Electronic article surveillance system utilizing synchronous integration

Claim 2

A detector for detecting the presence of a resonant tag in a swept frequency field, comprising: means for detecting the signal produced by a tag present in the swept frequency field, said tag produced signal having positive and negative polarity pulses; means for separating said positive and negative pulses; means including a synchronous digital integrator synchronized to the swept frequency field coupled to said separating means for sampling each positive polarity pulse a plurality of times and integrating each sample of the positive polarity pulses over a plurality of sweeps; means including a synchronous digital integrator synchronized to the swept frequency field coupled to said separating means for sampling each negative polarity pulse a plurality of times and integrating each sample of the negative polarity pulses over a plurality of sweeps; and means coupled to said positive pulse integrating means and to said negative pulse integrating means for providing a detect signal in response thereto upon the detection of a tag produced signal.

Claim 3

A detector as recited in claim 1 wherein said detect signal providing means is responsive to pulses received from said integrating means and includes means for determining the widths of the pulses received from said integrating means, said detect signal providing means being responsive to the widths of said received pulses for providing a detect signal only if the widths of said pulses exceed a predetermined width.

Claim 4

A detector as recited in claim 1 wherein said detect signal providing means is responsive to pulses received from said positive and negative pulse polarity integrating means, and includes means for counting the pulses received from the integrating means and for providing said detect signal only if a predetermined number of pulses are received within a predetermined time interval.

Claim 5

A detector as recited in claim 1 wherein said tag produced signal detecting means includes threshold means for passing signals detected by said tag produced signal detecting means only if the amplitude of the detected signals exceed a predetermined amplitude.

Claim 6

A detector as recited in claim 1 further including means interposed between said positive and negative polarity synchronous integrators and said detect signal providing means for combining the signals from said positive and negative synchronous integrators into a combined signal for application to said detect signal providing means.

Claim 7

A detector as recited in claim 5 wherein the combined signal provided by said providing means is a uni-polarity signal.

Claim 8

A detector for detecting the presence of a resonant tag in a swept frequency field, comprising: means for detecting the signal produced by a tag present in the swept frequency field, said tag produced signal having positive and negative polarity pulses; means for separating said positive and negative pulses; means including a synchronous integrator coupled to said separating means for integrating positive polarity pulses; means including a synchronous integrator coupled to said separating means for integrating negative polarity pulses; and means coupled to said positive pulse integrating means and to said negative pulse integrating means for providing a detect signal in response thereto upon the detection of a tag produced signal, wherein said detect signal providing means is responsive to pulses received from said positive and negative pulse polarity integrating means, and includes means for counting the pulses received from the integrating means and for providing said detect signal only if a predetermined number of pulses are received within a predetermined time interval, and wherein said counting means includes means for providing said detect signal only if at least a first predetermined number of pulses are received within a first predetermined time interval and no more than a second predetermined number of pulses are received in a second predetermined time interval.

Claim 9

A detector for detecting the presence of a resonant tag in a swept frequency field, comprising: means for detecting the signal produced by a tag present in the swept frequency field, said tag produced signal having positive and negative polarity pulses; means for separating said positive and negative pulses; means including a synchronous integrator coupled to said separating means for integrating positive polarity pulses; means including a synchronous integrator coupled to said separating means for integrating negative polarity pulses; and means coupled to said positive pulse integrating means and to said negative pulse integrating means for providing a detect signal in response thereto upon the detection of a tag produced signal, wherein said detect signal providing means is responsive to pulses received from said positive and negative pulse polarity integrating means, and includes means for counting the pulses received from the integrating means and for providing said detect signal only if a predetermined number of pulses are received within a predetermined time interval, and wherein said counting means includes means for providing said detect signal only if at least a first predetermined number of pulses are received within a first predetermined time interval and no more than a second predetermined number of pulses are received in a second predetermined time interval.

Claim 10

A detector as recited in claim 7 wherein said counting means further includes means for providing said detect signal only if at least a third predetermined number of pulses are received within a third predetermined time interval, said third predetermined time interval being longer than said first and second predetermined time intervals.

Claim 11

A detector as recited in claim 8 wherein the length of said third predetermined time interval is greater than twice the length of said second predetermined time interval.

Claim 12

A detector as recited in claim 8 wherein the length of said third predetermined time interval is on the order of approximately twice the length of said second predetermined time interval.

Claim 13

A detector for detecting the presence of a resonant tag in a swept frequency field that has a periodic sweep rate, comprising: means for detecting the signal produced by a tag present in the swept frequency field to provide a detected signal that contains a tag signal when a tag is present; means including a synchronous digital integrator coupled to said detecting means for sampling said tag signal a plurality of times during each sweep and in synchronism with the sweep rate, and integrating each sample over a plurality of sweeps; and means coupled to said integrating means for monitoring the value of the integrated samples and providing a detect signal in response thereto upon the detection of a predetermined number of integrated samples whose value exceeds a predetermined value.

Claim 14

A detector for detecting the presence of a resonant tag in a swept frequency field that has a periodic sweep rate, comprising: means for detecting the signal produced by a tag present in the swept frequency field to provide a detected signal that contains a tag signal when a tag is present; means including a synchronous digital integrator coupled to said detecting means for sampling said tag signal a plurality of times during each sweep and in synchronism with the sweep rate, and integrating each sample over a plurality of sweeps; and means coupled to said integrating means for monitoring the value of the integrated samples and providing a detect signal in response thereto upon the detection of a predetermined number of integrated samples whose value exceeds a predetermined value.

Claim 15

A detector as recited in claim 11 wherein said detect signal providing means is responsive to pulses received from said integrating means and includes means for determining the widths of the pulses received from said integrating means, said detect signal providing means being responsive to the widths of said received pulses for providing a detect signal only if the widths of said pulses exceed a predetermined width.

Claim 16

A detector as recited in claim 11 wherein said detect signal providing means is responsive to pulses received from said integrating means, and includes means for counting the pulses received from the integrating means and for providing said detect signal only if a predetermined number of pulses are received within a predetermined time interval.

Claim 17

A detector as recited in claim 11 wherein said tag produced signal detecting means includes threshold means for passing signals detected by said tag produced signal detecting means only if the amplitude of the detected signals exceed a predetermined amplitude.

Claim 18

A system as recited in claim 11 wherein said synchronous integrator includes means responsive to the polarity of the detected signal.

Claim 19

A system as recited in claim 11 wherein said synchronous integrator is responsive to the amplitude of the detected signal.

Claim 20

A detector for detecting the presence of a resonant tag in a swept frequency field, comprising: means for detecting the signal produced by a tag present in the swept frequency field; means including a synchronous integrator coupled to said detecting means for integrating the detected signals; and means coupled to said integrating means for providing a detect signal in response thereto upon the detection of a tag produced signal, wherein said detect signal providing means is responsive to pulses received from said integrating means, and includes means for counting the pulses received from the integrating means and for providing said detect signal only if a predetermined number of pulses are received within a predetermined time interval, and wherein said counting means includes means for providing said detect signal only if at least a first predetermined number of pulses are received within a first predetermined time interval and no more than a second predetermined number of pulses are received in a second predetermined time interval.

Claim 21

A detector for detecting the presence of a resonant tag in a swept frequency field, comprising: means for detecting the signal produced by a tag present in the swept frequency field; means including a synchronous integrator coupled to said detecting means for integrating the detected signals; and means coupled to said integrating means for providing a detect signal in response thereto upon the detection of a tag produced signal, wherein said detect signal providing means is responsive to pulses received from said integrating means, and includes means for counting the pulses received from the integrating means and for providing said detect signal only if a predetermined number of pulses are received within a predetermined time interval, and wherein said counting means includes means for providing said detect signal only if at least a first predetermined number of pulses are received within a first predetermined time interval and no more than a second predetermined number of pulses are received in a second predetermined time interval.

Claim 22

A detector as recited in claim 17 wherein in said counting means further includes means for providing said detect signal only if at least a third predetermined number of pulses are received within a third predetermined time interval, said third predetermined time interval being longer than said first and second predetermined time intervals.

Claim 23

A detector as recited in claim 18 wherein the length of said third predetermined time interval is greater than twice the length of said second predetermined time interval.

Claim 24

A detector as recited in claim 18 wherein the length of said third predetermined time interval is on the order of approximately twice the length of said second predetermined time interval.