Method and apparatus for authenticating a magnetic fingerprint signal using an adaptive analog to digital converter

• US 20050167496A1
• Filed: 12/17/2004
• Published: 08/04/2005
• Est. Priority Date: 07/22/1998
• Status: Active Grant

• Current Assignee: Washington University In St Louis
• Original Assignee: Edward J. Richter, George L. Engel, Robert E. Morley Jr
• Inventors: Morley, Robert E. Jr., Engel, George L., Richter, Edward J.
• Granted Patent: US 7,210,627 B2
• Time in Patent Office: Days
• US Class Current: 235/449
• CPC Class Codes: G06K 7/084 sensing magnetic material by relative movement detecting flux changes without altering its magnetised state
• CPC Class Codes: G06Q 20/347 Passive cards
• CPC Class Codes: G07D 7/004 using digital security elements, e.g. information coded on a magnetic thread or strip
• CPC Class Codes: G07F 7/08 by coded identity card or credit card or other personal identification means without personal verification means G07F7/02
• CPC Class Codes: G07F 7/0813 Specific details related to card security
• CPC Class Codes: G07F 7/12 Card verification

Abstract

A system for verifying the authenticity of data contained in a magnetic medium using the remanent noise characteristics of the magnetic medium. One embodiment of the invention includes an over-sampled modulator and at least one channel in communication with an output of the over-sampled modulator. The at least one channel is configured to filter the output of the over-sampled modulator and the at least one channel is configured to vary the bandwidth of the filter applied to the output of the over-sampled modulator in response to variations in the bandwidth of the signal generated by the sensing unit.

Claims

1. An analog-to-digital converter, comprising:

an over-sampled modulator;

at least one channel in communication with an output of the over-sampled modulator;

wherein the at least one channel is configured to filter the output of the over-sampled modulator;

wherein the at least one channel is configured to vary the bandwidth of the filter applied to the output of the over-sampled modulator in response to variations in the bandwidth of the signal generated by the sensing unit.

2. The analog-to-digital converter of claim 1, further comprising:

a plurality of delay lines between the over-sampled modulator and the at least one channel;

wherein each of the delay lines is configured to provide a specific delay.

3. The analog-to-digital converter of claim 2, wherein:

the plurality of delay lines each comprise seven taps;

one of the delay line taps provides a zero delay; and

the other six delay line taps provide varying degrees of delay.

4. The analog-to-digital converter of claim 2 wherein each of the plurality of channels comprises:

a delay line selector including a delay selection input;

a sinc filter;

a decimator including a decimated sampling rate selection input;

a half-band filter configured such that the bandwidth of the half-band filter changes in response to changes in the decimator output rate;

an up-sampler; and

a low pass filter.

5. The analog-to-digital converter of claim 4 wherein the sinc filter and decimator comprise:

an integrator;

a decimator; and

a differencer.

6. The analog-to-digital converter of claim 4, wherein:

the delay selection input is configured to receive a signal selective of a delay; and

the decimator sampling rate selection input is configured to receive a signal selective of a sampling rate.

7. The analog-to-digital converter of claim 6, comprising:

at least two channels;

wherein signals from the selection inputs configure the delay, sampling rate and bandwidth of a first channel;

wherein signals from the selection inputs configure the delay, sampling rate and bandwidth of a second channel; and

wherein signals from the selection inputs control the selection of the output of the first channel and the selection of the output of the second channel.

8. A method of converting an analog signal to a digital signal, the method comprising:

over-sampling the analog signal;

applying a specific delay associated with a specific bandwidth and sampling rate, the specific bandwidth substantially matching the bandwidth of the analog signal; and

filtering the over-sampled signal to remove aliasing;

decimating the over-sampled signal;

filtering the over-sampled signal to reduce noise outside the signal bandwidth;

up-sampling the signal; and

filtering the up-sampled signal to remove aliasing.

9. The method of claim 8, further comprising:

detecting a first peak;

detecting a second peak;

determining the bandwidth of a signal generated during the time between the detection of the first and second peaks.

10. The method of claim 9, further comprising:

selecting a delay, sampling rate and bandwidth for a first channel;

providing an input signal to the first channel;

generating an output using the output of the first channel;

selecting a delay, sampling rate and bandwidth for the second channel based on the determined bandwidth;

generating an output using the output of the second channel.

11. The method of claim 10, further comprising waiting for the output of the second channel to settle before generating an output using the output of the second channel.

12. A reader system for authenticating an object, the object comprising a magnetic medium including stored data and a remanent noise characteristic, the reader system comprising:

a sensing unit configured to generate a signal indicative of the sensed magnetic field;

an analog-to-digital converter (ADC) in communication with the sensing unit, the analog-to-digital converter comprising;

an over-sampled modulator;

at least one channel configured to filter the output of the over-sampled modulator;

wherein the at least one channel is configured to vary the bandwidth of the filter applied to the output of the over-sampled modulator in response to variations in the bandwidth of the signal generated by the sensing unit;

a filter in communication with the ADC output and configured to attenuate the portion of the digitized output signal component indicative of the data stored on the magnetic medium;

a data extraction unit, in communication with the ADC and the filter, configured to measure bit duration, swipe speed or peak location; and

an authentication extraction unit, in communication with the filter and the data extraction unit configured to extract a set of scaled samples representative of the remanent noise characteristic of the magnetic medium.

13. The reader system of claim 12, further comprising:

a plurality of delay lines between the over-sample modulator and the at least one channel;

wherein each of the delay lines configured to provide a specific delay.

14. The reader system of claim 13, wherein each of the plurality of delay lines comprise:

seven delay line taps,

wherein one of the delay line taps provides zero delay and the other six taps provide varying degrees of delay.

15. The reader system of claim 14, wherein each of the channels comprises:

a delay line selector in communication with the data extraction unit,

a sinc filter;

a decimator in communication with the data extraction unit;

a half-band filter in communication with the data extraction unit;

an up-sampler; and

a low pass filter.

16. The reader system of claim 15, wherein the data extraction unit is configured to determine the bandwidth of the signal generated by the sensing unit.

17. The reader system of claim 16, wherein the data extraction unit is configured to determine the bandwidth of the signal generated by the sensing unit by determining the time between peaks in the output of the sensing unit.

18. The reader system of claim 17, wherein the data extraction unit is configured to determine the time between peaks by:

detecting a first peak;

detecting a second potential peak; and

waiting a predetermined period of time to verify that the second potential peak is actually a peak.

19. The reader system of claim 15, wherein the sinc filter and decimator of the analog-to-digital converter comprises an integrator, decimator, and a differencer.

20. The reader system of claim 12, wherein the data extraction unit is configured to determine the bandwidth of the output of the sensor unit.

21. The reader system of claim 20, wherein the data extraction unit is configured to periodically provide information to one of the channels concerning the bandwidth of the output of the sensor system.

22. The reader system of claim 12, the analog-to-digital converter of claim further comprises a channel selector in communication with the data extraction unit and configured to select the output of one of the channels as the output of the ADC.

23. The reader system of claim 22, wherein:

the channel selector is configured to select the output of a first channel as an output;

the data extraction unit determines the bandwidth of the output of the sensor system;

a second channel is configured using the determined bandwidth information; and

the channel selector is configured to select the output of the second channel as an output.

24. The reader system of claim 23, further comprising:

a tapped delay line connected between the output of the over-sampled modulator and a delay line selector in each channel;

wherein the delay line selector is configured to select a delay line output as a channel input in response to the determined bandwidth information.