U.S. patent application number 17/548981 was filed with the patent office on 2022-03-31 for circuit for wireless data transfer comprising temperature regulation.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Gerald Holweg, Carolin Kollegger, Johannes Schweighofer, Inge Siegl, Christoph Steffan.
Application Number | 20220103206 17/548981 |
Document ID | / |
Family ID | 1000006024316 |
Filed Date | 2022-03-31 |
United States Patent
Application |
20220103206 |
Kind Code |
A1 |
Holweg; Gerald ; et
al. |
March 31, 2022 |
CIRCUIT FOR WIRELESS DATA TRANSFER COMPRISING TEMPERATURE
REGULATION
Abstract
A circuit for an NFC chip is described herein. According to one
exemplary configuration, the circuit comprises an antenna for near
field communication, an antenna resonant circuit which has an
adjustable resonant frequency, a temperature sensor and a
controller circuit coupled to the temperature sensor. The
controller circuit is designed to change the resonant frequency of
the antenna resonant circuit according to a temperature sensor
signal provided by the temperature sensor.
Inventors: |
Holweg; Gerald; (Graz,
AT) ; Kollegger; Carolin; (Stallhofen, AT) ;
Schweighofer; Johannes; (Graz, AT) ; Siegl; Inge;
(Graz, AT) ; Steffan; Christoph; (Graz,
AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
1000006024316 |
Appl. No.: |
17/548981 |
Filed: |
December 13, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
16555853 |
Aug 29, 2019 |
11228343 |
|
|
17548981 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 5/02 20130101; G06K
19/0726 20130101; H04B 5/0031 20130101; H04B 5/0062 20130101; G06K
19/07749 20130101; G06K 19/0773 20130101; G06K 19/0716 20130101;
G06K 7/10237 20130101 |
International
Class: |
H04B 5/00 20060101
H04B005/00; H04B 5/02 20060101 H04B005/02; G06K 19/077 20060101
G06K019/077; G06K 19/07 20060101 G06K019/07; G06K 7/10 20060101
G06K007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 2018 |
DE |
102018121408.1 |
Claims
1. An apparatus comprising: antenna hardware operative to receive
near field communications from a communication device; a resonant
circuit component to control a resonant frequency of operating the
antenna hardware; and a controller operative to: i) receive a
temperature sensor signal from a temperature sensor, the
temperature sense signal indicative of a temperature sensed by the
temperature sensor, and ii) adjust the resonant frequency of
operating the antenna hardware to regulate the temperature with
respect to a reference temperature.
2. The apparatus as in claim 1, wherein the controller is further
operative to adjust the resonant frequency and regulate the
temperature via adjustments to the resonant circuit component.
3. The apparatus as in claim 2, wherein the resonant circuit
component is a capacitor component whose capacitance is
adjustable.
4. The apparatus as in claim 3, wherein the controller is operative
to regulate the temperature with respect to the reference
temperature via application of the adjustments to the resonant
circuit component.
5. The apparatus as in claim 1, wherein the temperature represents
a temperature of a chip component including the resonant circuit
component.
6. The apparatus as in claim 1, wherein the controller is operative
to transmit a command to the communication device depending on the
temperature sensor signal, the command causing the communication
device to change the power of the near field communications
generated by the communication device to the antenna hardware.
7. The apparatus as claim 1, wherein the controller is operative to
send, depending on the temperature, a request from the antenna
hardware to the communication device to adjust a magnitude of the
near field communications transmitted from the communication
device.
8. The apparatus as in claim 1, wherein the resonant frequency is
defined by a combination of a capacitance of the resonant frequency
component and inductance of the antenna hardware.
9. The apparatus as in claim 1, wherein the controller circuit is
operative to adjust a magnitude of the resonant frequency with
respect to a carrier frequency of the near field communications
received from the communication device depending on the temperature
as indicated by the temperature sensor signal.
10. The apparatus as in claim 1 further comprising: a RF (Radio
Frequency) signal processing circuit coupled to the antenna
hardware, the RF signal processing circuit operative to convert
energy received from the near field communications received from
the communication device into a power supply voltage to power a
circuit; and wherein a magnitude of the energy received from the
near field communications through the antenna hardware is
controlled via adjustments to the resonant frequency, the
controller operative to generate the adjustments to the resonant
frequency based on a difference between the temperature as
indicated by the temperature sensor signal and the reference
temperature.
11. A method comprising: receiving near field communications at
antenna hardware, the near field communications transmitted from a
communication device; controlling a resonant frequency of operating
the antenna hardware via a resonant circuit component; and via a
controller: i) receiving a temperature sensor signal from a
temperature sensor, the temperature sense signal indicative of a
temperature sensed by the temperature sensor, and ii) adjusting the
resonant frequency of operating the antenna hardware to regulate
the temperature with respect to a reference temperature.
12. The method as in claim 11 further comprising: regulating the
temperature via adjustments to the resonant circuit component, the
adjustments the resonant frequency.
13. The method as in claim 12, wherein the resonant circuit
component is a capacitor component; and wherein adjusting the
resonant frequency includes adjusting a capacitance of the
capacitor component.
14. The method as in claim 11 further comprising: regulating the
temperature with respect to the reference temperature via
adjustments to the resonant circuit component.
15. The method as in claim 11, wherein the temperature represents a
temperature of a chip component in which the resonant circuit
component resides.
16. The apparatus as in claim 11 further comprising: transmitting a
command from the antenna hardware to the communication device
depending on the temperature sensor signal, the command causing the
communication device to change the power of the near field
communications generated by the communication device to the antenna
hardware.
17. The method as claim 11 further comprising: via a command
transmitted from the antenna hardware, sending a request to the
communication device to adjust a magnitude of the near field
communications transmitted from the communication device depending
on the temperature.
18. The method as in claim 11, wherein the resonant frequency is
defined by a combination of a capacitance of the resonant frequency
component and inductance of the antenna hardware.
19. The method as in claim 11 further comprising: adjusting a
magnitude of the resonant frequency with respect to a carrier
frequency of the near field communications received from the
communication device depending on the temperature as indicated by
the temperature sensor signal.
20. The apparatus as in claim 1 further comprising: via an RF
(Radio Frequency) signal processing circuit coupled to the antenna
hardware, converting energy received from the near field
communications into a power supply voltage to power a circuit; and
controlling a magnitude of the energy received from the near field
communications through the antenna hardware via adjustments to the
resonant frequency, a magnitude of the adjustments to the resonant
frequency being based on a difference between the temperature as
indicated by the temperature sensor signal and the reference
temperature.
Description
RELATED APPLICATION
[0001] This application is a continuation application of earlier
filed U.S. patent application Ser. No. 16/555,853 entitled "CIRCUIT
FOR WIRELESS DATA TRANSFER COMPRISING TEMPERATURE REGULATION,"
(Attorney Docket No. 2018P51034US), filed on Aug. 29, 2019, the
entire teachings of which are incorporated herein by this
reference.
[0002] U.S. patent application Ser. No. 16/555,853 claims priority
to earlier filed European Patent Application Serial Number EP10
2018 121408.1, filed on Sep. 3, 2018, the entire teachings of which
are incorporated herein by this reference.
TECHNICAL FIELD
[0003] The present description relates to the field of electronic
components for wireless data transfer such as NFC reader/writer
devices, RFIDs and the like.
BACKGROUND
[0004] Near field communication (NFC) is an international
transmission standard based on RFID technology for contactless
data-exchange by means of electromagnetically coupled coils over
relatively short distances (e.g. a few centimeters) and a data
transfer rate of currently 424 kbit/s maximum. This technology has
been used until now primarily in the "micropayment" field (cashless
payments involving small sums) and in access control. Examples of
other uses are the transfer of authentication data for establishing
communication via a Bluetooth or WLAN connection, for instance, and
opening weblinks when a URL (Uniform Resource Locator) of a website
is stored in an NFC chip. NFC is standardized in ISO/IEC 18092
(Near Field Communication Interface and Protocol-1) and ISO/IEC
21481 (Near Field Communication Interface and Protocol-2).
[0005] With regard to the payment function mentioned, many modern
mobile devices such as smartphones are equipped with an NFC
reader/writer. Such devices are known as NFC-enabled mobile
devices. An NFC chip, often also called an NFC tag or NFC
transponder, usually does not have its own energy supply and is
supplied with energy from the electromagnetic field generated by an
NFC-enabled mobile device. In other words, energy is transferred
from the NFC-enabled mobile device to the NFC chip, whereas data
transfer is possible in both directions. Currently available
NFC-enabled devices usually work at a fixed transmit power and do
not allow any power regulation. The set transmit power can vary
markedly depending on the type and manufacturer of the NFC-enabled
device. For example, there are NFC-enabled smartphones that work
with about ten times the NFC transmit power of other
smartphones.
[0006] The antennas of NFC-enabled devices and NFC chips (NFC
transponders) are, strictly speaking, simple conductor loops. In
the various antenna circuits, these conductor loops constitute an
inductance, which together with corresponding capacitances form
parallel resonant circuits. For efficient energy transfer from an
NFC-enabled device to an NFC chip, the antenna circuits are usually
operated at the same resonant frequency, thereby maximizing the
inductive coupling and the induced voltage. In standard
applications, this resonant frequency is typically 13.56 MHz.
[0007] When there is good inductive coupling of the antenna of an
NFC chip to the antenna of an NFC-enabled device (for instance when
the NFC chip is situated very close to the mobile device),
situations can arise in which more energy is transferred to the NFC
chip than is needed in the NFC chip. In such situations, the excess
energy must be dissipated in the NFC chip, for instance in shunt
transistors. The dissipation of the excess energy can result in
relatively high temperatures in an NFC chip.
BRIEF DESCRIPTION
[0008] A circuit for an NFC chip is described below. According to
one exemplary embodiment, the circuit comprises an antenna for near
field communication, an antenna resonant circuit which has an
adjustable resonant frequency, a temperature sensor and a
controller circuit coupled to the temperature sensor. The
controller circuit is designed to change the resonant frequency of
the antenna resonant circuit according to a temperature sensor
signal provided by the temperature sensor.
[0009] In accordance with further embodiments, the antenna resonant
circuit (R) comprises an adjustable capacitance, and wherein the
controller circuit is operative to change the adjustable
capacitance for the purpose of changing the resonant frequency.
[0010] In yet further embodiments, the circuit further includes: an
RF front end, which is coupled to the antenna and is operative to
generate a supply voltage on the basis of an RF signal received by
the antenna.
[0011] In still further embodiments, the RF front end (11) includes
a reader/writer for near field communication.
[0012] In further example embodiments, the circuit includes sensor
electronics for acquiring and processing one or more sensor
signals. A controller coupled to the sensor electronics is
operative to transfer, via the RF front end and the antenna, the
processed sensor signals, or information dependent thereon, to an
external device.
[0013] According to another exemplary embodiment, the circuit
comprises an antenna for near field communication (NFC), which is
designed to receive an RF signal from an external NFC-enabled
device. The circuit also comprises an RF front end connected to the
antenna and having an NFC reader/writer, and comprises a
temperature sensor, which provides a temperature sensor signal.
Coupled to the temperature sensor is a controller, which is
designed to transmit data to the NFC-enabled device using the NFC
reader/writer and on the basis of the temperature sensor signal,
which data causes the NFC-enabled device to change the power of the
RF signal. In accordance with further embodiments, the controller
is operative to send, depending on the temperature sensor signal,
using the NFC reader/writer, a request to the NFC-enabled device to
adjust the power of the RF signal.
[0014] In addition, a method for stabilizing the temperature in an
NFC chip is described. According to one exemplary embodiment, the
method comprises measuring a temperature of a chip (circuit) by
means of a temperature sensor, and varying a resonant frequency of
an antenna resonant circuit comprising an antenna that is coupled
to an NFC reader/writer arranged in the NFC chip. In accordance
with further embodiments, the method includes adjusting a
capacitance of a capacitor in the antenna resonant circuit to
change the resonant frequency.
[0015] According to one exemplary embodiment, the method comprises
receiving an RF signal by means of a reader/writer for near field
communication, measuring a chip temperature by means of a
temperature sensor, transferring data on the basis of the
temperature signal to an NFC-enabled device, and the NFC-enabled
device changing the power of the RF signal in response to the
transferred data.
SHORT DESCRIPTION OF THE DRAWINGS
[0016] Various exemplary embodiments are explained in greater
detail below with reference to figures. The diagrams are not
necessarily to scale and the exemplary embodiments are not limited
just to the aspects shown. The aim is rather to illustrate the
principles behind the exemplary embodiments. In the figures:
[0017] FIG. 1 is an example diagram illustrating the coupling of an
NFC chip to an NFC-enabled device such as a smartphone or the like
according to embodiments herein;
[0018] FIG. 2 is an example diagram illustrating a measurement
arrangement comprising an electrochemical converter element, an NFC
chip and an NFC-enabled device according to embodiments herein;
[0019] FIG. 3 is an example diagram illustrating an exemplary
embodiment of an NFC chip comprising an RF front end for near field
communication and an analog front end for processing sensor signals
according to embodiments herein;
[0020] FIG. 4 is an example diagram illustrating a control loop
used in the example of FIG. 3 for regulating or stabilizing the
temperature of the NFC chip according to embodiments herein;
[0021] FIG. 5 is an example diagram illustrating a graph by way of
example, the shift in the resonance peak of the antenna resonant
circuit of the NFC chip according to embodiments herein;
[0022] FIG. 6 is an example diagram illustrating a graph by way of
example, the change in the chip temperature as a function of the
resonant frequency of the antenna resonant circuit according to
embodiments herein;
[0023] FIG. 7 is an example diagram illustrating another exemplary
embodiment of an NFC chip comprising an RF front end for near field
communication and an analog front end for processing sensor signals
according to embodiments herein;
[0024] FIG. 8 is an example diagram illustrating the control loop
used in the example of FIG. 5 for regulating or stabilizing the
temperature of the NFC chip according to embodiments herein;
[0025] FIG. 9 is an example diagram illustrating illustrating an
example of a method for stabilizing the temperature of an NFC chip
according to embodiments herein;
[0026] FIG. 10 is a flow diagram for illustrating another example
of a method for stabilizing the temperature of an NFC chip
according to embodiments herein.
DETAILED DESCRIPTION
[0027] As mentioned in the introduction, near field communication
(NFC) is a standard for transferring energy and data between an
NFC-enabled device 2 such as a tablet computer or a smartphone, for
instance, and an NFC chip 1. This situation is shown in FIG. 1.
Usually NFC is used not just for (bidirectional) data transfer but
also for the (unidirectional) supply of energy to the NFC chip 1 by
the NFC-enabled device 2. The antennas of NFC chip 1 and of the
NFC-enabled device 2 are usually embodied as conductor loops (i.e.
flat coils), and the transfer of data and energy is based on
inductive coupling of the two antennas.
[0028] NFC chips can be employed in various applications. NFC is
mainly used for authentication, for example in association with
payment systems (e.g. micropayment) or systems for access control.
A relatively new use is coupling sensors to an NFC-enabled mobile
device such as a smartphone, for instance, by means of near field
communication. In this case, the sensor electronics comprises an
RFID front end (radiofrequency (RF) front end circuit) for near
field communication with the mobile device. The mobile device can
be used, for instance in a measurement application, for further
processing of measurement data transferred by means of NFC from the
sensor electronics to the mobile device, and to display this
measurement data on a screen of the mobile device. In addition, the
mobile device can receive user inputs and transfer these user
inputs by means of NFC to the sensor electronics. The mobile device
can thereby act as a human-machine interface for the sensor
electronics. FIG. 2 shows an example of an apparatus comprising a
sensor coupled to a mobile device by means of NFC.
[0029] FIG. 2 illustrates an example of an apparatus comprising a
biochemical sensor and comprising integrated sensor electronics
that include an interface for near field communication (NFC) in
order to be able to transfer measurement data to an NFC-enabled
mobile device 2. In the example shown in FIG. 2, the NFC chip 1
includes said sensor electronics and the NFC interface. The energy
can be supplied to the NFC chip also by means of NFC. The sensor
apparatus shown in FIG. 2 comprises a circuit board 4, on which are
arranged the NFC chip 1 and an antenna 10. As mentioned, the
antenna 10 can essentially be a conductor loop (i.e. a flat coil)
formed by strip conductors on the circuit board. As shown in FIG.
2, arranged on the circuit board 4 is a plug-in connector 3, by
means of which an electrochemical cell 6 arranged on a test strip 5
can be connected to the circuit board. The electrodes of the
electrochemical cell 6, which are labeled WE, RE and CE in FIG. 2,
are connected to the NFC chip 1 via the plug-in connector 3 and
strip lines arranged on the circuit board. As mentioned, the NFC
chip 1 contains the sensor electronics for acquiring and processing
the sensor signals and the circuits needed for near field
communication. The electrochemical cell 6 can be used, for example,
for voltammetry or similar techniques in order to determine
quantitatively one or more substances (analytes) present in the
electrolyte of the electrochemical cell. The sensor electronics
contained in the NFC chip 1 provide the drive for the electrodes
WE, RE and CE that is needed for this purpose. It is possible to
dispense with the test strip 5 and the plug-in connector 3 if the
electrochemical cell 6 is arranged directly on the circuit board
4.
[0030] Sensor apparatuses such as the example shown in FIG. 2 are
known per se, for instance for measuring the potassium
concentration in the blood (see e.g. Kollegger, C., Greiner, P.,
Siegl, I. et al., Intelligent NFC potassium measurement strip with
hemolysis check in capillary blood, in: Elektrotech. Inftech.
(2018) 135/1, S. 83-88, https://doi.org/10.1007/s00502-017-0572-5).
In this case, a drop of blood forms the electrolyte of the
electrochemical cell, which is operated as a potentiostat in order
to determine the concentration of potassium in the blood. A
potentiostat can be used, for instance, for cyclic voltammetry
(CV), which is a means of determining the chemical composition of
substance mixtures on the basis of the voltage-dependent current
variation in the electrochemical cell. Voltammetry is a form of
electrolysis in which the dependency of an electrode current on a
voltage applied to an electrochemical cell is ascertained. The
further examination of the sample includes analyzing the measured
current/voltage curves, for instance to ascertain the concentration
of an analyte (e.g. specific metal ions) present in the sample. The
mobile device 2 can perform, at least in part, this analysis and
the display of the measurement results. In particular, the CPU (not
shown) contained in the mobile device can be used to execute
software applications that are designed to perform the stated
analysis of the (digitized) measurement data and to display the
results.
[0031] As mentioned, the NFC chip 1 can also be supplied with
energy by means of NFC. Latest NFC-enabled devices, however, do not
allow any control of the transferred power (energy per unit of
time), and the NFC interfaces at both ends (NFC-enabled device 2,
NFC chip 1) are usually designed to achieve optimum inductive
coupling. The power that is not needed by the NFC chip 1 is
dissipated in the form of heat, for instance in an electrical
resistor, which in the NFC chip 1 results in a temperature rise. In
many uses, a raised temperature is of no further relevance, but in
sensor applications, temperature fluctuations have a negative
impact on the accuracy of the measurement. The following exemplary
embodiments provide a solution for regulating or stabilizing
(within certain limits) the temperature in the NFC chip.
[0032] FIG. 3 illustrates an exemplary embodiment of an NFC chip 1
comprising an RF front end 11 for near field communication, a
digital controller 15 (e.g. a microcontroller), an interface
circuit 16 for the sensor electrodes WE, RE, CE, and an analog
front end 14 for analog processing of the sensor signals. The
interface circuit 16 can include amplifiers, for example, that
provide the cell voltage. The analog front end 14 can include,
inter alia, one or more signal sources, which are used for driving
the electrochemical cell, and an analog-to-digital converter for
digitizing the sensor signals. The digitized signals can undergo
further digital processing by the controller 15 and be transferred
in the form of a serial data stream wirelessly by means of NFC to
the mobile device 2. This data transfer is facilitated by the RFID
front end, which includes all the radiofrequency circuit components
used for the data transfer. The NFC chip 1 can comprise one or more
controllable capacitors C.sub.R, which form with the antenna
(represented in FIG. 3 as the inductance L.sub.R) connected to the
NFC chip a resonator circuit (antenna resonant circuit R) that has
a specific resonant frequency f.sub.R. The design and operation of
RFID front end 11, controller 15, analog front end 14 and interface
circuit 16 are known per se and therefore are not described further
here. In particular, the RF front end 11 comprises an NFC
reader/writer and a rectifier circuit, which is designed to
generate on the basis of the received RF signal (carrier signal), a
supply voltage for the circuit components contained in the NFC chip
1.
[0033] Even though not shown explicitly in FIG. 3, the RFID front
end 11 also provides the supply voltage for the remaining
components of the NFC chip 1. The energy for generating the supply
voltage is received from the NFC-enabled mobile device 2 (not shown
in FIG. 3) via the antenna L.sub.R. In order to ensure optimum
transfer of data and energy, the resonant frequency f.sub.R can be
set to equal the carrier frequency used by the NFC-enabled mobile
device 2. As mentioned, a carrier frequency of 13.56 MHz is often
used.
[0034] A explained above, the temperature in the NFC chip 1 can
rise if too much power is transferred to the RFID front end 11 via
the NFC transmission channel In order to counteract this
temperature rise, the NFC chip 1 can comprise a temperature sensor
12, which provides a temperature measurement signal, which is input
to a controller circuit 13. This controller circuit 13 is designed
to change the resonant frequency f.sub.R of the antenna resonant
circuit R so that the resonant frequency f.sub.R is no longer
matched to the carrier frequency used for the near field
communication (NFC). The result of said detuning of the resonant
frequency f.sub.R is that the power received by the RFID front end
11 falls, and hence less power has to be dissipated, and the
temperature in the NFC chip can fall again. The detuning of the
resonant frequency f.sub.R of the antenna resonant circuit R can be
achieved, for example, by changing the capacitance of the capacitor
C.sub.R. For this purpose, the capacitor can be designed, for
example, as a digitally tunable capacitor (DTC) or as a
varactor.
[0035] The temperature controller 13 facilitates a closed control
loop, which is shown schematically in FIG. 4. As explained, the
temperature T.sub.Chip in the NFC chip 1 depends on the power
P.sub.R received by the antenna, which in turn depends on the
resonant frequency f.sub.R of the antenna resonant circuit R. For
the purpose of temperature regulation, the NFC chip can thus be
considered to be a system whose input variable is the resonant
frequency f.sub.R and whose output variable is the temperature
T.sub.Chip. This temperature T.sub.Chip is measured by the
temperature sensor 12, which provides a temperature signal
S.sub.TEMP representing the temperature T.sub.Chip. This
temperature signal S.sub.TEMP is input to the controller circuit
13, which is designed to adjust the resonant frequency f.sub.R
according to the temperature signal S.sub.TEMP (and optionally also
according to a reference signal S.sub.REF).
[0036] For example, the resonant frequency f.sub.R can be adapted
according to the difference S.sub.TEMP-S.sub.REF (difference
between measured temperature and reference temperature). If the
level of the temperature signal S.sub.TEMP is higher than the (e.g.
constant) level of the reference signal S.sub.REF, then the
resonant frequency f.sub.R can be increased until the (constant)
carrier frequency f.sub.C used by the NFC-enabled device 2 (e.g.
f.sub.C=13.56 MHz) lies no longer within (or at the edge of) the
resonance peak of the antenna resonant circuit R. If the level of
the temperature signal S.sub.TEMP is lower than the level of the
reference signal S.sub.REF, then the resonant frequency f.sub.R can
be shifted towards the carrier frequency used by the NFC-enabled
device 2 so that the carrier frequency lies in the central region
of the resonance peak. FIG. 5 shows the shift in the resonant
frequency f.sub.R and thus in the resonance peak of the antenna
resonant circuit R. The continuous line represents the resonance
peak of the antenna resonant circuit R for a resonant frequency of
e.g. 40 MHz. In this case, the difference .DELTA.f with respect to
the carrier frequency f.sub.C is approximately
.DELTA.f=f.sub.R-f.sub.C=26.44 MHz and the carrier frequency
f.sub.C lies at the edge of the resonance peak. The dashed line
represents the resonance peak of the antenna resonant circuit R for
a resonant frequency f.sub.R that is significantly less than 40 MHz
(e.g. 19 MHz). In this case, the carrier frequency f.sub.C lies in
the central region of the resonance peak. Given perfect matching of
the antenna resonant circuit R, the resonant frequency f.sub.R
would equal the carrier frequency f.sub.C. FIG. 6 shows in a
schematic diagram the increase in the chip temperature T.sub.Chip
while near field communication (NFC) is active and the resonant
frequency is gradually shifted, for instance starting from 40 MHz,
towards the carrier frequency f.sub.C. It is evident that the
smaller the difference .DELTA.f, the higher the temperature, with
the temperature no longer rising for a certain difference .DELTA.f
onwards.
[0037] FIG. 7 illustrates an alternative exemplary embodiment in
which the temperature information measured in the NFC chip 1 is
transferred to the NFC-enabled mobile device 2. The NFC-enabled
mobile device 2 then has the facility to reduce the transmit power,
whereby the power received by the NFC chip 1 is likewise reduced
without the need to change the resonant frequency f.sub.R of the
antenna resonant circuit. In the example of FIG. 7, the RFID front
end 11, the controller 15, the analog front end 14 and the
interface circuit 16 are essentially the same as in the previous
example from FIG. 3. Unlike the previous example, however, the
temperature information acquired by the temperature sensor 12 is
digitized and input to the controller 15. The controller 15 or the
temperature sensor 12 can comprise for this purpose an
analog-to-digital converter (not shown in FIG. 7). The controller
15 is designed to send to the NFC-enabled mobile device 2,
depending on the temperature measured in the NFC chip 1, a request
to change the transmit power. If, for example, the measured
temperature exceeds a reference value, then the controller 15, by
transferring a suitable request REQ by means of NFC to the
NFC-enabled mobile device 2, causes this device to reduce the
transmit power. This reduction in the transmit power can be
performed continuously or incrementally, depending on how the
NFC-enabled device 2 is implemented. A temperature control loop is
thereby formed that also contains the NFC-enabled mobile device 2.
The NFC-enabled mobile device 2, however, must support the
adaptation of the transmit power, and although this is not the case
for many devices currently on the market, this may be the case in
future.
[0038] FIG. 8 illustrates schematically the control loop realized
in the exemplary embodiment shown in FIG. 7. As explained, the
temperature T.sub.Chip in the NFC chip 1 depends on the power
P.sub.RF received by the antenna. For the purpose of temperature
regulation, the NFC chip can thus be considered in the present
example to be a system whose input variable is the power P.sub.RF
received in the near field communication (NFC) and whose output
variable is the temperature T.sub.Chip. This temperature T.sub.Chip
is measured by the temperature sensor 12, which provides a
temperature signal S.sub.TEMP representing the temperature
T.sub.Chip. This temperature signal S.sub.TEMP is input to the
controller 15, which is designed to call on the NFC-enabled device
2 via the NFC transmission channel to adapt the transmit power.
This adaptation can depend on the measured temperature T.sub.Chip
and, if applicable, on a reference value. Depending on the
capabilities of the NFC-enabled device 2, this device can also poll
the controller 15 regularly for the measured temperature
(temperature signal S.sub.TEMP) via the NFC transmission channel,
and adapt the transmit power according to the temperature.
[0039] The methods for regulating/stabilizing the temperature in an
NFC chip, which are implemented by the exemplary embodiments
described above, are summarized below. FIG. 9 illustrates in a flow
chart an example of a method that can be implemented, for instance,
using the circuit of FIG. 3. According to FIG. 9, the method
comprises measuring a chip temperature by means of a temperature
sensor (see FIG. 9, step S10) and varying a resonant frequency of
an antenna resonant circuit (see FIG. 9, step S11), which comprises
an antenna that is coupled to an NFC reader/writer arranged in the
NFC chip. In one exemplary embodiment, the resonant frequency is
varied by varying the capacitance of a capacitor contained in the
antenna resonant circuit. As explained above, detuning the antenna
resonant circuit results in a reduction in the power received by
the antenna and hence results in less power to be dissipated in the
NFC chip, which in turn leads to a reduction in the
temperature.
[0040] FIG. 10 is a flow chart for illustrating another example, in
which an NFC-enabled device (e.g. a smartphone) is part of the
temperature control loop. According to FIG. 10, the method
comprises receiving an RF signal by means of a reader/writer for
near field communication (see FIG. 10, step S20), measuring a chip
temperature by means of a temperature sensor (see FIG. 10, step
S21), transferring data to the NFC-enabled device on the basis of
the temperature sensor signal (see FIG. 10, step S22). The
NFC-enabled device changes the power of the RF signal in response
to the transferred data (see FIG. 10, step S23). This method can be
realized, for example, using the system shown in FIG. 7
(NFC-enabled device 2, NFC chip 1).
* * * * *
References