Method and apparatus for responding to an interrogation signal

Claim 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.

Claim 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 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.

Claim 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 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.

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 8

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.