MXPA06002677A - Systems and methods for amplifying a transmit signal in a rfid interrogator - Google Patents

Abstract

An RFID interrogator (200) comprises an amplifier (208) configured to amplify signals being transmitted by the RFID interrogator (200). The RFID interrogator (200) also comprises a bypass path (218) to direct received signals (222) around the amplifier (208) so that the amplifier (208) does no block the reception of signals (222) from an RFID tag (220).

Description

SYSTEMS AND METHODS FOR AMPLIFYING A TRANSMISSION SIGNAL IN AN IDENTIFYING INTERFACE RADIO FREQUENCY (RFID) BACKGROUND 1. Field of the Invention The field of the invention relates generally to Radio Frequency Identification (RFID) systems and more particularly to systems and methods for amplifying a transmission signal in an RFID interrogator. 2. Background Information Figure 1 is a diagram showing an illustrative RFID system 100. In the system 100, the RFID interrogator 102 communicates with one or more RFID tags 110. The data can be exchanged between the interrogator 102 and the RFID tag 110 through the a radio transmission signal 108 and a radio reception signal 112. The RFID interrogator 102 comprises a transceiver 104, which contains electronic transmitter and receiver components, and the antenna 106, which are configured to generate and receive the signal of radio transmission and radio reception signal 112, respectively. The exchange of data can be achieved through electromagnetic or electrostatic coupling in the RF spectrum in combination with various modulation and coding schemes. The RFID tag 110 is a transponder that can be attached to an object of interest and act as an information storage mechanism. In many applications, the use of passive RFID tags is desirable, because it has a virtually unlimited operational lifetime and can be smaller, lighter and more economical than active RFID tags that contain an internal power source, for example, a battery. Passive RFID tags are self-powered by rectifying the RF signal emitted by the RF scanner. Accordingly, the transmission signal range 108 determines the operating range of the RFID tag 110.

The RF transmitter 104 transmits RF signals to the RFID tag 110, and receives RF signals from the RFID tag 110, through the antenna 106. The data in the transmit signal 108 and the receive signal 112 may be contained in one or more bits for the purpose of supplying identification information or another relevant for the particular RFID tag application. When the RFID tag 110 passes within the range of the radiofrequency magnetic field emitted by the antenna 106, the RFID tag 110 is energized and transmits data to the RF interrogator 102. A change in the impedance of the RFID tag 110 can be used to signal the data for the RF interrogator 102 through the reception signal 112. The change of the impedance in the RFID tag 110 can be caused by the production of a short circuit through the antenna connections of the tag (not shown) in bursts of very short duration. The RF transceiver 104 detects the change in impedance as a change in the level of reflected or backscattered energy reaching the antenna. The digital electronic components 114, which may comprise a microprocessor with RAM, perform decoding and reading of the reception signal 112. Similarly, the digital electronic components 114 execute the encoding of the transmission signal 108. Therefore, the interrogator 102 facilitates the reading or writing of data for RFID tags, for example the RFID tag 110, which are within the range of the RF field emitted by antenna 104. Together, transceiver 104 and digital electronic components 114 comprise reader 118. Finally, digital electronic components 114 may be interfaced with an integral display and / or provide a serial or serial communication interface. parallel to a main computer or industrial controller, for example the main computer 1 16. A common method for increasing the range and controlling the area within which RFID tags 110 can operate is to switch between multiple antennas (not shown). Since the RF field strength of at least one of the antennas can be sufficient to feed the RFID tag 110, the range of the system can be increased in this way; however, there is a practical limit on the number of antennas 106 to which the RF transceiver 104 can be switched. The additional cable lengths required to generate spatial diversity between the antennas, together with the aggregate switching complexity required by the additional antennas, gives as a result a loss of energy for the antennas. With reduced energy, the operational range of the RFID tags 110 is reduced accordingly.

BRIEF DESCRIPTION OF THE INVENTION An RFID interrogator comprises an amplifier configured to amplify signals that are transmitted by the RFID interrogator. The RFID interrogator also comprises a deviation path for directing the received signals around the amplifier so that the amplifier does not block the reception of signals received from an RFID tag. These and other features, aspects and embodiments of the invention are described below in the section entitled "Detailed Description of the Preferred Modalities".

BRIEF DESCRIPTION OF THE DRAWINGS The features, aspects and embodiments of the inventions are described in conjunction with the accompanying drawings, in which: Figure 1 is a diagram showing an illustrative RFID system; Figure 2 is a diagram showing an illustrative RFID system configured in accordance with an embodiment of the invention; Figure 3 is a diagram showing an illustrative embodiment of an amplifier switch block included in the RFID system of Figure 2; Figure 4 is a diagram showing an illustrative RFID system comprising multiple amplifier switch blocks according to one embodiment of the invention; and Figure 5 is a flow chart illustrating an exemplary method for communication with an RFID tag using the system of Figure 2.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 2 shows an illustrative RFID interrogator 200 which is configured to use an amplifier 208 according to one embodiment of the systems and methods described herein. In the example of Figure 2, the amplifier 208, the energy director 212, and the RF return path 218, comprise an amplifier switch block 204. Therefore, the transceiver 202 can be configured to generate a transmission signal. 206 which can be passed to an amplifier 208 to produce the amplified transmission signal 210. The amplified transmission signal 210 can then be directed towards the antenna 214, to be transmitted outside the RFID tags 220. Therefore, when setting the gain amplifier 208 at an appropriate level, variation in the transmission ranges can be achieved without understanding the data classification. The amplifier 208 may even be a variable gain amplifier as explained in more detail below. However, briefly, the ability to vary the gain may allow the transmission range to be varied as required. As in a conventional RFID system, the RFID tag 220 may receive amplified radio transmission signal 229, encode the requisite data therein, and reflect the signal as radio reception signal 216. The radio reception signal 216 may be received by the antenna 214, which generally receives the reception signal 222. However, unlike a conventional RFID system, the reception signal 222 can not return to the transceiver 202 along the same path as the transmission signal 210 , due to the presence of the amplifier 208. Essentially, the amplifier 208 is a unidirectional device and can not allow the reception signal 222 to pass in another direction. Accordingly, the interrogator 202 also comprises an energy director 212 configured to allow the transmission signal 210 to pass from the amplifier 208 to the antenna 214, but also configured to direct the reception signal 222 around the amplifier 208 to a transceiver. RF 202 along the return path 218. Thus the power manager 212 is configured to pass a transmit signal 210 of a certain frequency from a transmit input port, and to pass a receive signal 222 of the same frequency from the antenna port to a receiving output port, while the transmission signal 210 is prevented from filtering on the return path 218 and the receiving signal 222 to be filtered over the transmission path. In a modality, for example, the energy director 212 comprises a circuitry. Circulators are well known and will not be described in detail herein. In another embodiment, the energy manager 212 may comprise a directional coupler, which are also well known and will not be described in detail herein. Figure 3 is a diagram illustrating an RF interrogator 300 comprising an amplifier switch block 204 illustrated in greater detail in accordance with one embodiment of the systems and methods described herein. In the embodiment of Fig. 3, the amplifier switch block 204 comprises an energy director 302, which is configured to act in much the same way as the energy director 212 (Fig. 2), as well as a power manager. energy 306. The inclusion of the power director 306 allows a common interface 318 with the RF transceiver 202 for the transmit and receive signals 206 and 222, respectively. Therefore, the RF transceiver 202 need not be redesigned to accommodate a separate return path 218 (FIG. 2). Accordingly, when a reception signal 222 is received, it is directed around an amplifier 208 via the energy director 302 to the energy director 306 through the return path 304. The energy director 306 can then be configured to direct the reception signal 222 to the RF transceiver 202 via the interface 318. Like the energy directors 302 and 212, the energy director 306 may be, for example, a circulator or a directional coupler. Essentially, the power director 306 will be able to direct a reception signal 222 from a reception port to an RF transceiver port while avoiding any undue filtering inside the amplifier 208. It will also be able to direct a signal of transmission 206 from the RF transceiver to a transmission port, without undue filtering to the receiving port. As mentioned before, the amplifier 208 can be a variable gain amplifier that allows the gain applied to the transmission signal 210 to be varied to achieve different ranges or other performance objectives. For example, as explained below, the RFID interrogator 300 may be placed in the interface with a plurality of antennas 214 through a plurality of switches configured to interface transmission signal 210 with the appropriate antenna 214; however, each time a device, for example, a switch, is placed in the transmission path there is an associated loss in transmission energy. Therefore, the gain of the amplifier 208 can be adjusted upward to explain the losses associated with devices placed in the transmission path such as switches configured to couple the transmission signal 210 with a plurality of antennas 214. In addition, the signal of Transmission radius 216 can be affected by interference, which can reduce the range in which the RFID 300 interrogator can operate. Often, such interference is variable and not predictable. Therefore, the gain of the amplifier 208 can not be adjusted only to explain the losses associated with the components inserted into the transmission path but also the losses associated with the interference that exists at any given time. Another interest is that the amplified signal 210 may exceed the maximum allowable for the energy output established by the regulatory bodies. Therefore, the gain of the amplifier 208 can be adjusted continuously to ensure that the maximum allowable are not exceeded. There are also other factors that can affect the energy level of the actual transmission signal 216 such as losses in the interfaces between the RF transceiver 202, the amplifier switch block 204 and the antenna 214. For example, the impedance of the antenna 214 must be matched to the interface impedance between the amplifier switch block 204 and the antenna 214. Any inequality in the impedance will result in signal energy losses. Accordingly, the gain of the amplifier 208 can be adjusted to explain any or all of the factors that affect the energy of the transmission signal of the transmission radio signal 216. Figure 3 illustrates a form for continuously adjusting the losses attributed to factors such as those described above. In the example of Figure 3, a small amount of RF energy is directed along path 316 and is feedback to control the gain of amplifier 208. In one implementation, a small portion of the energy is coupled to path 316 by means of the coupler 312 and rectified by the rectifier 310 to create a control voltage which is used by an energy leveling network 308 to control the gain of the amplifier 208. Therefore in an illustrative embodiment, a small portion of the energy in the transmission signal 210 can be coupled along the path 316 and used to create a control voltage which is in turn used by the power leveling network 308 to control the gain of the amplifier 208, ensuring that the level The energy of the transmission signal 210 does not exceed any of the legal limitations. In another implementation, a small portion of the energy signal in the reception signal 222 can be coupled to the path 316 and converted to a control voltage that can be used by the power leveling network 308 in order to control the gain of the amplifier 208 in a manner that would increase the range of the RFID 300 interrogator as required. For example, low reception signal energy levels may indicate that the RFID tag 220 is on an edge of the range of the RFID interrogator 300. Therefore, the energy leveling network 308 may, for example, be configured to compare the energy of the reception signal 222 with a predetermined threshold. When the signal energy falls below the threshold, the power leveling network 308 can be configured to determine that the RFID tag 220 is at an edge of the operating range of the RFID interrogator 300 and increases the gain of the amplifier 208 in response. The other way, as the energy level of the reception signal 222 is increased, the power leveling network 308 can be configured to reduce the gain of the amplifier 208. As can be seen, the gain of the amplifier 208 can be maintained in a optimal level to ensure the sufficient range of communication with all the RFID tags 220, while at the same time optimizing the energy consumed by the interrogator 300. In addition, the gain of the amplifier 208 can be monitored at the same time to ensure that it does not exceed any of legal limitations. Maintaining the optimal energy consumption through the gain control of the amplifier 208 may, for example, be important for portable applications that use batteries to power the RFID 300 interrogator. As mentioned above, the RFID 300 interrogator may be placed in interface with a plurality of antennas 214. For example, the RFID interrogator 300 could be placed in interface with a plurality of antennas through several switching mechanisms placed in the transmission path. Again, as mentioned before, each switching mechanism placed in the transmission path will reduce the transmission energy of the transmission signal 210. However, upon detecting the transmission power output by means of each antenna 214, the loss energy can be counteracted through controlled increases in the gain of the amplifier 208. The distance between the antenna 214 and the RFID interrogator 300 can also result in corresponding losses in the transmission energy of the transmission signal 210. For example, a antenna 214 is frequently placed in interface with the RFID interrogator 300 through a cable, such as a coaxial cable. A greater distance from the RFID interrogator 300 to where an antenna 214 is placed will require a longer cable length. Unfortunately, the longer the cable length, the greater the magnitude of the loss introduced by the cable. The inclusion of a feedback path such as the feedback path 316, can still work to counteract the effects of any loss. If the plurality of antennas 214 placed in interface with the RFID interrogator 300 increases beyond a certain point, then the ability to compensate for the losses introduced by any switching modules placed in the transmission path may be further complicated. One way to overcome this complication is to use multiple amplifier switch blocks 204 to interface the plurality of antennas with the RFID interrogator 300. For example, FIG. 4 illustrates an RFID system 400 comprising a plurality of amplifier switch blocks 402 of according to a modality of the systems and methods described herein. As can be seen the system 400 includes an RFID interrogator 300 placed in interface with a plurality of antennas 404 through a plurality of amplifier switch blocks 402. In other words, the plurality of antennas 404 are divided into smaller groups with each smaller group that is placed in interface with its own associated amplifier switch block 402. each amplifier switch block 402 could comprise a variable gain amplifier 408 as well as the energy director 410, the return path 416 and the director of energy 412 configured to direct the energy received by the antenna 404 around the amplifier 408 and back to the RF transceiver 202 within the interrogator 300. In addition, each amplifier switch block 402 may comprise a feedback cycle 406 configured to sense the energy of the signal at the output of the amplifier 408 and feedback it to control the gain of the amplifier 408. the output of the amplifier 408 can be placed in interface with the appropriate antenna 404 through a switching mechanism 418, which can, for example, be controlled by the RFID interrogator 300. Additionally, a switching mechanism can be placed between the interrogator 300 and a plurality of amplifier switch blocks 402 to control which amplifier switch block receives the transmit signal generated by the RFID interrogator 300. In fact, in certain embodiments each antenna 404 placed in interface with an amplifier switch block 402 receives a transmit signal generated by the associated amplifier 408. In other words, in certain embodiments , switching mechanisms 418 can be excluded. In embodiments using a large number of antennas, the ability to cascade amplifier switch blocks 402 can be important as they can reduce the number of RFID interrogators 300 required. Since interrogators 300 are often the most expensive component of an RFID system, the ability to reduce the number of RFID interrogators 300 required can therefore save substantial costs. In addition, the ability to promote the signal strength of the signals that are transmitted by each amplifier switch block402 can help increase the range and maintain performance, while at the same time ensuring that maximum energy levels are not exceeded. of transmission. Figure 5 is a flowchart of a method for sending RFID reception signals according to one embodiment of the systems and methods described herein. Therefore, in step 502, an RFID transmission signal can be generated. For example, the RFID transmission signal 206 can be generated by the RF transceiver 202. Then, in step 504 the transmission signal can be amplified, for example through an amplifier 208. The amplified transmission signal can then be transmitted. (step 516), for example, through an antenna 214; however, in certain embodiments, the energy of the transmission signal may be sampled in step 506. If the transmission energy is too high, as determined in step 508, it may then be reduced in step 510. For another In part, if it is determined that the transmission energy is too low, in step 512, then the transmission energy may be increased in step 514. In one embodiment, for example, a deflection path 316 may be included and may be configured to sample part of the energy in the transmission signal and to generate a control voltage that can be used to control the gain of the variable gain amplifier, such as the amplifier 208. In step 516, the amplified signal can be transmitted , for example, by means of an amplifier 214, in order to communicate with, or acquire information from, an RFID tag 220. In step 518, a reflex signal can be received. from an RFID tag 220. The reflected signal can then be directed around the amplifier used to amplify the transmission signal in step 504. While certain embodiments of the inventions have been described in the foregoing, it will be understood that the described modes they are only by way of example. Accordingly, while the modalities involving a forklift were described above, it will be clear that the systems and methods described herein apply equally to the tracking modes of a wide range of vehicles and articles. Therefore, the scope of the described inventions will be uniquely limited in light of the claims that follow when taken in conjunction with the foregoing description and the accompanying drawings.

Claims (16)

1. CLAIMS 1. An RFID interrogator, comprising: an antenna configured to transmit and receive signals; an amplifier configured to amplify a transmission signal; and an energy director coupled with the antenna and the amplifier, the power director configured to receive the amplified transmission signal from the amplifier and send the amplified transmission signal to the antenna, and to receive a reception signal from the antenna and direct the reception signal to a reception path.
2. 2. The RFID interrogator according to claim 1, characterized in that the antenna transmits signals to, and receives signals from, an RFID tag.
3. 3. The RFID interrogator according to claim 1, characterized in that the energy director comprises a director at the input of the amplifier, and a director at the output of the amplifier.
4. 4. The RFID interrogator according to claim 3, characterized in that the directors are circulators.
5. 5. The RFID interrogator according to claim 3, characterized in that the directors are directional couplers.
6. 6. The RFID interrogator according to claim 1, characterized in that the amplifier is a variable gain amplifier (VGA). The RFID interrogator according to claim 1, further comprising a feedback loop coupled with the output of the amplifier, the feedback loop configured to detect the output power from the amplifier and controlling the gain of the amplifier in response to the amplifier. output energy detected. 8. The RFID interrogator according to claim 7, characterized in that the feedback cycle maintains the transmit signal energy at or below a certain level. 9. The RFID interrogator according to claim 7, characterized in that the feedback cycle maintains the transmit signal energy at or above a certain level. 10. The RFID interrogator according to claim 7, characterized in that the feedback loop includes an energy coupler, a rectifier, and an energy leveling network. The RFID interrogator according to claim 1, characterized in that the energy director is coupled with an RF transceiver, configured to process the received signal. 12. The RFID interrogator according to claim 11, characterized in that the energy director is configured to direct the reception signal around the amplifier and towards the RF transceiver. The RFID interrogator according to claim 11, characterized in that the power manager is configured to direct the transmission signal from the RF transceiver to the amplifier and from the amplifier to the antenna. 14. The RFID interrogator according to claim 11, characterized in that the RF transceiver is configured to send the reception signal to a decoder. 15. The RFID interrogator according to claim 1, characterized in that the energy director is coupled with a switch, the switch configured to direct the transmission signal to one of the plurality of antennas. 16. The RFID interrogator according to claim 1, characterized in that the energy director is coupled with a plurality of switches, each of the plurality of switches configured to direct the transmission signal to one or more of the plurality of antennas. 18. The RFID interrogator according to claim 1, characterized in that the received signal contains data from the RFID tag. 19. A method for amplifying a transmission signal in an RFID interrogator, comprising: generating a transmission signal; amplify the transmission signal up to a certain energy level; and transmitting the amplified transmission signal to at least one RFID tag. The method according to claim 19, further comprising detecting the energy level of the amplified transmission signal and generating a control signal based on the detected energy level. The method according to claim 20, further comprising controlling the amplification of the transmission signal using the control signal. 22. The method according to claim 20, further comprising generating a voltage signal based on the detected energy level of the transmission signal and rectifying the voltage signal. The method according to claim 20, further comprising controlling the amplification of the transmission signal so that the energy level of the transmission signal is within certain limits. 24. The method according to claim 19, further comprising receiving a signal and routing the received signal around the amplifier by means of a deflection path. 25. An RFID interrogator system, comprising: a plurality of antennas configured to transmit and receive signals; and a plurality of amplifier switch blocks coupled with the plurality of antennas, each of the plurality of amplifier switch blocks comprising: an amplifier configured to amplify a transmission signal; and an energy director coupled with any of the plurality of antennas and the amplifier, the power manager configured to receive the amplified transmission signal from the amplifier and send the amplified transmission signal to the antennas, and to receive a reception signal from the antennas and direct the reception signal to a reception path. 26. The RFID interrogator system according to claim 25, characterized in that the plurality of antennas transmit signals to, and receive signals from, an RFID tag. 27. The RFID interrogator system according to claim 25, characterized in that the energy director comprises a director at the input of the amplifier, and a director at the output of the amplifier. 28. The RFID interrogator system according to claim 27, characterized in that the directors are circulators. 29. The RFID interrogator system according to claim 27, characterized in that the directors are directional couplers. 30. The RFID interrogator system according to claim 25, characterized in that the amplifier is a variable gain amplifier. 31. The RFID interrogator system according to claim 25, characterized in that each of the amplifier switch blocks further comprises a feedback loop coupled with the output of the amplifier, the feedback loop configured to detect the output power from the amplifier. and controlling the gain of the amplifier in response to the detected output power. 32. The RFID interrogator system according to claim 31, characterized in that the feedback cycle maintains the transmit signal energy at or below a certain level. 33. The RFID interrogator system according to claim 31, characterized in that the feedback loop includes an energy coupler, a rectifier and an energy leveling network. 34. The RFID interrogator system according to claim 25, characterized in that the energy director is coupled with an RF transceiver, configured to process the received signal. 35. The RFID interrogator system according to claim 34, characterized in that the energy director is configured to direct the reception signal around the amplifier and towards the RF transceiver. 36. The RFID interrogator system according to claim 33, characterized in that the power director is configured to direct the transmission signal from the RF transceiver to the amplifier and from the amplifier to the antenna. 37. The RFID interrogator system according to claim 33, characterized in that the RF transceiver is configured to send the reception signal to a decoder. 38. The RFID interrogator system according to claim 25, characterized in that the power manager is accommodated with a switch, the switch configured to direct the transmission signal to one of the plurality of antennas. 39. The RFID interrogator system according to claim 25, characterized in that the energy director is coupled with a plurality of switches, each of the plurality of switches configured to direct the transmission signal to one or more of the plurality of antennas . 40. The RFID interrogator system according to claim 25, characterized in that the transmission signal is transmitted to an RFID tag. 41. The RFID interrogator system according to claim 25, characterized in that the received signal contains data from an RFID tag.