Identification system - Patent Review 4818855

What is claimed is:

1. In a remotely powered portable member having circuitry for storing and transmitting coded information, the improvement comprising:

first coupling means for receiving a signal of a predetermined frequency transmitted via one of a magnetic field and an electric field;

power means connected to said first coupling means for deriving operating power from the received signal for use by said circuitry;

circuit means connecting said circuitry to said first coupling means, for utilizing said predetermined frequency as a clock signal for timing of said circuitry; and

second coupling means connected to said circuitry for transmitting coded information stored by said circuitry via the other one of the magnetic field and the electric field.

2. A portable member as defined in claim 1, wherein said first coupling means is a magnetic field coupling means for receiving a signal via a magnetic field and said second coupling means is an electrostatic coupling means for transmitting coded information via an electric field.

3. A portable member as defined in claim 1, wherein said circuitry includes a programmable read only memory for storing coded information.

4. A portable member as defined in claim 3, wherein: said programmable read only memory is an electrically alterable read only memory; said signal of a predetermined frequency is a modulated carrier signal; and said circuitry further includes programming means, connected to said first coupling means, for detecting a modulated carrier signal which contains programming information, said programming means being connected to said electrically alterable read only memory for programming said electrically alterable read only memory in accordance with said programming information.

5. A portable member as defined in claim 4, wherein said first coupling means is a magnetic field coupling means for receiving a signal via a magnetic field and said second coupling means is an electrostatic coupling means for transmitting coded information via an electric field.

6. A portable member as defined in claim 1, wherein said circuitry includes frequency dividing means connected to said first coupling means for deriving a carrier signal having a frequency which is sub-multiple of the predetermined frequency and modulating means having an output connected to said second coupling means, one input coupled to the carrier signal and another input coupled for receiving the coded information for modulating the carrier signal with the coded information.

7. A portable member as defined in claim 1, wherein said circuitry includes a local oscillator for producing a carrier signal which has a frequency generated independently of the predetermined frequency, and modulating means having an output connected to said second coupling means, one input coupled to the carrier signal and another input coupled for receiving the coded information for modulating the carrier signal with the coded information.

8. A portable member as defined in claim 7, wherein said local oscillator produces a carrier signal having a frequency substantially higher than the predetermined frequency.

9. A portable member as defined in claim 1, wherein said circuitry includes: carrier signal means for producing a carrier signal; modulating means having an input connected to said carrier signal means, another input coupled for receiving the coded information and an output, said modulating means modulating the carrier signal with the coded information to produce a modulated carrier signal at said output; and voltage multiplier means connected between said modulating means and said second coupling means for increasing the voltage magnitude of the modulated carrier signal.

10. A portable member as defined in claim 9, wherein said voltage multiplier means is passive.

11. A portable member as defined in claim 10, wherein said voltage multiplier means includes a series connected inductor and capacitor having a common connection point which is connected to said second coupling means

12. A portable member as defined in claim 10, wherein said voltage multiplier means includes an autotransformer.

13. A portable member as defined in claim 1, wherein said circuitry includes carrier signal means for producing a carrier signal; modulating means having an input connected to said carrier signal means, another input coupled for receiving the coded information, and an output connected to said second coupling means, said modulating means modulating the carrier signal to produce a modulated carrier signal at said output.

14. A portable member as defined in claim 13, wherein said modulating means comprises an amplitiude modulator.

15. A portable member as defined in claim 13, wherein said modulating means comprises a phase modulator.

16. A portable member as defined in claim 13, wherein said modulating means comprises a frequency modulator.

17. A portable member as defined in claim 2, wherein said first coupling means comprises a coil and said second coupling means comprises an electrostatic antenna and said coil and said antenna are mounted to be substantially coplanar with one another.

18. A portable member as defined in claim 17, wherein said coil and said antenna are coaxially positioned relative to one another.

19. A portable member as defined in claim 1, wherein said member is in the form of a tag, card, badge, ring, watch, or other similar type of portable article.

20. A remotely powered portable member having circuitry for storing and transmitting coded information comprising:

a read-only memory for storing coded information

first coupling means for receiving a signal of a predetermined frequency transmitted via a magnetic field;

power means connected to said first coupling means for deriving power from the received signal for use by the circuitry in said portable member;

circuit means, connected to said first coupling means and responsive to said predetermined frequency of a received signal, for reading said coded information from said read only memory;

means for generating a carrier signal;

modulating means for modulating said carrier signal with the read coded information from said memory;

and second coupling means connected to the output of said modulating means for transmitting the modulated carrier signal via an electric field.

21. A portable member as defined in claim 20, wherein said means for generating a carrier signal generates a carrier signal whose frequency is a sub-multiple of said predetermined frequency.

22. A portable member as defined in claim 21, wherein said means for reading said memory and said means for generating a carrier signal are both realized by a frequency divider having a plurality of outputs connected to address lines of said memory and a further output connected to said means for modulating.

23. A portable device as defined in claim 22, wherein said means for modulating comprises a phase modulator.

24. A portable device as defined in claim 23, wherein said phase modulator comprises an exclusive OR-gate.

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BACKGROUND OF THE INVENTION

The present invention relates to an identification system composed of a proximity powered and coded portable unit and a corresponding energization and interrogation device which has a fixed installation. The portable unit may be in the form of a tag or card, and for convenience is referred to herein as a tag. However, the portable unit may also be incorporated in a badge, watch, ring or other article.

The present invention thus relates to a system wherein a fixed installation sends out energy to activate a responsive device which would ordinarily be carried by personnel and the device so energized would send out a coded signal to be picked up by a receiver which in turn would activate some system which, for example, functions to provide access to a controlled area, to keep track of the person, or to perform siimilar purposes.

In known systems of the above type power is provided by means of magnetic coupling, and the coded information is returned via the same path. Typical methods of encoding which have been proposed include switching of the Q of the coded tag receiver loop, by switching its frequency, introducing harmonics of the basic frequency, and other similar coding methods. These methods have proved difficult in practice because of the direct or harmonic relationship between the very large powering signal and the much weaker information signal.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the limitations of the prior art identification systems by transmitting the coded information from the tag in a mode that is completely different from that which is used to transmit power to the tag. In accordance with a preferred embodiment of the present invention, power is transmitted to the tag via magnetic field coupling, while the coded information is transmitted back to the fixed receiver via electric field coupling. The provision of different coupling modes for the signal transmitting power and for the return coded signal has the advantage of being more practical in application with reduced cost and increased reliability relative to the known systems of this type.

In accordance with a preferred embodiment of the invention, further isolation between the transmitted and received signal is provided by operating the fixed receiver and the tag transmitter at a subharmonic of the frequency used to transmit the power.

Various additional features and advantages of the invention will be brought out in the balance of the application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block circuit diagram of an identification system according to one embodiment of the invention, it being understood that those portions of the drawing on the left are part of a fixed installation, while those on the right are on a portable unit, such as a card or a tag, carried by a person.

FIG. 2 is an enlarged plan view of a tag carried by a user of the system.

FIG. 3 is a plan view of a dual antenna for a fixed installation including a power transmitting antenna enclosed within a foil Faraday shield, together with a concentric electrostatic receiving antenna.

FIG. 4 is an enlarged section on the line 4--4 of FIG. 3.

FIG. 5 is a block circuit diagram illustrating a modification of the tag shown in FIG. 1.

FIGS. 6a and 6b are block circuit diagrams illustrating further modifications of the tag shown in FIG. 1.

FIG. 7 is a block circuit diagram of another embodiment of an identification system according to the invention.

FIG. 8 is a block circuit diagram of a further embodiment of an identification system according to the invention.

FIG. 9 is a block circuit diagram of yet another embodiment of an identification system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, a system embodying the present invention is shown in FIG. 1. In this figure, a fixed installation, generaly designated 5, is mounted on a convenient wall or window 7. The balance of the material shown in the drawing, which is generally designated 9, is contained on a card or tag and carried by personnel.

The power supply consists of an oscillator 11 which puts out power at a convenient frequency such as 400 KHz. This is connected to a coil antenna 13 tuned to the resonant frequency by means of capacitor 15. Coil 13 emits a strong magnetic field and, as later explained in detail, is preferably provided with a Faraday shield to avoid capacative or electrostatic coupling to the tag receiver.

The tag 9 includes a coil 17 and a capacitor 19 which form a tuned LC circuit resonant with coil 13 to provide a power supply as well as a clock signal of frequency fO for the tag circuits. A full wave rectifier 21 and filter capacitor 23, connected across coil 17 and capacitor 19, provide power for the coded transmitter circuits of the tag through lines 25 and 27, the connections of which are not shown for simplicity. The clock signal is taken through a line 29 to a frequency dividing counter 31 to produce an R.F. signal of frequency f0/2 on line 33 and address signals on a plurality of memory select lines, only two of which have been shown at 35 and 37 for activating a programmable read only memory 39 which provides a plurality of coded pulses through line 41. Lines 33 and 41 go to an AND gate 43 which produces output pulses on a line 45 which are fed to an electrostatic antenna 47. The coded pulses on line 41 are at a much lower rate than the signal of frequency f0/2 on line 33. The effect of AND gate 43 is to square wave modulate the signal on line 33 with the coded pulse train on line 41, producing a square wave modulated signal on line 45.

The pulses from the electrostatic antenna 47 are picked up at the fixed installation by a metal plate receiving antenna 49, tuned by a coil 51 and a capacitor 53, passed through an amplifier 55, and are detected by an RC amplitude detector and filter 57 and passed to a decoder 59 for validation in a manner well known in the art. Assuming that the right signal has been given, an operating device 61 is then triggered. Operating device 61 might take many forms, such as a security device for admitting one to a secure area, or a device for recording the location of the person carrying the badge and the like.

FIG. 2 shows a typical tag 62 which might be employed. Tag 62 includes a backing member 63 which supports a flattened coil of wire 65, which corresponds with coil 17 in FIG. 1 and a flat electrostatic antenna 67, which corresponds with antenna 47 in FIG. 1. Tag 62 further includes a programmable read only memory (PROM) 68 which can be programmed by making or breaking electrical connections. Other than the two antennas and the PROM, the other circuitry shown within the dotted line designated by the reference numeral 9 in FIG. 1 is embodied in a chip 69. The whole tag 62 is roughly 1".times.1.4" or smaller in size. It will be noted that the antennas 65 and 67 in FIG. 2 are coplanar and concentric.

In FIG. 3 the two antennas 13 and 49 which form part of the fixed equipment designated 5 in FIG. 1 are shown. Here, the transmitting antenna 71, which corresponds with coil 13 in FIG. 1, consists of many turns of wire 73 enclosed within a Faraday shield 75 mounted on a base 76. Faraday shield 75 is merely aluminum foil or other non-magnetic metal wrapped around the coil with a transverse gap. This of course allows the magnetic flux to escape, but prevents electrostatic coupling. The electostatic antenna 77 consists of a plate of metal 79 (see FIG. 4) with slots 81 which prevent the plate from becoming a shorted turn. Here again it will be seen that the transmitting and receiving antennas are coplanar and coaxial.

It will be noted that in FIG. 1, the antenna pairs 13, 49 and 17, 47 are coplanar but are in side-by-side configuration. It is important that the two antennas of each pair be roughly coplanar. It is not necessary that the two antennas be coaxial or that they be precisely on the same plane.

FIG. 5 shows a modification of the circuitry contained on the tag (designated 9 in FIG. 1) wherein, instead of employing the RF signal from line 33, a separate local, free-running oscillator 85 is employed to provide a carrier signal of frequency f1 which is modulated by the data on line 41 from read only memory 39. Preferably the frequency f1 is higher than the frequency f0 by at least an order of magnitude. By increasing the frequency of the modulated carrier signal fed to electrostatic antenna 47, the signal transmitted via the electric field will have increased power and will be effective over a greater distance. This is particularly useful in applications where the tag is spaced apart from the fixed installation by such a distance that the signal transmitted via the magnetic field reaches the tag with reduced power and generates an operating voltage VCC of insufficient magnitude for purposes of transmitting the coded information. As the distance between the tag and the fixed installation increases and the operating voltage VCC thus decreases, the voltage magnitude of the modulated carrier reaching electrostatic antenna 47 will be reduced to such a level that the power contained in the transmitted signal will be insufficient to provide a useful signal at the receiver end of the fixed installation. The reduction in voltage level of the carrier signal can be overcome in part by increasing the frequency of the carrier with the use of the local oscillator as shown in FIG. 5.

FIG. 6a shows another modification of the circuitry on the tag of FIG. 1 which provides an alternative resolution to the problem of reduced operating voltage VCC. In FIG. 6a, a coil 87 and a capacitor 88 are connected in series between the AND gate 43 and ground, with the junction between these two components being connected to the electrostatic antenna 47. The inductance and capacitance of the coil 87 and capacitor 88, respectively, are chosen to produce an LC circuit tuned to the frequency f0/2 and to have a Q which in essence constit