AU2008101062A4 - Radio Frequency Identification Reader Automatic Tuning Using Frequency Feedback - Google Patents
Radio Frequency Identification Reader Automatic Tuning Using Frequency Feedback Download PDFInfo
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- AU2008101062A4 AU2008101062A4 AU2008101062A AU2008101062A AU2008101062A4 AU 2008101062 A4 AU2008101062 A4 AU 2008101062A4 AU 2008101062 A AU2008101062 A AU 2008101062A AU 2008101062 A AU2008101062 A AU 2008101062A AU 2008101062 A4 AU2008101062 A4 AU 2008101062A4
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Description
30/10 2008 16:13 FAX 64 8 9148760 JAMES WELLS: AUCKLAND I005/022 James Wells Ref: 233302AU/61 LR 00 0 0 't RADIO FREQUENCY IDENTIFICATION READER AUTOMATIC TUNING USING FREQUENCY FEEDBACK TECHNICAL FIELD The present invention relates to Radio Frequency Identification readers and, in 0 particular, to a Radio Frequency Identification reader with automatic antenna 0 tuning allowing the Radio Frequency Identification reader to automatically adjust to 00 Svariations in the operating environment of the Radio Frequency Identification reader.
BACKGROUND ART In recent years Radio Frequency Identification (RFID) systems have become very popular. Such RFID systems include a large number of tags or transponders, and readers for reading the tags. Each tag emits a unique identifier when excited by one of the readers. By associating the tags with respective articles, such articles can be uniquely identified.
A need exists to increase the range between the reader and the tag to be read, while still reliably reading the unique identifier of that tag. An important element in determining the range is the antenna system of the RFID reader, as the antenna system is the element which transfers energy from the reader to the tag, and also receives a reply signal, including the unique identifier, from the tag. In order to transfer the maximum amount of energy from an excitation circuit of the RFID reader to its antenna system, the antenna system should be tuned to resonate at the frequency of excitation by the excitation circuit.
However, it is known that metals in proximity to the antenna system of the RFID 1 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:13 FAX 64 8 9146760 JAMES 8 WELLS: AUCKLAND l006/022 James Wells Ref: 233302AU/61 LR 00 Sreader adversely affect the performance of the reader. This is because proximity O to metals effectively lowers the antenna system's inductance, which in turn causes o an increase in resonant frequency and also a reduction in the quality factor of the antenna system. Temperature drift of circuit components may have a similar C 5 effect.
SA need therefore exists for automatically adjusting the reader to compensate for 00 variations in the operating environment of the reader.
0 0 A prior art technique used is "Amplitude Tuning", where the amplitude of the antenna system is measured and a digital capacitor bank is varied such that maximum amplitude is obtained. This technique however often requires a full sweep, or multiple stepping, of the capacitor bank to determine maximum amplitude and tune direction, causing the prior art tuning mechanism to be slow.
Other prior art techniques use mechanisms such as comparing the phase of the carrier frequency with the phase in the antenna system, or measuring the frequency received from the RFID tag, and adjusting the capacitor bank such that the difference between both is minimised. Due to circuit complexity and the processing of very small signal levels these techniques can reduce the signal to noise ratio hence reducing the performance of the RFID reader.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
All references, including any patents or patent applications cited in this specification, are hereby incorporated by reference. No admission is made that 2 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30110 2008 16:.13 FAX 64 8 8146760 JMS6YEL:ACLN 0/2 JAMES WELLS: AUCKLAND IR1007/022 James Weils Ref: 233302AU/61 LR 00 any reference constitutes prior art. The discussion of the reference states what o their authors assert, and the applicants reserve the right to challenge the accuracy 0 and pertinency of the cited documents. It will be clearly understood that, although prior art may be referred to herein, this reference does not constitute an admission that such prior art forms part of the common general knowledge in the art, in 0 Australia or in any other country.
00 It Is acknowledged that the term 'comprise' may, under varying jurisdictions, be o attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or comprising' is used in relation to one or more steps in a method or process.
DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a method performed in a Radio Frequency Identification reader, said method comprising the steps of: i) exciting an antenna resonant circuit with a carrier frequency signal; ii) removing said carrier frequency signal from said antenna resonant circuit; iii) measuring an oscillation frequency in said antenna resonant circuit; iv) comparing said oscillation frequency with the frequency of said carrier frequency signal; and v) adjusting one or more elements in said antenna resonant circuit based 3 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:14 FAX 64 8 8146760 JAMES WELLS: AUCKLAND I]008/022 James Wells Ref: 233302AU/61 LR 00 upon the result of said comparing step.
0 According to another aspect of the present invention there is provided a Radio en Frequency Identification reader comprising: i) means for exciting an antenna resonant circuit with a carrier frequency signal; ii) means for removing said carrier frequency signal from said antenna Sresonant circuit; iii) means for measuring an oscillation frequency in said antenna resonant circuit; iv) means for comparing said oscillation frequency with the frequency of said carrier frequency signal; and v) means for adjusting one or more elements in said antenna resonant circuit based upon the result of said comparing step.
Other aspects of the invention are also disclosed.
BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Fiqure 1 shows a schematic block diagram of a Radio Frequency Identification reader in accordance with a preferred embodiment of the present invention; 4 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:14 FAX 64 9 8146760 JAMES WELLS: AUCKLAND 1]008/022 James Wells Ref: 233302AU/61 LR 00 ci SFigure 2 shows voltage as measured at the input of a squarer of the Radio SFrequency Identification reader of Figure 1 and a state of a RF cycle c signal when the resonant frequency of the antenna resonant circuit of the RFID member is equalised;
I\N
Figure 3 shows the voltage and state of Figure 2 when the resonant frequency of an antenna resonant circuit of the Radio Frequency 00 SIdentification reader is not equalised with a carrier frequency; and Figure 4 shows the voltage and state of Figure 3, an "open" signal provided to a gate circuit of the Radio Frequency Identification reader, and a digital signal output by the gate circuit.
DETAILED DESCRIPTION Where reference is made in any one or more of the accompanying drawings to steps and/or features which have the same reference numerals, those steps and/or features have, for the purposes of this description, the same function(s) or operation(s) unless the contrary intention appears.
Figure 1 shows a schematic block diagram of a Radio Frequency Identification (RFID) reader 100 in accordance with a preferred embodiment of the present invention. The RFID reader 100 forms part of an RFID system including the RFID reader 100 and a number of tags (not illustrated). The reader 100 initiates wireless communication between respective tags and the reader 100 to enable reading and/or writing to the tags.
Each tag generally includes a resonant circuit and a processor circuit, with the resonant circuit having a predetermined resonant frequency.
COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:14 FAX 64 3 8146760 JAMES S WELLS: AUCKLAND @1010/022 James Wells Ref: 233302AU/61 LR 00 0
O
0 The reader 100 includes a microprocessor 102 which controls the operations of the reader 100, an antenna resonant circuit 151, an excitation circuit 150 for providing c an excitation signal to the antenna resonant circuit 151, and a measurement circuit 152 for measuring the oscillation frequency of the antenna resonant circuit 151.
IN
o 5 The excitation circuit 150 includes a crystal oscillator 101 which outputs a signal o 111 at a crystal frequency. The excitation circuit 150 also includes control logic 00 0 103 which receives as inputs the signal 111 from the crystal oscillator 101, and a C0 radio frequency (RF) cycle signal 112 from the microprocessor 102, and provides as output a digital signal 113. The RF cycle signal 112 is an "ON/OFF" signal which controls when the antenna resonant circuit 151 is excited. Typically, the RF cycle signal 112 is in an ON state for 50ms to 100ms, followed by an OFF state for 3ms or 20ms. However, these range of times for each state should not be seen as a limitation on the embodiments envisaged for this invention. Other times outside these ranges including isometric values could conceivably be used with this invention. The control logic 103 divides the signal 111 from the crystal oscillator 101 to a carrier (nominal) frequency, which is typically 125kHz or 134.2kHz. The digital signal 113 is the carrier frequency amplitude modulated by the RF cycle signal 112. The excitation circuit 150 also includes an RF power stage 104 which receives as input the digital signal 113, and converts the digital signal 113 to an amplified sine wave source with specific output impedance. The amplified sine wave source drives the antenna resonant circuit 151.
The antenna resonant circuit 151 includes a coil antenna 161 connected in parallel to a capacitor 162. The amplified sine wave source output by the RF power stage 104 causes the antenna 161 to emit a magnetic field required to excite RFID tags.
The inductance value of the coil antenna 161 and the capacitance value of the 6 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:14 FAX 64 9 9146780 JAMES WELLS: AUCKLAND 2~011/022 James Wells Ref: 233302AU161 LR 00 capacitor 162 determines a resonant frequency of the antenna resonant circuit o151. However, as the inductance value of the coil antenna 161 and the 0 capacitance value of the capacitor 162 are affected by external factors including temperature and proximity of metal objects, the resonant frequency of the antenna resonant circuit 151 changes, 2 Also provided is a "digital capacitor bank" 154 connected in parallel to the coil 00 antenna 101 and the capacitor 162. The digital capacitor bank 154 includes a 0 number of parallel connected capacitors 163-1 to 163-N, each of which is selectively, under control from the microprocessor 102, connectable to the coil antenna 161 and the capacitor 162. By connecting one or more of the capacitors 163-n in parallel to the coil antenna 161 and the capacitor 162, the resonant frequency of the antenna resonant circuit 151 is altered.
The measurement circuit 152 includes an over-voltage protected squarer 107, or zero crossing comparator, connected to the antenna resonant circuit 151. A gate circuit 110 receives as input the output of the squarer 107, and produces a digital signal 115 with identical frequency to the actual resonant frequency of the antenna resonant circuit 151 when an "open" signal 116 is received from the microprocessor 102. The gate circuit 110 is opened by the microprocessor 102 shortly after the RF cycle signal 112 has switched to the OFF state and for a given time so that only the digital signal representing the resonant frequency is passed through to the microprocessor 102. It should be appreciated by 'those skilled in the art' that the microprocessor 102 may be a Digital Signal Processor (DSP) or similar device.
The signal 115 allows the microprocessor 102 to determine the resonant frequency of the antenna resonant circuit 151. The microprocessor 102 then compares the 7 COMS ID No: ARCS-211684 Received by IP Australia: lime 15:19 Date 2008-10-30 30/10 2008 16:14 FAX 64 9 9146760 JAMES 8 WELLS: AUCKLAND I]012/022 James Wells Ref: 233302AU/61 LR 00
O
determined resonant frequency of the antenna resonant circuit 151 with the carrier O frequency, and determines a capacitance value for the digital capacitor bank 154 in 0 an attempt to equalise the resonant frequency of the antenna resonant circuit 151 and the carrier frequency. More particularly, one or more of the switches 164-n are Cl 5 open or closed to affect a change in the total capacitance of the digital capacitor Va Sbank 154.
0 00 In an alternative implementation the "tuning" of the digital capacitor bank 154 is o performed iteratively. The microprocessor 102 determines the resonant frequency of the antenna resonant circuit 151 after each cycle in which the antenna 161 is excited, compares that resonant frequency with the nominal carrier frequency, and controls the digital capacitor bank 154 to increase or decrease its capacitance until minimum (or zero) difference between the frequencies is achieved. A non-linear or derivative function after the difference value is obtained is preferably implemented to reduce the time required to reach the minimum difference.
The total combined capacitance of the digital capacitor bank 154 is determined in conjunction with the antenna capacitor 162 such that the digital capacitor bank 1,54 will compensate for the worst possible total change in frequency caused by metal objects in the vicinity of the antenna 161 and change of component values due to changing operating temperatures. To reduce the number of capacitor 163-n switch 164-n combinations in the digital capacitor bank 154, as well as control lines 155 from the microprocessor 102 to the switches 164-n. the capacitors 162-n are preferably binary weighted the values of the capacitors 162-n are multiples of a base value).
The microprocessor 102 stores the states of the switches 164-n, and preferably adjusts the capacitance of the digital capacitor bank 154 each RF cycle 8 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:.14 FAX 64 3 9146760JAE &YLS: UCANIj01/2 JAMES WELLS". AUCKLAND [a 0 13/022 James Wells Ref: 233302AU161 LR 00 (approximately every S0ms to lO0ms), and includes signal redundancy and safety Q margins. Further functions are performed by the microprocessor 102 in order to 0 obtain a fully functional RFID Reader 100 as would be understood by a person skilled in the art.
Figure 2 shows the voltage 201 as measured at the input of squarer l07- Also 2 shown in Figure 2 is the state 202 of RF cycle signal 112 (Figure 1) output by 00 microprocessor 102. While the state 202 of the RIF cycle signal 112 is high (or 0 o the frequency of the voltage 201 is determined by the signal Ill (Figure 1) derived from the output of the crystal oscillator 101. Accordingly, while the state 202 of the RIF cycle signal 112 is high, the frequency of the voltage 201 is the carrier frequency. Once the state 202 of the RF cycle signal 112 goes to low (or the frequency of the voltage 201 Is determined by the resonant frequency of the antenna resonant circuit 151. For this reason, the resonant frequency of the antenna resonant circuit 151 is measured from the oscillating (and decaying) cycles following excitation of the antenna resonant circuit 151, and preferably immediately after the state 202 goes to a low state.
The above assumes that the antenna resonant circuit 151 has a given quality factor that allows the antenna resonant circuit 151 to continue to resonate for some time after the excitation signal 113 has been removed. Most RFlD readers are using tuned antenna resonant circuits with reasonable 0 to amplify the antenna current (thereby increasing the emitted magnetic field), and reduce the harmonic content of the transmitted signal and contribute to the required filtering of the received signal.
The above also requires excitation of the antenna resonant circuit 151I to cease, as is regulated by the IS01 1785 standards. In situations where it is not mandatory for 9 COMS ID No: ARCS-21 1684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:14 FAX 64 8 8146760 JAMES WYELLS.' AUCKLAND R~014/022 James Wells Ref. 233302AU/61 LR 00 the excitation of the antenna resonant circuit 151 to cease, the present invention o may be applied with the RF cycle signal 112 going to low for a very short period, allowing the resonant frequency to be measured.
Figure 3 also shows the voltage 201 as measured at the input of squarer 107 and INO 5 the state 202 of RF cycle signal 112, but before the resonant frequency of the antenna resonant circuit 151 is equalised with the carrier frequency. Due to the 00 mismatch of the resonant and carrier frequencies, the voltage 201 is lower that the 0 corresponding period shown in Figure 2.
Figure 4 shows the voltage 201 as measured at the input of squarer 107. the state 202 of RF cycle signal 112, the 'open" signal 116 provided by the microprocessor 102 as input to the gate circuit 110. and digital signal 115 output by the gate circuit 110.
Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.
The preferred embodiment described above includes capacitor 162 and coil antenna 161 arranged in parallel. "flowever. as would be understood by persons in the art, other coil antenna-capacitor configurations in combination with means for adjusting the resonant frequency of that configuration are feasible.
For example, the digital capacitor bank 154 may be placed in series with capacitor 162 in which case at least one switch 164-n remains in a closed state.
Alternatively, the digital capacitor bank 154 may be replaced by a digital inductor bank (not illustrated) in parallel or in series with the coil antenna 161.
The described invention may also be applied to RFID readers using a series COMS ID No: ARCS-21 1684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 18:14 FAX 64 9 9146760 JAMES WELLS: AUCKLAND R015/022 James Wells Ref: 233302AU/61 LR 00
O
0 resonant antenna system where a digital capacitor bank is switched in parallel or in 0 O series to series antenna inductor-capacitor configuration. Again, the digital Scapacitor bank may be replaced by a digital inductor bank in parallel or in series with the antenna inductor-capacitor configuration.
O 00 00 0 11 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30
Claims (3)
- 2. A method performed in a radio frequency identification as claimed in claim 1, wherein the carrier frequency signal is in an ON state for 50 ms to 100 ms followed by an OFF state for 3 ms or 20 ms.
- 3. A radio frequency identification reader comprising: i) means for exciting an antenna resonant circuit with a carrier frequency signal; ii) means for removing said carrier frequency signal from said antenna resonant circuit; iii) means for measuring an oscillation frequency in said antenna resonant circuit; iv) means for comparing said oscillation frequency with the frequency of 12 COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30 30/10 2008 16:15 FAX 64 9 9146760 JAMES WELLS: AUCKLAND @1017/022 James Wells Ref: 233302AU/61 LR 00 O said carrier frequency signal; and o v) means for adjusting one or more elements in said antenna resonant O circuit based upon the result of said comparing step. 0
- 4. A method performed in a radio frequency identification reader substantially as herein described with reference to and as illustrated by the Va Saccompanying drawings. 0 A radio frequency identification reader substantially as herein described 00 0 with reference to and as illustrated by the accompanying drawings. EDIT ID LIMITED by its authorised agents JAMES WELLS INTELLECTUAL PROPERTY COMS ID No: ARCS-211684 Received by IP Australia: Time 15:19 Date 2008-10-30
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NZ56304107 | 2007-10-31 | ||
| NZ563041 | 2007-10-31 |
Publications (1)
| Publication Number | Publication Date |
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| AU2008101062A4 true AU2008101062A4 (en) | 2008-11-27 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2008101062A Expired AU2008101062A4 (en) | 2007-10-31 | 2008-10-30 | Radio Frequency Identification Reader Automatic Tuning Using Frequency Feedback |
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| AU (1) | AU2008101062A4 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101902234A (en) * | 2009-05-28 | 2010-12-01 | 卡西欧计算机株式会社 | Radio wave receiver |
| GB2470825A (en) * | 2009-06-03 | 2010-12-08 | Casio Computer Co Ltd | Tuning a receiver antenna tank circuit |
| US8358985B2 (en) | 2009-01-14 | 2013-01-22 | Casio Computer Co., Ltd. | Radio wave receiving apparatus |
| CN108063605A (en) * | 2014-03-14 | 2018-05-22 | 谐振公司 | The method of radio-frequency filter and tuned radio frequency wave filter |
| WO2022063550A1 (en) | 2020-09-23 | 2022-03-31 | Saint-Gobain Glass France | Insulating glazing unit and glazing |
-
2008
- 2008-10-30 AU AU2008101062A patent/AU2008101062A4/en not_active Expired
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8358985B2 (en) | 2009-01-14 | 2013-01-22 | Casio Computer Co., Ltd. | Radio wave receiving apparatus |
| CN101902234A (en) * | 2009-05-28 | 2010-12-01 | 卡西欧计算机株式会社 | Radio wave receiver |
| GB2470656A (en) * | 2009-05-28 | 2010-12-01 | Casio Computer Co Ltd | Tuning a receiver antenna tank circuit |
| GB2470656B (en) * | 2009-05-28 | 2011-10-12 | Casio Computer Co Ltd | Radio wave receiver |
| US8428531B2 (en) | 2009-05-28 | 2013-04-23 | Casio Computer Co., Ltd. | Radio wave receiver |
| CN101902234B (en) * | 2009-05-28 | 2013-05-08 | 卡西欧计算机株式会社 | Radio wave receiver |
| GB2470825A (en) * | 2009-06-03 | 2010-12-08 | Casio Computer Co Ltd | Tuning a receiver antenna tank circuit |
| GB2470825B (en) * | 2009-06-03 | 2011-12-07 | Casio Computer Co Ltd | Radio wave receiver |
| US8270922B2 (en) | 2009-06-03 | 2012-09-18 | Casio Computer Co., Ltd. | Radio wave receiver |
| CN108063605A (en) * | 2014-03-14 | 2018-05-22 | 谐振公司 | The method of radio-frequency filter and tuned radio frequency wave filter |
| CN108063605B (en) * | 2014-03-14 | 2022-01-18 | 谐振公司 | Radio frequency filter and method for tuning radio frequency filter |
| WO2022063550A1 (en) | 2020-09-23 | 2022-03-31 | Saint-Gobain Glass France | Insulating glazing unit and glazing |
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Legal Events
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| FGI | Letters patent sealed or granted (innovation patent) | ||
| PC | Assignment registered |
Owner name: TRU-TEST LIMITED Free format text: FORMER OWNER WAS: EDIT ID LIMITED |
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| MK22 | Patent ceased section 143a(d), or expired - non payment of renewal fee or expiry |