Magnetic stripe reader
The invention relates to a magnetic stripe reader, and more particularly, to systems, devices and methods of directly extracting binary information embedded in a magnetic stripe using simple analog and digital signal processing techniques. Once information stored in the magnetic stripe is extracted as a F-2F waveform by the magnetic stripe reader, peaks, valleys and mid-level transition points between every consecutive peak and valley are detected. A peak-to-peak period and an average time are directly derived to determine whether the corresponding peak-to-peak transition is associated with a binary bit of “1” or “0”. This magnetic stripe reader spares a need for a multi-bit analog-to-digital converter (ADC) and a large memory, and thus, constitutes a simple and self-contained solution that may read out the binary information stored on the magnetic stripe with reduced power consumption and improved cost efficiency.
1. A magnetic stripe reader, comprising:
a stripe interface, coupled to generate a F-2F waveform from binary information stored in a magnetic card;
a zero-cross detector, coupled to the stripe interface, the zero-cross detector detecting a plurality of zero cross events when the F-2F waveform crosses a mid-level transition point located between each adjacent peak and valley pair;
a peak detector, coupled to the stripe interface, the peak detector generating a peak detect output to track the F-2F waveform as it reaches each peak and valley;
a frequency analyzer, coupled to the zero-cross and peak detectors, the frequency analyzer calculating a plurality of peak-to-peak periods for a plurality of adjacent peak and valley pairs, and deriving a bit time based on the plurality of peak-to-peak periods; and
a bit decoder, coupled to the frequency analyzer, the bit decoder generating a stream of digital data according to the plurality of peak-to-peak periods and the bit time.
2. The magnetic stripe reader according to claim 1 , further comprising:
a timing controller, coupled to the peak detector and the frequency analyzer, the timing controller synchronizing the peak detector, the zero-cross detector and the frequency analyzer.
3. The magnetic stripe reader according to claim 1 , further comprising:
an amplifier, coupled to the stripe interface, the amplifier amplifying the F-2F waveform by a gain prior to zero cross detection and peak detection.
4. The magnetic stripe reader according to claim 3 , further comprising:
an automatic gain controller, coupled to the amplifier, the automatic gain controller receiving the amplified F-2F waveform at the output of the amplifier and controlling the gain according to the level of the amplified F-2F waveform.
5. The magnetic stripe reader according to claim 3 , wherein the amplifier, the peak detector and the zero-cross detector are implemented using current-mode techniques.
6. The magnetic stripe reader according to claim 1 , wherein the F-2F waveform alternates between peaks and valleys at two frequencies including a first frequency and a second frequency that doubles the first frequency, and wherein a peak-to-peak period at the first frequency is associated with a bit of “1” and two consecutive peak-to-peak periods at the second frequency is associated with a bit of “0”.
7. The magnetic stripe reader according to claim 6 , wherein the bit time is derived according to a bit average method, such that the bit time may be scaled to substantially smaller than a first peak-to-peak time associated with the first frequency and larger than a second peak-to-peak time associated with the second frequency.
8. The magnetic stripe reader according to claim 1 , wherein the frequency analyzer calculates each of the plurality of peak-to-peak periods for a corresponding adjacent peak and valley pair, and updates the bit time at a zero cross event immediately following the corresponding adjacent peak and valley pair.
9. The magnetic stripe reader according to claim 1 , wherein the peak detect output indicates that the F-2F waveform increases towards a peak in a mountain domain and drops towards a valley in a valley domain, and a secondary noisy peak is accordingly differentiated from the peak in each mountain domain of the F-2F waveform.
10. The magnetic stripe reader according to claim 1 , wherein the plurality of zero cross events is detected based on hysteresis using an upper zero-cross threshold and a lower zero-cross threshold to adjust the mid-level transition point and accommodate noises around the mid-level transition point, a first subset of the plurality of zero cross events being detected at a plurality of rising edges of the F-2F waveform when the voltage of the F-2F waveform is larger than the mid-level transition point by the upper zero-cross threshold, a second subset of the plurality of zero cross events being detected at a plurality of falling edges of the F-2F waveform when the voltage of the F-2F waveform is smaller than the mid-level transition point by the lower zero-cross threshold.
11. The magnetic stripe reader according to claim 1 , wherein the frequency analyzer further comprising:
a clock generator that generates a clock, the clock being further used for sampling control in the zero cross detector, and peak and valley stamping in the peak detector; and
a free running counter, coupled to the clock generator, the free running counter tracking the peaks and valleys in the F-2F waveform for calculating the plurality of peak-to-peak periods.
12. The magnetic stripe reader according to claim 1 , wherein the zero-cross detector further comprising:
a comparator that is controlled by a periodic sampling control to compare a voltage sampled from the F-2F waveform to a tentative peak value; and
a switched capacitor that holds the tentative peak value and updates the tentative peak value according to the voltage sampled from the F-2F waveform as the F-2F waveform increases towards the peak in each mountain domain and drops towards the valley in each valley domain.
13. A method of reading a magnetic stripe, comprising the steps of:
extracting a F-2F waveform according to binary information stored in the magnetic card;
detecting a plurality of zero cross events when the F-2F waveform crosses a mid-level transition point located between each adjacent peak and valley pair;
tracking a plurality of peaks and valleys in the F-2F waveform;
calculating a plurality of peak-to-peak periods for a plurality of adjacent peak and valley pairs;
deriving a bit time based on the plurality of peak-to-peak periods, the bit time being used to differentiate a bit of “1” and a bit of “0”; and
generating a stream of digital data according to the plurality of peak-to-peak periods and the bit time.
14. The method according to claim 13 , wherein the F-2F waveform alternates between peaks and valleys at two frequencies including a first frequency and a second frequency that doubles the first frequency, and wherein a peak-to-peak period at the first frequency is associated with a bit of “1” and two consecutive peak-to-peak periods at the second frequency is associated with a bit of “0”.
15. The method according to claim 13 , wherein the bit time is updated at a zero cross event immediately following each adjacent peak and valley pair.
16. The method according to claim 13 , wherein the step of tracking a plurality of peaks and valleys in the F-2F waveform is associated with a peak detect output that indicates the F-2F waveform increases towards a peak in a mountain domain and drops towards a valley in a valley domain, and a secondary noisy peak is differentiated from the peak in each mountain domain of the F-2F waveform.
17. The method according to claim 13 , wherein the plurality of zero cross events is detected based on hysteresis using an upper zero-cross threshold and a lower zero-cross threshold to adjust the mid-level transition point and accommodate noises around the mid-level transition point, a first subset of the plurality of zero cross events being detected at a plurality of rising edges of the F-2F waveform when the voltage of the F-2F waveform is larger than the mid-level transition point by the upper zero-cross threshold, a second subset of the plurality of zero cross events being detected at a plurality of falling edges of the F-2F waveform when the voltage of the F-2F waveform is smaller than the mid-level transition point by the lower zero-cross threshold.
18. A method of converting a F-2F waveform to a stream of digital data, comprising the steps of:
tracking a plurality of peaks and valleys in the F-2F waveform, the F-2F waveform alternating between peaks and valleys at two frequencies including a first frequency and a second frequency that doubles the first frequency;
calculating a plurality of peak-to-peak periods for a plurality of adjacent peak and valley pairs;
deriving a bit time based on the plurality of peak-to-peak periods, the bit time being used to differentiate a bit of “1” and a bit of “0”; and
generating the stream of digital data according to the plurality of peak-to-peak periods and the bit time, wherein a peak-to-peak period at the first frequency is associated with a bit of “1” and two consecutive peak-to-peak periods at the second frequency is associated with a bit of “0”.
19. The method according to claim 18 , wherein the step of tracking a plurality of peaks and valleys in the F-2F waveform is associated with a peak detect output that indicates the F-2F waveform increases towards a peak in a mountain domain and drops towards a valley in a valley domain, and a secondary noisy peak is differentiated from the peak in each mountain domain of the F-2F waveform.
20. The method according to claim 18 , wherein a plurality of zero cross events is detected between the plurality of adjacent peak and valley pairs based on hysteresis, an upper zero-cross threshold and a lower zero-cross threshold being used to adjust a mid-level transition point and accommodate noises around the mid-level transition point, a first subset of the plurality of zero cross events being detected at a plurality of rising edges of the F-2F waveform when the voltage of the F-2F waveform is larger than the mid-level transition point by the upper zero-cross threshold, a second subset of the plurality of zero cross events being detected at a plurality of falling edges of the F-2F waveform when the voltage of the F-2F waveform is smaller than the mid-level transition point by the lower zero-cross threshold.