Patent Publication Number: US-2009221240-A1

Title: Low power device activated by an external near-field reader

Description:
FIELD 
     The embodiments disclosed relate to improvements in power saving in mobile devices. 
     BACKGROUND 
     Near-field transponders, such as radio frequency identification (RFID) transponders and Near-Field Communication (NFC) transponders, include an integrated circuit microchip with data storage capability and a radio frequency (RF) interface, which couples an antenna to the electronic circuit. 
     RFID transponders can be the passive type or the active type. A passive RFID transponder requires no internal power source to communicate with an RFID reader, and is only active when it is near an RFID reader, which energizes the transponder with a continuous radio frequency signal at a resonant frequency of the antenna. The small electrical current induced in the antenna by the continuous radio frequency signal provides enough power for the integrated circuit in the transponder to power up and transmit a modulated response, typically by backscattering the continuous carrier wave from the RFID reader. A passive RFID transponder can include writable electrically erasable, programmable, read-only memory (EEPROM) for storing data received from the RFID reader, which modulates the continuous carrier wave sent by the RFID reader. Reading distances for passive RFID transponders typically range from a few centimeters to a few meters, depending on the radio frequency and antenna design. By contrast, active RFID transponders require a power source to receive and transmit information with an RFID reader. 
     NFC transponders communicate with NFC readers via magnetic field induction, where two loop antennas are located within each other&#39;s near field, effectively forming an air-core transformer. An example NFC transponder operates within the unlicensed radio frequency ISM band of 13.56 MHz, with a bandwidth of approximately 2 MHz over a typical distance of a few centimeters. 
     Mobile devices exist in a variety of forms such as personal digital assistants (PDAs), portable audio/video players, wireless cellular telephones, smartcards, or the like and are used for a variety of applications, such as data storage, entertainment, communications, e-commerce, banking, personal identification, mobile ticketing, or similar applications. Mobile devices include a central processing unit (CPU) and a memory and may include a touch screen keyboard and a flat screen display. Mobile devices are self-contained and can include a battery to power the CPU for carrying out the application programs stored in the memory. A mobile device can be combined with a passive near-field transponder, which can receive a coded message from proximate near-field readers to enable the mobile device to perform a programmed function based on the coded message. 
     A significant problem with mobile devices is that their frequent use imposes a significant drain on their battery. What is needed is an improved way to save power in mobile devices. 
     SUMMARY 
     Method, apparatus, and computer program product embodiments are disclosed to improve power saving in mobile devices. A mobile device includes a controller with a central processing unit (CPU) and a programmed memory. In one embodiment, the mobile device includes a battery to power the CPU in a run mode. In its unused state, the controller maintains a sleep mode with the CPU off and peripherals off, such as for a flat screen display, thereby drawing substantially less or even no power from the battery. The mobile device also includes a passive near-field transponder with an electrically erasable, programmable, read-only memory (EEPROM) storage device. The near-field transponder can be, for example, a radio frequency identification (RFID) transponder, a Near-Field Communication (NFC) transponder, or any other near-field communications device. The near-field transponder is activated by a continuous radio frequency signal from a proximate near-field reader. The passive near-field transponder backscatters a response modulated with the existing data in the EEPROM. The near-field transponder can receive data from the near-field reader, which the transponder can write into the EEPROM. 
     The mobile device also includes an activation coil energized by the continuous radio frequency signal from the proximate near-field reader and signals the controller when so energized. The controller then transitions to an idle mode and turns on the peripherals, drawing some of the battery&#39;s power. The controller then reads the received data from the transponder&#39;s EEPROM and the controller checks the validity of the received data to be sure that it is not the result of a spurious signal received by the near-field transponder. If the received data is determined to be valid, the controller then transitions to a run mode and turns on the CPU, drawing the normal operating power of the battery. The CPU then reads the received data either from the controller or from the transponder&#39;s EEPROM, which can be a branch address to a selected program stored in the memory of the mobile device. Since the received data is determined to be valid, the branch address is used by the CPU to select the desired program and the CPU executes the selected program. When the CPU completes the execution of selected program, it signals the completion to the controller. In another embodiment, the received data from the transponder&#39;s EEPROM can generate an alarm or can enable the controller to activate a special communication medium. If the activation coil is no longer energized by a proximate near-field reader, the controller then returns to the sleep mode with the CPU off and peripherals off, thereby drawing substantially less or even no power from the battery. In this manner, power saving in mobile devices is improved. 
     In another embodiment, the controller, peripherals, and CPU are not powered by a battery, but instead are powered by the activation coil, which is energized by inductive coupling with the continuous radio frequency signal from the proximate near-field reader. When the activation coil is energized by the continuous radio frequency signal from the proximate near-field reader, it energizes the controller, turning it on. The controller then reads the received data from the transponder&#39;s EEPROM and checks the validity of the received data to be sure that it is not the result of a spurious signal received by the near-field transponder. If the received data is determined to be valid, then the energized controller energizes the peripherals and the CPU and causes received data to be transferred the CPU. The CPU operates on the data, such as by branching to a stored program, sounding an alarm, activating a communication channel, or other functions. If the activation coil is no longer energized by a proximate near-field reader, the controller, the peripheral devices, and the CPU are no longer energized and the controller returns to the sleep mode with the CPU off and peripherals off. In this manner, power saving in mobile devices is improved. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates an external view and a functional block diagram of an example embodiment of the mobile device  100 . 
         FIG. 2  is a flow diagram of the operation of the mobile device of  FIG. 1 , using the activation coil to activate the controller from its quiescent sleep mode when in the vicinity of an RFID reader. 
         FIG. 3  is a circuit diagram of an example activation coil  11  and activation coil circuit  12 . 
     
    
    
     DISCUSSION OF EXAMPLE EMBODIMENTS 
       FIG. 1  illustrates an external view and a functional block diagram of an example embodiment of the mobile device  100 . The mobile device  100  includes a controller  20  with a central processing unit (CPU)  60 , a programmable random-access memory (RAM) volatile memory  62 , a programmable read only memory (PROM)  64 , interface circuits  66 , and a battery  10  to power the CPU  60  in a run mode. The interface circuits  66  are connected to and control the user interface, which can include various types of audio devices, such as microphones, speakers, or earphones, various types of still digital cameras or video digital cameras, various types of visual displays, such as the flat screen display  102 , and various types of input devices, such as a trackball, mouse, stylus, button keys, or the touch screen keys  104 . In its unused state, the controller  20  maintains a sleep mode with the CPU  60  off and peripherals  102  and  104  off, thereby drawing substantially less or even no power from the battery  10 . 
     The mobile device  100  also includes a passive radio frequency identification (RFID) transponder  16  with an electrically erasable, programmable, read-only memory (EEPROM)  14  storage device. The passive RFID transponder  16  is activated by a continuous radio frequency signal  120  from a proximate RFID reader  150 , at the resonant frequency of the transponder&#39;s antenna. The passive RFID transponder  16  backscatters a response signal  122  modulated with the existing data in the EEPROM  14 . The RFID transponder  16  can receive data from the RFID reader  150 , in the form of a modulation of the continuous wave from the reader, which the transponder  16  can write into the EEPROM  14 . 
     The mobile device  100  also includes an activation coil  11 , which is energized by inductive coupling with the continuous radio frequency signal  120  from the proximate RFID reader  150  and the activation coil circuit  12  signals the controller  20  when so energized. The controller  20  then transitions to an idle mode and turns on the peripherals  102  and/or  104 , drawing some of the battery&#39;s power  10 . The controller  20  then reads the received data from the transponder&#39;s EEPROM  14  and the controller checks the validity of the received data to be sure that it is not the result of a spurious signal received by the transponder  16 . The spurious signal, for example, could be from a mobile phone or an invalid RFID reader. If the received data is determined to be valid, the controller  20  then transitions to a run mode and turns on the CPU  60 , drawing the normal operating power of the battery  10 . 
     The CPU  60  then reads the received data either from the controller  20  or from the transponder&#39;s EEPROM  14 , which can be a branch address to a selected program  30 ,  40 , or  50  stored in the memory  62  of the mobile device  100  and the CPU executes the selected program. The programs  30 ,  40 , and  50  can provide various services for the user associated with the geographic location of the particular RFID reader  150  that energizes the RFID transponder  16 . 
     In another embodiment, the received data from the transponder&#39;s EEPROM can enable the controller to generate an alarm or can enable the controller to activate a special communication medium, such as the Near-Field Communication (NFC) circuit  18  to enable contactless communication with an NFC reader device. 
     For example, program  30  can be a Subway Pass program, which enables the mobile device  100  to maintain a current stored-value used for payment for trips within a subway system of a city. In its unused state, the controller  20  maintains a sleep mode with the CPU  60  off and peripherals  102  and  104  off, thereby drawing substantially less or even no power from the battery  10 . At the start of a subway trip from a subway station in the city, when the user approaches an entrance turnstile having an RFID reader  150 , the passive RFID transponder  16  receives from the RFID reader  150  a branch address value for the Subway Pass program  30 , which the RFID transponder  16  writes into the EEPROM  14 . The passive RFID transponder  16  also receives from the RFID reader  150  a location value identifying the location of the RFID reader  150  and its turnstile in the subway system, which the RFID transponder  16  writes into the EEPROM  14 . 
     The activation coil  11  is energized by the continuous radio frequency signal  120  from the proximate RFID reader  150 . The controller  20  is thus energized by the activation coil  11 , transitions to an idle mode and turns on the peripherals, drawing some of the battery&#39;s power. The controller  20  then reads the received data from the transponder&#39;s EEPROM  14  and the controller  20  checks the validity of the received data to be sure that it is not the result of a spurious signal received by the transponder  16 . If the received data is determined to be valid, the controller  20  then transitions to a run mode and turns on the CPU  60 , drawing the normal operating power of the battery. The CPU  60  then reads the received data either from the controller  20  or from the transponder&#39;s EEPROM  14 . The CPU  60  then accesses the branch address value that the RFID reader has sent to the EEPROM  14  of the RFID transponder  16  and uses the branch address to access the Subway Pass program  30  and load it into the RAM  62  for execution by the CPU. The program  30  then instructs the CPU  60  to write into the PROM  64  the location value of the entrance turnstile and RFID reader  150  in the subway system, as a starting location for the trip. 
     As the user walks through the turnstile and leaves the vicinity of the entrance RFID reader  150 , activation coil  11  is no longer energized by the continuous radio frequency signal  120 . In response, the controller  20  returns to the sleep mode with the CPU  60  and the peripherals  102  and  104  off, thereby drawing substantially less or even no power from the battery  10 . The user then rides the subway to the intended destination station. 
     When the user reaches the destination station and approaches an exit turnstile having an RFID reader  150 , the passive RFID transponder  16  receives from the exit RFID reader  150  a branch address value for the subway Pass program  30 , which the RFID transponder  16  writes into the EEPROM  14 . The passive RFID transponder  16  also receives from the exit RFID reader  150  a location value identifying the location of the exit RFID reader  150  and its turnstile in the subway system, which the RFID transponder  16  writes into the EEPROM  14 . 
     The activation coil  11  is energized by the continuous radio frequency signal  120  from the exit RFID reader  150 . The controller  20  is thus energized by the activation coil  11 , transitions to an idle mode and turns on the peripherals, drawing some of the battery&#39;s power. The controller  20  then reads the received data from the transponder&#39;s EEPROM  14  and the controller  20  checks the validity of the received data to be sure that it is not the result of a spurious signal received by the transponder  16 . If the received data is determined to be valid, the controller  20  then transitions to a run mode and turns on the CPU  60 , drawing the normal operating power of the battery. The CPU then reads the received data either from the controller  20  or from the transponder&#39;s EEPROM  14 . The CPU  60  then accesses the branch address value that the RFID reader has sent to the EEPROM  14  of the RFID transponder  16  and uses the branch address to access the Subway Pass program  30  and load it into the RAM  62  for execution by the CPU. The program  30  instructs the CPU  60  to access the PROM  64  to determine whether this is the beginning or the end of a subway trip. Since the PROM  64  stores the location value of the entrance turnstile as a starting location for the trip, program  30  instructs the CPU  60  to write the starting location value into the EEPROM  14  of the RFID transponder  16  and to signal the RFID transponder  16  to transmit the starting location value to the exit RFID reader  150  in a modulated response, by backscattering the continuous carrier wave from the RFID reader. The exit RFID reader  150  then computes the charge for the subway trip as a function of the difference between the starting location and the destination location of the exit RFID reader  150 . The passive RFID transponder  16  then receives from the exit RFID reader  150  the amount charged for the trip, which the CPU  60  accesses from the EEPROM  14  of the RFID transponder  16 , deducts from the current stored-value in the PROM  64 , and stores the balance in the PROM  64 . The CPU  60  can output the balance value to the LCD display  102  for presentation to the user. 
     As the user walks through the exit turnstile and leaves the vicinity of the exit RFID reader  150 , activation coil  11  is no longer energized by the continuous radio frequency signal  120 . In response, the controller  20  returns to the sleep mode with the CPU  60  and the peripherals  102  and  104  off, thereby drawing substantially less or even no power from the battery  10 . 
     Other example programs stored in the mobile device  100  can include a city map program  40  and an event tickets program  50 . When the CPU  60  completes the execution of selected program  30 ,  40 , or  50 , it signals the completion to controller  20 . If the activation coil  11  is no longer energized by a proximate RFID reader, the controller  20  then returns to the sleep mode with the CPU  60  off and peripherals  102  and  104  off, thereby drawing substantially less or even no power from the battery  10 . In this manner, power saving in mobile devices is improved. 
     The mobile device  100  of  FIG. 1  can also include a Near-Field Communication (NFC) circuit  18  to enable contactless communication with a reader device, such as would be associated with the turnstiles in the above subway pass example. The NFC circuit  18  can exchange data with a reader device, such as the amount charged for the subway trip. NFC communicates via magnetic field induction, where two loop antennas are located within each other&#39;s near field, effectively forming an air-core transformer. It operates within the unlicensed radio frequency ISM band of 13.56 MHz, with a bandwidth of approximately 2 MHz over a typical distance of a few centimeters. 
     In another embodiment, the transponder  16  can be a Near-Field Communication (NFC) transponder to enable contactless communication with the reader device  150 , which can be an NFC reader device. In this embodiment, the activation coil  11  is energized by inductive coupling via the near field of the loop antenna of the reader  150 . 
     In another embodiment, the CPU  60  is not powered by a battery, but instead is powered by the activation coil  11 , which is energized by inductive coupling with the continuous radio frequency signal  120  from the proximate near-field reader  150 . When the activation coil  11  is energized by the continuous radio frequency signal  120  from the proximate near-field reader  150 , it energizes the controller  20 , turning it on. The controller  20  then reads the received data from the transponder&#39;s EEPROM  14  and checks the validity of the received data to be sure that it is not the result of a spurious signal received by the transponder  16 . If the received data is determined to be valid, then the energized controller  20  energizes the peripherals and the CPU  60  and transfers the received data to the CPU  60 . The CPU  60  can read the received data either from the controller  20  or from the transponder&#39;s EEPROM  14  and operate on the data, such as by branching to a stored program, sounding an alarm, activating a communication channel, or other functions. If the activation coil is no longer energized by a proximate near-field reader  150 , the controller  20 , the peripheral devices  102  and  104 , and the CPU  60  are no longer energized and the controller  20  returns to the sleep mode with the CPU  60  off and peripherals  102  and  104  off. In this manner, power saving in mobile devices is improved. 
       FIG. 2  is a flow diagram of the operation of the mobile device of  FIG. 1 , using the activation coil to activate the controller from its quiescent sleep mode when moving into the vicinity of an RFID reader. The method of the flow diagram can be embodied as program logic stored in the RAM  62  and/or PROM  64  in the form of sequences of programmed instructions which, when executed in the controller  20  and/or the CPU  60 , carry out the functions of the disclosed embodiments. 
     The method of  FIG. 2  includes the following example steps: 
     Step  200 : In its unused state, the controller  20  maintains a sleep mode with the CPU  60  off and peripherals  102  and  104  off, thereby drawing substantially less or even no power from the battery  10 . 
     Step  204 : The passive RFID transponder  16  is activated by a continuous radio frequency signal  120  from a proximate RFID reader  150 . The passive RFID transponder  16  backscatters a response  122  modulated with the existing data in the EEPROM  14 . 
     Step  208 : The RFID transponder  16  receives data from the RFID reader  150 , which the transponder  16  can write into the EEPROM  14 . 
     Step  212 : The mobile device  100  also includes an activation coil  11  that is energized by the continuous radio frequency signal  120  from the proximate RFID reader  150  and the activation coil  11  signals the controller  20  when so energized. 
     Step  216 : In one example embodiment, the controller  20  then transitions to an idle mode and turns on the peripherals  102  and/or  104 , drawing some of the battery&#39;s power  10 . In another example embodiment, the controller, peripherals, and CPU are not powered by a battery, but instead are powered by the activation coil  11 , which is energized by inductive coupling with the continuous radio frequency signal from the proximate RFID reader. 
     Step  220 : The energized controller  20  then reads the received data from the transponder&#39;s EEPROM  14 , and checks the validity of the received data to be sure that it is not the result of a spurious signal received by the transponder  16 . 
     Step  224 : If the received data is determined to be valid, then the energized controller energizes the peripherals and the CPU and transfers the received data to the CPU, which can be a branch address to a selected program  30 ,  40 , or  50  stored in the memory  62  of the mobile device  100 . 
     Step  228 : The CPU  60  then executes the selected program  30 ,  40 , or  50 . 
     Step  232 : When the CPU  60  completes the execution of selected program  30 ,  40 , or  50 , it signals the completion to controller  20 . 
     Step  236 : If the activation coil is no longer energized by a proximate RFID reader, the controller  20  then returns to the sleep mode with the CPU  60  off and peripherals  102  and  104  off. Where the CPU is powered by a battery, power is no longer drawn from the battery  10 . 
     In this manner, power saving in mobile devices is improved. 
       FIG. 3  is a circuit diagram of an example activation coil  11  and activation coil circuit  12 . The activation coil  11  will have an induced voltage when exposed to the continuous radio frequency signal  120  from a nearby RFID reader  150 . The diodes in the circuit rectify the pulses of induced voltage from the inductance of the coil  11  and the parallel capacitors build a positive DC voltage that is applied to the regulator. The output of the regulator is the enabling signal applied to the controller  20  to initiate its transition from the sleep mode to the idle mode and the run mode. The regulator limits the magnitude of voltage input to the controller  20  to avoid damaging it. When the mobile device  100  is moved away from an RFID reader  150  so that the activation coil  11  is no longer exposed to the continuous radio frequency signal  120 , the DC voltage applied to the regulator quickly dissipates. This causes the controller  20  to transition back to the sleep mode. This transition back to the sleep mode can be delayed for a predetermined interval by means of programming a timer in the controller  20 . 
     The controller  20  can be, for example, a PIC18F8527 Flash Microcontroller, manufactured by Microchip Technology Inc. The PIC Microcontroller device includes a 16-bit CPU, programmable instruction and data memories, various timers and peripheral interfaces. The transition from the sleep mode to the idle mode and the run mode can be staged to occur after predetermined intervals by means of programming a timer in the controller  20 . The PIC Microcontroller device is packaged in an 80-pin, thin quad flat pack (TQFP), which is a type of integrated circuit packaging designed for use in limited space applications such as mobile devices. The PIC Microcontroller device has the power managed modes of: 
     [1] Run: CPU on, peripherals on; 
     [2] Idle: CPU off, peripherals on; and 
     [3] Sleep: CPU off, peripherals off. 
     The PIC Microcontroller device&#39;s idle mode currents can be as low as 15 μA and the sleep mode current can be as low as 0.2 μA. The device is described in  PIC 18F8722  Family Data Sheet,  64/80- Pin,  1- Mbit, Enhanced Flash Microcontrollers with  10- bit A/D and nanoWatt Technology,  published by Microchip Technology Inc., 2004. 
     CONCLUSION 
     The resulting embodiments of the invention improve power saving in mobile devices. Using the description provided herein, the embodiments may be implemented as a machine, process, or article of manufacture by using standard programming and/or engineering techniques to produce programming software, firmware, hardware or any combination thereof. 
     Any resulting program(s), having computer-readable program code, may be embodied on one or more computer-usable media such as resident memory devices, smart cards or other removable memory devices, or transmitting devices, thereby making a computer program product or article of manufacture according to the embodiments. As such, the terms “article of manufacture” and “computer program product” as used herein are intended to encompass a computer program that exists permanently or temporarily on any computer-usable medium or in any transmitting medium which transmits such a program. 
     As indicated above, memory/storage devices include, but are not limited to, disks, optical disks, removable memory devices such as smart cards, SIMs, WIMs, semiconductor memories such as RAM, ROM, PROMS, etc. Transmitting mediums include, but are not limited to, transmissions via wireless communication networks. 
     The transponder  16  can be a radio frequency identification (RFID) transponder, a Near-Field Communication (NFC) transponder, or any other near-field communications device. 
     Although specific example embodiments have been disclosed, a person skilled in the art will understand that changes can be made to the specific example embodiments without departing from the spirit and scope of the invention.