Title:
RFID READER WITH ACTIVE BLOCKING REJECTION IN RECEIVER
Kind Code:
A1


Abstract:
An RFID reader is operable to receive an inbound RF signal from an RFID tag during transmission of an outbound RF signal. The inbound RF signal from the RFID tag is a modulated, backscattered signal that includes a desired RF signal component and a blocking RF signal component. The receiver section of the RFID reader includes a preprocessing module operable to process the inbound RF signal. The preprocessing module includes an adjustable attenuation module operable to attenuate the inbound RF signal to produce an attenuated inbound RF signal and an active blocking rejection module operable to increase a ratio of the desired RF signal component to blocking RF signal component in the attenuated inbound RF signal.



Inventors:
Safarian, Aminghasem (Irvine, CA, US)
Rofougaran, Ahmadreza (Reza) (Newport Coast, CA, US)
Rofougaran, Maryam (Rancho Palos Verdes, CA, US)
Application Number:
12/040685
Publication Date:
10/02/2008
Filing Date:
02/29/2008
Assignee:
BROADCOM CORPORATION (IRVINE, CA, US)
Primary Class:
Other Classes:
455/73
International Classes:
H04Q5/22; H04B1/38
View Patent Images:



Primary Examiner:
FLORES, LEON
Attorney, Agent or Firm:
Foley & Lardner LLP/ Broadcom Corporation (Washington, DC, US)
Claims:
What is claimed:

1. A radio frequency identification (RFID) reader, comprising: a receiver section that includes: a preprocessing module including: an attenuation module operable to attenuate an inbound radio frequency (RF) signal having a desired RF signal component and a blocking RF signal component to produce an attenuated inbound RF signal; an active blocking rejection module operable to attenuate the blocking RF signal component in the attenuated inbound RF signal to increase a ratio of the desired RF signal component to the blocking RF signal component in the preprocessed inbound RF signal; a down conversion module coupled to convert the preprocessed inbound RF signal into a down converted signal; a post processing module operable to process the down converted signal to generate a desired near baseband signal; and an analog to digital conversion module coupled to convert the desired near baseband signal into an encoded inbound signal.

2. The RFID reader of claim 1, wherein the active blocking rejection module comprises: a low noise amplifier (LNA) module coupled to amplify the attenuated inbound RF signal to generate an amplified inbound RF signal; a limiting module operable to limit the desired RF signal component in the attenuated inbound RF signal to generate a limited inbound RF signal; and a subtraction module operable to subtract the amplified inbound RF signal and limited inbound RF signal to generate the preprocessed inbound RF signal.

3. The RFID reader of claim 2, wherein the limiting module suppresses amplitude modulation of the desired RF signal component to generate the limited inbound RF signal, wherein the limited inbound RF signal includes the blocking RF signal component and a signal residual component.

4. The RFID reader of claim 3, wherein the signal residual component is proportional to a first component of the desired RF signal component not suppressed by the limiting module.

5. The RFID reader of claim 4, wherein the preprocessed inbound RF signal is proportionate to a second component of the desired RF signal and a phase difference between the desired RF signal component and the blocking RF signal component.

6. The RFID reader of claim 1, further comprising: a transmitter section that includes: an oscillation module coupled to convert a reference oscillation into a radio frequency (RF) oscillation; and a power amplifier module coupled to amplify and to modulate the RF oscillation in accordance with outbound modulation information to produce an outbound RF signal.

7. The RFID reader of claim 6, wherein the blocking RF signal component of the attenuated inbound RF signal includes a component of the outbound RF signal.

8. The RFID reader of claim 7, wherein the attenuation module is adjustable.

9. The RFID reader of claim 8, wherein the attenuation module is adjusted in response to a power level of the outbound RF signal to reduce a dynamic range of the inbound RF signal and produce the attenuated inbound RF signal

10. The RFID reader of claim 6, wherein the active blocking rejection module comprises: a clock module operable to convert the RF oscillation into an in-phase (I) RF clock signal and a quadrature (Q) RF clock signal; a multiplexing module operable to output the I RF clock signal or the Q RF clock signal; a power detection module coupled to determine a power level of the attenuated inbound RF signal; an adjustable amplifier coupled to amplify the output of the multiplexing module based on the power level of the attenuated inbound RF signal to produce an amplified I or Q RF clock signal; a summing module coupled to sum the amplified I or Q RF clock signal with the attenuated inbound RF signal to produce a phase adjusted inbound RF signal; a low noise amplifier module coupled to amplify the phase adjusted inbound RF signal to produce an amplified inbound RF signal; a limiting module coupled to limit the phase adjusted inbound RF signal to produce a limited inbound RF signal; and a subtraction module coupled to subtract the limited inbound RF signal from the amplified inbound RF signal to produce the preprocessed inbound RF signal.

11. The RFID reader of claim 10, wherein the summing module is coupled to sum the amplified I or Q RF clock signal with the attenuated inbound RF signal to decrease a phase difference between the desired RF signal component and the blocking RF signal component to produce the phase adjusted inbound RF signal.

12. The RFID reader of claim 11, wherein the preprocessed inbound RF signal has an improved ratio of the desired RF signal component to the blocking RF signal component from the attenuated inbound RF signal.

13. A transceiver, comprising: a transmitter section that includes: an oscillation module coupled to convert a reference oscillation into a radio frequency (RF) oscillation; and a power amplifier module coupled to amplify and to modulate the RF oscillation in accordance with outbound modulation information to produce an outbound RF signal. a receiver section that includes: a preprocessing module operable to process an inbound RF signal to produce a preprocessed inbound RF signal, wherein the preprocessing module includes: an adjustable attenuation module operable to attenuate the inbound RF signal to produce an attenuated inbound RF signal, wherein the attenuated inbound RF signal includes a desired RF signal component and a blocking RF signal component; and an active blocking rejection module operable to adjust a phase of the blocking RF signal component to increase a ratio of the desired RF signal component to blocking RF signal component in the preprocessed inbound RF signal.

14. The transceiver of claim 13, wherein the active blocking rejection module comprises: a clock module operable to convert the RF oscillation into an in-phase (I) RF clock signal and a quadrature (Q) RF clock signal; a multiplexing module operable to select and output the I RF clock signal or the Q RF clock signal; a power detection module coupled to determine a power level of the attenuated inbound RF signal; an adjustable amplifier coupled to amplify the output of the multiplexing module based on the power level of the attenuated inbound RF signal to produce an amplified I or Q RF clock signal; a summing module coupled to sum the amplified I or Q RF clock signal with the attenuated inbound RF signal to adjust the phase of the blocking RF signal component to produce a phase adjusted inbound RF signal.

15. The transceiver of claim 14, wherein the active blocking rejection module, further comprises: a low noise amplifier (LNA) module coupled to receive the phase adjusted inbound RF signal and operable to amplify the phase adjusted inbound RF signal to generate an amplified inbound RF signal; a limiting module coupled to limit the phase adjusted inbound RF signal to generate a limited inbound RF signal; and a subtraction module coupled to the LNA module and limiting module and operable to subtract the amplified inbound RF signal and limited inbound RF signal to increase the ratio of the desired RF signal component to the blocking RF signal component and to output the preprocessed inbound RF signal.

16. The transceiver of claim 15, further comprising: a down conversion module coupled to receive the preprocessed inbound RF signal and produce a down converted signal; a post processing module operable to process the down converted signal to generate a desired near baseband signal; and an analog to digital conversion module coupled to convert the desired near baseband signal into an encoded inbound signal.

17. The transceiver of claim 16, further comprising: a baseband processing module operable to: convert outbound data into the outbound modulation information; and convert the encoded inbound signal into inbound data.

18. A transceiver, comprising: a transmitter section that includes: an oscillation module coupled to convert a reference oscillation into a radio frequency (RF) oscillation; and a power amplifier module coupled to amplify and to modulate the RF oscillation in accordance with outbound modulation information to produce an outbound RF signal. a preprocessing module that includes: an adjustable attenuation module operable to attenuate an inbound RF signal in response to a power level of the outbound RF signal to reduce a dynamic range of the inbound RF signal and produce an attenuated inbound RF signal, wherein the attenuated inbound RF signal includes a desired RF signal component and a blocking RF signal component; and an active blocking rejection module operable to substantially attenuate the blocking RF signal component of the attenuated inbound RF signal to produce a preprocessed inbound RF signal.

19. The transceiver of claim 18, wherein the active blocking rejection module comprises: a low noise amplifier (LNA) module coupled to receive the attenuated inbound RF signal and operable to amplify the attenuated inbound RF signal to generate an amplified inbound RF signal; a limiting module coupled to limit the attenuated inbound RF signal to generate a limited inbound RF signal; and a subtraction module coupled to subtract the limited inbound RF signal from the amplified inbound RF signal to generate the preprocessed inbound RF signal.

20. The transceiver of claim 19, wherein the limiting module suppresses amplitude modulation of the desired RF signal component to generate the limited inbound RF signal, wherein the limited inbound RF signal includes the blocking RF signal component and a signal residual component proportional to a first component of the desired RF signal component not suppressed by the limiting module.

Description:

CROSS-REFERENCE To RELATED PATENTS

The present U.S. Utility patent application claims priority pursuant to 35 U.S.C. § 119(e) to the following U.S. Provisional Patent Applications which are hereby incorporated herein by reference in their entirety and made part of the present U.S. Utility patent application for all purposes:

1. U.S. Provisional Application Ser. No. 60/921,221, entitled “RFID System,” (Attorney Docket No. BP6250), filed Mar. 30, 2007, pending; and

2. U.S. Provisional Application Ser. No. 60/932,411, entitled “RFID System,” (Attorney Docket No. BP6250.1), filed May 31, 2007, pending.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to communication systems and more particularly to RFID systems.

2. Description of Related Art

A radio frequency identification (RFID) system generally includes a reader, also known as an interrogator, and a remote tag, also known as a transponder. Each tag stores identification or other data for use in identifying a person, item, pallet or other object or data related to a characteristic of a person, item, pallet or other object. RFID systems may use active tags that include an internal power source, such as a battery, and/or passive tags that do not contain an internal power source, but instead are remotely powered by the reader.

Communication between the reader and the remote tag is enabled by radio frequency (RF) signals. In general, to access the identification data stored on an RFID tag, the RFID reader generates a modulated RF interrogation signal designed to evoke a modulated RF response from a tag. The RFID reader then also generates an unmodulated, continuous wave (CW) signal to activate and power the tag. The RFID tag converts the CW signal into stored power to respond to the RFID reader and uses a backscattering technique in which the tag modulates and reflects the CW signal back to the RFID reader. The RF response from the tag includes the coded data stored in the RFID tag. The RFID reader decodes the coded data to identify or determine the characteristics of a person, item, pallet or other object associated with the RFID tag.

RFID systems typically employ either far field or near field technology. In far field technology, the distance between the RFID reader and the tag is great compared to the wavelength of the carrier signal. Typically, far field technology uses carrier signals in the ultra high frequency or microwave frequency ranges. In far-field applications, the RFID reader generates and transmits an RF signal via an RF antenna to all tags within range of the RF antenna. Tags employing far field technology RF coupling at microwave or UHF have been used in applications involving shipping units such as pallets or carton level tracking or other applications needing long-distance reads.

In near-field technology, the operating distance is usually less than one wavelength of the carrier signal, and the reading range is approximately limited to 20 cm or less depending on the frequency. In near field applications, the RFID reader and tag communicate via electromagnetic or inductive coupling between corresponding reader and tag coil antennas. Typically, the near field technology uses carrier signals in the low frequency range. Generally, tags employing near field technology operating at LF or HF have been used in applications involving item-level tagging for inventory control in the supply chain management or applications involving short range reads such as smart cards or vicinity credit cards, e.g. for access control or monetary use, passports, money bills authentication, bank documents, etc. Such applications do not need long range reads of the tags but may need more security provided by near field technology. In addition, near field technology is known for better performance on tags near fluids, such as fluid medications, wherein far field RF coupling tends to incur interference from the fluids.

Currently, an RFID reader consists of a controller or microprocessor implemented on a CMOS integrated circuit and a transmitter and receiver implemented on one or more separate CMOS, BiCMOS or GaAs integrated circuits. It is desirable to reduce the size and power consumption and cost of the RFID reader for both near field and far field applications. In addition, to avoid blocking RF component from the transmitted signal, currently RFID readers and tags operate wherein the RF signal from the reader to tag must end before the RF signal from the tag to reader can begin. This mode of operation is undesirable and slows communications between readers and tags. Therefore, a need exists for a highly integrated, low-cost RFID reader that can operate with passive and active tags in both near field mode and far field mode while simultaneously transmitting and receiving.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an embodiment of an RFID system in accordance with the present invention;

FIG. 2 is a schematic block diagram of an embodiment of an RFID reader in accordance with the present invention;

FIG. 3 is a schematic block diagram of an embodiment of a transmitter section of an RFID reader in accordance with the present invention;

FIG. 4 is a schematic block diagram of an embodiment of a receiver section of an RFID reader in accordance with the present invention;

FIG. 5 is a schematic block diagram of an embodiment of a preprocessing module in a receiver section of an RFID reader in accordance with the present invention;

FIGS. 6a and 6b are a schematic block diagram of an embodiment of an active blocking rejection module in the preprocessing module in accordance with the present invention; and

FIGS. 7a and 7b are a schematic block diagram of another embodiment of an active blocking rejection module in the preprocessing module in accordance with the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic block diagram of an RFID (radio frequency identification) system that includes a computer/server 12, a plurality of RFID readers 14-18 and a plurality of RFID tags 20-30. The RFID tags 20-30 may each be associated with a particular object for a variety of purposes including, but not limited to, tracking inventory, tracking status, location determination, assembly progress, et cetera. The RFID tags 20-30 may be active devices that include internal power sources or passive devices that derive power from the RFID readers 14-18.

Each RFID reader 14-18 wirelessly communicates with one or more RFID tags 20-30 within its coverage area. For example, RFID tags 20 and 22 may be within the coverage area of RFID reader 14, RFID tags 24 and 26 may be within the coverage area of RFID reader 16, and RFID tags 28 and 30 may be within the coverage area of RFID reader 18. In far field mode of operation, the RF communication scheme between the RFID readers 14-18 and RFID tags 20-30 is a backscatter coupling technique using far field technology whereby the RFID readers 14-18 request data from the RFID tags 20-30 via an RF signal, and the RF tags 20-30 respond with the requested data by modulating and backscattering the RF signal provided by the RFID readers 14-18. In a near field mode of operation, the RF communication scheme between the RFID readers 14-18 and RFID tags 20-30 is a magnetic or inductive coupling technique whereby the RFID readers 14-18 magnetically or inductively couple to the RFID tags 20-30 to access the data on the RFID tags 20-30. Thus, in one embodiment of the current invention, the RFID readers 14-18 may communicate in a far field mode to an RFID tag 20-30 with far field mode capabilities and in a near field mode to an RFID tag 20-30 with near field mode capabilities.

The RFID readers 14-18 collect data as may be requested from the computer/server 12 from each of the RFID tags 20-30 within its coverage area. The collected data is then conveyed to computer/server 12 via the wired or wireless connection 32 and/or via peer-to-peer communication 34. In addition, and/or in the alternative, the computer/server 12 may provide data to one or more of the RFID tags 20-30 via the associated RFID reader 14-18. Such downloaded information is application dependent and may vary greatly. Upon receiving the downloaded data, the RFID tag 20-30 can store the data in a non-volatile memory therein.

As indicated above, the RFID readers 14-18 may optionally communicate on a peer-to-peer basis such that each RFID reader does not need a separate wired or wireless connection 32 to the computer/server 12. For example, RFID reader 14 and RFID reader 16 may communicate on a peer-to-peer basis utilizing a back scatter technique, a wireless LAN technique, and/or any other wireless communication technique. In this instance, RFID reader 16 may not include a wired or wireless connection 32 to computer/server 12. In embodiments in which communications between RFID reader 16 and computer/server 12 are conveyed through the wired or wireless connection 32, the wired or wireless connection 32 may utilize any one of a plurality of wired standards (e.g., Ethernet, fire wire, et cetera) and/or wireless communication standards (e.g., IEEE 802.11x, Bluetooth, et cetera).

In other embodiments, the RFID system of FIG. 1 may be expanded to include a multitude of RFID readers 14-18 distributed throughout a desired location (for example, a building, office site, et cetera) where the RFID tags 20-30 may be associated with access cards, smart cards, mobile phones, personal digital assistants, laptops, personal computers, inventory items, pallets, cartons, equipment, personnel, et cetera. In addition, it should be noted that the computer/server 12 may be coupled to another server and/or network connection to provide wide area network coverage.

FIG. 2 is a schematic block diagram of an embodiment of an RFID reader 40 which can be used as one of the RFID readers 14-18 in FIG. 1. The RFID reader 40 includes a transmitter section 42, a receiver section 44 and baseband processing module 46. The baseband processing module 46 is also coupled to a host interface module 50. The host interface module 50 may include a communication interface (USB dongle, compact flash or PCMCIA) to a host device, such as the computer server 12. The multi-mode RFID reader 40 also includes an antenna structure 48 that is coupled to both the transmitter section 42 and receiver section 44.

The transmitter section 42, receiver section 44, baseband processing module 46 and host interface module 50 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. One or more of the modules may have an associated memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of the module. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the module implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory element storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Further note that, the memory element stores, and the module executes, hard coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in FIGS. 1-7.

In operation, the baseband processing module 46 may receive one or more commands or requests for data from the host interface module 50 that requires communication of data to one or more RFID tags 20-30. Alternatively, or in addition to, the baseband processing module 46 may receive data from an RFID tag 20-30 that requires a response to be generated by the multi-mode RFID reader 40. As another alternative, or in addition to, the baseband processing module 46 may determine itself that a command or other communication is necessary to one or more RFID tags 20-30. In response to the required communication, the baseband processing module 46 converts outbound data to the outbound modulation information 52 for communication to one or more RFID tags 20-30.

The outbound modulation information 52 is transmitted to the transmitter section 42. In response to the outbound modulation information 52, the transmitter section 42 is operable to generate a modulated, up-converted outbound RF signal 54 at a carrier frequency FB in the RF band or microwave band. In one embodiment, the carrier frequency FB is a standardized carrier frequency in the RFID field, such as one or more frequencies specified in the ISO 18000 series or specified by the EPCglobal standards or other RFID standards. Upon completion of the modulated outbound RF signal 54, the transmitter section 42 then generates an unmodulated, continuous wave (CW) outbound RF signal 54 at the carrier frequency FB. The CW outbound RF signal 54 is operable to power a passive or semi-passive RFID tag 20-30.

The antenna structure 48 is operable to transmit the outbound RF signal 54. The antenna structure 48 may be an RF type antenna structure operable to transmit the outbound RF signal 54 via RF coupling in a far field RFID reader 40 or a coil type antenna structure operable to transmit the outbound RF signal 54 via inductive or magnetic coupling in a near field RFID reader 40.

To receive signals, an inbound RF signal 58 is detected by the antenna structure 48. The antenna structure 48 is operable to receive the inbound RF signal 58 via RF coupling in a far field RFID reader 40 or via inductive or magnetic coupling in a near field RFID reader 40. In one embodiment, the RFID reader 40 is operable to receive the inbound RF signal 58 during transmission of the outbound RF signal 54, as explained in more detail below. The inbound RF signal 58 is a modulated, backscattered signal from the RFID tag 20-30.

The antenna structure 48 provides the inbound RF signal 58 to the receiver section 44. The receiver section 44 is operable to down convert the inbound RF signal 54 by using a transmitter signal 56 generated by the transmitter section 42. The receiver section 44 then processes and digitizes the down converted inbound RF signal to produce an encoded inbound signal 60. The encoded inbound signal 60 is transmitted to the baseband processing module 46 for converting the encoded inbound signal 60 into inbound data.

FIG. 3 illustrates an embodiment of the transmitter section 42 of the RFID reader 40 in more detail. As seen in FIG. 3, the transmitter section 42 includes an oscillation module 68, power amplifier module 66 and antenna structure 48. In one embodiment, the oscillation module 68 receives a reference oscillation signal 62 and generates an RF oscillation signal 64 at a desired frequency FB. The RF oscillation signal 64 is then directly modulated by the power amplifier module 66 in response to the outbound modulation information 52. The power amplifier module 66 then amplifies and outputs a generated outbound RF signal 54. To generate an unmodulated, continuous wave (CW) signal, the power amplifier module 66 amplifies the RF oscillation signal 64 to generate the outbound RF signal 54 without modulation. In this embodiment, the outbound modulation information 52 is one or more of amplitude shift keying (ASK), amplitude modulation (AM) or other types, variations or extensions thereof.

In another embodiment, the oscillation module 68 may be operable to receive the outbound modulation information 52, as shown in dotted lines in FIG. 3, generated by the baseband processing module 46. In this embodiment, the outbound modulation information 52 includes phase and/or frequency modulation information. The oscillation module 68 would also be operable to modulate the RF oscillation signal 64 in response to the phase and/or frequency outbound modulation information 52. The power amplifier module 66 then amplifies the modulated RF oscillation signal 64 and outputs the generated outbound RF signal 54. To generate an unmodulated, continuous wave (CW) signal, the oscillation module 68 does not modulate the RF oscillation signal 64. In this embodiment, the outbound RF signal 54 may have one or more of the following modulations: binary phase shift keying (BPSK), quadrature PSK (QPSK), phase shift keying (PSK), frequency shift keying (FSK) or other types, variations or extensions of phase or frequency type modulation.

In an embodiment, the modulation by the tag of the backscattered signal creates one or more subcarrier frequencies and so the frequency FS of the desired modulated signal from the tag may be slightly higher or lower depending on the encoding of the modulation data information at the tag. For example, if the carrier frequency FB of the outbound RF signal is 13.56 MHz, and the tag switches the load resistor at a rate of 500 kHz to modulate the backscattered signal, then two new subcarrier frequencies will appear at 13.810 MHz and 13.310 MHz. Such subcarrier frequencies are common when the tag employs Manchester coding or FM0 or FM1 type coding wherein each bit includes one or more transitions. Due to reflections of the outbound RF signal 54 back to the antenna structure 48, the inbound RF signal 58 includes a blocking RF signal component derived from the outbound RF signal 54 at a carrier frequency FB. The inbound RF signal 58 will also include a desired RF signal component of the modulated backscattered signal at the subcarrier frequency Fs.

FIG. 4 illustrates an embodiment of the receiver section 44 of the RFID reader 40 in more detail. The receiver section 44 includes a preprocessing module 70, a down conversion module 72, a post processing module 74 and analog-to-digital (ADC) module 76. In an embodiment of the receiver section 44, the inbound RF signal 58 has been modulated by the tag as described above with one or more of amplitude shift keying (ASK), amplitude modulation (AM) or other type, variations or extensions thereof.

The preprocessing module 70 receives the inbound RF signal 58 from the antenna structure 48. The preprocessing module is operable to attenuate the blocking RF signal component of the inbound RF signal 58. The preprocessing module 70 generates a preprocessed inbound RF signal 82 for transmission to the down conversion module 72.

The down conversion module 72 includes a clock recovery circuit 78 and a mixing module 80. In one embodiment, the down conversion module 72 employs direct conversion. In direct conversion, the frequency of the preprocessed inbound RF signal 82 is down converted to the desired frequency in one conversion without first down converting to an intermediate frequency as in heterodyne type receivers. Using direct conversion eliminates components and decreases the size and cost of the RFID receiver 40. In operation, the clock recovery circuit 78 in the down conversion module 72 receives a transmitter signal 56 from the transmitter section 42. Using the transmitter signal 56, the clock recovery circuit 78 is operable to generate at least one local oscillation signal 84. The mixing module 80 is operable to mix the at least one oscillation signal 84 with the preprocessed inbound RF signal 82 to produce a down converted signal 86.

In another embodiment, the down conversion module 72 may also be a heterodyne or superheterodyne type conversion module wherein the down conversion module 72 is operable to first down convert the preprocessed inbound RF signal 82 into an intermediate frequency signal. The down conversion module 72 would then be operable to mix the intermediate frequency signal with the at least one oscillation signal 84 to produce a down converted signal 86.

The down converted signal 86 is then processed by the post processing module 74. The post processing module 74 is operable to filter the down converted signal 86 to reduce blocking RF signal components and DC offset in the down converted signal 86 and to produce a baseband signal 88. The post processing module 74 is described in more detail in U.S. patent application Ser. No. 11941,740, filed Nov. 16, 2007, entitled, “RFID Reader with Receiver Clock Derived from Transmitter Output”, Attorney Docket No. BD6579. The baseband signal 88 is digitized by the ADC module 76 into the encoded inbound signal 60. The encoded inbound signal 60 is processed by the baseband processing module 46.

In another embodiment of the receiver section 44, the inbound RF signal 58 may have been modulated with one or more of the following modulations: binary phase shift keying (BPSK), quadrature PSK (QPSK), phase shift keying (PSK), frequency shift keying (FSK) or other type, variations or extensions of phase or frequency type modulation. In such an embodiment, the receiver section 44 would need to be revised accordingly.

FIG. 5 illustrates an embodiment of the preprocessing module 70 in the receiver section 44 in more detail. The preprocessing module 70 receives the inbound RF signal 58. The inbound RF signal 58 includes a desired RF signal component of the modulated, backscattered signal from the RFID tag 20-30 at the subcarrier frequency Fs. Due to reflections of the outbound RF signal 54 back to the antenna structure 48 or from leakage of the transmitter section, the inbound RF signal 58 also includes a blocking RF signal component at the carrier frequency FB. For better performance of the receiver section 44, the preprocessing module 70 operates to increase the ratio of the desired RF signal component to the blocking RF signal component.

The inbound RF signal 54 is input to the attenuation module 90. The attenuation module 90 attenuates the inbound RF signal 54 and outputs an attenuated inbound RF signal 94. In an embodiment, the attenuation module 90 may be adjusted to attenuate the inbound RF signal 58 in response to a power level of the outbound RF signal 54. Since it is a reflection of the outbound RF signal 54, the blocking RF signal component in the inbound RF signal 58 will have a power level proportionate to the outbound RF signal 54. By adjusting the attenuation module 90 in response to the power level of the outbound RF signal 54, a dynamic range of the inbound RF signal 58 is reduced. The attenuation module 54 is thus operable to increase the sensitivity of the preprocessing module 70 such that the preprocessing module 70 may detect the desired RF signal component from the stronger interfering blocking RF signal component in the inbound RF signal 58.

The attenuated inbound RF signal 94 from the attenuation module 54 is received by the active blocking rejection module 92. The active blocking rejection module 92 is operable to attenuate the blocking RF signal component in the attenuated inbound RF signal 94 to increase a ratio of the desired RF signal component to the blocking RF signal component in the preprocessed inbound RF signal 82.

FIGS. 6a and 6b are a schematic block diagram of an embodiment of the active blocking rejection module 92 in the preprocessing module 70. The active blocking rejection module 92 includes an amplifier module 100, a limiting module 102 and a subtraction module 104. The amplifier module 100 amplifies the attenuated inbound RF signal 94 to produce an amplified inbound RF signal 96. The limiting module 102 limits the attenuated inbound RF signal 94 to produce a limited inbound RF signal 98. The subtraction module 104 subtracts the limited inbound RF signal 98 from the amplified inbound RF signal 96 to attenuate the blocking RF signal component in the preprocessed inbound RF signal 82.

An operation of an embodiment of the blocking rejection module 92 in FIG. 6a is explained in more detail in FIG. 6b. In the embodiment in FIG. 6b, the attenuated inbound RF signal 94 includes the desired RF signal component 110 and the blocking RF signal component 116. The desired RF signal component 116 is the modulated, backscattered signal from one of the RFID tags 20-30. The attenuated inbound RF signal 94 also includes the blocking RF signal component 116 due to reflections of the outbound RF signal 54 and leakage from the transmitter section 42. FIG. 6b depicts a phase graph 108b with the blocking RF signal component 116 set at a zero phase or at the X axis on the phase grid. The desired RF signal component 110 is shown on a phase grid at a phase θ with respect to the X axis. As such, the phase θ is the difference in phase between the desired RF signal component 110 and the blocking RF signal component 116. The desired RF signal component 110 can be decomposed into desired signal X component 112 and desired signal Y component 114 as shown on the phase grid 108a. The desired signal X component 112 and the desired signal Y component 114 are related to the desired RF signal component 110 as follows:

sin θ=Y/S, such that Y=S sin θ

cos θ=X/S, such that X=S cos θ

wherein S is the desired RF signal component 110, X is the desired signal X component 112 and Y is the desired signal Y component 114. The phase grid 108c depicts the combined desired RF signal component 110 and the blocking RF signal component 116.

The amplifying module 100 amplifies the attenuated inbound RF signal 94 including both the desired RF signal component 110 and a blocking RF signal component 116 to produce the amplified RF signal 96. The amplified RF signal 96 includes an amplified signal X component 118 and an amplified signal Y component 120.

The limiting module 102 also receives the attenuated inbound RF signal 94 which includes both the desired RF signal component 110 and the blocking RF signal component 116. In an embodiment, the desired RF signal component 110 is amplitude modulated by the RFID tags 20-30. The limiting module 102 substantially suppresses the amplitude modulation from the desired RF signal component 110 to remove the desired signal X component 112. Any remaining X component may be scaled to approximately equal the blocking RF signal component 116. The scaling of the desired signal X component may be based on the received power of the blocking RF signal component 116 or based on the gain of the amplifier module 100. The limiting module 102 thus produces the limited inbound RF signal 98 including a limited blocking RF signal component 122 and a signal residual component 124. Since the signal residual component 124 is due to amplitude modulation of the desired RF signal component 110 that was not suppressed by the limiting module 102, this signal residual component 124 is proportionate to the desired signal Y component 114.

The subtraction module 104 subtracts the amplified inbound RF signal 96 from the limited inbound RF signal 98. The output of the subtraction module 104 is the preprocessed inbound RF signal 82. The preprocessed inbound RF signal 82 is approximately proportional to the gain of the desired signal X component 112 and cos θ. Though the preprocessed inbound RF signal 82 may still include gain from the amplification of the blocking RF signal component 116, the ratio of the desired RF signal component 110 to blocking RF signal component 116 in the preprocessed inbound RF signal is increased and compares favorably from that of the attenuated inbound RF signal 94.

FIGS. 7a and 7b are a schematic block diagram of another embodiment of the active blocking rejection module 92. The active blocking rejection module 92 in an embodiment described with respect to FIG. 7a and 7b is operable to reduce the effect of cos θ and θ on the preprocessed inbound RF signal 82 by decreasing the phase θ between the desired RF signal component 110 and the blocking RF signal component 116. To decrease the phase θ, the active blocking rejection module 92 is operable to rotate the phase of the blocking RF signal component 116.

Referring to FIG. 7a, a quadrature clock module 130 receives the RF oscillation signal 64 from the oscillation module 68 in the transmitter section 42 shown in FIG. 3. The quadrature clock module 130 produces an in-phase (I) injection signal 132 and a quadrature (Q) injection signal 134. The multiplexing module 136 selects and outputs either the in-phase (I) injection signal 132 or the quadrature (Q) injection signal 134. The in-phase (I) injection signal 132 or the Q injection signal 134 is amplified by the adjustable amplifier module 138 to produce the amplified injection signal 144. The adjustable amplifier module 138 receives an input from power detection module 140. The power detection module 140 measures a power level of the attenuated inbound RF signal 94 and produces power level signal 142. The adjustable amplifier 138 adjusts the amplification of the I injection signal 132 or the Q injection signal 134 in response to the power level signal 142 to produce the amplified injection signal 144. The summing module 146 combines the attenuated inbound RF signal 94 with the amplified injection signal 144 to produce a phase adjusted inbound RF signal 148.

The amplifier module 100 amplifies the phase adjusted inbound RF signal 148 to produce an amplified inbound RF signal 96. The limiting module 102 filters the phase adjusted inbound RF signal 148 to produce a limited inbound RF signal 98. The subtraction module 104 subtracts the limited inbound RF signal 98 from the amplified inbound RF signal 96 to produce the preprocessed inbound RF signal 82. The addition of the injection signal 144 by the summing module 146 rotates the phase of the blocking RF signal component 116 to decrease the phase difference θ between the desired RF signal component 110 and the blocking RF signal component 116. As such, the effect of cos θ and θ on the preprocessed inbound RF signal 82 is decreased by the active blocking rejection module 92.

Operation of an embodiment of the active blocking rejection module 92 in FIG. 7a is explained in more detail with respect to FIG. 7b. The oscillation module 68 from the transmitter section 42 outputs the oscillation signal 64. The oscillation signal 64 is at the same frequency as the blocking RF signal component 116 since the blocking RF signal component 116 is the reflection of the outbound RF signal 54 or leakage from the transmitter section 42. The quaddrature clock module produces in-phase (I) injection signal 132 or the quadrature (Q) injection signal 134 from the oscillation signal 64. Depending on the phase difference between the blocking RF signal component 116 and the desired signal RF component 110, either the in-phase (I) injection signal 132 or the quadrature (Q) injection signal 134 is selected by the multiplexing module 136. As shown in graph 152, in this example of an operation of an embodiment of the active blocking rejection module 92, the Q injection signal 134 is selected by the multiplexing module 136. The adjustable amplifier amplifies the Q injection signal 134 to produce the amplified injection signal 144 shown in Graph 154. The amplification of the injection signal is determined in response to the power level signal from the power detection module 140. The amplitude of the injection signal 144 also determines the degree of rotation of the phase of the blocking RF signal component 116. By measuring the attenuated inbound RF signal 94, the power detection module 140 may determine from prior calibrations, the power level needed for the amplified injection signal 144 to obtain the desired degree of rotation of the phase of the blocking RF signal component 116.

The graph 156 illustrates the attenuated inbound RF signal 94 while graph 158 illustrates the desired RF signal component 110 and blocking RF signal component 116 of the attenuated inbound RF signal 94 in this example of an operation of an embodiment of the active blocking rejection module 92. The summing module 146 adds the amplified injection signal 144 to the attenuated inbound RF signal 94 as shown in graph 160. As a result, the phase of the blocking RF signal component 116 is rotated as shown in graph 162. The phase of the desired signal RF component 110 may also be rotated however, the power level and phase of the amplified injection signal 144 is selected such that the rotation of the blocking RF signal component and the desired signal RF component 110 results in a decrease of their phase difference. Thus, the phase difference 0 between the blocking RF signal component and the desired signal RF component 110 is decreased as seen in this example from graph 158 to graph 162.

The subtraction module outputs the difference of the limited inbound RF signal from the limiting module 102 and the amplified phase adjusted inbound RF signal 96 from the amplifying module 100 as the preprocessed inbound RF signal 82. As explained with respect to FIGS. 61 and 6b, the preprocessed inbound RF signal 82 is proportional to the amplified X signal component 112 derived from the desired RF signal component 110 and cos θ. The effect of cos θ on the preprocessed inbound RF signal 82 decreases as cos θ decreases and cos θ approaches 1. By decreasing the phase difference θ between the desired RF signal component 110 and the blocking RF signal component 116, the ratio of the desired RF signal component 110 to the blocking RF signal component 116 is increased in the preprocessed inbound RF signal.

Auto calibration may be performed by the active blocking rejection module 92 to obtain a maximum or desired ratio of the desired RF signal component 110 to blocking RF signal component 116 in the preprocessed inbound RF signal 82. During calibration, the active blocking rejection module 92 injects the I injection signal 132 and then the Q injection signal 134 and adjusts the respective power levels of the injected I injection signal 132 or Q injection signal 134 to rotate the phase of the blocking RF signal component from θ to 180 degrees. The ratio of the desired RF signal component 110 to blocking RF signal component 116 in the preprocessed inbound RF signal 82 may be determined at each calibration setting to determine a maximum or desired ratio or other criteria.

As may be used herein, the terms “substantially” and “approximately” provides an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to fifty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As may also be used herein, the term(s) “coupled to” and/or “coupling” and/or includes direct coupling between items and/or indirect coupling between items via an intervening item (e.g., an item includes, but is not limited to, a component, an element, a circuit, and/or a module) where, for indirect coupling, the intervening item does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As may further be used herein, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two items in the same manner as “coupled to”. As may even further be used herein, the term “operable to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform one or more its corresponding functions and may further include inferred coupling to one or more other items. As may still further be used herein, the term “associated with”, includes direct and/or indirect coupling of separate items and/or one item being embedded within another item. As may be used herein, the term “compares favorably”, indicates that a comparison between two or more items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.

The present invention has also been described above with the aid of method steps illustrating the performance of specified functions and relationships thereof. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for convenience of description. Alternate boundaries and sequences can be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are thus within the scope and spirit of the claimed invention.

The present invention has been described above with the aid of functional building blocks illustrating the performance of certain significant functions. The boundaries of these functional building blocks have been arbitrarily defined for convenience of description. Alternate boundaries could be defined as long as the certain significant functions are appropriately performed. Similarly, flow diagram blocks may also have been arbitrarily defined herein to illustrate certain significant functionality. To the extent used, the flow diagram block boundaries and sequence could have been defined otherwise and still perform the certain significant functionality. Such alternate definitions of both functional building blocks and flow diagram blocks and sequences are thus within the scope and spirit of the claimed invention. One of average skill in the art will also recognize that the functional building blocks, and other illustrative blocks, modules and components herein, can be implemented as illustrated or by discrete components, application specific integrated circuits, processors executing appropriate software and the like or any combination thereof.