DE4339669A1 - Reading moving transponder output e.g. for traffic system contg. tram running on railway track of street - Google Patents

Abstract

The system has a HF module (H), an evaluation unit (AW), an antenna (A) and a transponder (T). The transponder contains a data memory (D), modulator (M) and a receiver/transmitter (T). The HF module has a 2.5 GHz generator (G), a demodulator (DM) and a circulator. The transponder is tuned to the generated signal and a component is reflected back with modulated data from the memory. The signal is decoded by the evaluation unit.

Description

The invention relates to a device according to the preamble of Claim 1.

Such a device is e.g. B. from US Patent No. 4,739,328 known. It is used to read card-shaped Transponders, so-called TAGS, the z. B. on animals, on vehicles or are attached to containers and assigned to these objects Data encoded included.

The known reading device emits a high-frequency signal from e.g. B. 915 MHz as a continuous wave signal in the direction of to be read out Transponders. The transponder that is broadcast on the Radio frequency is tuned, reflects part of the received high-frequency power back to the reading device, using a modulator provided by a data store is driven, the back-radiated signal corresponding to the im Data storage modulated data.  

The retroreflected radio-frequency signal is in the reading device coherently demodulated and the code of evaluated by an evaluation unit.

The reading device known from the US patent receives all Signals whose frequency is in the range of the radio frequency emitted lies. Such signals not only provide all of the radiated radio frequency reached objects made of metal or other conductive material, but also other transponders that z. B. further away from the reading device and shouldn't actually be queried. The reader takes hence many unnecessary signals that are undesirable because of them can interfere with the reception and evaluation of useful signals.

From DE-OS 26 12 996 a similar device is known, the for the evaluation of retroreflective signals from transponders (Registration transmitters) is suitable compared to the interrogation signal are shifted in frequency. By the transponders frequency shift is created the possibility Transponder signals from reflections of passive objects to be able to distinguish and thus disturbing background hide. However, this device cannot be used either avoid that in the presence of several transponders too Reflection signals from transponders further away are received and there is therefore a risk that the reception of Signals of a transponder to be read is disturbed or that Signals from the wrong transponder are evaluated.

The object of the invention is therefore a device of the beginning described type, which is largely undisturbed reading individual transponder allowed.

This task is carried out in the characterizing part of the Features specified claim 1 solved.  

By inserting a runtime filter, as z. B. from the Radar technology for distance measurement is known here Distance gate created such signals when received hides that come from objects or transponders that come from the Reading device are further or less distant than that transponders to be read.

Embodiments of the device according to the invention are in the Subclaims specified.

Claim 2 relates to the implementation of a runtime filter by means of two phase modulators that the broadcast High frequency signal (interrogation signal) and the retroreflected signal (Received signal) staggered in time according to one key code in the phase between 0 ° and 180 °, so that if the time offset coincides with the between the reader and the transponder required signal runtime the phase modulation impressed on the received signal disappears and the received signal is coherent in a high frequency mixer can be demodulated. The received signal is low frequency modulated data can then via a low pass filter Evaluation are fed.

On conductive objects that do not modulate the interrogation signal reflected received signals at the output of the High frequency mixer a static or due to Doppler shift cause low-frequency modulated signal, can, according to claim 3, on the low pass of a display device be fed. In this way, e.g. B. at the Vehicle registration, including vehicles that do not have a transponder wear, be grasped.  

Claim 4 provides for additional runtime filters, whose in Phase modulators arranged in the receiving branch have the characteristic Receive code with time delays, the signal propagation times correspond as they are when querying from closer or further away than the transponder to be read lying down to be expected would be. Is the evaluation of the read information for the Case prevents from being closer or farther away lying distance range a received signal arrives, the low-frequency signal component modulated by a transponder has a high level, so the security of the Information transfer increased significantly. It can then, e.g. B. at Use of the device for the transmission of route information Railway vehicles, can be prevented safely in the event of failure of a Track-side transponders incorrectly on one Transponders located on the adjacent track are read out and therefore incorrect Information is recorded.

The subject of claims 5 and 6 is as Modulation signal more suitable for the phase modulators characteristic code, while claims 7 to 9 advantageous embodiments of the circuit of the reading device affect.

Claims 10 and 11 relate to configurations of the device according to the invention, which is used to receive and evaluate Transponder signals are suitable which are opposite in their frequency the query signal are shifted.

Here, claim 10 relates to a device with a Phase modulator, claim 11 a device with two or several phase modulators.  

The independent claims 12 and 13 relate to the Use of the device according to the invention for the detection of Data or for the transmission of route information track-bound vehicles.

Based on four figures, embodiments of the Device according to the invention described and the function of Device will be explained.

Fig. 1 a block diagram shows a reading device according to the prior art,

Fig. 2 shows an apparatus according to the invention,

Fig. 3 shows schematically the level curve of the output signals of two, range gates forming filter time depending on the distance between reading device and transponder auszulesendem,

Fig. 4 shows a device according to the invention, which is suitable for receiving and evaluating frequency-shifted transponder signals.

In Fig. 1, an RF module H, an evaluation unit AW, an antenna A and a transponder T are shown. The latter contains a data memory D, a modulator M and a transmit / receive antenna TA.

A high frequency generator G generates a high frequency in the RF module in the range of 2.5 GHz, which via a circulator Z of antenna A fed and from this as a query signal towards the Transponder is emitted too.  

The transponder is tuned to the frequency of the interrogation signal and reflects a part of those recorded via its antenna TA RF power back to antenna A of the reader. The The reflectivity of the transponder can be controlled by the modulator M change according to a code stored in data memory D, see above that the reflected signal with the transponder code, the z. B. Data can contain via an object carrying the transponder is.

The reflected signal is in the RF module by means of the circulator Z separated from the interrogation signal and as a reception signal to a demodulator DM supplied it, with the interrogation signal frequency as Reference signal, coherently demodulated and the evaluation unit feeds. The evaluation unit AW decodes those from the transponder transmitted modulation and causes processing or Forwarding of the contained, read from the transponder Information.

The device shown in FIG. 2 has, in its RF module H, two transit time filters which represent distance gates for incoming received signals, ie only allow those receive signals that come from a predetermined distance range to pass through. The two runtime filters each consist of two phase modulators PM1, PM2; PM1, PM3, in each case one RF mixer DM1, DM2 working as a demodulator, which multiplicatively mixes received signals arriving via the second phase modulator with the frequency of the high-frequency generator G, and in each case a downstream low-pass filter TP1, TP2. All phase modulators receive the same signal S1 as a modulation signal from a code generator CG.

Modulated by the phase modulators of the runtime filters one phase modulator PM1 common to the two runtime filters, the interrogation signal, the other from the antenna incoming reception signals. Interrogation signal and reception signals  must therefore be managed separately. this causes the circulator Z, the one coming from the phase modulator PM1 Query signals to antenna A and from the antenna incoming reception signals via an amplifier V to the Phase modulators PM2 and PM3 leading reception path switches.

The second phase modulator PM3 of the second runtime filter receives the modulation signal S1 generated by the code generator via a Delay element VG supplied with a time delay τ.

The outputs of the low-pass filters TP1, TP2 are on one Threshold circuit SW performed, the output of which is a gate circuit TS controls the output signal of the first Runtime filter, which at the output of the first low-pass filter TP1 is pending, can be switched through to the evaluation unit AW.

To interrogate a transponder, the high-frequency generator G supplies a continuous wave signal of the frequency 2.5 GHz. This arrives in the first phase modulator PM1 and is there there with the signal S1 provided by the code generator CG, a digital pseudo-random code which, for. B. generated phase shifts of 0 ° and 180 °, modulated. This code has a clock frequency of z. B. 20 MHz and has good auto and cross correlation properties. It can have a length of 1023 bits, for example, and can be read cyclically in the code generator from a data memory corresponding to the code length.

The query signal modulated in this way reaches a broadband via the circulator Z to the antenna A, which emits it. Meets the emitted interrogation signal on a reflecting object, so part of the radiated power is returned to antenna A. reflected and as a received signal via the circulator Z and Amplifier V fed to the second phase modulator PM2. There there is a further modulation with the pseudo-random code.  

However, due to the signal transit time required for the object and back, this is shifted in time from the received signal and generally does not correlate with the modulation impressed on the interrogation signal in the first phase modulator. A broadband modulated RF signal appears at the output of the phase modulator PM2, which generates an RF signal containing the clock frequency of the code generator at the output of the RF mixer DM1, which cannot overcome the downstream low-pass filter TP1. The reflected signal is therefore not detected by the reading device. A detection takes place only if the distance between antenna A and the reflecting object z. B. the transponder to be read out, as provided in Fig. 2, is very small, so that the signal delay may be neglected, or if the modulation signal S1 is supplied to the second phase modulator via a delay element, delayed by the amount of the expected signal delay, as this is the case with the phase modulator PM3 of the second runtime filter.

Corresponds to the transit time of an RF signal at reflective object and back the time delay of the Modulation signal S1, so it is done by the second Phase modulator PM2 made second modulation with the Pseudo-random code except for minor deviations, e.g. B. can result from Doppler shift in moving objects, coherent with the first one made in the phase modulator PM1 Modulation, phase shifts of 180 ° in the received signal thus reversed by another 180 ° shift and that Received signal thus freed from its phase modulation.

The HF mixer now delivers a static or, when Doppler shift occurs, a very low frequency Signal that does not pass through the low-pass filter TP1 to one in the figure Display device D shown arrives. The object becomes detected.  

If the object is a transponder matched to the query signal, the modulation impressed in the transponder appears, e.g. Legs Scanning of the reflected signal in the frequency range from 20 to 400 KHz also at the output of the HF mixer. From there it arrives as relatively low-frequency signal via the low-pass filter TP1 to the Detection signaling display device D and Gate circuit TS to evaluation unit AW. In the evaluation unit the modulation impressed in the transponder in a decoder DC decoded and fed to a processor P for further processing.

The second time-of- flight filter in FIG. 2 works like the first time-of-flight filter, with the difference that, due to a delay in the supply of the modulation signal S1 to the phase modulator PM3, it detects reception signals which come from objects or transponders which are further away than those via the first runtime filter can be detected. The second runtime filter also does not deliver an output signal to the display device or the evaluation unit.

Its output signal only affects the threshold circuit SW and has the effect that the gate circuit TS for Output signals of the low pass TP1 is blocked as soon as its level that of the low pass TP1. Instead of the level of Leave low pass TP1, which is used here as a reference signal others, e.g. B. preset fixed level as Use reference signals.

In Fig. 3, the levels of the output signals of two time-of-flight filters of a readout device are shown schematically as a function of the distance d of a transponder to be read out. The runtime filters here form distance gates for two distance zones: a central zone, which covers the immediate vicinity of a transponder T1, via which the readout device, e.g. B. can be attached to a track-bound vehicle, is led away, and a distance zone that surrounds the central zone in a ring and delivers a maximum signal at a distance a from the transponder T1.

The first runtime filter delivers near the transponder T1 - in the figure in hatched area B - a signal S2 with a high Level, the second runtime filter only provides a very good one weak signal S3. The signal S2 is in the shaded area therefore not maximum because the signal delay between the z. B. on a railway vehicle attached readout device and the z. B. Transponder T1 laid in the track, which is small here, however is not zero, not here by delaying the second Phase modulator of the first delay element supplied Modulation signal is exactly compensated.

Since the level of the signal S2 in the shaded area B is significantly higher than that of the signal S3, the gate circuit TS in FIG. 2 is switched to be permeable and the signal S2 is evaluated.

If the reading device moves away from the location of the transponder T1, the transponder gets more and more into the area of the distance gate formed by the second transit time filter. Thus, at location C in FIG. 3, the output signal S3 of the second runtime filter already outweighs the signal S2 supplied by the first runtime filter. The threshold value circuit thus blocks the gate circuit TS and the signal S2 can no longer reach the evaluation unit.

Signal S3 always remains larger than signal S2 even if the reading device even further away from the transponder T1 to in an area is moved in which, for reasons of range, none Received signal can be recorded more.  

Another transponder T2 is located at a distance a from the Line on which the reading device is moved and on which too the transponder T1 is located - this case is e.g. B. given if in a first track of a railway line the transponder T1 and in Neighboring track, offset against the transponder T1, a transponder T2 is relocated - here too, due to the removal of the Transponders T2 from the readout device, the signal S3 of the second runtime filter must always be higher than that of the first Runtime filter. It is therefore not used to evaluate the Information coming from transponder T2. In the event that Transponders T1 and T2 arranged at the same height in the tracks are, the signal S2 of the transponder T1 predominates due to the greater distance of the transponder T2 from the reading device weaker incoming signal S3 even if this at the output of the second runtime filter is present at maximum level.

FIG. 4 shows a device on the left that is suitable for receiving and evaluating received signals whose frequency is shifted in relation to the frequency of the interrogation signal.

A transponder T schematically reproduced in FIG. 4 contains a phase shifter PH, which is supplied by a generator TG with a clock frequency which causes a frequency shift in the reflected interrogation signal. A modulator M controls the phase shifter according to a code stored in a read-only memory of the transponder, so that the shifted frequency is emitted in time with this code. The amount of the frequency shift is so great that the shifted frequency can be processed separately from the interrogation frequency on the one hand, but can be received on the other hand with the same antenna with which the interrogation signal is transmitted. The device shown in FIG. 4 differs from the device of FIG. 2 described above primarily in that the two demodulators DM3 and DM4 are followed by bandpass filters BP1, BP2 instead of low-pass filters. To evaluate the transponder signal, the output signal of the first delay filter, which is taken from the first bandpass filter BP1, is fed to a further demodulator QM, which is controlled by an oscillator whose frequency corresponds to the frequency shift generated in the transponder. The real part and imaginary part of the demodulated signal are fed via an analog / digital converter to a signal processor DSP in the evaluation unit AW. The output signals of both bandpasses are also fed to a changeover switch SW1, which alternately switches them on to the signal processor of the evaluation unit. First, it is determined in the signal processor of the evaluation unit whether the level of the output signal of the second runtime filter exceeds the level of the output signal of the first runtime filter and thus the evaluation of the received signal must be prevented. Secondly, the level maxima of the output signals of both runtime filters are determined and the times of their arrival are recorded. The latter enables the time of passing a transponder and thus z. B. to record the passing of a vehicle carrying the transponder at a location marked by the interrogator.

If the device shown in FIG. 4 is also to detect reflective objects which do not carry a transponder, a low-pass filter TP3 must be provided parallel to the bandpass filter BP1 of the first delay filter, from which a detection signal can be taken at an output D.

Claims (13)

1. Device for detecting and reading out of this device movable transponders (T), which carry coded information, with a transmitting and receiving unit (H), which emits a high-frequency interrogation signal via an antenna (A) and one from one Transponder (T) tuned to the frequency of the interrogation signal in accordance with its coded information, receives as a reception signal modulated on the same frequency or a portion of this interrogation signal that is reflected for the purpose of suppressing unwanted reflections on a frequency shifted from the frequency of the interrogation signal, demodulates this and demodulates the signal of an evaluation unit (AW) for decoding and evaluation, characterized in that the transmitting and receiving unit contains a runtime filter, which forwards a received signal to the evaluation unit (AW) only if it arrives within a predetermined time window after the query signal has been sent is reached. 2. Device according to claim 1, characterized in that the runtime filter two Contains phase modulators, one of which is used as a modulation signal characteristic code generated to a code generator is that the first phase modulator in the transmission path of the transmission and Receiving unit, the second phase modulator in a receiving path the transmitting and receiving unit is arranged and both Phase modulators fed signals corresponding to them key code in phase between 0 ° and 180 °, that the second phase modulator the modulation signal via Delay element is supplied, the time delay of the sum the transit times of the interrogation signal and the reception signal on the Distance between reading device and transponder corresponds and that the second phase modulator with a frequency of Interrogation signal operated as a reference frequency high-frequency mixer and a low pass are connected in series. 3. Device according to claim 2, characterized in that the output of the low pass of Runtime filter is connected to a display device that the Presence of a transponder or one of the interrogation signal reflecting object. 4. Apparatus according to claim 2 or claim 3, characterized in that the transmitting and receiving unit further Contains runtime filters, each from the in the send path arranged first phase modulator (PM1) and another, the second phase modulator (PM2) connected in parallel or in one another receive path lying phase modulator (PM3) and this downstream high frequency mixer (DM2) and low pass (TP2) are formed, the modulation signal for the further Phase modulator supplied via a further delay element (VG) whose time delay (T) is smaller or larger than that Sum of the transit times of the interrogation signal and the reception signal the distance between the reading device and the transponder.   5. Device according to one of the claims 2 to 4, characterized in that the characteristic code digital pseudo random code. 6. Device according to claim 5, characterized in that the clock frequency of the characteristic Codes is less than a third of the frequency of the interrogation signal and that the reciprocal of the clock frequency of the pass width of the corresponds to the first runtime filter. 7. Device according to one of the preceding claims, characterized in that for sending the query signal and the same antenna (A) is provided for receiving the received signal is and that the antenna is preceded by a circulator (Z) which the interrogation signal and reception signals running in the opposite direction separates from each other. 8. Device according to one of claims 4 to 7, characterized in that a threshold circuit (SW) is provided, the control input with the outputs of the Low pass filter (TP2) is connected to the further runtime filter the output of the threshold circuit (SW) to a control input a gate circuit (TS) is guided, via which the output of the first low-pass filter output signal of the first Runtime filter can be switched through to the evaluation circuit (AW) and is only switched through if no other runtime filter delivers a signal at the output of its low-pass filter (TP2) Level is higher than a predetermined threshold. 9. The device according to claim 8, characterized in that as a predetermined threshold Output signal of the first runtime filter is used and the output of the Low pass filter (TP1) of the first runtime filter with a Reference voltage input of the threshold circuit is connected.   10. The device according to one of claims 1 to 3, characterized in that for obtaining the output signal of the Runtime filter when receiving frequency in relation to the Frequency of the interrogation signal shifted received signals instead a low-pass filter, a band-pass filter is provided, the Pass frequency corresponds to the frequency shift and that Output signal of the bandpass filter via a further demodulator, that of an oscillator oscillating with the displacement frequency is controlled, the evaluation unit is supplied. 11. The device according to one of claims 4 to 9, characterized in that to obtain the output signals of the Runtime filter when receiving frequency in relation to the Frequency of the interrogation signal shifted received signals instead of low-pass filters band-pass filters (BP1, BP2) are provided, the Pass frequencies of the frequency shift correspond to that Output of the first runtime filter another demodulator (QM) is connected downstream of one with the shift frequency vibrating oscillator (G1) is controlled and the Output signal of the first runtime filter of the evaluation unit (AW) is supplied, and that the outputs of both runtime filters on a switch (SW1) are guided, which the pending Output signals alternately switched through to the evaluation unit and that the evaluation unit in addition to a gate function, the an evaluation of the output signal of the first runtime filter prevented as soon as the level of the output signal of the second Runtime filter that of the output signal of the first runtime filter exceeds a maximum localization in which the Times are determined and recorded at which the Output signals of the individual runtime filters maximum levels to reach.   12. Use of a device according to one of the preceding Claims for selective readout of individual, in predetermined Removal of transponders, especially transponders, those on different lanes of a road Vehicles are attached. 13. Use of a device according to one of the claims 1 to 11 in a traffic system with track-bound vehicles and with route information arranged along lanes Vehicles using the lanes Transponders, for hiding interference and signals from Transponders delivered outside a lane used in each case become.