Patent Publication Number: US-2021174158-A1

Title: Method and apparatus for transmitting data via nfc for mobile applications inlcuding mobile payments and ticketing

Description:
CLAIM FOR PRIORITY 
     This application is a continuation of, and claims the benefit of priority to U.S. patent application Ser. No. 16/791,609, filed Feb. 14, 2020, which is a continuation of, and claims the benefit of priority to U.S. patent application Ser. No. 16/393,275, filed Apr. 24, 2019, now issued on Mar. 31, 2020 as U.S. Pat. No. 10,607,129, which is a continuation of, and claims the benefit of priority to U.S. patent application Ser. No. 15/904,328, filed on Feb. 24, 2018, now issued on Jun. 11, 2019 as U.S. Pat. No. 10,318,855, which is a continuation of, and claims the benefit of priority to U.S. patent application Ser. No. 15/338,436, filed Oct. 30, 2016, now issued on Feb. 27, 2019, as U.S. Pat. No. 9,904,887, which is a continuation of, and claims the benefit of priority to U.S. patent application Ser. No. 14/517,585, filed Oct. 17, 2014, now issued on Nov. 8, 2016, as U.S. Pat. No. 9,489,608, which is a continuation of, and claims priority to U.S. patent application Ser. No. 14/460,647, filed Aug. 15, 2014, now issued on Jan. 20, 2015, as U.S. Pat. No. 8,937,549, which is a continuation of, and claims the benefit of priority to U.S. patent application Ser. No. 13/871,849, on Apr. 26, 2013, now issued on Oct. 21, 2014, as U.S. Pat. No. 8,866,614, which is a continuation of, and claims the benefit of priority to, U.S. patent application Ser. No. 13/038,341, filed Mar. 1, 2011, now issued on May 28, 2013, as U.S. Pat. No. 8,451,122, which is a continuation-in-part of, and claims the benefit of priority to U.S. patent application Ser. No. 12/188,346, filed Aug. 8, 2008, now issued on Jun. 14, 2011, as U.S. Pat. No. 7,961,101 and which are incorporated by reference in their entirety. 
    
    
     FIELD 
     The present invention relates generally to contactless communications devices, and more specifically to contactless smartcard devices. 
     BACKGROUND 
     RFID “tags” can be separated into two broad categories: active tags and passive tags. Active tags are characterized by a local power source such as a battery. Active tags generally transmit information by broadcasting on an RF carrier frequency of choice using a locally generated RF carrier. Active tags are typically used to transmit over long distances, often referred to as “far field communications” (FFC). Antennas used with active RFID tags tend to be large to allow for the communications over long distances. 
     Passive tags are not powered. Passive tags derive the energy needed to power the tag from an interrogating RF field, and use that energy to transmit response codes by modulating the impedance that the antenna presents to the interrogating field, thereby modulating the signal reflected back to the reader antenna. Passive tags are typically used to transmit over short distances, often referred to as “near field communications” (NFC). For example, passive tags operating at 13.56 MHz are typically designed to communicate with RFID readers a few centimeters away. 
     Passive tags are typically connected to “loop antennas.” One example of a loop antenna is shown in U.S. Pat. No. 6,568,600, issued to Carpier et al. on May 27, 2003 (the &#39;600 patent). The device described in the &#39;600 patent is recognizable as a “credit card sized” passive RFID card (more specifically, a card that conforms to ISO 7816 size requirements). The loop antenna is necessarily large because passive tags are powered using energy received by the antenna from signals transmitted by the RFID reader. 
       FIG. 12  shows a power supply voltage developed over time by rectifying a voltage induced in a loop antenna in the presence of an interrogating RF field. Once the power supply voltage reaches a critical value, the tag is powered up and can operate. As the antenna size is reduced, it takes longer for the power supply voltage to reach the critical value, and the tag operation may not meet response time specifications. Below a certain antenna size, the power supply voltage may never reach the critical value, and the tag may never power up. 
     Antenna design for RFID applications is described in a Microchip Technology, Inc. application note entitled “Antenna Circuit Design for RFID Applications” by Youbok Lee, Ph.D., published in 2003 (no month given). Dr. Lee&#39;s application note describes in great detail how to determine size requirements for a passive RFID tag antenna to operate at 13.56 MHz. On page 5 of the application note, Dr. Lee shows that the optimum radius of the loop antenna coil is equal to 1.414 times the required read range. This analysis confirms that for a read range on the order of a few centimeters, a credit card sized loop antenna can be made near optimal. 
     Passive tags are seeing widespread use in many applications. For example, mobile device manufacturers are embedding passive RFID tags in mobile devices for NFC applications. Example mobile applications include, but are not limited to, ticketing and mobile payments. U.S. Pat. No. 7,333,062 issued to Leizerovich et al. on Feb. 19, 2008 (the &#39;062 patent) shows a mobile phone with an integrated loop antenna for an NFC device. As shown in the &#39;062 patent, the mobile phone provides the real estate necessary to implement a loop antenna at 13.56 MHz. 
     There have been attempts to implement passive tags in smaller mobile devices. These attempts have met with limited success due in part to the size of the loop antenna. For example,  FIG. 13  shows an RFID tag implementation in a secure digital (SD) memory card manufactured by Wireless Dynamics, Inc. of Calgary, Alberta Canada. Card  1300  includes an antenna, but the SD card is significantly oversized as a result. Also for example, U.S. Patent Application Publication No.: US 2006/0124755 A1 shows a memory card having a passive tag, but the card must be inserted into a slot to access a loop antenna on a different device. In this implementation, mobile device real estate is still relied upon for loop antenna implementation. It can be seen, therefore, that the size of antennas are proving to be a barrier to further miniaturization of passive RFID tags. 
       FIG. 14  shows a prior art smartcard controller and antenna in combination. Smartcard controller  330  includes a contactless interface that includes two pads  1472  and  1474  intended for connection to a coil (antenna  1480 ). Smartcard controller  330  also includes bridge rectifier  1420  to rectify an alternating voltage present on pads  1472  and  1474  when antenna  1480  is inductively coupled to another device and in the presence of an interrogating RF field. Capacitor  1440  is typically tuned to create a resonant circuit at the frequency of interest (e.g., 13.56 MHz). When antenna  1480  is a large loop antenna, then bridge rectifier  1420  provides power to internal circuits as shown in  FIG. 12 . Demodulator  1430  demodulates data present in the interrogating RF field, and load modulation driver circuit  1410  modulates an impedance seen by the device presenting the interrogating RF field when the coil (antenna  1480 ) is inductively coupled to a separate device that is presenting the interrogating RF field. This creates a half-duplex communications path between the device presenting the interrogating RF field and smartcard controller  330 . Examples of smartcard controllers are the “SmartMX” controllers sold by NXP Semiconductors N.V. of Eindhoven, The Netherlands. 
     A need exists for a small footprint RFID tag that does not rely on an external device to house an antenna. A need also exists for a memory card compatible RFID tag that is compatible with standard memory card slots on mobile devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a mobile computing device and a small RFID card compatible with a memory card slot; 
         FIG. 2  shows a block diagram of a mobile computing device; 
         FIGS. 3A-3B  show block diagrams of memory card compatible RFID cards with integrated inductive elements; 
         FIG. 4  shows a memory card compatible RFID card with an integrated inductive element; 
         FIG. 5  shows a data portion of a memory card write command; 
         FIGS. 6-11  show flowcharts of methods in accordance with various embodiments of the present invention; 
         FIG. 12  shows a power supply voltage developed over time by rectifying a voltage induced in a loop antenna in the presence of an interrogating RF field; 
         FIG. 13  shows a prior art RFID tag implementation in a secure digital (SD) memory card; 
         FIG. 14  shows a prior art smartcard controller and antenna in combination; 
         FIG. 15  shows a smartcard controller with performance enhancement circuits including a load modulation driver circuit and a single antenna in accordance with various embodiments of the present invention; 
         FIG. 16  shows frequency spectrum used in RFID communications; 
         FIG. 17  shows a smartcard controller with performance enhancement circuits including a load modulation driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 18  shows frequency spectrum used in RFID communications; 
         FIG. 19  shows a smartcard controller with performance enhancement circuits including a load modulation driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 20  shows frequency spectrum used in RFID communications; 
         FIG. 21  shows a smartcard controller with performance enhancement circuits including an active transmit driver circuit and a single antenna in accordance with various embodiments of the present invention; 
         FIG. 22  shows a smartcard controller with performance enhancement circuits including an active transmit driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 23  shows a smartcard controller with performance enhancement circuits including an active transmit driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 24  shows a smartcard controller with a pad to provide digital data output; 
         FIG. 25  shows a smartcard controller with digital data output and performance enhancement circuits including a load modulation driver circuit and a single antenna in accordance with various embodiments of the present invention; 
         FIG. 26  shows a smartcard controller with digital data output and performance enhancement circuits including a load modulation driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 27  shows a smartcard controller with digital data output and performance enhancement circuits including a load modulation driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 28  shows a smartcard controller with digital data output and performance enhancement circuits including an active transmit driver circuit and a single antenna in accordance with various embodiments of the present invention; 
         FIG. 29  shows a smartcard controller with digital data output and performance enhancement circuits including an active transmit driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention; 
         FIG. 30  shows a smartcard controller with digital data output and performance enhancement circuits including an active transmit driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention; 
         FIGS. 31-34  show performance enhancing application specific integrated circuits (ASICs) coupled to various smartcard controllers in accordance with various embodiments of the present invention; 
         FIG. 35  shows a memory card with integrated smartcard controller, performance enhancement circuits and antennas in accordance with various embodiments of the present invention; 
         FIG. 36  shows a memory card with integrated smartcard controller and performance enhancement circuits in accordance with various embodiments of the present invention; 
         FIG. 37  shows a subscriber identity module (SIM) card with integrated smartcard controller, performance enhancement circuits and antennas in accordance with various embodiments of the present invention; 
         FIG. 38  shows a subscriber identity module (SIM) card with integrated smartcard controller and performance enhancement circuits in accordance with various embodiments of the present invention; and 
         FIG. 39  shows a mobile device with a smartcard controller, enhancement circuits, and antenna(s). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, various embodiments of an invention. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views. 
       FIG. 1  shows a mobile computing device and a small RFID card compatible with a memory card slot. Mobile computing device  110  is shown as a mobile phone in  FIG. 1 , but this is not a limitation of the present invention. For example, mobile computing device  110  may be a personal digital assistant (PDA), a smartphone, a mobile phone, a handheld computer, a desktop computer, or any other device capable of operating as described herein. 
     Mobile computing device  110  includes memory card slot  112 . Memory card slot  112  is a slot capable of accepting RFID card  120 . For example, memory card slot  112  may have physical dimensions compatible with RFID card  120 , and may have a communications interface that operates using a protocol compatible with RFID card  120 . In some embodiments of the present invention, memory card slot  112  is a memory card slot designed to accept and communicate with memory cards. As used herein, the term “memory card slot” refers to any add-on slot capable of accepting a card having memory accessible by a mobile computing device such as that shown in  FIG. 1 . For example, a memory card slot may be compatible with an industry standard communications protocol, or may be compatible with a widely accepted communications protocol that is not necessarily formally documented as an industry standard. Examples include slots that are compatible with the Multimedia Memory Card (MMC) protocol, Memory Stick DUO protocol, secure digital (SD) protocol, and Smart Media protocol. The foregoing list is meant to be exemplary, and not exhaustive. Memory card slot  112  may be compatible with many memory card slot protocols other than those explicitly listed above without departing from the scope of the invention. Further, in some embodiments, memory card slot  112  accepts a subscriber identity module (SIM) card. Memory card slot  112  may be exposed on an edge of mobile computing device  110  as shown, or may be behind a cover. For example, memory card slot  112  may be behind a battery cover, behind a battery, or anywhere else on mobile computing device  110 . 
     RFID card  120  includes electrical contacts  122  as part of a host interface that communicates with memory card slot  112 . For example, electrical contacts  122  may provide connectivity compliant with a communications protocol for memory cards. RFID card  120  includes RFID functionality, and may also include memory accessible by mobile computing device  110 . For example, in some embodiments, RFID card  120  includes a smartcard controller and an inductive element capable of interacting with an NFC reader (e.g., an ISO 14443 compliant interface). In other embodiments, RFID card  120  does not include memory accessible by mobile computing device  110 . RFID card  120  may include functionality beyond memory and RFID. Electrical contacts  122  may also be compliant with a smartcard “contact” interface (e.g., ISO 7816). 
     In various embodiments of the present invention, the RFID functionality in RFID card  120  is accessed by mobile computing device  110  using memory card access commands already defined for use in memory card slot  112 . Accordingly, the various embodiments of the present invention enable the implementation of RFID functions beyond memory accesses without defining new commands. In some embodiments, new commands for the RFID card are embedded inside the data bits subsequent to memory card read/write commands. RFID card  120  then decides if the incoming data bits are meant for regular read/write memory functions or for RFID functions. In other words, functions in addition to standard memory card functions may be accessed through commands “hidden” in the data stream that can be exchanged using existing memory card access commands and functions. According to the various embodiments of the invention, both existing memory card functions and RFID functions may be implemented without requiring changes in how the host protocol is built. 
     The combination of mobile computing device  110  and RFID card  120  may be used for any purpose. For example, in some embodiments, RFID card  120  may interact with a point-of-sale payment device to effect mobile payments. Also for example, in some embodiments, RFID card  120  may be used in wave-and-pay ticketing in mass transit environments, such as MIFARE. 
       FIG. 2  shows a block diagram of a mobile computing device. Mobile computing device  110  includes antenna  240 , radio circuits  230 , processor  210 , memory  220 , and memory card slot  112 . In some embodiments, mobile computing device  110  is a mobile phone, or includes mobile phone functionality. For example, antenna  240  and radio circuits  230  may be utilized to communicate with a cellular telephone network. Further, in some embodiments, mobile computing device  110  is a wireless local area network (WLAN) or wireless wide area network (WWAN) device. For example, antenna  240  and radio circuits  230  may be utilized to communicate with a wireless access point. In some embodiments, antenna  240  and radio circuits  230  are omitted, and mobile computing device  110  does not utilize wireless connectivity. 
     Processor  210  represents a processor capable of communicating with the other blocks shown in mobile computing device  110 . For example, processor  210  may be a microprocessor, a digital signal processor (DSP), a microcontroller, or the like. Further, processor  210  may be formed from state machines or other sequential logic. In operation, processor  210  may read instructions from memory  220  and perform actions in response thereto. For example, processor  210  may execute program instructions that influence communications between mobile computing device  110  and a device coupled to memory card slot  112 . 
     Memory card slot  112  is described above with reference to  FIG. 1 . Memory card slot  112  includes circuitry compatible with RFID card  120 . Mobile computing device  110  may communicate with RFID card  120  by using a standard set of memory card access commands. For example, processor  210  may use memory card write commands to write to memory in RFID card  120 , and may use memory card read commands to read from memory in RFID card  120 . Mobile computing device  110  may also communicate with RFID card  120  using an ISO 7816 compatible interface or the like. For example, when RFID card  120  is a SIM card, mobile computing device  110  may communicate with a smartcard controller within the SIM card. 
     Mobile computing device  110  may access the RFID functionality in RFID card  120  using “hidden” commands embedded in memory card access commands. For example, a memory card write command may include a unique data string to identify the memory card write command as a command to be diverted for purposes other than a memory write. In addition, the sector address provided with the memory card write command may be set to a particular address value to further identify the memory card write command as a command to be diverted. In addition to specific address/data values to identify the memory card access command as a command to be diverted for a purpose other than a memory access, the memory access command may include data bits to further specify the type and function of hidden command. Example formats of hidden commands are described further below. In some embodiments, a read command is issued right after a write command to enable data flow from the non-memory card functions to the host, where the write command&#39;s data had the hidden commands. The combination of a memory card write command and a memory card read command can be used in this manner to form a hidden read command. 
     In some embodiments, memory card slot  112  is powered down after periods of inactivity to save power. For example, memory card slot  112  may be powered up when processor  210  issues a memory card write or read command, but may then be powered down to save power. When memory card slot  112  is powered down, any device coupled to the memory card slot is also powered down. For example, if RFID card  120  ( FIG. 1 ) is coupled to the memory card slot, then RFID card  120  is powered down when memory card slot  112  is powered down. 
     In various embodiments of the present invention, processor  210  executes software resident in memory  220  to maintain power to memory card slot  112  (and to RFID card  120 ). For example, periodic hidden commands may be sent to RFID card  120  for the purpose of keeping power applied while RFID card  120  is expected to be providing RFID functionality. Also for example, a hidden command may be sent to RFID card  120  for the purpose of cycling power to a smartcard controller resident on the card. These hidden commands are described further below with respect to later figures. 
       FIG. 3A  shows a block diagram of a memory card compatible RFID card with an integrated inductive element. RFID card  300  represents possible embodiments of RFID card  120  ( FIG. 1 ). RFID card  300  includes host interface  310 , memory card controller  340 , memory  360 , smartcard controller  340 , program memory  332 , and small inductive element  350 . RFID card  300  is capable of communicating with a memory card slot in a mobile computing device. Further, RFID card  300  does not require memory card slots to implement extended input/output functions. For example, and not by way of limitation, in SD and micro SD embodiments, RFID card  300  is operable in any SD or microSD memory card slot, and does not require a secure digital input output (SDIO) memory card slot. 
     Host interface  310  includes electrical contacts to interface with a memory card slot. For example, host interface  310  includes contacts such as contacts  122  ( FIG. 1 ). Also for example, in some embodiments, host interface  310  includes recessed electrical contacts. Host interface  310  may also include circuitry such as drivers, receivers, terminations, and the like. 
     In embodiments represented by  FIG. 3A , memory card controller  340  communicates with the mobile device using memory card access commands. Memory card controller  340  also communicates with memory  360 . Memory card controller  340  determines whether each command should result in a memory operation with memory  360 , whether a hidden command should be diverted to smartcard controller  330 , or whether memory card controller  340  should take action in response to a hidden command. In some embodiments, memory card controller  340  executes instructions that are stored in an internal memory or stored in memory  360 . In some embodiments, memory card controller  340  includes special purpose hardware useful to determine whether a command should be diverted. In other embodiments, memory card controller  340  may be a microcontroller identical in all respects to a controller found in memory cards, except for the program that it executes. 
     Memory  360  may be any type of volatile or non-volatile memory. For example, memory  360  may be volatile memory such as static random access memory (SRAM) or dynamic random access memory (DRAM). Also for example, memory  360  may be nonvolatile memory such as NOR FLASH memory or NAND FLASH memory. In various embodiments of the present invention, memory  360  represents memory that is accessed by a mobile computing device using memory card access commands defined for that purpose. 
     When RFID card  300  is communicating with a memory card slot in a mobile computing device, the mobile computing device may send a memory card access command in order to access memory  360 . Also for example, the mobile computing device may send a memory card access command that contains a hidden command. Memory card controller  340  detects the presence of the hidden command, and diverts all or a portion of the memory access command to smartcard controller  330  using communication bus  342 . Communication bus  342  may have any number of conductors and may take any form. For example, communication bus  342  may be a serial port, a parallel port, or may include multiple data conductors, multiple address conductors, and/or conductors to carry control signals such as clock signals. In some embodiments, memory card controller  340  takes one or more actions in response to a hidden command. For example, memory card controller  340  may modify clock signals in response to a hidden command. 
     Memory card controller  340  can detect the hidden command in many ways. For example, in some embodiments, the memory card access command may include a specific address value or a specific data value. Memory card controller  340  detects commands that include one or both of the specific address value or specific data value and routes the command appropriately. The specific address value and specific data value used for this purpose are referred to herein as the hidden command address value and the hidden command data value. 
     In some embodiments, memory card controller  340  detects the presence of hidden commands based only on the hidden command address value. In these embodiments, memory card controller  340  checks the address value included in a memory card access command, and diverts the command (or takes some other action) if it matches the hidden command address value. In some embodiments, memory card controller  340  detects the presence of hidden commands based only on the hidden command data value. In these embodiments, memory card controller  340  checks a data value included in the memory card access command, and diverts all or a portion of the command if it matches the hidden command data value. In still further embodiments, memory card controller  340  detects the presence of hidden commands based on both the hidden command address value and the hidden command data value. In these embodiments, memory card controller  340  diverts the command only if both the memory card access address and data match the hidden command address value and data value, respectively. 
     The hidden command address value and hidden command data value may be specified in many ways. For example, all RFID cards may be issued with fixed values. In these embodiments, each time the RFID functions are accessed, the same hidden command address and/or data value is included in the memory card access command. Also for example, different RFID cards may be issued with unique values. In these embodiments, each RFID card may provide these values to a mobile computing device when queried. Also for example, hidden command address and/or data values may be specified by the mobile computing device. In still further embodiments, hidden command address and data values may be dynamic. The hidden command address and data values may change each time power is applied or on a periodic basis. 
     Smartcard controller  330  receives hidden commands diverted by memory card controller  340 . Smartcard controller  330  further interprets the hidden commands and performs actions in response thereto. Smartcard controller  330  executes instructions stored in program memory  332 . In some embodiments, program memory  332  is embedded in smartcard controller  330 , and in other embodiments, program memory  332  is part of memory  360 . 
     Smartcard controller  330  is a dual interface smartcard controller with one of the interfaces including RFID functionality. In some embodiments, smartcard controller  330  is compatible with passive RFID tag readers in NFC applications. For example, smartcard controller  330  may be a device capable of implementing all or part of the ISO 14443 standard for contactless NFC devices. Also for example, smartcard controller  330  may be a dual interface smartcard controller capable of implementing both ISO 7816 and ISO 14443 standards for contact/contactless requirements. The “SmartMX” family of controllers available from NXP Semiconductors N.V. of The Netherlands are examples of suitable dual interface smartcard controllers. These controllers provide RFID functionality at 13.56 MHz. The various embodiments of the present invention operate at 13.56 MHz, but are not limited to operation at this frequency. In some embodiments, smartcard controller interoperates with MIFARE systems for ticketing applications. 
     Smartcard controller  330  receives power from the host interface. By not receiving power from the interrogating RF field, the necessity of a loop antenna for power generation is negated. Smartcard controller  330  includes a contactless interface that in turn includes antenna port  334 . Antenna port  334  includes at least two pads for connection to an antenna, shown as  1742  and  1744  in  FIG. 14  and later figures. In  FIG. 3A , antenna port  334  is coupled to small inductive element  350 . 
     Small inductive element  350  includes a coil wound around a magnetic core. As described with reference to later figures, small inductive element may include one or more coils or antennas. The coil of small inductive element is too small to draw power from the interrogating RF field, but this is not necessary since smartcard controller  330  is powered by the host device through host interface  310 . Small inductive element  350  interacts with an antenna in an RFID reader similar to the way that primary and secondary coils in a transformer interact. The RFID reader has a coil resonant at 13.56 MHz functioning as the primary coil of a transformer. Small inductive element  350  functions as the secondary coil of the transformer. Accordingly, the transmitter “sees” the impedance of the secondary coil (small inductive element  350 ). Smartcard controller  330  is able to modulate reflected RF signals using circuitry to modify the impedance at the antenna port  334 . 
     Small inductive element  350  can be made very small. For example, in some embodiments, RFID card  120  is a miniSD card, microSD card, or SIM card, and small inductive element  350  is small enough to be completely contained in the miniSD, microSD, or SIM form factor. A specific embodiment of a small inductive element in a memory card form factor is described below with reference to  FIG. 4 . 
     In various embodiments of the invention, memory card controller  340  and smartcard controller  330  are implemented in many different ways. For example, in some embodiments, the various components are implemented in hardware. In these embodiments, the various components may be implemented as separate integrated circuits, or in a combined integrated circuit. Also for example, in some embodiments, the various components may be implemented in software, or in a combination of hardware and software. In some embodiments, RFID card  300  may include a microprocessor, and the components may be implemented as software modules running on the microprocessor. In other embodiments, RFID card  300  may include multiple processors, and the components may be implemented as software modules distributed across the multiple processors. 
       FIG. 3B  shows a block diagram of a memory card compatible RFID card with an integrated inductive element. RFID card  302  represents possible embodiments of RFID card  120  ( FIG. 1 ). RFID card  302  includes host interface  310 , memory card controller  340 , memory  360 , smartcard controller  340 , program memory  332 , and small inductive element  350 , all of which are described above with reference to  FIG. 3A . RFID card  302  is capable of communicating with a memory card slot in a mobile computing device. Further, RFID card  302  does not require memory card slots to implement extended input/output functions. For example, and not by way of limitation, in SD and microSD embodiments, RFID card  302  is operable in any SD or microSD memory card slot, and does not require a secure digital input output (SDIO) memory card slot. 
     In embodiments represented by  FIG. 3B , smartcard controller  330  receives power from memory controller  340 . In these embodiments, memory controller  340  has direct control over the power provided to smartcard controller  330 . Memory controller  340  may apply and/or remove power from smartcard controller  330  in response to commands received over the host interface. For example, memory controller  340  may receive a hidden command to reset smartcard controller  330  by causing a reboot through a power cycle. 
       FIG. 4  shows a memory card compatible RFID card with an integrated inductive element. RFID card  120  is shown in an SD card form factor, although this is not a limitation of the present invention. For example, other form factors within the scope of the present invention include, but are not limited to, microSD form factors and SIM card form factors. RFID card  120  includes electrical contacts  122 , memory card controller  340 , smartcard controller  330 , memory  360 , magnetic core  450 , and coil  452 , all affixed to circuit board  402 . 
     Magnetic core  450  and coil  452  implement small inductive element  350  ( FIGS. 3A, 3B ). As can be seen in  FIG. 4 , the small inductive element fits entirely within the memory card form factor. The small inductive element does not provide power generation for smartcard controller  330 , and so does not need to be made large for that purpose. 
       FIG. 5  shows a data portion of a memory card write command. Included are hidden command data value  510 , status field  520 , password field  530 , device ID  532 , command index  540 , and hidden command related data  550 . In the example of  FIG. 5 , the data portion is 512 bytes in length, although this is not a limitation of the present invention. Any amount of data may be included in the write command, and each field shown in  FIG. 5  may be any length. 
     In the example of  FIG. 5 , the hidden command data value is 256 bits long, although any length may be used without departing from the scope of the present invention. In some embodiments, hidden command data value  510  is used to identify a memory write command as a hidden command. When a write command is received having data in the first 256 bits that match the hidden command data value, the command is identified as one to be diverted to the smartcard controller. As described above, a hidden command address value may be used in conjunction with, or instead of, a hidden command data value to identify the memory write command as a hidden command. 
     The remaining fields have significance when the memory write is a hidden command. For example, if the first 256 bits do not match the hidden command data value (or if the write address does not match the hidden command address value, or both) then the remaining bits in the data field are to be treated as data in a normal memory write command. In contrast, when the memory write is a hidden command, the remaining fields are used to further interpret the hidden command. 
     Memory card controller  340  ( FIGS. 3, 4 ) inspect the hidden command data value  510 , status field  520 , and possibly password field  530  and device ID  532 . In some embodiments, if the command is identified as a hidden command, memory card controller  340  forwards the password  530 , command index  540 , and related data  550  to smartcard controller  330 . In other embodiments, memory card controller  340  may directly take actions based on the hidden command. 
     Status field  520  may include any information relating to the status of the hidden command. For example, status field  520  may include one or more bits to signify to memory card controller  340  whether the host (mobile computing device) is expecting the smartcard controller to return data in response to the hidden command. For example, when status field  520  signifies a write, memory card controller  340  forwards the password, device ID, command index, and related data without expecting to return any data to the host. Also for example, when status field  520  signifies a read, memory card controller  340  forwards the password, device ID, command index, and related data with the expectation that smartcard controller  330  will provide data to be sent to the host in response to a memory card read command. The combination of a memory card write command followed shortly thereafter by a memory card read command may be used to provide “read” functionality to the smartcard controller. Read operations from the smartcard controller are described further below with reference to  FIG. 8 . 
     Password field  530  includes a password to allow smartcard controller  330  to authenticate the host to the RFID card. In some embodiments, every hidden command includes a password. Each time the password, device ID, command index, and related data is diverted to the smartcard controller, the password is checked to authenticate the host to the RFID card. 
     Device ID  532  uniquely identifies the host (mobile computing device). The device ID may be checked by the smartcard controller to ensure that the RFID card is inserted in the host to which it is authenticated. Some embodiments of the present invention enforce a unique host/card pairing using the device ID, and other embodiments allow smartcard controller functions to be accessed by any host. 
     Command index  540  identifies the type of hidden command. The number of possible hidden commands is limited only by the number of bits allocated thereto. Any number of bits may be allocated to command index  540  without departing from the scope of the present invention. Hidden command related data  550  may be utilized differently for each type of hidden command. Any number of bits may be used for hidden command related data  550 . 
     The data shown in  FIG. 5  is provided as an example, and the data field of a memory card access command may include more or fewer data fields than those shown in  FIG. 5 . The present invention is not limited by the number or content of the fields in a memory card access command. 
       FIG. 6  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  600  may be used by a mobile computing device to communicate with an RFID card in a memory card slot. In some embodiments, method  600 , or portions thereof, is performed by a mobile computing device with a memory card slot, and in other embodiments, method  600 , or portions thereof, is performed by software. The various actions in method  600  may be performed in the order presented, in a different order, or simultaneously. Further, in some embodiments, some actions listed in  FIG. 6  are omitted from method  600 . 
     Method  600  begins at  610  in which a data pattern and an address value are received from an RFID card in a memory card slot. The data pattern corresponds to the hidden command data value, and the address value corresponds to the hidden command address value. In some embodiments, the mobile device only receives the data value and in other embodiments, the mobile device only receives the address value. In some embodiments, the actions of  610  may occur once when the RFID card is first inserted in the memory card slot. The mobile computing device may then use the address and data values each time it creates a hidden command. In other embodiments, the actions of  610  may occur each time the RFID card is inserted in the memory slot. In still further embodiments, the actions of  610  may occur periodically. Each time the actions  610  occur, the data pattern may be the same or different, and the address value may be the same or different. 
     At  620 , a data field of a memory card access command is populated with the data pattern to cause the command to be diverted to a smartcard controller on the RFID card. For example, the data pattern may be written to the data field as the hidden command data value  510  ( FIG. 5 ). 
     At  630 , an address field of the memory card access command is populated with the address value to further cause the command to be diverted to the smartcard controller. In some embodiments, only one of  620  or  630  is utilized. In these embodiments, the presence of a hidden command is signified by the data pattern alone, or the address value alone. 
     At  640 , the data field of the memory card access command is populated with a command string to specify a purpose other than a memory card access. For example, the command string may be written to the data field as the command index  540  for the smart card controller. This command may be used for any purpose. For example, one or more hidden commands may have as a sole purpose keeping power provided to the memory card slot so that the RFID card continues to receive power. 
     At  650 , the data field of a memory card access command is populated with a password to authenticate access to the RFID card coupled to the memory card slot. In some embodiments, a password is included in the data field for every hidden command. In other embodiments, a password is only included at the beginning of an exchange. 
     At  660 , the memory card access command is sent to the RFID card coupled to the memory card slot. For example, a mobile computing device ( 110 ,  FIGS. 1, 2 ) may send the memory card access command to an RFID card ( 120 ,  FIGS. 1, 3, 4 ) in a memory card slot ( 112 ,  FIGS. 1, 2 ). The RFID card includes a memory card controller ( 340 ,  FIG. 3 ) to divert the command (or take some other action) based on the data fields populated in method  600 . 
       FIG. 7  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  700  may be used by an RFID card in a memory card slot. In some embodiments, method  700 , or portions thereof, is performed by a memory card controller within a memory card compatible RFID card, and in other embodiments, method  700 , or portions thereof, is performed by software. The various actions in method  700  may be performed in the order presented, in a different order, or simultaneously. Further, in some embodiments, some actions listed in  FIG. 7  are omitted from method  700 . 
     Method  700  begins at  710  in which a memory card access command is received from a mobile computing device via a host interface. The actions of  710  correspond to an RFID card in a memory card slot of a mobile computing device receiving a memory card access command. 
     At  720 , the memory card controller checks criteria in the memory card access command to determine if the memory card access command should be diverted to a smartcard controller resident on the RFID card. The criteria may be one or both of a hidden command data value, a hidden command address value, or both. If there is a criteria match at  730 , then a hidden command is present, and at least a portion of the memory card access command is diverted at  740 . If there is not a criteria match, then no hidden command is present, and a memory access is performed at  750 . 
       FIG. 8  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  800  may be used by an RFID card in a memory card slot. In some embodiments, method  800 , or portions thereof, is performed by a memory card controller within an RFID card, and in other embodiments, method  800 , or portions thereof, is performed by software. The various actions in method  800  may be performed in the order presented, in a different order, or simultaneously. Further, in some embodiments, some actions listed in  FIG. 8  are omitted from method  800 . 
     Method  800  begins at  810  in which a memory card write command is received from a mobile computing device via a host interface. If the memory card write command is determined to be a hidden command, processing continues with  840 ; otherwise, a memory write is performed at  830 . 
     At  840 , the hidden command is diverted to a smartcard controller. In some embodiments, this corresponds to sending command index  540  and hidden command related data  550  ( FIG. 5 ) to the smartcard controller. If the hidden command is determined to be a “read” at  850 , processing continues at  860 ; otherwise, the hidden command processing is done. At  860 , the memory card controller retrieves non-memory data from the smartcard controller, and at  870 , a memory card read command is received from the mobile computing device. At  880 , the non-memory data is returned to the mobile computing device. 
     Method  800  demonstrates how a mobile computing device can perform a read from a smartcard controller in a memory card compatible RFID card. The mobile computing device issues a memory card write command with a hidden command having a status field designating a read, and then the mobile computing device issues a memory card read command. The processing in the card receives the hidden command, identifies it as a read, and then returns data to the mobile computing device in response to a subsequent memory card read command. 
       FIG. 9  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  900  may be used by an RFID card in a memory card slot. In some embodiments, method  900 , or portions thereof, is performed by a smartcard controller within an RFID card, and in other embodiments, method  900 , or portions thereof, is performed by software. The various actions in method  900  may be performed in the order presented, in a different order, or simultaneously. Further, in some embodiments, some actions listed in  FIG. 9  are omitted from method  900 . 
     Method  900  begins at  910  in which a smartcard controller receives a command from the memory card controller. This command corresponds to a hidden command received by the memory card controller. At  950 , the smartcard controller determines whether the command is a “dummy” command used solely for the purpose of maintaining power to the memory card slot. If no, then the smartcard function specified in the command is performed at  930 . If yes, then the command is disregarded at  960 . 
     Method  900  allows a memory card compatible RFID card in a memory card slot to remain powered during periods when the memory card slot in the host device would otherwise remove power to save energy. This is a coordinated effort between software building hidden commands in a memory card access command, the memory card controller diverting the hidden command to the smartcard controller, and the smartcard controller disregarding the command. According to embodiments represented by  FIG. 3A , providing power to the RFID card also provides power the smartcard controller, thereby allowing the use of a small inductive device such as those shown in  FIGS. 3 and 4 . 
       FIG. 10  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  1000  may be used by an RFID card in a memory card slot. In some embodiments, method  1000 , or portions thereof, is performed by a memory card controller within an RFID card, and in other embodiments, method  1000 , or portions thereof, is performed by software. The various actions in method  1000  may be performed in the order presented, in a different order, or simultaneously. Further, in some embodiments, some actions listed in  FIG. 10  are omitted from method  1000 . 
     Method  1000  begins at  1010  in which a memory card controller receives a hidden command from a mobile computing device. If at  1020 , the memory card controller determines that the hidden command is to be diverted to the smartcard controller, then the command is diverted at  1030 . In some embodiments, this corresponds to sending command index  540  and hidden command related data  550  ( FIG. 5 ) to the smartcard controller. If the command is not to be diverted, then the memory card controller does not divert the command; however, the memory card controller may take other actions at  1040  based on the hidden command. For example, the memory card controller may modify a clock signal provided to the smartcard controller. Also for example, the memory card controller may assert a reset signal to the smartcard controller. Still for example, the memory card controller may cycle power to the smartcard controller. The memory card controller is able to cycle power to the smartcard controller in embodiments represented by  FIG. 3B . 
     Cycling power to the smartcard controller may be a coordinated effort between the hosting computing device and the memory card controller in the RFID card. For example, power to the memory card slot may be maintained by supplying dummy hidden commands to the RFID card as described above with reference to  FIG. 9 . While power is maintained to the memory card slot, hidden commands may be used to cause the memory card controller to cycle power to the smartcard controller. 
       FIG. 11  shows a method authenticating a mobile computing device to one or more functions in a memory card compatible RFID card. Method  1100  begins at block  1110  in which an activation code is received at an RFID card from a mobile computing device. At  1120 , the received activation code is compared to a code stored in the RFID card. If the activation code matches, the RFID card receives a password from the mobile computing device at  1140 , and stores the password in the RFID card for later use at  1150 . If the activation code does not match, the RFID card determines whether a number of allowable tries has been exceeded at  1160 . If the number of allowable tries has been exceeded, the RFID card issuer is contacted at  1170 , and if the number of allowable tries has not been exceeded, the method repeats until either the activation code matches or the number of allowable tries has been exceeded. 
     Method  1100  may be performed when an RFID card is issued to a user. For example, the RFID card may be a mobile payment card issued by a financial institution. The user may be provided an activation code to “activate” the RFID card. When the user successfully enters the activation code, the user is prompted for a password, and that password is stored for use in future hidden commands. 
     In some embodiments, multiple non-memory functions in an RFID card are authenticated using method  1100 . For example, each of multiple non-memory functions may have stored activation codes, and each is activated separately. Each of the separately activated functions may have a different password, or the multiple functions may share a password. 
     Embodiments described thus far include a power delivery mechanism from the host to the smartcard controller that allow the antenna or coil to be very small. The small antenna or coil allows for higher levels of integration, but may also reduce the maximum distance at which the RFID card will function. For example, referring to  FIG. 14 , the voltage produced by the antenna needs to overcome the diode drops of the bridge rectifier before data can be demodulated within the smartcard controller. As the antenna shrinks in size, the RFID card needs to be closer to the device producing the interrogating RF field in order to produce a large enough voltage to overcome the bridge rectifier diode drops, thereby reducing the maximum usable distance. 
       FIG. 15  shows a smartcard controller with performance enhancement circuits including a load modulation driver circuit and a single antenna in accordance with various embodiments of the present invention. Antenna  1542  is a small inductive element as described above. Capacitor  1544  is in parallel with antenna  1542  and together they form tuned circuit  1540  that is tuned to be resonant at the frequency of operation (e.g., 13.56 MHz). The performance enhancement circuits include an amplifier  1510 , outgoing data extraction circuit  1520 , and load modulation driver circuit  1530 . Amplifier  1510  amplifies the voltage received at antenna  1542 , and the amplified voltage is provided to the smartcard controller. This increases the maximum distance at which the RFID card can operate while receiving data, but also creates a unidirectional data path where a bidirectional data path previously existed. In other words, amplifier  1510  forms a simplex communication path where a half duplex path previously existed. 
     In order to restore the outgoing data path and re-create a half duplex communications system, the RFID card includes outgoing data extraction circuit  1520  and load modulation driver circuits  1530 . Outgoing data extraction circuit  1520  receives a signal that is formed by the interrogating RF field having been load modulated by the smartcard controller. For example, the impedance of the antenna port is modulated by load modulation driver circuit  1410  ( FIG. 14 ), where the modulating signal is the data. Outgoing data extraction circuit  1520  recovers the data, and then load modulation driver circuit  1530  modulates the impedance of the tuned circuit  1540  to form the outgoing data path. 
     Outgoing data extraction circuit  1520  may include one or more filters to extract the data. For example, referring now to  FIG. 16 , the load modulation driver circuit within the smartcard controller creates frequency sidebands  1610  about the carrier frequency  1620  of the interrogating RF field. Outgoing data extraction circuit  1520  may include conventional filters to isolate one or more sidebands and extract the data. As shown in  FIG. 16 , in some 13.56 MHz embodiments, the bandwidth of the carrier frequency of the interrogating RF field may be on the order of 850 KHz and the bandwidth of the sidebands may be on the order of 100-200 KHz, although this is not a limitation of the present invention. 
     Load modulation driver circuit  1530  receives the extracted data from outgoing data extraction circuit  1520 , and load modulates the tuned circuit  1540  in response thereto. Load modulation driver circuits are generally well known, and may be as simple as a switched transistor that adds and removes a reactive element from tuned circuit  1540 . In some embodiments, load modulation driver circuit  1530  substantially duplicates the load modulation driver circuit  1410  within smartcard controller  330 . 
     Amplifier  1510  is shown coupled to smartcard controller pad  1472 , and data extraction circuit  1520  is shown coupled to smartcard controller pad  1474 , but this is not a limitation of the present invention. For example, outgoing data extraction circuit  1520  may be coupled to smartcard controller pad  1472  while amplifier  1510  may be coupled to smartcard controller pad  1474 . Also for example, both circuit  1520  and amplifier  1510  may be coupled to either pad  1472  or pad  1474  without departing from the scope of the present invention. 
       FIG. 17  shows a smartcard controller with performance enhancement circuits including a load modulation driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention.  FIG. 17  shows smartcard controller  330 , amplifier  1510 , outgoing data extraction circuit  1520 , and load modulation driver circuit  1530 , all of which are described above.  FIG. 17  also shows tuned circuits  1740  and  1750 . Tuned circuit  1740  includes receive antenna  1742  and capacitor  1744 . Tuned circuit  1750  includes transmit antenna  1752  and capacitor  1754 . In some embodiments, receive antenna  1742  and transmit antenna  1752  are small inductive elements as described above. 
     Separate transmit and receive antennas allow for different tuning, both in frequency and bandwidth, or “Q.” For example, tuned circuit  1740  may be tuned with relatively high Q for receive as shown at  1820  in  FIG. 18 , while tuned circuit  1750  may be tuned for a lower Q to envelope both sidebands for transmit as shown at  1830  in  FIG. 18 . The higher Q tuning for the receive antenna may further increase the maximum usable distance when the RFID card is receiving. 
       FIG. 19  shows a smartcard controller with performance enhancement circuits including a load modulation driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention.  FIG. 19  shows smartcard controller  330 , amplifier  1510 , outgoing data extraction circuit  1520 , load modulation driver circuit  1530 , and tuned receive circuit  1740 , all of which are described above.  FIG. 19  also shows two tuned transmit circuits  1950  and  1960 . Tuned circuit  1950  includes antenna  1952  and capacitor  1954 , and tuned circuit  1960  includes antenna  1962  and capacitor  1964 . Antennas  1952  and  1962  may be small inductive elements as described above. 
     Separate transmit antennas allow separate tuning for the two sidebands. For example, tuned circuit  1950  may be tuned for the lower sideband tuned circuit  1960  may be tuned for the upper sideband as shown in  FIG. 20 . Higher Q tuning of the transmit antennas for the separate sidebands may further increase the maximum usable distance when the RFID card is transmitting. 
       FIG. 21  shows a smartcard controller with performance enhancement circuits including an active transmit driver circuit and a single antenna in accordance with various embodiments of the present invention. The circuits shown in  FIG. 21  are similar to  FIG. 15  except the load modulation driver is replaced with an active transmit driver circuit  2130 . Active transmit driver circuit  2130  may include circuits to actively transmit a signal rather than simply load modulate tuned circuit  1540 . For example, active transmit driver circuit  2130  may include one or more amplifiers, filters, oscillators, modulators, etc., to form a signal that mimics the sidebands  1610  ( FIG. 16 ) as if the interrogating RF field experienced load modulation. Active transmission can make use of power available on the RFID card and can further increase the usable distance when smartcard controller  330  is transmitting. 
       FIG. 22  shows a smartcard controller with performance enhancement circuits including an active transmit driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention. The circuits shown in  FIG. 22  are similar to  FIG. 17  except the load modulation driver is replaced with an active transmit driver circuit  2130 . Active transmit driver circuit  2130  is described above with reference to  FIG. 21 . 
       FIG. 23  shows a smartcard controller with performance enhancement circuits including an active transmit driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention. The circuits shown in  FIG. 23  are similar to  FIG. 19  except the load modulation driver is replaced with an active transmit driver circuit  2130 . Active transmit driver circuit  2130  is described above with reference to  FIG. 21 . 
       FIG. 24  shows a smartcard controller with a pad to provide a digital data output. Smartcard controller  2430  includes the antenna pads  1472  and  1474  as described above. Smartcard controller  2430  also includes pad  2410  which provides the digital data output directly. By providing the digital data output directly, smartcard controller  2430  enables various embodiments of the invention to eliminate the outgoing data extraction circuit. 
       FIG. 25  shows a smartcard controller with digital data output and performance enhancement circuits including a load modulation driver circuit and a single antenna in accordance with various embodiments of the present invention.  FIG. 25  shows smartcard controller  2430 , amplifier  1510 , load modulation driver circuits  1530 , and tuned circuit  1540 , all of which are described above. Note that because smartcard controller  2430  provides digital data directly, the outgoing data extraction circuit  1520  ( FIG. 15 ) can be omitted, thereby reducing parts count and cost. 
       FIG. 26  shows a smartcard controller with digital data output and performance enhancement circuits including a load modulation driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention.  FIG. 26  shows circuits similar to those shown in  FIG. 25 , except that separate transmit and receive antennas are provided. Separate transmit and receive antennas (and associated tuned circuits) allow for a higher Q tuning of the receive antenna, thereby increasing the maximum usable distance when RFID card is receiving. See  FIG. 18 . 
       FIG. 27  shows a smartcard controller with digital data output and performance enhancement circuits including a load modulation driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention.  FIG. 27  shows circuits similar to those shown in  FIG. 26 , except that multiple transmit antennas are provided. Multiple separate transmit antennas (and associated tuned circuits) allow for a higher Q tuning of each transmit antenna, thereby increasing the maximum usable distance when RFID card is transmitting. See  FIG. 20 . 
       FIG. 28  shows a smartcard controller with digital data output and performance enhancement circuits including an active transmit driver circuit and a single antenna in accordance with various embodiments of the present invention. The circuits shown in  FIG. 28  are similar to  FIG. 25  except the load modulation driver is replaced with an active transmit driver circuit  2130 . Active transmit driver circuit  2130  is described above with reference to  FIG. 21 . In general, the term “driver” as used herein refers to an active transmit driver or a load modulation driver or any other method of driving the transmit output data. 
       FIG. 29  shows a smartcard controller with digital data output and performance enhancement circuits including an active transmit driver circuit and separate receive and transmit antennas in accordance with various embodiments of the present invention. The circuits shown in  FIG. 29  are similar to  FIG. 26  except the load modulation driver is replaced with an active transmit driver circuit  2130 . Active transmit driver circuit  2130  is described above with reference to  FIG. 21 . 
       FIG. 30  shows a smartcard controller with digital data output and performance enhancement circuits including an active transmit driver circuit and multiple transmit antennas in accordance with various embodiments of the present invention. The circuits shown in  FIG. 30  are similar to  FIG. 27  except the load modulation driver is replaced with an active transmit driver circuit  2130 . Active transmit driver circuit  2130  is described above with reference to  FIG. 21 . 
       FIGS. 31-34  show performance enhancing application specific integrated circuits (ASICs) coupled to various smartcard controllers in accordance with various embodiments of the present invention.  FIGS. 31 and 32  show ASICs coupled to smartcard controller  330 . Both ASICs include amplifier  1510  and outgoing data extraction circuits  1520 . The ASIC of  FIG. 31  includes load modulation driver circuits  1530  and the ASIC of  FIG. 32  includes active transmit driver circuit  2130 .  FIGS. 33 and 34  show ASICs coupled to receive direct digital data from smartcard controller  2430 . Accordingly, the outgoing data extraction circuits are omitted. The ASIC of  FIG. 33  includes amplifier  1510  and load modulation driver circuits  1530 , and the ASIC of  FIG. 34  includes amplifier  1510  and active transmit driver circuit  2130 . 
     By combining a smartcard controller and an ASIC as described herein, the performance of an RFID card may be enhanced with a reduced parts count. Further, any of ASICs shown may be used with separate receive and transmit antennas, multiple transmit antennas, or any combination. Further, one ASIC may be provided with all of the functionality shown in  FIGS. 31-34  and the manner in which it is connected to a smartcard controller will dictate which functional blocks (e.g., data extraction, load modulation, active transmit) are utilized. 
       FIG. 35  shows a memory card with integrated smartcard controller, performance enhancement circuits, and antennas in accordance with various embodiments of the present invention. Host interface  310 , memory card controller  340 , and memory  360  are described above. Smartcard controller  3520  may be any smartcard controller described herein, including smartcard controller  330  or smartcard controller  2430 . Enhancement circuits  3550  may include any of the enhancement circuits described herein including any combination of amplifier  1510 , outgoing data extraction circuits  1520 , load modulation driver circuits  1530  and active transmit driver circuit  2130 . Antenna(s)  3560  may include any number or type of antennas. For example, antenna(s)  3560  may include one antenna, separate transmit and receive antennas, or a receive antenna and multiple transmit antennas. 
       FIG. 36  shows a memory card with integrated smartcard controller and performance enhancement circuits in accordance with various embodiments of the present invention. The memory card of  FIG. 36  shows circuits similar to  FIG. 35  with the exception of antenna(s)  3560 . Instead, the memory card of  FIG. 36  is intended for use with a host device that includes antenna(s). In some embodiments, antenna(s)  3560  are included in the memory card of  FIG. 36 , thereby allowing the host device to decide whether to use the antennas on the memory card, or the antennas on the host device. The form factor of the memory card in  FIGS. 35 and 36  is shown as a microSD card, but this is not a limitation of the present invention. Any form factor may be employed. 
       FIG. 37  shows a subscriber identity module (SIM) card with integrated smartcard controller, performance enhancement circuits and antennas in accordance with various embodiments of the present invention. Smartcard controller  3520 , enhancement circuits  3550 , and antenna(s)  3560  are described above with reference to  FIG. 35 . 
       FIG. 38  shows a subscriber identity module (SIM) card with integrated smartcard controller and performance enhancement circuits in accordance with various embodiments of the present invention. The SIM card of  FIG. 38  shows circuits similar to  FIG. 37  with the exception of antenna(s)  3560 . Instead, the SIM card of  FIG. 38  is intended for use with a host device that includes antenna(s). In some embodiments, antenna(s)  3560  are included in the SIM card of  FIG. 38 , thereby allowing the host device to decide whether to use the antennas on the SIM card, or the antennas on the host device. 
       FIG. 39  shows a mobile device with a smartcard controller, enhancement circuits, and antenna(s). The mobile device of  FIG. 39  includes a built-in smartcard controller for RFID functionality as opposed to accepting a separate RFID card as described above. The mobile device may be any electronic device including a mobile phone, a tablet computer, or the like. 
     Although the present invention has been described in conjunction with certain embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the invention and the appended claims.