Patent Publication Number: US-2018053079-A1

Title: Systems and methods for drive circuits for dynamic magnetic stripe communications devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/305,021, titled “SYSTEMS AND METHODS FOR DRIVE CIRCUITS FOR DYNAMIC MAGNETIC STRIPE COMMUNICATIONS DEVICES,” filed Feb. 16, 2010 (Attorney Docket No. D/032 PROV), which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to magnetic cards and devices and associated payment systems. 
     SUMMARY OF THE INVENTION 
     A card may include a dynamic magnetic communications device. Such a dynamic magnetic communications device may take the form of a magnetic encoder or a magnetic emulator. A magnetic encoder may change the information located on a magnetic medium such that a magnetic stripe reader may read changed magnetic information from the magnetic medium. A magnetic emulator may generate electromagnetic fields that directly communicate data to a magnetic stripe reader. Such a magnetic emulator may communicate data serially to a read-head of the magnetic stripe reader. 
     All, or substantially all, of the front as well as the back of a card may be a display (e.g., bi-stable, non bi-stable, LCD, LED, or electrochromic display). Electrodes of a display may be coupled to one or more capacitive touch sensors such that a display may be provided as a touch-screen display. Any type of touch-screen display may be utilized. Such touch-screen displays may be operable of determining multiple points of touch. Accordingly, a barcode may be displayed across all, or substantially all, of a surface of a card. In doing so, computer vision equipment such as barcode readers may be less susceptible to errors in reading a displayed barcode. 
     A card may include a number of output devices to output dynamic information. For example, a card may include one or more RFIDs or IC chips to communicate to one or more RFID readers or IC chip readers, respectively. A card may include devices to receive information. For example, an RFID and IC chip may both receive information and communicate information to an RFID and IC chip reader, respectively. A device for receiving wireless information signals may be provided. A light sensing device or sound sensing device may be utilized to receive information wirelessly. A card may include a central processor that communicates data through one or more output devices simultaneously (e.g., an RFID, IC chip, and a dynamic magnetic stripe communications device). The central processor may receive information from one or more input devices simultaneously (e.g., an RFID, IC chip, dynamic magnetic stripe devices, light sensing device, and a sound sensing device). A processor may be coupled to surface contacts such that the processor may perform the processing capabilities of, for example, an EMV chip. The processor may be laminated over and not exposed such that such a processor is not exposed on the surface of the card. 
     A card may be provided with a button in which the activation of the button causes a code to be communicated through a dynamic magnetic stripe communications device (e.g., the subsequent time a read-head detector on the card detects a read-head). The code may be indicative of, for example, a merchant code or incentive code. The code may be received by the card via manual input (e.g., onto buttons of the card) or via a wireless transmission (e.g., via light, electromagnetic communications, sound, or other wireless signals). A code may be communicated from a webpage (e.g., via light and/or sound). A card may include a display such that a received code may be visually displayed to a user. In doing so, the user may be provided with a way to select, and use, the code. 
     A dynamic magnetic stripe communications device may include a magnetic emulator that comprises an inductor (e.g., a coil). Current may be provided through this coil to create an electromagnetic field operable to communicate with the read-head of a magnetic stripe reader. The drive circuit may fluctuate the amount of current travelling through the coil such that a track of magnetic stripe data may be communicated to a read-head of a magnetic stripe reader. A switch (e.g., a transistor) may be provided to enable or disable the flow of current according to, for example, a frequency/double-frequency (F2F) encoding algorithm. In doing so, bits of data may be communicated. 
     A closed loop linear analog drive circuit may be provided to precisely define the current flow at any and all points in time. In doing so, the closed loop linear analog drive circuit may create any desired electromagnetic field at any time. Accordingly, the accuracy and reliability of a magnetic emulator may be enhanced. 
     Each track of magnetic stripe information may utilize, for example, a separate instance of a drive circuit coupled to a separate magnetic emulator having a coil. Enabling circuitry may be coupled to one or more drive circuits and/or magnetic emulators to enable the use of such components. 
     An input signal may be provided from, for example, a microprocessor or other circuitry. Several microprocessors may, for example, be included on a card or other device (e.g., a mobile telephonic device). A ramp generator may be provided, for example, to convert a positive or negative going level transition of an input signal into either a positive going or negative going linear ramp of defined slope. This signal of, for example, alternative positive and negative ramps may be passed to additional signal processing circuitry. 
     Signal shaping circuitry may be provided and may, for example, receive the signal provided by the ramp generator. The signal shaping circuitry may be utilized to shape the ramp signals provided by the ramp generator. 
     The shaped signals may be provided to current control circuitry. The current control circuit may be utilized, for example, to control the level of current at an output node. 
     A control input may be provided, for example, that provides a muting function. When such a control signal is pulled high to the supply voltage, for example, the drive current may be forced to approximately 0 A (e.g., 0 A). Such a muting function may be utilized, for example, to silence a dynamic magnetic stripe communications device during power-up and power-down of the drive circuits. When such circuits are not in use, for example, power may be removed to increase battery life. During a power transition, for example, the mute function may prevent unwanted signals (e.g., pulses) from being generated. 
     A reference voltage may be utilized by a voltage regulator. In doing so, for example, the dependence on a supply voltage may be eliminated. For example, a battery may be supercharged and this battery may have different voltage levels during the battery&#39;s use. A reference voltage provided from a voltage regulator may, for example, provide a more reliable source of electrical energy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The principles and advantages of the present invention can be more clearly understood from the following detailed description considered in conjunction with the following drawings, in which the same reference numerals denote the same structural elements throughout, and in which: 
         FIG. 1  is an illustration of cards constructed in accordance with the principles of the present invention; 
         FIG. 2  is an illustration of a process flowchart and waveforms constructed in accordance with the principles of the present invention; 
         FIG. 3  is an illustration of an architecture constructed in accordance with the principles of the present invention; 
         FIG. 4  is a schematic of a circuit constructed in accordance with the principles of the present invention; 
         FIG. 5  is a schematic of a circuit constructed in accordance with the principles of the present invention; and 
         FIG. 6  is an illustration of a process flow chart constructed in accordance with the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows card  100  that may include, for example, a dynamic number that may be entirely, or partially, displayed via display  112 . A dynamic number may include a permanent portion such as, for example, permanent portion  111 . Permanent portion  111  may be printed as well as embossed or laser etched on card  100 . Multiple displays may be provided on a card. For example, display  113  may be utilized to display a dynamic code such as a dynamic security code. Display  125  may also be provided to display logos, barcodes, as well as multiple lines of information. A display may be a bi-stable display or non bi-stable display. Permanent information  120  may also be included and may include information such as information specific to a user (e.g., a user&#39;s name or username) or information specific to a card (e.g., a card issue date and/or a card expiration date). Card  100  may include one or more buttons such as buttons  130 - 134 . Such buttons may be mechanical buttons, capacitive buttons, or a combination or mechanical and capacitive buttons. Card  100  may include button  199 . Button  199  may be used, for example, to communicate information through dynamic magnetic stripe communications device  101  indicative of a user&#39;s desire to communicate a single track of magnetic stripe information. Persons skilled in the art will appreciate that pressing a button (e.g., button  199 ) may cause information to be communicated through device  101  when an associated read-head detector detects the presence of a read-head of a magnetic stripe reader. Button  198  may be utilized to communicate (e.g., after button  198  is pressed and after a read-head detects a read-head of a reader) information indicative of a user selection (e.g., to communicate two tracks of magnetic stripe data). Multiple buttons may be provided on a card and each button may be associated with a different user selection. 
     Architecture  150  may be utilized with any card. Architecture  150  may include processor  120 . Processor  120  may have on-board memory for storing information (e.g., drive code). Any number of components may communicate to processor  120  and/or receive communications from processor  120 . For example, one or more displays (e.g., display  140 ) may be coupled to processor  120 . Persons skilled in the art will appreciate that components may be placed between particular components and processor  120 . For example, a display driver circuit may be coupled between display  140  and processor  120 . Memory  142  may be coupled to processor  120 . Memory  142  may include data that is unique to a particular card. For example, memory  142  may store discretionary data codes associated with buttons of card  150 . Such codes may be recognized by remote servers to effect particular actions. For example, a code may be stored on memory  142  that causes a promotion to be implemented by a remote server (e.g., a remote server coupled to a card issuer&#39;s website). Memory  142  may store types of promotions that a user may have downloaded to the device and selected on the device for use. Each promotion may be associated with a button. Or, for example, a user may scroll through a list of promotions on a display on the front of the card (e.g., using buttons to scroll through the list). 
     Any number of reader communication devices may be included in architecture  150 . For example, IC chip  152  may be included to communicate information to an IC chip reader. IC chip  152  may be, for example, an EMV chip. As per another example, RFID  151  may be included to communicate information to an RFID reader. A magnetic stripe communications device may also be included to communicate information to a magnetic stripe reader. Such a magnetic stripe communications device may provide electromagnetic signals to a magnetic stripe reader. Different electromagnetic signals may be communicated to a magnetic stripe reader to provide different tracks of data. For example, electromagnetic field generators  170 ,  180 , and  185  may be included to communicate separate tracks of information to a magnetic stripe reader. Such electromagnetic field generators may include a coil wrapped around one or more materials (e.g., a soft-magnetic material and a non-magnetic material). Each electromagnetic field generator may communicate information serially to a receiver of a magnetic stripe reader for a particular magnetic stripe track. Read-head detectors  171  and  172  may be utilized to sense the presence of a magnetic stripe reader (e.g., a read-head housing of a magnetic stripe reader). This sensed information may be communicated to processor  120  to cause processor  120  to communicate information serially from electromagnetic generators  170 ,  180 , and  185  to magnetic stripe track receivers in a read-head housing of a magnetic stripe reader. Accordingly, a magnetic stripe communications device may change the information communicated to a magnetic stripe reader at any time. Processor  120  may, for example, communicate user-specific and card-specific information through RFID  151 , IC chip  152 , and electromagnetic generators  170 ,  180 , and  185  to card readers coupled to remote information processing servers (e.g., purchase authorization servers). Driving circuitry  141  may be utilized by processor  120 , for example, to control electromagnetic generators  170 ,  180 , and  185 . 
       FIG. 2  shows process  201  that may include, for example, ramp generator  202 , signal shaping  203 , and current control  204 . A control signal may be generated by, for example, a microprocessor or other control circuitry. Such a control signal may be utilized by ramp generator  202  to, for example, generate a linear increasing or a linear decreasing signal. The slope of the signal may be pre-determined and stored in memory. The slope of the signal may be changed. For example, the slope of the signal may be different depending on, for example, the environment that is sensed by a card or other device (e.g., a determination by a read-head detector that a particular type of reader is being utilized). The signal produced by ramp generator  202  may also be controlled to produce frequency/double-frequency (F2F) encoded information by the microprocessor. Such information may be shaped by, for example, signal shaping  203 . Signal shaping  203  may be utilized to shape the signal produced by ramp generator  202  to provide, for example, a non-linear shape in the signal. Current control circuitry  204  may be utilized, for example, to control the current of the output signal from process  201 . 
     Signal  210  may be provided, for example, from a ramp generator providing a ramp generator signal. The ramp generator may receive, for example, a control signal on when ramp generator should produce an increasing signal, decrease the signal, or leave the output signal steady. The increasing signal may be limited, for example, at a voltage threshold in the positive or negative directions. The decreasing signal may be limited, for example, at a voltage threshold in the positive or negative directions. For example, the ramp may occur in a single polarity or across both the positive and negative polarities. 
     Signal  215  may be provided, for example, to provide a ramped signal in the positive polarity. The maximum threshold may be, for example, between approximately 2.2 and 3.6 volts (e.g., approximately 2.7 volts). The minimum threshold may be, for example, between approximately 0 and 0.1 volts (e.g., 0 volts). Person skilled in the art will appreciate that the ramp generator may hold a peak for a particular amount of time. For example, the ramp generator may hold a peak at an amount of time greater than it took the predecessor (or successor) ramp to be provided from the ramp generator. In doing so, for example, a cleaner signal may be provided to a read-head of a magnetic stripe reader. Alternatively, for example, the ramp generator may hold a peak at an amount of time less than, or equal to, the time it took the predecessor (or successor) ramp to be provided from the ramp generator. Signal  215  may, for example, be provided as a trapezoidal wave signal. 
     Signal  220  may be, for example, the shaped signal provided to a current control circuit (e.g., from a signal shaping circuit). The shaped signal may provide, for example, shaped trapezoidal segments (e.g., segment  221 ) to a current control circuit. A current may then be provided, for example, to a coil of a magnetic emulator from the current control circuitry that is a function, for example, of the voltage provided from the signal shaping circuit. Signal  220  may include, for example, sinusoidal and arctangent signal characteristics beyond the characteristics present in the ramped signal from the ramp generator. More particularly, the shaped signal may smooth and curve the transition points in the ramped signal (e.g., point  219  of signal  215 ). In doing so, a signal with less noise and ringing may, for example, be provided to a read-head of a magnetic stripe reader. Persons skilled in the art will appreciate that constant voltage portions of a ramp signal (e.g., portion  217  of signal  215 ) may also provide areas of constant voltage in shaped signal. The areas of constant voltages between a ramp generated signal and a shaped signal, however, may differ in length (e.g., the length of constant voltages in a shaped signal may be shorter). 
     Signal  225  may be, for example, the change in current with respect to change in time signal received by a read-head of a magnetic stripe reader as a result of receiving a signal from a coil driven by the current signal produced by control circuit  204 . Persons skilled in the art will appreciate increases in voltages in signal  220  may result in positive pulses (e.g. pulse  226 ) of signal  225  and decreases in voltages in signal  220  may result in negative pulses (e.g., pulse  227 ) in signal  225 . 
       FIG. 3  shows processor  310  that provides drive (e.g., signal  311 ) and mute signals (e.g., signal  312 ) to drive circuitry (e.g., drive circuitry  320 ) as well as control signals (e.g., signal  319 ) to enabling circuitry  360 . Drive circuitry may provide dynamic magnetic communications device drive signals (e.g., signal  321 ) to dynamic magnetic communications devices (e.g., device  370 ). A different drive circuit may be utilized, for example, for a different dynamic magnetic communications device (e.g., a different emulator, having a coil, for communicating a different track of magnetic stripe data). A different processor may provide, for example, drive and mute signals to such different drive circuit. 
     A drive circuit may include, for example, a ramp generator circuit (e.g., ramp generator  202  of  FIG. 2 ), signal shaping circuit (e.g., signal shaping circuit  203  of  FIG. 3 ), and current control circuit (e.g., current control circuit  204  of  FIG. 2 ). Drive circuitry (e.g., drive circuitry  320 ) may provide a shaped signal to a dynamic magnetic stripe communications device (e.g., device  370 ). Similarly, for example, enabling circuitry  360  may provide enabling signals (e.g., signals  361 ) to, for example, drive circuitry and dynamic magnetic stripe communication devices. 
     A single processor may be utilized, for example, to control one, two, three, or four drive circuits and magnetic emulators for communication of separate tracks of magnetic stripe data. A single enabling circuit may be utilized to enable, for example, one, two, three, or four magnetic emulators. For example, a single enabling circuit may be utilized to enable two magnetic emulators while a single processor may be utilized to provide control and mute signals to drive two circuits (e.g., one for each emulator). Alternatively, more than one processor may be utilized, for example, to control separate drive circuits and more than one enabling circuit may be utilized to enable separate magnetic emulators. 
       FIG. 4  may include circuitry  400  that may include, for example, first source voltage  401 , second source voltage  402 , ground  499 , drive signal  412 , mute signal  411 , output signal  413 , transistors  441 - 445 , capacitors  451  and  452 , resistors  421 - 431 , diodes  471 - 473 , and operational amplifiers  461  and  462 . Persons skilled in the art will appreciate that circuitry  400  may be utilized as a drive circuit for communicating a track of magnetic stripe data through a magnetic emulator. A magnetic emulator may include, for example, an inductor such as a coil. Such a coil may be fabricated, for example, on a flexible, printed circuit board such as a multiple-layer flexible, printed circuit board. 
     Capacitor  451  may have approximately, for example, between 1800 and 3500 pF (e.g., approximately 2200 pF). Capacitor  451  may be utilized, for example, to control the width of pulses in a signal received by a read-head of a magnetic stripe reader (e.g., the width of pulse  226  of signal  225  of  FIG. 2 ). 
     Drive signal  412  may be provided, for example, from a processor. A ramp generator circuit may be provided that may include, for example, resistors  421  and  422 , transistors  441 - 444 , capacitor  451 , and operational amplifier  461 . 
     The ramp generator circuit may include operational amplifier  461 , which may serve as an impedance buffer for the output of the ramp generator circuit. Accordingly, for example, the voltage across capacitor  451  may not be loaded by subsequent circuitry. Transistors  443  and  444  may, for example, be coupled to form a temperature compensated constant current source. The current level may be defined, for example, by resistor  422 . The input signal (e.g., drive signal  412 ) may be, for example, either grounded (e.g., at zero voltage equal to ground  499 ) or left floating (e.g., open collector active pull-down driven). The resulting constant current may be, for example, selectively applied to capacitor  451 , whose voltage may then be linearly increased when desired to form a positive going ramp reaching, but not exceeding, for example, supply voltage  401 . 
     A microprocessor may be configured to provide the characteristics of a ramp generator, shaping signal circuit, as well as a current control circuit. Alternatively, for example, such ramp generator, shaping signal, and current control circuits may be provided on an ASIC or multiple ASICs. Multiple drive circuits may be provided on an ASIC. For example, a single ASIC may provide two or three drive circuits which, in turn, may be utilized to cause two or three, respectively, dynamic magnetic communications devices (e.g., magnetic emulators) to communicate different tracks of data to a read-head of a magnetic stripe reader. 
     Transistors  441  and  442  may be coupled, for example, to form a temperature compensated constant current sink with a current level defined by resistor  421 . The circuit comprising transistors  441  and  442  may, for example, consistently draw a constant current which, in turn, may deplete the charge on capacitor  451  when the current source from transistors  443  and  444  is inoperative and deducts from the sourced current when the current source from transistors  443  and  444  is operative. 
     The current source created by transistors  443  and  444 , for example, may deliver approximately twice the current utilized by the current sink created by  441  and  442 . This may be achieved, for example, by setting resistor  421  to approximately twice the value of resistor  422 . As a result, for example, the state of input  412  may define whether capacitor  451  is charged or depleted by matched current values of opposing sign. The result, for example, may be an output of positive going or negative going linear ramps of equal, but opposite sign slope. 
     A signal shaping functionality may be applied to, for example, the signal produced by the ramp generator circuit. Accordingly, for example, a signal shaping circuit may be provided and may include, for example, resistors  423 - 428  and diodes  471 - 472 . The ramp signal from the ramp circuit may be provided to, for example, resistor  423 . The resulting shaped signal from the shaping circuit may be provided, for example, at the common point between resistors  424  and  428 . 
     The signal shaping circuit may include diodes  471  and  472 . The signal shaping circuit may include additional diodes. Such diodes may be biased to impart their linear characteristics onto the signal being received by the shaping circuit. Resistors  423 - 426  and  428  may be bias resistors that are selected to provide a smooth transition from, for example, the zero volt level through to the reference voltage  401  beginning with a slope of approximately zero volts/second and finishing with a slope of approximately zero volts/second. The resultant shape may be similar to, for example, approximately an arctangent curve. The resistor pair  424  and  438  may present, for example, a portion of the resulting shaped signal to the positive terminal of operational amplifier  462 . 
     A current control functionality may be applied to, for example, the signal produced by the signal shaping circuit. Accordingly, for example, a current control circuit may be provided and may include, for example, resistors  429 - 431 , operational amplifier  462 , transistor  445 , capacitor  452  and diode  473 . The shaped signal from the signal shaping circuit may be provided to, for example, the positive terminal of operational amplifier  462 , which is operable to control the level of current at output  413 . The current from output  413  may, for example, be passed through a magnetic emulator (e.g., through a coil) connected between output  413  and a positive supply voltage (e.g., supply voltage  402 ). The coil may be utilized to serial transmit a track of magnetic stripe data. 
     Operational amplifier  462  and feedback resistor  430  may control, for example, the collector-base current of transistor  445  so as to establish a voltage across sense resistor  431  related to the incoming signal. In this manner, the current drawn through a coil of a magnetic emulator, for example, may be precisely controlled. 
     Resistor  429  may, for example, provide an offset such that the driven current corresponding to the zero volt level of the signal input comes close to approximately, but does not reach, zero milliamps. For example, the current may be, for example, limited to approximately 2-3 milliamps (e.g., approximately 2 milliamps). Accordingly, transistor  445  may remain active and not shut-off, thereby avoiding, for example, non-linear and abrupt changes in current that are undesirable in the final output signal. 
     Resistor  431  may be, for example, a sense resistor. Resistor  431  may be selected, for example, so as to scale the current to levels needed to operate a dynamic magnetic stripe communications device. The current associated with the maximum input signal (e.g., at reference voltage  401 ) may have, for example, a range between 50-100 milliamps. Alternatively, for example, the current may be above or below this range. 
     A dynamic magnetic stripe communications device may, for example, be provided between output  413  and supply voltage  402 . A high pass filter may be provided. Such a high pass filter may include, for example a capacitor such as capacitor  452 . Such a high pass filter may, for example, prevent abrupt signal changes that include high frequency components from reaching the dynamic magnetic stripe communications device. 
     Diode  473  may be provided. Diode  473  may provide back-EMF protection for the drive circuitry when, for example, the output drives an inductive load. 
     An auxiliary control signal may be provided, for example, to provide a mute functionality. Such a mute signal (e.g., signal  411 ) may be utilized to force the drive current, for example, to zero amperes (e.g., if pulled up). The signal, for example, may be left floating as needed during normal feedback control. The muting functionality may be utilized, for example, to silence a dynamic magnetic stripe communications device during power-up and power-down of the drive circuits. When not in use, for example, the power may be removed from these circuits to increase battery life. During a power transition, however, undesirable signals/pulses may be generated. The muting functionality may be utilized to prevent such undesirable signals/pulses. 
     A sequence may include, for example, holding the mute signal high, applying power to the drive circuits, releasing the mute signal, driving data to the dynamic magnetic stripe communications device, pulling the mute signal high, removing power from the drive circuits, and setting circuitry for optimum low-power stand-by operation. 
     Persons skilled in the art will appreciate that low-power operation may be optimized.  FIG. 5  shows power control circuit  500  that may include, for example, enable circuitry  511 , resistor  531 , switching component  521 , component  561 , capacitors  551 - 563 , source voltages  501 ,  502 , and  503 , and ground  599 . 
     Switching component  521  may be, for example, a MOSFET. Switching component  521  may be used to, for example, switch current and therefore power from a power supply that may be a battery (e.g., power source  501 ). A MOSFET may be utilized as a switching component, for example, that has a low series resistance in an ON mode. A control signal (e.g., signal  511 ), which may be supplied by a microprocessor or other circuit, may be utilized to turn ON or OFF switching component  521 . 
     Persons skilled in the art will appreciate that power usage may be minimized by, for example, providing control signal  511  in a high-impedance state (floating) when switching device  521  is to be in the OFF state. For this reason, for example, resistor  531  is provided to hold switching device  521  in the OFF state. 
     The output of switching device  521  may, for example, supply the VCC power to the output stages of the current control circuit of circuit  400  of  FIG. 4  as well as, for example, the operational amplifiers of circuit  400  of  FIG. 4 . Additionally, for example, power may be supplied to additional circuits utilizing reference voltages. 
     A reference voltage (e.g., voltage  401  of  FIG. 4  and voltage  503  of  FIG. 5 ) may be provided, for example, by a voltage regulator (e.g., component  561  of  FIG. 5 ). A reference voltage may, for example, remove the dependence on a supply voltage (e.g., voltage  402  of  FIG. 4 ). The supply voltage may vary in cases where, for example, a battery is utilized as the overall power source and the battery may discharge through use. 
     A low drop-out (LDO) linear regulator may be utilized as a voltage regulator. Zener diode circuits may also be utilized. A resulting voltage reference may be filtered by, for example, capacitor  563  or other circuits. The voltage reference may be provided, for example, at a point below the minimum possible supply voltage. Accordingly, a battery may be provided and discharged to approximately 2.8 volts. Accordingly, a reference voltage may be provided at approximately 2.7 volts. Accordingly, the difference between a supply voltage and reference voltage may be between 0.2 volts and 0.5 volts (e.g., approximately 0.1 volts). 
     A signal shaper circuit may, for example, utilize any number of diodes (e.g., approximately 9 diodes) and bias resistors to provide a more precise implementation of an arctangent waveform. Additional diodes may introduce, for example, additional breakpoints in a piecewise approximation of the desired waveform. Resistors  425 ,  427 , and  426  may, for example, be replaced with two adjustable voltage references, which may be different from voltage  401  (e.g., half of voltage of voltage  401  and/or may differ from voltage  401  by approximately 0.5−1.5 or 1 volts). 
     The current drive may be, for example, provided by replacing the operational amplifier with one or more individual transistors in an open loop control configuration. Persons skilled in the art will appreciate that transistors may be, for example, replaced with MOSFETs (e.g., in circuit  400  of  FIG. 4 ). The operational amplifier in a ramp generator circuit may, for example, be replaced with a pair of transistors in a push-pull arrangement. 
       FIG. 6  shows a sequence to communicate magnetic stripe data to a magnetic stripe reader. The sequence may include, for example, holding the mute signal high (e.g., step  601  of  FIG. 6 ), applying power to the drive circuits (e.g., step  602  of  FIG. 6 ), releasing the mute signal (e.g., step  603  of  FIG. 6 ), driving data to the dynamic magnetic stripe communications device (e.g., step  604  of  FIG. 6 ), pulling the mute signal high (e.g., step  605  of  FIG. 6 ), removing power from the drive circuits, and setting circuitry for optimum low-power stand-by operation. All or a portion of the process may be repeated multiple times such that a card may be swiped multiple times at a magnetic stripe reader. Read-head detectors may be provided on a card to determine if, for example, a card is being re-swiped at a magnetic stripe reader. Low-power stand-by operation may include, for example, placing a microprocessor in a sleep mode. A microprocessor may be awakened from sleep mode, for example, by a card (or other device) receiving manual input from a user. For example, a user may press a button on a card to select a feature, the microprocessor may be awakened from sleep mode, and magnetic stripe data may be communicated by a drive circuit and dynamic magnetic stripe communications device to a magnetic stripe reader when circuitry on the card determines that dynamic magnetic stripe communications device is within the proximity of a read-head of a magnetic stripe reader to communicate magnetic stripe data (e.g., via one or more magnetic stripe read-head detectors provided on the card or other device). 
     Persons skilled in the art will appreciate that a boost circuit may be provided. A battery (e.g., a battery having approximately 3.6 volts for normal operation) may be supercharged to a higher voltage (e.g., approximately 3.8 to 4.5 volts such as approximately 4.2 volts). The microprocessor, however, may not be able to directly utilize the voltage from a supercharged battery. As a result, for example, a boost circuit may be provided to step down the voltage of a supercharged battery to a level that may be utilized by a microprocessor. The boost circuitry may determine when the battery discharges past a particular threshold (e.g., to a voltage suitable to directly power a microprocessor) so that the boost circuitry may stop stepping down the voltage of the battery. The boost circuitry may also change the voltage the battery is stepped down. Accordingly, for example, as the voltage supplied by a battery decreases, the boost circuitry may decrease the amount of voltage the battery is stepped down. In doing so, additional power may be obtained from a battery without, for example, damaging the microprocessor or causing the microprocessor to malfunction. 
     Persons skilled in the art will also appreciate that the present invention is not limited to only the embodiments described. Instead, the present invention more generally involves dynamic information. Persons skilled in the art will also appreciate that the apparatus of the present invention may be implemented in other ways then those described herein. All such modifications are within the scope of the present invention, which is limited only by the claims that follow.