Coded data generation or conversion – Sample and hold – Having variable sampling rate
Reexamination Certificate
2001-11-09
2002-11-05
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Sample and hold
Having variable sampling rate
C341S071000, C341S132000, C235S449000, C360S043000
Reexamination Certificate
active
06476743
ABSTRACT:
This invention relates to a method for decoding information contained in a waveform having a series of peaks which is particularly but not exclusively directed to a method for reading a magnetic stripe that allows the information on the stripe to be read without the need for unidirectional, single stroke swiping motion of the stripe.
The embodiment as disclosed hereinafter which is directed to the primary but not exclusive function of decoding magnetic strip data includes features that permit the accurate decoding of magnetic stripe data in the presence of signal degradations caused specifically, but not exclusively, by variations in the read speed. The embodiment includes the capability to accurately decode stripe data even when the read motion includes stop events (0 read velocity) and reversals.
BACKGROUND OF THE INVENTION
Prior art US patents in this field are as follows:
U.S. Pat. No. 4,141,494 February 1979 Fisher
U.S. Pat. No. 5,168,275 December 1992 Harrison et al.
U.S. Pat. No. 4,529,872 July 1985 Dinges
U.S. Pat. No. 5,559,317 September 1996 Wong et al.
U.S. Pat. No. 5,912,446 June 1999 Wong et al.
Current magnetic stripe technology is based on F/2F coding (frequency/2 times frequency, also known as Aiken or biphase coding) in which the spatial frequency of flux reversals magnetically encoded on the stripe is used to represent binary information. Spatial frequency F represents a zero bit and spatial frequency 2F represents a one bit. Magnetic stripes are used in many applications, perhaps the most common being on credit or debit cards.
The reading of a magnetic stripe on a card in a situation where the stripe is not read at a suitable speed in a single direction has to date raised significant difficulties. While implementations have been created which operate over wider than typical dynamic ranges, little commercial success has been achieved and none of these implementations are capable of reading over a range of speeds including stop events. Typical magnetic stripe readers require read speeds in excess of 1.5 inches/second. This is particularly a problem where such magnetic stripes are read in a machine that can also read smart cards. Since the smart card reader typically requires a construction that precludes swiping of the card, two options are available. Two individual readers may be used (one for each card type); a solution that is sub-optimal with respect to the amount of space used and potentially confusing for an operator who has to decide which reader to insert a given card into. The other option is to use an insert style reader. Insert style readers, unless motorized, typically suffer low read speeds, card motion stop events and reversals as the card is inserted. A common mode of operation for an insert style combined magnetic stripe/smart card reader (a “hybrid” reader) is to request that the operator perform two different actions, depending on the card type being read. For a smart card, the card is inserted and left in place until the transaction is complete. For a magnetic stripe card, the card is first inserted and then immediately withdrawn. Reading of the magnetic stripe during withdrawal of the card tends to suffer from fewer problems of low card read speed or stops. The card reader is then able to make two read attempts and has a significantly higher probability of successfully reading the stripe. Unfortunately this mode of operation causes significant operator confusion, particularly given the fact that most smart cards also have magnetic stripes. Premature removal of a smart card (before the terminal has completed its communication with the card integrated circuit) can cause significant application problems.
Mechanical means to provide reliable magnetic stripe reads in a hybrid reader, other than using a motor for card transport, have been devised U.S. Pat. Nos. 4,529,872, 5,559,317, 5,912,446. All suffer from significant barriers to commercial success. In particular, they are not easily retrofitable into existing products due to significant mechanical differences from standard practice. They also require a number of precision mechanical components that are expensive to manufacture and assemble, and may lead to product reliability problems.
At least one prior art implementation, U.S. Pat. No. 4,141,494 to Fisher, attempts to deal with the large speed variations encountered when reading stripes moved past a read head by hand. The basic technique employed is to use a special read head to make the read head signal a function of the spatial frequency of the spatially encoded data on the stripe. A significant problem is, once again, changes required to standard practice for the read head making retrofitting to current implementations difficult. The technique also makes use of extensive analogue signal processing which is impractical at the extremely low frequencies encountered leading up to, or away from, a stripe motion stop event.
Prior art in U.S. Pat. No. 5,168,275 has attempted to minimize card read failures due to read signal degradation. While the system disclosed is capable of correcting read errors resulting from magnetic strip degradation, it is not capable of correcting errors caused by variations in read speed or direction. Most of the error correcting features disclosed are also limited to working in a system where the read speed is controlled (motorized reader).
SUMMARY OF THE INVENTION
One object of the invention is to provide a method and apparatus for reading data from magnetic stripes with F/2F encoded data.
It is another object of the present invention to provide a reader for a magnetic stripe that can accommodate read signal degradations caused by several factors, including large changes in read velocity as the stripe is moved past a standard inductive read head.
It is yet another object of the present invention to provide a method for digitally capturing the raw stripe read signals in both a memory and computationally efficient manner.
It is still another object of the present invention to provide a method that permits capture of all of the required magnetic stripe signal data in a single pass and also permits minimization of the amount of that data which must be stored at any given time.
These, and other objects, are provided by a method and apparatus for decoding F/2F signals in which samples of the F/2F data signal are repeatedly obtained and are converted into a series of digital values representing typically consistent integrated signal areas (+K or −K volt seconds). The signal area is integrated on a sample by sample basis by forming the integral of the current signal amplitude from which a signal offset has been subtracted. The signal offset is determined by a low pass filtered version of the read signal itself. The cut-off frequency of the filter is set lower than the product of the magnetic stripe encoding density (bits per inch) and the lowest possible stripe read speed (inches per second). The speed referred to is that speed which may be typically encountered in the specific mechanical arrangement associated with the reader (not including stop events). In a specific implementation, all digitally converted samples will either be of area +K or −K, or will be of a maximal time duration based on the limits of the digital representation of the sample duration. The sampled signal is thus converted into digital data that consists of a series of area-duration sample pairs in a novel analogue to digital conversion technique.
Those skilled in the art will recognize that integration of the read signal over a variable period represents filtering over a similarly variable bandwidth. As read speeds increase, the read signal amplitude increases causing the sample duration to decrease. The decrease in sample duration results in an increased filter signal bandwidth. Read signal levels are proportional to read speeds with a standard inductive head, leading to a filter signal bandwidth that exactly tracks the frequency of the read signal.
There is another useful aspect of the variable sample duration and its response
Brown Bradley Dale
Mukhi Shamir Nizar
Battison Adrian D.
Dupuis Ryan W.
Iders Incorporated
Williams Howard L.
Williams Michael R.
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