Homodyne RFID receiver and method
View Patent ↗An RFID circuit comprising an RF carrier signal source, a hybrid coupled to the RF carrier signal source operable to generate first and second phase-shifted RF carrier signals, first and second mixers coupled to the hybrid each operable to multiply a respective one of the first and second carrier signals and a received backscattered modulated carrier signal and generate first and second baseband signals, respectively, and first logic coupled to the first and second mixers operable to select one of the first and second baseband signals having a larger amplitude as a demodulated RFID output signal.
1. An RFID circuit comprising:
an RF carrier signal source;
a hybrid coupled to the RF carrier signal source operable to generate first and second phase-shifted RF carrier signals;
first and second mixers coupled to the hybrid each operable to multiply a respective one of the first and second carrier signals and a received backscattered modulated carrier signal and generate first and second baseband signals, respectively; and
first logic coupled to the first and second mixers operable to select one of the first and second baseband signals having a larger amplitude as a demodulated RFID output signal, further includes:
second logic coupled to the first and second mixers and operable to determine whether the first and second baseband signals have the same polarity;
third logic coupled to the first and second mixers and operable to determine which of the first and second baseband signals have a larger amplitude; and
fourth logic coupled to the third logic operable to determine when signal having larger amplitude is switching from the first baseband signal to the second, and vice versa.
2. The RFID circuit of claim 1 , wherein the first logic further includes:
a multiplexer coupled to the first and second mixers and operable to select one of the first and second baseband signals as the demodulated RFID output signal, the multiplexer makes the selection in response to an output from the third logic; and
a polarity switch coupled to the multiplexer operable to flip the polarity of the demodulated RFID output signal in response to an output of the second logic and fourth logic substantially simultaneously as the multiplexer switching from one of the first and second baseband signals to the other as its output.
3. The RFID circuit of claim 1 , wherein the second logic further comprises an XOR gate coupled to a delay line and a majority decision block.
4. The RFID circuit of claim 1 , wherein the third logic comprises a comparator operable to compare the amplitudes of the first and second baseband signals.
5. The RFID circuit of claim 1 , wherein the fourth logic comprises a delay line and an XOR gate.
6. The RFID circuit of claim 1 , wherein the hybrid is operable to generate 0 degree and 90 degree phase-shifted RF carrier signals.
7. The RFID circuit of claim 1 , further comprising first and second amplifiers respectively coupled to the first and second mixers and operable to amplify the first and second baseband signals.
8. The RFID circuit of claim 1 , further comprising first and second data slicers respectively coupled to the first and second mixers and operable to generate first and second digital baseband signals corresponding to the first and second baseband signals.
9. The RFID circuit of claim 1 , further comprising:
an information signal source;
a transmitter receiving the RF carrier signal and the information signal and operable to modulate the RF carrier signal according to the information signal; and
an antenna transmitting the modulated RF carrier signal.
10. The RFID circuit of claim 8 , further comprising a splitter coupled to the RF carrier signal source and operable to pass the RF carrier signal to the hybrid and the transmitter.
11. A method comprising:
generating a carrier signal;
receiving a modulated carrier signal;
multiplying the received modulated carrier signal and first and second phase-shifted carrier signals and generating first and second baseband signals, respectively; and
selecting one of the first and second baseband signals having a larger amplitude as a demodulated RFID output signal, further includes:
determining whether the first and second baseband signals have the same polarity;
determining which of the first and second baseband signals has a larger amplitude; and
determining when the signal having larger amplitude is switching from the first baseband signal to the second, and vice versa.
12. The method of claim 11 , wherein selecting one of the first and second baseband signals further includes:
selecting one of the first and second baseband signals as the demodulated RFID output signal in response to which of the first and second baseband signals have a larger amplitude; and
flipping the polarity of the demodulated RFID output signal, in response to whether the first and second baseband signals have the same polarity, substantially simultaneously as when selecting one of the first and second baseband signals is switching to the other.
13. The method of claim 11 , wherein determining whether the first and second baseband signals have the same polarity comprises:
obtaining an XOR output of the first and second baseband signals;
inserting a plurality of delays in the XOR output and generating a plurality of variably delayed XOR outputs;
generating a majority decision output in response to the plurality of variably delayed XOR outputs.
14. The method of claim 11 , wherein determining which of the first and second baseband signals have a larger amplitude comprises:
determining the amplitude levels of the first and second baseband signals;
comparing the amplitude levels of the first and second baseband signals.
15. The method of claim 11 , wherein determining when the signal having larger amplitude is switching from the first baseband signal to the second, and vice versa comprises:
receiving a determination of which of the first and second baseband signals has a larger amplitude;
inserting variable delays;
generating an XOR output of at least two variably delayed determination of signal with the larger amplitude.
16. The method of claim 11 , further comprises generating 0 degree and 90 degree phase-shifted RF carrier signals.
17. The method of claim 11 , further comprising amplifying the first and second baseband signals.
18. The method of claim 11 , further comprising generating first and second digital baseband signals corresponding to the first and second baseband signals.
19. An RFID device comprising:
an RF carrier signal source;
means coupled to the RF carrier signal source operable to generate first and second phase-shifted RF carrier signals;
mixer means coupled to the hybrid each operable to multiply a respective one of the first and second carrier signals and a received backscattered modulated carrier signal and generate first and second baseband signals, respectively;
multiplexer means operable to select one of the first and second baseband signals as the demodulated RFID output signal, the multiplexer makes the selection in response to a determination of which one of the first and second baseband signals has a larger amplitude; and
polarity switching means operable to flip the polarity of the demodulated RFID output signal in response to a determination of whether the first and second baseband signals have the same polarity and a determination of when the signal having the larger amplitude switches to the other signal substantially simultaneously as switching selection from one of the first and second baseband signals to the other as the demodulated RFID output signal.
20. The RFID device of claim 19 further comprising:
second logic coupled to the first and second mixers and operable to determine whether the first and second baseband signals have the same polarity;
third logic coupled to the first and second mixers and operable to determine which of the first and second baseband signals have a larger amplitude; and
fourth logic coupled to the third logic operable to determine when signal having larger amplitude is switching from the first baseband signal to the second, and vice versa.
21. An RFID circuit, comprising:
an RF carrier signal source;
a hybrid coupled to the RF carrier signal source operable to generate first and second phase-shifted RF carrier signals;
a first and a second mixer coupled to the hybrid each operable to multiply a respective one of the first and second carrier signals and a received backscattered modulated carrier signal and generate first and second baseband signals, respectively; and
a first logic coupled to the first and second mixers, wherein the first logic is configured to:
include a second logic coupled to the first and second mixers operable to determine whether the first and second baseband signals have the same polarity; and
select one of the first and second baseband signals having a larger amplitude as a demodulated RFID output signal.
22. A method comprising:
generating a carrier signal;
receiving a modulated carrier signal;
multiplying the received modulated carrier signal and first and second phase-shifted carrier signals and generating first and second baseband signals, respectively; and
selecting one of the first and second baseband signals having a larger amplitude as a demodulated RFID output signal, wherein selecting includes determining whether the first and second baseband signals have the same polarity.