Data demodulation

• US 6,674,786 B1
• Filed: 04/19/2000
• Issued: 01/06/2004
• Est. Priority Date: 04/23/1999
• Status: Expired due to Term

• Current Assignee: Sankyo Seiki Manufacturing Co., Ltd. (Nidec Corporation)
• Original Assignee: Sankyo Seiki Manufacturing Co., Ltd. (Nidec Corporation)
• Inventors: Nakamura, Hiroshi, Yokozawa, Mitsuo
• Primary Examiner(s): Ghayour, Mohammad H.
• Application Number:
  US09/551,960
• Time in Patent Office: 1,357 Days
• Field of Search: 375/340, 375/342, 375/324, 369/59.1, 369/59.1 B, 369/13.37, 386/96, 386/99, 386/104
• US Class Current: 375/340
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: G11B 20/1403 characterised by the use of two levels
• CPC Class Codes: G11B 20/1419 to or from biphase level coding, i.e. to or from codes where a one is coded as a transition from a high to a low level during the middle of a bit cell and a zero is encoded as a transition from a low to a high level during the middle of a bit cell or vice versa, e.g. split phase code, Manchester code conversion to or from biphase space or mark coding, i.e. to or from codes where there is a transition at the beginning of every bit cell and a one has no second transition and a zero has a second transition one half of a bit period later or vice versa, e.g. double frequency code, FM code
• CPC Class Codes: H04L 27/1563 using transition or level detection

Abstract

The accuracy of demodulation of data from a magnetic stripe is enhanced by comparing time intervals between successive peaks of each character of the signal read from the stripe against a set of predetermined reference successive peak time intervals for the data characters.

Claims

1. A data demodulating method in which binary data are defined by two-frequency encoded signal composed of a combination of high and low frequency signals, binary data for one character are defined by a predetermined number of said binary data and a parity bit, peak points are detected in a reproduced signal waveform obtained by reproducing a recorded data signal to demodulate said binary data, comprising the steps of:

preparing in advance a reference line pattern for each character, composed of peak interval values of bits that constitute one character;

measuring time intervals between successive peaks of said reproduced signal; and

comparing each of said peak interval values that constitute one character with said reference line patterns by a pattern matching to determine the character corresponding to said reference line pattern having the highest degree of similarity as the character.

2. The data demodulating method as set forth in claim 1 wherein reference line patterns for comparison are selected from said reference line patterns according to the number of peak intervals that constitute one character.

3. The data demodulating method as set forth in claim 1, further comprising steps of:

converting said reproduced signal waveform to a digital signal by an AD conversion;

measuring time intervals between successive peaks of said digitized reproduced signal to create a peak interval value line;

determining the end of one character by successively adding each of peak interval values of said peak interval value line; and

comparing each of said peak interval values that constitute one character with said reference line patterns.

4. The data demodulating method as set forth in claim 3, further comprising steps of:

predetermining a character time interval for one character of said recorded data by a predetermined number of bits in a given range;

determining said end of one character based on a peak position within said character time interval for one character;

detecting if the number of peak interval values up to said peak position within said character time interval satisfies the characteristic condition of parity bit;

when said condition is not satisfied, adding the next peak interval value to determine the end of one character.

5. The data demodulating method as set forth in claim 1 wherein time intervals of said reference line patterns are expressed by binary numbers based on the length of said time intervals, and a pattern matching is performed to compare said peak interval values of said reproduced signal with said reference line patterns expressed by binary numbers.

6. A data demodulating method in which binary data are defined by a two-frequency encoded signal composed of a combination of high and low frequencies, data for one character are produced with a predetermined number of said binary data and a parity bit, and peak points of a reproduced signal waveform obtained by reproducing a recorded data are detected to read said binary data, comprising steps of:

measuring peak time intervals between successive peaks of said reproduced signal waveform;

comparing each of said peak interval values that constitute one character with a reference value to convert said signal waveform to a bit line composed of said binary data;

for demodulating data of one character,

selecting a plurality of segment length candidates for demodulation, on the basis of a reference segment length equal to a data interval for one character and peak positions; and

performing pattern matching on a plurality of said segment length candidates with reference waveform data to determine the character according to the similarity.

7. The data demodulating method as set forth in claim 6 wherein said pattern matching is a time pattern matching, and said segment length candidates are prioritized according to the closeness to said reference segment length.

8. The data demodulating method as set forth in claim 6 wherein said reference segment length is determined by the average of a plurality of segment lengths successively preceding the target segment.

9. The data demodulating method as set forth in claim 8 wherein said reference segment length is reset for each segment, said segment length candidates are selected such that the peak positions of the same polarity as that of said reference segment are used for segmenting, and it is determined if the evaluation result of said pattern matching satisfies the reference value.

10. The data demodulating method as set forth in claim 9 wherein, when said evaluation result of said pattern matching does not satisfy the reference value, the segment length candidate having the length closest to said reference segment length is selected.

11. A data demodulating apparatus in which binary data are defined by a two-frequency encoded signal composed of a combination of high and low frequencies, data for one character are produced with a predetermined number of said binary data, and peak points of a reproduced signal waveform obtained by reproducing a recorded data are detected to read said binary data, comprising:

a means of measuring peak time intervals between successive peaks of said reproduced signal waveform;

a means of demodulating data for one character by comparing each of said peak interval values that constitute one character with a reference value to convert said signal waveform to a bit line composed of said binary data; and

for demodulating data of one character,

a means of determining the character, wherein a plurality of segment length candidates for demodulation are selected on the basis of a reference segment length equal to a data interval for one character and peak positions;

pattern matching is performed on a plurality of said segment length candidates with reference waveform data to determine the character according to the similarity.