Abstract:
A near field communication (NFC) device operating in a tag emulator mode, including a controller to output a control signal to control operation of a transistor, a waveform shaper to shape the control signal and to generate a shaped signal by increasing a rise time and a fall time of the control signal, and the transistor to receive the shaped signal and to output a switching waveform to drive an antenna of the NFC device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the design of a Tag block of an NFC (near field communication) device. Circuitry in the Tag block detects a magnetic field output by a Reader block included in another NFC device, and demodulates the magnetic field to establish communication with the Reader block included in the another NFC device. 
         [0003]    2. Background Art 
         [0004]      FIG. 1A  shows a conventional communication system  100  including two NFC devices  110 ,  120  for communicating with each other. NFC device  110  includes a Reader block  114  and the NFC device  120  includes a Tag block  122 , along with other supporting circuitry (not shown). The communication between the NFC devices  110 ,  120  is initiated when an antenna driver included in a Reader block drives an antenna of one of the NFC devices to output a magnetic field that can power a Tag block included in the other NFC device. The communication is established when the powered Tag block modulates the magnetic field with a communications signal and transmits the modulated signal to the Reader block. For example, to initiate communication, the Reader block  114  includes an antenna driver that drives an antenna associated with the NFC device  110  to output a magnetic field that powers the Tag block  122  included in the NFC device  120 . The communication is established when the Tag block  122  is powered by the output magnetic field, and when Tag block  122  modulates the magnetic field with a communications signal and transmits the modulated signal back to Reader block  114 . 
         [0005]    Alternatively, in the communication system  150  illustrated in  FIG. 1B , the NFC device  110  may communicate with a Radio-Frequency Identification (RFID) device. The RFID device  130  includes a Tag  134  and other supporting circuitry (not shown). The communication between the NFC device  110  and the RFID device  130  is similar to the communication between the NFC device  110  and the NFC device  120  discussed above. In particular, to initiate communication, the Reader block  114  includes an antenna driver that drives an antenna associated with the NFC device  110  to output a magnetic field that powers the Tag block  134  included in the RFID device  130 . The communication is established when the Tag block  134  is powered by the output magnetic field, and when Tag block  134  modulates the magnetic field with a communications signal and transmits the modulated signal back to Reader block  114 . The RFID device  130  can be similar to a RFID device according to ISO 14443, ISO 15693, or a contactless RFID smart card. The NFC device  120  and the RFID  130  function in a tag emulator mode while communicating with the NFC device  110 . 
         [0006]      FIG. 2  shows a conventional topology of a Tag block included in the NFC devices  110 ,  120  or the RFID  130 . In this conventional topology, the Tag block  122 ,  134  includes a linear shunt regulator. In particular, the Tag block  122 ,  134  includes an antenna  200 , a field effect transistor (FET)  201 , rectifying diodes  202 ,  203 , a capacitor  203 , and an error amplifier  205 . The antenna  200  detects the output magnetic field and provides a differential pair of signals  210 ,  212 , which are rectified by rectifying diodes  202 ,  203 . The rectified output  214  is then compared by the error amplifier  205  with a reference signal (Ref). Based on the results of the comparison, the error amplifier  205  outputs signal  216  to adjust the operation of the FET  201 , which is functioning as the shunt regulator. Upon receiving signal  216 , the FET  201  regulates and clamps the waveform which drives the antenna  200 . However, when the FET  201  regulates and clamps the waveform, the FET  201  dissipates a lot of energy (by sinking current) and thereby distorts the waveform. The distortion of the waveform which drives the antenna  200  results in undesired out-of band emissions which interfere with other peripheral radio communication. Therefore, in summary, the conventional topology of the Tag block  122 ,  134  using a linear shunt regulator is inefficient for dissipating a lot of power and results in undesirable out-of-band emission. The NFC device  110  may include a Tag block, and each of the NFC device  120  and the RFID device  130  may include a Reader block. 
         [0007]    To resolve the inefficiencies of the conventional linear shunt topology shown in  FIG. 2 , it has been suggested that a class-D amplifier configuration be used to drive the antenna  200 . This configuration is shown in  FIG. 3A . 
         [0008]    The class-D amplifier configuration includes an antenna  300 , differential signals  310 ,  312 , P-FETs  301 ,  303  and N-FETs  302 ,  304  connected in the class-D configuration, a controller  305 , and other supporting circuitry (not shown). The P-FETs  301 ,  303  are connected to a source V DD  and the N-FETs  302 ,  304  are connected to ground. In this configuration, the FETs  301 ,  302 ,  303 ,  304  are switched on and off to output the switching waveform that drives the antenna  300 . Since the FETs are switched on and off as opposed to linearly regulating a FET as shown in  FIG. 2 , this switching configuration is more efficient because is does not sink a lot of current. However, as shown in  FIG. 3B , the switching on and off of the FETs  301 ,  302 ,  303 ,  304  using signals  314 ,  316  is very abrupt. This abrupt switching on and off significantly distorts the switching waveform which drives the antenna  300 , and thereby exacerbates the out-of-band emissions. 
         [0009]    In particular, as shown in  FIG. 3B , the abrupt switching of signals  310 ,  312  causes overshoots and undershoots in the switching waveforms  310 ,  312  which drive the antenna  300 . This is because of the variations in the average impedance across the antenna  300 , leading to out-of-band emissions. Further, the harmonics of these overshoots and undershoots exacerbate the undesired out-of-band emissions. Therefore, the conventional class-D amplifier configuration is impractical because it exacerbates the undesired out-of-band emissions. 
         [0010]    As such, there is a need for a solution which minimizes the undesired out-of-band emissions without dissipating a lot of power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
           [0012]      FIG. 1A  illustrates a block diagram of a conventional communication system  100  including NFC devices  110 ,  120 . 
           [0013]      FIG. 1B  illustrates a block diagram of a conventional communication system  150  including an NFC devices  110  and a RFID device  130 . 
           [0014]      FIG. 2  illustrates a block diagram of a conventional Tag block including a shunt regulator configuration in a NFC device  110 ,  120  or RFID device  130 . 
           [0015]      FIG. 3A  illustrates a block diagram of a conventional Tag block including a class-D amplifier configuration in a NFC device  110 ,  120  or RFID device  130 . 
           [0016]      FIG. 3B  illustrates a representation of input and output waveforms generated by the conventional Tag block illustrated in  FIG. 3A . 
           [0017]      FIG. 4A  illustrates an exemplary block diagram of a Tag block according to an embodiment of the present invention, 
           [0018]      FIG. 4B  illustrates an exemplary representation of input and output waveforms generated by the Tag block illustrated in  FIG. 4A  according to an embodiment of the present invention. 
           [0019]      FIG. 5  illustrates an exemplary configuration of a waveform shaper according to an embodiment of the present invention 
       
    
    
       [0020]    The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number. 
       DETAILED DESCRIPTION 
       [0021]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to lost effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the invention. 
         [0022]    References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
         [0023]    As discussed above, the conventional configurations of the Tag block  122 ,  134  are unable to minimize the undesired out-of-band emissions without dissipating a lot of power. The present invention minimizes the undesired out-of-band emissions without dissipating a lot of power, as shown in  FIG. 4A . 
         [0024]    The inventive configuration of the Tag block includes an antenna  400  having differential signals  410 ,  412 , P-FETs  401 ,  403  and N-FETs  402 ,  404  forming the class-D amplifier configuration, shaped signals  414 ,  416 ,  418 ,  420 , the waveform shaper  406 , controller signals  422 ,  424 , the controller  405 , rectifying diodes  407 ,  408  to output a rectified signal  426 , and a capacitor  409 . 
         [0025]    The antenna  400  detects the magnetic field output by a Reader block of another NFC device, and provides differential signals  410 ,  412 . These differential signals  410 ,  412  are rectified by rectifying diodes  407 ,  408  to produce the rectified signal  426 . The rectified signal  426  is received by the controller and compared to a reference signal  428 . The reference signal is associated with a strength of the magnetic field detected by the antenna  400 . In particular, the controller  405  compares the rectified signal  426  with the reference signal to determine a desired peak-to-peak voltage of the switching waveform that drives the antenna  400 . This determination assists in modulating the phase and/or the amplitude and/or the frequency of the carrier of the detected magnetic field in accordance with the measured strength of the detected magnetic field. Based on the results of the comparison, the controller  405  outputs a set of controller signals  422 ,  424  to turn on and off the FETs  401 ,  402 ,  403 ,  404 . The controller signals  422 ,  424  are generated as PWM signals having desired pulse widths (duty cycle) based on the strength of the magnetic field detected by the antenna  400 . Further, controller signals  422 ,  424  are mirror images of each other. 
         [0026]    The controller signals  422 ,  424  are provided to the waveform shaper  406 . The waveform shaper  406  processes the controller signals  422 ,  424  (as discussed below) to generate shaped signals  414 ,  416 ,  418 ,  420 , which turn on and off the FETs  401 ,  402 ,  403 ,  404  respectively. Now, because the signals which turn on and off the FETs are shaped, these signals linearly turn on and linearly turn off the FETs. In other words, the class-D amplifier FETs  401 ,  402 ,  403 ,  404  are smoothly turned on and off, thereby eliminating the abrupt switching on and off of the same. In one embodiment, the waveform shaper  406  shapes the control signals by increasing a rise time and a fall time of the control signal. As one can appreciate, the undesired overshoots and undershoots do not occur due to elimination of the abrupt switching. 
         [0027]      FIG. 4B  shows an exemplary graph of the effect of the shaped signals on the switching waveform which drives the antenna  400 . As shown in  FIG. 4B , the shaped signals  414 ,  416 ,  418 ,  420  enable the FETs  401 ,  402 ,  403 ,  404  to turn on and off smoothly. This results in an equivalent transition of the switching waveform which drives the antenna  400 . As such, the undesired overshoots and undershoots, and the resulting undesired out-of-band emissions, are minimized and/or eliminated. In this way, the present invention enables the minimization of the undesired out-of-band emissions without dissipating a lot of power. 
         [0028]    Now, the process/method of driving the antenna  400  starts with providing the controller signals  422 ,  424  to the waveform shaper  406 . In particular, control signal  422  is provided to control the P-FET  401  and N-FET  402 , and the control signal  424  is provided to control P-FET  403  and N-FET  404 . 
         [0029]      FIG. 5  shows an exemplary configuration of the waveform shaper  406  according to an embodiment of the present invention. The waveform shaper  406  includes inverting amplifiers  501 ,  502 ,  503 ,  504  (shown as inverting gates for simplicity), P-FETs  511 ,  513 , N-FETs  512 ,  514 , resistors  521 ,  522 ,  523 ,  524 , inverting amplifiers  531 ,  532 ,  533 ,  534  (shown as inverting gates for simplicity), multipliers  541 ,  542 ,  543 ,  544 , and feedback resistors  551 ,  552 ,  553 ,  554 . 
         [0030]    The controller signal  422  is provided as the input to inverting amplifiers  501 ,  502 . The outputs of the inverting amplifiers are provided to FETs  511 ,  512  to generate a voltage waveform based on a process and/or voltage and/or temperature match with respect to the FET  401 ,  402  whose operation is being controlled by the respective shaped signal  414 ,  416 . The FETs  511 ,  512  modulate the output of the inverting amplifiers  501 ,  502 , to generate voltage waveforms in accordance with the type of FETs  401 ,  402  being controlled. For example, because shaped signal  414  controls the P-FET  401 , FET  511  used to generate shaped signal  414  should be a P-FET. Likewise, because shaped signal  416  controls N-FET  402 , FET  512  used to generate shaped signal  416  should be an N-FET. 
         [0031]    The signals generated by the FETs  511 ,  512  are input to inverting amplifiers  531 ,  532 . The outputs of the inverting amplifiers  531 ,  532  are provided to multipliers  541 ,  542  respectively. The multipliers multiply the outputs of the inverting amplifiers  531 ,  532  with the outputs themselves to generate square functions of the same. The square functions are then provided as inputs to inverting amplifiers  531 ,  532  via feedback resistors  551 ,  552 . The inverting amplifiers then invert the square functions by performing a function inverse to a square function, and output shaped signals  414 ,  416  to smoothly turn on and off the switching FETs  401 ,  402 . 
         [0032]    Controller signal  424  is processed in a similar way to output shaped signals  418 ,  420  which smoothly turn on and off FETs  403 ,  404  respectively. 
         [0033]    Therefore, by shaping the signals used to switch on and off the FETs that output the switching waveform to drive the antenna, undesired out-of-band emissions are minimized. The above inventive configuration of the Tag block including the waveform shaper allows co-existence of other radio communication around the Tag block. 
         [0034]    Although, the description of the present invention is to be described in terms of NFC, those skilled in the relevant art(s) will recognize that the present invention may be applicable to other communications that use the near field and/or the far field without departing from the spirit and scope of the present invention. For example, although the present invention is to be described using NFC capable communication devices, those skilled in the relevant art(s) will recognize that functions of these NFC capable communication devices may be applicable to other communications devices that use the near field and/or the far field without departing from the spirit and scope of the present invention. 
         [0035]    It is to be appreciated that the Detailed Description section, and not the Abstract section, is intended to be used to interpret the claims. The Abstract section may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, is not intended to limit the present invention and the appended claims in any way. 
         [0036]    The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. 
         [0037]    The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 
         [0038]    It should be noted that any exemplary processes described herein can be implemented in hardware, software, or any combination thereof. For instance, an exemplary process described herein can be implemented using computer processors, computer logic, application specific circuits (ASICs), digital signal processors (DSP), etc., as will be understood by one of ordinary skill in the arts based on the discussion herein. 
         [0039]    Moreover, the exemplary process can be embodied by a computer processor or any one of the hardware devices listed above. The computer program instructions cause the processor to perform the signal processing functions described herein. The computer program instructions (e.g., software) can be stored in a computer useable medium, computer program medium, or any storage medium that can be accessed by a computer or processor. Such media include a memory device such as a computer disk or CD ROM, or the equivalent. Accordingly, any computer storage medium having computer program code that causes a processor to perform the functions described herein are with the scope and spirit of the present invention. 
         [0040]    The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.