Interrogator for electronic identification system

• US 6,204,750 B1
• Filed: 10/27/1997
• Issued: 03/20/2001
• Est. Priority Date: 04/27/1995
• Status: Expired due to Fees

• Current Assignee: BTG International Limited (Boston Scientific Corporation)
• Original Assignee: British Technology Group Inter-Corporate Licensing Limited (Invesco Limited)
• Inventors: Scheelen, Jos
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Jeanglaude, Jean Bruner
• Application Number:
  US08/958,491
• Time in Patent Office: 1,240 Days
• Field of Search: 375/371, 327/23, 455/113, 455/12.1, 340/825.5, 340/10.1, 342/358
• US Class Current: 340/10.1
• CPC Class Codes: G01R 25/005 Circuits for comparing several input signals and for indicating the result of this comparison, e.g. equal, different, greater, smaller, or for passing one of the input signals as output signal
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• CPC Class Codes: G01S 13/78 discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe G01S13/75, G01S13/79 take precedence
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: H03D 13/004 the logic means delivering pulses at more than one terminal, e.g. up and down pulses
• CPC Class Codes: H04L 7/027 extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop

Abstract

Interrogator for an electronic identification system having a first oscillator arranged to vary in frequency in accordance with the frequency of a received signal, a second oscillator arranged to vary in accordance with the frequency of the first oscillator after a delay of a number of cycles of the received signal, a phase discriminator for detecting the phase difference between respective output signals of the first and second oscillators and a phase-change detector arranged to determine the frequency at which the phase changes occur. In this way, a modulation frequency of the received signal can be determined.

Claims

1. An interrogator for an electronic identification system, comprising:

a first oscillator arranged to vary in frequency in accordance with the frequency of a received signal;

a second oscillator arranged to vary in accordance with the frequency of the first oscillator after a delay of a number of cycles of the received signal;

phase discriminator means to detect the phase difference between respective output signals of the first and second oscillators; and

phase-change detection means for determining the frequency at which the phase changes occur and thereby determining a modulation frequency of said received signal.

2. An interrogator according to claim 1, and further comprising a loop filter in phase discriminator means to provide said delay.

3. An interrogator according to claim 1, wherein the first oscillator is sensitive to impedance changes and the second oscillator is insensitive to impedance changes.

4. An interrogator according to claim 3, wherein the first oscillator is a Colpitts oscillator arranged to be unstable and the second oscillator is a voltage controlled oscillator.

5. An interrogator according to claim 1, and further comprising means to identify from said modulation frequency the identity of a passive transponder.

6. An interrogator according to claim 1, wherein the phase-change detection means comprises a digital filter.

7. An interrogator according to claim 6, and comprising

an input for said digital filter comprising an array of flipflop circuits;

a delay line associated with each flipflop circuit and arranged so that the time delay provided by each delay line increases incrementally along the array; and

means for providing signals from the Colpitts oscillator and the second oscillator V₃, V₅ as first and second clock signals and for providing said clock signals to each flipflop-delay line pair so that when the phase difference between the clock signals corresponds to a time which is less than the time delay provided by a delay line, the associated flipflop circuit provides a first logical output, and when said time is greater than the time delay provided by a delay line, the associated flipflop circuit provides a second logical output.

8. An interrogator according to claim 7, wherein there is further provided a second array of flipflop circuits and delay lines connected in opposition to the first array so that if the first clock signal leads the second clock signal the logical output of the first array changes and if the first clock signal lags the second clock signal the logical output of the second array changes.

9. An interrogator for an electronic identification system, comprising:

a first oscillator arranged to vary in frequency in accordance with the frequency of a received signal;

a second oscillator arranged to vary in accordance with the frequency of the first oscillator after a delay of a number of cycles of the received signal;

a phase discriminator for detecting the phase difference between respective output signals of the first and second oscillators; and

a phase-change detector for determining the frequency at which the phase changes occur and thereby determining a modulation frequency of said received signal.