Intermodulation mitigation technique in an RFID system

• US 7,772,977 B2
• Filed: 12/18/2008
• Issued: 08/10/2010
• Est. Priority Date: 05/26/2005
• Status: Active Grant

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: TC License Limited
• Inventors: Tiernay, Robert
• Primary Examiner(s): Wu; Daniel
• Assistant Examiner(s): Tang; Son M
• Application Number:
  US12/337,962
• Publication Number:
  US 20090206998A1
• Time in Patent Office: 600 Days
• Field of Search: 340/928, 340/10.1, 340/10.3, 340/933, 340/935, 340/825.73, 340/572.5
• US Class Current: 340/572.1
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures
• CPC Class Codes: G06K 7/10009 sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
• CPC Class Codes: G06K 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08
• CPC Class Codes: G06K 7/10069 the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other frequency hopping or spread spectrum techniques H04B7/00
• CPC Class Codes: G06K 7/10475 arrangements to facilitate interaction with further interrogation devices, e.g. such that at least two interrogation devices may function and cooperate in a network of such devices
• CPC Class Codes: G07B 15/063 using wireless information transmission between the vehicle and a fixed station identification of vehicles G08G
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

When multiple readers for RF transponders have to be placed in close proximity, such as in adjacent lanes of a highway toll barrier, they can be set to operate at different frequencies. When signals from two adjacent ones of the readers interfere, the resulting signal includes interference terms whose frequencies equal the sum of the reader frequencies and the difference between the reader frequencies. To remove such interference terms while passing the desired terms, a tag includes a low-pass or other frequency-selective filter.

Claims

1. A transponder for receiving an interrogation signal from a reader at a first frequency and sending a response signal from the transponder at a third frequency, while mitigating interference effects from an interfering signal at a second frequency, the transponder comprising:

an antenna for receiving the interrogation signal from the reader;

a detector in communication with the antenna, said detector detecting the interrogation signal and outputting a baseband analog signal representing the interrogation signal;

a frequency-selective filter comprising a low-pass filter in communication with the detector to receive the baseband analog signal output by the detector, said frequency-selective filter performing frequency-selective filtering of the baseband analog signal to output an analog signal with reduced interference; and

a signal processor in communication with the frequency-selective filter to receive the analog signal with the reduced interference, said signal processor processing the analog signal with the reduced interference to extract information from the analog signal with the reduced interference;

wherein the low-pass filter has a cutoff frequency which is less than a difference between the first frequency and the second frequency.

2. The transponder of claim 1, wherein the low-pass filter comprises an input, an output, a resistor coupled between the input and the output, and a capacitor coupled between the output and a ground.

3. The transponder of claim 1, wherein the signal processor comprises:

a limiter for receiving the analog signal with reduced interference from the frequency-selective filter and generating a digital signal; and

a baseband decoder for receiving the digital signal from the limiter.

4. A transponder for receiving an interrogation signal from a reader at a first frequency and sending a response signal from the transponder at the first frequency, while mitigating interference effects from an interfering signal at a second frequency, the transponder comprising:

an antenna for receiving the interrogation signal from the reader and the interfering signal at the second frequency;

a detector in communication with the antenna, said detector detecting the interrogation signal and the interfering signal and outputting a baseband analog signal representing the interrogation signal, the interfering signal, and a combination of the interrogation signal and the interfering signal;

a frequency-selective filter comprising a high-pass filter in communication with the detector to receive the baseband analog signal output by the detector, said frequency-selective filter performing frequency-selective filtering of the baseband analog signal to output an analog signal, wherein the interfering signal is reduced by an amount proportional to a square of the interfering signal; and

a signal processor in communication with the frequency-selective filter to receive the analog signal output by the frequency-selective filter, said signal processor processing the analog signal output by the frequency-selective filter to extract information from the analog signal output by the frequency-selective filter;

wherein the high-pass filter has a cutoff frequency which is greater than a difference between the first frequency and the second frequency and less than a frequency of modulation of the interrogation signal from the reader.

5. The transponder of claim 4, wherein the signal processor comprises:

a limiter for receiving the analog signal with reduced interference from the frequency-selective filter and generating a digital signal; and

a baseband decoder for receiving the digital signal from the limiter.

6. A transponder for receiving an interrogation signal from a reader at a first frequency and sending a response signal from the transponder at a third frequency, while mitigating interference effects from an interfering signal at a second frequency, the transponder comprising:

an antenna for receiving the interrogation signal from the reader and the interfering signal at the second frequency;

a detector in communication with the antenna, said detector detecting the interrogation signal and the interfering signal and outputting a baseband analog signal representing the interrogation signal, the interfering signal, and a combination of the interrogation signal and the interfering signal;

a frequency-selective filter comprising a high-pass filter in communication with the detector to receive the baseband analog signal output by the detector, said frequency-selective filter performing frequency-selective filtering of the baseband analog signal to output an analog signal, wherein the interfering signal is reduced by an amount proportional to a square of the interfering signal; and

a signal processor in communication with the frequency-selective filter to receive the analog signal output by the frequency-selective filter, said signal processor processing the analog signal with the reduced interference to extract information from the analog signal output by the frequency-selective filter;

wherein the high-pass filter has a cutoff frequency which is greater than a difference between the first frequency and the second frequency and less than a frequency of modulation of the interrogation signal from the reader.

7. The transponder of claim 6, wherein the signal processor comprises:

a limiter for receiving the analog signal with reduced interference from the frequency-selective filter and generating a digital signal; and

a baseband decoder for receiving the digital signal from the limiter.