U.S. patent application number 15/799626 was filed with the patent office on 2018-02-22 for systems and methods for drive circuits for dynamic magnetic stripe communications devices.
The applicant listed for this patent is Dynamics Inc.. Invention is credited to Bruce S. Cloutier, David Lambeth, James H. Workley.
Application Number | 20180053079 15/799626 |
Document ID | / |
Family ID | 44483284 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180053079 |
Kind Code |
A1 |
Cloutier; Bruce S. ; et
al. |
February 22, 2018 |
SYSTEMS AND METHODS FOR DRIVE CIRCUITS FOR DYNAMIC MAGNETIC STRIPE
COMMUNICATIONS DEVICES
Abstract
Dynamic magnetic stripe communications devices are provided as
magnetic stripe emulators. A magnetic stripe emulator may include a
coil. Drive circuits may be coupled to this coil in order to
produce electromagnetic fields from the coil operable to
communicate with a magnetic stripe reader.
Inventors: |
Cloutier; Bruce S.;
(Jeannette, PA) ; Lambeth; David; (Pittsburgh,
PA) ; Workley; James H.; (Imperial, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dynamics Inc. |
Cheswick |
PA |
US |
|
|
Family ID: |
44483284 |
Appl. No.: |
15/799626 |
Filed: |
October 31, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15047036 |
Feb 18, 2016 |
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15799626 |
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14063140 |
Oct 25, 2013 |
9373069 |
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15047036 |
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13028423 |
Feb 16, 2011 |
8602312 |
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14063140 |
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61305021 |
Feb 16, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 7/10297 20130101;
H04W 4/80 20180201; G06K 19/06206 20130101 |
International
Class: |
G06K 19/06 20060101
G06K019/06; G06K 7/10 20060101 G06K007/10; H04W 4/00 20090101
H04W004/00 |
Claims
1-17. (canceled)
18. A power control circuit, comprising: a switching device with
low ON mode series resistance operable to switch a power supply
signal from a power source to a drive circuit in response to a
non-high impedance state of a control signal; a circuit component
configured to hold the switching device in an OFF state in response
to a high-impedance state of the control signal; and a voltage
regulator configured to provide at least one reference signal to
the drive circuit.
19. The device of claim 18, further comprising a filter configured
to filter the at least one reference signal.
20. The device of claim 18, further comprising a capacitor
configured to filter the reference signal.
21. The device of claim 18, wherein the voltage regulator is a low
drop-out linear regulator.
22. The device of claim 18, wherein the voltage regulator is a
zener diode circuit.
23. The device of claim 18, wherein a magnitude of the at least one
reference signal below a minimum magnitude of the supply
signal.
24. The device of claim 18, wherein the switching device is a metal
oxide semiconductor field effect transistor.
25. The device of claim 18, wherein the control signal is a control
signal of a processor.
26. The device of claim 18, wherein the power supply signal is a
current provided by a battery.
27. The device of claim 18, wherein the switching device is
operable to provide an output signal to at least one output stage
of a current control circuit of the drive circuit.
28. The device of claim 18, wherein the drive circuit includes a
plurality of operational amplifiers, and the switching device is
operable to provide an output signal to at least one output stage
of a current control circuit of the drive circuit and to the
plurality of operational amplifiers.
29. The device of claim 18, wherein the voltage regulator is
configured to provide the reference signal independent of a
magnitude of the power supply signal.
30. The device of claim 18, wherein the power supply signal is
received by the voltage regulator from a battery, the power supply
signal varies based on a charge of the battery, and the voltage
regulator is configured to provide the reference signal independent
of a magnitude of the power supply signal.
31. The device of claim 18, wherein the reference signal is a
plurality of reference signals, the power supply is a battery; the
plurality of reference signals are a first voltage and a second
voltage, and a magnitude of each of the first voltage and second
voltage is selected from the group consisting of (0.5)*(the battery
voltage less 0.2 v-0.5 v) and the battery voltage less 0.7 v-2
v.
32. The device of claim 18, wherein the drive circuit includes an
operational amplifier and one or more transistors of a ramp
generator in an open loop control configuration, and the switching
device is operable to provide an output signal to the operational
amplifier, at least one output stage of a current control circuit,
and the one or more transistors.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] 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
[0002] This invention relates to magnetic cards and devices and
associated payment systems.
SUMMARY OF THE INVENTION
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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'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
[0015] 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:
[0016] FIG. 1 is an illustration of cards constructed in accordance
with the principles of the present invention;
[0017] FIG. 2 is an illustration of a process flowchart and
waveforms constructed in accordance with the principles of the
present invention;
[0018] FIG. 3 is an illustration of an architecture constructed in
accordance with the principles of the present invention;
[0019] FIG. 4 is a schematic of a circuit constructed in accordance
with the principles of the present invention;
[0020] FIG. 5 is a schematic of a circuit constructed in accordance
with the principles of the present invention; and
[0021] 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
[0022] 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'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'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.
[0023] 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'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).
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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).
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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).
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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).
[0056] 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).
[0057] 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.
[0058] 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).
[0059] 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.
[0060] 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.
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