WO2003081802A1 - Temperature sensitive radio frequency device - Google Patents

Temperature sensitive radio frequency device Download PDF

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Publication number
WO2003081802A1
WO2003081802A1 PCT/IB2003/001086 IB0301086W WO03081802A1 WO 2003081802 A1 WO2003081802 A1 WO 2003081802A1 IB 0301086 W IB0301086 W IB 0301086W WO 03081802 A1 WO03081802 A1 WO 03081802A1
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WO
WIPO (PCT)
Prior art keywords
radio frequency
temperature sensitive
frequency device
sensitive radio
antenna
Prior art date
Application number
PCT/IB2003/001086
Other languages
French (fr)
Inventor
Dirk Leman
Original Assignee
Melexis Nv
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Melexis Nv filed Critical Melexis Nv
Priority to AU2003215791A priority Critical patent/AU2003215791A1/en
Publication of WO2003081802A1 publication Critical patent/WO2003081802A1/en

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0716—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising a sensor or an interface to a sensor
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0701—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising an arrangement for power management
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0701—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising an arrangement for power management
    • G06K19/0715—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising an arrangement for power management the arrangement including means to regulate power transfer to the integrated circuit
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0723—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0723—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
    • G06K19/0726—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/077—Constructional details, e.g. mounting of circuits in the carrier
    • G06K19/0772—Physical layout of the record carrier
    • G06K19/0773—Physical layout of the record carrier the record carrier comprising means to protect itself against external heat sources

Definitions

  • the present invention relates to a radio frequency (RF) device which includes one or more elements e.g. a sensor, which are temperature sensitive.
  • RF radio frequency
  • a transceiver emits an RF field with predetermined known characteristics and when a suitable RF device which is responsive to the known characteristics of the field, for example in the form of a responder or tag, enters the field, it extracts sufficient energy from the RF field to power the device and can, if desired, initiate data transmission to the receiver.
  • data can be transmitted back to the transceiver and this data can be fixed, that is the data can simply serve merely to identify the existence or proximity of the radio frequency device to the transceiver, or alternatively, in more sophisticated applications, the data transmitted may be variable and may identify the device or any other parameter relating to any aspect of the device, its environment or any other device or sensor which is communicating with the RF device.
  • the data transmitted can also, if desired, be any combination of fixed and variable data.
  • a conventional radio frequency tag usually comprises an antenna to receive the radio frequency signal from the transceiver, means to extract power from the RF signal and may also include means to store and transmit data to the transceiver.
  • the antenna is conventionally formed by an antenna coil and a suitable capacitor and is tuned to the RF frequency at which the device is to operate by appropriate selection of the value of the variable capacitor.
  • the power extraction means operates to extract power from the signals in the antenna and rectifies these signals to provide a voltage supply to operate the radio frequency tag.
  • There may also be means within the radio frequency tag which variously stores the identity of the known characteristics of the radio frequency field, store fixed data for return transmission to the transceiver, generate variable data for return transmission to the transceiver and can also be configured to carry out any such timing and control functions as may be required to comply with any protocol or procedures as associated with the transmission and reception of the data.
  • the tag can also include fixed memory, non-volatile memory and may be interfaced to receive digital data, and interfaced to generate digital data from applied analogue signals and integral or co-packaged sensors generating such analogue signals.
  • the tag includes a temperature sensor which generates a signal indicative of a sensed temperature which can be transmitted back to the transceiver along with a tag identifying signal.
  • any heat dissipation within any of the components of the radio frequency device can introduce errors in the temperature measurement by locally heating the sensor. This is especially the case when components of the tag, including the sensor, are all embodied within the same integrated circuit of the radio frequency device.
  • the extraction of energy from the radio frequency signal from the transceiver and the rectification of the energy to form a suitable power supply voltage for the radio frequency device can also cause a problem.
  • a maximum operating distance between the transceiver and the radio frequency device is determined in part by the magnitude of the radio frequency field generated. If the radio frequency device is far from the transceiver then the magnitude to the radio frequency field will be low. The energy extracted at the radio frequency device will also be low and at the limit will generate a voltage too small to power the device and any required communication of data between the device and the transceiver will not be possible. If the radio frequency device is close to the transceiver, then the magnitude of the radio frequency field generated will be relatively high. The energy extracted from the field at the device will be correspondingly high and may generate a higher operating voltage for the device and cause a higher heat dissipation in the radio frequency device. This will give rise to an increase in temperature which can affect the temperature in the vicinity of the sensor or other temperature sensitive element and thereby introduce errors.
  • the present invention seeks to provide a temperature sensitive radio frequency device which overcomes or minimises the problems associated with RF devices of this type.
  • a temperature sensitive radio frequency device comprising an antenna to receive signals from a transceiver, tuning means to tune the antenna to a predetermined operational frequency and control means to control operation of the antenna and tuning means, said control means including energy limiting means connected to the antenna, monitoring means to monitor the energy absorbed by said energy limiting means from the antenna and tuning control means to control tuning of the tuning means whereby the tuning of the antenna can be varied to maintain energy absorption in said energy limiting means within a predetermined range.
  • the antenna comprises a conventional wound coil.
  • the antenna can be formed as part of an integrated circuit.
  • the tuning means preferably includes a variable capacitor whose value can be varied between predetermined limits determined by the total value of the capacitance of the capacitor.
  • the capacitor may have a capacitance value which may be made up by a combination of one or more fixed and or variable capacitor elements dependent upon the range of capacitance values required for the correct operation of the antenna device and RF device.
  • Any fixed capacitor elements used may be formed as standard discrete component capacitors and any variable capacitor elements used may comprise a plurality of conventional standard discrete component capacitors selectable to operate singly or in combination.
  • the fixed and or variable capacitor elements may be suitably configured as elements within an integrated circuit and, in this case, the total capacitance may be variable electronically.
  • the energy limiting device is preferably connected across the antenna device between the outputs thereof.
  • the energy limiting device preferably comprises a diode, most preferably a zener diode, and is arranged to conduct when the voltage across the terminals of the antenna device exceeds a predetermined value.
  • the current flowing in the energy limiting device is detected and the tuning control means may alter the selected value of the variable capacitor, if necessary, to alter the tuning of the antenna to maintain the energy absorbed by the energy limiting device to within a predetermined range.
  • the predetermined range is chosen such that values within that range such that unwanted heat dissipation does not occur in the RF device.
  • a data memory is provided, the data memory most preferably comprising fixed or non- volatile memory.
  • the data memory is preferably adapted to receive analogue or digital data from an external source.
  • the external source may be provided as part of the control means or may alternatively be provided as a separate external source to which the device is linked.
  • the external source may be a sensor such as for example a temperature sensor.
  • a power extraction circuit operable to extract from the signal sufficient energy to power the device.
  • FIG. 1 an RF device comprising an RF transponder, or a tag, which is in communication with a remote transceiver (not shown).
  • the tag comprises an antenna 101 to receive signals from the remote transceiver and an integrated circuit 100 which includes control circuitry to control operation of the tag.
  • control circuitry may be formed externally to the integrated circuit 100.
  • the control circuitry includes a variable capacitor 111, an energy limiting device 112 and tuning control circuit 103 linked to the variable capacitor 111 and a data memory 104 linked to the tuning control circuit 103.
  • a power extraction circuit 102 is also linked to the antenna 101 and the energy limiting device.
  • variable capacitor 111 may comprise any combination of fixed and/or variable capacitive elements as desired or as appropriate.
  • Each of the fixed and/or variable capacitive elements which make up the variable capacitor may be provided as discrete electronic components or may be provided as part of an integrated circuit.
  • the energy limiting device 112 comprises a diode and most preferably a zener diode.
  • the energy limiting device can be any other suitable device which is capable of operation above a predetermined threshold linked to a signal received from the antenna.
  • the power extraction 102 circuit is of conventional form and is operable to extract from the signal received by the antenna 101 sufficient energy to generate an electrical voltage sufficient to power the various components of the tag.
  • the tuning control circuit 103 operates to monitor the voltage received from the antenna 101 along with any modulation of that voltage which indicates the radio frequency field is originating from a transceiver to which the tag is expected to respond.
  • the data memory 104 can comprise any suitable memory such as for example fixed memory or non-volatile memory.
  • the data memory may be adapted to receive analogue or digital data from an external sensor such as for example a temperature sensor which can be provided either as part of the control circuitry i.e. as a part of the tag or may be provided as a separate external sensor to which the tag is linked.
  • a remote transceiver emits a radio frequency signal with predetermined known characteristics. If the tag is sufficiently close to the transceiver to detect this signal then the signal is detected by the antenna 101.
  • the power extraction circuit 102 generates a suitable voltage from the detected signal to power the components of the tag.
  • the tuning control circuit 103 will operate to detect the voltage received by the antenna 101 and will determine whether there is any modulation of that voltage. If there is modulation of that voltage, the tuning control circuit 103 will check whether the frequency or type of that modulation is such as to indicate that the signal has been received from a transceiver to which the tag is expected to respond.
  • the tuning control circuit 103 determines that the modulation is of such a kind that the tag should respond, the tuning control circuit is operable to cause the antenna 101 to transmit any data stored in the data memory or any other data generated by any sensor whether in the tag or communicated to the tag from an external source.
  • each of the component parts of the control circuitry 103 may in certain circumstances generate unwanted heat which can affect the operation of the tag and in particular, the operation of any temperature sensitive sensor or other element present in the tuning control circuitry 103.
  • the tag of the present invention is operable such that the energy limiting device 112 will only conduct once the voltage across the antenna 101 exceeds a predetermined value. When the voltage exceeds a predetermined value, the energy limiting device 112 will conduct and the current flowing in this energy limiting device 112 is detected by the tuning control circuitry 103.
  • the tuning control circuitry 103 will recognise that the amount of heat dissipated in the components of the tag will exceed an ideal value and may have an unwanted effect on the operation of the tag. In these circumstances the tuning control circuit 103 is operable to vary the value of the variable capacitor 111 thereby affecting the frequency at which the antenna 101 is operating. This in turn will reduce, or increase, dependant upon circumstances, the efficiency with which the antenna 101 will receive signals from the remote transceiver. Therefore, by de-tuning or tuning of the antenna by variation of the variable capacitor 111 value, it is possible to control the voltage which is applied across the energy limiting device 112 and therefore the current which is supplied to the components of the tag. In this way, the dissipation of heat within the components of the tag can be maintained within predetermined selected values.

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  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Near-Field Transmission Systems (AREA)
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Abstract

An RF transponder or tag comprises an antenna (101) to receive signals from a remote transceiver and an integrated circuit (100). The integrated circuit incorporates a variable capacitor (111), an energy limiting device (112), a tuning control circuit (103) linked to the variable capacitor and a data memory device (104). Power is provided by a power extraction circuit (102) adapted to extract energy from signals received by antenna (101). The energy limiting device (112) operates in conjunction with the tuning control circuit (103) to prevent unwanted heat dissipation occurring within the tag.

Description

TEMPERATURE SENSITIVE RADIO FREQUENCY DEVICE
The present invention relates to a radio frequency (RF) device which includes one or more elements e.g. a sensor, which are temperature sensitive.
Use of radio frequency transmission for communication with a remote device is known. In such systems, a transceiver emits an RF field with predetermined known characteristics and when a suitable RF device which is responsive to the known characteristics of the field, for example in the form of a responder or tag, enters the field, it extracts sufficient energy from the RF field to power the device and can, if desired, initiate data transmission to the receiver. Where radio frequency transmission is used, data can be transmitted back to the transceiver and this data can be fixed, that is the data can simply serve merely to identify the existence or proximity of the radio frequency device to the transceiver, or alternatively, in more sophisticated applications, the data transmitted may be variable and may identify the device or any other parameter relating to any aspect of the device, its environment or any other device or sensor which is communicating with the RF device. The data transmitted can also, if desired, be any combination of fixed and variable data.
A conventional radio frequency tag usually comprises an antenna to receive the radio frequency signal from the transceiver, means to extract power from the RF signal and may also include means to store and transmit data to the transceiver.
The antenna is conventionally formed by an antenna coil and a suitable capacitor and is tuned to the RF frequency at which the device is to operate by appropriate selection of the value of the variable capacitor. The power extraction means operates to extract power from the signals in the antenna and rectifies these signals to provide a voltage supply to operate the radio frequency tag. There may also be means within the radio frequency tag which variously stores the identity of the known characteristics of the radio frequency field, store fixed data for return transmission to the transceiver, generate variable data for return transmission to the transceiver and can also be configured to carry out any such timing and control functions as may be required to comply with any protocol or procedures as associated with the transmission and reception of the data. The tag can also include fixed memory, non-volatile memory and may be interfaced to receive digital data, and interfaced to generate digital data from applied analogue signals and integral or co-packaged sensors generating such analogue signals.
In one particular known application, the tag includes a temperature sensor which generates a signal indicative of a sensed temperature which can be transmitted back to the transceiver along with a tag identifying signal.
However, problems can arise with the use of known radio frequency devices which incorporate sensors or other elements which are temperature sensitive.
For example, whereas known devices can operate over a range of distances away from the transceiver, when the radio frequency tag contains a temperature sensitive element for example a sensor, intended to measure the temperature of the environment in which the radio frequency device is situated, any heat dissipation within any of the components of the radio frequency device can introduce errors in the temperature measurement by locally heating the sensor. This is especially the case when components of the tag, including the sensor, are all embodied within the same integrated circuit of the radio frequency device. Furthermore, the extraction of energy from the radio frequency signal from the transceiver and the rectification of the energy to form a suitable power supply voltage for the radio frequency device can also cause a problem. For example, a maximum operating distance between the transceiver and the radio frequency device is determined in part by the magnitude of the radio frequency field generated. If the radio frequency device is far from the transceiver then the magnitude to the radio frequency field will be low. The energy extracted at the radio frequency device will also be low and at the limit will generate a voltage too small to power the device and any required communication of data between the device and the transceiver will not be possible. If the radio frequency device is close to the transceiver, then the magnitude of the radio frequency field generated will be relatively high. The energy extracted from the field at the device will be correspondingly high and may generate a higher operating voltage for the device and cause a higher heat dissipation in the radio frequency device. This will give rise to an increase in temperature which can affect the temperature in the vicinity of the sensor or other temperature sensitive element and thereby introduce errors. The present invention seeks to provide a temperature sensitive radio frequency device which overcomes or minimises the problems associated with RF devices of this type.
Thus and in accordance with the present invention therefore there is provided a temperature sensitive radio frequency device comprising an antenna to receive signals from a transceiver, tuning means to tune the antenna to a predetermined operational frequency and control means to control operation of the antenna and tuning means, said control means including energy limiting means connected to the antenna, monitoring means to monitor the energy absorbed by said energy limiting means from the antenna and tuning control means to control tuning of the tuning means whereby the tuning of the antenna can be varied to maintain energy absorption in said energy limiting means within a predetermined range.
With this arrangement it is possible to provide a temperature sensitive RF device which is less prone to inaccuracies during operation due to internal heat dissipation.
Preferably the antenna comprises a conventional wound coil. Alternatively, the antenna can be formed as part of an integrated circuit.
The tuning means preferably includes a variable capacitor whose value can be varied between predetermined limits determined by the total value of the capacitance of the capacitor.
The capacitor may have a capacitance value which may be made up by a combination of one or more fixed and or variable capacitor elements dependent upon the range of capacitance values required for the correct operation of the antenna device and RF device. Any fixed capacitor elements used may be formed as standard discrete component capacitors and any variable capacitor elements used may comprise a plurality of conventional standard discrete component capacitors selectable to operate singly or in combination. Alternatively, the fixed and or variable capacitor elements may be suitably configured as elements within an integrated circuit and, in this case, the total capacitance may be variable electronically.
The energy limiting device is preferably connected across the antenna device between the outputs thereof. The energy limiting device preferably comprises a diode, most preferably a zener diode, and is arranged to conduct when the voltage across the terminals of the antenna device exceeds a predetermined value. The current flowing in the energy limiting device is detected and the tuning control means may alter the selected value of the variable capacitor, if necessary, to alter the tuning of the antenna to maintain the energy absorbed by the energy limiting device to within a predetermined range. The predetermined range is chosen such that values within that range such that unwanted heat dissipation does not occur in the RF device.
Preferably, a data memory is provided, the data memory most preferably comprising fixed or non- volatile memory.
The data memory is preferably adapted to receive analogue or digital data from an external source. The external source may be provided as part of the control means or may alternatively be provided as a separate external source to which the device is linked. Typically the external source may be a sensor such as for example a temperature sensor.
In order that the device is able to operate, preferably a power extraction circuit is provided, operable to extract from the signal sufficient energy to power the device.
The invention will now be described further by way of example only and with reference to the accompanying drawings, a single figure of which shows the schematic representation of one embodiment of temperature sensitive RF device in accordance with the present invention. Referring now to figures there is shown in Figure 1 an RF device comprising an RF transponder, or a tag, which is in communication with a remote transceiver (not shown). The tag comprises an antenna 101 to receive signals from the remote transceiver and an integrated circuit 100 which includes control circuitry to control operation of the tag. However, in alternative embodiments one or more of the components of the control circuitry may be formed externally to the integrated circuit 100.
The control circuitry includes a variable capacitor 111, an energy limiting device 112 and tuning control circuit 103 linked to the variable capacitor 111 and a data memory 104 linked to the tuning control circuit 103. A power extraction circuit 102 is also linked to the antenna 101 and the energy limiting device.
The variable capacitor 111 may comprise any combination of fixed and/or variable capacitive elements as desired or as appropriate. Each of the fixed and/or variable capacitive elements which make up the variable capacitor may be provided as discrete electronic components or may be provided as part of an integrated circuit.
The energy limiting device 112 comprises a diode and most preferably a zener diode. Alternatively, the energy limiting device can be any other suitable device which is capable of operation above a predetermined threshold linked to a signal received from the antenna.
The power extraction 102 circuit is of conventional form and is operable to extract from the signal received by the antenna 101 sufficient energy to generate an electrical voltage sufficient to power the various components of the tag.
The tuning control circuit 103 operates to monitor the voltage received from the antenna 101 along with any modulation of that voltage which indicates the radio frequency field is originating from a transceiver to which the tag is expected to respond.
The data memory 104 can comprise any suitable memory such as for example fixed memory or non-volatile memory. The data memory may be adapted to receive analogue or digital data from an external sensor such as for example a temperature sensor which can be provided either as part of the control circuitry i.e. as a part of the tag or may be provided as a separate external sensor to which the tag is linked.
In use, a remote transceiver emits a radio frequency signal with predetermined known characteristics. If the tag is sufficiently close to the transceiver to detect this signal then the signal is detected by the antenna 101. The power extraction circuit 102 generates a suitable voltage from the detected signal to power the components of the tag. The tuning control circuit 103 will operate to detect the voltage received by the antenna 101 and will determine whether there is any modulation of that voltage. If there is modulation of that voltage, the tuning control circuit 103 will check whether the frequency or type of that modulation is such as to indicate that the signal has been received from a transceiver to which the tag is expected to respond. If the tuning control circuit 103 determines that the modulation is of such a kind that the tag should respond, the tuning control circuit is operable to cause the antenna 101 to transmit any data stored in the data memory or any other data generated by any sensor whether in the tag or communicated to the tag from an external source.
As previously explained, each of the component parts of the control circuitry 103 may in certain circumstances generate unwanted heat which can affect the operation of the tag and in particular, the operation of any temperature sensitive sensor or other element present in the tuning control circuitry 103. In order to address this problem, the tag of the present invention is operable such that the energy limiting device 112 will only conduct once the voltage across the antenna 101 exceeds a predetermined value. When the voltage exceeds a predetermined value, the energy limiting device 112 will conduct and the current flowing in this energy limiting device 112 is detected by the tuning control circuitry 103. If the current flow detected is above a predetermined value then the tuning control circuitry 103 will recognise that the amount of heat dissipated in the components of the tag will exceed an ideal value and may have an unwanted effect on the operation of the tag. In these circumstances the tuning control circuit 103 is operable to vary the value of the variable capacitor 111 thereby affecting the frequency at which the antenna 101 is operating. This in turn will reduce, or increase, dependant upon circumstances, the efficiency with which the antenna 101 will receive signals from the remote transceiver. Therefore, by de-tuning or tuning of the antenna by variation of the variable capacitor 111 value, it is possible to control the voltage which is applied across the energy limiting device 112 and therefore the current which is supplied to the components of the tag. In this way, the dissipation of heat within the components of the tag can be maintained within predetermined selected values.
It will be appreciated that with the arrangement of the present invention, it is possible to reduce the possibilities for interference with any temperature sensitive device or element which is provided within the tag, or associated therewith, of heat dissipation within the components of the tag itself.
It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which is described by way of example only.

Claims

1. A temperature sensitive radio frequency device comprising an antenna to receive signals from a transceiver, tuning means to tune the antenna to a predetermined operational frequency and control means to control operation of the antenna and tuning means, said control means including energy limiting means connected to the antenna, monitoring means to monitor the energy absorbed by said energy limiting means from the antenna and tuning control means to control tuning of the tuning means whereby the tuning of the antenna can be varied to maintain energy absorption in said energy limiting means within a predetermined range.
2. A temperature sensitive radio frequency device according to claim 1 wherein the antenna comprises a conventional wound coil.
3. A temperature sensitive radio frequency device according to claim 1 or claim 2 wherein the antenna is formed as part of an integrated circuit.
4. A temperature sensitive radio frequency device according to any preceding claim wherein the tuning means preferably includes a variable capacitor whose value can be varied between predetermined limits.
5. A temperature sensitive radio frequency device according to claim 4 wherein the capacitor has a capacitance value which is made up of a combination of one or more capacitor elements.
6. A temperature sensitive radio frequency device according to claim 5 wherein said capacitor elements include one or more fixed value capacitor elements.
7. A temperature sensitive radio frequency device according to claim 6 wherein said capacitor elements include one or more variable capacitor elements.
8. A temperature sensitive radio frequency device according to any of claims 5 to 7 wherein any fixed value capacitor elements used comprise standard discrete component capacitors
9. A temperature sensitive radio frequency device according to claim 7 or claim 8 wherein said variable capacitor elements comprise a plurality of conventional standard discrete component capacitors selectable to operate singly or in combination.
10. A temperature sensitive radio frequency device according to any of claims 5 to 9 wherein the capacitor elements are configured as elements within an integrated circuit.
11. A temperature sensitive radio frequency device according to claim 10 wherein the total capacitance is variable electronically.
12. A temperature sensitive radio frequency device according to any preceding claim wherein the energy limiting device is connected across the antenna between the outputs thereof.
13. A temperature sensitive radio frequency device according to any preceding claim wherein the energy limiting device comprises a diode.
14. A temperature sensitive radio frequency device according to claim 13 wherein the energy limiting device comprises a zener diode.
15. A temperature sensitive radio frequency device according to any . preceding claim wherein the energy limiting device is arranged to conduct when the voltage across the terminals of the antenna device exceeds a predetermined value.
16. A temperature sensitive radio frequency device according to any preceding claim wherein the tuning control means is operative to alter the selected value of the variable capacitor in response to variations in the current flowing in the energy limiting device.
17. A temperature sensitive radio frequency device according to any preceding claim wherein the tuning control means operates to maintain the energy absorbed by the energy limiting device to within a predetermined range.
18. A temperature sensitive radio frequency device according to any preceding claim wherein the predetermined range is chosen such that values within that range such that unwanted heat dissipation does not occur in the RF device.
19. A temperature sensitive radio frequency device according to any preceding claim wherein a data memory is provided.
20. A temperature sensitive radio frequency device according to claim 19 wherein the data memory comprises fixed or non- volatile memory
21. A temperature sensitive radio frequency device according to claim 19 or claim 20 wherein the data memory is adapted to receive analogue or digital data from an external source.
22. A temperature sensitive radio frequency device according to claim 21 wherein said external source is provided as part of the control means.
23. A temperature sensitive radio frequency device according to claim 22 wherein said external source is provided as a separate external source to which the device is linked.
24. A temperature sensitive radio frequency device according to claim 23 wherein said external source is a temperature sensor.
25. A temperature sensitive radio frequency device according to any preceding claim wherein a power extraction circuit is provided, operable to extract from the signal received by the antenna sufficient energy to power the device.
PCT/IB2003/001086 2002-03-25 2003-03-25 Temperature sensitive radio frequency device WO2003081802A1 (en)

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EP4095755A1 (en) * 2021-05-29 2022-11-30 Nxp B.V. Rfid tag self tuning
FR3136121A1 (en) * 2022-05-25 2023-12-01 Stmicroelectronics Sa Remotely powered contactless card

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EP4095755A1 (en) * 2021-05-29 2022-11-30 Nxp B.V. Rfid tag self tuning
FR3136121A1 (en) * 2022-05-25 2023-12-01 Stmicroelectronics Sa Remotely powered contactless card

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