Multimode transceiver circuit

1. A multimode transceiver circuit, comprising:

a) a four port coupler for splitting an input signal into split signals which are phase shifted by a known amount, the coupler having a first port for receiving the input signal and for outputting an output signal therefrom;

b) a controllable oscillator connected to a second port of the coupler;

c) switchable impedances connected to the remaining ports of the coupler; and

d) control means for controlling operation of the oscillator and the impedances such that:

i) in one mode of operation, the oscillator is inoperative, and at least one of the impedances is switched to operate as a non-linear impedance to detect amplitude modulation of the input signal applied to the first port,

ii) in a further mode of operation, the oscillator is operable, and the impedances are switched to operate as non-linear impedance elements to operate as a mixer to produce an intermediate frequency signal in dependence on the input signal applied to the first port, and

iii) in yet a further mode of operation, the oscillator is operable, and the impedances are switched such that an oscillator frequency appears at the first port for transmission therefrom.

2. The transceiver circuit according to claim 1 , in which the control means controls the switchable impedances by controlling a bias voltage applied thereto.

3. The transceiver circuit according to claim 1 , in which at least one of the switchable impedances comprises a diode.

4. The transceiver circuit according to claim 1 , in which at least one of the switchable impedances comprises a transistor.

5. The transceiver circuit according to claim 1 , in which the split signals are phase shifted by zero and ninety degrees.

6. The transceiver circuit according to claim 1 , in which the split signals are phase shifted by zero and one hundred and eighty degrees.

7. The transceiver circuit according to claim 1 , in which the coupler comprises a branch arm coupler.

8. The transceiver circuit according to claim 1 , in which the coupler comprises a rat race coupler.

9. The transceiver circuit according to claim 1 , in which each mode of operation of the circuit is determined by an impedance match or mismatch of the switchable impedance to its respective port.

10. The transceiver circuit according to claim 1 , in which in the yet further mode of operation, each impedance is switched such as to present an impedance mismatch to its respective port thereby reflecting a signal from the oscillator to the first port.

11. The transceiver circuit according to claim 10 , and further comprising a fixed impedance element between the port and its respective switchable impedance, wherein the impedance of the fixed element is selected such that the switchable impedance is substantially matched to its respective port when it is operated as a non-linear impedance.

12. A tag incorporating a transceiver circuit comprising:

a) a four port coupler for splitting an input signal into split signals which are phase shifted by a known amount, the coupler having a first port for receiving the input signal and for outputting an output signal therefrom;

b) a controllable oscillator connected to a second port of the coupler;

c) switchable impedances connected to the remaining ports of the coupler; and

d) control means for controlling operation of the oscillator and the impedances such that:

i) in one mode of operation, the oscillator is inoperative, and at least one of the impedances is switched to operate as a non-linear impedance to detect amplitude modulation of the input signal applied to the first port,

ii) in a further mode of operation, the oscillator is operable, and the impedances are switched to operate as non-linear impedance elements to operate as a mixer to produce an intermediate frequency signal in dependence on the input signal applied to the first port, and

iii) in yet a further mode of operation, the oscillator is operable, and the impedances are switched such that an oscillator frequency appears at the first port for transmission therefrom.

13. A multimode transceiver circuit, comprising:

a) a four port coupler configured to split an input signal into split signals, the coupler having a first port for receiving the input signal and for outputting an output signal therefrom;

b) a controllable oscillator connected to a second port of the coupler;

c) switchable impedances connected to the remaining ports of the coupler; and

d) a controller operable to control the oscillator and the impedances such that:

i) in one mode of operation, the oscillator is inoperative and at least one of the impedances is switched to operate as a non-linear impedance to detect amplitude modulation of the input signal applied to the first port,

ii) in a further mode of operation, the oscillator is operable and the impedances are switched to operate as non-linear impedance elements to operate as a mixer to produce an intermediate frequency signal in dependence on the input signal applied to the first port, and

iii) in yet a further mode of operation, the oscillator is operable and the impedances are switched such that an oscillator frequency appears at the first port for transmission therefrom.

14. The transceiver circuit according to claim 13, in which the controller is operable to control the switchable impedances by controlling a bias voltage applied thereto.

15. The transceiver circuit according to claim 13, in which at least one of the switchable impedances comprises a diode.

16. The transceiver circuit according to claim 13, in which at least one of the switchable impedances comprises a transistor.

17. The transceiver circuit according to claim 13, in which the coupler is configured to phase shift the split signals by zero and ninety degrees.

18. The transceiver circuit according to claim 13, in which the coupler is configured to phase shift the split signals by zero and one hundred and eighty degrees.

19. The transceiver circuit according to claim 13, in which the coupler comprises a branch arm coupler.

20. The transceiver circuit according to claim 13, in which the coupler comprises a rat race coupler.

21. The transceiver circuit according to claim 13, in which each mode of operation of the circuit is determined by an impedance match or mismatch of the switchable impedance to its respective port.

22. The transceiver circuit according to claim 13, in which in the yet further mode of operation, the controller is operable to switch each impedance to present an impedance mismatch to its respective port, thereby reflecting a signal from the oscillator to the first port.

23. The transceiver circuit according to claim 22, further comprising a fixed impedance element between a port and its respective switchable impedance, wherein the impedance of the element is selected such that the switchable impedance is substantially matched to its respective port when it is operated as a non-linear impedance.

24. The transceiver circuit according to claim 13, wherein the transceiver circuit is incorporated into a transponder tag.

25. A method of operating a transceiver circuit in multiple modes, comprising:

receiving an input signal at a first port of a coupler;

coupling a controllable oscillator to a second port of the coupler;

coupling switchable impedances to the remaining ports of the coupler; and

controlling the oscillator and the impedances such that:

in one mode of operation, the oscillator is inoperative and at least one of the impedances is switched to operate as a non-linear impedance to detect amplitude modulation of the input signal received at the first port,

in a further mode of operation, the oscillator is operable and the impedances are switched to operate as non-linear impedance elements to operate as a mixer to produce an intermediate frequency signal depending on the input signal received at the first port, and

in yet a further mode of operation, the oscillator is operable and the impedances are switched such that an oscillator frequency appears at the first port for transmission therefrom.

26. The method according to claim 25, wherein controlling the switchable impedances comprises controlling a bias voltage applied thereto.

27. The method according to claim 25, further comprising splitting the input signal in the coupler into split signals and phase shifting the split signals by zero and ninety degrees.

28. The method according to claim 25, further comprising splitting the input signal in the coupler into split signals and phase shifting the split signals by zero and one hundred and eighty degrees.

29. The method according to claim 25, further comprising controlling the mode of operation of the transceiver circuit by matching or mismatching the impedance of the switchable impedance to its respective port.

30. The method according to claim 25, further comprising, in the yet further mode of operation, switching each impedance to present an impedance mismatch to its respective port, thereby causing a signal to be reflected from the oscillator to the first port.

31. The method according to claim 30, further comprising coupling a fixed impedance element between a port and its respective switchable impedance, and selecting the impedance of the element such that the switchable impedance is substantially matched to its respective port when it is operated as a non-linear impedance.

32. The method according to claim 25, further comprising incorporating the transceiver circuit into a transponder tag.