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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a system which uses smart cards for processing
and communicating, and more particularly, to a system which interacts with
such cards through a contactless interface.
DESCRIPTION OF THE PRIOR ART
The use of credit cards for purchases and for banking and other
transactions has become so popular that most travelers today do so with
very little cash. The card, typically made of plastic embossed with an
account number and the name of the account owner, serves solely to
identify an authorized account at a bank or credit house to be charged for
a transaction. A magnetic stripe on the back of some cards contains the
same information, but is machine-readable to speed the transaction. All
accounting information is stored at the bank or credit house.
In that transactions generally occur at a location remote from the bank or
credit house, it is easy for a person to use a misappropriated card, or
for a legitimate owner to inadvertently exceed his credit limit. Most
merchants, therefore, require that before purchases above a relatively
modest amount such as $50.00 are completed, the authorization must be
verified with the bank or credit house as appropriate. Even with automatic
telephone dialing, the procedure is cumbersome and timeconsuming.
Furthermore, a separate card is needed for each account.
With the advent of recent advances in microelectronics, however, it is now
possible to put a vast amount of computing power and memory right in the
card to produce a "smart card" or "personal memory card". The card could,
therefore, carry personal identification data to virtually eliminate
fraudulent use--such data as personal characteristics, driver license,
social security number, personal identification numbers, and even a voice
print. The card could also carry the account numbers of all of the owner's
charge accounts, the balances of all of the accounts, the credit limits of
all of the accounts, and other such personal data as, for example, the
sizes of family members for clothing purchases, personal telephone
directories, etc. The types of personal data are limited only by one's
imagination.
The technology for putting all of this on the standard size card is here.
What is holding up this very convenient card, however, is what at first
appears to be the mundane problem of a suitable interface for supplying
operating power to the card and reliably coupling data to and from the
card.
Smart cards known in the art are being read and written into by various
contact methods. One problem that arises if metallic contacts are used,
however, is increased ohmic resistance due to the oxidation that takes
place over time on the contact surfaces. This is of concern since the
accuracy of the data transfer between a card and a reader or writer device
decreases as the ohmic resistance of these contacts increases. In
addition, the contacts, while in the exposed position, allow air-borne
particles to deposit on the surfaces decreasing the contact area and
causing intermittent connections. Inasmuch as operating power for reading
and writing into a card is also transferred from an associated station in
a system to the card via these contacts, there is a loss in the amount of
energy transferred after some time of use, rendering the card inoperative.
A second problem associated with the use of metallic contacts in providing
operating power and data onto the smart cards is the possibility of
electrostatic discharge (ESD) occurring which can damage the
microelectronics on the card. High voltages that build up on a person or
card or that are inadvertently coupled thereto from other sources may very
easily be coupled directly to the electronics on the card when metallic
contacts are used. Clamping diodes employed at the various inputs of a
card provide some measure of protection, but are not capable of protecting
against some of the higher voltage levels a card might occasionally
encounter during normal use in its expected environment.
SUMMARY OF THE INVENTION
In accordance with the invention, a personal memory card system is usable
in a variety of applications, from custom repertory dialing to storage of
individual medical and/or banking records. The system is arranged for use
with a personal memory card which looks and feels much like an ordinary
credit card. The need for exposed electrical contact in reading and
writing data into the memory card is avoided through use of a capacitive
interface. This interface comprises conductive plates or electrodes with
outer dielectric surfaces both on the card and a reader/writer in an
associated station and is formed when each plate in the card is aligned in
close proximity with its corresponding plate in the reader/writer.
No direct ohmic electrical contact is made between the card and the
reader/writer in transferring operating power to the card. A transformer
primary section is located in the reader/writer and an inductor embedded
in the card functions as the secondary section of the transformer. These
sections along with ferrite cores respectively located in the
reader/writer and the card comprise an inductive interface that is formed
when the secondary section of the transformer is aligned in close
proximity to the primary section in the reader/writer. Sufficient power
for operation of electonics in the card and also a clock signal for
providing the required timing is coupled to the card over this inductive
interface.
When the card is in place in the reader/writer, data to and from the card
and power to the card are reliably transferred. This remains true even
after some time of use since there are no exposed metallic surfaces to
corrode or to which particles may collect. In addition, the potential of
damage to the card from electrostatic discharges to the electronics in the
card is minimized since an insulator in the form of a dielectric is
provided between the conductors of the card and any sources from which
this discharge might occur. By way of operation, the personal memory card
system is arranged to permit an authorized user at the associated station
to selectively reprogram a personal memory card with new and different
data as desired.
BRIEF DESCRIPTION OF THE DRAWING
The invention and its mode of operation will be more clearly understood
from the following detailed description when read with the appended
drawing in which:
FIG. 1 is a functional block representation of a personal memory card
system operative in accordance with the principles of the present
invention;
FIG. 2 shows the basic structure of the personal memory card and the
placement of the major components thereon in accordance with the
principles of the present invention;
FIG. 3 shows a schematic diagram illustrating in greater detail the major
functional components of the analog interface circuit depicted in the
memory card of FIG. 1; and
FIG. 4 shows a schematic diagram illustrating in greater detail the major
functional components of the reader/writer of FIG. 1.
Throughout the drawings, the same elements when shown in more than one
figure are designated by the same reference numerals.
DETAILED DESCRIPTION
Referring now to FIG. 1, there is shown a block diagram of a portable data
or personal memory card 10 and a card reader/writer 15 in accordance with
the invention. Some of the principle components located in the card 10 are
a microcomputer 110, an electrical erasable programmable read-only memory
(EEPROM) 115, an analog interface circuit 300, the secondary winding 121
of a transformer 120, and capacitive plates 125 through 128.
The microcomputer 110 includes a central processing unit and memory units
in the form of randomaccess memory and read-only memory. A microcomputer
available from Intel Corporation as Part No. 80C51 may be used for
microcomputer 110 with the proper programming. Operating under firmware
control provided by its internal read-only memory, the microcomputer 110
formats data to the EEPROM 115 and to the reader/writer 15 via the analog
interface circuit 300. The microcomputer 110 also interprets commands from
the reader/writer received through the analog interface 300. In addition,
the microcomputer 110 checks for errors in reading and writing data to the
EEPROM 115 and in transmissions to and from the reader/writer 15.
By employing EEPROM 115 in the card 10, an authorized user has the ability
to reprogram certain sections of the card while at an authorized
associated application station with new and different data as desired.
EEPROMS are available from a number of suppliers, many of whom are
mentioned in an article entitled "Are EEPROMS Finally Ready To Take Off?"
by J. Robert Lineback, Electronics, Vol. 59, No. 7, (Feb. 17, 1986), pp.
40-41. Data may be written to and read or erased from an EEPROM repeatedly
while operating power is being applied. When operating power is removed,
any changes made to the data in the EEPROM remain and is retrievable
whenever the card 10 is again powered.
The analog interface circuit 300 provides a means for interfacing the
memory card 10 to the reader/writer 15. This interface performs a
multitude of functions including providing operating power from magnetic
energy coupled from the reader/writer 15 to the card 10, and also coupling
data between the reader/writer 15 and the microcomputer 110 in the card
10. Power for operating the card 10 is provided to the analog interface
circuit 300 via an inductive interface provided by the secondary winding
121 of a transformer 120. This transformer is formed when this secondary
winding in the card 10 is mated to a primary winding 122 in the
reader/writer 15.
The transformer 120 may advantageously include a ferrite core 123 in the
reader/writer for increased coupling between the transformer primary
winding 122 and secondary winding 121. A second such core 124 may also be
included in the transformer 120 and associated with the secondary winding
121 in the card for a further increase in coupling efficiency. In those
arrangements where ample power is available and efficiency is not a
consideration, one or both of these cores may be omitted. The use of a
transformer for coupling power into a credit card was proposed by R. L.
Billings in U.S. Pat. No. 4,692,604, dated Sept. 8, 1987, this patent and
this pending application being commonly assigned to the same assignee.
Data reception to and data transmission from the card 10 are provided to
the analog interface 300 by a capacitive interface comprising four
capacitors formed when electrodes or plates 125 through 128 on the memory
card 10 are mated with corresponding electrodes or plates 155 through 158
in the reader/writer 15. Two of these capacitors are used to transfer data
to the memory card 10 from the reader/writer 15 and the remaining two are
used to transfer data to the reader/writer 15 from the card 10. The
combination of the inductive interface and the capacitive interface
provides the complete communication interface between the reader/writer 15
and the memory card 10. The analog interface circuit 300 is shown in
greater detail in FIG. 3 and further described in the accompanying
description later herein.
The organization of some of the components in the reader/writer 15
functionally mirror those in the card. Such components are, for example,
an analog interface circuit 400 and a microcomputer 410. In addition, the
reader/writer 15 also includes a power supply 162 and an input/output
interface 160. The power supply 162 is used to provide power and also to
couple a clock signal from the reader/writer 15 to the card 10 through the
transformer 120. The input/output interface 160 is principally a universal
asynchronous receiver transmitter (UART) and may be advantageously
included in the microcomputer 410. This UART is used for externally
communicating with a suitably configured application station.
With reference to FIG. 2, there is shown the basic structure of the card 10
and the relative placement of the principal components thereon. The card
generally comprises a laminated structure including a 0.005 inch thick
single or double sided printed wiring board 201. Capacitive plates 125
through 128 are shown deployed on the top side of this printing wiring
board, but it is understood that it is well within the capabilities of one
skilled in the art to deploy these plates on the bottom or opposite side
of the board as long as they are covered by a suitable insulator or
dielectric sheet. Pads for bonding the analog interface circuit 300,
microcomputer 110, EEPROM 115, transformer secondary 121 and
surfacemounted capacitors 302 and 315 are located on the top side of board
201. The intergrated circuits, i.e., the microcomputer 110, EEPROM 115 and
analog interface circuit 300, are wire bonded and the capacitors are
conductively epoxied to the printed wiring board 201. It is to be
understood that other means of electrically connecting the integrated
circuits to the printed wiring board 201 are known to those skilled in the
art. Tape automated bonding is an example of one such means.
In the construction of the card 10, the printed wiring board 201 has
laminated to it a structural member 202 which is approximately 0.020
inches thick. This structural member has multiple openings 203 to
accommodate the physical size of the above mentioned components which are
mounted to the printing wiring board 201. A potting material is
subsequently applied in sufficient quantity in the openings 203 of the
structural member 202 to cover the components located therein and build up
the slightly depressed upper surface of each of these components to align
with the topmost surface of the structural member 202.
A top cover sheet 204 is laminated to the structural member 202. To this
cover sheet an appropriate label and logos are either affixed thereto or
embedded therein. A dielectric sheet is also laminated to the bottom side
of the double sided printed wiring board 201 thereby covering up the
conductor leads (and possibly conductive plates) located on the lower side
of this board that would otherwise be exposed. It is this lower exterior
side of the card that generally has instructions and also a magnetic
stripe and signature panel as desired.
Referring next to FIG. 3, there is shown in greater detail the analog
interface circuit 300 of FIG. 1. A number of functions for the memory card
10 are provided by this interface circuit, such as power rectification and
regulation, transmitting data to and receiving data from the reader/writer
15, obtaining a clock signal from the transformer secondary 121 for
operation of the microcomputer 110 and also providing a power reset
operation for resetting this microcomputer whenever power is removed and
then reapplied to the memory card 10.
Magnetically coupled from the reader/writer 15 through the transformer 120
to the secondary winding 121 is an approximate 1.8 megahertz AC signal.
The output of this secondary winding 121 is applied to a full wave bridge
rectifier 301. The DC voltage generated by the bridge rectifier 301 is
filtered by a capacitor 302 and then coupled into a two-part regulator 303
which has a shunt regulator section on the front end and a series pass
regulator on the back end.
The shunt regulator serves to keep the current drawn out of the transformer
secondary winding 121 fairly constant and thereby insures operation in an
optimal area on the power transfer curve of transformer 120. This is
desirable, since if the power demand in the card 10 decreases, the shunt
regulator section dissipates the extra power to keep the load constant on
the reader/writer 15 and on the transformer secondary winding 121 which is
receiving the AC power. And if the power demand goes up in the card
because an operation that requires greater power is occurring, the shunt
regulator section reduces its power dissipation when it detects the
voltage decreasing. The current then passes through the series pass
voltage regulator and provides operating power for all of the other
circuitry in the card. Capacitor 315 provides additional filtering to the
DC output of the shunt and series pass regulator 303.
A clock recovery circuit 304 is coupled to the secondary winding 121 of the
transformer 120 for providing a clock signal suitable for operation of the
microcomputer 110. This circuit 304 comprises a comparator which
differentially compares one side of the secondary winding 121 of the
transformer 120 relative to the ground node of bridge rectifier 301. The
pulses that are provided are shaped by the comparator giving relative fast
turn-on and turn-off times suitable for driving the microcomputer 110.
A reset circuit 305, comprising a voltage reference 306, a comparator 307
and a monostable multivibrator 308, monitors the regulated output of the
shunt and series pass regulator 303. This circuit inhibits the operation
of the microcomputer 110 if the supply voltage at the output of the shunt
and series pass regulator 303 is not within a predetermined operating
range.
A resistor string comprising resistors 309 and 310 form a divider circuit
which reduces the voltage coupled to the comparator 307 from the regulator
303. And the voltage reference 306 sets a threshold voltage level
corresponding to the minimum allowable of the required operating level
which is then compared with the voltage from the resistor string in
comparator 307. In operation, as the voltage from the shunt and
series-pass regulator 303 rises from zero, the voltage provided to the
comparator 307 from the voltage reference 306 is higher than the voltage
provided to the comparator from the resistor string and the microcomputer
remains reset. When the voltage from the shunt and series-pass regulator
303 rises above the minimum operating voltage, the output of the resistor
string becomes higher that the voltage reference. The comparator 307 then
switches states and the monostable multivibrator 308 provides a pulse of
approximately 200 milliseconds in length to the microcomputer 110 which is
enabled thereby and a processor contained therein starts running.
If some time after reaching the required operating level, the regulated
voltage happens to dip below the threshold voltage level, the reset
circuit 305 detects this decrease and again inhibits the microcomputer
110. This insures against extraneous operations which might occur and in
some way affect the data in the EEPROM 115. The reset circuit 305 thus
causes the microcomputer 110 to be inhibited whenever the voltage is less
than the predetermined operating voltage and guards against improper
operation of the card 10 in such low voltage state.
Such an incorrect voltage could occur possibly because the card 10 is not
fully seated into the reader/writer 15 or if there is too much of a gap
between the surface of the card 10 and the mating surface in the
reader/writer 15 because of some obstruction lodged on either surface. And
since any interruption of the voltage to the card also causes the reset
circuit 305 to be activated, occurrences such as an interruption of AC
power to the reader/writer 15, or a user pulling the card 10 out of the
reader/writer 15 at an inappropriate time will also cause the
microcomputer 110 to be inhibited. Operation of the microcomputer 110 is
resumed once the supply voltage returns to the proper operating level.
A data out drive circuit 311, comprising driver amplifiers 312 and 313,
receive serial data from the microcomputer 110 and differentially drive
the capacitive plates 125 and 126 which, respectively, interface with the
capacitive plates 155 and 156 in the reader/writer 15. These drivers 312
and 313 convert the serial data from the microcomputer 110, which is of
one polarity, into a differential polarity such that for each transition
of the signal from the microcomputer 110, one of the drivers goes
positive, while the other goes negative.
A data receive circuit 320 is comprised of a differential amplifier and is
used in receiving differential data coupled to the capacitive plates 127
and 128 from capacitive plates 157 and 158 in the reader/writer 15. This
data from the reader/writer 15 is coupled to the microcomputer 110 in the
card 10 for the appropriate processing. Hysteresis is built into the data
receive circuit 320 such that a differential pulse greater than the
hysteresis is all that is required to switch the output of the amplifier
from a high state to a low state or from a low state to a high state. The
hysteresis aids in preventing noise from causing false triggering of the
data receive circuit by ignoring small differential noise signals and
switching only on large differential data signals. Thus once the data
receive circuit switches states, if there is no further input, it will
remain in whatever state it is then switched into and not drift back to
the other state.
Although ESD problems are minimized with a contactless card, the addition
of protective diodes to clamp the voltage on the outputs of data drive
circuits 311 and the inputs of data receive circuit 32 may be designed and
included in the card circuitry. The design of such clamping circuits for
clamping and also integrating voltages to safe levels is well known and
within the capability of those skilled in the art.
Referring next to FIG. 4, there is shown a schematic diagram illustrating
in greater detail the major functional components of the reader writer 15
shown in FIG. 1. The memory card 10, shown schematically in FIG. 1 and
graphically in FIG. 2,is shown in FIG. 4 in operable contact with the data
and power couping components of the reader/writer 15. Power to the card is
provided from the reader/writer 15 via the primary winding 122 of the
transformer 120 formed when the secondary winding 121 in the card 10 is
mated to the primary winding 122 in the reader/writer.
As earlier indicated, the transfer of data between the reader/writer 15 and
the card 10 is provided by a capacitive interface formed when plates 125
through 128 on the card are mated with corresponding plates 155 through
158 in the reader/writer 15. The reader/writer 15 has a number of
components comparable in operation to those found in the memory card 10.
Like the card 10, the reader/writer 15 includes a data-out drive circuit
comprising non-inverting driver amplifier 401 and inverting driver
amplifier 402. These amplifiers receive serial data from a UART 403 and
differentially drive the capacitive plates 157 and 158 which interface
with the capacitive plates 127 and 128 in the card 10. Data for the memory
card 10 is transmitted to the UART in parallel arrangement over an 8-bit
bus 411 from a microcomputer 410.
The reader/writer 15 also includes a data receive circuit 404 which is
comprised of a differential amplifier and is used by the reader/writer 15
in receiving data coupled to the capacitive plates 155 and 156 from the
capacitive plates 125 and 126 in the card 10. This serial data from the
card 10 is coupled to the UART 403 where it is reformatted into parallel
data and then coupled to the microcomputer 410 over the 8-bit data bus
411. The microcomputer 410, through use of an internal UART reconverts the
data into a serial format with start and stop bits before coupling the
data to a particular application station 440 with which the card 10 and
reader/writer 15 are configured to communicate.
The application station may comprise a number of configurations. It may be
configured as a factory editing station, an office editing station, an
issuer editing station, public telephone station, or any other station
suitably configured for interacting with the card 10.
Circuitry for efficiently controlling the transfer of power into the card
10 is advantageously included in the reader/writer 15. A power driver 420
controls the power level that is transmitted into the primary winding 122
of the transformer 120. The power provided to the card 10 via the
transformer secondary winding 121 is proportional to the current in this
transformer primary winding 122. The amount of power being provided to the
card 10 at any given time by the driver 420 is sampled and the information
provided to the analog-to digital converter 421. This converter provides
to the microcomputer 410 a digital signal equivalent of the sampled analog
power level. The microcomputer 410, in turn, adjusts the power transfer to
the card 10 to the desired level with a signal provided to a
digital-to-analog converter 422. The output of this digital-to-analog
converter is coupled to a voltage regulator 423 which provides continually
corrected drive power for the card 10 into the power driver 420. In this
way, power into the card 10 is controlled to within the desired range for
proper and efficient operation.
Using a card with the reader/writer 15 requires inserting the card in an
accommodating slot in the reader/writer 15. In order to insure proper
mating between the card 10 and the interface components within the
reader/writer 15 and also to insure correct turn-on of the reader/writer
circuitry, proximity sensors are located in the slot in the reader/writer
15. A card-in sensor 425 is located approximately half way in the card
slot. This is an optical sensor with illuminating and detecting elements.
A mechanical arm is arranged to interrupt an optical beam generated by the
illuminating element and being detected by the detecting element as the
card progresses approximately half-way into the slot. This card-in sensor
425 provides a signal to the microcomputer 410 once a card is at the
halfway point on its way in or on its way out of the station.
A card fully-in sensor 426 is comparable to the card-in sensor in
operation, but is located in the innermost part of the card slot. This
sensor informs the microcomputer 410 when the card is fully seated in the
card slot.
The reader/writer 15 is conveniently designed to accommodate not only
personal memory cards with reprogrammable microelectronics therein, but
also cards that have only a magnetic stripe affixed thereto. Once a card
is fully seated, a test is performed to determine if the card is a
contactless personal memory card or a card having only a magnetic stripe.
This test is initiated by having the microcomputer 410 apply power to the
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