GB2309605A

GB2309605A - Adjusting power delivered to an aerial to ensure that it is sufficient to operate a remote device

Info

Publication number: GB2309605A
Application number: GB9701348A
Authority: GB
Inventors: Manfred Glehr
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1996-01-23
Filing date: 1997-01-23
Publication date: 1997-07-30
Anticipated expiration: 2017-01-23
Also published as: GB9701348D0; MX9700571A; FR2743962B1; FR2743962A1; GB2309605B; DE19602316C1

Abstract

The device has an antenna oscillating circuit (3, 4). The oscillation is transmitted to a transponder oscillating circuit (5, 6). In order that the transmission of energy or data is as effective as possible, the current or the voltage in the antenna oscillating circuit (3, 4) is measured and compared with a desired variable. In the event of deviation, a correction value is produced, by which the excitation current is increased or the resonance frequency f R , as a result of connecting an impedance (* capital Greek delta *C, * capital Greek delta *L) into the antenna oscillating circuit (3, 4), is adjusted to the excitation frequency f E .

Description

2309605 A METHOD OF DETERMINING THE COMPATIBILITY OF AN ANTENNA

OSCILLATING CIRCUIT AND AN EXCITATION UNIT OF A TRANSCEIVER MEANS, AND A TRANSCEIVER MEANS FOR TRANSMITTING DATA OR ENERGY The invention relates to a method of determining the compatibility of an antenna oscillating circuit and an excitation unit of a transceiver means, and to such a transceiver means for transmitting data or energy. Such a device can be used in particular for an antitheft system for a motor vehicle, in which anti-theft system items of coded information are sent between a key and a lock.

A device known from DE 44 30 360 Cl has a stationary transceiver, which contains an oscillating circuit. In the transceiver, an oscillation is forced by an excitation variable and the energy of said oscillation is transmitted to a transponder. The transponder likewise has an oscillating circuit, by which the energy is received and coded data is transmitted back to the transceiver.

In this known device, if initially there is no success with the first detection of the coded data, the oscillating circuit of the transceiver is lldetunedll. For this purpose, the resonance frequency of the oscillating circuit or its excitation frequency is altered. If the oscillating circuit is detuned as a result of component tolerances, this detuning is retained even if the transceiver is used in an antitheft system. For this reason, each transmission operation has to be carried out at least twice.

The problem underlying the invention is to develop a device for transmitting data or energy, in which device the energy or the data is transmitted as effectively as possible.

According to the present invention, there is provided a method of determining the compatibility of is an antenna oscillating circuit with an excitation unit arranged to supply an excitation variable having an excitation frequency to the antenna oscillating circuit, which antenna oscillating circuit and excitation unit form transceiver means for transmitting data or supplying energy to a transponder, the method comprising the step of determining, during an initial operation of the transceiver, whether the signal induced in the antenna oscillating circuit by the excitation variable is sufficient for reliable operation, and, if not, calculating a correction value to be applied during every subsequent operation of the transceiver means, so as to ensure reliable operation of the antenna oscillating circuit.

In this connection, a stationary transceiver has a first oscillating circuit which has a coil and a capacitor. The oscillating circuit is excited by an excitation variable having an excitation frequency in order to produce an oscillation. The current and/or the voltage of the excitation variable is/are measured and if the current or the voltage deviates from a desired value, a correction value is produced.

Advantageously, this correction value is stored and used in later inductive transmissions of data or energy in an anti-theft system.

For a better understanding of the present invention. and to show how it may be brought into effect, reference will now be made, by way of example to the accompanying drawings, in which:

Figure 1 shows a diagrammatic block-circuit diagram of the device in accordance with the invention; Figure 2 shows a resonance curve of an oscillating circuit of the device according to Figure 1; and Figure 3 shows a circuit diagram of a transceiver of the device according to Figure 1.

A device in accordance with one embodiment of the is invention, for transmitting data or energy is shown in Figure 1, and has a stationary transceiver 1, which cooperates with a portable transponder 2 by way of a transformative coupling if the transponder 2 is in the vicinity of the transceiver 1. The transceiver 1 first of all transmits energy to the transponder 2. Stored in the transponder 2 is an item of code information, which is transmitted back to the transceiver 1 (energy transmission and data return transmission are shown by a double arrow which is drawn with a dashed line) In order to transmit energy or data, the transceiver 1 has an antenna 3 in the form of a coil, which together with a capacitor 4 forms a first oscillating circuit (termed antenna oscillating circui 3, 4, in the following). The antenna 3 is coupled inductively or transformatively with a coil 5 of the transponder 2. The coil 5 of the transponder 2 forms together with a capacitor 6, which is arranged in series or in parallel therewith, a second oscillating circuit (termed transponder oscillating circuit 5, 6 in the following).

A generator or an oscillator 7 feeds the antenna oscillating circuit 3, 4 with an alternating voltage or an alternating current in time with an excitation frequency f. as soon as a supply unit 8 of the oscillator 7 is switched on. As a result of this, the antenna oscillating circuit 3, 4, is excited to oscillation with the excitation frequency fE. The field which is excited by the antenna 3 induces a voltage in a coil 5 of the transponder 2 if the transponder 2 is arranged in the vicinity of the transceiver 1.

The transponder oscillating circuit 5, 6 is in turn excited to oscillation by the oscillation of the antenna oscillating circuit 3, 4. The transponder oscillating circuit 5, 6 can be loaded in the rhythm of the code information by a connected transponder-IC 9, is in which an item of code information is stored. As a result of this, the antenna oscillating circuit 3, 4 is loaded or modulated in the rhythm of the code information due to the transformative coupling.

The oscillator 7 having an excitation variable forces the antenna oscillating circuit 3, 4 to oscillate with an excitation frequency fE. The output voltage or output current of the oscillator 7 is used as an excitation variable. The oscillator 7 oscillates with the oscillator frequency f.. There can also be arranged between the oscillator 7 and the antenna oscillating circuit 3, 4 a frequency divider (not shown), which divides the oscillator frequency f. down to the desired excitation frequency f.. By means of the excitation variable, there results a forced oscillation of the antenna oscillating circuit 3, 4, which then oscillates with the excitation frequency f..

Each oscillating circuit has a natural frequency, also termed resonance frequency f,,, which is determined by the components of the oscillating circuit, i.e. by the inductance of the antenna 3 and the capacitance of the capacitor 4 in the antenna oscillating circuit 3, 4. The excitation current which flows through the antenna 3 is greatest when the oscillating circuit is excited with the excitation frequency f. equal to the resonance frequency f. (see continuous curve in Figure 2). As a result of this, the magnetic f ield, which is generated by the current I flowing through the antenna 3, is at its greatest. Consequently, maximum energy is transmitted to the transponder 2. The maximum amplitude of the current I depends on the quality of the oscillating circuit. In the case of high quality, the amplitude of the current I is high, and in the case of low quality, the amplitude of the current I is lower.

The power balance is illustrated with the aid of a 5_ resonance curve (Figure 2), in which the frequency f is plotted on the abscissa (x-axis) and the amplitude of the current I through the antenna 3 is plotted on the ordinate (y-axis).

The excitation frequency fE can be kept very constant by a regulated oscillator 7, while the resonance frequency f. is dependent on the components and their tolerances. If the excitation frequency f. is equal to the frequency fl and the resonance frequency f. is likewise equal to the frequency f., the current I which flows through the antenna 3 is at its greatest with a maximum amplitude of I, If the resonance frequency f. (= frequency f2) deviates from the excitation frequency f. (resonance curve drawn with a dashed line in Figure 2), the antenna oscillating circuit 3, 4, is no longer optimally excited and only a current having the amplitude 12 flows through the antenna 3. The magnetic field generated therewith can be too small for the transmission of data or energy.

During manufacture of the transceiver 1, deviations from desired values in the case of the inductance of the antenna 3 and the capacitance of the capacitor 4 can arise as a result of component tolerances. Consequently, the resonance frequency f. of the antenna oscillating circuit 3, 4 alters with respect to the constant excitation frequency f.. If the device in accordance with the invention is to be operated under such conditions, the maximum amount of energy is no longer transmitted to the transponder 2 and the data received thereby can likewise be received only with very low amplitude.

After manufacture of the transceiver 1, it is first of all necessary to establish whether the resonance frequency fR deviates from the excitation frequency fE by more than a certain predetermined is amount. For this purpose, the amplitude of the current I through the antenna 3 or the voltage U at the capacitor 4 is measured with the aid of a measuring device 10. The amplitude which is measured is compared with a desired value which is determined and stored beforehand. If there is too grea t a deviation, a correction value is produced and stored in the measuring device 10. Depending on the correction value, the antenna oscillating circuit 3, 4 is then corrected in the case of all transmissions between transceiver 1 and transponder 2, in order that a transmission between transceiver 1 and transponder 2 that is as effective as possible takes place.

The antenna oscillating circuit 3, 4 can be altered in two different ways in dependence on the correction value, in order that a transmission of energy and data that is as effective as possible takes place. on the one hand, the resonance frequency f,, of the antenna oscillating circuit 3, 4 can be approximated to the excitation frequency f., and on the other hand, the current I through the antenna 3, i.e. the excitation current, can be increased.

First of all, the alteration of the resonance frequency fR 'S considered (path in Figure 1 drawn with a dashed line). By measuring the current I through the antenna 3, first of all the maximum amplitude of said current is compared with a desired amplitude. If the current deviates too much from a desired current, the resonance frequency fR deviates from a desired resonance frequency.

By measuring the phase of the current and of the voltage, it can be established whether the antenna oscillating circuit 3, 4 is detuned inductively or capacitively. Then, in the case of an inductive detuning, the current I through the antenna 3 lags behind the voltage U by a phase angle p, and in the is case of a capacitive detuning, the current I leads the voltage U by the phase angle o. By means of the measured amplitude of the current I, the magnitude of the detuning is known. By means of the comparison of the phases of current I and voltage U, the direction of the detuning is known. The amplitude I and the phase angle (p then determine the correction value.

Subsequently, in dependence on the correction value, a capacitance AC or an inductance AL is connected into or out of the antenna oscillating circuit 3, 4 by way of a capacitive and/or inductive network 11. As a result of this, the resonance frequency fR of the antenna oscillating circuit 3, 4, is altered. The capacitance AC and the inductance AL are determined in such a way that the resonance frequency fR approaches the excitation frequency f. by connecting the capacitance AC and/or the inductance AL into or out of the circuit. This corresponds in Figure 2 to a displacement of the resonance curve which is drawn with a dashed line to the left into the resonance curve which is drawn with a continuous line. Consequently, in the case of the excitation frequency fE, a current I flows through the antenna 3, the amplitude of which current approaches the desired amplitude I,.

Connecting the capacitance AC and/or the inductance AL into or out of the circuit occurs only once after manufacture of the transceiver 1. For subsequent transmission operations, these corrections, i.e. connecting the capacitance AC and/or the inductance AL inwards or outwards, are retained. Consequently, the antenna oscillating circuit 3, 4 is adapted to the excitation unit having the oscillator 7. Advantageously, the antenna oscillating circuit 3, 4 is produced in such a way that its resonance frequency f., taking into account production tolerances, is above the excitation frequency f. or the desired resonance is frequency. Consequently, the device is more simple because only capacitors need to be connected into it.

If the antenna oscillating circuit 3, 4 is only slightly capacitively detuned, the resonance frequency f. can be altered by connecting a capacitance AC outwards. If on the other hand the antenna oscillating circuit 3, 4 is slightly inductively detuned, the resonance frequency fR can be altered by connecting a capacitance AC inwards.

Next, an alteration of the current I through the antenna 3 is considered. If the antenna oscillating circuit 3, 4 is detuned, then in the case of the excitation frequency f., only a current having the amplitude 12 flows through the antenna 3, thus the excitation current can also be increased to such an extent that the amplitude of the current through the antennae is approximately equal to the amplitude I, (resonance curve in Figure 2 shown with dotted line).

For this purpose, first of all the current 12 'S measured. Since the amplitude I, of the ideal current is known, the correction value by which the current 12 has to be amplified can be determined. In this procedure, the amplitude 13 of the maximum current through the antenna 3 increases if the latter was excited with an excitation frequency f. equal to the frequency f2. Because the current is increased, more energy therefore has to be fed into the device, i.e. the excitation current has to be increased considerably.

Increasing the excitation current in dependence on the correction value occurs only once after manufacture of the transceiver 1. For subsequent transmission operations, these correction values are retained, i.e. in the case of all later transmissions of data or energy, the excitation current determined by the correction value remains constant. This has the -g- is advantage that a constant magnetic field is generated. Consequently, sufficient voltage is induced in the transponder oscillating circuit 5, 6 to transmit data in the reverse direction from the transponder 2 to the transceiver 1.

The correction value can be stored and can influence in each transmission operation the excitation current or the connection inwards or outwards of the capacitance AC and/or the inductance AL.

In the case of the device in accordance with the invention, both corrections can also be carried out one after the other, i.e. first of all alteration of the resonance frequency f. and then of the current I by correcting the excitation current. This can then be the case if a good approximation to the desired resonance frequency is still not achieved by altering the resonance frequency fR.

Figure 3 shows a circuit diagram of the device in accordance with the invention. In this connection, the antenna 3 is activated by way of a bridge circuit, in the branches of which is located a respective switching transistor T, to T4. The transistors T1 to T, are in this connection switched on or off in pairs, i.e. the pair T1 and T3 and the pair T2 and T4. The transistors T1 to T4 are activated during this time with the excitation frequency f. in such a way that a positive voltage and a negative voltage are alternately applied to the antenna 3. As a result of this, a sinusaidal current having the frequency f, which is equal to the excitation frequency f., flows through the antenna 3.

Between the antenna 3 and the capacitor 4 is a tapping point, which is connected to the measuring device 10 for measuring current I and voltage U. With the measuring device 10, both amplitude and phase of current I and voltage U can be measured. The measured values are compared with desired values, which are at is the heart of the design of the device and are stored in the measuring device 10. In the event of deviation beyond a predetermined tolerance width, the correction value is produced and stored.

The transistors T, to T, can each comprise several individual transistors connected in parallel, in which case the individual transistors are each switched on according to the correction value. Thus the individual transistors can be, for example, connected directly to the individual memory cells of a memory (not shown), in which the correction value is stored as a binary value. In this connection, the correction value determines the number of individual transistors which are arranged in parallel with each other and are activated according to the correction value.

In this connection, the memory can be contained in the oscillator 7, by way of which the antenna 3 is then activated according to the correction value. The oscillator 7 then acts as a current driver stage of the antenna 3.

The transistors T1 to T, in the bridge circuit can also be activated by a pulse-width modulated signal by way of the oscillator 7. Depending on the length of the switching-on pulse and a subsequent variable interpulse period (duration of pulse and interpulse period depend on the correction value), the pairs of transistors T1 and T3. and T2 and T4 respectively are switched on and off for different lengths of time. Consequently, the current I through the antenna 3 can be controlled in dependence on the correction value.

Activation with a pulse-width modulated signal has the advantage that at the same time an amplitudemodulated signal can be transmitted to the transponder 2.

The excitation current, and consequently the current I through the antenna 3, is, however, altered is only within a predetermined tolerance width, in dependence on the correction value. If a greater alteration were necessary, it is possible to conclude from this that the corresponding transceiver 1 contains faults which are too great and as a result of this is sorted out.

In the device in accordance with the invention, the correction value is determined at least once after manufacture of the transceiver 1 at the end of the assembly line. In the case of all subsequent transmission operations, the correction value is already included, so that the efficiency of the transmission is high, i.e. in order that the received amplitudes of the transmitted signals are high enough.

In the device in accordance with the invention, the correction value can then be determined if the transponder 2 is arranged in the vicinity of the transceiver 1. The transponder oscillating circuit 5, 6, however, has only a slight effect on the resonance frequency f. of the antenna oscillating circuit 3, 4 and the current I through the antenna 3, because its coil 5 and its capacitor 6 have only low impedance values because of the small dimensions of the transponder 2. For this reason, the resonance frequency fR of the antenna oscillating circuit 3, 4 and of the current I through the antenna 3 can also be established without the transponder 2.

The desired values for the resonance frequency f. and the current I, can be established beforehand on a laboratory pattern. The desired values can, however, also be calculated with the aid of a model.

In an advantageous manner, a device in accordance with the invention is used in an anti-theft system for a motor vehicle. In this connection, energy is transmitted from the transceiver 1 to the transponder 2, which uses this energy in order to transmit coded is data from the transponder 2 back to the transceiver 1. In an advantageous manner, the oscillation of the transponder oscillating circuit 5, 6, is load-modulated or frequency-modulated in the rhythm of the code information. As a result of the inductive coupling, the oscillation of the antenna oscillating circuit 3, 4 is likewise modulated.

The modulated oscillation of the antenna oscillating circuit 3, 4 is detected either by the measuring device 10 or by an evaluation unit (not shown). A demodulator demodulates the code information from the modulated oscillation and passes it on to a comparator. The comparator compares the detected code information with an item of desired code information, and in the event of agreement gives a release signal to a safety unit. Such a safety unit can be, for example, an immobiliser or a door lock.

In this connection, the transceiver 1 can be arranged on a door lock or ignition lock, while the transponder 2 is accommodated on an ignition key or on a chip card.

The measuring device 10 can be a microprocessor, which detects the current by way of an A/D converter and takes over the connection inwards of the capacitance AC and/or of the inductance AL or the control of the excitation current. other functions, such as demodulation and comparison of variables, can be taken over by the microprocessor.

Instead of the amplitude of the current, the amplitude of the voltage at the antenna 3 can also be measured. In order to measure the phase angle p and the capacitive or inductive detuning of the antenna oscillating circuit, the phase of both the voltage and the current through the antenna 3 is measured. Such measurements are sufficiently known. They do not need to be explained in greater detail here.

The capacitive and/or inductive network 11, by which the capacitance AC and/or the inductance AL is connected into of out of the antenna oscillating circuit 3, 4 as parallel or series impedance, comprises various impedances, such as capacitors and coils. In this connection the magnitude of the impedance which alters the antenna oscillating circuit 3, 4 depends on the detuning of the antenna oscillating circuit 3, 4 and therefore on the resonance frequency f. and the excitation frequency f..

is

Claims

1. A method of determining the compatibility of an antenna oscillating circuit with an excitation unit arranged to supply an excitation variable having an excitation frequency to the antenna oscillating circuit, which antenna oscillating circuit and excitation unit form transceiver means for transmitting data or supplying energy to a transponder, the method comprising the step of determining, during an initial operation of the transceiver, whether the signal induced in the antenna oscillating circuit by the excitation variable is sufficient for reliable operation, and, if not, calculating a correction value to be applied during every subsequent operation of the transceiver means, so as to ensure reliable operation of the antenna oscillating circuit.

2. A method according to claim 1 in which the current and/or the voltage in the antenna oscillating circuit is/are measured, wherein if the current or the voltage deviates from a desired value, a correction value is calculated.

3. A method according to claim 1 or 2, wherein the current and/or the voltage in the antenna oscillating circuit are measured according to magnitude and phase, and in that in dependence on this, the correction value is established.

4. A method according to any preceding claim, wherein the resonance frequency of the antenna oscillating circuit is altered in dependence on the correction value by connecting at least one series or parallel inductance and/or at least one series or parallel capacitance into or out of the antenna oscillating circuit.

5. A method according to any preceding claim, wherein the correction value is stored in a memory of the excitation unit connected to a driver stage of the -is- is excitation unit, the driver stage being controlled in dependence on the correction value, as a result of which the current in the antenna oscillating circuit is increased or decreased.

6. A method according to claim 5, wherein the current in the antenna oscillating circuit is altered by the correction value only within a predetermined tolerance band.

7. A transceiver means for transmitting data or supplying energy to a transponder comprising: an antenna oscillating circuit having a resonant frequency; an excitation unit for supplying an excitation variable, having an excitation frequency, to the antenna oscillating circuit; and an evaluation unit for carrying out the method of any preceding claim.

8. A device comprising a transceiver means for transmitting data or supplying energy to a transponder as claimed in claim 7, and a transponder having a transponder oscillating circuit.

9. A device for transmitting data or supply energy from/to a transponder, having a stationary transceiver, which has an antenna oscillating circuit having an antenna in the form of a first coil and a first capacitor, with the resonance frequency being determined by the components of said oscillating circuit, a portable transponder, which has a transponder oscillating circuit having a second coil and a second capacitor, and an excitation unit, which oscillates with an oscillator frequency and the output variable of which is used as an excitation variable having an excitation frequency in order to force an oscillation of the antenna oscillating circuit, and an evaluation unit, in which the current and/or the voltage in the antenna oscillating circuit is/are measured and in which if the current or the voltage deviates from a desired value, a correction value is produced, with the aid of which the antenna oscillating circuit is subsequently corrected in the case of all transmissions between the transceiver and the transponder.

10. A device according to claim 8 or 9, wherein the antenna oscillating circuit is inductively coupled with the transponder oscillating circuit, if the transponder is in the vicinity of the transceiver.

11. A device according to claim 10, wherein the transponder has an item of code information which, as a result of the inductive coupling, produces a modulated oscillation of the antenna oscillating circuit, the modulated oscillation is detected by the evaluation unit, the code information is demodulated from the modulated oscillation, the item of code information that is detected is compared with an item of desired code information, and in that in the event of agreement, a release signal for releasing a safety unit is produced.

12. A device for transmitting data or energy to a responder substantially as herein described with reference to the accompanying drawings.

13. A method of determining the compatibility of an antenna oscillating circuit with an excitation unit, which antenna oscillating circuit and excitation unit form transceiver means for transmitting data or supplying energy to a transponder substantially as herein described with reference to the accompanying drawings.