the filtered signals to the first signal port.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 depicts a block diagram of a data communications system having a multi-mode bidirectional communications device according to an embodiment of the present invention;  
         [0009]    [0009]FIG. 2 depicts a block diagram of a diplexer suitable for use in the multi-mode bidirectional communications device of FIG. 1;  
         [0010]    [0010]FIG. 3 depicts a graphical representation of a response curve for the diplexer FIG. 2;  
         [0011]    [0011]FIG. 4 depicts an illustrative schematic diagram of a low-pass filter LPF having a notch filter NF selectively coupled thereon and suitable for use in the diplexer of FIG. 2; and  
         [0012]    [0012]FIG. 5 depicts an illustrative schematic diagram of a high-pass filter HPF suitable for use in the diplexer of FIG. 2.  
         [0013]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    While the invention will be primarily described within the context of a cable modem in a data communications system, it will be appreciated by those skilled in the art that other multi-mode/standard, bidirectional communications devices, such as a satellite terminal, digital subscribe line (DSL), and the like may benefit from the present invention. According to one embodiment of the invention, a cable modem includes a single diplexer, which is used to facilitate the coupling of, for example, a computer device to a service provider via a cable transport network. In particular, the exemplary cable modem is utilized to provide downstream broadband data signals from the service provider to the computer device. Additionally, the exemplary cable modem is utilized to transfer upstream baseband data signals from the illustrative computer back to the service provider. More specifically, the exemplary cable modem is capable of selectively operating within the different downstream bandwidth constraints under both the North American Data Over Cable Service Interface Specifications (DOCSIS) and the European DOCSIS standards, which are incorporated by reference herein in their respective entireties. The cable modem is also capable of selectively passing through upstream data signals in compliance with both the European and North American DOCSIS standards.  
         [0015]    [0015]FIG. 1 depicts a block diagram of a data communications system  100  having a multi-mode bidirectional communications device  102  according to an embodiment of the present invention. The data communications system  100  comprises a service provider  160  that provides electronically transmitted, digital data to an end user having an input/output (I/O) device  104 , such as a computer, hand-held device, laptop, or any other device capable or transmitting and/or receiving data. The service provider  160  is coupled to the multi-mode bi-directional communications device (e.g., cable modem)  102  via a cable transport network  150 .  
         [0016]    The service provider  160  may be any entity capable of providing low, medium and/or high-speed data transmission, multiple voice channels, video channels, and the like. In particular, data is transmitted via radio frequency (RF) carrier signals by the service provider  160  in formats such as the various satellite broadcast formats (e.g., Digital Broadcast Satellite (DBS)), cable transmission systems (e.g., high definition television (HDTV)), DVB-C (i.e., European digital cable standard), and the like.  
         [0017]    The service provider  160  provides the data over the cable transport network  150 . In one embodiment, the cable transport network  150  is a conventional bi-directional hybrid fiber-coax cable network, such as specified under the North American or European DOCSIS standards.  
         [0018]    In operation, the service provider  160  modulates the downstream data signals with an RF carrier signal, and provides such signals via the cable transport network  150  to the cable modem  102 , where the RF signals are received, tuned, and filtered to a predetermined intermediate frequency (IF) signal. The IF signal is then demodulated into one or more respective baseband signals, and otherwise processed into, illustratively, data packets. The data packets are further transmitted through, illustratively, cabling  105  (e.g., universal serial bus (USB), coaxial cable, and the like) to the computer device  104 . Similarly, a user of the computer device  104  may send upstream data signals to the cable modem  102  via the cabling  105 . The cable modem  102  receives upstream baseband data signals from the computer device  104 , and then modulates and upconverts the data signals onto a RF carrier for transmission back to the service provider  160 , via the cable transport network  150 .  
         [0019]    The cable modem  102  comprises diplexer  130 , upstream processing circuitry  106 , downstream processing circuitry  108 , and a media access controller (MAC)  124 . The diplexer  130  is coupled to the upstream and downstream processing circuitry  106  and  108 . The diplexer  130  comprises a high-pass filter  132 , and a low-pass filter  134  having a notch filter  136  which may be selectively coupled. The high-pass filter HPF  132  passes the downstream data signals to the downstream processing circuitry  108 , while the low-pass filter LPF  134  receives return signals from the upstream processing circuitry  106 . The notch filter NF  136  is selectively decoupled from the low-pass filter LPF  134  during operation under the European DOCSIS standard, while the notch filter  136  is coupled to the low-pass filter LPF  136  during operation under the North American DOCSIS standard. In particular, the high-pass filter  132  provides processed downstream RF signals to a tuner  112 . Specifically, RF signals having a frequency greater than, illustratively, 88 MHz are passed through, while those frequencies below 88 MHz are filtered, as will be discussed in further detail below.  
         [0020]    The downstream processing circuitry  108  comprises the tuner  112 , a demodulator  118 , which is selectively coupled to the tuner  112  through a first surface acoustic wave (SAW) filter  114  or through a second SAW filter  116 , and other support circuitry  115 , such as voltage regulators, amplifiers, and the like. The tuner  112  may illustratively be model type DIT9210, manufactured by Thomson Consumer Electronics, Inc. When operating under the European DOCSIS mode, the first SAW filter  114  provides an IF signal having an 8 MHz bandwidth to the demodulator  118 , which operates within the requirements under the ITU J.83 Annex A standard. Alternately, when operating under the North American DOCSIS mode, the second SAW filter  116  provides an IF signal having a 6 MHz bandwidth to the demodulator  118 , which then operates within the requirements under the ITU J.83 Annex B standard. Although, the illustrative embodiment depicts a single demodulator  118 , one skilled in the art will recognize that separate modulators operating under the ITU J.83 Annex A and B standards may alternately be utilized.  
         [0021]    The downstream processing circuitry  108  selectively tunes, demodulates, and otherwise “receives” at least one of a plurality of downstream data signals in response to a selection signal provided by, for example, the computer device  104 . The diplexer  130  passes all downstream data signals above 88 MHz to the tuner  112  via the high-pass filter HPF  132 . The tuner  112  downconverts the received downstream RF signals from the HPF  132  to a predetermined IF frequency signal. At least one switch selectively passes the IF frequency signal from the tuner  112  to the demodulator  118  via either the first SAW filter  114  or the second SAW filter  116 . In one embodiment, the first and second SAW filters  114  and  116  are each coupled between the tuner  112  and demodulator  118 , in parallel, via electronic switching devices  120 , and  1202  (collectively “switches”  120 ), such as PIN diodes. That is, each illustrative PIN diode functions as an electronic switch for selectively coupling and decoupling each of the SAW filters  114  and  116  between the tuner  112  and the demodulator  118 .  
         [0022]    For example, a first PIN diode (not shown), which is coupled to the first SAW filter  114 , is forward biased by a controller (not shown) to allow the first PIN diode to act as a short circuit as between the tuner  112  to the first SAW filter  114 . As such, the first SAW filter  114  is coupled to the tuner  112 . Additionally, a second PIN diode (not shown), which is coupled between the tuner  112  and the second SAW filter  116 , is reversed biased by the controller to allow the PIN diode to act as an open circuit as between the tuner  112  to the second SAW filter  116 . As such, the second SAW filter  116  is decoupled from the tuner  112 . In this manner, only one of the two SAW filters is coupled to the tuner  112  at a time. Additionally, in a similar manner, a third and fourth PIN diode (not shown) may be utilized in conjunction with the controller to couple and decouple the first and second SAW filters  114  and  116  to the demodulator  118 . One skilled in the art will recognize that other switching components (e.g., transistors, electromechanical switches, and the like) and circuits may be utilized to selectively couple and decouple the SAW filters  116  and  114  to the tuner  112  and demodulator  118 . The downconverted IF signals are demodulated by the downstream processing circuitry  108  to provide one or more respective baseband signals, which are transferred to the computer device  104  for processing.  
         [0023]    When operating under the North American DOCSIS standard, the exemplary second SAW filter  116  provides a 44 MHz centered IF signal having a 6 MHz bandwidth to the demodulator  118 , where the demodulator  118  extracts the baseband signal(s) therein. Similarly, when operating under the European DOCSIS standard, the exemplary first SAW filter  114  provides a 36.125 MHz centered IF signal having an 8 MHz bandwidth to the demodulator  118 , where the demodulator  118  extracts the baseband signal(s) therein. In any case, the baseband signals are sent to the media access controller (MAC)  124  for subsequent transport to the computer device.  
         [0024]    The baseband signals are illustratively formed into packets (e.g., MPEG elementary stream packets). The media access controller and other digital circuitry  124  may further process the packetized data (e.g., attach or encapsulate in appropriate transport packets) and then distribute the processed, packetized data to the computer devices  104 .  
         [0025]    The upstream processing circuitry  106  comprises a modulator  110  and other support circuits such as amplifiers, filters, voltage regulators, and the like (not shown). The modulator  110  modulates upstream signals from the computer device  104  for subsequent transmission to the service provider  160 . In particular, a user sends data, data requests, or some other user request to the service provider. The user request is up converted and modulated to an upstream RF signal.  
         [0026]    [0026]FIG. 2 depicts a block diagram of a diplexer  130  according to the present invention. A high-pass filter  132  is coupled between a first signal port  206   1  and a second signal port  206   2 . The high-pass filter  132  provides an RF frequency path to the downstream processing circuitry  108  from the cable transport network  150 , as discussed above. Additionally, a low-pass filter  134  is coupled between the first signal port  206 , and a third signal port  206   3 . The low-pass filter LPF  134  has a notch filter NF  136  selectively coupled thereon via switch  202 . The low-pass filter LPF  134 , either singularly or in combination with the notch filter NF  136 , provides an RF frequency path from the upstream processing circuitry  106  to the cable transport network  150 . The modulated upstream RF signal is filtered by the low-pass filter  134  (and, selectively, the notch filter  136 , depending on the DOCSIS standard the cable modem is operating) for transmission to the service provider  160  via the cable transport network  150 . In the instant embodiment of the present invention, it is noted that the low-pass filter LPF  134  is utilized without coupling to the notch filter  136  for operation under the European DOCSIS standard such that signals between 5-42 MHz may be passed. Alternately, the low-pass filter LPF  134  is coupled to the notch filter  136  for operation under the North American DOCSIS standard to pass signals between 5-65 MHz.  
         [0027]    [0027]FIG. 3 depicts a graphical representation of a response curve  300  for the diplexer of FIG. 2, and should be viewed along with FIG. 2. The response curve  300  comprises an ordinate  302  and an abscissa  304 . The ordinate  302  represents insertion loss (measured in decibels (dB)), and the abscissa  304  represents frequency (measured in megahertz (MHz)).  
         [0028]    Referring to FIGS. 2 and 3 together, it can be seen that the high-pass filter HPF  132  passes RF signals having a frequency greater than 88 MHz. Under the North American DOCSIS standard, the downstream data signals are transmitted at a frequency greater than 88 MHz, while under the European DOCSIS standard the downstream data signals are transmitted at a frequency greater than 110 MHz. In this case, only a single high-pass filter HPF  132  is utilized in the diplexer  130 . Specifically, the HPF  132  passes RF data signals above a frequency of 88 MHz. Since all downstream RF signals are above 88 Mhz, the single HPF  132  is suitable for passing through such downstream RF data signals for further processing in the cable modem  102  under both the North American and European DOCSIS standards. The HPF response curve  306  in FIG. 3 depicts a low level of insertion loss  302  for frequencies greater than 88 MHz.  
         [0029]    Under the North American DOCSIS standard, the upstream data signals are transmitted in a frequency range between 5 Mhz and 42 MHz, while under the European DOCSIS standard the upstream data signals are transmitted in a frequency range between 5 MHz and 65 MHz. In this case, the low-pass filter LPF  134  and selectively coupled notch filter NF  136  are provided to illustratively pass through data signals up to 42 MHz and 65 MHz respectively. In particular, the low-pass filter LPF  134  when coupled to the notch filter NF  136  passes through the upstream data signals, illustratively, having a frequency between 5 Mhz and 42 MHz as required under the North American DOCSIS standard. The LPF response curve  310  in FIG. 3 depicts a low level of insertion loss  302  for frequencies less than 42 MHz when operating under the North American DOCSIS standard.  
         [0030]    Similarly, the low-pass filter  134  passes through the upstream data signals, illustratively, having a frequency between 5 MHz and 65 MHz as required under the European DOCSIS standard. In this instance, the notch filter NF  136  is selectively decoupled from the low-pass filter LPF  134 . The LPF response curve  308  in FIG. 3 depicts a low level of insertion loss  302  for frequencies less than 65 MHz when operating under the European DOCSIS standard.  
         [0031]    Referring to FIG. 2, switch  202  is a schematic representation for selectively coupling and decoupling the notch filter NF  136  to the low-pass filter  134 , thereby permitting the diplexer  130  to be set for operation under either of the DOCSIS standards. In one embodiment, the switch  202  may be an electromechanical relay. Preferably, the switch  202  is a digitally operable switch, such as a PIN diode, transistor, and the like, controlled by a controller, such as a microprocessor, as discussed in further detail below. In an instance where the switch  202  selectively decouples the notch filter NF  136  from the LPF low-pass filter  134 , the diplexer  130  passes through frequencies less than 65 MHz along the cable transport network  150 , as set forth under the European DOCSIS standard. Similarly, in an instance where the switch  202  selectively couples the notch filter NF  136  to the LPF low-pass filter  134 , the diplexer  130  passes through frequencies less than 42 MHz along the cable transport network  150 , as set forth under the North American DOCSIS standard.  
         [0032]    It is noted that two separate de facto filters (e.g., the low-pass filter LPF  134 , and the low-pass filter LPF  134  in conjunction with the notch filter NF  136 ) are utilized for passing the upstream RF signal, as compared to only a single high-pass filter HPF  132  being utilized to pass downstream RF signals. It is further noted that a single low-pass filter may not be used for both the North American and European cable modems. In particular, there are stringent limits on the energy that can be transmitted upstream in the frequency band above the upstream data band. For example, the low-pass filter for the North American system must have low attenuation for frequencies between 5 and 42 MHz and high attenuation for frequencies above 54 MHz (see response curve  310 ). The low-pass filter for the European system must have low attenuation for frequencies between 5 and 65 MHz and high attenuation for frequencies above 88 MHz (see response curve  308 ). The requirements between 54 and 65 MHz are in direct confict, therefore different responses, and hence, different low-pass filters are required under each DOCSIS standard.  
         [0033]    [0033]FIGS. 4 and 5 depict illustrative schematic representations of the components in the diplexer  130 . In general, the low-pass filter LPF  134  comprises a plurality of inductors connected in series between the first and third signal ports  206   1  and  206   3  each of the inductors being coupled to ground via a respective capacitor forming thereby a plurality of single pole filter elements, a portion of the inductors being bypassed by respective capacitors. Furthermore, the notch filter NF  136  comprises a second plurality of inductors, where each inductor is respectively coupled between a portion of the capacitors of the single pole filter elements of the low-pass filter LPF  134  and ground.  
         [0034]    In particular and referring to FIG. 4, the low-pass filter LPF  134  comprises inductors L 1  through L 5  coupled to capacitors C 1  through C 7  for passing frequencies less than 65 MHz. In particular, the inductors L 1  through L 5  are coupled end-to-end in series, where inductor L 1  is coupled to an input  402  and L 5  is coupled to an output  404  of the LPF filter  134 . Capacitor C 1  is coupled from ground to the node between L 1  and L 2 . Capacitor C 2  is coupled from ground to the node between L 2  and L 3 . Capacitor C 3  is coupled from the node between L 3  and L 4  to inductor L 7 , which is then coupled to ground. Capacitor C 4  is coupled from the node between L 4  and L 5  to inductor L 8 , which is then coupled to ground. Capacitor C 5  is coupled from the node between L 5  and the output  404  to inductor L 9 , which is then coupled to ground. Capacitor C 6  is coupled in parallel to inductor L 2  and capacitor C 7  is coupled in parallel to inductor L 3 . It is noted that the notch filter NF  136  is formed by inductors L 7  through L 9 , which are serially coupled between capacitors C 3  through C 5 , respectively, and ground.  
         [0035]    In one embodiment, a mechanism for coupling and decoupling the notch filter NF  136  to the low-pass filter  34  is illustratively provided by a plurality of PIN switch diodes coupled to a controller. Alternately, other switching mechanisms may be utilized, such as transistors, electromechanical devices, and the like. Referring to FIG. 4, PIN switch diode D 1  is coupled in parallel to inductor L 7  between capacitor C 3  and ground. PIN switch diode D 2  is coupled in parallel to inductor L 8  between capacitor C 4  and ground. PIN switch diode D 3  is coupled in parallel to inductor L 9  between capacitor C 5  and ground. Furthermore, the PIN diodes D 1  through D 3  have their respective cathodes tied to ground and their anodes coupled to the controller (e.g., a microprocessor in the MAC  124 ).  
         [0036]    In operation, the microprocessor selectively provides a voltage control signal to the anodes of the pin diodes D 1  through D 3 . In particular, when the pin diodes D 1  through D 3  are forward biased (i.e., act as a short circuit), the current discharged from capacitors C 3  through C 5  bypasses the notch filter  136 , (which comprises inductors L 7  through L 9 ) and goes directly to ground. Such is the case when the diplexer  130  is operating under the European DOCSIS standard. Alternately, when the PIN diodes D 1  through D 3  are reversed biased (i.e., act as an open circuit), the current discharged from capacitors C 3  through C 5  passes through the notch filter  136 , (which comprises inductors L 7  through L 9 ) prior to being coupled to ground. Such is the case when the diplexer  130  is operating under the North American DOCSIS standard.  
         [0037]    Table 1 depicts one embodiment of the values of the inductors and capacitors L 1 -L 5  and C 1 -C 7  of the low-pass filter LPF  134  without the components of the notch filter NF  136  selectively coupled thereto. Additionally, Table 1 also depicts one embodiment of the values of the three inductors L 7 -L 9 , which primarily form the notch filter NF  136  portion of the low-pass filter. Regarding Table 1, inductor and capacitance values are illustratively measured, respectively, in nano Henry and pico farads.  
                                                                                                           TABLE 1                           LPF (FIG. 4)   NF (FIG. 4)   HPF (FIG. 5)            L   (nH)   C   (pF)   L   (nH)   L   (nH)   C   (pF)                    L1   250   C1   38   L7   160   L10   210   C8   15       L2   160   C2   33   L8   250   L11   310   C9   150       L3   220   C3   36   L9   200   L12   160   C10   13       L4   330   C4   36                   C11   12       L5   300   C5   39                   C12   72               C6   26                   C13   69               C7   10                   C14   93                  
 
         [0038]    In general, the high-pass filter HPF  132  comprises a plurality of capacitors connected in series between the first and the second signal ports  206   1  and  206   2 , each of the capacitors being coupled to ground via serially coupled circuit elements forming thereby a plurality of single pole filter elements, each of the serially coupled circuit elements comprising a capacitor and inductor. In particular and referring to FIG. 5, the high-pass filter HPF  132  comprises inductors L 10  through L 12  coupled to capacitors C 8  through C 14  for passing frequencies greater than 88 MHz. In particular, capacitors C 8  through C 11  are coupled end-to-end in series, where capacitor C 8  is coupled to an input  502  and C 11  is coupled to an output  504  of the HPF filter  132 . Capacitor C 12  is coupled to the node between capacitors C 8  and C 9  and serially coupled to inductor L 10 , which is coupled to ground. Capacitor C 13  is coupled to the node between capacitors C 9  and C 10  and serially coupled to inductor L 11 , which is coupled to ground. Capacitor C 14  is coupled to the node between capacitors C 10  and C 11  and serially coupled to inductor L 12 , which is coupled to ground. Table 1 above also depicts a preferred embodiment of the values of the inductors and capacitors L 10 -L 12  and C 8 -C 14  of the high-pass filter HPF  132 .  
         [0039]    [0039]FIGS. 4 and 5 depict one of many possible embodiments to implement a multi-mode bi-directional communications device (e.g., cable modem)  102 , which can be operated under multiple standards, for example, between the European and North American DOCSIS standards. The diplexer  130  utilizes a single high-pass filter HPF  132  to adjust the cutoff frequency of the diplexer&#39;s forward (i.e., downstream) channel, and switches between two de facto filters low-pass and notch filters LPF and NF  134  and  136  to adjust the cutoff frequency of the diplexer&#39;s return (i.e., upstream) channel. It should be apparent to those skilled in the art and informed by the present disclosure that a novel diplexer for passing RF signals for multi standard data communication systems operating, illustratively, under both the North American and European DOCSIS standards has been provided. It should also be noted that FIG. 1 depicts the upstream processing circuitry  106 , downstream circuitry  108 , and media access controller  124  as separate components. However, one skilled in the art will understand that these illustratively distinct components may also be fabricated, for example, as a single integrated circuit (e.g., ASIC) as well.  
         [0040]    Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.