AU631170B2 - Electronic article surveillance system with improved differentiation - Google Patents

Description

~i il- OPI DATE 01/08/90 AOJP DATE 30/08/90 APPLN. ID 48287

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PCT NUMBER PCT/US89/05874 INTERNATIONAL APPLICATION PUBLISHED UNDEI THE BATF C PERATION TREATY (PCT) (51) International Patent Classification 5 yj Inte ation' Pub tio mber: WO 90/07760 G08B 13/24 (43) International Publication Date: 12 July 1990 (12.07.90) (21) International Application Number: PCT/US89/05874 (81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (European pa- (22) International Filing Date: 27 December 1989 (27.12.89) tent), DK, ES (European patent), FI, FR (European patent), GB (European patent), IT (European patent), JP, KR, LU (European patent), NL (European patent), NO, Priority data: SE (European patent).

295,064 9 January 1989 (09.01.89) US Published (71)Applicant: CHECKPOINT SYSTEMS, INC. [US/US]; With international search report.

550 Grove Road, Thorofare, NJ 08086 (US).

(72) Inventors: LIZZI, Phillip, J. 110 Redstone Ridge, Deptford, NJ 08096 SHANDELMAN, Richard, A. Flamehill Road, Levittown, PA 19056 (US).

(74) Agent: STAPLER, Alfred; Checkpoint Systems, Inc., 550 Grove Road, Thorofare, NJ 08086 (US).

(54) i'itle: ELECTRONIC ARTICLE SURVEILLANCE SYSTEM WITH IMPROVED DIFFERENTIATION (57) Abstract An electronic article surveillance system which is capable of identifying and discriminating between the different signatures of tags improving the reliability of the system and even permitting the tags to be classified by type, and separately addressed, includes a receiver which incorporates improvements in its filtering and processing sections. A linear phase filter is used to more effectively preserve the signal which is received, and thereby improve the signal which is ultimately delivered to the processor The processor (11) is provided with a "hysteresis-type" threshold detector (70 and 71) which operates to preserve the original signal by improving the shape of the pulse which is ultimately delivered to the processor (1 and an adaptive processing routine which varies the subsequent processing of detected signals according to changes within the system to improve the system's ability to discriminate between the different signals which are received.

L i i; t: WO 90/07760 PCT/US89/05874

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Description ELECTRONIC ARTICLE SURVEILLANCE SYSTEM WITH IMPROVED DIFFERENTIATION

APPENDIX

An appendix containing a total of 13 sheets pertaining to a computer listing is -submitted with this specification.

I n co rporc- G.A The present invention generally relates to electronic security systems, and in particular, to an improved electronic article surveillance system.

A variety of electronic article surveillance systems have been proposed and implemented to restrict the unauthorized removal of articles from a particular premises. One common form of this is the electronic article surveillance system which has come to be placed 15 near the exits of retail establishments, libraries and the like. However, electronic article surveillance systems are also used for purposes of process and inventory controls, to track articles as they pass through a particular system, among other applications.

Irrespective of the application involved, such electronj- article surveillance systems generally operate upon a common principle. Articles to be monitored are provided with tags (of various different types) which contain a circuit (a resonant circuit) for reacting with an applied radio-frequency field. A transmitter and a transmitting antenna are provided to develop this applied field, and a receiver and a receiving antenna are provided to detect disturbances in the applied field. If the resonant circuit of a tag is passed between the transmitting and receiving antennas (which are generally placed near the point of exit from a given premises), the applied field is affected in such fashion that a detectable event is produced within the receiver. This

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fe WO 90/07760 PCT/US89/05874 is then used to produce an appropriate alarm. Systems of this general type are available from manufacturers such as Checkpoint Systens, Inc., of Thorofare, New Jersey, among others.

Although such systems have proven effective in both security as well as inventory and process management, it has been found that certain improvements to such systems would be desirable. Perhaps foremost is the ever-present desire to reduce to the extent possible any errors false alarms) which are produced by such systems, particularly in terms of their discrimination between the presence of a tag (signifying the presence of a protected article) and other interference which may be present in the vicinity of the electronic article surveillance system. Any steps which can be taken to improve the accuracy of the system will tend to reduce such undesirable results.

More recently, it has become of interest to provide an electronic article surveillance system with sufficient resolution to actually distinguish between different types of tags, resulting from differences in the resonant circuits which they contain. It has long been recognized that different types of tags have different "signatures" (responses) corresponding to the configuration of the resonant circuits which they contain. For example, the resonant circuit of a so-called "hard" tag will generally tend to produce a signal which is somewhat stronger than other types of tags, such as hang-tags and labels, resulting from differences in the size and configuration of the components which comprise these particular labeling devices. As a result, it becomes conceptually possible to differentiate between these various types of tags and labels by analyzing their signatures, by discriminating between the different signals which are possible. However, to date, available systems did not WO 90/07760 PCYr/US89/05874 -3posgess the sensitivity to detect these differences in a reliable fashion.

iL Summary of the Invention 0 It is therefore an object of the present invention to attempt to overcome one or more of the aforementioned problems.

Therefore, in one aspect there is provided an electronic article surveillance system comprising: a transmitter providing a signal to a transmitting antenna to develop an electromagnetic field; and a receiver having a receiving antenna for receiving signals including signals produced by a first resonant circuit forming part of a first tag means associated with an article to be protected in response to the electromagnetic field and a second resonant circuit different from said first resonant circuit and forming part of a second tag means associated with a different article to be protected also in response to the electromagnetic 20 field, and for providing said received signals to the receiver, the receiver further having means for identifying said tag signals, and means for discriminating.between first tag signals produced by the first resonant circuit of said first tag means and second tag signals produced by the second resonant circuit of said second tag means.

In order that the invention may be more fully explained, examples of preferred embodiments will now be described with reference to the accompanying drawings, in which:

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WO 90/07760 PCT/US89/05874 Brief Description of the Drawings Figure 1 is a block diagram of a conventional electronic article surveillance system.

Figures 2a and 2b are diagrammatic plan views showing an improved antenna system for use in conjunction with the transmitting and receiving portions of the electronic article surveillance system of Figure 1.

Figure 3 is a schematic diagram of an equivalent circuit for the antenna systems shown in Figures 2a and 2b.

Figure 4 is a graph which illustrates the frequency and phase response of the antenna systems shown in Figures 2a and 2b.

Figure 5 is a schematic diagram of an improved receiver used in conjunction with the electronic article surveillance system of Figure 1.

Figure 6 is a graph which illustrates the manner in which a received signal is processed by the receiver of Figure Figure 7 is a graph which illustrates the manner in which the analog signals shown in Figure 6 are converted to a digital representation, fo- presentation to the processor.

Figure 8 is a graph which illustrates the manner in which the processor operates to discriminate between the various digital signals which are received.

Figure 9 is a schematic representation of a security system which incorporates a plurality of surveillance devices and supporting equipment in a single interactive environment.

In the several views provided, like reference numerals denote similar elements.

I--I"--illlrlll WO 90/07760 PCT/US89/05874 Detailed Description of the Preferred Embodiment Figure 1 shows (in block diagram form) what generally constitutes the conventional components of an electronic article surveillance system 1 of the type manufactured by and available from Checkpoint Systems, Inc., of Thorofare, New Jersey. This system 1 includes a tag 2 which can be applied to any of a variety of different articles in accordance with known techniques. For example, the tag 2 may take the form of a "hard" tag which is attachable to an article using the connecting pin with which this type of tag is gene).' ly provided.

Alternatively, the tag 2 may take the form of a hang-tag which is appropriately tied to the article. The tag 2 may also take the form of a label adhesively affixed to the article. Any of a variety of types of tags and application techniques may be used to accomplish this general task.

Irrespective of the type of tag which is used, or its manner of attachment to the associated article, the tag 2 incorporates a resonant circuit (not shown) which is capable of reacting to applied fields of electromagnetic energy. A transmitting antenna 3 is provided which is capable of developing these applied fields responsive to the operation of associated transmitter circuitry 4. A receiving antenna 5 is provided for receiving electromagnetic energy both from the transmitting antenna 3 and the resonant circuit of the tag 2 to develop a signal which is in turn applied to a receiver 6. The receiver 6 then operates upon this detected signal to determine that the tag 2 is present in the vicinity of the transmitting and receiving antennas 3, 5, and give an alarm if such is the case.

This is generally accomplished by applying the signal which is picked up by the receiving antenna 5 to an -4 WO 90/07760 Pcr/US89/05874 amplifier 7, which operates to improve this received signal. The amplified signal is then applied to a detector 8 which essentially operates to recover (or demodulate) the active (base band) component which is used to detect the presence of a tag 2 in the vicinity of the electronic article surveillance system 1 from the high frequency (carrier) component of the signal which is required for use in conjunction with the transmitting and receiving antennas 3, 5. The base band signal which is isolated by the detector 8 is then applied to a filter 9 which operates to further attenuate undesirable low and high frequency signal components, including noise and other interference inherent in the isolated signal. The filtered signal is then applied to a converter 10 which operates to convert the analog signal received from the filter 9 to a digital signal which is suitable for presentation to a digital processor 11. Operations are then performed within the processor 11 to interpret the signal which is received, and to determine whether this received signal indicates the presence of a tag 2 in the vicinity of the transmitting antenna 3 and the receiving antenna 5, thereby representing a detectable event.

As previously indicated, and in accordance with the present invention, this otherwise conventional configuration is modified in various ways to improve the resolution of the resulting system, thereby improving its ability to differentiate between signals representative of a tag 2 passing near the transmitting antenna 3 and the receiving antenna 5, and other signals (noise, interference, etc.) which do not represent a properly detected event, and developing the ability to actually distinguish between different types of tags based upon differences in the signatures of the resonant circuits which they contain. This includes modifications to the transmitting antenna 3 and their receiving antenna 5, as 'i ci!~~ i'' WO 90/07760 PCT/US89/05874 well as modifications to the filter 9 and converter which operate to provide signals to the processor 11, and the routine (software) which is employed to then process these received signals. Further detail regarding each of these improved components is provided below.

The transmitter circuitry 4 substantially corresponds in structure to the transmitters of prior electronic article surveillance systems of this general type.

However, where possible, steps are taken to reduce distortion within the unit.

Referring now to Figures 2a and 2b of the drawings, these show the manner in which antennas embodying the present invention may be configured and mounted.

Figure 2a shows this for the transmitting antenna 3, Figure 2b for the receiving antenna In each case, there is provided a housing 7. In its presently preferred embodiment, this housing 7 is made of a hollow synthetic plastic body, in whose interior all the other elements are positioned. Specifically, in the base portion 7a of Figure 2a, there is located the transmitter circuitry 4 (Figure 1) while, in the base portion 7a of Figure 2b, there is located the receiver circuitry 6 (Figure 1).

Each housing 7 has a pair of uprights 7b and 7c, which are connected by cross-members 7d and 7e. In each housing 7, the antenna loop 15 starts at the base portion 7a and extends upwardly on one side of the loop into upright portion 7b and on the other side into upright portion 7c. However, at cross-member 7d, these sides of the antenna loop 15 change places, i.e. the portion extending along upright 7b switches over to upright 7c and vice-versa. The antenna loop 15 is then completed within cross-member 7e.

This crossing over of the upper and lower portions of each antenna loop 15 is what creates far-field

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WO 90/07760 pCT/US89/05874 cancellation of the antenna patterns, as appropriate to satisfy FCC regulations, as well as to reduce interference from remote sources of extraneous radio frequency energy. This technique of using one or more such cross-overs is known, and in itself, does not constitute an element of the present invention.

However, in accordance with the present invention, the antenna loop 15 is now formed of paired leads, which are preferably embodied in a twin-axial cable (a cable suitable for this purpose is available from Belden Wire and Cable Company, P.O. Box 1980, Richmond, Indiana 47375, under their product number 9271). Such a cable comprises an insulating sleeve, within which extends a pair of separate leads, surrounded by a conductive shield. A conductor for grounding the shield is also provided, and spacers are twisted in with the leads to maintain substantially uniform spacing of the elements within the outermost insulating sleeve.

It is also possible to make use of two discrete, generally parallel wires to form the antenna loop Paired coaxial cables may also be used. In any case, the individual leads are preferably uniformly spaced from one another throughout their lengths. Further, it is preferable for the paired leads to.be uniformly twisted along their lengths since this reduces the effect of local irregularities.

When using a shielded set of paired leads, as in the case of the twin-axial cable previously discussed, it is appropriate to provide a break in that shield, to assist the leads inside the shield in performing their basic function as antenna elements. Such a break is represented at 9a in Figure 2a, where the leads inside shield 9 become exposed. To maintain electrical continuity for shield 9, the upper and lower portions separated by the break are conductively connected by conductors 9b ahd 9c.

i 1- WO 90/07760 0 PCT/US89/05874 Although not illustrated, the same break arrangement is preferably provided for the antenna 5 of Figure 2b.

In Figures 2a and 2b, the preferred twin-axial cable is represented somewhat diagrammatically by a tubular element 9 and by conductor pairs 17a, 17b and 18a, 18b, which are seen to emerge from the open lower ends of the element 9. Specifically, element 9 represents the conductive shield of the twin-axial cable; conductor pairs 17a, 17b and 18a, 18b represent the separate leads inside the cable, which become visible in Figures 2a and 2b where they emerge from the inside of shield 9, near the transmitter circuitry 4 and receiver circuitry 6, respectively.

More specifically, conductors 17a and 17b represents the so-emerging opposite ends of the same one of the two separate leads inside shield 9; conductors 18a and 18b represent the opposite ends of the second one of the two separate leads inside shield 9.

As shown in Figure 2a, transmitter circuitry 4 is connected to that one lead whose emerging ends are designated by reference numerals 17a, 17b in Figure 2a.

This transmitting circuitry thus constitutes an "active" load for this lead and the loop which that lead forms inside shield 16 constitutes the "active" loop of the transmitting antenna.

In Figure 2b, it is the receiver circuitry 6 which is connected to that one lead whose emerging ends are similarly designated by reference numerals 17a, 17b in Figure 2b. Accordingly, in Figure 2b, it is the receiving circuitry which constitutes and "active" loop of the receiving antenna.

S Turning now to the other lead inside each shield 9, the emerging ends of that lead, which are designated by reference numerals 18a, 18b in each of Figures 2a and 2b, are not connected to the respective active loads (namely 1 I t l WO 90/07760 PC1/US89/05874 to transmitter or receiver circuitry 4, Rather the emerging portions 18a, 18b of these leads are connected in each of Figures 2a and 2b to a "passive" load 20 and the loop which each of these leads forms inside its shield 9 thus constitutes the "passive" loop of the respective antenna.

Each of these passive loops is in turn coupled to the active loop inside the same shield 9 by means of the mutual coupling which exists between two closely adjacent leads.

The impedance of passive load 20 is so chosen that, when it is reflected back into the respective active load through the above-mentioned mutual coupling, the overall effect will be to impart to each antenna loop 15 a much flatter amplitude response and a much more linear phase response than could otherwise have been obtained, without substantially reducing the antenna efficiency.

Because of the distributed nature of the mutual coupling between the leads inside each shield 9, it is difficult to provide a precise equivalent circuit for the arrangement. An approximation of such an equivalent circuit for the transmitter portion of the system is shown in Figure 3 within the broken line rectangle designated by reference numeral 19.

As illustrated in Figure 4, to which reference may now be made, the use of a second lead in the manner embodying the present invention changes the antenna amplitude response from one which is generally similar to that shown at 21 in Figure 4, to one which is generally similar to that shown at 22, i.e. to one which is significantly more uniform throughout the operative frequency band. Also illustrated in Figure 4 is a corresponding improvement in the antenna's phase response, from a response generally like that shown at 23, to a comparatively more linear response such as shown WO 90/07760 1- PCT/US89/05874 at 24 By so flattening the antennas' amplitude response and linearizing their phase response, it becomes possible to effectively detect tag signals over a wider range of frequencies, without creating more false alarms. This is important because the resonant circuit which is part of each tag 2 tends to vary in resonant frequency from one tag to another. Because of this, conventional practice requires a swept frequency to be utilized by the system 8.2 MHz 800 KHz) so as to effectively interact with such tags despite their variation in resonant frequency. Even then, some tags had to be rejected following their manufacture because they could not satisfy the tolerance requirements for the electronic article surveillance system with which they were to be used. By making it possible to effectively detect a broader range of frequencies, the electronic article surveillance system 1 of the present invention will operate to detect a wider range of resonant tags, in turn permitting a significantly reduced number of tags to be rejected in the course of their manufacture.

Using a twin-axial cable as the receiving antenna provides an additional advantage for the system 1. It is the principal function of the receiver 6 to activate an appropriate alarm when the presence of a tag 2 is detected between the transmitting antenna 3 and the receiving antenna 5. To that end, there may be mounted inside the upper cross member 7e of housing 7 in Figure 2b a conventional warning light arrangement diagrammatically represented by rectangle 25. In order -s to energize this warning light when required, a d-c connection needs to be provided between it and the receiver 6 located in the base 7a of the housing 7. The passive lead (the one whose emerging ends are designated by reference numerals 18a and 18b in Figure 2b) may be

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I I WO 90/07760 PCT/US89/05874 used for that purpose. Specifically, d-c output from receiver 6 may be applied to that lead via a connection which is diagrammatically represented by lead 26 in Figure 2b. At the top of the loop formed by the twin-axial cable, a connection is made to the same passive lead near the warning light arrangement 25, as diagrammatically represented by connecting lead 27 in Figure 2b. As a result, there is no need for a separate, additional lead between receiver 6 and warning light Potential adverse effects on antenna performance, resulting from the presence of such an additional lead, are thereby averted.

The result is a highly effective transmitting antenna 3 and receiving antenna 5 which are more uniformly responsive to signals received in the operating frequency range for the system. In addition to the effect of reducing the number of tags which must be rejected for being out of specification (thereby reducing waste), this has the further advantage of providing a relatively "clean" (distortion-free) signal to the improved receiver 6' of the present invention, which is more fully illustrated in Figure 5 of the drawings, for further processing as follows.

Referring now to Figure 6, the signal 28 which is received at the antenna 5 (Figure 6a) will primarily constitute a base band signal 20 KHz) modulated upon the system's operating frequency 8.2 MHz) and contained within an "envelope" corresponding to the intensity (amplitude) of the field which is then being received. The operative frequency (8.2 MHz) is preferably swept 800 KHz approximately 82 times each second) to account for variations in the resonant circuits of the tags 2. When the tag 2 is caused to pass between the transmitting antenna 3 and the receiving antenna 5, a small deflection 29 will develop in this

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BLANKING 103 (57) Abstract B I G

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An electronic article surveillance system which is capable of identifying and discriminating between the different signatures of tags improving the reliability of the system and even permitting the tags to be classified by type, and separately addressed, includes a receiver which incorporates improvements in its filtering and processing sections. A linear phase filter is used to more effectively preserve the signal which is received, and thereby improve the signal which is ultimately delivered to the processor The processor (11) is provided with a "hysteresis-type" threshold detector (70 and 71) which operates to oreserve the original signal by improving the shape of the pulse which is ultimately delivered to the processo?r and an adaptive processing routine which varies the subsequent processing of detected signals according to changes within the system to improve the system's ability to discriminate between the different signals which are received.

WO 90/07760 PCT/US89/05874 envelope, which must then be detected by the receiver 6' to provide an appropriate alarm signal. To be noted is that this deflection will occur in both phase and amplitude, but will be very small in magnitude (generally 1/1000 to 1/10000) in relation to the carrier signal.

Careful detection techniques must therefore be used to isolate this signal, and then identify it, as follows, with reference to both Figure 5 and Figure 6 of the drawings.

The received wave form is first amplified (amplifier 7) and the.. introduced to the detector 8. This amplification may include a pre-filtering (at 30) and/or post-filtering (at 31) step, if desired. The detector 8 essentially operates to recover (demodulate) the base band (0-20 KHz) signal from its swept carrier (swept about a nominal 8.2 MHz) frequency. The resulting wave form (Figure 6b) will therefore substantially correspond to the isolated base band signal 32, with an added perturbation 33 which corresponds to the deflection 29 (change in amplitude and phase) produced by the presence of the tag 2 between the transmitting antenna 3 and the receiving antenna 5. To be noted is that this signal will tend to vary depending upon the location and orientation of the tag 2 relative to the antennas 3, including variations in both the base band signal 32 and the detected perturbation 33. The resulting signal is preferably then amplified (amplifier 34) prior to introduction to the filter 9.

The filter 9 then operates to isolate the detected signal 32 from other signals which may come to be received by the antenna 5, such as the basic (8.2 MHz) carrier signal, other interfering signal (including signals received from the transmitter and noise outside of the useful band. Preferably used for this purpose is a series combination of a high-pass filter 4 X

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WO 90/07760 PCr/US89/05874 for eliminating undesired lower frequency components followed by a low-pass filter 36 for eliminating undesired higher frequency components.

It is a particular goal of the electronic article surveillance system 1 of the present invention to preserve those wave forms which are being processed through the system 1 responsive to a detected tag 2, to the extent possible. Filtering inherently tends to adversely affect such signals, not only in terms of their amplitude, but also by imparting time-delay distortion to the signals which are being processed. The amplitude of the resulting signal is preferably restored in an amplifier 40 which follows the filter 9. However, preservation of the original wave form remains compromised as a result of the encountered time-delay distortion.

Previously, and referring now to Figure 6c, such distortion had been compensated for by operating upon not only the primary signal 41 produced by a tag passing between the transmitting and receiving antennas of the system, but also one or more of the distortion products 42 produced by tha filtering step. In accordance with the present intention, the filter 9 is presently configured as a linear phase (constant group delay) filter to avoid the adverse effects of time-delay distortion. Any of a variety of known linear phase filter configurations may be used for this purpose. The result is a filtered signal 43 (Figure 6d) which as closely as possible corresponds to the initial signal produced by the transmitter circuitry 4 and isolated by the detector 8 (Figure 6b). As will be further addressed below, this has significant advantages in connection with the subsequent processing which is to take place, contributing to the various improvements which are provided in accordance with the present invention. A

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L 1 i V .Q.L.LaAJ.L%= L JIW WO 90/07760 G, PCT/US89/05874 smoothing filter 44 preferably follows the amplifier to further remove noise components within the operating base band.

What is more, such filtering permits the received signal to be more effectively distinguished from that of the transmitter within a significantly lower frequency band, when the detected signal resulting from the presence of the tag 2 is exhibiting an increased magnitude from previously available systems. By way of explanation, and referring now to Figures 6e and 6f, the receiver 6' will operate to detect both a signal 45 from the transmitter 4 and a signal 46 from the tag 2 (including the signals and their harmonics). As shown in Figure 6e, the tag signal 46 will not be easily distinguished from the transmitter signal 45 (which are of the same general type) until the frequency band 47 is reached. However, referring now to Figure 6f, it is seen that the above-described filtering causes the transmitter signal 45' to roll off more rapidly than the tag signal 46, allowing the tag signal 46' to be differentiated from the transmitter signal 45' within the frequency band 48, where the tag signal 46' exhibits an increased magnitude. This operates to preserve more of the available tag signal 46' for further processing.

Referring now to Figure 7, the filtered signal shown in Figure 7a (including responses 51 representing detected tags and responses 52 representing interfering signals) is then applied to the converter 10 to be converted from the analog signal which is received from the filter 9 to a digital signal which is appropriate for presentation to the processor 11. As with prior processors of this general type, the received analog signal is digitized to a one-bit resolution (a "one" or a "zero") since this has been found to provide sufficient resolution for interpretation by the processor 11. To be i WO 90/07760 PC/US89/05874 noted is that while this is presently preferred in view of its simplicity, it would be equally possible for higher resolution conversions to be used in conjunction with a multi-bit processor, if desired.

Referring now to Figure 7b, such conversion was previously accomplished using a threshold detector which operated to detect levels exceeding certain selected thresholds 55, 56 centered about a pre-selected level 57, to produce desired transitions (forming pulses) according to variations in the level of the applied analog signal (developing a positive pulse for both positive-going and negative-going signals), in this case the tag signal of Figure 6c. This in turn developed a series of positive pulses 58, 59, 60, 61 having pulse widths which would vary according to the analog signal which was then received from the filter 9.

The widths of these resulting pulses defined the "signature" for a particular tag 2 detected between the transmitting antenna 3 and the receiving antenna Other pulses would also be developed resulting from other signals, particularly interference in the vicinity of the electronic article surveillance system. However, since these additional pulses had characteristics (widths) which differed from the signature of the tag 2 which was being searched for, it was possible for the processor of the system to determine whether a particular series of pulses corresponded to the signature (pattern) of a tag 2, or an interfering signal.

As previously indicated, a broader range of signals for enabling this determination to proceed will be made available by the transmitter and receiver components which have earlier been described, as well as the associated transmitting antenna 3 and receiving antenna which cooperate to better preserve the signals which are to be operated upon. However, even with these e% i WO 90/07760 PCI/US89/05874 employed by previous processors to make such a determination were still generally insufficient to distinguish between these various pulses with sufficient particularity for the processor 11 to be able to discriminate between different signatures corresponding to different types of tags, in addition to its primary function of distinguishing between tag signatures and interfering signals.

The primary reason for this arises from certain considerations relating to the tag 2 which is then being passed between the transmitting antenna 3 and receiving antenna 5. As is the case with any tag, and particularly in connection with an unauthorized removal of an article it can be expected that the tag 2 will not always be placed in an optimum position relative to the transmitting antenna 3 and the receiving antenna 5 to produce a maximized signal at the receiving antenna generally parallel to the plane of the transmitting antenna 3 and the receiving antenna Rather, it can be expected that the tags will come to be placed at different angles relative to the antennas 3, As a result, signals of different quality will often come to be applied to the converter 10, producing widely different signals for interpretation by the processor 11.

For example, and referring now to Figure 7c (somewhat expanded in scale for illustrative purposes), a signal of relative strength will tend to cross the selected threshold 55 rather quickly, and will return to that selected threshold rather late, developing a relatively "wide pulse 66. However, a signal 67 of reduced strength will more rapidly reach and return to the selected threshold 55, producing a pulse 68 of significantly reduced width. This has been found to complicate, and often compromise the signal processing steps which are to L 111 WO 90/07760 pCr/US89/05874 follow.

The technique which is generally used to distinguish between pulses which correspond to the signature of a tag and pulses which correspond to an interfering signal is to determine whether the received pulse has a duration (width) which falls within a predefined "window". This window is established (set) within the processor 11 and must be broadly defined to accommodate not only the variety of different tag configurations which can be anticipated, but also the broad spectrum of detected pulses which might correspond to an interfering signal.

As a result, it was not possible for such systems to distinguish between different types of tags (and their signatures), and it was not uncommon for these systems to fail to distinguish a valid pulse of reduced width the pulse 68) from a source of interference, failing to detect the presence of a tag 2 between the antennas 3, Broadening the defined window would help the system to recognize a greater number of tags. However, this has the corresponding disadvantage of also identifying and accepting a greater number of interfering signals as the presence of a tag, leading to an increased number of false alarms. This generally necessitated the striking of a balance which was at times less than optimum.

In accordance with the present invention, various steps are taken within the converter 10 and the processor 11 to improve the overall detection process, and to more carefully distinguish between the signature of a tag and other signals which may come to be received in the course of operating the electronic article surveillance system 1.

The first of these improvements forms part of the converter 10, and relates to the manner in which the initial threshold comparisons are made. Specifically, a "hysteresis-type" threshold comparison is made, making

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L which is picked up by the receiving antenna 5 to an iA WO 90/07760 PCT/US89/05874 use of two different thresholds (developed by the two different comparator circuits 70, 71 of Figure 5) which are selected to define (detect) the leading and trailing edges of the converted pulse, respectively. Referring now to Figure 7d, by properly selecting the two different thresholds 72, 73, the same initial signals 65, 67 which are shown in Figure 7c will result in pulses 74, 75 which are significantly closer in proportion to one another than were the pulses 66, 68. As a result, the pulses 74, 75 constitute a more accurate representation of the initial signal. This applies not only to the stronger signals, but also to the signals of reduced strength, which operates to significantly expand upon the range of signals which are effectively detectable by the converter 10, for subsequent processing.

Selection of the two different thresholds 72. 73 is made according to the particular signature (characteristics) of the tag 2 which is to be operated upon, as well as the anticipated environment for the system. Consequently, these levels are preferably made adjustable to accommodate different applications. This may include both adjustments in relative level upper and lower thresholds varied as a pair) as well as adjustments in the difference between the two selected thresholds, as desired. It is even possible to adjust the thresholds 72, 73 so that one is positive while the othRr is negative, should this be indicated for a particular application.

Referring now to Figure 8 of the drawings, this improved signal is in turn applied to the processor 11, which incorporates additional improvements for further discriminating between tag signatures and interference, as follows. As is conventional, following the detection of a leading edge 82 of a first pulse 81 resulting from a detected signal 80 (either a tag signature as .1 i I WO 90/07760 PCT/US89/05874 illustrated, or an interfering signal), steps are taken to determine whether that pulse's trailing edge 83 falls within a predefined window 85 established for the anticipated pulse width of a desired tag signature. If so, steps are then taken to analyze the next piise 90 in the detected series Previously, this was accomplished by similarly comparing the width of the second pulse 90 with a preestablished (fixed) window for that pulse. However, in accordance with the present invention, this prior technique is replaced with an analysis of the second pulse 90 according to a variable window 91 which is "redefined" (computed and adjusted) according to a routine established within the processor 11. The computational adjustment which is made is based upon the analysis of the first pulse 81 in the series 80, and certain assumptions which are made regarding the anticipated characteristics of the second pulse 90 which is to follow. If the second pulse 90 is then determined to constitute the signature of a tag 2, a counter (conventionally provided in software within the processor 11) is incremented as before. However, to be noted is that this incrementing is perfo:med after only two pulses 81, 90 have been successfully analyzed, as distinguished from the prior systems which would generally require a third pulse 95 of the detected signal 80 to be analyzed before this determination could be made.

As previously indicated, electronic article surveillance systems of this general type are configured to repeatedly sweep about the nominal operating frequency of the system, thereby developing repeated signals corresponding to the presence of a tag 2 between the antennas 3, 5. This in turn produces plural signatures which must then be detected by the processor 11, in similar fashion. In addition to making a determination

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i i i WO 90/07760 r22-- PC'/US89/05874 as to whether or not a subsequently received signal corresponds to the signature of a tag 2 or some other signal interference), as described above, steps are also taken to determine whether or not the detected signal corresponds in time to a scheduled sweep by the transmitter circuitry 4. If an identified signature is detected during a scheduled sweep of the system, steps are again taken to increment the system's counter.

Otherwise, a spurious signal is deemed to exist and that signal is ignored.

In prior systems, this continued until the counter reached a selected number six or seven counts), when a tag 2 would be deemed to be present and an alarm sounded. However, when a tag 2 passes through the electromagnetic field which is produced by the system, it is often the case that the relationship between the field (flux) which is produced and the resonant circuit of the tag 2 which is moving through that field will vary. This would in turn cause variations in the tag signals (primarily in magnitude) which were detected responsive to successive sweeps of the transmitter circuitry, which at times prevented an effective recognition of a tag signature by the processor 11. The improvements described in connection with the electronic article surveillance system 1 of the present invention operate to improve the reliability of this detection process.

However, it is still possible for tag signatures to go undetected. It is for this reason that there is yet another improvement which is incorporated into the processor 11.

Specifically, it was previously the practice to reset the counter to zero if an anticipated tag signature was not detected during a scheduled sweep of the system, prior to reaching the designated count. This was done to avoid false alarms and the like, but could also result in 11) i i break are conductively connected by conductors 9b and 9c.

WO 90/07760 -23 PCT/US89/05874 the failure to detect a tag 2. In accordance with the present invention, this technique is replaced with an up/down counter (within the processor 11) which operates to track both successfully detected signatures, and other events, responsive to periodic sweeps of the transmitter.

To this end, if a tag signature is detected, and if the detected signature occurs following a scheduled sweep (within a defined window), the counter is incremented.

Detected events occurring outside of the windows defined for the swept signal are ignored. If no tag signature is detected within the prescribed window, the counter is decremented. This continues until such time as the counter either reaches a prescribed threshold five counts) or returns to zero (no tag present), significantly diminishing the effects of undetected signatures. To be noted is that a variety of different counts may be selected for use in this regard. For example, it is possible for an increment to result in an increase of one, or more than one. Similarly, a decrement may correspond to one, or some greater number.

The count established for an increment may be the same as that established for a decrement one to one), or different counts may be used, as desired in a particular application.

Referring again to Figure 5, a system for providing these functions generally comprises a processor 11 which receives its primary signal 100 from the dual threshold detectors 70, 71, and appropriate controlling signals from an external signal detector 101 which precedes the linear phase filter 9 (which provides a logic level for timing purposes), and is provided with the computer program listing which follows this specifications (Appendix). If desired, the processor 11 is additionally controllable (programmable) at 102 to vary the window which is used to analyze the first pulse of a received i WO 90/07760 2- PCT/US89/05874 signal (subsequent pulses are analyzed according to computationall3y adjusted windows as previously described).

To be noted is that the processor 11 can also be controlled, at 103, to change the sweep rate of the electronic article surveillance system 1 from the previously described rate of 82 Hz to a different sweep rate if desired. This permits the electronic article surveillance system 1 to separately address tags using different sweep rates, for reasons which are best illustrated with reference to Figure 9.

In practice, it is not uncommon for a complete security system 105 to employ a plurality of electronic article surveillance devices 106, 107, 108, in addition to other support equipment such as tag deactivators 109, 110 and the like. In many cases, these structures must be positioned relatively close to one another, which can give rise to interference between these various devices.

Such interference results from operating each of the several units at the same basic frequency. Small differences in these operating frequencies (resulting from design tolerances and the like), or their sychronization, can produce beat patterns which at times generate false alarms and other spurious signals.

Previously, this was accommodated by sychronizing the several units employed to one master unit synchronizing the devices 106, 107 and deactivators 109, 110 to the device 108), thereby avoiding interference between the various units employed. However, this often complicated the installation of such systems, in view of the wires which needed to be run between the several units, and could also at times produce unacceptable interference on such connecting wires (which would themselves tend to act as antennas producing interfering signals). In any event, when initially installing a I L ,1 WO 90/07760 pCT/US89/05874 security system of this general type, it was necessary to very carefully adjust (tune) the various components of that system to reduce the foregoing problems to the extent possible. At times, it was even necessary to readjust the various components of the system to maintain this careful balance.

In accordance with the present invention, the need for such special measures is eliminated by causing each of the several components which comprise the installed system to operate at different sweep rates, thus avoiding the potential for interference between these respective components. For example, the devices 106, 107, 108 could be operated at three different sweep rates, with the deactivators 109, 110 operating at a fourth and different sweep rate (it is not necessary for the deactivators to operate at different rates so long as their rate of operation differs from those of the accompanying electronic article surveillance devices). Due to the programmability of the processor 11, this improvement in system operation is achieved in a straightforward manner which can be tailored to particular applications, as desired.

To be noted is that the different sweep rates which are used can be selected, as desired, although it is presently considered important to maintain the selected sweep rates above 70 Hz and below 90 Hz to avoid impairment of the system's overall function, and to separate the selected sweep rates by at least 3 Hz to permit the system to distinguish between the sweep rates which are available.

These above-described adjustments can either be incorpcrated into the system by pre-established programming of the processor 11, if desired, or by switchably selecting between them according to the particular application which is needed. This would j; i WO 90/07760 PCT/US89/05874 include both the selection of basic sweep rate for the system, as well as the selection of window parameters for detecting tag signatures.

Accordingly, it is seen that a variety of improvements are combined in accordance with the present invention to significantly reduce distortions within the system, to better preserve the basic signals which are developed responsive to the presence of a tag, and to more effectively interpret the signals which result. This includes not only the careful design of various components to reduce distortion, but also the specific improvements of the present invention including the improved configurations for the transmitting antenna 3 and the receiving antenna 5, the improved configuration for the filter 9 and the converter 10, and the improved processing routines which are performed within the processor 11. The result is a system which not only improves the differentiation of tag signals from other interfering signals, but which is sufficiently sensitive to even permit a discrimination between different tag signatures.

Such improved discrimination gives rise to capabilities which were not achievable with previously available electronic article surveillance systems. For example, it now becomes possible to actually discriminate between different types of tags, permitting a classification of tag groups according to their signature (characteristics). This can be used to better match the electronic article surveillance system 1 to the particular tag which is to be used, to achieve a more error-free result, or to distinguish between different types of tags used with the electronic article surveillance system i. This can also be used to change the sweep rate used in conjunction with operation of the electronic article surveillance system i, to avoid i '1 jli 1 WO 90/07760 PCT/US89/05874 interference with adjacent components. What is more, these functions are easily varied by adjusting (programming) the parameters to be used within the processor 11, as previously described.

111 in the details, materials and arran nt of parts which have been herein described nillustrated in order to explain the natur this invention may be made by those skilled e art within the principle and scope of the i.nt xpressed in Lhe following claims.

4 7- YUYbUL series comJm1nation of a high-pass filter 35 1 WO 90/07760 PCrIUS89I05874 PROGRAM FOR 63(AB)01 /637(AB)01 VOC MICROPROCESSOR IN ALPHA RECEIVER (6 MHZ Resonator) (Fixed sweep rate selects) (Panasonic smoothing filter) 1.2A

DEFINITIONS

MICRO IS SET UP IN MODE 7 (SINGLE CHIP) PORT 1 P17 P16 P15 P14 P13 P12 P11 MSB Pgm Sel LS13 AIm Time Am Src Ji a Jib in in in in in- in- swpsel in PORT 2 P27 P26 P25 P24 P23 P22 P21 N Video En ICR(Video) Mode Set out- in in in- PORT 4 P47 P46 P45 P44 P43 P42 P41 P4 01 TP4 P.S. PS En Ext lnh Aim AImfIgout out in- in in out out- EQUATE TABLE pl ddr equ 00h p2ddr equ 01 h pi data equ 02h padata equ 03h p4ddr equ p4data equ 07h stacktop equ Off h romstart equ 01 OO0h SUBSTITUTE SHEET WO 90/07760 PCT/US89/05874 ramstart equ r amstop equ Off h pstmax equ tcsr equ 08h ocr equ Obh beeptime equ 0c000h icr e~qu Odh timer equ 09h twoffset equ 1200 onesec equ 22 ;one sec. timer fivsec equ 112 jfive sec. timer maskon equ 02h swp78 equ 19230 swp82 equ 18290 swp86 equ 17440 equ 16670 swpmin78 equ 19480 swpmin82 equ 18520 swpmin86 equ 17650 swpmin90 equ 16850 swpmax78 equ 18990 swpmax82 equ 18070 I swpmax86 equ 17240 swpmax9o equ 16480 swpadj78 equ swpadj82 equ 0 swpadj86 equ equ MICRO SETUP The 6301 is configured in a mode 7 t,,.t5 as follows: 1. Internal RAM from 40h to FFh 2. Internal ROM from FOO0h to FFFFh 3. NMI tied to ground 4. IRQ line tied to beat note detection ckt- SUBSTITUTE SHEET WO 90/07760 PC1'/US89/05874 Output (P41) used for Alarm Level 6. Timer input (P20) used for +thresh ored -thresh input 7. P42 is output used for Sonalert and lamp driver 8. P1O0/P1 1 (J1) select sweep rate parameters status ds 1 signflg ds 1 tlead ds 2 tfall ds 2 tend ds 2 temp ds 2 tlimits ds 4 pcnt ds 1 vflag dls 1 almenflg ds 1 pstimflg dls 1 pstimer dls 1 almcntr ds 1 windowi dls 2 window2 dls 2 tpcnt ds 1 dls 2 almflg ds 1 tmark ds 2 tagcnt ds 1 srchflg ds 1 vcnt ds 1 atimer dls 1 atimfig dls 1 rtclk ds 1 tripcnt dls 1 tdletlim ds 4 tdrop dls 2 tbuff ds 2 bniflg ds 1 SIU B S T; T S HIE ever even witn thiese Ni WO 90/07760 PCT/US89/05874 inhflg cis 1Iswptime ds 2 swpmin dis 2 swpmax ds 2 baslimit ds 4 Initialization Procedure reset ldaa #00000000b staa plddr ldaa #00000000t staa p1 data ldaa #00001000~b staa p2ddr ldaa #00001000~b staa p2data Idlaa #11000110b staa p4ddr ldaa #00000000 staa p4data Ids #stacktop ramchk Idx #ramstart Idaa #Oaah ramlpi staa 0,x cmpa 0,x bne ramerror inx cpx #ramstop+1 bne ramipi Idx #ramstart Idaa ramlp2 staa 0,x cmpa 0~x bne ramerror org romstart ;init i/o port 1 ;init i/o port 2 ;disable composite video ;init i/o port 4 b ;init top of stack ;write read ram SUBSTITUJTE

SHEET

WO 90/07760 WO 9007760PCJr/US89/05874 inx cpx bne bra ramerror Idlaa staa 1--ra ramok clr romchk Idx clra romip adda inx bne, tsta beq Idlaa oraa bra romok Idlaa anda romexit staa iochk Idlaa anda cmpa bne lcdaa anda cmpa bne, bra ioerror Idlaa oraa bra io-ok Idlaa anda #ramstop+ 1 ramlp2 ramok #01 h status romchk status #romstart ;set bit 0 of status ;reset bit 0 ;cornpare rorm chksum ;set bit 1 of status romip romok #02h status romexit #Ofdh status status p2data #00001111 b #00001111lb ioerroar p4data #11000110b #00000000b ioerror io-ok status #04h loexit status #Ofbh ;clear bit 1 ;get levels on port 2 ;normal reset'leveis ;get port4 levels ;update status byte ;set bit 2 of status ;clear bit 2

V

SUBSTITUTE SHEET f WO 90/07760 PCrIUS89/05874 r33 ioexit staa beepcode Idlaa anda beq bita bne bita bne bita bne notault Idab bra rambeep Idab bra rombeep Idab bra iobeep Idab bra beep Idaa oraa staa Idaa bsr Idaa anda staa Idaa bsr decb bne bra bdelay Idx bipl bne status status #07h not auft #01 h rambeep #02h rombeep #04h iobeep #1 beep #2 beep #3 beep #4 beep p4data #06h p4data #2 bdelay p4data #0f9h p4data #3 bdelay ;get status code ;test ram bit ;test rom bit ;test i/o bit ;alarms on ;alarm off beep rnext #OcOOOh dex bipi deca SUBSTITUTE

SHEET

-A

WO 90/07760 PCJr/US89/05874 bne bdelay rts rnext Idaa #2 ;init tdet counter staa pcnt cir pstimflg cir vcnt clr vflag cir almenfig cdr srchflg cir tagcnt clr aimfig cir pstimer clr almcntr clr rtclk clr atimfig clr atimer cir bniflg clr inhflg ldd timer ;init valid reply timers std tend std tmark Read target type selector switches option Idaa p1 data ;read option jumper anda #OcOh bne ji Idx #t1 limits ;get ti pulse limits Idd 0,x std baslimit Idd 2,x std baslimit+2 ldlaa staa tripcnt bra riast SUBSTITUTE SHEET

L

WO 90/07760 WO 9007760Pcr/US89/05874 ji cmpa bne ldx ldd stdl ldd stdl ldlaa staa bra j2 cmpa bne ldx ldd std ldd std ldlaa staa bra j3 ldx ldd stdl ldd stdl ldlaa staa bra riast ldd stdl ldd stdl ldx ldd stdl 12 #t3limits O,x baslimit 2,x baslimit+2 tripcnt riast #R-Oh j3 #t2limits O,x baslimit 2,x baslimit+2 ;get ti pulse limits ;get ti pulse limits tripcnt rlast #t4limits O,x baslimit 2,x baslimit+2 tripcnt rlast baslimit tdletlim baslimit +2 tdetlim+2 #swptbl O,x swptime ;get ti pulse limits ;initialize time windows ;init sweep rate windows k,~ SUBSTITUTE

SHEET

WO 90/07760 WO 9007760PCT7/US89/05874 Idab abx Idd std Idab abx Idd 0,x stdl Idaa anda oraa staa Idaa anda staa #8 O,x swpmin #8 swpmax tcsr #11111101 b #00011 000b tcsr p2data #Of7h p2data ;enable oci, iedg ;enable composite video cli imp main Main Routine main Idx #swptbl ;get J1 position and Idab p1 data ;convert to sweep rate data andb #03h asib abx Idd 0,x ;get sweep period std swptime Idab #8 ;get min. sweep time abx Idd 0,x std swpmin Idab #8 ;get max. sweep time abx Idd 0,x std swpmax SUBSTITUTE

SH-EET

WO 90/07760 WO 9007760PC/US89/05874 Adjust timing windows for selected sweep rate Idab abx #8 make sweep window adjustments Idd O,x addd baslimit std tI~mits Idd O~x addd baslimit+2 stdl tlimits+2 Check external flags and sensors ldaa bita beq ldaa staa ldaa oraa staa bra no inh dlr ldaa anda staa alarmen Idab stab Idaa bita bne clr bra ptimstat tst p4data #08h no inh #Offh inhflg p2data #08h p2data alarmen inhflg p2data ;check external inhibit ;set external inhibit flag ;disable video input ;clear external inhibit flag ;enable video input #f7h p2data #Offh almenflg p4data #00010000~b ptimstat pstimflg valchk pstimflg ;set alarm enable flag ;test people sensor enable sensor enabled ;people sensor timer running? -7 SUBSTITUTE SHEET fr WO 90/07760 PCI'/US89/05874 beq psense ldaa #pstmax ;check for people sensor timeout cmpa pstimer bhi valchk ptinh dr almenfig dr pstimflg bra valchk psense bita #00100000~b ;sensor active? bne ptInh dr pstimer ;start people sensor timer ldaa #Offh staa pstimflg Check and time sort valid target responses valch< tst beq cir ldd std ldd std tst beq ldd subd bmi vnexti subd addd bpl ldd addd std vflag timechk vflag tmark tbuff tend tmark srchflg pulsel tmark early swprnin swpmax failsrch tmark swpmax ;valid reply? ;save last valid time ;get new valid time ;aquire mode (clear) ;reply in window? ;reply too early ;reply too late ;update next windc~w Adjust up down alarm threshold counter SUBSTITUTE

SHEET

p~r/US89/05874 WO 90/07760 inc Idaa tsta bpi clr imp thresh cmpa bit ldaa staa cntest Idaa cmpa blo idaa staa clr bra timechk Idd addd subd bmi bra failsrch cira staa staa dec bgt staa staa fnext Idd addd std addd std tagcnt tagcnt thresh tagcnt noalarm #10 cntest tagcnt tagcnt tripcnt noalarm #Off h aimfig vcnt vexit tmark swpmin timer failI.rch vexit aimflg vcnt tagcnt fnext srchflg tagcnt trnark swptime tmark swpmax ;alarm condition? ;valid tag threshold det.

;zero negative count ;limit counter ;test for thresh. count ;set alarm flag ;check for timeout ,reset flags :Ic~ie aquisition ;update time slots

A

SUBSTITUTE

SHEET

WO 90/07760 P~U8/57 PCr/US89/05874 bra pulsel ldd addd std cira staa staa coma staa inc bra early Idd std inc ldaa cmpa bgt cira staa staa staa staa bra noalarm dlr clr vexit ldaa anda staa alarm tst bne tst beq tst bgt dlr vexit tmark swpmax :init. search effort ;adjust counters timers vcnt almf 19 srchflg tagcnt: vexit tbuff tmark vcnt vcnt vexit ;restore original valid time inhibit function ;too many replies almflg srchflg tagcnt vcnt vexit vcnt almflg p4data #01111111b p4data almflg setline atimfig alarmoff atimer a enbl atimfig ;tp4 low ;check alarm status ;timer running? ;tiineout? SUBSTITUTE

SHEET

WO 90/07760 bra alarmoff setime ldaa p1 data bita #00100000b PCT/US89/05874 beq ldaa staa bra five ldaa staa aflag ldaa staa a-enbi tst beq Idaa oraa staa ldaa bita bne ldaa oraa staa bra alarmoff Idaa anda 3 ataa bra beeper Idab andb bne ldaa anda staa bra hipulse laa five #onesec atimer aflag #fivsec atimer #Offh atimflg almenfig alarmoff p4data #02h p4data pidata beeper p4d,' a #04h p4data next p4data #Of9h p4data next #maskon rtclk hipulse p4data #Ofbh p4data next p4data ;read alarm time select ;set alarm timer flag ;alarm enabled? ;turn alarms on ;read alarm select ;steady alarm ;turn off alarms ;pulsed alarm ;reset pulse output ;set pulse output SUBSIrNTUT

SHEET

SUBSTITUTE SHEET WO 90/07760 PCTIUS89/05874 oraa #04h staa p4data next imp main Internal time clock routine (interrupt) timeclk Idlaa tcsr ;clear ocr flag Idd stdl ;reset interrupt flag rtclk pstimer atimer Composite video processing routine tdlet Idaa anda cmpa beq bita bne dr bra tminusl ldaa staa window Idd std addd std idx nslope Idaa oraa staa pi data #00001100~b #Och tfaultl #00000100~b tminusl signflg window #Offh signflg icr tlead #twoff set tdrop #tdetlim tcsr #02h tcsr ;determine threshold ;false level detect threshold? ;get t~l ,twi ;compute end time window ;delta time table ;arm falling edge(+ SUBSTITUTE

SHEET

WO 90/07760 WO 9007760PCr/US89/05874 ldaa icflpl ldaa bita bne ldd subd bmi bra tfaultl imp ftimesav ldaa anda staa ldd std subd std subd bmi Idab abx ldd subd bpl icr tcsr ftimesav tdrop timer tfaultl icflpl texit tcsr #Ofdh tcsr icr tfall dlead temp 0,x texit #2 temp 0,x texit ,clear icf flag ;wait for icf lag ;arm leading edge(- ;get tf(n) ;delt(n) tf(n) tl(n) ;delt delt(min) ;update limit addr. pointer ;delt delt(max) Next pulse adaptive computation ldd temp ;update plse limits addd std ldx Idd addd std dec beq #180 0,x #tdetlim temp #2 0,x pcnt valid

V

4t.~ ~JJA~41A~ SUBSTITUTE SHEET WO 90/07760 PCTr/US89/05874 icf'p2 ldaa tcsr ;wait for ictlag(-) bita bne signchk ldd tdrop ;check for window overflow subd timer bmi texit bra icflp2 Video sign alternation check signchk Idaa anda cmpa -)eq bita bne tst beq clr bra tminus2 tst bne corn tnext Idd std bra valid ldaa staa ldd std Idaa anda oraa staa S Idab p1 data #00001100b #Och texft #00000100~b tminus2 signflg texit signfig tnext signflg texit signflg icr tlead nslope #Off h vf lag tdrop tend p4data *l0llllllb #01000000~b p4data #25 ;get threshold sign ;check for false levels threshold? ;check for sign change threshold ;get t(n) ;set valid reply flag ;update valid time ;valid reply ind. on ;set valid pulse width SUBSTITUXTE SHEE-e SUBSTITUJTE SHEET WO 90/07760 LFS PCJ/US89/05874 tpdly decb bne anda staa Idaa ldaa texit ldaa anda staa ldaa ldaa staa ldd std ldd std tpdly #10111111b p4data tcsr icr tcsr #Ofdh tcsr icr #2 pcnt tlimits tdetlim tlimts+2 tdetlim+2 ;clear tag ringing edge ;rearm negative slope ;clear icf flag ;restore counter pointer ;restore ti pulse limits External signal adaptive inhibit function bni tst bne ldaa staa ldaa oraa staa ldx bnidly cli dex bne sei tst bne anda bniflg xrestore #Offh bniflg p2data #08h p2data #320 ;already in this routine? ;restore index register on stack ;set bni active flag ;inhibit video for a time ;delay time (20 2.5 N) us.

bnidly inhflg bnext #Of7h ;check external inhibit flag ;enable video line

V

SUBSTITUTE SHEET SUBSTITUTE SHEET WO 90/07760 PCr/US89/05874 staa p2data bnext ldaa tcsr ;clear possible icr flag Idlaa icr ;when video is enabled clr bnfflg rti xrestore tsx ;form pointer to stacked xreg ldd #500 ;restore original delay value std 3,x nti i 0 Initial pulse window table ti limits dw 320,500 ;window times t2limits dxv 360,500 t3limits dw 400,500 t4limits dw 420,500 Sweep rate select parameter table swptbl dw swp78 dw dw swp86 dw swp82 dw swpmin78 dw dw swpmin86 dw swpmin82 dw swpmax78 dw swpmax9o dw swpmax86 dw swpmax82 dw swpadj78 dw swpadj9o dw swpadj86 dw swpadj82

A%

SUBSTITUTE SHEET deca SUBSTITUTE

SHEET

WO 90/07760 PCTP/US89/05874 x OM ;version iW. string 'ALPHA RECEIVER VER. I.2A 10/10/88' Offeeh reset ;lost processor recovery ti Offf4h timecik ;coarse real time cik usinc rap ;ocr overflow Offf6h tdet Offf8h bON Offfeh reset reset ;threshhold detector (timer) interrupt ;beat note detection interrupt ;start of reset section

C

SUBSTITUTE sHEeT Oh.-

Claims (9)

1. An electronic article surveillance system sai comprising: a transmitter providing a signal to a transmitting antenna to develop an electromagnetic field; are and rec a receiver having a receiving antenna for sig receiving signals including signals produced by a first for resonant circuit forming part of a first tag means has associated with an article to be protected in response to me- the electromagnetic field and a second resonant circuit pu] different from said first resonant circuit and forming va part of a second tag means ssociated with a different article to be protected also response to the 6. X electromagnetic field, and for providing said received wi signals to the receiver, the receiver further having means to Ifor identifying said tag signals, and means for discriminating between first tag signals produced by the 7 first resonant circuit of said first tag means and second in tag signals produced by the second resonant circuit of sa said second tag means. 'in pr

2. The system of claim 1 wherein said receiver p r includes a filter for separating said tag signals from other signals received by said receiver, and wherein said filter is a linear phase filter. SI.

3. The system of claim 1 wherein said tag signals a are analog signals, wherein said receiver includes means for converting said analog signals to digital signals, and wherein said converting means operates responsive to two B different threshold levels.

4. The system of claim 3 wherein one of said two different threshold levels operates to define a leading b> i I 49 edge of a digital pulse, and another of said two different threshold levels operates to define a trailing edge of said digital pulse.

The system of claim 1 wherein said tag signals are in the form of a series of pulses, wherein said receiver includes processor means for identifying said tag signals, and wherein said identifying means includes means for determining if a first pulse in said series of pulses has a durauion which falls within a selected window, and means for determining if a second pulse in said series of pulses has a duration which falls within a window which varies responsive to the duration of said first pulse.

6. The system of claim 5 wherein said selected window is adjustable according to the tag means which is to be detected.

7. The system of claim 5 wherein said receiver includes a counter for counting tag signals identified by said processor means, and wherein said counter is incremented when said tag signals are identified within a o prescribed time period, and decremented when said tag signals are not identified within said prescribed time o period.

8. The system of claim 1 wherein said transmitter produces a primary signal which is periodically swept about a centre frequency at a defined rate, and wherein said rate is adjustable. said rate is adjustable. go o e A JU f

9. The system of claim 1 wherein said system has an operating frequency range, and wherein said first resonant circuit and said second resonant circuit are both operative within said operating frequency range. A system as claimed in any one of claims 1 to 9 and substantially as herein described with reference to figures 2 to 9 of the accompanying drawings. DATED THIS 16th DAY OF SEPTEMBER 1992 CHECKPOINT SYSTEMS, INC By Its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia *o 1 ft i LC