Method and apparatus for responding to an interrogation signal

• US 5,453,748 A
• Filed: 11/15/1993
• Issued: 09/26/1995
• Est. Priority Date: 11/15/1993
• Status: Expired due to Fees

• Current Assignee: Siemens Rail Automation Ltd. (Siemens AG)
• Original Assignee: Siemens Rail Automation Ltd. (Siemens AG)
• Inventors: Lindell, Kevin W.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/152,800
• Time in Patent Office: 680 Days
• Field of Search: 342/51, 342/43, 342/103, 342/45, 342/30, 342/31, 342/32
• US Class Current: 342/51
• CPC Class Codes: G01S 13/767 Responders; Transponders teaching or practice apparatus for gun-aiming or gun-laying using reflecting targets or active targets F41G3/26
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs

Abstract

A transponder receives a stable reference frequency transmitted from an interrogator and compares the stable reference frequency to a local oscillator frequency that has short term stability. A comparison signal is provided to a synchronous oscillator for providing a locked signal that briefly locks onto the comparison signal and "remembers" its phase and frequency characteristics. The locked signal, which is inherently locked to the stable reference signal of the interrogator, is then combined with the short-term stable local oscillator frequency, and the combined signal is used in the up-converted reply back to the interrogator.

Claims

1. A transponder, comprising:

a local oscillator for providing a local oscillator frequency signal;

a comparator, responsive to a reference frequency signal from an interrogator and to the local oscillator frequency signal, for providing a comparison signal;

a synchronous oscillator, responsive to the comparison signal, for providing a locked signal; and

a combiner, responsive to the locked signal and the local oscillator frequency signal, for providing a combined signal to the interrogator.

2. A transponder comprising:

a local oscillator for providing a local oscillator frequency signal;

a comparator, responsive to a reference frequency signal from an interrogator and to the local oscillator frequency signal, for providing a comparison signal;

a synchronous oscillator, responsive to the comparison signal, for providing a locked signal; and

a combiner, responsive to the locked signal and the local oscillator frequency signal, for providing a combined signal to the interrogator,

wherein the reference frequency signal from the interrogator and the combined signal to the interrogator are both at a same first frequency, wherein the local oscillator frequency signal is at a second frequency, wherein the comparator provides the compared signal at a third frequency equal to a difference between the first and second frequencies, wherein the locked signal is at the third frequency, and wherein the combined signal is at a frequency equal to a sum of the second and third frequencies which sum frequencies equal the first frequency.

3. A transponder, comprising:

a local oscillator for providing a local oscillator frequency signal;

a comparator, responsive to a reference frequency signal from an interrogator and to the local oscillator frequency signal, for providing a comparison signal;

a synchronous oscillator, responsive to the comparison signal, for providing a locked signal; and

a combiner, responsive to the locked signal and the local oscillator frequency signal, for providing a combined signal to the interrogator,

wherein the reference frequency signal from the interrogator is two reference frequency signals at different first and second frequencies provided simultaneously, wherein the comparator is responsive to the two reference frequency signals for providing first and second comparison signals and wherein the transponder further comprises;

first and second dividers, respectively responsive to the first and second comparison signals, for providing first and second divided signals; and

a mixer, responsive to the first and second divided signals, for providing a summed signal as the comparison signal provided to the synchronous oscillator, wherein the combined signal to the interrogator is at a third frequency different from the first and second frequencies.

4. A transponder, comprising:

a local oscillator for providing a local oscillator frequency signal;

a comparator, responsive to a reference frequency signal from an interrogator and to the local oscillator frequency signal, for providing a comparison signal;

a synchronous oscillator, responsive to the comparison signal, for providing a locked signal; and

a combiner, responsive to the locked signal and the local oscillator frequency signal, for providing a combined signal to the interrogator,

wherein the reference frequency signal from the interrogator is two reference frequency signals provided sequentially at different frequencies, wherein the comparator is responsive to the two reference frequency signals for providing two corresponding intermediate frequency signals, wherein the synchronous oscillator is responsive to one of the intermediate frequency signals for providing a first locked signal and wherein the transponder further comprises;

a second synchronous oscillator, responsive to a second one of the intermediate frequency signals, for providing a second locked signal;

a mixer, responsive to the first and second locked signals, for providing a mixed signal to the combiner; and

wherein the combined signal is a third frequency different from the frequencies of the two reference signals.

5. A method, comprising the steps of:

receiving a reference frequency signal transmitted from an interrogator during an interrogation period;

comparing the reference frequency signal to a local oscillator frequency signal for providing a comparison signal during the interrogation period wherein the comparison signal has phase and frequency characteristics of the reference frequency signal;

providing during a reply period after the interrogation period, in response to the comparison signal, a locked signal also having the phase and frequency characteristics of the reference frequency signal; and

combining the local oscillator frequency signal with the locked signal for providing a combined signal to the interrogator during the reply period.

6. A method, comprising the steps of:

interrogating, from an interrogator, a plurality of transponders with an interrogation signal over a plurality of successive interrogation and reply periods, wherein the interrogation signal is derived from an interrogator oscillator having a reference frequency stable within selected limits over a term greater than the plurality of successive interrogation and reply periods, and wherein the method, at each of a plurality of receivers, further comprises the steps of;

comparing a signal indicative of the interrogator reference frequency to a signal indicative of a local oscillator frequency that is stable within the selected limits over a term greater than at least one of the interrogation and reply periods for providing a comparison signal having frequency and phase characteristics derived from both the interrogator and local reference frequency signals;

providing, in response to the comparison signal, a locked signal that retains the frequency and phase characteristics of the comparison signal for at least one of the interrogation and reply periods;

combining the locked signal and the local reference frequency signal for providing a combined signal; and

providing the combined signal to the interrogator.