Method and apparatus for generating dedicated data channels in inductive coupled RFID systems
An inductive coupling apparatus for modifying an incoming radio frequency (RF) signal includes an inductive element for modifying the incoming RF signal in accordance with a coupled impedance characteristic of the inductive element. A variable impedance circuit includes an output electrically coupled to the inductive element. A low pass delta sigma modulator is coupled to the variable impedance circuit and digitally controls the output of the variable impedance circuit, the coupled impedance of the inductive element being adjusted based on the output of the variable impedance circuit.
1. An inductive coupling apparatus for modifying an incoming radio frequency (RF) signal comprising:
an inductive element;
a variable impedance circuit having an output electrically coupled to the inductive element; and
at least one low pass delta sigma (ΔΣ) modulator coupled to the variable impedance circuit and digitally controlling the output of the variable impedance circuit;
wherein the incoming RF signal is modified as the coupled impedance (Z) of the inductive element is adjusted in accordance with the output of the variable impedance circuit.
2. The inductive coupling apparatus of claim 1 wherein an output of the at least one low pass delta sigma modulator switches the output of the variable impedance circuit between at least two states to adjust the coupled impedance.
3. The inductive coupling apparatus of claim 1 wherein an input signal applied to the low pass delta sigma modulator comprises a complex modulation signal offset from the incoming radio frequency signal by +/−ω 0 .
4. The inductive coupling apparatus of claim 3 wherein the complex modulation signal consists of one of a GMSK, QPSK, nPSK, nQAM, and an OFDM signal.
5. The inductive coupling apparatus of claim 1 wherein an output of the low pass delta sigma modulator is one of a return to zero (RTZ) and a non-return to zero (NRZ) type signal.
6. The inductive coupling apparatus of claim 1 further comprising at least a second low pass delta sigma modulator coupled to the variable impedance circuit, wherein the output of the variable impedance circuit is further digitally controlled by the at least a second low pass delta sigma modulator.
7. The inductive coupling apparatus of claim 6 wherein input signals to the first and second low pass delta sigma modulators comprise in-phase (I) and quadrature (Q) signals respectively.
8. The inductive coupling apparatus of claim 6 wherein a combined output of the first and second said low pass delta sigma modulators switches the output of the variable impedance circuit between four states to adjust the coupled impedance of the inductive element.
9. The inductive coupling apparatus of claim 8 wherein the coupled impedance comprises four states which are relative from each other by) Z 0 exp(j0°), Z 0 exp(j180°), Z 0 exp(j90°), and Z 0 exp(j270°).
10. The inductive coupling apparatus of claim 9 wherein the first said low pass delta sigma modulator ((ΔΣ) I ) switches the states between 0 degrees and 180 degrees.
11. The inductive coupling apparatus of claim 10 wherein the second low pass delta sigma modulator ((ΔΣ) Q ) switches the states between 90 degrees and 270 degrees.
12. The inductive coupling apparatus of claim 11 wherein outputs of the first and second low pass delta sigma modulators alternately switch between each other, wherein if (ΔΣ) I generates 0, 180, 180, 0, 0, 180. . . and (ΔΣ) Q generates 90, 90, 270, 270, . . . , Z is controlled to adjust by 0, 90, 180, 90, 180, 270, 0, 270, . . . .
13. The inductive coupling apparatus of claim 6 wherein the input signals applied to the low pass delta sigma modulators comprise sine and cosine wave forms offset from a frequency of the incoming RF signal by ω 1 , where ω 1 can be either positive or negative.
14. The inductive coupling apparatus of claim 6 wherein the input signals applied to the low pass delta sigma modulators consists of a complex modulation signal offset from a frequency of the incoming RF signal by one of +ω 0 , ω 0 and zero.
15. The inductive coupling apparatus of claim 14 wherein the complex modulation signal consists of one of a GMSK, nPSK, QPSK, nQAM, and OFDM signal.
16. The inductive coupling apparatus of claim 6 wherein outputs of the low pass delta sigma modulators consist of one of a return to zero (RTZ) and a non-return to zero (NRZ) type signal.
17. The inductive coupling apparatus of claim 7 wherein the I and Q signals are adjusted to compensate for errors that may arise in generating Z 0 exp(j0°), Z 0 exp(j180°), Z 0 exp(j90°), and Z 0 exp(j270°).
18. The inductive coupling apparatus of claim 17 wherein the errors are compensated for in a radio frequency identification (RFID) reader device electromagnetically coupled to the inductive element.
19. The inductive coupling apparatus of claim 1 further comprising at least one filter device at the variable impedance circuit to filter out of band noise output from the at least one low pass delta sigma modulator.
20. The inductive coupling apparatus of claim 1 wherein the inductive element comprises part of a tag terminal, the tag terminal electromagnetically coupled to a reader device within a radio frequency identification (RFID) system, the reader device providing the incoming RF signal at a carrier signal frequency, the RFID system comprising clocking the low pass delta sigma modulator, generation of the clocking consisting of one of a clock circuit within the tag reader and a clock circuit generated based on the carrier signal frequency.