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BACKGROUND AND SUMMARY OF THE INVENTION
The sources of noise in a readback signal from a magnetic recording medium
have been investigated and identified. One of those sources includes the
irregularities and defects in the microstructure of the magnetic medium
itself. For many years, the noise generated from this source has been
thought, as with the noise generated from other identified sources, to be
random and subject only to statistical analysis for its determination. The
inventors herein have recently demonstrated that this noise component is
instead deterministic, i.e. is permanent and repeatable, depending
entirely on the head-medium position and on the magnetic history of the
medium. As confirmed by experiments conducted by the inventors herein,
when the medium has had no signal written on it and has been exposed only
to DC fields, the observed readback signals are almost identical. The
magnetic contribution to the readback signal under these conditions
results from spatial variations in the medium's magnetization: magnetic
domains, ripple, local fluctuations of the anisotropy field and saturation
magnetization. These local properties, in turn, are affected by the
morphology and magnetic properties of the individual grains which make up
the domain and which do not change after deposition. Hence, the noise from
a nominally uniformly magnetized region measured at a fixed position on a
magnetic medium is reproducible. As shown by the inventors herein, a
magnetic medium may be DC saturated and its output then measured to
determine its remanent state or remanent noise. The inventors have
confirmed that this remanent noise is a function of the magnetic
microstructure by comparing the remanent noise after a positive DC
saturation with the remanent noise after a negative DC saturation. It has
been found that these wave forms are virtual "mirror images" of each other
thereby demonstrating a close correlation. Similarly, other methodologies
were used to confirm that the remanent noise was deterministic,
repeatable, and related to the physical microstructure of the magnetic
medium itself. Remanent noise arising from the permanent microstructure
exhibits identifiable features characteristic of that permanent
microstructure after practically any magnetic history. See Spatial Noise
Phenomena of Longitudinal Magnetic Recording Media by Hoinville, Indeck
and Muller, IEEE Transactions on Magnetics, Volume 28, No. 6, November
1992, the disclosure of which is incorporated herein by reference.
There is a long felt need in the art for a method and apparatus to identify
or fingerprint various kinds of documents as well as the wide variety of
prerecorded magnetic media presently being marketed and/or distributed in
the United States and throughout the world. Examples of these magnetic
media include those produced and sold in the entertainment industry
including magneto-optic discs and tapes, cassette tapes, reel to reel
tapes, videotapes, etc. Still another major market in magnetic media is
the tremendous volume of computer programs routinely sold and/or
distributed on floppy diskettes. Magnetic media are also used for other
purposes for which it is important to be able to identify and authenticate
originals including videotapes, cassette tapes, and other prerecordings on
magnetic media of telephone conversations, video recordings of criminal
activities, and other such investigative and documentary uses. Still
another example of a need in the art for authentication and verification
of magnetic media lies in the magnetic data card field. Examples of
magnetic data cards include the well known credit card as well as ATM
cards, debit cards, security or ID cards, mass transit cards, and even
airline tickets or other vouchers which have magnetic stripes thereon for
the magnetic recording of data. As well known in the art, virtually every
magnetic data card has a magnetic stripe of prerecorded magnetic data
which is used to record the customer's account number or some other such
identifying data. Tremendous sums of money are lost annually through
forgery and other fraudulent copying and use schemes which could be
virtually eliminated if an apparatus and methodology could be implemented
for reliably authenticating and verifying the identity of a magnetic data
card prior to its being approved for its associated transaction. Still
other examples extend to paper documents and the like for which there has
been some specific efforts of which the inventors herein are aware.
As related in an article entitled Novel Applications of Cryptography in
Digital Communications by Omura, IEEE Communications Magazine, May 1990, a
technique is disclosed for creating counterfeit-proof objects. As related
therein, the basic idea is to measure some unique "fingerprint" of the
paper and to sign (encrypt) it using the secret key of the manufacturer
of, for example, a stock certificate. The fingerprint is obtained by
moving a narrow intense light beam along a line on the paper and measuring
the light intensity that passes through the paper. The light intensity
function determined by the unique random pattern of paper fibers along the
line then forms the fingerprint of the particular piece of paper. This
fingerprint is then digitized and encrypted by the secret encryption
function. The encrypted fingerprint is then separately printed onto the
paper in digital form such as a bar code. At a later date, the
authenticity of the stock certificate may be verified by using a
non-secret public decryption function to decrypt the encrypted data on the
paper and reconstruct the intensity function, or fingerprint, that was
recorded thereon. Next, the actual intensity function of the stock
certificate is measured. If this newly measured intensity function agrees
with the intensity function reconstructed from the decrypted data, the
document may be declared authentic. This scheme takes advantage of a well
know secrecy system referred to as a public key cryptosystem. This system
employs a trap door one way function. A user chooses a secret key (the
trap door) and after applying the trap door one way function to the data,
the procedure determines an algorithm used for decoding which is made
publicly known. The trap door one way function is also used to produce the
encrypted message. Then every other user can understand the original
message by applying the algorithm to the cryptogram. In this system no one
else can produce a publicly readable message attributable to the original
user's trap door as only the user has knowledge of that algorithm. This
prevents the simplistic forgery attempt of changing the pre-recorded
fingerprint to agree with a forged document's fingerprint.
Still another example of an attempt in the prior art to fingerprint or
counterfeit-proof objects is shown in U.S. Pat. No. 4,806,740. As shown
therein, an object, such as a stock certificate, has deposited thereon a
stripe of magnetic medium having a variable density resulting from the
non-uniformity of the paper, the process of depositing the magnetic medium
on the document, and the dispersion of magnetic particles within the
medium. The density variations are randomly created as the magnetic medium
is applied, which affords a unique document as these density variations
are fixed and repeatable to identify the document. A second magnetic
stripe is also applied to the document, but this magnetic stripe is
comprised of a medium that is tightly specified and highly controlled in
accordance with well known standards in the recording art to be part of a
magnetic read/write system. In operation, the non-uniform magnetic stripe
is erased, recorded by a standard recording comprised of a linear DC
signal or a linear AC signal or a linear bias signal. After recording,
another head senses the magnetic characteristic of the recorded magnetic
stripe which is translated into a digital, machine readable format, and
then separately recorded on the second magnetic stripe in a simple write
function. For authentication, the stock certificate is passed under
another set of heads which first reads the digitally recorded machine
readable representation of the sensed noise signal and then a second set
of heads reads the variable density magnetic stripe by first erasing it,
recording the same standard noise function, and then sensing the output of
the prerecorded noise function as it is "distorted" by the variable
density magnetic stripe. If it matches the recorded representation
thereof, then the document is declared to be authentic and original. Thus,
with the method of the '740 patent, a pair of magnetic stripes must be
applied to the document and a specified signal (denominated as noise) must
be recorded, measured, and then its output digitally recorded.
Furthermore, one of the magnetic stripes must be applied in other than
recording industry standard and in a random manner to ensure the
randomness of the output thereof. These steps make the '740 patent method
difficult and inconvenient to implement.
Yet another example of a prior art attempt to utilize a magnetic
fingerprint of a magnetic medium for authenticating credit cards,
documents, and the like is found in Pease et al U.S. Pat. No. 4,985,614
issued on Jun. 15, 1991. This '614 patent is actually quite similar in
concept to the '740 patent discussed above in that it focuses on the
macroscopic, hereinafter denoted "macro" variations in a magnetic medium,
and their effect on an "enhancing" signal recorded thereon in one
embodiment or standing alone in a second embodiment. With either
embodiment, these "macro" variations are determined by reading a chosen
length of approximately 2.6 inches of a magnetic stripe between 3 and 9
times (5 in the preferred embodiment) and then correlating the collected
data points to "average out" the effects of head noise, electrical noise,
and any other non-medium noise. This correlation results in a
"representative profile" which represents the variances which would be
induced by these macro effects to a signal if it were recorded on this
2.6 inch portion of magnetic stripe. If these variations are not
significant enough to produce a reliable correlation, indicating a lack of
significant macroscopic nonuniformities in the medium, the medium is
discarded. This is an indication that the medium has been manufactured too
closely to tolerance, or otherwise does not have enough macro level
variation which might be present due to a manufacturer's watermark or the
like, to induce reliably detectable and repeatable variations to a
recorded signal. The '614 patent also suggests that macro level noise may
be enhanced by locally altering the apparent magnetic characteristics of
the stripe such as by placing magnetic symbols on the substrate underlying
the magnetic region, or by embossing selected regions of the magnetic
material so as to physically move some amount of the material. As the
noise levels measured have significant effects on the peaks of a recorded
enhancing signal, a simple peak detect and hold circuit is taught as
sufficient to collect the data, and a simple "comparison" of the
pre-recorded "representative profile" with the presently sensed data
points is taught as sufficient to determine if the medium is authentic.
Therefore, not only does the '614 patent focus on the use of macro level
noise, its device and methodology disclosed for implementing a macro level
noise detector is believed to be incapable of reliably creating a
microstructure noise level fingerprint and validating its existence at a
later time in order to authenticate an original.
In order to solve these and other problems in the prior art, the inventors
herein have developed a method and apparatus for utilizing the unique,
deterministic, remanent noise characteristic of the magnetic medium itself
due to its magnetic microstructure to fingerprint not only documents, but
other objects and more importantly, the magnetic medium itself so that it
can be identified and authenticated. This inventive technique relies upon
the discovery that the microscopic structure of the magnetic medium itself
is a permanent random arrangement of microfeatures and therefore
deterministic. In other words, once fabricated, the recording medium's
physical microstructure remains fixed for all conventional recording
processes. In particulate media, the position and orientation of each
particle does not change within the binder for any application of magnetic
field; in thin film media, the microcrystalline orientations and grain
boundaries of the film remain stationary during the record and reproduce
processes. It is the magnetization within each of these fixed
microfeatures that can be rotated or modified which forms the basis of the
magnetic recording process. If a region of a magnetic medium is saturated
in one direction by a large applied field, the remanent magnetization
depends strongly on the microstructure of the medium. This remanent state
is deterministic for any point on the recording surface. Each particle or
grain in the medium is hundreds to thousands of Angstroms in dimension.
Due to their small size, a small region of the magnetic surface will
contain a very large number of these physical entities. While the
fabrication process normally includes efforts to align these particles,
there is always some dispersion of individual Orientations and positions.
The actual deviations will be unique to a region of the medium's surface
making this orientation a signature or a "fingerprint" of that medium. To
reproduce this distribution, intentionally or not, is practically
impossible since this would entail a precise manipulation of the
orientation of numerous particles at the submicrometer level. Thus, the
orientation of a large set of particles on a specific portion of a
recording surface can uniquely identify that medium. In experiments, the
inventors have found that the remanent noise from a length of between
about 30 micrometers and 4300 micrometers provides enough data to
"fingerprint" a magnetic medium. This may be contrasted with the 66,040
micrometers (2.6 inches) of length required in the '614 patent in order to
fingerprint a magnetic medium with macro noise.
In essence, the present invention is elegantly simple and adapted for
implementation by conventional recording heads as are commonly found and
used in virtually every read or read/write device presently utilized by
the public at large. Such examples include credit card readers,
magneto-optic disc players, cassette players, VCRs and personal computers.
Furthermore, a card reader may be coupled with virtually any device or
process, and the card reader used as a "Gatekeeper" to permit input or
access only by those who can present a valid passcard for authentication.
In its simplest implementation, a conventional recording head need merely
DC saturate a specified portion of a magnetic medium, and then "read" or
"play back" the remanent noise which remains. For convenience, the
fingerprint may be obtained from the region between two recorded magnetic
transitions already in place on the medium. This remanent noise, which is
an analog signal, may then be digitized and recorded, in the medium itself
or elsewhere, in machine readable format perhaps using a trap door
function. Thusly, the magnetic medium has become "labeled" with its
fingerprint. Verification or authentication of that magnetic medium is
simply achieved by reversing this process except that in the more security
sensitive applications the digitally recorded fingerprint must be
decrypted using the publicly known key. Should the measured remanent noise
match the remanent noise as recorded, the magnetic medium is
authenticated.
There are many variations in utilization of the inventors' method and
apparatus which expand its universe of applications. For example, some
applications need not require the use of a trap door function such as, for
example, when the encoded objects are not publicly distributed and instead
are being identified solely for the user's purposes. One such example
would be for use with inventory items.
Still another application involves the "copy protection" of mass
distributed application software. Over the years, many schemes have been
tried and almost uniformly abandoned for copy protecting publicly
distributed diskettes of prerecorded software. This has happened for many
reasons including the problem that almost all of the copy protection
schemes previously implemented interfere with the running of the software
on the user's computer. With the present invention, a copy protection
scheme may be implemented which does not interfere with the running of the
software and instead merely provides a precondition to running of what is
otherwise normally written code. In its implementation, a software
diskette may first instruct the computer in which it is inserted to read a
fingerprint of a specified portion of the diskette and compare it with a
prerecorded version of the same fingerprint. If the fingerprints match,
then the software may permit the computer to further read and implement
the application software stored thereon. However, if the fingerprint
detected by the computer does not match that which is stored in the
software, then the software itself may inhibit further reading of the
program and prevent its implementation. This would absolutely prevent a
user from making a copy of a program for use by someone else. This scheme
may also be slightly modified as discussed in the detailed description of
the preferred embodiment to permit a user to make a single archive or
backup copy such that the fingerprint comparison permits the first
non-matching fingerprint copy to be run but then prevents any other
non-matching fingerprinted copies to run. This implementation is easily
achieved and "copy protects" application software reliably, inexpensively,
and requires only minor hardware changes to the massive number of
computers already in consumers' hands.
Still another significant application of the present invention involves
authenticating credit cards using the single magnetic stripe already
implemented on most major credit cards. Again, this may be contrasted with
the '614 patent which suggests that a second stripe be added because of
the required 2.6 inches of stripe length which must be dedicated to the
macro fingerprint techniques. The same method would be used as explained
above to measure and record the "fingerprint" of the particular magnetic
stripe contained on a particular credit card and then a credit card reader
would require that same fingerprint to be matched every time it is used to
verify its authenticity. While there are already a large number of credit
cards in circulation, these cards are routinely subject to expiration such
that there is a continual replacement of these cards in the public's
hands. Thus, over time the installed base of credit cards could be readily
transformed to those which have been "fingerprinted".
In a variation to this application, the present invention may be coupled
with a data base or processor, such as in so-called Smart Cards. These
credit card-like devices actually contain, in addition to perhaps the
standard credit card magnetic stripe, an on-board electronic memory and/or
microprocessor. This memory or microprocessor may contain all sorts of
information including money substitute data. For example, at present a
large number of these smart cards are in use in Europe as pre-paid
telephone cards which are pre-loaded with a monetary amount which is
charged against by a pay phone. The cards are used until their pre-loaded
monetary equivalent has been depleted and then they are discarded. While
various security methodologies have been developed to protect against
fraud, these are subject to breach. The present invention is uniquely
suited as a security scheme for smart cards as it depends solely on the
magnetic microstructure of the particular magnetic medium. In use, the
magnetic fingerprint could be stored on the magnetic stripe, in the smart
card memory (on board the card), or in a central computer. When coupled
with a trap door function, no fraudulent card could be created without
access to the trap door function and every transaction could be quickly
pre-authorized at a local card reader, without phoning a central clearing
authority. In an extension to all credit card applications, the
fingerprint data may be stored along with each transaction so that a
complete record or trail is created which traces a particular card's
history. Thus, the present commonly used scheme where a number of
fraudulent cards are created with a correct but stolen account number
could either be thwarted or effectively prosecuted.
Another level of security incorporates random placement of the fingerprint
position. This might be a function of the card's number. For example, the
card number modulo "P" might point the read electronics to a particular
data bit around which the fingerprint will be found.
Still another significant category of applications involves utilizing the
present invention in its gatekeeper function. Any system, process,
machine, location, or other function to which access is desired to be
restricted to only those who are authorized, the present invention
provides a unique and reliable solution. In its simplest implementation, a
passcard may be created with a magnetic stripe which is fingerprinted in
accordance with the present invention. Although examples will be discussed
in terms of utilizing a passcard, it should be understood that any
magnetic medium can be similarly used in accordance with the teachings
herein. As such, all other such examples and implementations are intended
to be included within the present invention and shall be understood to be
included within the term "passcard". This passcard may then become a
personal ID card which may be used not only to control access, but also
identify the particular person accessing the service, function, etc. by
storing the particular magnetic fingerprint of the card being used.
Numerous examples may be readily considered. For example, access to a
computer network through a remote terminal may be controlled utilizing a
passcard of the present invention. This would be implemented through the
use of a diskette which may be readily inserted in any floppy disk drive
which could authenticate the fingerprint on the diskette. Alternatively,
an inexpensive card reader, adapted to read a passcard, could be utilized
as well. Many other applications would utilize the modified card reader.
For example, a bank teller may be assigned a passcard which could then be
used to track all of the transactions entered by the teller and thereby
more reliably guard against teller fraud. The myriad of identification
cards utilized by businesses, health plans, universities, hospitals, and
other organizations or facilities could readily adopt and use a passcard
to more securely identify and preauthorize the users of its services,
facilities, etc. Not only would existing uses be readily amenable to
replacement with the passcard of the present invention, but other new
services and systems could be implemented because of the high degree of
security provided by the present invention. This may include home shopping
and pay-per-view video. This may well lead to the creation of national
data bases, national ID cards, and other more universal implementations of
credit cards or passcards. This is especially true if a system utilizes
not only the magnetic fingerprint of a particular passcard, but also
utilizes a secondary security check such as a picture ID, human
fingerprint, hologram (presently imprinted on credit cards), or other such
methodology which would thereby render the passcard system virtually
impregnable. With such security, individuals may be more willing to turn
over such detailed personal financial and health information as would make
these systems feasible.
While the principal advantages and features of the invention have been
described above, and a number of examples given, a greater understanding
of the invention may be attained by referring to the drawings and the
description of the preferred embodiment which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a magnified representative depiction of the microscopic structure
of a region of magnetic medium;
FIG. 2 is a magnified depiction of several tracks of a magnetic medium
having microscopic structure representatively shown thereon;
FIG. 3 is a partial view of a track of magnetic media having its
fingerprint recorded thereon in machine readable code;
FIG. 4 depicts three conventional recording heads and a magnetic medium
traveling thereunder;
FIG. 5 is a view of a credit card having fingerprint data encoded thereon
for reading by a credit card reader;
FIG. 6 depicts a personal computer with a computer diskette for insertion
in a floppy disk drive thereof;
FIG. 7 is a perspective view of a magneto-optic disc player with a
magneto-optic disc in its tray;
FIG. 8 is a cassette player depicting a cassette tape for play therein;
FIG. 9 is a perspective view of a VCR with a tape ready for insertion;
FIG. 10 is a block diagram of a magnetic fingerprint verification circuit;
FIG. 11 is a block diagram of the magnetic trigger circuit shown in FIG.
10;
FIG. 12 is a schematic diagram of an implementation of the present
invention utilizing a PC;
FIG. 13 is a schematic diagram of the memory utilized in the implementation
of FIG. 12;
FIG. 14 is a schematic diagram of the trigger circuits utilized in the
implementation of FIG. 12;
FIG. 15 is a schematic diagram of the preamp circuits utilized in the
implementation of FIG. 12;
FIG. 16 is a block diagram of a magnetic fingerprint verification circuit
set up for implementation in an IC;
FIG. 17 is a schematic diagram of a correlation circuit utilizing single
bit data streams;
No FIG. 18;
FIG. 19 is a schematic diagram of an active differentiator;
FIG. 20 is a schematic diagram of the threshold generator;
No FIG. 21;
FIG. 22 is a schematic diagram of the ADC reference generator;
FIG. 23 is a schematic diagram of a gain circuit;
FIG. 24 is a plot from a read of a magnetic credit card stripe;
FIG. 25 is an enlarged view of the encircled portion of the waveform in
FIG. 24; and
FIG. 26 is a waveform giving the correlation of two fingerprints.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1, a region of magnetic medium is built up with a
plurality of microcrystalline structures 22 in a random pattern. This
microcrystalline structure 22 is comprised of particles or grains varying
from hundreds to thousands of Angstroms in diameter. The view of FIG. 1 is
greatly enlarged and magnified in order to depict this physical
microstructure. As shown in FIG. 2, this microcrystalline structure
extends throughout the magnetic medium even though the magnetic medium 24
shown in FIG. 2 may be itself comprised of tracks 26, 28, 30 as well known
in the art. Although shown schematically as separate regions, the
fingerprint can be obtained from any portion of the medium 24.
Referring now to FIGS. 3 and 4, a plurality of conventional recording heads
32, 34, 36 are shown mounted in a head transport 37 with a traveling
magnetic medium 38 controllably driven past recording heads 32, 34, 36 all
as is well known in the art. These recording heads 32-36 may be any
magnetic transducer or magneto-optic transducer head, as known in the art.
Recording heads 32-36 are all connected to electronic circuitry 39, as
well known in the art, to control and read their input and output and to
further process signals for playback or other use. Although only three
heads 32, 34, 36 are being shown in FIG. 4, it will be well understood to
those of ordinary skill in the art that a plurality of recording heads of
any number may just as easily be provided and, as taught herein, may be
required in order to effect the purposes of the present invention. As
shown in FIG. 3, the magnetic "fingerprint" at a specified region 40 of a
thin film magnetic medium or tape 42, shown representationally in FIG. 3
as a thin film tape, may be recorded at a second position 44 on said thin
film magnetic medium or tape 42 in a digitized, machine readable code 46
or the like.
As their preferred embodiment, the inventors have utilized a methodology
for reading or determining the remanent microstructural noise
characteristic of the region 40 of the magnetic medium which is being
"fingerprinted". Preferably, this region 40 is on the order of several
tens to hundreds of micrometers. This region is then DC saturated and then
subjected to a "read" step for determining the remanent noise produced
thereby.
While this is the preferred embodiment, it should be understood that the
fingerprint is always there, whether the medium has been recorded over or
not. Therefore, it is not strictly necessary that the specified portion of
medium containing the fingerprint be DC saturated, or DC saturated in the
same polarity in order to obtain the fingerprint. Instead, it is only
important that the remanent noise be determined in a manner which
facilitates its being correlated successfully with the earlier determined
remanent noise.
If this information is obtained in a "single shot" measurement, then the
results will obviously include both electronics noise as well as the
remanent noise attributable to the particles' orientation. As this "noise"
or "remanent noise" is electronically determined as an analog signal, this
information may then be digitized and recorded with about a hundred to two
hundred digital bits of information as may be representationally shown as
code 46 in FIG. 3. In experiments, the inventors have made multiple
measurements and averaged their results in order to eliminate the
electronics noise present in the measured wave form. However, there was
observed a high correlation coefficient when the two sets of data, i.e.
single shot and averaged, were compared thereby demonstrating that a
single shot reading could readily be used in comparison to an averaged set
of data in commercial application. The normalized cross correlation
coefficient r is used where
##EQU1##
as explained by the inventors in their earlier published article mentioned
above.
In order to recover or measure the "fingerprint" or remanent noise, the
process is similarly repeated and, when comparing two single shot wave
forms, a smaller correlation therebetween was experienced. However, the
correlation experienced with two single shot wave forms was significant
and clearly demonstrated this method's feasibility for commercial
application as well.
As shown in FIG. 24, the portion of the signal used for fingerprinting is
very small with respect to the rest of the recorded signal. As shown in
FIG. 25, the encircled portion or fingerprint from FIG. 24 may be
amplified to show in greater detail the waveform. In FIG. 26, a
correlation using the present invention produces a definable "peak" which
verifies the existence of the fingerprint in the medium.
As shown in FIG. 5, a practical implementation for the subject invention
includes a magnetic data card 48 which has a magnetic stripe 50 thereon
with magnetic stripe 50 being encoded with a code 52 representative of a
fingerprint of a region 54 of magnetic stripe 50. Thus, as the magnetic
data card 48 is "swiped" through a card reader 56, the card reader 56 may
read the code 52 to determine the stored fingerprint data, read the
fingerprint at region 54 of the magnetic stripe 50, compare them for a
match, and if they match then authenticate magnetic data card 48 as a
genuine card which has not been altered and which may be approved.
Alternatively, the fingerprint need not be stored on the card but may
instead be stored centrally, as in a data base elsewhere.
As shown in FIG. 10, a schematic block diagram for a magnetic fingerprint
prototype includes a read head 100 for reading the magnetic medium 102
which may be on a credit card or passcard 104 as previously described. A
magnetic trigger circuit 106 (including the gain circuit shown in FIG. 23)
pulses on a logic element 108 which activates an analog to digital
converter 110 (including a reference voltage generator shown in FIG. 22)
to convert the output from read head 100, V.sub.s, into a stream of
digital data which is stored in a memory 112. A microcontroller 114 then
processes the data and compares it with the original fingerprint in order
to authenticate the credit card or passcard 104. The magnetic trigger
circuit 106 is shown in greater detail in FIG. 11. It includes a preamp
116 (shown in greater detail in FIG. 15) which amplifies the output from
read head 100 to produce, through a set of analog comparators (see FIG.
21) with thresholds produced by threshold generators (see FIG. 20), a
positive pulse output 118 and a negative pulse output 120, as shown by the
timing graph in the lower half of FIG. 11. The logic 108 may be
implemented as shown in FIG. 12 by connection to an IBM PC through
connector 122. A memory element 124 is shown in greater detail in FIG. 13,
trigger circuits 126 are more completely shown in FIG. 14, and preamp
circuits 128 are shown in FIG. 15. A block diagram 130 for a magnetic
fingerprint device is shown in FIG. 16 which is arranged for
implementation in a custom integra | | |
