LU93286B1

LU93286B1 - Signal Generator Circuit

Info

Publication number: LU93286B1
Application number: LU93286A
Authority: LU
Inventors: Orlando Grigoriadis; Thomas John
Original assignee: Iee Sa
Priority date: 2016-11-03
Filing date: 2016-11-03
Publication date: 2018-05-14

Abstract

Signal generator circuit for providing a measurement signal to a sensor system, the signal generator circuit comprising at least a clock generator for generating a clock signal, a clock calibration unit configured to calibrate at least the frequency of the clock signal using a built-in clock register, and a signal configuration circuit adapted to derive the measurement signal from the clock signal. The signal generator circuit further comprises a frequency shifting unit including the clock calibration unit, and the frequency shifting unit is configured to modify the measurement signal frequency using the built-in clock register of the clock calibration unit.

Description

Signal generator circuit

Technical field [0001] The invention relates to a signal generator circuit, and more particularly to a signal generator circuit for providing a measurement signal to a sensor system.

Background of the Invention [0002] Use of sensor systems is widely spread in modern technology. In particular in automotive vehicle, sensor systems are important assistants to the driver.

[0003] As a result, in an automobile for example, many sensor systems are installed in a very close environment. The first problem resulting from this multiplication of the sensors is the increase in the manufacturing cost. A new need for sensors comprising low cost hardware that are nevertheless performing well is growing.

[0004] Another problem of the multiplication of the number of sensors in a close vicinity is the apparition of interferences. The phenomenon is more obvious when identical sensors are operating at the same time by transmitting an identical measurement frequency. One sensor may receive a signal containing sensing information from another sensor using its same measurement frequency. The sensor will then interpret the other sensor's signal as a response to its own signal, and send an erroneous message to activate or modify a functionality of the vehicle. There is thus also a need for identical sensors that are able to operate at the same time in restricted areas.

[0005] Capacitive sensor systems are one type of commonly used sensor systems in automotive vehicle, in which a frequency measurement signal is generated to measure, for example, a change in a capacitive load between an electrode and ground. A measurement result is translated into information relative to a position of an object, a state of an apparatus or any relevant information regarding the functioning of the vehicle. The information is further treated and used to trigger a warning for the driver, another functionality of the vehicle or to adjust a driving parameter. For example sensors are used to open/close a door, to enable/disable airbags or to warn against the immediate proximity of potential collisions with an object.

[0006] There are solutions existing in the art to provide low cost hardware sensors. For example, a capacitive sensor operated in loading mode is disclosed in document WO 2016/071416. The solution disclosed in this document provides a capacitive sensor using common electronic components, and offering a substantive protection against interfering effects like temperature drift or electromagnetic interference. In this solution, a low cost signal generator of the sensor system uses a microprocessor with basic capabilities and a circuit for building a sine wave sensing measurement signal comprising basic electronic components.

[0007] Another solution is disclosed in document WO 2016/062824, disclosing a guard-sense capacitive sensor operated in loading mode. This solution involves similar advantages as the preceding solution, namely that it can be achieved using low-cost hardware components, and that it offers a sufficient reliability in the measurements results.

[0008] The prior art solutions exposed above offer both a solution to sensor systems using basic electronic components, particularly in the circuit generating the measurement signal. Their main inconvenient is that they do not offer any solution to interferences arising when using identical sensor systems very close to one another and operating at the same with the same measurement frequency.

Object of the invention [0009] It is therefore an object of the invention to provide a solution for a simple sensor system that has an improved robustness against interferences, and in particular against interferences arising when a plurality of sensor systems are operating at the same with the same measurement frequency in a close vicinity.

General Description of the invention [0010] In one aspect of the present invention, the object is achieved by a signal generator circuit for providing a measurement signal to a sensor system, the signal generator circuit comprising at least a clock generator for generating a clock signal with a given frequency; a clock calibration unit configured to calibrate at least the frequency of the clock signal using a built-in clock register; and a signal configuration circuit adapted to derive the measurement signal from the clock signal; [0011] According to the invention, the signai generator circuit further comprises a frequency shifting unit including the clock calibration unit, and the frequency shifting unit is configured to modify the measurement signal frequency using the built-in clock register of the clock calibration unit.

[0012] The clock signal is generated in order to provide a time reference for any sensitive operation performed by the circuit. Generation of further frequency signals is consequently dependent of the clock signal. The invention is based on the insight that a frequency shift of the clock signal will produce a frequency shift of the measurement signal.

[0013] In order to avoid a phenomenon of interference due to the use of two identical sensor system operating in proximate vicinity from one another, it has been found that just a slight modification of the measurement signal frequency of one of the systems is sufficient. The signal generator according to the invention enables the measurement signal frequency to be slightly modified through a related modification of the clock signal frequency and consequently avoid any phenomenon of interferences between two or more identical sensor system using the signal generator.

[0014] An important advantage of the system is that with the ability to remove interferences, the invention increases the robustness and the reliability of a sensor system. Another important advantage is that the resulting generator system uses only basic electrical components. The system can thus be developed at a low production cost.

[0015] Advantageously, the modification of the clock signal is small enough so that it does not really impact other actions performed by the sensor system that also require timing from the microcontroller. For example the modification of the clock signal may shift the clock frequency by 10 to 100 kHz.

[0016] In embodiments, the signal generator further comprises a microcontroller, wherein the clock generator, and the clock calibration unit, are included in the microcontroller.

[0017] It is remarkable that a clock generator and a clock calibration unit are basic components of microcontrollers, even with restricted capabilities. The signal generator circuit can then be produced using low-cost microcontroller. It is also remarkable that most signal generators comprise a microcontroller. The invention is therefore implementable using most of the existing signal generator.

[0018] In embodiments, the signal configuration circuit comprises a signal configuration unit connected to the microcontroller and configured to derive a sine measurement signal from the clock signal. In these embodiments, the signal generator is particularly adapted to produce a measurement signal for a capacitive sensor system, or another sensor system requiring a sine frequency measurement signal.

[0019] In embodiments, the microcontroller further comprises a timer unit for dividing the clock frequency of the clock generator.

[0020] Typically the timer unit is used to produce a square signal that is derivative from the clock signal, with a lower frequency. It is advantageous to keep a clock signal with a high frequency to perform automated tasks, and aside to produce a signal with lower frequency more suitable for the generation of a measurement signal. The timer unit is also a common component of the microcontroller, and does not imply a relevant increase in the overall cost of the signal generator.

[0021] It will be appreciated, that the clock signal may also be fed to the signal configuration circuit without being divided to a lower frequency. This may e.g. be implemented by feeding the clock signal directly to the signal configuration circuit without passing by a timer unit or by setting the divisor of the timer unit to 1. In this case, the frequency of the measurement signal substantially corresponds to the clock signal, i.e. both the clock signal and the measurement signal may have a frequency of 8 MHz.

[0022] In another aspect, the present invention also relates to a capacitive sensor system comprising at least a sense electrode connected to a signal sensing circuit, and to a signal generator circuit as disclosed above.

[0023] In modern automotive vehicle, capacitive sensors are intensively used to detect occupant related status, like occupancy or nature of the occupant to activate child restraint security devices. According to the invention, a plurality of capacitive sensors may be Installed proximate to one another, in order to avoid Interferences due lo their use of frie seme measurement frequency, sold measurement frequency Is set to a different value for each proximate sensor. 100241 tn embodiments, the capacitive sensor system further comprises an interference defector system configured to detect a proximate interfering signal, in such an embodiment the interference defector system may automatically detect teat a proximate system is transmitting a Signal with tee same frequency as the s;gnai generator, Once the interference is detected, the circuit may transmit a warning signal to another component or device In order to tell a user that the frequency of the Signal generator has to ho modified. (60261 The addition cf an interference detector system may add more complexity m the sensor system circuit, with tea addition of more components. A technician is required to identify which sensor might cause interferences with which other proximate sensor before modifying tea measurement frequencies. (00261 in embodiments, the Interference detector system ss further configured to modify tea frequency of the measurement signal vie the frequency shifting unit controlling the clock register, when defecting an interfering signal. (00271 Advantageously, the interference detector system Is able to send a command to the signal frequency shilling unit in order to modify tee frequency of the clock signal automatically. Accordingly, the meesurement signal frequency shifting In the presence of Interferences Is automatized. The automatization of the shifting of Ilia measurement frequencies of the sensor makes the sensors more reliable than when if requires the intervention of a technician, it Is also interesting when elements of the vehicle are movable during normal usage, such as e.g. vehicle seats. A sensor might come close io another identical sensor during normal usage operations of the vehicle, causing interferences. With an automatic shift of measurement frequencies, the sensor system ss more flexible in its location, 100281 te yet another aspect, frie invention relates to a sensor system arrangement comprising a plurality of sensor systems as disclosed hereinabove, [00261 In embodiments, each sensor system of the sensor system anztegornent is configured wilts e dilferenf measurement signal frequency, via the frequency shifting unit controlling the clock register. Advantageously, the sensor system may be manipulated to shift their frequency only when they are installed proximately to another sensor system of the arrangement. More advantageously, the sensor systems comprise an interference detector system and adjust their frequency when needed.

[0030] In another aspect, the invention relates to a method for modifying a frequency of a measurement signal in a sensor system comprising a signal generator circuit, the signal generator circuit comprising at least a clock generator for generating a clock signal, a clock calibration unit configured to calibrate at least the frequency of the clock signal using a built in clock register, a signal configuration circuit adapted to derive the measurement signal from the clock signal. The sensor system further comprising a frequency shifting unit configured to modify the measurement signal frequency. The frequency shifting unit including the clock calibration unit. The method comprising the step of modifying the clock frequency with the frequency shifting unit, using the built-in clock register of the clock calibration unit.

[0031] The invention is based on the insight that the measurement signal frequency is produced using signal derived or calculated based on the clock signal of a sensor system. By modifying the clock frequency, it directly impacts the frequency of the measurement signal without having to add additional costs of components to the sensing circuit.

Brief Description of the Drawings [0032] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

Ftg.1 is a layout of an embodiment of a sensor system comprising a signal generator circuit according to the invention.

Fig.2 shows graphical representation of the time response of simultaneous signals coming out from different elements of the sensor system of Fig. 1.

Fig.3 is a layout of an embodiment of a sensor system arrangement according to the invention.

Description of Preferred Embodiments [0033] Fig. 1 shows a preferred embodiment of a capacitive sensor system 10 comprising a signal generator circuit 12. The capacitive sensor system 10 comprises a sense electrode 14, a sensing circuit 16, and the signal generator 12.

[0034] The signal generator circuit 12 is configured to provide a measurement signal 18 to the sense electrode 14, The measurement signal 18 is e.g. a sine frequency signal with a predetermined frequency. The measurement signal frequency is chosen to provide less interference in the measurement and depends on the type and the surrounding of the capacitive sensor.

[0035] The signal generator 12 comprises a microcontroller 20 for generating at one of its output, a square frequency output signal 22 with a frequency corresponding to the frequency of the measurement signal 18.

[0036] The signal generator 12 further comprises a signal configuration circuit 24 configured to generate the sine measurement signal 18 as derived from the square frequency output signal 22.

[0037] The microcontroller 20 includes a clock generator 26 for generating a clock signal 28, a timer unit 30, and a frequency shifting unit 32.

[0038] The frequency shifting unit 32 includes a clock calibration unit 34 configured to calibrate at least the frequency of the clock signal 28 using a built-in clock register. The frequency shifting unit 32 is further configured to modify the clock signal 28 and as a consequence to modified the derived measurement signal 18.

[0039] The clock register is a code pre-installed in the memory of the microcontroller 20 and defines the frequency of the on-chip oscillator which generates the clock signal 28.

[0040] The clock calibration unit 34 is comprised inside the microcontroller 20 and is primarily used during or before installation of the microcontroller 20 in order to preset a fix clock signal frequency and amplitude. The clock calibration unit 34 may also be used for maintenance operations of a system to reset the clock signal frequency that has shifted due, for example, to a change in the temperature conditions of the system.

[0041] It is an important feature of the invention that the clock calibration unit 34 is part of the frequency shifting unit 32. The measurement signal is a frequency signal, and more generally a time based signal. It is thus generated based on the clock signal which provides a base for all time related operations of the system. As it will be explained below, the measurement signal is generated by applying various transformations on the clock square pulse signal in order to obtain a sine frequency signal with a suitable predetermined frequency. These operations form a proportional relation between the clock signal and the measurement signal, and consequently a modification of the clock signal frequency produces a proportional modification of the measurement signal 18. According to the invention, the clock calibration unit 34 has thus an additional function of modifying the frequency of the final measurement signal 18.

[0042] The shifting unit 32 further comprises an interface 36 in order to send and receive signals to/from another device acting as a controlling device (not shown) for the shifting unit 32. For example, the controlling device for the shifting unit 32 may be a knob directly activated by the hand of a technician, a computer that is carried by the technician when performing the modification of the measurement signal frequency, or any suitable means for controlling the shifting unit 32.

[0043] In Fig. 2, we see the simultaneous time response of the signals inside the sensor system 10. In operation, the clock signal 28 is first generated by the clock generator. The signal 28 is used by the timer unit 30 to generate the square frequency output signal 22 which is further used in the signal configuration circuit 24 to generate the measurement signal 18.

[0044] The clock signal 28 is a square signal with a given frequency that is built-in with the microcontroller 20.The clock signal 28 oscillates between a low state and a high state to provide a beat that is used to provide a time lapse reference to the sensor system and to coordinate every actions of the microcontroller 20.

[0045] As we see in Fig. 2, the square frequency output signal 22 produced by the timer unit 30 is merely a signal identical to the clock signal 28 but with a frequency which is a subdivision of the frequency of the clock signal 28. The timer unit 30 is used to uncorrelate the signal that will be processed to obtain the measurement signal from the clock signal. Although the timer unit’s output signal 22 is still proportional to the clock signal 28, it is a signal of a lower frequency, leaving a higher frequency clock signal 28 to be used for other operations in the sensor system.

[0046] Other time based operations of the system may include for example, an interference detection operation in embodiments in which the sensor system 10 includes an interference detector circuit. In that case, the interference detector may need to timely check the presence of an interference signal and modify in real-time the clock signal.

[0047] Once the signal has been modified through the timer unit 30, the square output signal 22 is sent to an output of the microcontroller 20 and further to the signal configuration unit 24. The signal configuration unit 24 receives the square output signal 22 and produces the measurement signal 18. The signal configuration unit 24 comprises for example a low pass filter unit with an LC filter circuit, or another suitable circuit. In any case the resulting signal generator does not involve complex nor costly electrical components.

[0048] The sine frequency measurement signal 18 is finally output from the signal configuration unit 24 and sent to the sensing circuit 16 and the sense electrode 14. The sensing circuit 16 may be a typical capacitive sense electrode circuit with a configured to send a current to the sense electrode in order to compensate the current going from the sense electrode to ground and indicative of the presence of a body between the sense electrode and ground, then measuring a produced voltage indicative of the current sent to the sense electrode.

[0049] Fig. 3 shows an arrangement of two sensor systems installed proximate to one another. This situation may happen for example in an automotive vehicle like an automobile, in the area of the trunk where a capacitive sensor may be used for a smart trunk opener, located next to a sensor for collision prevention in reverse drive assistance.

[0050] In that case the measurement signal of a first sensor 38 may be sensed by the sensing circuit 16 of the second sensor 40, and vice versa, as indicated by the arrows S in Fig. 3. During installation of the sensors, the technician needs then to adjust the measurement signal frequency of one of the sensors.

[0051] The method used to adjust the measurement signal of one sensor according to the invention requires only one step of modifying the clock frequency with the frequency shifting unit 32. The frequency shifting unit 32 using the built-in clock register of the clock calibration unit 34. Advantageously, the technician may use an external device that is connected to the frequency shifting unit controlling the clock generator.

[0052] It appears that just a slight modification of the measurement signal frequency of one of the two sensor systems is enough to avoid any phenomenon of interference due to the use of the same measurement signal. Accordingly, the shifting of the clock signal frequency does not need to be relatively important and other operations using the clock signal of the microcontroller will not be significantly affected by the frequency shifting.

[0053] In other embodiments of the invention (not shown), the frequency shifting unit further comprises a controller connected to an interference detector circuit. The interference detector is configured to compare all the characteristic features of the received signal with the ones of the measurement signal, for example amplitude, frequency and phase, and decide whether the received signal comprises an interfering signal. If an interfering signal is detected, the interference detector sends a signal to the clock generator controller which automatically shifts the clocks signal frequency through the clock calibration unit of a predetermined value to remove the interference signal from the measurements.

List of Reference Symbols 10 capacitive sensor system 12 signal generator circuit 14 sense electrode 16 sensing circuit 18 measurement signal 20 microcontroller 22 square frequency output signal 24 signal configuration circuit 26 clock generator 28 clock signal 30 timer unit 32 frequency shifting unit 34 clock calibration unit 36 interface 38 first sensor system 40 second sensor system

Claims

A first generation invention for providing a massing signal to a sensor system, the signal generator circuit at least comprising: a clock generator for encoding a clock signal having a given frequency; a clock signaling unit designed to delay the frequency of the alarm signal using the integration of ïaktreyisfars; and a signal conditioning circuit adapted to derive the measurement signal from the clock signal, characterized in that the signal generator circuit further comprises a frequency beating means. which includes the clock chirp unit and that the frequency varieburnorhed is adapted to modify the sample loop frequency using the integrated timing switch of the clock arbitration unit.

The signal generator circuit of claim 1, further comprising a micro-controller, wherein the clock generator and the clock calibration unit are included in the micro-controller.

A signal generator circuit as claimed in claim 2, wherein said signal conditioning circuit comprises a transistor connected to said micro-controller and adapted to conduct a clock signal from said token signal.

The signal generator circuit according to claim 2 or 3, wherein the micro-controller further comprises a Zaltsteuerungselnheit for dividing the Taktfrepuenz the ïaklgenerators

A capacitive sensor system comprising at least one Fdhielekfrcde, which is connected to a SignsFühlschaltung and with a Slgnalgeneratorschailang according to any one of the preceding claims,

The capacitive sensor system of claim 5, further comprising an interference detector system configured to detect a near interference signal.

The capacitive sensor system of claim 6, wherein the interference detection system is further configured to modify the frequency of the measurement signal via the frequency shift unit that controls the clock register when an interference signal is detected.

8. Sensor system arrangement, comprising a plurality of sensor systems according to claim 7.

The sensor system arrangement of claim 8, wherein each sensor system is configured with a different measurement signal frequency via the clock register controlling frequency shift unit.

10. A method for modifying a frequency of a measurement signal in a sensor system, comprising a signal generator circuit, the signal generator circuit having at least one clock generator for generating a clock signal; wherein a clock calibration unit is adapted to calibrate at least the frequency of the clock signal using an integrated clock register; a signal configuration circuit adapted to derive the measurement signal from the clock signal; and a frequency shifting unit configured to modify the measurement signal frequency; wherein the frequency shifting unit comprises the clock calibration unit; the method comprising the step of: modifying the clock frequency with the frequency shifting unit using the integrated clock register of the clock calibration unit.