Transmission apparatus for a wireless device using delta-sigma modulation

1. A method comprising:

receiving, on an antenna of a wireless device, an original signal transmitted by a detecting device;

responsive to receiving a digital waveform at a decoder of the wireless device, generating an impedance value, wherein the digital waveform has a modulation type and represents the information from the wireless device and wherein the decoder is coupled to a delta-sigma modulator of the wireless device;

responsive to receiving the impedance value at the delta-sigma modulator, modulating a variable impedance value of a variable impedance circuit of the wireless device, wherein the delta-sigma modulator is coupled to the variable impedance circuit and wherein the antenna is coupled to the variable impedance circuit; and

backscattering a modulated signal, wherein a backscattering coefficient of the antenna changes responsively to the modulated variable impedance value so as to backscatter the original signal as the modulated signal that (i) conveys the information and (ii) has a modulation type matching the modulation type of the digital waveform.

2. The method of claim 1 , wherein the information is an N-bit digital waveform that is applied to the decoder, and wherein the delta-sigma modulator generates a control signal for the variable impedance circuit that modulates the variable impedance value and that is related to the N-bit digital waveform.

3. The method of claim 1 , wherein the information is a complex modulation signal that is offset in frequency from the original signal.

4. The method of claim 1 , wherein the information is a complex modulation signal that alternates between an in-phase signal and a quadrature signal via a control signal, and wherein modulating the variable impedance value switches between backscattering coefficients that are 90 degrees offset from each other depending on whether the complex modulation signal is the in-phase signal or the quadrature signal.

5. The method of claim 1 , further comprising compensating for an error in at least one of the decoder, the delta-sigma modulator, and the variable impedance circuit, wherein the information is an N-bit digital waveform that is adjusted to compensate for the error.

6. The method of claim 1 , further comprising filtering noise received by the variable impedance circuit, wherein the received noise is generated by at least one of the decoder and the delta-sigma modulator.

7. The method of claim 1 , wherein the detecting device is an RFID reader that is configured to correct for errors in at least one of the decoder, the delta-sigma modulator, and the variable impedance.

8. A method comprising:

receiving, at an inductor of a wireless device, an original signal transmitted by a detecting device;

responsive to receiving a digital waveform at a decoder of the wireless device, generating an impedance value, wherein the digital waveform has a modulation type and represents the information from the wireless device and wherein the decoder is coupled to a delta-sigma modulator of the wireless device;

responsive to receiving the impedance value at the delta-sigma modulator, modulating a variable impedance value of a variable impedance circuit of the wireless device, wherein the delta-sigma modulator is coupled to the variable impedance circuit and wherein the inductor is coupled to the variable impedance circuit; and

transmitting by mutual inductance a modulated signal, wherein a value of the mutual inductance of the inductor changes responsively to the modulated variable impedance value so as to transmit by mutual inductance the modulated signal that (i) conveys the information and (ii) has a modulation type matching the modulation type of the digital waveform.

9. The method of claim 8 , wherein the information is an N-bit digital waveform that is applied to the decoder, and wherein the delta-sigma modulator generates a control signal for the variable impedance circuit that modulates the variable impedance value and that is related to the N-bit digital waveform.

10. The method of claim 8 , wherein the information is a complex modulation signal that is offset in frequency from the original signal.

11. The method of claim 8 , wherein the information is a complex modulation signal that alternates between an in-phase signal and a quadrature signal via a control signal, and wherein modulating the variable impedance value switches between backscattering coefficients that are 90 degrees offset from each other depending on whether the complex modulation signal is the in-phase signal or the quadrature signal.

12. The method of claim 8 , further comprising compensating for an error in at least one of the decoder, the delta-sigma modulator, and the variable impedance circuit, wherein the information is an N-bit digital waveform that is adjusted to compensate for the error.

13. The method of claim 8 , further comprising filtering noise received by the variable impedance circuit, wherein the received noise is generated by at least one of the decoder and the delta-sigma modulator.

14. The method of claim 8 , wherein the detecting device is an RFID reader that is configured to correct for errors in at least one of the decoder, the delta-sigma modulator, and the variable impedance.

15. The method of claim 1 , wherein the delta-sigma modulator is one of a low-pass delta-sigma modulator and a band-pass delta-sigma modulator.

16. The method of claim 1 , wherein the delta-sigma modulator is a single bit delta-sigma modulator.

17. The method of claim 1 , wherein modulating the variable impedance value switches the impedance value between at least two states.

18. The method of claim 8 , wherein the delta-sigma modulator is one of a low-pass delta-sigma modulator and a band-pass delta-sigma modulator.

19. The method of claim 8 , wherein the delta-sigma modulator is a single bit delta-sigma modulator.

20. The method of claim 8 , wherein modulating the variable impedance value switches the impedance value between at least two states.