Abstract:
Disclosed is a circuit apparatus including an input section configured to receive an electromagnetic (EM) transmission, a voltage divider section configured to divide the EM transmission into a plurality of voltage levels, a rectifier portion configured to rectify AC power received in the EM transmission, and a load configured to receive DC power from the rectifier portion, wherein one level of the voltage divider section is configured to supply power to a radio frequency identification integrated circuit (RFID-IC).

Description:
TECHNICAL FIELD 
       [0001]    Various exemplary embodiments disclosed herein relate to power harvesting circuitry in combination with RFID and NFC applications. 
       SUMMARY 
       [0002]    A brief summary of various embodiments is presented below. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various embodiments, but not to limit the scope of the invention. Detailed descriptions of embodiments adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections. 
         [0003]    Various exemplary embodiments are related to a circuit apparatus including an input section configured to receive an electromagnetic (EM) transmission, a voltage divider section configured to divide the EM transmission into a plurality of voltage levels, a rectifier portion configured to rectify AC power received in the EM transmission, and a load configured to receive DC power from the rectifier portion, wherein one voltage level of the voltage divider section is configured to supply power to a radio frequency identification integrated circuit (RFID-IC). 
         [0004]    The RFID-IC may include a data port configured to communicate with electrical components on the circuit apparatus. 
         [0005]    The RFID-IC may be in parallel with a capacitor of the voltage divider portion. 
         [0006]    The circuit apparatus may include at least one capacitor configured to store charge to be rectified. The at least one capacitor may be arranged asymmetrically. 
         [0007]    The input section may include an antenna with multiple taps. The voltage divider may include a plurality of capacitors. The voltage divider may include a plurality of resistors. 
         [0008]    Various exemplary embodiments are also related to a power harvesting apparatus including an RFID circuit, including an antenna configured to receive an electromagnetic (EM) transmission, the antenna including a plurality of taps configured to vary the voltage received from the EM transmission, at least one capacitor configured to store charge received in the EM transmission, and a rectifier portion configured to rectify power received in the EM transmission and provide the rectified power to a load, wherein one voltage level of the antenna taps is configured to supply power to a radio frequency identification integrated circuit (RFID-IC). 
         [0009]    The at least one capacitor may be arranged asymmetrically. A plurality of capacitors may be arranged symmetrically. 
         [0010]    The rectifier portion may be configured to produce two voltages across an output load. The two voltages may be a positive voltage and a negative voltage. 
         [0011]    Various exemplary embodiments are also related to a power harvesting circuit including an antenna configured to receive an electromagnetic (EM) transmission, a low power circuit configured to receive a low voltage from the EM transmission, a voltage divider circuit having a plurality nodes configured to produce a plurality of voltages across different sets of the plurality of nodes, a rectification circuit configured to receive a high AC voltage from the EM transmission and rectify the high AC voltage to a DC voltage, and a high power circuit configured to receive the high voltage and power a load using the high voltage. 
         [0012]    The low power circuit may be a radio-frequency identification integrated circuit (RFID-IC). 
         [0013]    The power harvesting circuit may include a load delivery circuit configured to deliver a stepped down voltage to a load. 
         [0014]    The voltage divider circuit may include a plurality of capacitors. The low power circuit may be an RFID integrated circuit. 
         [0015]    The power harvesting circuit may include a galvanic connection between the low power circuit and the high power circuit. The voltage divider circuit may include an antenna having a center tap. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings. Although several embodiments are illustrated and described, like reference numerals identify like parts in each of the figures, in which: 
           [0017]      FIG. 1  illustrates an RFID apparatus in accordance with embodiments described herein; 
           [0018]      FIG. 2  illustrates an RF-power harvesting apparatus in accordance with embodiments described herein; 
           [0019]      FIG. 3  illustrates a power harvesting apparatus including an RFID-IC, antenna coil, symmetrical capacitive RF-voltage divider, symmetrical series capacitors, and bridge rectification in accordance with embodiments described herein; 
           [0020]      FIG. 4A  illustrates another power harvesting apparatus including an RFID-IC, antenna coil, asymmetrical capacitive RF-voltage divider, a single asymmetrical series-capacitor, and bridge rectifier in accordance with embodiments described herein; 
           [0021]      FIG. 4B  illustrates another power harvesting apparatus including an RFID-IC, antenna coil, asymmetrical capacitive RF-voltage divider, an asymmetrical series-capacitor, and a half wave voltage doubling circuit in accordance with embodiments described herein; 
           [0022]      FIG. 5A  illustrates yet another power harvesting apparatus including an RFID-IC, a multiple tap antenna coil, symmetrical series-capacitors, and two half wave voltage doubling circuits in parallel in accordance with embodiments described herein; 
           [0023]      FIG. 5B  illustrates another power harvesting apparatus including an RFID-IC, a multiple taps antenna coil, a double half wave rectification circuit, in accordance with embodiments described herein; 
           [0024]      FIG. 5C  illustrates another power harvesting apparatus including an RFID-IC, a multiple tap antenna coil, symmetrical series-capacitors, bridge rectification, dual output-voltages in accordance with embodiments described herein; 
           [0025]      FIG. 5D  illustrates another power harvesting apparatus including an RFID-IC, a multiple tap antenna coil, symmetrical series-capacitors, two half wave voltage doubling circuits in series, and dual output-voltages in accordance with embodiments described herein; 
           [0026]      FIGS. 6A, 6B and 6C  illustrate respective power harvesting apparatuses including an RFID-IC in accordance with embodiments described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts. 
         [0028]    The descriptions and drawings illustrate the principles of various example embodiments. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Additionally, the term, “or,” as used herein, refers to a non-exclusive or (i.e., and/or), unless otherwise indicated (e.g., “or else” or “or in the alternative”). Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. As used herein, the terms “context” and “context object” will be understood to be synonymous, unless otherwise indicated. Descriptors such as “first,” “second,” “third,” etc., are not meant to limit the order of elements discussed, are used to distinguish one element from the next, and are generally interchangeable. 
         [0029]    Embodiments described herein include systems to increase output power from apparatuses that include Radio Frequency Identification Integrated Circuits (RFID-ICs), and apparatuses that receive power without interfering or destroying the RF communication or the RFID-IC itself. The RFID-IC may be used for Near Field Communication (NFC). 
         [0030]    Passive RFID tags obtain their operating power by receiving energy from an electromagnetic field of a reader&#39;s communication signal. The limited resources of a passive tag require it to both receive its energy and communicate with a reader within a specified frequency band. RFID tags are inductive capacitive (LC) devices that may transmit signals at a resonance frequency. 
         [0031]    Passive RFID tags and surrounding electronics may form an apparatus that obtains its power from the communication signal through inductive coupling and far field harvesting. Inductive coupling uses a magnetic field generated by a communication signal to induce a current in its coupling element, such as a coiled antenna and a capacitor. An antenna may receive an electromagnetic transmission from a transmitter. The current induced in the coupling element charges the on-apparatus capacitor(s) that provides an operating voltage, and power, for the apparatus. Inductive coupling works in the near-field of the communication signal. 
         [0032]    Related art power harvesting circuits have outputs in the range of 15-20 mW, representing an efficiency of 4-5%. Embodiments described herein include circuitry that can yield up to 400 mW on a 315 mm 2  or similar size integrated circuit, which can yield an efficiency of 20-32%. An amount of output power may be influenced by available antenna-coil area and RF-field-strength. 
         [0033]      FIG. 1  illustrates a RFID apparatus  100  in accordance with embodiments described herein. The RFID apparatus  100  includes an RFID-IC  105  that is connected via the two IC-nodes  110  and  120 . The RFID-IC  105  may be implemented on a tag or the like. The RFID-IC  105  is connected to an antenna-coil  130  to receive near-field communication from external sources (not illustrated). The RFID-IC  105  may have a certain capacitance (C_IC) on silicon which may create a resonance circuit with the inductance of the antenna-coil  130 . If C_IC is too low, an additional capacitor  145  may be used to make the RFID-IC  105  work as a resonance circuit at a predetermined frequency. 
         [0034]    The RFID-IC  105  is a passive device and uses a small amount of power (e.g. 0.025 mW) to operate. To prevent distortion or damage of the RFID-IC  105  by exposing a label or tag on which an RFID-IC  105  may be mounted to a very strong RF-field, the RFID-IC  105  has a limiter circuit  108  integrated on the chip, which clips the peak-to-peak RF voltage across the RFID-IC  105  antenna nodes to be under a highest allowed voltage level. This limiter circuit  108  may designed to operate in a range from 6.0 to 6.5 volts, but limiter circuits to be used with embodiments described herein are not limited thereto. 
         [0035]    RFID-IC  105  may include a connection  125  to connect the RFID-IC  105  to external components such as via a data-bus, a switch (e.g. open drain of a MOSFET in the RFID-IC  105 ), or an auxiliary voltage, etc. RFID-IC  105  is grounded at V SS  node  135 , which may be a common bus for other connected circuit components. 
         [0036]    Combining lower voltage circuits such as RFID-IC  105  with higher voltage circuits for harvesting may be embodied in various circuits and apparatuses as described herein. Low voltages may be circuits generally using below 3.5V and may be in the range of as 2.0-2.5V. High voltage circuits may be above about 5V and up to at least 15V and may be 7V or 12V. 
         [0037]    Embodiments may include a capacitive voltage-divider, a single antenna coil, low cost circuits and components, and other methods will be described for universal usage, and a power range of 50 to 400 mW. The output power can be used to drive passive and active devices. Applications where RFID with power harvesting may be used include battery recharging via NFC/smart phone, “battery-less devices” that include high level electronics on board, such as a bike-computer or price-display in a store, where power is delivered by a mobile or smart-phone during operation. Games with interactive components, such as tokens or figurines that have status changes or use LEDs may make use of the harvested power. Appliances like coffee makers could be implemented to get a “personal coffee” out of a brewer, and more. 
         [0038]      FIG. 2  illustrates a power harvesting apparatus  200  in accordance with embodiments described herein. Additional electronic components (e.g. voltage converter, voltage-regulator, micro-controllers, sensors, LEDs, battery-charger, etc.) that can be used on a label, tag, or other RFID/NFC device require more power than used by the RFID-IC  105 , and may make use of the power harvesting apparatus  200 . The power harvesting apparatus  200  includes a rectification circuit  270  to convert AC to DC to power a load(s)  280 . The RF-input-voltage of the rectification circuit  270  in the power harvesting apparatus  200  may be high to compensate internal losses of the receiving antenna-coil  230  and the voltage-drop(s) across the rectification circuit  270 . In idle-mode (without a load after rectification) the output-voltage across an output capacitor  275  could climb very high (e.g. &gt;30 V). 
         [0039]    For the power harvesting apparatus, several rectification technologies may be used. One challenge to ordinary circuits is a high operation frequency. Mains frequencies are in the range of 50 or 60 Hz. For RFID/NFC circuits, a frequency of 13.56 MHz is specified. Resonance adjustment of the power harvesting apparatus  200  could be managed in several ways such as a parallel-capacitor method using a parallel capacitor  235 . Output capacitor  275  is a storage capacitor and may be used to keep the rectified voltage above a lower voltage limit of electronic circuitry during RF reception. 
         [0040]    There is also a series-capacitor method that may use capacitors  250 ,  255 ,  260 , and/or  265  in combination with the parallel capacitor  235  in different combinations. This method could be split into a symmetrical method using, e.g. capacitors  255  and  265  or an asymmetrical method using, e.g., capacitors  255  or  265  only). 
         [0041]    The parallel-capacitor method and the series-capacitor method could be combined. In that case the series-capacitor(s)  250  and  260  could be placed before the parallel-capacitor  235 . Capacitors  250  and  260  could be used for symmetrical operation. Capacitor  250  or  260  for asymmetrical. In implementation, all series capacitors  250 ,  255 ,  260 , and  265  could be used in combination with parallel capacitor  235 . 
         [0042]    The RFID apparatus  100  and power harvesting apparatus  200  may operate in a configuration with two separate antenna-coils  130  and  230 . The standalone RFID apparatus  100  and power harvesting apparatus may be connected at the VSS  135  of the RFID apparatus  100  to a GND line (not illustrated) of the electronic load(s)  280 . In such a case there is no cross-current between nodes VSS  135  and the GND of the load(s)  280  when they are not positioned near the antenna-coils  130  and  230 . For data exchange or communication between RFID apparatus  100  and power harvesting apparatus  200 , an additional communication line is needed. This may create residual current flow between the RFID apparatus  100  and power harvesting apparatus  200 , depending on what else is connected. 
         [0043]    This residual current may reduce efficiency and performance because the current does not contribute to power harvesting. A residual current might work at one half-wave (e.g. the positive half-wave) but it could work poorly or not work at all at the other half-wave (e.g. negative half-wave). The residual current could interfere with RFID communication as well. 
         [0044]      FIG. 3  illustrates a power harvesting apparatus  300  including an RFID-IC  305 , antenna coil  315 , symmetrical capacitive RF-voltage divider, symmetrical series capacitors, and bridge rectification in accordance with embodiments described herein. The power harvesting apparatus  300  may combine RFID with RF-power harvesting by having multiple connections between the two apparatuses. In embodiments described herein, by sharing one antenna-coil there can be multiple galvanic and electrical connections between an RFID apparatus  100  and a power harvesting apparatus  200 . 
         [0045]      FIG. 3  illustrates three series capacitors  340 ,  350 , and  360 , which separate the different voltage levels used for a RFID-IC  305  within the power harvesting apparatus  300 , using a voltage divider. The capacitors  340  and  360  may reduce the high voltage received at nodes  301  and  302  for power harvesting, allowing RF to pass, which may be used for RFID-IC  305  powering and communication at lower voltage levels. As illustrated in  FIG. 3 , using a shared antenna coil  315 , there is only one galvanic connection used to provide low power to the RFID-IC  305  higher power to an electronic load(s)  380  of the power harvesting apparatus  300 . 
         [0046]    The RFID-IC  305  may use on-chip electronics to convert AC power received via shared antenna coil  315  and capacitor  350  into small direct current (DC) voltages. The RFID-IC  305  has a node  325  to connect to a data bus or the like, which may connect to a node  318  of load(s)  380 . Node  325  may have several uses such as a low power voltage output, an open-drain pin, or a bus with SCL (Serial CLock) and SDA (Serial DAta). In other embodiments, node  310  or  320  may act as a supply input for the RFID-IC  305  when a battery is used and RF is switched off. In these various instances the RFID-IC  305  uses a reference V SS  (ground) node  335  that may be connected to other power harvesting apparatus  300  components. In general, the power harvesting apparatuses  300 , and RFID-IC  305  may operate when no current flows across RFID-IC  305  node V SS    335 , or if a little cross-current flows in or out of VSS node  335 , or from elsewhere. Symmetrical configurations as discussed herein may be used for data communications between nodes  325  and  318 . 
         [0047]    Energy received through the shared antenna coil  315  may be stored in the capacitors  340 ,  350 ,  360 ,  355 , and  365  as a DC voltage. The power harvesting apparatus  300  includes a rectification circuit  370  which may be, for example, a bridge rectifier also known as a full-wave rectifier that converts AC to DC. The rectification circuit  370  may include a plurality diodes, connected in a bridge configuration. Other diodes that may be used include Schottky diodes, fast silicon rectifiers having a short reverse recovery time characteristic, and small signal universal diodes. In the rectification circuit  370 , inputs for RF-voltage are at nodes  371  and  372 , and rectified output are at nodes  373  and  374 . The rectified output at nodes  373  and  374  is smoothed into a DC output by the output capacitor  375 . For power harvesting a full-wave-rectifier has excellent efficiency, though embodiments described herein are not limited to these types of rectifiers. 
         [0048]    The chain of capacitors  340 ,  350 , and  360  has multiple purposes. One purpose is a capacitive voltage divider. This divider reduces the high RF-voltage from the shared antenna coil  315  down to a lower RF-voltage across the IC-nodes  310  and  320 . In a second purpose, an incoming RF-communication passes the capacitors  340  and  360  in a same ratio as input voltage is reduced. A third purpose, this chain of capacitors  340 ,  350 , and  360  becomes a collective parallel capacitor, similar to parallel capacitor  235  illustrated in  FIG. 2 , which may be a resonant capacitor as later described in Equation 3 and elsewhere, to adjust a resonance frequency of a receive side of the power harvesting apparatus  300 . 
         [0049]    The series-capacitors  355  and  365  to the rectification circuit  370  may be arranged symmetrically, using both capacitor  355  and capacitor  365 , or asymmetrical using either capacitor  355  or capacitor  365  (illustrated in  FIG. 4A  for example with capacitor  455 ). Capacitors  340 ,  350 , and  360  may be used as a voltage divider as capacitors are relatively lossless when used in this capacity. 
         [0050]    Once a carrier frequency is determined to communicate with the RFID-IC  305 , various component values can be determined for the capacitors in the power harvesting apparatus  300 . 
         [0051]    For example, the combination circuit may be defined to work at a defined frequency (target of 13.56 MHz). The value of an effective resonance capacitor (C eff ) may be determined. Equation 1 may be derived for frequency calculation: 
         [0000]    
       
         
           
             
               
                 
                   f 
                   = 
                   
                     1 
                     
                       2 
                       · 
                       π 
                       · 
                       
                         
                           L 
                           · 
                           
                             ( 
                             
                               
                                 C 
                                 eff 
                               
                               + 
                               
                                 k 
                                 · 
                                 
                                   C 
                                   s 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0052]    Cs represents de-coupling low-ohm rectification circuit  370  and load(s)  380  circuitries and making a series resonance circuit therewith. Cs is not 100% in parallel to the antenna-coil, and therefore k is the reduction ratio. 
         [0053]    To determine a value of C eff , an antenna-inductance (L), frequency (f) and Cs are given, and k is estimated. By solving for C eff , a value may be obtained. 
         [0000]    
       
         
           
             
               
                 
                   
                     C 
                     eff 
                   
                   = 
                   
                     
                       1 
                       
                         L 
                         · 
                         
                           
                             ( 
                             
                               2 
                               · 
                               π 
                               · 
                               f 
                             
                             ) 
                           
                           2 
                         
                       
                     
                     - 
                     
                       k 
                       · 
                       
                         C 
                         s 
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0054]    Using the elements of the power harvesting apparatus  300 , and taking C_IC to be the capacitance of the RFID-IC  305 , C 1  to be the capacitance of capacitor  350 , C 2  to be the capacitance of capacitor  340 , and C 3  to be the capacitance of capacitor  360 , C eff  can be further defined as: 
         [0000]    
       
         
           
             
               
                 
                   
                     C 
                     eff 
                   
                   = 
                   
                     1 
                     
                       
                         1 
                         
                           C 
                           2 
                         
                       
                       + 
                       
                         1 
                         
                           
                             C 
                             IC 
                           
                           + 
                           
                             C 
                             1 
                           
                         
                       
                       + 
                       
                         1 
                         
                           C 
                           3 
                         
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
         [0055]    The capacitance of the RFID-IC  305  in equation 3 may be given by data sheet. Various combinations of C 1 , C 2  and C 3  would fulfill the requirement of equation 3. Capacitor value relationships may be based on several factors, such as the voltage drops across the capacitors. 
         [0056]    Assuming the output voltage across an output capacitor  375  (respectively node  373  to node  374  may be 7.4 V DC ). Next assume the voltage drop over the rectification circuit  370  (e.g. 2 Schottky diodes in series for each half-wave of the bridge-rectifier) is 2 times 0.3 V, which means the voltage across node  371  and node  372  is 8.0 V RMS  at maximum. By assuming to have a sine wave-shape there is 22.6 volts peak-to-peak across the antenna-coil. 
         [0057]    The behavior inside of the RFID-IC  305  from IC node  310  to Vss is different than from node  320  to V SS . This difference may cause a delta-voltage of 0.4 V, for example. For an ordinary application capacitors  340  and  360  could have the same value. For TOP-power harvesting it is recommended to calculate the voltage drops across all three capacitors  340 ,  350 , and  360  to get a highest possible efficiency, measured in a minimum of losses. A target is to have no current flowing out of or into the V SS  node  335 . In this condition a current flows through capacitor  340 , capacitor  350  in parallel with C_IC, and capacitor  360 , without any current at the V SS  node  335 . 
         [0058]    The impedance of a capacitor is calculated by Equation 4: 
         [0000]    
       
         
           
             
               
                 
                   
                     X 
                     C 
                   
                   = 
                   
                     1 
                     
                       2 
                       · 
                       π 
                       · 
                       f 
                       · 
                       C 
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
         [0059]    Applied to the capacitive voltage-divider, for each capacitor the voltage across it could be calculated. The labeling of voltages in the following equations are in accordance to the power harvesting apparatus  300 , for example. 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     
                       C 
                       2 
                     
                   
                   = 
                   
                     
                       V 
                       
                         
                           node 
                            
                           
                               
                           
                            
                           _ 
                            
                           
                               
                           
                            
                           301 
                         
                         - 
                         302 
                       
                     
                      
                     
                       
                         C 
                         eff 
                       
                       
                         C 
                         2 
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   5 
                 
               
             
             
               
                 
                   
                     V 
                     
                       
                         C 
                         IC 
                       
                       // 
                       
                         C 
                         1 
                       
                     
                   
                   = 
                   
                     
                       V 
                       
                         
                           node 
                            
                           
                               
                           
                            
                           _ 
                            
                           
                               
                           
                            
                           301 
                         
                         - 
                         302 
                       
                     
                      
                     
                       
                         C 
                         eff 
                       
                       
                         
                           C 
                           IC 
                         
                         + 
                         
                           C 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   6 
                 
               
             
             
               
                 
                   
                     V 
                     
                       C 
                       3 
                     
                   
                   = 
                   
                     
                       V 
                       
                         
                           node 
                            
                           
                               
                           
                            
                           _ 
                            
                           
                               
                           
                            
                           301 
                         
                         - 
                         302 
                       
                     
                      
                     
                       
                         C 
                         eff 
                       
                       
                         C 
                         3 
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   7 
                 
               
             
           
         
       
     
         [0060]      FIG. 4A  illustrates another power harvesting apparatus  400  including an RFID-IC  405 , antenna coil  415 , asymmetrical capacitive RF-voltage divider, a single asymmetrical series-capacitor, and rectification circuitry  470  such as a bridge rectifier in accordance with embodiments described herein.  FIG. 4A  illustrates a reduction in the number of capacitors as compared to other embodiments. As illustrated in  FIG. 4A , a reduction in capacitors may produce an asymmetrical behavior and a reduction an amount of power that is harvested, if desirable for a given output load. Because of a reduction of capacitors in this manner to produce an asymmetrical arrangement, cross currents in the power harvesting apparatus  400  may increase which may lead to signal interference between an RFID-IC  405  and a load(s)  480 . In this embodiment, an RFID-IC  405  may not have a data connection with a load(s)  480 , to avoid the cross currents. Output capacitor  475  is a capacitor and may be used to keep the rectified voltage above a lower voltage limit of electronic circuitry during RF reception. 
         [0061]    As illustrated in  FIG. 4A , an RFID-IC  405  is connected in parallel with capacitor  450 , which becomes a voltage source for the RFID-IC  405 . With capacitor  450  powering the RFID-IC  405 , the voltage available to the load(s)  480  is decreased and may only be stored in capacitors  440  and  455 , and rectified by rectification circuitry  470 . 
         [0062]      FIG. 4B  illustrates another power harvesting apparatus  425  including an RFID-IC  405 , antenna coil  415 , asymmetrical capacitive RF-voltage divider, an asymmetrical series-capacitor, and a half wave voltage doubling circuit  471  in accordance with embodiments described herein. 
         [0063]      FIG. 4B  differs from  FIG. 4A  in that the rectification circuit may be a half wave voltage doubling circuit  471 . The use of this half wave doubling circuit  471  may change the series capacitance value of capacitor  456  and may change a value of capacitor  476  and Vout as well. 
         [0064]      FIG. 5A  illustrates yet another power harvesting apparatus  500  including an RFID-IC  505 , a multiple tap antenna coil  515 , symmetrical series-capacitors  555  and  565 , and two half-wave voltage rectifier pairs  571  and  572  in parallel in accordance with embodiments described herein. Using the multiple tap antenna coil  515  allows different voltages to be used without a capacitive RF-voltage divider. The power harvesting apparatus  500  uses a single capacitor  545  in parallel, for fine tuning or resonance frequency adjustment, with the multiple tap antenna coil  515  and the RFID-IC  505 . 
         [0065]    As illustrated in  FIG. 5A , the multiple tap antenna coil  515  has multiple taps  0 ,  1 ,  2 ,  3 , and  4 , from which various lengths of multiple tap antenna coil  515  may be selected to generate different voltage levels in the RFID-IC  505  and in the capacitors  555  and  565 . For example, the RFID-IC  505  may use taps  1  and  2  to receive a certain AC voltage across the multiple tap antenna coil  515  to obtain a required voltage across capacitor  545  in parallel with the RFID-IC  505  for proper operation. The harvesting circuitry may use taps  3  and  4  to garner a larger segment of antenna to produce higher voltages in capacitors  555  and  565 . Thus the multiple tap antenna coil  515  is able to deliver different voltages for the RFID-IC and for power harvesting to separate the RFID-IC  505  from the rest of the power harvesting apparatus  500 . By delivering different voltages in this manner, the RFID-IC  505  is spared the larger voltages and currents used by the load(s)  580 , and multiple circuits with different power requirements may be implemented in the power harvesting apparatus  500 . 
         [0066]    To manage different voltages used by the RFID-IC  505  at pin  510  relative to ground, and pin  520  relative to ground, the multiple taps of the multiple tap antenna coil  515  may not be symmetrical in relation to the center tap  0 , and may be offset by a predetermined voltage as discussed herein. This non-symmetrical behavior is compensable by shifting the taps  1  and  2  to  1   a  and  2   a  as illustrated in  FIG. 5A . Asymmetry is then compensated by another asymmetry, or a “shift” could be to compensated by an offset which was caused from an asymmetry. As illustrated in  FIG. 5A , both series capacitors  555  and  565  are used. 
         [0067]    The RFID-IC  505  may have node  530  (as described above in reference to  FIG. 3 ) to connect to a data bus or the like, which may connect to a node  518  of load(s)  580 . 
         [0068]    The power harvesting apparatus  500  including an RFID-IC illustrated in  FIG. 5A  may include a two half-wave voltage doubling rectification circuit  570  including half-wave rectifier pairs  571  and  572 . For this kind of rectification, the multiple tap antenna coil  515  may be extended to tap  3  and tap  4  and the center tap  0  may be connected to ground. In this configuration, a reduction of series-capacitors to one instead of two is possible. A strong “cross current” may arise, and outputs  535  and  530  may be interrupted because of strong asymmetry. Thus, in embodiments described herein, asymmetry may be used when no data is exchanged. 
         [0069]      FIG. 5B  illustrates another power harvesting apparatus  525  including an RFID-IC  505 , a multiple tap antenna coil  515 , and a double half wave rectification circuit  573  in accordance with embodiments described herein. The power harvesting apparatus  525  may be implemented without a capacitive RF-voltage divider and without symmetrical series capacitors. 
         [0070]    As illustrated in  FIG. 5B , without the use of series capacitors, the multiple taps antenna may operate without the coil tap  4 , resulting in a reduction in antenna coil size. A smaller number of diodes may be used for one wave rectification, reducing current and power by half. 
         [0071]      FIG. 5C  illustrates another power harvesting apparatus  550  including an RFID-IC  505 , a multiple tap antenna coil  515 , symmetrical series-capacitors  556  and  566 , bridge rectification  574 , and dual (positive/negative) output-voltages in accordance with embodiments described herein. The power harvesting apparatus  550  may be implemented without a capacitive RF-voltage divider. 
         [0072]      FIG. 5C  illustrates a power harvesting apparatus having an antenna-coil and bridge-rectification for positive and negative output voltages in accordance with embodiments described herein.  FIG. 5C  illustrates an output scheme for a power harvesting apparatus  550  that differs from power harvesting apparatus  500  in that V OUT  may be taken as dual output voltages V POS  and V NEG  across capacitors  576   a  and  576   b.    
         [0073]    In accordance with embodiments described herein, using different rectification circuitry may change the series capacitance values and voltage handling capabilities of the power harvesting apparatuses. The various embodiments described herein could be used for different applications such as higher or lower voltage, higher or lower output current, higher or lower power, less read-sensitivity versus the opposite, and so on. 
         [0074]    Regarding power harvesting apparatus  550  illustrated in  FIG. 5C , series capacitors  556  and  566  may be omitted. This arrangement would cause a reduction in power harvesting and less of a read range. 
         [0075]    In a multi-tap arrangement of multiple tap antenna coil  515 , a center-tap  0  of the multiple tap antenna coil  515  may be connected to ground. Using the multiple tap antenna coil  515 , voltage divider capacitors are not used. 
         [0076]    In accordance with embodiments described herein, the capacitor that is parallel to the RFID-IC is the frequency adjustment/fine tuning component. As illustrated in  FIG. 5C , having a positive output voltage and a negative voltage may be useful for special operational amplifiers and other circuits. When a positive and negative output are used, two capacitors  576   a  and  576   b  may be used. 
         [0077]      FIG. 5D  illustrates another power harvesting apparatus  575  including an RFID-IC  505 , a multiple tap antenna coil  515 , symmetrical series-capacitors  557  and  567 , two half wave voltage doubling circuits  577  and  578  in series, and dual (positive/negative) output-voltages in accordance with embodiments described herein. The power harvesting apparatus  575  may be implemented without a capacitive RF-voltage divider. 
         [0078]    As illustrated in  FIG. 5D , instead of a bridge rectifier as illustrated in  FIG. 5C , for example, a positive half-wave voltage doubling circuit  577  having diodes  591  and  592  such as Zener diodes or others as described herein, and a negative half-wave voltage doubling circuit  578  having diodes  593  and  594  such as Zener diodes or others as described herein for voltage limitation in rectification circuitries. The overall rectification circuit may be denoted  590 . To produce a dual voltage output as illustrated, series capacitors  557  and  567  are used. In comparison to other embodiments such as the one illustrated in  FIG. 5A , the power harvesting apparatus  575  may produce a higher voltage, less current, and little impact to the read-range of the apparatus. 
         [0079]      FIGS. 6A and 6B  illustrate respective power harvesting apparatuses  600  and  625  including an RFID-ICs in accordance with embodiments described herein.  FIG. 6A  may use  FIG. 3  as a basis, replacing capacitors  340  and  360  with resistors  640  and  660 .  FIG. 6B  may use  FIG. 4A  as a basis, replacing capacitor  440  with resistor  641 . 
         [0080]      FIGS. 6A, 6B and 6C  illustrate respective power harvesting apparatuses  600 ,  625 , and  650  including an RFID-IC  605  in accordance with embodiments described herein. As illustrated, the capacitive voltage divider could be replaced with a resistive voltage divider using resistors  640  and  660 , for example in  FIG. 6A . In  FIG. 6A , for power harvesting apparatus  600 , when connecting a signal from node  630  of the RFID-IC  605  to a node  618  of a load(s), symmetrical capacitors  655  and  665  may be used. Rectifier  670  may convert AC voltage and current to DC to voltage and current to be used by load(s)  680 . 
         [0081]    In another power harvesting apparatus  650  illustrated in  FIG. 6B , when RFID-IC  605  does not communicate with the load(s)  680 , a single capacitor  656  may be used in an asymmetrical configuration. The value of capacitor  656  of  FIG. 6B  may be half of the combined capacitor values of  655  and  665  of  FIG. 6A , when the value of capacitor  655  equals the value of capacitor  665 . 
         [0082]      FIG. 6C  illustrates another power harvesting apparatus  650  including an RFID-IC  605  in accordance with embodiments described herein.  FIG. 6C  may be based on  FIG. 4B , where the capacitor  440  of the RF-voltage divider is replaced by the resistor  641 . In  FIGS. 4B and 6C , bridge rectification circuits may be replaced by one half-wave voltage doubling circuit. 
         [0083]    As illustrated in  FIG. 6C , when RFID-IC  605  does not communicate with the load(s)  680 , the bridge rectification is replaced by one half-wave voltage doubling circuit, and a single capacitor  657  with a slight change in capacitance from capacitor  656  may be used in an asymmetrical configuration. For the embodiments of  FIG. 6B  and  FIG. 6C , respective series capacitors  656  and  657  may be omitted, but with a drop in RFID-performance. 
         [0084]    Although the various embodiments have been described in detail with particular reference to certain aspects thereof, it should be understood that the embodiments described herein are capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be effected while remaining within the spirit and scope of the embodiments described herein. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the embodiments described herein, which is defined only by the claims.