CA1272787A

CA1272787A - Transponder useful in a system for identifying objects

Info

Publication number: CA1272787A
Application number: CA000538986A
Authority: CA
Inventors: Alfred R. Koelle
Original assignee: Amtech Corp
Current assignee: Amtech Systems Inc
Priority date: 1986-07-14
Filing date: 1987-06-05
Publication date: 1990-08-14
Anticipated expiration: 2007-08-14
Also published as: KR880002093A; JPS6329282A; JP2644496B2; EP0254954B1; DE3773571D1; KR970000545B1; AU585825B2; ES2025599T3; HK143596A; IL82578A0; AU7533987A; US4786907A; EP0254954A1; IL82578A

Abstract

TRANSPONDER USEFUL IN A SYSTEM
FOR INDENTIFYING OBJECTS

Abstract of the Disclosure A reader transmits interrogating rf signals to a transponder including an antenna having a particular impedance.
The signals received by the antenna are converted to a direct voltage which is introduced to a first terminal of a switch such as an emitter of a semi-conductor device having conductive and non-conductive states of operation. A second terminal of the switch, such as the base of the semi-conductor device, receives a voltage variable between first and second magnitudes in accordance with a pattern of binary 1's and 0's in a data source such as a read-only memory (ROM). This pattern of binary 1's and 0's is individual to an object identified by the transponder. The variable voltage on the base of the semi-conductor device causes the emitter-collector current of the semi-conductor device to vary between first and second amplitudes. When this current has the first amplitude, the impedance of the semi-conductor device and the ROM substantially matches the antenna impedance. When this current has the second amplitude, the impedance of the semi-conductor device and the ROM is substantially greater than the antenna impedance.
Capacitance may be connected to the collector of the semi-conductor device and the ROM to store energy in accordance with the current flow through the semi-conductor device. This stored energy provides for an energizing of the semi-conductor device and the ROM. A diode may be connected between the emitter and collector of the semi-conductor device to increase the second amplitude of the current through the semi-conductor device.
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Description

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1 This invention relates to systems for identifying

2 objects on a remote basis. More particularly, this invention

3 relates to transponders in such systems for providing for an

4 identification of goods through a greater distance and with more accuracy and reliability than in the prior art.

7 As commerce becomes increasingly complex, increased 8 amounts of goods have had to be handled. The difficulties of 9 identifying individual items of goods have accordingly become aggravated. For example, merchant ships now carry large numbers 11 of containers holding different types of products. When the 12 merchant ship reaches a particular destination, individual ones 13 of such containers have to be unloaded at such destination port.
14 Systems are now in use for identifying and segregating such individual containers without requiring a personal inspection of ~6 the containers. Such id~ntification has been made by systems 17 which provide such ident~fications at positions displaced from 18 the containers.

The systems now in use employ a reader which transmits 21 interrogating signals to a transponder associated with an 22 individual one of the objects such as an individual one of the 23 containers on the merchant ship. The transponder then transmits 24 pluralities of signals to the displaced reader. The pluralities of signals are in a a sequence of binary l's and binary signals 26 in a code individual to the object. The reader decodes the 27 successive pluralities of signals in the seguence to identify 28 the object.

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1 The systerns now in use haYe had certain difficulties.2 One difficulty has resulted from the limited range o~
3 transmission of the identifying signals ~rom the transponder to 4 the reader. Another related difficulty has resulted from the inter~erence produced by noise signals. These noise signals have often prevented the reader from properly detecting the 7 pattern of binary l's and binary O's in the sequence 8 individually identi~ying the ohject.
9 ..
A considerable effort has been devoted over a 11 significant number of years to eliminate or at least minimize 12 the problems discussed in the previous paragraphs. In spite of 13 such efforts, such problems have persisted. The range of 14 communications between the reader and the transponder ~ontinues to be limited by the effects of noise. This has tended to limit 16 the ranges of uses to wh~h systems for identifying objects can 17 be applied.
1~ .
19 This invention provides a transponder which elimina~es or at least minimizes the difficulties discussed above. The 21 transponder of this inven$ion prov;des an enhanced signal-22 to-noise ratio in comparison to the transponders of the prior 23 art. As a result, the range o~ the effective distance o~ the Z4 transponder constituting this invention is considerably expanded relative to the transponders of the prior art.

27 In one embodiment of the invention, a reader transmits 28 interrogating rf signals to a transponder including an antenna 29 having a particular impedance~ The signals received by the ~1 ., . . .. , . ~ .. . .

1 antenna are converted to a direct voItage which is introduced to 2 a first terminal of a switch such as an emitter of a semi-3 conductor device having conductive and non-conductive states of 4 operation.

6 A second terminal of the switch, such as the base of 7 the semi-conductor device, receives a voltage variable between 8 first and second magnitudes in accordance with a pattern of g binary l's and O's in a data source such as a read-only memory (ROM). This pattern of binary l's and O's is individual to an 11 object identified by the transponder. The variable voltage on 12 the base of the semi-conductor device causes the emitter-13 collector current of the semi-conductor device to vary between 14 first and second amplitudes. When this current has the first amplitude, the impedance sf the semi-conductor device and the 16 ROM substantially matche~ the antenna impedance. When this 17 current has the second amplitude, the impedance of the 18 semi-conductor device and the ROM is substantially greater than 1~ the antenna impedance.

21 A capacitance may be connected to the collector of the 22 semi-conductor device and the ROM to store energy i~ accordance 23 with the current flow through the semi-conductor device. This 24 stored energy provides for an energizing of the semi-conductor device and the ROM. A diode may be connected between the 26 emitter and the collector of the semi-conductor device to pass a 27 limited amplitude of current around the semi-conductor device.

29 In the drawings:

2~

1. Figure 1 is a some~hat schemat.ic diayram iliustratiny 2 a system incl.uding a reader and a transponder Eor identifying at 3 the reader an individual pattern of binary ].'s and binary O's 4 identifying a displaced transponder;

6 Figure 2 is a somewhat schematic block diagram of an 7 improved transponder constituting one embodiment of this 8 invention; and .
Figure 3 is a curve somewhat schematically 11 illustrating certain of the advantages of the transponder of 12 this invention relative to the prior art in providing enhanced 1~ signal-to-noise ratios in the signals produced in the 14 transponder and transmitted to the reader to identify the transponder.

17 In embodiment ~f the invention, a reader generally 18 indicated at 10 generates interrogating rf signals in a 19 generator 12. These signals may have a suitable frequency such as approximately nine hundred and fiteen megahertz (915 MHz).
21 These signals are introduced to an antenna 14 for transmission 22 to an antenna 15 in a transponder ~enerally indicated ~t 16.
23 The antenna 15 may be a dipole antenna. The transponder 16 thPn 24 produces pluralities of signal cycles in an individual pattern of binary l's and binary O's identifying an object with which 26 the transponder i5 associated. The individual pattern of binary 27 l's and binary O's may be gene rated in a suitable data source 28 such as a read-only memory 18. This individual pattern of 29 binary l's and binary ~'s ~enerated in the read-only memory 18 causes pluralities of sign~l cycles to be produced in a 31 modulator 22, ... . . .. . ~ .. .. . . .

1 Th~ modulator ~2 produces a ~irst plurality of signal cycles for a b~nary ~1" and a second plurality o~ signal cycle~
3 for a blnary "0". For example, ln the system disclosed and 4 claimed in u.s. patent no. 4,739,32R, issued April 197 19~ in the names of Jeremy ~andt and Alfred R. Koelle and assigned 6 of record to the assignee of record of this application, a 7 binary llO" is produced in the modulator 20 by providing a ~irst 8 slgnal cycle at a relatively low frequency such as twenty 0 kilohertz ~20 ~Hz) and then providing two additional signal cycle at a relatively high frequency, pre~erably a harmo~ic o~
11 the ~irst ~requency. Thi~ ~econd frequency may be forty 12 kilohertz (40 X~z) when the first frequency is twenty kilohertz 13 (20 kHz). In l~ke manner, a binary ~1N may be produced in the 14 modulator b~ signal cycle~ at the relativel~ high ~re~uency such a~ forty kilohertz (40 ~) and then a single signal cycle at 16 the relatively low frequ~ncy o~ ~wenty kilohertz ~ 20 kHz~.

18 Th~ ~gnal cycles produced in the modulator 22 are 19 introduced to the antenna 15 for transmis~ion to the reader 10.
Th~ reader 10 receive~ these signal cycle~ and mixes these 21 signal~ in a mixer 24 with the signals from the source 12 oE
22 slgnals at ths interrogating r~ frequency. The mixed signals 23 are ampli~ed as at 26 and are demodulated as at 28 in 24 accordance with the pattern~ o~ frequencies in ea~h o the plurallties of s~gnal cycle~ to obtain a recovery o~ the 26 individual pattern o~ binary l's and binary 0'~ generated at the 27 transpond~r 16.

2~ A simplified embodiment of a transponder con~tituting th~ inventio~ is shown in Figure 2. The transponder, generally 31 indicated at 29, ~ncludes a d~pole antenna 30 constructed to

- 5 l receive signals from the reader at a suitable ~requency such as 2 nine hundred and Eifteen megahertz (915 MHz). An impedance 3 matching section 31 i.5 connected to the dipole 30 to match the 4 impedance oE the dipole to the impedance of the remaining circuitry shown in Figure 2. The construction of the impedance

6 matching section 31 is well known in the art.

q 8 The siynals from the dipole 30 are introduced to a g voltage-doubling rectifier generally indicated at 32. The voltage-doubling rectifier includes a pair of diodes 34 and 36 ll and a pair of capacitances 38 and 40 each having a suitable 12 value such as 100 picofarads. The cathode of the diode 34 is 13 connected to one leg of the dipole 30. The anode of the diode 14 34 is connected to one terminal of the capacitance 38, the other terminal of which has a common connection with the other leg of ~6 the dipole 30.. The anodeiof the diode 36 is common wi~h the 17 cathode of the diode 34 and the cathode of the diode 3b has a l8 common connection with one terminal of the capacitance 40. The l9 other terminal of the capacitance 40 i~ connected to the other terminal of the dipole 30.

Z2 The anode of the diode 36 is connected to one terminal 23 of a suitable switch. This terminal may constitute the emitter 24 of a pnp-type of semi-conductor device ~uch as a transistor 42.
The semi-conductor device 42 may constitute a 2~3906. A pair of 26 resistors 44 and 46 are in series between the base of the 27 transistor 4~ and the anode of the diode 34. The resistors 44 28 and 46 may respectively have values of 47 kilo-ohms and lO0 29 kilo-ohms.

- ~ ... . .

~L~2~2~87 1 A capacitance 50 having ~ suitable value such as 0.01 2 microfarads is connected between a data sources such as a r~ad-3 only memory 52 and the terminal common to the resistance~ 44 and 4 46. The read-only memory 52 may be constructed in a rnanner conventional in the prior art. Another terminal of the 6 read-only memory has a co~non connection with the collector of

7 the transistor 42. A capacitance 54 having a suitable value

8 such as 0.2 microfarads is in parallel with the read-only memory

9 52. An anode of a diode 56 may be common at one end with the collector of the semi-conductor device 42 and at the opposite 11 end with the emitter of the semi-conductor device. The diode lZ may be a type lN914.

14 When signals a~e received by the dipole 30 from the reader 10, the signals are introduced to the rectifier 32. The 16 positive portions of the~received signals cause current to flow .
17 through a circuit incluc~1ng the diode 36 and the capacitance 40.

18 The negative portions of the signals cause current to flow 19 through a circuit including the capacitance 38 and the diode 34.

As a result t rectified voltage~ are produced in the capacitances 21 40 and 38. These rectified voltages are in an additive series 22 relationship so tha~ the rectifier 32 acts to produce a voltage 23 which is approximately double t~e amplitude of the signal 24 received by the dipole antenna 30.

26 The positive voltage on the cathode of the diode 36 is 27 introduced to the emitter of the semi-conductor device 42 to 28 bias the semi-conductor device to a state of conductivity. The 29 semi-conductor device 42 accordingly becomes conductive when the voltage on the base of the semi-conductor device becomes 31 negative relative to the voltage on the emi~ter of the ~2~ 7 1 semi-conductor device. The voltage on the base of the 2 semi-conductor device 42 is controlled by ~he operation of the 3 data source such as the read only memory 52.

The read-only memory 52 produces pluralities of 6 signal cyclP 9 each plurality indicating in coded form the value 7 of a di~ferent binary bit. For example, a binary "0" may be 8 represented by a single signal cyclè at a first frequency such 9 as twenty kilohertz (20 kHz) and two subsequent signal cycles at a second freque~cy constituting a harmonic of the first 11 frequency. Preferably~ the second fre~uency is forty kilohertz 12 (40 k~z) when the first frequency is twenty kilohertz (20 kH7.).
13 Similarly, a binary n 1 n may be represented by two signal cycles 14 at the second frequency (e.g. 40 k~z) and then a single signal cycle at the first frequency (e.g. 20 K~z). The read-only 16 memory 52 is programmed ~ provide a sequence of binary l's and 17 binary O's in a code ind~vidual to an object with which the 18 transponder 16 is associated.

The read-only memory 52 produces signals at first and 21 second amplitudes in accordance with the frequencies of the 22 pluralities of signal cycles coding for the successive binary 23 bits in the code generaked by the read-only memory. When the 24 signals from the read only memory 52 have a low amplitude, the semi-conductor device 4~ becomes fully conductive so that a 26 relatively large current flows through a circuit including the 27 dipole 30, the impedance matching section 31, the diode 36, the 28 emitter and collecto~ o~ the semiconductor device 42, the 29 capacitance 54 and the capacitance 38. This current is 1 sufficiently large to procluce a relatively low volkage ~lrop 2 across the semi-conductor 42. For example, this voltage drop 3 may be in the order of 0.1 volts~

When the voltage introduced to the base of the 6 -semi-conductor device 42 from the read-only memory 52 is 7 relatively high, the semi-conductor device 42 is driven toward a 8 state of non-conductivity. However~ the semi-conductor 42 9 de~ice remains slightly conductive to provide a "leak-through"
current through the semi-conductor device. This causes a 11 relatively high impedance to be produced across ~he 12 semi-conductor device 42. The "leak-through" current through 13 the semi-conductor device 42 contributes to the production of a 14 supply voltage across the capacitance 54.

16 When the semi-~pnductor device 42 is in the fully 17 conductive state, its imp~dance is relatively low. This causes 18 the circuit including the semi-conductor device 42 and the 19 read-only memory 52 to provide an impedance approaching that provided by the dipole antenna 30 and the impedance matching 21 section 31. This facilitates the production of currents of 22 relatively high amplitude through this circuit~ ~owever, when 23 the semi-conductor device 42 is only slightly conductive, its 24 impedance is large. As will be appreciated, the resultant impedance of the semi-conductor device 42 and he read-only 26 memory 52 is considerably greater than that provided by the 27 dipole antenna 30 and the impedance matching section 31.
28 Figure 3 illustrates the relationship between the 29 nback scatter" signal and the requency of the signals being ~0 generated by the system shown in Figure 2. The ~back scatter~

_ g _ 1 signals are equivalerlt to the ~mplitudes of the signals 2 introduced to the dipole antenna 30. In Figure 3, a point 60 ~ illustrates the amplitude of the signals introducecl to the 4 antenna when the semiconductor 42 is highly conductive. The amplitude of the signals introduced to the dipole 62 is 6 illustrated in Figure 3 at 6~ when the semi-conductor 42 is only 7 slightly conductive. As will be seen, there is a considerable 8 difference between the amplitudes 60 and 62. This is in 9 contrast to the operation of the circuitry of the prior art since the circuitry of the prior art provides a short circuit in 11 a first state of operation and provides the amplitude 60 in a 12 second state of operation. The amplitude of the signal with the 13 circuitry of the prior art in a short circuit condition is 14 illustrated at 64. As will be seen, there is a relatively small difference between the a~plitudes 60 and 64, particularly in 16 comparison to the differ~nce in the amplitudes 60 and 62.
17 ;
18 Because of the considerable difference between the 19 ampli~udes 60 and 62, the strength of ~he signals transmitted by the dipole 30 to the reader 10 is considerably enhanced in 21 relation to any noise received by the reader. As a result, the 22 reader 10 is able to detect the signals from the transponder 29 23 through a greater distance than in the prior art. The reader 10 24 is also able to detect the signals from the ~ransponder 29 with a greater reliability than in the prior art. This causes the 26 reader 10 to identify the transponder 29 and its associated 27 object through an increased distance and an enhanced reliability 28 relative to the capabilities of the transponders of the prior 29 art.

., . .. , j . . ~ . . . -.: , , .

72~7~3''7 l The ability o the reader 10 to detect the object is 2 also enhanced because of other advantages provided by the 3 transponder shown in Figure 2. For example, approximately one 4 tenth volt ~0.1V) is produced across the semi-conductive device 42 when the semi-conductive device is highly conductive. This 6 is in contrast to the prior art which produces voltage drops as 7 high as three tenths of a volt (0.3V). This difEerence is quite 8 considerable in comparison to the voltage produced across the 9 capacitance 54. Thîs voltage may be in the order of one and eight tenths volts (1.~V). As a result, the voltage used to ll generate the transponder signals in the transponder shown in 12 Figure 2 and described above is significantly greater than the 13 voltage used to generate such signal in the prior art.

l~ The capacitance 54 has considerably higher values than 16 the capacitances 38 and ~0. The capacitance 54 accordingly 17 serves as the primary so~rce of energy for the read only memory 18 52 and the semi-conductor device 42. The capacitances 38 and 40 19 provide energy for the emitter-base current in the semi-conductor device 42. The capacitance 50 serves as a coupling 21 capacitance ~etween the read only memory 52 and the base of the 22 semi-conductor device 42. The resistance 44 limits the current 23 between the emitter and the base of the semi-conductor device 24 42. The resistan~e 46 provides an impedance between the coupling capacitance 50 and a reference potential such as 26 ground.

28 Although this invention has been disclosed and 29 illustrated with reference to particular embodiments, the principles lnvo:Lved are susceptible for use in numerous other ' ~ , " , ' : ' ' ' ~ ' ~27~7 1 embodiments which will be apparent to person~ skilled in the 2 art. The invention i9~ thereEore, to be limited only as ~ indicated by the scope of the appended claims.

~6 ~6 2g ~2

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGEIS CLAIMED ARE DEFINED AS FOLLOWS:

1. In combination for use in a transponder for sending signals to a reader to identify an object associated with the transponder, antenna means for receiving interrogating signals from the reader, the antenna having a particular impedance, means responsive to such received signals for storing energy, switching means having first and second states of operation and having a low impedance in the first state of operation and a high impedance in the second state of operation, the switching means including a semi-conductor having first, second and third electrodes, a data source for providing a sequence of binary indications individually identifying the object, the first and third electrodes of the semi-conductor being connected between the energy storing means and the data source, means including the data source and the switching means for defining a load, with the switching means having an impedance in the first state of operation corresponding to the impedance of the antenna means and having an impedance in the second state of operation considerably higher than the impedance of the antenna means, and means responsive to the sequence of binary indications in the data source for introducing the sequence of binary indications to the second electrode of the semi-conductor to obtain the operation of the switching means in the first and second states of operation in accordance with the sequence of binary indications individually identifying the object.

2. In a combination as set forth in claim 1, the switching means being connected in series with the data source and the antenna means.

3. In a combination as set forth in claim 1, means connected across the switching means to pass a limited flow of current around the switching means in the second state of operation of the switching means.

4. In a combination as set forth in claim 3, the storage means being connected to the switching means to receive energy in the first and second state of operation of the switching means for operating the data source to provide the sequence of binary indications individually identifying the object.

5. In combination for use in a transponder for sending signals to a reader to identify an object associated with the transponder, antenna means for receiving interrogating signals from the reader and for transmitting to the reader signals in a pattern to identify the object, rectifier means connected to the antenna means for storing energy received by the antenna means, a semi-conductor having a base, an emitter and a collector and having first and second states of operation and operative in the first state to provide a low impedance and operative in the second state to provide a high impedance, means for introducing the voltage from the rectifier means to the emitter of the semi-conductor, a data source constructed to provide a sequence of signal cycles coding for binary 1's and binary 0's in an individual pattern identifying the object, means for introducing the signal cycles in the sequence from the data source to the base of the semi-conductor to obtain an operation of the semi-conductor in the first and second states in accordance with the sequence of signal cycles coding for the binary 1's and binary 0's in the individual pattern identifying the object, and means connected to the collector of the semi-conductor for providing for a flow of current through the semi-conductor between the emitter and the collector of the semi-conductor in accordance with the sequence of the signal cycle introduced to the base of the semi-conductor.

6. In a combination as set forth in claim 5, the antenna means having particular impedance and the semi-conductor and the means, including the data source, connected to the semi-conductor providing an impedance substantially corresponding to the particular impedance in the first state of operation of the semi-conductor and providing an impedance considerably higher than the particular impedance in the second state of operation of the semi-conductor.

7. In a combination as set forth in claim 6, means connected between the collector and the base of the semi-conductor for receiving energy from the current flowing through the semi-conductor in the first and second states of operation of the semi-conductor to facilitate the flow of current through the semi-conductor.

8. In a combination as set forth in claim 6, means connected to the collector of the semi-conductor for receiving energy from the flow of current through the semi-conductor to energize the data source.

9. In combination for use in a transponder for sending signals to a reader to identify an object associated with the transponder, means for receiving interrogating rf signals from the reader and for sending to the reader the signals identifying the object, means responsive to the received signals for producing a voltage, semi-conductor switching means having first, second and third electrodes, the semi-conductor switching means having conductive and non-conductive states and having an impedance decreasing with increases in the amplitude of the current through the semi-conductor switching means, means responsive to the voltage produced by the receiving means for biasing the first electrode of the semi-conductor switching means to a state of conductivity, data source means for providing a code of binary 1's and binary 0's individual to the object and for introducing, to the second electrode of the semi-conductor switching means, signals having first and second amplitudes in a pattern dependent upon the binary 1's and binary 0's provided in the data source means to obtain in the semi-conductor switching means the flow of currents at first and second amplitudes between the first and third electrodes of the semi-conductor switching means, and means operatively coupled to the data source means and the third electrode of the semi-conductor switching means for applying a voltage to the data source means to obtain the generation of the signals by the data source means and for applying a voltage to the third electrode of the semi-conductor switching means to obtain a flow of current between the first and third electrodes of the semi-conductors switching means in accordance with the generation of signals by the data source means.

10. In a combination as set forth in claim 9, the receiving means providing a particular impedance and the semi-conductor switching means and the read-only memory means providing the particular impedance with the first amplitude of the current through the semi-conductor switching means and the first amplitude of the current through the semi-conductor switching means being greater than the second amplitude of the current through the semi-conductor switching means.

11. In a combination as set forth in claim 9, a diode connected between the first and third electrodes of the semi-conductor switching means to limit the first amplitude of the current through the semi-conductor switching means.

12. In a combination as set forth in claim 10, means responsive to the flow of current through the semi-conductor switching means for storing energy to bias the third electrode of the semi-conductor switching means in a direction for producing a flow of current between the first and third electrodes of the semi-conductor switching means.

13. In a combination as set forth in claim 10, a diode connected between the first and third electrodes of the semi-conductor switching means to limit the first amplitude of the current through the semi-conductor switching means, and means responsive to the flow of current through the semi-conductor switching means for storing energy to bias the third electrode of the semi-conductor switching means in a direction for producing a flow of current between the first and third electrodes of the semi-conductor switching means.