Patent Publication Number: US-7899428-B2

Title: Radio receiver and radio receiver front-end

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 11/513,685, filed Aug. 30, 2006, which application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This invention relates generally to wireless communications systems and more particularly to radio receivers used within such wireless communication systems. 
     2. Description of Related Art 
     Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), and/or variations thereof. 
     Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network. 
     For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna. 
     As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier (LNA) receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard. 
     For a receiver to reliably recover data from received inbound RF signals it must be able to isolate desired signal components of the inbound RF signals from interferers (e.g., interference from adjacent channel(s), interference from other devices and/or systems using frequencies near the frequency band of interest, and/or transmission blocking signals that occur in RFID systems). For example, in a cellular system, it is fairly common to have significant nearby interferers of the frequency band of interest (e.g., one or more desired channel(s) of 5-60 MHz centered at a frequency of about 900 MHz, 1800 MHz, 1900 MHz, and/or 2100 MHz) that adversely affect the ability of a receiver to accurately recover data. 
     One solution to reduce the adverse affects caused by interferers is to use an off-chip band pass filter (BPF) prior to the LNA to attenuate the interferers and pass the desired channel(s). However, with nearby interferers (e.g., within 100 MHz), the BPF needs a steep roll off to sufficiently attenuate the interferers making it an expensive part. In addition, an off-chip BPF typically reduces the magnitude of the desired channel(s) by about 3 dB. 
     Another solution is to use a less expensive BPF with less roll off. While this reduces the cost and the attenuation of the desired channel(s), it does not sufficiently attenuate large nearby interferers. 
     Therefore, a need exists for a radio receiver and radio receiver front-end that sufficiently attenuated interferers without the use of costly BPFs and with negligible attenuation of the desired channel(s). 
     SUMMARY OF THE INVENTION 
     The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a schematic block diagram of a wireless communication system in accordance with the present invention; 
         FIG. 2  is a schematic block diagram of a radio frequency identification system in accordance with the present invention; 
         FIG. 3  is a schematic block diagram of a wireless communication device in accordance with the present invention; 
         FIG. 4  is a schematic block diagram of an embodiment of a radio receiver front-end in accordance with the present invention; 
         FIG. 5  is a schematic block diagram of another embodiment of a radio receiver front-end in accordance with the present invention; 
         FIG. 6  is a schematic block diagram of another embodiment of a radio receiver front-end in accordance with the present invention; and 
         FIG. 7  is a schematic block diagram of another embodiment of a radio receiver front-end in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic block diagram illustrating a communication system  10  that includes a plurality of base stations and/or access points  12 ,  16 , a plurality of wireless communication devices  18 - 32  and a network hardware component  34 . Note that the network hardware  34 , which may be a router, switch, bridge, modem, system controller, et cetera provides a wide area network connection  42  for the communication system  10 . Further note that the wireless communication devices  18 - 32  may be laptop host computers  18  and  26 , personal digital assistant hosts  20  and  30 , personal computer hosts  24  and  32  and/or cellular telephone hosts  22  and  28  that include a wireless transceiver. The details of the wireless transceiver will be described in greater detail with reference to  FIGS. 3-7 . 
     Wireless communication devices  22 ,  23 , and  24  are located within an independent basic service set (IBSS) area and communicate directly (i.e., point to point). In this configuration, these devices  22 ,  23 , and  24  may only communicate with each other. To communicate with other wireless communication devices within the system  10  or to communicate outside of the system  10 , the devices  22 ,  23 , and/or  24  need to affiliate with one of the base stations or access points  12  or  16 . 
     The base stations or access points  12 ,  16  are located within basic service set (BSS) areas  11  and  13 , respectively, and are operably coupled to the network hardware  34  via local area network connections  36 ,  38 . Such a connection provides the base station or access point  12   16  with connectivity to other devices within the system  10  and provides connectivity to other networks via the WAN connection  42 . To communicate with the wireless communication devices within its BSS  11  or  13 , each of the base stations or access points  12 - 16  has an associated antenna or antenna array. For instance, base station or access point  12  wirelessly communicates with wireless communication devices  18  and  20  while base station or access point  16  wirelessly communicates with wireless communication devices  26 - 32 . Typically, the wireless communication devices register with a particular base station or access point  12 ,  16  to receive services from the communication system  10 . 
     Typically, base stations are used for cellular telephone systems and like-type systems, while access points are used for in-home or in-building wireless networks (e.g., IEEE 802.11 and versions thereof, Bluetooth, RFID, and/or any other type of radio frequency based network protocol). Regardless of the particular type of communication system, each wireless communication device includes a built-in radio and/or is coupled to a radio. Note that one or more of the wireless communication devices may include an RFID reader and/or an RFID tag. 
       FIG. 2  is a schematic block diagram of an RFID (radio frequency identification) system that includes a computer/server  112 , a plurality of RFID readers  114 - 118  and a plurality of RFID tags  120 - 130 . The RFID tags  120 - 130  may each be associated with a particular object for a variety of purposes including, but not limited to, tracking inventory, tracking status, location determination, assembly progress, et cetera. 
     Each RFID reader  114 - 118  wirelessly communicates with one or more RFID tags  120 - 130  within its coverage area. For example, RFID reader  114  may have RFID tags  120  and  122  within its coverage area, while RFID reader  116  has RFID tags  124  and  126 , and RFID reader  118  has RFID tags  128  and  130  within its coverage area. The RF communication scheme between the RFID readers  114 - 118  and RFID tags  120 - 130  may be a backscattering technique whereby the RFID readers  114 - 118  provide energy to the RFID tags via an RF signal. The RFID tags derive power from the RF signal and respond on the same RF carrier frequency with the requested data. 
     In this manner, the RFID readers  114 - 118  collect data as may be requested from the computer/server  112  from each of the RFID tags  120 - 130  within its coverage area. The collected data is then conveyed to computer/server  112  via the wired or wireless connection  132  and/or via the peer-to-peer communication  134 . In addition, and/or in the alternative, the computer/server  112  may provide data to one or more of the RFID tags  120 - 130  via the associated RFID reader  114 - 118 . Such downloaded information is application dependent and may vary greatly. Upon receiving the downloaded data, the RFID tag would store the data in a non-volatile memory. 
     As indicated above, the RFID readers  114 - 118  may optionally communicate on a peer-to-peer basis such that each RFID reader does not need a separate wired or wireless connection  132  to the computer/server  112 . For example, RFID reader  114  and RFID reader  116  may communicate on a peer-to-peer basis utilizing a back scatter technique, a wireless LAN technique, and/or any other wireless communication technique. In this instance, RFID reader  116  may not include a wired or wireless connection  132  to computer/server  112 . Communications between RFID reader  116  and computer/server  112  are conveyed through RFID reader  114  and the wired or wireless connection  132 , which may be any one of a plurality of wired standards (e.g., Ethernet, fire wire, et cetera) and/or wireless communication standards (e.g., IEEE 802.11x, Bluetooth, et cetera). 
     As one of ordinary skill in the art will appreciate, the RFID system of  FIG. 2  may be expanded to include a multitude of RFID readers  114 - 118  distributed throughout a desired location (for example, a building, office site, et cetera) where the RFID tags may be associated with equipment, inventory, personnel, et cetera. Note that the computer/server  112  may be coupled to another server and/or network connection to provide wide area network coverage. 
       FIG. 3  is a schematic block diagram of a wireless transceiver, which may be incorporated in an access point or base station  12  and  16  of  FIG. 1 , in one or more of the wireless communication devices  18 - 32  of  FIG. 1 , in one or more of the RFID readers  114 - 118 , and/or in one or more of RFID tags  120 - 130 . The wireless transceiver includes a transmitter and a receiver. The receiver includes a radio receiver front-end  140 , a down conversion module  142 , and a receiver processing module  144 . The transmitter includes a transmitter processing module  146 , an up conversion module  148 , and a radio transmitter front-end  150 . 
     As shown, the receiver and transmitter are each coupled to an antenna, however, the receiver and transmitter may share a single antenna via a transmit/receive switch and/or transformer balun. In another embodiment, the receiver and transmitter may share a diversity antenna structure. In another embodiment, the receiver and transmitter may each use its own diversity antenna structure. In another embodiment, the receiver and transmitter may share a multiple input multiple output (MIMO) antenna structure. Accordingly, the antenna structure of the wireless transceiver will depend on the particular standard(s) to which the wireless transceiver is compliant. 
     In operation, the transmitter receives outbound data  162  from a host device or other source via the transmitter processing module  146 . The transmitter processing module  146  processes the outbound data  162  in accordance with a particular wireless communication standard (e.g., IEEE 802.11, Bluetooth, RFID, GSM, CDMA, et cetera) to produce baseband or low intermediate frequency (IF) transmit (TX) signals  164 . The baseband or low IF TX signals  164  may be digital baseband signals (e.g., have a zero IF) or digital low IF signals, where the low IF typically will be in a frequency range of one hundred kilohertz to a few megahertz. Note that the processing performed by the transmitter processing module  146  includes, but is not limited to, scrambling, encoding, puncturing, mapping, modulation, and/or digital baseband to IF conversion. Further note that the transmitter processing module  146  may be implemented using a shared processing device, individual processing devices, or a plurality of processing devices and may further include memory. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module  146  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. 
     The up conversion module  148  includes a digital-to-analog conversion (DAC) module, a filtering and/or gain module, and a mixing section. The DAC module converts the baseband or low IF TX signals  164  from the digital domain to the analog domain. The filtering and/or gain module filters and/or adjusts the gain of the analog signals prior to providing it to the mixing section. The mixing section converts the analog baseband or low IF signals into up converted signals  166  based on a transmitter local oscillation  168 . 
     The radio transmitter front end  150  includes a power amplifier  84  and may also include a transmit filter module. The power amplifier amplifies the up converted signals  166  to produce outbound RF signals  170 , which may be filtered by the transmitter filter module, if included. The antenna structure transmits the outbound RF signals  170  to a targeted device such as a base station, an access point and/or another wireless communication device. 
     The receiver receives inbound RF signals  152  via the antenna structure, where a base station, an access point, or another wireless communication device transmitted the inbound RF signals  152 . The antenna structure provides the inbound RF signals  152  to the receiver front-end  140 , which will be described in greater detail with reference to  FIGS. 4-7 . In general, without the use of bandpass filters, the receiver front-end  140  blocks one or more undesired signals components  174  (e.g., one or more interferers) of the inbound RF signal  152  and passing a desired signal component  172  (e.g., one or more desired channels of a plurality of channels) of the inbound RF signal  152  as a desired RF signal  154 . 
     The down conversion module  70  includes a mixing section, an analog to digital conversion (ADC) module, and may also include a filtering and/or gain module. The mixing section converts the desired RF signal  154  into an analog baseband or low IF signal based on a receiver local oscillation  158 . The ADC module converts the analog baseband or low IF signal into a digital baseband or low IF signal. The filtering and/or gain module high pass and/or low pass filters the digital baseband or low IF signal to produce a baseband or low IF signal  156 . Note that the ordering of the ADC module and filtering and/or gain module may be switched, such that the filtering and/or gain module is an analog module. 
     The receiver processing module  144  processes the baseband or low IF signal  156  in accordance with a particular wireless communication standard (e.g., IEEE 802.11, Bluetooth, RFID, GSM, CDMA, et cetera) to produce inbound data  160 . The processing performed by the receiver processing module  144  includes, but is not limited to, digital intermediate frequency to baseband conversion, demodulation, demapping, depuncturing, decoding, and/or descrambling. Note that the receiver processing modules  144  may be implemented using a shared processing device, individual processing devices, or a plurality of processing devices and may further include memory. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the receiver processing module  144  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. 
       FIG. 4  is a schematic block diagram of an embodiment of a radio receiver front-end  140  that includes a first radio frequency (RF) receiver section  180 , a second RF receiver section  182 , and an RF combining module  184 . The first RF receiver section  180  is coupled to receive the inbound RF signal  152  and provide to a first representation  186  of the inbound RF signal. Note that the inbound RF signal  152  includes a desired signal component  172  and an undesired signal component  174 . 
     The second RF receiver section  182  is coupled to receive the inbound RF signal  152  and to provide a second representation  188  of the inbound RF signal. The RF combining module  184  is coupled to combine the first and second representations  186  and  188  of the inbound RF signal to produce the desired RF signal  154 . Note that the desired RF signal  154  includes the desired signal component  172  and an attenuated representation (e.g., 10 dB or more) of the undesired signal component  174 . 
       FIG. 5  is a schematic block diagram of another embodiment of a radio receiver front-end  140  that includes a first RF receiver section  180 , a second RF receiver section  182 , and an RF combining module  184 . In this embodiment, the first RF receiver section  180  includes a low noise amplifier (LNA)  190 ; the second RF receiver section  182  includes a LNA  192  and a notch filter module  194 ; and the RF combining module  194  includes a subtraction module. 
     The LNA  190  of the first RF receiver section  180  amplifies the inbound RF signal  152  to produce the first representation  186  of the inbound RF signal. As shown, the first representation  186  of the inbound RF signal includes the desired signal component  172  (e.g., one or more desired channels) and the undesired signal component  174  (e.g., interferers), but at a different magnitude than the inbound RF signal  152 . For example, the inbound RF signal  152  may be generated in accordance with a cellular system, as such, it includes a desired signal component  172  or a frequency band of interest (e.g., one or more desired channel(s) of 5-60 MHz centered at a frequency of about 900 MHz, 1800 MHz, 1900 MHz, and/or 2100 MHz) and may further include a significant nearby interferer(s) (e.g., interference from adjacent channel(s), interference from other devices and/or systems using frequencies near the frequency band of interest, and/or transmission blocking signals that occur in RFID systems). Note that the interferers may be at frequencies within a few hundred Mega Hertz from of the frequency of the desired signal component  172 . Further note that the bandwidth of the received inbound RF signal  152  is at least partially dependent upon the bandwidth of the LNAs  190  and  192 . 
     LNA  192  of the second RF receiver section  182  amplifies the inbound RF signal  152  to produce a second amplified RF signal  198 . The level of amplification used by LNA  192  is substantially equal to the level of amplification used by LNA  190  such that the second amplified RF signal  198  is substantially equal to the first representation  186  of the inbound RF signal. 
     The notch filter module  194 , which may include one or more notch filters having a total roll off of 40 dB or more, notch filters the second amplified RF signal  198  to produce the second representation  188  of the inbound RF signal. The properties of the notch filter module  194  are such that the desired signal component  172  is substantially attenuated while the remaining portion of the inbound RF signal  152 , including the undesired signal component  174 , is passed substantially unattenuated as shown. Note that the notch filter module  194  may be adjustable, where the notch filter adjustment is based on a channel selection signal  196 . As such, the notch filter module  194  may be tuned to accommodate different channels of a plurality of channels. 
     In another embodiment, the notch filter module  194  may include a mixer that down-converts the second amplified RF signal  198  to a baseband signal or an intermediate frequency (IF) signal. The notch filter module  194  further includes a notch filter, low pass filter, and/or high pass filter coupled to filter the baseband signal or IF signal such that the baseband or IF representation of the desired signal component  172  is attenuated while the baseband or IF representation of the undesired signal component  174  is passed substantially unattenuated. The notch filter module  194  further includes a second mixer that mixes the baseband or IF representation of the undesired signal component  172  with an RF or IF oscillation to produce the second representation  188  of the inbound RF signal. 
     The subtraction module  195  of the RF combining module  184  subtracts the second representation  188  of the inbound RF signal from the first representation  186  of the inbound RF signal to produce the desired RF signal  154 . As such, the desired RF signal  154  includes the desired signal component  172  and minimal other portions of the inbound RF signal, including the undesired signal component  174 . Thus, the interferers are substantially attenuated without the use of bandpass filters and without the up to 3 dB loss of the desired signal component associated with the use of bandpass filters. 
       FIG. 6  is a schematic block diagram of another embodiment of a radio receiver front-end  140  that includes a first RF receiver section  180 , a second RF receiver section  182 , and an RF combining module  184 . In this embodiment, the first RF receiver section  180  includes a transconductance low noise amplifier (LNA)  206 ; the second RF receiver section  182  includes a transconductance LNA  208  and a current based notch filter module  204 ; and the RF combining module  194  includes a pair of current to voltage conversion modules  200  and  202  and a subtraction module  205 . 
     The transconductance LNA  206  of the first RF receiver section  180  amplifies the inbound RF signal  152  to produce the first representation  186  of the inbound RF signal. In this embodiment, the first representation  186  of the inbound RF signal is a current-based (I) signal while the inbound RF signal  152  is a voltage-based (V) signal. As such, the first representation  186  of the inbound RF signal includes the desired signal component  172  (e.g., one or more desired channels) and the undesired signal component  174  (e.g., interferers). 
     Transconductance LNA  208  of the second RF receiver section  182  amplifies the inbound RF signal  152  to produce a second amplified RF signal  210 , where the second amplified RF signal  210  is a current-based (I) signal. The level of amplification used by LNA  208  is substantially equal to the level of amplification used by LNA  206  such that the second amplified RF signal  210  is substantially equal to the first representation  186  of the inbound RF signal. 
     The current-based (I) notch filter module  204 , which may include one or more notch filters having a total roll off of 40 dB or more, notch filters the second amplified RF signal  210  to produce the second representation  188  of the inbound RF signal. The properties of the notch filter module  204  are such that the desired signal component  172  is substantially attenuated while the remaining portion of the inbound RF signal  152 , including the undesired signal component  174 , is passed substantially unattenuated. Note that the notch filter module  204  may be adjustable, where the notch filter adjustment is based on a channel selection signal  196 . As such, the notch filter module  204  may be tuned to accommodate different channels of a plurality of channels. 
     The current (I) to voltage (V) module  200 , which may be implemented via a transistor, a cascode transistor pair, or any circuit that converts a current-based signal into a voltage-based signal, converts the first representation  186  of the inbound RF signal into a voltage-based signal. The I to V module  200 , which may be implemented via a transistor, a cascode transistor pair, or any circuit that converts a current-based signal into a voltage-based signal, converts the second representation  188  of the inbound RF signal into a voltage-based signal. The subtraction module  205  of the RF combining module  184  subtracts the second representation  188  of the inbound RF signal from the first representation  186  of the inbound RF signal to produce the desired RF signal  154 . As such, the desired RF signal  154  includes the desired signal component  172  and minimal other portions of the inbound RF signal, including the undesired signal component  174 . Thus, the interferers are substantially attenuated without the use of bandpass filters and without the up to 3 dB loss of the desired signal component associated with the use of bandpass filters. 
       FIG. 7  is a schematic block diagram of another embodiment of a radio receiver front-end  140  that functions to: receive an inbound radio frequency (RF) signal  152 , wherein the inbound RF signal  152  includes a desired signal component  224  and a blocker signal  222 ; separate the blocker signal  222  from the desired signal component  224  to produce a separate blocker signal  222 ; and produce a desired RF signal  154  from the inbound RF signal  152  and the separate blocker signal  222 . In this embodiment, the blocker signal  222  may be at or near the same frequency as the inbound RF signal  152 , which is typically the case for RFID systems. 
     In an embodiment, the radio receiver front-end utilizes a separation module  220  to separate the blocker signal from the desired signal component. The separation module  220  amplifies the inbound RF signal to produce an amplified RF signal. The separation module  220  then notch filters the amplified RF signal to attenuate the desired signal component of the amplified RF signal and to pass, substantially unattenuated, the blocker signal of the amplified RF signal to produce the separate blocker signal. In another embodiment, the notch filtering includes: receiving a channel selection signal, wherein the desired signal component of the amplified RF signal corresponds to at least one desired channel of a plurality of channels and wherein the at least one desired channel is identified by the channel selection signal; and adjusting the notch filtering based on the channel selection signal. 
     In an embodiment, the radio receiver front-end produces the desired RF signal from the inbound RF signal and the separate blocker signal by: amplifying the inbound RF signal to produce an amplified RF signal; and subtracting the separate blocker signal from the amplified RF signal to produce the desired RF signal. 
     As may be used herein, the terms “substantially” and “approximately” provides an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to fifty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As may also be used herein, the term(s) “coupled to” and/or “coupling” and/or includes direct coupling between items and/or indirect coupling between items via an intervening item (e.g., an item includes, but is not limited to, a component, an element, a circuit, and/or a module) where, for indirect coupling, the intervening item does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As may further be used herein, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two items in the same manner as “coupled to”. As may even further be used herein, the term “operable to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform one or more its corresponding functions and may further include inferred coupling to one or more other items. As may still further be used herein, the term “associated with”, includes direct and/or indirect coupling of separate items and/or one item being embedded within another item. As may be used herein, the term “compares favorably”, indicates that a comparison between two or more items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal  1  has a greater magnitude than signal  2 , a favorable comparison may be achieved when the magnitude of signal  1  is greater than that of signal  2  or when the magnitude of signal  2  is less than that of signal  1 . 
     While the transistors discussed above may be field effect transistors (FETs), as one of ordinary skill in the art will appreciate, the transistors may be implemented using any type of transistor structure including, but not limited to, bipolar, metal oxide semiconductor field effect transistors (MOSFET), N-well transistors, P-well transistors, enhancement mode, depletion mode, and zero voltage threshold (VT) transistors. 
     The present invention has also been described above with the aid of method steps illustrating the performance of specified functions and relationships thereof. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for convenience of description. Alternate boundaries and sequences can be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are thus within the scope and spirit of the claimed invention. 
     The present invention has been described above with the aid of functional building blocks illustrating the performance of certain significant functions. The boundaries of these functional building blocks have been arbitrarily defined for convenience of description. Alternate boundaries could be defined as long as the certain significant functions are appropriately performed. Similarly, flow diagram blocks may also have been arbitrarily defined herein to illustrate certain significant functionality. To the extent used, the flow diagram block boundaries and sequence could have been defined otherwise and still perform the certain significant functionality. Such alternate definitions of both functional building blocks and flow diagram blocks and sequences are thus within the scope and spirit of the claimed invention. One of average skill in the art will also recognize that the functional building blocks, and other illustrative blocks, modules and components herein, can be implemented as illustrated or by discrete components, application specific integrated circuits, processors executing appropriate software and the like or any combination thereof.