Method and apparatus for modulating and detecting a subcarrier signal for an inductively coupled transponder

• US 5,095,309 A
• Filed: 10/12/1989
• Issued: 03/10/1992
• Est. Priority Date: 05/26/1989
• Status: Expired due to Term

• Current Assignee: Algernon Promotions Inc
• Original Assignee: Trovan Ltd
• Inventors: Troyk, Philip R., DeMichele, Glenn A.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Weissman, Peter
• Application Number:
  US07/423,833
• Time in Patent Office: 880 Days
• Field of Search: 340/825.54, 340/825.31, 340/825.34, 340/825.72, 340/572, 340/825.7, 343/867, 343/742, 324/207.18, 324/207.22, 324/207.26, 336/125, 336/126, 375/52
• US Class Current: 340/10.3
• CPC Class Codes: B61L 25/04 Indicating or recording train identities
• CPC Class Codes: B61L 25/043 using inductive tags
• CPC Class Codes: G06K 7/10178 including auxiliary means for focusing, repeating or boosting the electromagnetic interrogation field comparable booster antennas integrated on the record carrier itself G06K19/07794
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil

Abstract

A transponder system including a transponder and an interrogator having a transmission coil for producing a high-intensity electromagnetic field for inductively powering the transponder and two receiver coils for receiving a low-intensity electromagnetic field reradiated by the transponder. The transmission coil includes one or more conductive windings circumscribing a substantially polygonal volume of space. The receiver coils are diametrically disposed opposite one another within the volume space of the transmitter and are electrically connected to each other in a differential circuit relationship, the output of which is at a minimum when the two receiver coils receive approximately equal quantities of energy and is at a maximum when one of the receiver coils receives more electromagnetic energy from the transponder than the other receiver coil. The transponder uses a coil to derive both a power source and a clock pulse from the high-intensity field for powering and driving an identification circuit. The frequency of the clock pulse is then divided by 8 to drive the memory array and logic network of the identification circuit so that it clocks out a new data bit every 16 cycles of the carrier frequency. The output of the memory array is then used to phase modulate a subcarrier, which is at 1/2 the frequency of the carrier frequency. The subcarrier frequency of 1/2 the carrier frequency is chosen to maximize the amplitude of the transmitted subcarrier. The transponder also includes a double pulse lockout circuit which prevents rapid consecutive short-outs of the transponder'"'"'s coil.

Claims

1. An inductively coupled information retrieval system, comprising:

interrogator means for transmitting an electromagnetic field, receiving a phase modulated subcarrier signal, and analyzing said phase modulated subcarrier signal to detect information conveyed thereby, said interrogator means including;

a support means;

means for generating a first power signal for use in generating said field;

a transmitter coil affixed to said support means for receiving said first power signal and transmitting said field, said transmitter coil including one or more conductive windings circumscribing a substantially polygonal volume of space having a central axis, said transmitter coil being adapted to generate a magnetic flux field within said volume;

first and second receiver coils disposed within said volume of space at significantly separated points and adapted to have linking relationships with portions of said flux field, said first and second receiver coils being electrically connected to each other in a differential circuit relationship such that the magnitude of electrical signals induced in said first and second receiver coils by electromagnetic energy transmitted by said transmitter coil are substantially equal and opposite to each other, said first and second receiver coils being further disposed such that electromagnetic energy generated by said phase modulated subcarrier signal and passing through at least one of said first and second receiver coils will induce an electrical signal of greater magnitude in one receiver coil than will be induced in the other receive coil and cause a current to flow in said differential circuit which corresponds to the amount of energy generated and the information conveyed by said subcarrier signal; and

processing means responsive to said current flowing in said differential circuit and operative to analyze and display said information;

a transponder, including

a transponder coil operative to receive said flux field and convert electromagnetic energy contained therein into an Ac power signal, said transponder coil also being operative to receive a phase modulated power signal and modulate said field with said phase modulated subcarrier signal; and

a transponder circuit assembly encoded with said information and in communication with said transponder coil for receiving said AC power signal and outputting said information to cause periodic shortening of said transponder coil the change of phase of which results in a shift in the phase of said subcarrier signal, said phase modulated power signal being modulated to change phase when a logic "0" data bit representing some of said information is to be transmitted and to not change phase when a logic "1" data bit representing some of said information is to be transmitted, whereby said interrogator means need only analyze absolute changes in the phase of said subcarrier signal in order to correctly determine the logic of the data bits being transmitted and to detect said information.

2. An inductively coupled information retrieval system as recited in claim 1, wherein said transponder circuit assembly includes:

means for converting said AC power signal into a plurality of control signals for operating said circuit assembly; and

coded signal retrieval means for receiving said control signals and outputting said information.

3. An inductively coupled information retrieval system as recited in claim 2, wherein said converting means includes:

rectifier means for receiving said AC power signal and producing a DC power signal for operating said retrieval means; and

timing means for receiving said AC power signal and producing a clock pulse signal for driving said retrieval means.

4. An inductively coupled information retrieval system as recited in claim 3, wherein said rectifier means includes a shunt regulator for shunting excess current produced by said rectifier to ground when said transponder coil receives an excessive AC power signal, whereby the voltage level of said DC power signal is maintained within an operating range of said retrieval means.

5. An inductively coupled information retrieval system as recited in claim 3, wherein said rectifier means is a full-wave bridge rectifier.

6. An inductively coupled information retrieval system as recited in claim 5, wherein said full-wave bridge rectifier includes a shunt regulator for shunting excess current produced by said rectifier to ground when said transponder coil receives an excessive AC power signal, whereby the voltage level of said DC power signal is maintained within an operating range of said retrieval means.

7. An inductively coupled information retrieval system as recited in claim 6, wherein said shunt regulator is a parasitic transistor.

8. An inductively coupled information retrieval system as recited in claim 2, wherein said retrieval means includes:

timing means for receiving said AC power signal and creating a clock pulse signal;

memory retrieval means for receiving said clock pulse signal and outputting an identity code signal containing said information;

and further wherein said digital control means includes;

logic means for receiving said identity code signal and outputting a digital data signal representing said indentity code signal;

phase modulating means for receiving said clock pulse signal and said digital data signal and modulating said clock pulse signal in such a manner so as to change the phase of said clock pulse signal when a logic "0" data bit from said digital data signal is to be transmitted and to not change the phase of said clock pulse signal when a logic "1" data bit from said digital data signal is to be transmitted; and

driving means for receiving said modulated clock pulse signal and outputting said phase modulated power signal, whereby said transponder coil is caused to transmit said subcarrier signal within said field at the frequency of said modulated power signal.

9. An inductively coupled information retrieval system as recited in claim 8, wherein said phase modulating means includes:

phase selection means for receiving said clock pulse signal and said digital data signal and phase modulating said clock pulse signal with said digital data signal by causing said clock pulse signal to skip one cyclic pulse to change the phase of said clock pulse signal and by causing said clock pulse signal to add one cyclic pulse when the phase of said clock pulse signal is reversed; and

double pulse lockout means for removing the positive voltage component from each cyclic pulse added to said clock pulse signal and outputting said modulated clock pulse signal, whereby two consecutive cyclic pulses will not be received by said driving means.

10. An inductively coupled information retrieval system as recited in claim 8, wherein said converting means includes a shunt regulator for shunting excess current produced by said converting means to ground when said transponder coil receives and excessive AC power signal, whereby the voltage level of said DC power signal is maintained within an operating range of said retrieval means.

11. An inductively coupled information retrieval system as recited in claim 8, wherein said converting means includes a full-wave bridge rectifier.

12. An inductively coupled information retrieval system as recited in claim 11 wherein said rectifier includes a shunt regulator for shunting excess current produced by said rectifier to ground when said transponder coil receives an excessive AC power signal, whereby the voltage level of said DC power signal is maintained within an operating range of said retrieval means.

13. An inductively coupled information retrieval system as recited in claim 12, wherein said shunt regulator is a parasitic transistor.