Phase modulation for backscatter transponders
First Claim
1. A radio frequency (RF) identification system, comprising:
- a transponder, including an antenna for receiving a continuous wave RF signal and converting it into a received signal;
a first impedance;
a second impedance;
a controller; and
a switch operating under control of the controller, said switch being coupled to said antenna and selectively connecting said antenna to said first impedance or said second impedance,
wherein said received signal is returned to said antenna as a reflected signal and wherein said reflected signal includes a first portion corresponding to a reflection from said first impedance and a second portion corresponding to a reflection from said second impedance, and wherein said first portion is out-of-phase with said second portion by a phase difference;
a reader, including a reader antenna for propagating said continuous wave RF signal and receiving said reflected signal, and a phase detection module for detecting relative phase shifts within said reflected signal.
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Accused Products
Abstract
A radio frequency identification system having a passive backscatter transponder employing phase modulation. The transponder selectively couples its antenna to one of two or more impedances, wherein the impedances each produce a reflected signal when coupled to the antenna in the presence of a continuous RF wave from the reader. The reflected signals produced by the impedances are out-of-phase with each other. The transponder switches between impedances to encode transponder information into a reflected signal through phase shifts in the reflected signal. The reader detects the phase shifts in the reflected signal received at the reader to obtain the transponder information. The impedances are selected so as to produce reflected signals having a desired phase relationship or difference and having sufficient amplitude.
106 Citations
19 Claims
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1. A radio frequency (RF) identification system, comprising:
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a transponder, including an antenna for receiving a continuous wave RF signal and converting it into a received signal;
a first impedance;
a second impedance;
a controller; and
a switch operating under control of the controller, said switch being coupled to said antenna and selectively connecting said antenna to said first impedance or said second impedance,
wherein said received signal is returned to said antenna as a reflected signal and wherein said reflected signal includes a first portion corresponding to a reflection from said first impedance and a second portion corresponding to a reflection from said second impedance, and wherein said first portion is out-of-phase with said second portion by a phase difference;
a reader, including a reader antenna for propagating said continuous wave RF signal and receiving said reflected signal, and a phase detection module for detecting relative phase shifts within said reflected signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A radio frequency (RF) identification system, comprising:
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a transponder, including an antenna for receiving a continuous wave RF signal and converting it into a received signal, and for propagating a reflected signal;
reflection means for receiving said received signal and reflecting said received signal back to said antenna as said reflected signal, wherein said reflection means includes phase modulation means for encoding said reflected signal with transponder information by creating phase shifts within said reflected signal; and
a reader, including a reader antenna for propagating said continuous wave RF signal and receiving said reflected signal, and phase detection means for detecting said phase shifts within said reflected signal and extracting said transponder information. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A reader for use in a radio frequency (RF) identification system employing phase modulation, the system having a transponder, wherein the transponder produces a reflected signal in response to a continuous wave RF signal, and wherein the reflected signal includes transponder information encoded using phase shifts within the reflected signal, the reader comprising:
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a reader antenna for propagating the continuous wave RF signal and receiving the reflected signal; and
a phase detection module for detecting relative phase shifts within said reflected signal and extracting said transponder information. - View Dependent Claims (18, 19)
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Specification