Method for correcting a transmission frequency as a function of temperature
A software-based frequency correction method for quartz oscillators in tire-mounted sensors addresses temperature-induced drift, enhancing communication efficiency and reducing energy use without bulky TCXO circuits.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MICHELIN & CO (CIE GEN DES ESTAB MICHELIN)
- Filing Date
- 2025-11-07
- Publication Date
- 2026-06-04
AI Technical Summary
Existing wireless sensors in vehicles face challenges with frequency drift due to temperature variations, leading to inefficient communication between transmitters and receivers, particularly in tire-mounted sensors using quartz oscillators, which are energy-intensive and bulky when using TCXO compensation circuits.
A method involving a temperature-compensated lookup table in software to adjust the emission frequency of quartz oscillators based on temperature measurements, eliminating the need for bulky TCXO circuits and reducing power consumption by implementing unidirectional communication.
Improves communication performance and reduces energy consumption by correcting frequency drift, allowing higher-quality components to be used while maintaining efficient transmission across varying temperatures.
Smart Images
Figure FR2025051029_04062026_PF_FP_ABST
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: Method for correcting an emission frequency as a function of temperature
[0003] technical field
[0004] The present invention relates to an electronic device for emitting an electromagnetic wave via an oscillator, for example a quartz oscillator.
[0005] In particular, the present invention relates to the compensation of a frequency drift of the oscillator due to the temperature of said oscillator.
[0006] In general, the invention applies to any oscillator, quartz or otherwise, whose electromagnetic wave emission properties are altered by a change in the oscillator's temperature.
[0007] Previous techniques
[0008] Electronic components such as wireless sensors are becoming commonplace in a growing number of applications.
[0009] In particular, vehicles, especially motor vehicles, are increasingly equipped with wireless sensors, notably using the Bluetooth® or even BLE protocol (“Bluetooth® Low Energy”, i.e., low power consumption).
[0010] Such an electronic device can, for example, be positioned within a tire, then called a "Tire Mounted Sensor" (TMS) in English. It is, for instance, glued to the inner side of the tread to collect information on temperature, pressure, or from an accelerometer. This information is then transmitted by a transmitter located within the electronic device to a receiver, for example, located in the vehicle's passenger compartment and directly connected to the vehicle's onboard computer.
[0011] A transmitter can generally send information to a receiver unidirectionally or bidirectionally. A bidirectional link is advantageous because it allows the receiver to send confirmation to the transmitter that it has successfully received the information initially sent by the transmitter.
[0012] However, since it cannot be powered by a cable, such a sensor is equipped with a battery or cell whose lifespan must be maximized. Therefore, any unnecessary energy expenditure must be avoided, and bidirectional connections hinder this reduction in energy consumption as they are extremely power-intensive.
[0013] On the other hand, a unidirectional link cannot guarantee that the information sent by a transmitter is received by the receiver.
[0014] To reduce the risk of not receiving information, one solution is to increase the power of the transmitter, a solution which nevertheless remains energy-intensive.
[0015] A second solution involves directing the transmission straight towards the receiver. However, a sensor positioned inside a tire, with a metallic layer in its tread forming a Faraday cage, cannot guarantee the correct directionality of an electromagnetic wave transmission. Furthermore, in a rotating tire, it is virtually impossible to accurately orient the antenna to achieve good transmission and / or reception at all times.
[0016] A third solution is to ensure that the receiver's receiving frequency matches the transmitter's transmitting frequency. To achieve this, the receiver must be tuned to the transmitting frequency, otherwise it may not receive the correct information. Note that a receiver with a wider reception bandwidth can be used, but this will compromise sensitivity and range.
[0017] Most modern transmitters include an oscillator, for example a quartz oscillator.
[0018] Quartz is a material that, when electrically excited, emits an electromagnetic wave at a specific frequency, which depends, among other things, on its cutting angle. However, quartz is also sensitive to temperature, and its emission frequency can vary with temperature. This phenomenon is amplified in a tire, which can reach extreme temperatures: low in winter when the vehicle is stationary and high in summer during vehicle use.
[0019] Thus, a non-linear drift in the transmitter's emission frequency can be observed when its temperature varies, impairing the proper frequency alignment between the transmitter and the receiver.
[0020] In order to address this drift, it is necessary to compensate for it.
[0021] The most popular current solution is the use of a temperature-compensated quartz crystal. This type of crystal houses a thermal compensation electronic circuit, also called a TCXO, which corrects the transmission frequency according to temperature drift. However, this system is energy-intensive because it operates continuously, expensive, and bulky due to the inclusion of additional electronic components such as a variable-capacitance diode.
[0022] Description of the invention
[0023] The present invention therefore aims to overcome the aforementioned drawbacks and to provide an electronic component and a method for correcting the emission frequency emitted by a transmitter of said electronic component as a function of the ambient temperature.
[0024] The present invention relates to a method for correcting an emission frequency for an electronic device comprising a data module, a temperature sensor, a transmitter adapted to emit an electromagnetic wave transmitting the data captured and / or stored by the data module to an external receiver, and a microprocessor adapted to transmit an emission instruction to the transmitter.
[0025] The process includes the following steps implemented for each transmission by the sender:
[0026] - Measurement of the emitter temperature by the temperature sensor; - Determination of a correction coefficient by searching in a table of correspondence between different emitter temperatures and correction coefficients adapted to compensate for a frequency drift of the emitter as a function of its temperature, the table of correspondence being stored in the electronic component;
[0027] - Adjustment by the microprocessor of the emission setpoint according to the determined correction coefficient; and
[0028] - Emission by the transmitter of an electromagnetic wave according to the adjusted emission instruction.
[0029] Thus, the electronic component does not require a TCXO-type compensation circuit and consumes very little power in comparison. Its size is also minimal because the lookup table is implemented solely in software, and not using an additional circuit.
[0030] Moreover, for two final products obtained at equal cost, one comprising a TCXO and the other the present invention, it is possible to use higher-quality electronic components in the final product comprising the present invention. In addition, information transmission performance is greatly improved when the electronic component is subjected to extreme temperatures.
[0031] Finally, in the event of a change in transmitter reference, it is sufficient to create a new lookup table and implement it in the electronic component as a software update of the embedded code, historically loaded during the manufacture of the electronic component: it is not necessary to change the configuration of an electronic circuit of said electronic component, unlike the solution including a TCXO.
[0032] Advantageously, the transmitter includes a quartz oscillator.
[0033] In a particular implementation mode, the transmission step between the transmitter and the external receiver is unidirectional.
[0034] Advantageously, the transmission stage is implemented at a carrier frequency of the electromagnetic wave between 2402 MHz and 2480 MHz, preferably only at 2402 MHz, and / or at 2426 MHz, and / or at 2480 MHz.
[0035] In one implementation method, the lookup table was previously established empirically with an identical electronic device.
[0036] Preferably, the lookup table is established by implementing the following steps:
[0037] - Setting the emitter to a predefined temperature;
[0038] - Sending a number of messages greater than a predefined number by the sender to an external receiver;
[0039] - Measurement of the rate of messages sent but not received by the external receiver;
[0040] - Adjustment by the microprocessor of the transmission setpoint so as to introduce a correction coefficient of the carrier frequency emitted by the transmitter until the rate of messages sent not received by the external receiver is less than 10%, preferably 1%;
[0041] - Recording in the lookup table the correspondence between the predefined temperature and the correction coefficient for which the rate of messages sent but not received by the external receiver is less than 10%, preferably 1%; and
[0042] - Repeat the previous steps for a different temperature.
[0043] Alternatively, the lookup table is established by implementing the following steps:
[0044] - Setting the emitter to a predefined temperature;
[0045] - Transmission of a message by the transmitter to a spectrum analyzer;
[0046] - Measurement of the carrier frequency emitted by the transmitter using the spectrum analyzer;
[0047] - Adjustment by the microprocessor of the emission setpoint to introduce a correction coefficient for the carrier frequency emitted by the transmitter until the carrier frequency emitted by the transmitter corresponds to a theoretical emission frequency, within a margin of error; - Recording in the lookup table the correspondence between the predefined temperature and the correction coefficient for which the carrier frequency emitted by the transmitter corresponds to the theoretical emission frequency; and
[0048] - Repeat the previous steps for a different temperature.
[0049] Advantageously, the correspondence table includes correction coefficients corresponding to emitter temperatures extending over a temperature range from -20°C to +100°C, preferably from -40°C to +125°C.
[0050] The present invention also relates to an electronic device comprising a power source and an electronic board comprising a microprocessor, a data module, a temperature sensor, a memory, and an electromagnetic wave emitter, the microprocessor being adapted to implement the process as defined above, the microprocessor and / or the memory being adapted to store the lookup table.
[0051] The present invention also relates to a tire comprising the electronic component as defined above, mounted securely on said tire.
[0052] Brief description of the drawings
[0053] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:
[0054] [Fig 1] is a schematic perspective representation of an electronic component according to the invention;
[0055] [Fig 2] is a schematic representation of the different stages of the process according to the invention; and
[0056] [Fig 3] is a variant of Figure 2 in which the steps of establishing the correspondence table are carried out with a spectrum analyzer.
[0057] Detailed description of at least one embodiment
[0058] Figure 1 schematically represents an electronic component 1 for which the method of correcting an emission frequency according to the invention is implemented.
[0059] The electronic component 1 is, for example, intended to be mounted securely on a tire, such as a motor vehicle tire.
[0060] The electronic component 1 comprises a power source 3 and an electronic board 5 on which are mounted a microprocessor 7, a data module 9, a temperature sensor 11, a memory (not shown), and a transmitter 13 adapted to emit an electromagnetic wave transmitting the data captured and / or stored by the data module 9 to an external receiver. Each element of the electronic component 1 is housed in a plastic casing, for example, made of polyamide, and an epoxy resin is injected into the casing to prevent any movement or degradation within it.
[0061] The power source 3 is, for example, a rechargeable battery or a cell, such as a button cell. Its capacity is, for example, between 20 and 500 mAh.
[0062] The data module 9 is for example a data sensor, such as a motion sensor sensitive to the movement of the electronic organ 1, for example an accelerometer.
[0063] Alternatively, data module 9 is a memory block containing information, for example, identification information for electronic component 1,
[0064] Optionally, the electronic board 5 also includes a pressure sensor, allowing the internal pressure of the tire to be measured.
[0065] The temperature sensor 11 is suitable for measuring the temperature of the environment of the electronic component 1. The thermal inertia of the electronic component 1 and in particular of the emitter 13 being low, the temperature sensor 11 allows in practice to measure the temperature of the emitter 13 and / or of the electronic component 1 in a global way.
[0066] The microprocessor 7 may include the memory, or the memory may be a separate electronic memory module connected to the microprocessor 7. In the variant where the data module 9 is a memory block 9, said memory block may optionally be the memory and be included in the microprocessor or in a separate electronic memory module.
[0067] Memory can be volatile or non-volatile, preferably non-volatile so that data can be stored in it for life from the moment of programming and without erasure of the data.
[0068] The microprocessor 7 is adapted to transmit an instruction to emit an electromagnetic wave to the transmitter 13.
[0069] According to one embodiment, the electromagnetic wave emitter 13 includes an oscillator, preferably a quartz oscillator.
[0070] The electronic component 1 does not emit continuously and its emission regularity depends on several parameters according to the needs.
[0071] For example, electronic component 1 might emit every minute if it remains stationary, then emit a certain number of times every 5 seconds when it starts moving, and then every 30 seconds thereafter until it remains stationary for more than 3 minutes. This represents a significant number of emissions, for example, more than 3,000,000 emissions if electronic component 1 is mounted in a tire stored for 6 years in a workshop.
[0072] Given the small capacity of a button cell battery, every mWh saved counts towards achieving optimized performance.
[0073] In the case where the electromagnetic wave emitter 13 includes an oscillator, in particular a quartz oscillator, the electromagnetic waves emitted are called radio-frequency waves.
[0074] Radio frequency emissions are based on the oscillation frequency of the quartz crystal, usually multiplied by a coefficient calculated by the microprocessor 7. Thus, for example: to emit a radio frequency wave at a carrier wave frequency of 2.440 GHz with a quartz crystal oscillating at 48 MHz, the microprocessor 7 will apply a coefficient of 50.83 to the quartz signal to obtain the desired emission frequency.
[0075] Furthermore, a signal emitted by the electronic organ 1 at a frequency of 2.440 GHz must in practice be emitted in a frequency band between 2.439 and 2.441 GHz to be correctly received by an external receiver, in other words on an occupancy bandwidth of 2 MHz with a deviation between the center value and the peak value of 1 MHz.
[0076] The external receiver is, for example, a receiver positioned in a motor vehicle, for example in the dashboard.
[0077] When the quartz oscillator drifts by only 10 kHz due to a change in its temperature, the carrier wave frequency can be shifted by 0.5 MHz if left uncorrected. A temperature variation is therefore highly likely to cause the transmitter 13 to emit a frequency outside the predefined 2 MHz wide frequency band.
[0078] To mitigate this risk, the present invention proposes a method for correcting the emission frequency of the electronic component 1, the steps of which are schematically represented in figures 2 or 3.
[0079] The process is implemented, for example, by microprocessor 7.
[0080] To implement the process, a first step E is carried out to measure the temperature of the emitter 13 by the temperature sensor 1 1.
[0081] Next, a step E2 is performed to determine a correction coefficient by searching a lookup table that links different emitter 13 temperatures to correction coefficients adapted to compensate for a frequency drift of emitter 13 as a function of its temperature. The lookup table is stored in the electronic component 1, for example directly in the microprocessor 7 and / or in memory.
[0082] The correspondence table includes, for different emitter temperatures 13, the associated correction coefficient allowing the emission setpoint that the microprocessor 7 sends to the emitter 13 before each emission to correct so that the carrier frequency emitted by said emitter 13 is as close as possible to the desired theoretical value, namely a theoretical emission frequency.
[0083] Next, an E3 adjustment step is performed by the microprocessor 7 of the emission setpoint according to the aforementioned determined correction coefficient.
[0084] Finally, an emission step E4 is carried out by the transmitter 13 of an electromagnetic wave according to the adjusted emission instruction.
[0085] Advantageously, the transmission step E4 is carried out unidirectionally from transmitter 13 to the external receiver. In other words, the external receiver does not send a signal back to transmitter 13 to indicate successful signal reception, making the communication less energy-intensive.
[0086] In particular, the E4 emission step is implemented at an electromagnetic wave carrier frequency between 2402 MHz and 2480 MHz, which are the frequencies used in the Bluetooth® Low Energy protocol, a protocol widely used in motor vehicles and allowing the electronic component 1 to adapt to an existing infrastructure.
[0087] Since the communication is unidirectional, the carrier frequency for transmission is preferably only at 2402 MHz, and / or at 2426 MHz, and / or at 2480 MHz, namely the three so-called "advertising" frequencies among the 40 frequencies used for the Bluetooth® Low Energy protocol, the channels of these frequencies being channels 37, 38 and 39.
[0088] The correspondence table is first established empirically with an electronic organ 1 identical with regard to its hardware, then stored in the memory of each electronic organ 1 intended for use.
[0089] In particular, the correspondence table is established by implementing the following steps.
[0090] Firstly, a step T l is carried out to set the emitter 13 to a predefined temperature, for example a temperature between -40°C and + 125°C.
[0091] Then, a step T2 is performed by sending a number greater than a predefined number of messages from the sender 13 to an external receiver, for example more than 100 messages.
[0092] This allows us to obtain a measure of the rate of messages sent but not received by the external receiver during the implementation of a T3 step.
[0093] In particular, messages are not received by the external receiver when the temperature of transmitter 13 changes the carrier frequency too much, the latter not being corrected.
[0094] Then, a step T4 is performed by the microprocessor 7 to adjust the transmission setpoint in order to introduce a correction coefficient of the carrier frequency emitted by the transmitter 13 until the rate of messages sent not received by the external receiver is less than 10%, preferably 1%.
[0095] As soon as a correction coefficient is found so that the rate of messages sent not received by the external receiver is less than 10%, preferably 1%, a step T5 is carried out of registering in the correspondence table the correspondence between the predefined temperature and said correction coefficient.
[0096] Thus, it is concluded that the emitter 13, subjected to the predefined temperature, must receive an emission instruction from the microprocessor 7 taking into account this correction coefficient.
[0097] Finally, the previous steps T1 to T5 are repeated for another temperature, and so on preferably until a lookup table is obtained whose temperature range extends from -20°C to +100°C, preferably from -40°C to +125°C. In the alternative illustrated in Figure 3, the lookup table is established by implementing the following steps.
[0098] Firstly, a step VI is carried out to set the emitter 13 to a predefined temperature, for example a temperature between -40°C and +125°C.
[0099] Then, a V2 step is performed, emitting a message from transmitter 13 to a spectrum analyzer which will measure the carrier frequency emitted by the transmitter during a V3 step.
[0100] Then, a step V4 is performed by the microprocessor 7 to adjust the emission setpoint in order to introduce a correction coefficient of the carrier frequency emitted by the transmitter 13 until the carrier frequency emitted by the transmitter corresponds to a theoretical emission frequency, within a margin of error, for example 0.1 MHz.
[0101] Optionally, a V45 validation step is performed by sending a greater than predefined number of messages with sender 13 to an external receiver, as presented in step T2, in order to verify that the rate of messages sent not received by the external receiver is well below 10%, preferably 1%.
[0102] As soon as a correction coefficient is found so that the carrier frequency emitted by the transmitter corresponds to the theoretical emission frequency, a step V5 is carried out of registering in the correspondence table the correspondence between the predefined temperature and said correction coefficient.
[0103] Thus, it is concluded that the emitter 13, subjected to the predefined temperature, must receive an emission instruction from the microprocessor 7 taking into account this correction coefficient.
[0104] Finally, we repeat the previous steps VI to V5 for another temperature, and so on preferably until we obtain a lookup table whose temperature range extends from -20°C to +100°C, preferably from -40°C to +125°C.
[0105] A temperature measurement is, for example, taken every 5°C, or every 10°C, or every 20°C. Alternatively, the number of temperature measurements varies according to the temperature range of the measurement, in order to take into account the non-linear response of an emitter 13 to a change in temperature.
[0106] Table 1 below illustrates a correspondence table in which a correction coefficient is defined for each 20°C range of temperature, from -40°C to +80°C.
[0107] [Table 1]
[0108] The resulting lookup table is valid for a specific type of transmitter 13. If the transmitter 13 in the electronic component 1 is replaced by a transmitter 13 of a different brand or with different characteristics, it will be necessary to repeat steps T1 to T5 to obtain a new lookup table adapted to the new transmitter 13.
Claims
DEMANDS 1. Method for correcting an emission frequency for an electronic device (1) comprising a data module (9), a temperature sensor (11), a transmitter (13) adapted to emit an electromagnetic wave transmitting the data captured and / or stored by the data module (9) to an external receiver, and a microprocessor (7) adapted to transmit an emission command to the transmitter (13), characterized in that it comprises the following steps implemented for each emission by the transmitter (13): Measurement (step El) of the temperature of the emitter (13) by the temperature sensor (11); Determination (step E2) of a correction coefficient by searching in a table of correspondence between different temperatures of the emitter (13) and correction coefficients adapted to compensate for a frequency drift of the emitter (13) as a function of its temperature, the table of correspondence being stored in the electronic organ (1); - Adjustment (step E3) by the microprocessor (7) of the emission setpoint according to the determined correction coefficient; and Emission (step E4) by the transmitter (13) of an electromagnetic wave according to the adjusted emission instruction.
2. Method according to claim 1, wherein the transmitter (13) comprises a quartz oscillator.
3. A method according to any one of claims 1 and 2, wherein the transmission step (E4) between the transmitter (13) and the external receiver is unidirectional.
4. A method according to any one of claims 1 to 3, wherein the emission step (E4) is carried out at an electromagnetic wave carrier frequency between 2402 MHz and 2480 MHz, preferably only at 2402 MHz, and / or at 2426 MHz, and / or at 2480 MHz.
5. A method according to any one of claims 1 to 4, wherein the lookup table has been previously established empirically with an identical electronic device 1.
6. A method according to claim 5, wherein the lookup table is established by implementing the following steps: Setting the emitter (13) to a predefined temperature (step T1); Sending a number greater than a predefined number of messages by the sender (13) to an external receiver (step T2); Measurement of the rate of messages sent but not received by the external receiver (step T3); - Adjustment by the microprocessor (7) of the transmission setpoint so as to introduce a correction coefficient for the carrier frequency emitted by the transmitter (13) until the rate of messages sent but not received by the external receiver is less than 10%, preferably 1% (step T4); Entry in the lookup table of the correspondence between the predefined temperature and the correction coefficient for which the rate of messages sent but not received by the external receiver is less than 10%, preferably 1% (step T5); and Repeating the previous steps (T1; T2; T3; T4; T5) for another temperature.
7. A method according to claim 5, wherein the lookup table is established by implementing the following steps: Setting the emitter (13) to a predefined temperature (step VI); Transmission of a message by the transmitter (13) to a spectrum analyzer (step V2); Measurement of the carrier frequency emitted by the transmitter using the spectrum analyzer (step V3); - Adjustment by the microprocessor (7) of the emission setpoint in order to introduce a correction coefficient of the carrier frequency emitted by the transmitter ( 13) until the carrier frequency emitted by the transmitter corresponds to a theoretical emission frequency, within a margin of error (step V4); Entering in the lookup table the correspondence between the predefined temperature and the correction coefficient for which the carrier frequency emitted by the transmitter corresponds to the theoretical emission frequency (step V5); and Repeat the previous steps for a different temperature.
8. A method according to any one of claims 1 to 7, wherein the correspondence table includes correction coefficients corresponding to emitter 13 temperatures extending over a temperature range from -20°C to +100°C, preferably from -40°C to +125°C.
9. Electronic component (1) comprising a power source (3) and an electronic board (5) comprising a microprocessor (7), a data module (9), a temperature sensor 11, a memory, and an electromagnetic wave emitter (13), the microprocessor (7) being adapted to implement the method according to any one of claims 1 to 8, the microprocessor (7) and / or the memory being adapted to store the lookup table.
10. Pneumatic comprising the electronic component (1) according to claim 9 mounted securely on said pneumatic.