Transponder

Abstract

A transponder for receiving a wireless electromagnetic interrogation signal (AS) and for transmitting a wireless electromagnetic response signal, comprising a first coil (L1) acting as an antenna for generating a first wired electrical receive signal (E1) from the interrogation signal (AS) and at least one further coil (L2, L3) acting as an antenna for generating a further wired electrical receive signal (E2, E3) from the interrogation signal (AS), wherein an axis (A1) of the first coil (L1) and an axis (A2, A3) of the further coil (L2, L3) are oriented differently in space, characterized in that each coil (L1, L2, L3) is assigned a full-wave rectifier (6.1, 6.2, 6.3) for rectifying the respective receive signal (E1, E2, E3), wherein a summing element (7) is provided for summing the signals produced by the full-wave rectifiers (6.1, 6.2, 6.3) generated rectified received signals (GE1, GE2, GE3) are provided to generate a pulsating sum signal (SG) whose frequency corresponds to twice the frequency of the query signal (AS) and that a comparator (8) is provided to compare the pulsating sum signal (SG) with a reference signal (RS) to generate a first clock signal (TS1) whose frequency corresponds to twice the frequency of the query signal (AS).

Description

The present invention relates to a transponder for receiving a wireless electromagnetic interrogation signal and for transmitting a wireless electromagnetic response signal, having a first coil acting as an antenna for generating a first wired electrical reception signal from the interrogation signal and having at least one further coil acting as an antenna for generating a further wired electrical reception signal from the interrogation signal, wherein an axis of the first coil and an axis of the further coil are aligned differently in space.A transponder having three coils arranged orthogonally to one another is known from EP 0 783 190 A1. In this case, the signals of the three coils are each rectified by means of a diode and used for charging a capacitor arrangement. The direct voltage present at the capacitor arrangement is then used as a supply voltage for the transponder. The supply voltage can be provided by using the three coils, which are arranged in each case orthogonally to one another, substantially independently of the position and the spatial orientation of the transponder with respect to the interrogator generating the interrogation signal.However, it is not possible in this way to generate from the interrogation signal a time base signal corresponding to the frequency of the interrogation signal, which time base signal may be required for synchronizing the transponder with the interrogator.DE 197 17 505 C2 discloses a transponder communication device which has a high-frequency coupling field between two antenna coils of a transmission device operated phase-shifted with respect to one another for approximately orthogonal action, on the one hand, and on the other hand, the antenna coil of a passive transponder. The phase-shifted high-frequency channels are combined on the receiving side via a two-channel demodulator to a summer.DE 10 2009 019 724 A1 relates to a transponder for RFID applications having an electronics unit and at least two antennas which are designed as coils and are arranged substantially orthogonally with respect to one another and are connected to the electronics unit. The coils are connected in parallel or in series as an antenna unit connected to an input of the electronics.DE 601 23 087 T2 discloses a portable receiver comprising a receiving stage in which at least two antennas are oriented according to different receiving axes, wherein the antennas can each receive a component of an external signal in a given frequency range according to their receiving axes, a processing stage for the at least two components received by the receiving stage and a recombination stage for at least two signals provided at the output of the processing stage. The processing stage comprises squarers each connected between an antenna and an input of the recombination stage.DE 10 2004 029 439 A1 relates to a rectifier circuit for providing a rectified voltage, having a first AC voltage connection to which an AC voltage can be applied, having a first DC voltage connection to which a DC voltage can be provided, and having a control switching element between the first AC voltage connection and the first DC voltage connection, which couples the first AC voltage connection to the first DC voltage connection only when the electrical potential at the first AC voltage connection has a predefinable polarity compared to a reference potential and when the magnitude of the electrical potential at the first DC voltage connection is less than or equal to the magnitude of the electrical potential at the first AC voltage connection.It is an object of the present invention to provide a transponder which is designed to generate a time base signal from an interrogation signal, wherein the generation of the time base signal is to be possible substantially independently of the position and the spatial orientation of the transponder with respect to the interrogator generating the interrogation signal.The object is achieved in a transponder of the type mentioned at the beginning in that a full-wave rectifier for rectifying the respective received signal is assigned to each of the coils, wherein a summing element is provided for summing the rectified received signals generated by the full-wave rectifiers in order to thus generate a pulsating sum signal whose frequency corresponds to twice the frequency of the interrogation signal.A transponder is understood to mean a transmitting and receiving device which transmits a wireless electromagnetic response signal upon the receipt of a wireless electromagnetic interrogation signal. The interrogation signal is generated by an interrogation device specifically designed for this purpose, which is generally also designed to receive the response signal. Such combinations of transponders and interrogators can be used in particular for keyless access control and / or keyless use control in motor vehicles.Coils, particularly cylindrical coils, can generally be used as antennas for receiving wireless electromagnetic signals, substantially responding to the magnetic component of the field and converting it into a wired electrical signal. However, they have a pronounced directional effect. If the axis of the coil points to the transmitter, a reception minimum results, if it is at right angles to the direction to the transmitter, then a reception maximum results, on the other hand.Since the transponder according to the invention now has at least two coils, the axes of which are oriented differently in space, i.e. do not run parallel, it is ensured that at least one coil operates outside the reception minimum independently of the position and the spatial orientation of the transponder with respect to the interrogator generating the interrogation signal. In this way, at least one wired electrical reception signal is generated from the interrogation signal, which has a level which is clearly above the level at the reception minimum.A full-wave rectifier is generally understood to mean a rectifier in which both half-waves of the supplied signal are provided with the same sign, so that a pulsating DC signal is produced which has twice the frequency of the supplied signal. The full wave rectifier may be a bridge rectifier formed by four diodes arranged in series. According to the invention, a full-wave rectifier is provided for each coil, so that a rectified received signal is obtained from each received signal.The rectified received signals are then summed by means of a summing element, so that a pulsating sum signal is generated, the frequency of which corresponds to twice the frequency of the interrogation signal. In this case, full-wave rectification ensures that the magnitudes of the received signals are added up independently of their sign. In this way, it is ensured that the received signals do not weaken each other or even cancel each other out during the adding-up, which would occur without rectification if the transponder is oriented such that one of the receiving coils is penetrated by the interrogation signal in the one direction and another of the receiving coils is penetrated in the other direction. In this case, the (non-rectified) received signal of one coil and the (non-rectified) received signal of the other coil would namely have a phase shift of 180°, so that the two received signals would cancel one another out partially, in the extreme case even completely, when added up. In this case, the complete extinction would occur if the levels of the two received signals have the same value.In contrast, in the transponder according to the invention, each half wave of each of the received signals is used to increase the level of the sum signal, so that a stable sum signal is generated independently of the position and the spatial orientation of the transponder with respect to the interrogator generating the interrogation signal. The frequency of the sum signal corresponds to twice the frequency of the received interrogation signal, so that it can be used as a time base signal, in particular for synchronizing the transponder with the interrogator.The transponder according to the invention enables in particular the generation of a time base signal from an amplitude-modulated interrogation signal, in which the amplitude is varied in order to transmit different values, since the sum signal can be reliably generated even if the amplitude of the interrogation signal is very low due to the modulation.According to the invention, a comparator is provided for comparing the pulsating sum signal with a reference signal so as to generate a first clock signal whose frequency corresponds to twice the frequency of the interrogation signal. A comparator is generally a circuit for comparing two input signals. Depending on which of the two input signals is greater, the output signal of the comparator will assume a first value or a second value. By now comparing the sum signal with a reference signal by means of the comparator, a binary clock signal is obtained at the output of the comparator, the frequency of which binary clock signal corresponds to twice the frequency of the interrogation signal, wherein the binary clock signal can be processed further in a simple manner. The comparator may be formed by a conventional operational amplifier.According to an advantageous development of the invention, a total of three coils are provided, the axes of which are each arranged at right angles to one another. In this way, a coil arrangement is produced which in its entirety has a possibly very low directivity, so that the sum signal can be reliably formed with any desired orientation of the transponder in space.According to an advantageous development of the invention, a low-pass filter is provided for filtering the pulsating sum signal, wherein a filtered pulsating sum signal generated by means of the low-pass filter is the reference signal supplied to the comparator. A low-pass filter is generally a filter which allows signal components below a cut-off frequency to pass through in an approximately unattenuated manner and increasingly attenuates signal components above the cut-off frequency. If a filtered pulsating sum signal is now generated from the sum signal by means of such a low-pass filter and is used as a reference signal, an automatic adaptation of the reference signal to the level of the sum signal results, so that changes in the instantaneous value of the sum signal lead to a reversal of the value of the first binary clock signal, so that the first clock signal comprises the clock information independently of the level of the sum signal.According to an advantageous development of the invention, the first clock signal is fed to a frequency divider in order to generate a second clock signal with a lower frequency. A frequency divider is generally an arrangement which reduces the frequency of an input signal by a factor, preferably by an integer factor. The use of a frequency divider makes it possible to generate the second clock signal with a frequency according to requirements, wherein the information as to which frequency the interrogation signal has is also contained in the second clock signal.According to an advantageous development of the invention, the frequency divider is a frequency divider, so that the second clock signal has the frequency of the interrogation signal. In a frequency divide-by-half, the output signal generally has a frequency equal to half the frequency of the input signal. In the present case, a second clock signal is thus easily generated, the frequency of which corresponds to the frequency of the interrogation signal.According to an advantageous development of the invention, a limiter for limiting the amplitude of the respective received signal is assigned to each of the coils. A limiter is understood to mean an arrangement which processes an input signal in such a way that the output signal of the limiter does not exceed a maximum value. In the present case, the limiters can be designed to limit the voltage of the respective received signal in order to protect downstream components from high voltages which can arise when strong interrogation signals and / or interference signals are received. The limiters can expediently be connected directly conductively to the respective coil, that is to say without the interposition of further components, in order to protect all the components connected downstream of the coil in this way.According to a preferred development of the invention, the coils are each assigned an amplifier for amplifying the respective received signal. The received signals can be brought to a level which is sufficient for further processing, in particular for full-wave rectification, even if the interrogation signal is very weak. The amplifiers can be voltage amplifiers in particular. The amplifiers are preferably directly connected downstream of the limiter.According to a preferred development of the invention, the limiter and the amplifier are designed as a structural unit. In this way, the construction of the transponder is simplified.According to a preferred development of the invention, a voltage-current converter is assigned to each of the coils in order to supply the respective received signal to the summing element as a current signal. A voltage-current converter is generally understood to mean a voltage-controlled current source. In the present case, the received signal can thus be converted into a current signal, which facilitates the summation of the received signals. In particular, the summing element can thus be designed as a feedback operational amplifier, wherein the received signals are fed together directly to the inverting input, i.e. without series-connected ohmic resistors, which simplifies the construction of the transponder. Expediently, the voltage-current converters can each be arranged between the associated full-wave rectifier and the associated amplifier.According to an advantageous development of the invention, the voltage-current converters are transconductance operational amplifiers. Transconductance operational amplifiers (abbreviated: VC-OPV) are special operational amplifiers which have a high-impedance current output. By means of such transconductance operational amplifiers, the received signals can be converted into current signals in a particularly simple manner.According to an advantageous development of the invention, the transponder is at least partially designed as a CMOS integrated circuit. An integrated circuit is an integrated circuit, which is understood to mean that an electronic circuit, which comprises a plurality of electronic components and an associated wiring, is formed on a common substrate, also referred to as a chip. A fully integrated construction can be provided in which all electronic components of the transponder are arranged on exactly one substrate.Furthermore, the transponder according to the invention can be manufactured using CMOS technology, which is understood to mean that both PMOS transistors, also called p-channel metal oxide semiconductor transistors, and NMOS transistors, also called n-channel metal oxide semiconductor transistors, can be arranged on a common substrate.The invention and its developments are explained in more detail with reference to the following figures. The following are shown: FIG. 1 shows an exemplary embodiment of a transponder according to the invention and of an associated interrogator in a schematic illustration, and FIG. 2 is a circuit diagram of the transponder of FIG. 1.FIG. 1 shows a transponder system 1, which consists of an interrogator 2 and a transponder 3. Such a combination 1 of interrogator 2 and transponder 3 can be used in particular for keyless access control and / or keyless use control in motor vehicles. However, other applications are also possible.The principle of operation is that the interrogator 2 emits a wireless interrogation signal AS having a frequency f 0. If a transponder 3 is now within range, it receives the interrogation signal AS, evaluates it and generates a wireless response signal, which is emitted by the transponder 3 and received and evaluated by the interrogator.For this purpose, the interrogator 2 has at least one coil acting as an antenna with the connections P + and P -. The transponder 3 has a first coil L 1 acting as an antenna, in particular a cylindrical coil, having an axis A 1 and connections S 1 + and S 1 -, a second coil L 2 acting as an antenna, in particular a cylindrical coil, having an axis A 2 and connections S 2 + and S 2 - and a third coil L 3 acting as an antenna, in particular a cylindrical coil, having an axis A 3 and connections S 3 + and S 3 -.The coils L 1, L 2, L 3 each have a distinct directivity per se. If the respective axis A 1, A 2, A 3 of a coil L 1, L 2, L 3 points to the interrogator 2, a reception minimum results, while if it is at right angles to the direction to the interrogator 2, a reception maximum results.Since the axes A 1, A 2, A 3 of the coils L 1, L 2, L 3 are arranged at right angles to one another, it is ensured, regardless of the position and orientation of the transponder 3 in space, that at most one of the coils L 1, L 2, L 3 is operated at a reception minimum and that the two remaining ones of the coils L 1, L 2, L 3 are operated under favorable conditions. In this way, interrogation signals AS can be received substantially independently of the position and the spatial orientation of the transponder 3 with respect to the interrogator 2 generating the interrogation signal AS.FIG. 2 shows a circuit diagram of the transponder 1 of FIG. 1, only that part of the circuit of the transponder 1 which is essential for understanding the invention being shown. The coils L 1, L 2, L 3 are used as antennas for receiving the interrogation signal AS, wherein they are substantially responsive to the magnetic component of the interrogation signal AS and each convert it into a wired electrical reception signal E 1, E 2, E 3.The received signals E1, E2, E3 are each fed to a structural unit 4.1, 4.2, 4.3, which has a limiter 4.1, 4.2, 4.3 on the input side and a downstream amplifier 4.1, 4.2, 4.3.The limiters 4.1, 4.2, 4.3 are designed to limit the voltage of the respective received signal E1, E2, E3 in order to protect downstream components from high voltages which can arise when strong interrogation signals and / or interference signals are received. The limiters 4.1, 4.2, 4.3 are expediently connected directly conductively to the respective coil L1, L2, L3, that is to say without the interposition of further components, in order to protect all the components connected downstream of the respective coil L1, L2, L3. The amplifiers 4.1, 4.2, 4.3 are directly connected downstream of the respective limiter 4.1, 4.2, 4.3 and are designed as voltage amplifiers. In this way, the received signals E1, E2, E3 can be brought to a level which is sufficient for the further processing, even if the interrogation signal is very weak.The limited and amplified received signals E1', E2', E3' are now each fed to a voltage-current converter 5.1, 5.2, 5.3 in order to convert the respective received signal E1', E2', E3' into a current signal. The voltage-current converters 5.1, 5.2, 5.3 can preferably be designed as transconductance operational amplifiers 5.1, 5.2, 5.3.The received signals E1", E2", E3", which are now present as current signals, are each fed to a full-wave rectifier 6.1, 6.2, 6.3. A full-wave rectifier 6.1, 6.2, 6.3 is generally understood to mean a rectifier 6.1, 6.2, 6.3 in which both half waves of the supplied signal E1", E2", E3" are provided with the same sign, so that a pulsating DC signal GE1, GE2, GE3 arises which has twice the frequency of the supplied signal E1", E2", E3". The respective full-wave rectifier 6.1, 6.2, 6.3 can be a bridge rectifier which is formed by four diodes arranged in series connection. According to the invention, a full-wave rectifier 6.1, 6.2, 6.3 is provided for each coil L1, L2, L3, so that a rectified received signal GE1, GE2, GE3 is obtained from each received signal E1", E2", E3".The rectified received signals GE1, GE2, GE3 are then summed by means of a summing element 7, so that a pulsating sum signal SG is generated, the frequency of which corresponds to twice the frequency of the interrogation signal AS. In this case, full-wave rectification ensures that the magnitudes of the received signals E 1'', E 2'', E 3'' are added up independently of their sign. In this way, it is ensured that the received signals E 1'', E 2'', E 3'' do not weaken or even cancel each other during the adding-up, which would occur without rectification if the transponder is oriented such that one of the receiving coils L 1, L 2, L 3 is penetrated by the interrogation signal AS in the one direction and another of the receiving coils L 1, L 2, L 3 in the other direction. In this case, the (non-rectified) received signal E 1'', E 2'', E 3'' of one coil L 1, L 2, L 3 and the (non-rectified) received signal E 1'', E 2'', E 3'' of the other coil L 1, L 2, L 3 would have a phase shift of 180°, so that the two received signals E 1'', E 2'', E 3'' would cancel one another out partially, in the extreme case even completely, during the addition. In this case, the complete extinction would occur if the levels of the two received signals E1", E2", E3" have the same value.In contrast, in the transponder 3 according to the invention, each half wave of each of the received signals E 1'', E 2'', E 3'' is used to increase the level of the sum signal SG, so that a stable sum signal SG is generated independently of the position and the spatial orientation of the transponder 3 with respect to the interrogator 2 generating the interrogation signal AS. The frequency of the sum signal SG corresponds to twice the frequency of the received interrogation signal AS, so that it can be used as a time base signal, in particular for synchronizing the transponder 3 with the interrogator 2.The sum signal SG is supplied to a comparator 8 which compares the pulsating sum signal SG with a reference signal RS so as to generate a first clock signal TS1 whose frequency corresponds to twice the frequency of the interrogation signal AS. A comparator 8 is generally a circuit for comparing two input signals SG, GS. Depending on which of the two input signals SG, GS is greater, the output signal TS 1 of the comparator 8 becomes a first value or a second value. By now comparing the sum signal SG with a reference signal RS by means of the comparator 8, a binary clock signal TS1 results at the output of the comparator 8, the frequency of which binary clock signal TS1 corresponds to twice the frequency of the interrogation signal AS, wherein the binary clock signal TS1 can be further processed in a simple manner. The comparator 8 may be formed by a conventional operational amplifier.A low-pass filter 9 is provided for filtering the pulsating sum signal SG, wherein a filtered pulsating sum signal RS generated by means of the low-pass filter 9 is the reference signal RS supplied to the comparator 8. A low-pass filter 9 is generally a filter which allows signal components below a cut-off frequency to pass through in an approximately unattenuated manner and increasingly attenuates signal components above the cut-off frequency. If a filtered pulsating sum signal RS is now generated from the sum signal SG by means of such a low-pass filter 9 and is used as the reference signal RS, then an automatic adaptation of the reference signal RS to the level of the sum signal SG results, so that changes in the instantaneous value of the sum signal SG lead to a skipping of the value of the first binary clock signal TS1, so that the first clock signal TS1 comprises the clock information independently of the level of the sum signal SG.Furthermore, the first clock signal TS1 is supplied to a frequency divider 10 so as to generate a second clock signal TS2 having a lower frequency. A frequency divider 10 is generally an arrangement which reduces the frequency of an input signal TS1 by a factor, preferably by an integer factor. The use of a frequency divider 10 makes it possible to generate the second clock signal TS 2 with a frequency according to requirements, wherein the information as to which frequency and phase the interrogation signal AS has is also contained in the second clock signal TS 2.Frequency divider 10 is preferably a frequency divider 10. In the present case, a second clock signal TS2 is thus generated in a simple manner, the frequency of which corresponds to the frequency of the interrogation signal AS.The transponder 1 is preferably at least partially embodied as a CMOS integrated circuit. An integrated circuit is an integrated circuit, which is understood to mean that an electronic circuit, which comprises a plurality of electronic components and an associated wiring, is formed on a common substrate, also referred to as a chip. A fully integrated construction can be provided in which all electronic components of the transponder 1 are arranged on exactly one substrate.Furthermore, the transponder 1 according to the invention can be manufactured using CMOS technology, which is understood to mean that both PMOS transistors, also called p-channel metal oxide semiconductor transistors, and NMOS transistors, also called n-channel metal oxide semiconductor transistors, can be arranged on a common substrate.The transponder 3 according to the invention enables in particular the generation of a time base signal SG, T1, T2 by means of a plurality of coils L1, L2, L3 from an amplitude-modulated interrogation signal AS, in which the amplitude is changed in order to transmit different values, since the sum signal SG can be reliably generated even if the amplitude of the interrogation signal AS is very low due to the modulation.List of reference characters1 Transponder system 2 interrogator 3 transponder 4.1 first limiter and amplifier 4.2 second limiter and amplifier 4.3 third limiter and amplifier 5.1 first voltage-current converter 5.2 second voltage-current converter 5.3 third voltage-current converter 6.1 first full wave rectifier 6.2 second full wave rectifier 6.3 third full wave rectifier 7 summing element 8 comparator 9 low pass 10 frequency divider L coil of interrogator P connections of the coil of interrogator AS interrogation signal f 0 frequency of interrogation signal L1 first coil of transponder S1 connections of the first coil of transponder A1 axis of the first coil of transponder E1 first received signal GE1 rectified first received signal L2 second coil of the transponder AS Transponder S2 Connections of the second coil of the transponder A2 Axis of the second coil of the transponder GE2 rectified second receive signal L3 Third coil of the transponder S3 Connections of the third coil of the transponder A3 Axis of the third coil of the transponder GE3 rectified third receive signal SG pulsating sum signal RS reference signal TS1 first binary clock signal TS2 second binary clock signal TS1 second binary clock signal

Claims

Transponder for receiving a wireless electromagnetic interrogation signal (AS) and for transmitting a wireless electromagnetic response signal, having a first coil (L1) acting as an antenna for generating a first wired electrical reception signal (E1) from the interrogation signal (AS) and having at least one further coil (L2, L3) acting as an antenna for generating a further wired electrical reception signal (E2, E3) from the interrogation signal (AS), wherein an axis (A1) of the first coil (L1) and an axis (A2, A3) of the further coil (L2, L3) are aligned differently in space, characterized in that a full-wave rectifier (6.1, 6.2, respectively, is associated with the coils (L1, L2, L3), 6.3) for rectifying the respective received signal (E1, E2, E3) is assigned, wherein a summing element (7) is provided for summing the rectified received signals (GE1, GE2, GE3) generated by the full-wave rectifiers (6.1, 6.2, 6.3) in order to generate a pulsating sum signal (SG) whose frequency corresponds to twice the frequency of the interrogation signal (AS), and that a comparator (8) is provided for comparing the pulsating sum signal (SG) with a reference signal (RS) in order to generate a first clock signal (TS1) whose frequency corresponds to twice the frequency of the interrogation signal (AS).Transponder according to claim 1, characterised in that a total of three coils (L1, L2, L3) are provided, the axes (A1, A2, A3) of which are each arranged at right angles to one another.Transponder according to Claim 1, characterized in that the one low-pass filter (9) is provided for filtering the pulsating sum signal (SG), wherein a filtered pulsating sum signal (RS) generated by means of the low-pass filter (9) is the reference signal (RS) supplied to the comparator (8).Transponder according to claim 1, characterized in that the first clock signal (TS1) is supplied to a frequency divider (10) so as to generate a second clock signal (TS2) with a lower frequency.Transponder according to the preceding claim, characterized in that the frequency divider (10) is a frequency divider (10), so that the second clock signal (TS2) has the frequency of the interrogation signal (AS).Transponder according to one of the preceding claims, characterized in that the coils (L1, L2, L3) are each assigned a limiter (4.1, 4.2, 4.3) for limiting the amplitude of the respective received signal (E1, E2, E3).Transponder according to one of the preceding claims, characterized in that the coils (L1, L2, L3) are each assigned an amplifier (4.1, 4.2, 4.3) for amplifying the respective received signal (E1, E2, E3).Transponder according to Claims 6 and 7, characterized in that the limiter (4.1, 4.2, 4.3) and the amplifier (4.1, 4.2, 4.3) are designed as a structural unit (4.1, 4.2, 4.3).Transponder according to one of the preceding claims, characterized in that a voltage-current converter (5.1, 5.2, 5.3) is assigned to each of the coils (L1, L2, L3) in order to supply the respective received signal (E1, E2, E3) to the summing element (7) as a current signal (E1", E2", E3").Transponder according to the preceding claim, characterized in that the voltage-current converters (5.1, 5.2, 5.3) are transconductance operational amplifiers (5.1, 5.2, 5.3).Transponder according to one of the preceding claims, characterized in that it (3) is at least partially designed as a CMOS integrated circuit (3)

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