WO2007068283A1 - Sensor interface - Google Patents

Sensor interface Download PDF

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Publication number
WO2007068283A1
WO2007068283A1 PCT/EP2005/056689 EP2005056689W WO2007068283A1 WO 2007068283 A1 WO2007068283 A1 WO 2007068283A1 EP 2005056689 W EP2005056689 W EP 2005056689W WO 2007068283 A1 WO2007068283 A1 WO 2007068283A1
Authority
WO
WIPO (PCT)
Prior art keywords
frequency
sensor
electronic device
circuit
excitation
Prior art date
Application number
PCT/EP2005/056689
Other languages
French (fr)
Inventor
Michel Chevroulet
Michel Pierre
Original Assignee
Semtech Neuchâtel SA
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 Semtech Neuchâtel SA filed Critical Semtech Neuchâtel SA
Priority to PCT/EP2005/056689 priority Critical patent/WO2007068283A1/en
Publication of WO2007068283A1 publication Critical patent/WO2007068283A1/en

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00Measuring force or stress, in general
    • G01L1/14Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
    • G01L1/142Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators using capacitors
    • G01L1/144Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators using capacitors with associated circuitry
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01DMEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D21/00Measuring or testing not otherwise provided for
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01DMEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/243Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the phase or frequency of ac
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/12Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in capacitance, i.e. electric circuits therefor
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03LAUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00Automatic control of frequency or phase; Synchronisation
    • H03L7/06Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08Details of the phase-locked loop
    • H03L7/099Details of the phase-locked loop concerning mainly the controlled oscillator of the loop
    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03LAUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L2207/00Indexing scheme relating to automatic control of frequency or phase and to synchronisation
    • H03L2207/06Phase locked loops with a controlled oscillator having at least two frequency control terminals

Abstract

A UHF sensor interface (20), specially adapted for the interfacing of low-Q sensors (10), comprising a control device (30), preferably a digital PLL, for constraining the excitation frequency of the sensor to a narrow programmable frequency band. The frequency band can be accommodated in the allowed frequency bands in order to comply with EMC regulation in force in different countries.

Description

Sensor interface

Field of the invention

The present invention concerns a sensor interface and particularly, but not exclusively, a digital interface for a low-Q sensor operated in the UHF range. The object of the present invention can be usefully employed for the lecture of capacitive-, inductive- or resonant sensors, among others.

Description of related art

Several sensor are known in the art, which rely on the variation of an electrical parameter, for example capacitance, resistance, inductance or any other suitable electrical parameter, in response to an external quantity, like temperature, pressure, stress or other, whose value is to be measured.

A known way of interfacing such devices, as shown in enclosed figure 1, is to connect the sensor to an oscillator circuit, whereupon the variations in the quantity to be measured are reflected in a detuning of the oscillator, hence in variation of its output frequency. In this way the value of the quantity to be measured can be obtained by comparing the frequency generated by the oscillator circuit with a fixed reference frequency. Examples of this kind of sensor interface can be found in international patent application WO200334080 or in USA patent US3595084.

It is often desirable that the frequency of the oscillator circuit should be rather high, for example in the VHF or in the UHF region of the radio spectrum, because a high frequency implies a lower influence of parasitic resistances, and therefore a higher precision of the circuit. This is even more desirable for low-Q sensors, as often found in MEMS (Micro- Electro-Mechanical Systems). A high operating frequency is also a natural choice for highly miniaturized sensors. This is however difficult because of the strict emission limitations existing in the VHF and UHF bands. Very often, the use of these desirable frequency bands is barred by the emission regulation. As a general rule, EMC regulation allow UHF operation only in very narrow and well controlled frequency windows and, to further complicate matters, these windows are different in different countries.

It is a goal of the present invention to propose a sensor interface overcoming the above problems. In particular it is a goal of the present invention to propose a sensor interface that can function at a high operating frequency without violating the emission limitations in force.

Brief summary of the invention

According to the invention, these aims are achieved by means of an electronic device, connectable to a sensor having a variable electrical parameter responsive to a variable quantity to be measured; the device comprising an oscillator circuit, generating a signal having a frequency, the oscillator circuit comprising: a sensor connection, for coupling the sensor to the oscillator circuit, the frequency of the signal generated by the oscillator circuit being dependent from the variable electrical parameter of the sensor, a frequency variation means, for changing the frequency of the signal generated by the oscillator circuit, the electronic device being characterized by a frequency control circuit connected to the frequency variation means, arranged to compensate the variations of the electrical parameter of the sensor and maintain the frequency of the signal generated by the oscillator circuit into a predetermined interval of frequency.

Brief Description of the Drawings

The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which: Fig. 1 shows schematically and in a simplified way a known sensor interface.

Figure 2 shows schematically and in a simplified way a sensor interface circuit according to the present invention.

Detailed Description of possible embodiments of the Invention

According to figure 1, a sensor 10 is connected to a known circuit interface. In a MEMS, for example, the sensor 10 may be a variable capacity, whose value depends on chemistry, humidity, light, external force, pressure, acceleration, position, or other suitable external quantity.

The sensor 10 is connected, with reference to figure 1, to a free- running oscillator 15, which generates a variable frequency signal whose value is dependent from the capacity of the sensor 10 or, if the sensor 10 should be other than a capacitive sensor, from the value of an electrical parameter of the sensor 10. The free-running oscillator could be, for example an electronic LC oscillator.

The interface of figure 1 comprises also a reference frequency generator 75, which generates a fixed frequency which is compared, in circuit block 40, with the output frequency of the free-running oscillator 15. An output signal 50 is generated, on the base of the frequency difference.

The known circuit of figure 1 is hardly suitable for operation in the UHF frequency bands, because the free-running oscillator can not be constrained to maintain the excitation frequency of the sensor 10 in the narrow allowed bands. Furthermore it does not afford an easy way of programming the excitation frequency, to comply with different local regulations.

Turning now to figure 2, which represents a sensor interface 20 according to the present invention, the sensor 10 is connected, by an input terminal 12, to an oscillator 17. The oscillator 17, whose circuitry is not represented here in detail, could be any circuit suitable for the purpose, for example a electronic LC oscillator, a relaxation oscillator, a multivibrator, or any of the many suitable circuit which would be too long to enumerate here. The oscillation frequency of oscillator 17, present on output terminal 18, depends from the variable parameter of the sensor 10, thus on the quantity which one wants to measure. In most cases the output frequency of the oscillator 17, as seen at the terminal 18, is identical to the excitation frequency of the sensor 10. The invention comprises however also the general case in which the sensor excitation frequency and the oscillator's output frequency are not identical, but in a predefined relationship, for example in a harmonic relationship.

In the following of the application reference is made to a capacitive sensor 10, this being the most common case. It is noted however that other kind of sensors are possible and known, for example inductive or resistive sensors, whose value is dependent form a variable quantity to be measured, or even variable resonant cavities or transmission lines, whose frequency response or transit time are altered by the value of the external quantity to be measured. These and other sensors exhibiting a variable electrical parameter responsive to a variable quantity to be measured are comprised in the scope of the present invention.

The oscillator 17 comprises an additional means 36 of varying the oscillation frequency. In the example of figure 2 the frequency of oscillator 17 can be controlled independently, by the value of the capacitive sensor 10, connected on input 12, and by the voltage applied on the control means 36 consisting, in the case illustrated, in a varactor. In a simpler realization, a control varactor could be also connected to the input 12, in parallel with the sensor 10. In general, however, any way of controlling the output frequency of the oscillator 18 could be adopted, according to the circumstances. The oscillator may have for example an independent VCO input pin, which allows to vary its output frequency, for example by an internal variable capacitor, or by changing a gain or a threshold of an internal stage, or on any other suitable manner. The oscillator 17 is preferably dimensioned to operate, when the sensor 10 is connected, in the VHF or, more preferably, in the UHF region of the spectrum. As it is generally understood, for the purposes of the present invention the VHF region extends form 30 MHz to 300 MHz, while the UHF region goes from 300 MHz to 3 GHz.

Preferably the oscillation band of the oscillator 17 sports a range selection input 16, by which the oscillation frequency can be programmed, for example in coarse steps. In the presented example the sensor interface 20 comprises a frequency selection unit 80, which acts on the range selection input of the oscillator 17 and can be programmed from the outside, for example by means of a digital interface, not represented. Alternatively the programming of the frequency selection unit could also be done permanently in the factory.

Thanks to this feature the same sensor interface can be programmed for use with different sensors, and the exact excitation frequency of the sensor can be chosen, for example for adapting to local electromagnetic emission regulations.

A reference quartz oscillator 75 provides a stable reference frequency to the sensor interface 20 of figure 2. The autonomous reference oscillator 75 could be substituted by an external reference source, for example a clock of a host digital system, if available.

A frequency control circuit 30 is used to compare the frequency of the signal at the output 18 of the oscillator 17 and the reference frequency generated by the reference oscillator 75. Advantageously the circuit 30 includes a frequency divider 32, for bringing the frequency at the output 18 to the frequency of the reference source 75. Therefore, the reference circuit can operate at a lower frequency than the oscillator 17. The reference circuit 75 could be, for example, a conventional and convenient 13 MHz quartz oscillator. If the sensor interface is realized, as it is preferable, in a single custom integrated circuit the quartz crystal 77 can be added as an external component. More preferably the divider 32 has a programmable division ratio. In this way the same circuit interface 20 can be programmed to several excitation frequencies of the sensor 10, according to the frequency windows allowed by national regulations. The same effect of tuning precisely the excitation frequency of the sensor 10 may be obtained also by varying the frequency generated by the reference source 75. The programmable divider 32 is controlled, in the presented example, by the frequency selection unit 80.

The frequency control circuit 30 is completed by the phase detector 34 and the low-pass filter circuit 30, and the correction output signal is applied to the frequency variation means which consist, in this embodiment, in the varactor 36. It will be appreciated that the frequency of oscillator 17, and thus the excitation frequency of the sensor 10 are maintained at a constant value by the feedback action of the frequency control circuit.

Although the frequency control circuit of this embodiment consists in a PLL (Phase Locked Loop) circuit, the invention is not limited to this particular feature. PLL of figure 2 could be replaced, for example, by a FLL circuit (Frequency Locked Loop), by a digital PLL or, if available and when the rate of variation of the quantity to be measured is sufficiently low to allow it, by a suitably programmed microcontroller.

In general, the interface of the invention could operate in a fast loop mode or in a slow loop mode, according to the loop bandwidth of the PLL 30, mainly determined by the filter 38.

In the fast loop mode the control loop is very fast with respect to the signal bandwidth, i.e relative to the variation of the value of the sensor 10. In this case the variation of the correction signal applied to the varactor 36 keep the excitation frequency of the sensor 10 strictly constant and in a defined phase relation with the reference frequency generated by the circuit 75. The correction signal 33 is then, in the fast loop mode, a copy of the sensor output. In the illustrated case of a capacitive sensor, for example, the correction signal 33 is a copy of the sensor capacitance variations and can be directly used for generation of the output signal 50 of the sensor interface.

In the slow loop mode, the control loop speed is adequate to maintain a mean value of the excitation frequency constant, with respect to the reference frequency, but not to follow completely the fast variations of the sensor's parameter, the instantaneous frequency will therefore differ slightly from the mean value. In this case the correction signal 33 will reflect a low frequency component of the sensor output, while the fast variations can be captured using a counter (not represented) connected, for example, to the output of the phase detector 34.

Practically, if the control loop is implemented by means of a digital PLL, both the fast term and the average term can be obtained numerically.

An output signal conditioning module 60 optionally complete the circuit and comprises appropriate amplification and conversion means for providing a digital or analogue output signal 50 as required by the application.

It is to note that the circuit of the invention allows a precise selection of the excitation frequency of the sensor 10, and that, both in the fast loop mode and in the slow loop mode, the excitation of the sensor 10 can be limited to an extremely narrow interval of frequency, by providing the appropriate programming to the frequency selection unit 80. This allows one to exploit the narrow frequency windows which are allowed by the regulation, for example the 868.0-870.0 MHz or 433.05-434.79 MHz European frequency bands allocated to unregulated short-range communication.

At the same time, the sensor interface of the invention can be easily programmed or customized to different rules prescribing other frequency intervals.

Claims

Claims
1. An electronic device (20), connectable to a sensor (10) having a variable electrical parameter responsive to a variable quantity to be measured; the device (20) comprising: an oscillator circuit (17), for providing a AC excitation to the sensor (10) a frequency variation means (36), for changing the oscillation frequency of the oscillator circuit (17), a frequency control circuit (30) connected to the frequency variation means (36), arranged to compensate the variations of the electrical parameter of the sensor (10) and maintain the frequency of excitation of the sensor (10) into a predefined interval of frequency.
2. Electronic device (20) according to the previous claim, wherein the oscillator circuit generates an output signal (18) having a frequency identical or related to the frequency of excitation of the sensor (10), the frequency of the signal generated by the oscillator circuit (18) being dependent from the variable electrical parameter of the sensor (10).
3. Electronic device (20) according to any of the previous claims, wherein the frequency control circuit (30) comprises a PLL or a FLL device for synchronizing the frequency of the signal (18) generated by the oscillator circuit (17) to a reference frequency (75).
4. Electronic device (20) according to any of the previous claims, further comprising an output connection (50), for delivering an output signal relative to the variable quantity to be measured, the output signal being derived from the signal applied by the frequency control circuit (30) to the frequency variation means (36).
5. Electronic device (20) according to any of the previous claims, further comprising a programmable frequency selection circuit (80), arranged to determine, in a programmable way, the interval of frequency of the sensor's (10) excitation.
6. Electronic device (20) according to claim 5, wherein the frequency selection circuit (80), can be programmed to determine the interval of frequency of the sensor's (10) excitation within the 868-869 MHz band or within the 433-435 MHz band.
7. Electronic device (20) according to any of the previous claims, wherein the predetermined interval of frequency value is in the UHF or VHF bands.
PCT/EP2005/056689 2005-12-12 2005-12-12 Sensor interface WO2007068283A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2005/056689 WO2007068283A1 (en) 2005-12-12 2005-12-12 Sensor interface

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2005/056689 WO2007068283A1 (en) 2005-12-12 2005-12-12 Sensor interface

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WO2007068283A1 true WO2007068283A1 (en) 2007-06-21

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017534860A (en) * 2014-09-30 2017-11-24 ローズマウント インコーポレイテッド High temperature pressure sensing
EP3312568A1 (en) * 2016-10-18 2018-04-25 Commissariat à l'Energie Atomique et aux Energies Alternatives Sensor interface for hostile environments
WO2019190780A1 (en) * 2018-03-29 2019-10-03 Cirrus Logic International Semiconductor Ltd. False triggering prevention in a resonant phase sensing system

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US3448401A (en) * 1967-08-24 1969-06-03 Bendix Corp Digital frequency synthesizer eliminating high speed counters
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US6744324B1 (en) * 2001-03-19 2004-06-01 Cisco Technology, Inc. Frequency synthesizer using a VCO having a controllable operating point, and calibration and tuning thereof
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3448401A (en) * 1967-08-24 1969-06-03 Bendix Corp Digital frequency synthesizer eliminating high speed counters
US3595084A (en) * 1970-02-27 1971-07-27 Continental Can Co Digital transducer system
EP0226813A2 (en) * 1985-12-14 1987-07-01 Wandel & Goltermann GmbH & Co Synthesizer with a sum-compensation
US4851816A (en) * 1987-02-24 1989-07-25 Helene Macias Crib death (SIDS) warning device
JPH02100510A (en) * 1988-10-07 1990-04-12 Matsushita Electric Ind Co Ltd Automatic frequency controller
GB2279757A (en) * 1990-11-16 1995-01-11 Moonstone Technology Ltd Device for determining the presence and/or characteristics of an object or a substance
GB2258048A (en) * 1991-07-25 1993-01-27 Jalco Co Ltd Capacitance variation detection circuit
EP0945984A2 (en) * 1998-03-25 1999-09-29 i f m electronic gmbh Method for operating a capacitive switch and capacitive switch circuit
US6504420B1 (en) * 1998-11-12 2003-01-07 Broadcom Corporation Temperature compensation for internal inductor resistance
US20020175814A1 (en) * 2001-02-07 2002-11-28 David Wadlow Control system with capacitive detector
US6744324B1 (en) * 2001-03-19 2004-06-01 Cisco Technology, Inc. Frequency synthesizer using a VCO having a controllable operating point, and calibration and tuning thereof
WO2003034080A1 (en) * 2001-10-17 2003-04-24 Delphi Technologies, Inc. Method and apparatus for detecting a change in capacitance of a capacitive proximity sensor
EP1411630A1 (en) * 2002-10-15 2004-04-21 Marvell Semiconductor, Inc. Crystal oscillator emulator
EP1596208A1 (en) * 2004-05-14 2005-11-16 Fujitsu Limited Capacitance difference detecting circuit and mems sensor

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017534860A (en) * 2014-09-30 2017-11-24 ローズマウント インコーポレイテッド High temperature pressure sensing
EP3312568A1 (en) * 2016-10-18 2018-04-25 Commissariat à l'Energie Atomique et aux Energies Alternatives Sensor interface for hostile environments
US10436666B2 (en) 2016-10-18 2019-10-08 Commissariat à l'énergie atomique et aux énergies alternatives Sensor interface for hostile environments
WO2019190780A1 (en) * 2018-03-29 2019-10-03 Cirrus Logic International Semiconductor Ltd. False triggering prevention in a resonant phase sensing system
US10642435B2 (en) 2018-03-29 2020-05-05 Cirrus Logic, Inc. False triggering prevention in a resonant phase sensing system

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