WO1995020797A1

WO1995020797A1 - Method using a transceiver to read out data stored in transponders

Info

Publication number: WO1995020797A1
Application number: PCT/FR1995/000086
Authority: WO
Inventors: Franz Blatnik
Original assignee: Allflex S.A.
Priority date: 1994-01-26
Filing date: 1995-01-26
Publication date: 1995-08-03
Also published as: MA23437A1; EP0741888A1; ZA95634B; UY23897A1; IL112442A0; AT401211B; IL112442A; CO4340583A1; ATA13994A; TNSN95006A1; AU1581395A

Abstract

A method using a transceiver to read out data stored in transponders, particularly duplex transponders with varying data encoding modes. The data received via the transceiver are digitised (11) and the data encoding mode is determined, whereafter a digital evaluation circuit (7) performs the various data evaluation functions on the basis of said mode. The method may also be used to read out data from alternately operating transponders.

Description

Method for reading data stored in answering machines by means of a transceiver.

The present invention relates to a method for reading, by means of a transceiver, data stored in answering machines. Radio identification systems consisting of a transceiver and associated answering machines in which data are stored, which data can be read by the transceiver, are used in various fields, in particular in the field of breeding. cattle for animal identification. The various known systems use different types of data coding and operate at different data transmission frequencies. In addition, there are distinctions to be made between duplex processing and half-duplex processing applied to data transmission. Responders that operate in duplex are activated by the transceiver via the transmission of a carrier wave field and transmit the data they contain during the activation carried out by the carrier wave field. '' Alternating responders use carrier wave energy to charge an internal power source and return their data after activation by the carrier wave, at frequencies which are generally different from the ^carrier wave of the frequency.

Due to the large number of systems used, it may happen, for example in livestock breeding operations following the purchase of animals with answering machines that are already established or the transition to a new system, that several systems are used simultaneously. Until today, in this case, it was unfortunately necessary to use several transceivers to be able to read the desired data coming from the different answering machines.

An object of the invention is to provide a method by which different types of coding and, possibly even, different frequencies can be read by means of a single transceiver. In addition, it would be advantageous to also be able to read the answering machines operating in alternation. Another object of the invention is to produce a device making it possible to implement this method.

All this is achieved according to the invention by the fact that, for the reading of different responders operating in duplex, the data of which are coded in different ways, - the data received by the transceiver are converted into digital form, - the type of data coding is determined, and

- the data are evaluated by a digital evaluation circuit which performs various functions making it possible to evaluate the data according to the type of data coding. An important advantage of digitizing data is that data can be evaluated in many different ways, for which otherwise several different analog circuits would have been required.

In a preferred embodiment of the invention, the type of data encoding is determined by implementing a Fourier analysis of the data, and the amplitude of characteristic frequency components is examined in the Fourier spectrum of the data. . For each of the commonly used types of coding, characteristic frequencies appear, such as those indicated in the description by means of various examples.

Since the response frequencies of the various types of responders may be different, it is advantageous to transmit a plurality of carrier wave frequencies in a particular time sequence. To also be able to read the answering machines operating in alternating mode, it is advantageous to check, during a pause made during the transmission of the carrier wave frequencies by the transceiver, whether a field returned by an answering machine operating in alternating mode is or is not being received. If this is not the case, the pause is advantageously ended and the sequence of carrier wave frequencies is then transmitted again; otherwise, the pause is extended until a complete data record has been read.

The precise evaluation of the digitized data will be explained in the description given below, which is intended to illustrate the invention and aims to allow a better understanding of its characteristics and advantages; it is based on the appended drawings, among which:

- Figure 1 is a simplified circuit diagram of a transceiver according to the invention; - Figure 2a shows the simplified time progression of an input signal from the transceiver for a duplex responder;

- Figure 2b shows the rectified, filtered and digitized signal;

- Figure 2c is the associated Fourier spectrum;

- Figures 3a, 3b, 3c are representations of time amplitude progressions for different types of amplitude coding, Figure

3a concerning a Manchester coding of the amplitude levels, FIG. 3b concerning a Manchester coding of the switching frequency of the amplitude levels, and FIG. 3c concerning a phase coding of the amplitude levels;

- Figure 4 is a simplified representation of the evaluation process of a phase coded signal;

- Figures 5a and 5b are representations of two temporal sequences of the frequencies of the carrier waves transmitted by transceiver; and

- Figure 6 shows a frequency coded signal.

As shown in FIG. 1, a simplified circuit diagram of the transceiver according to the invention comprises a series resonant circuit 1 having a capacitor 4 and an antenna winding 2, to which the antenna 3 is connected. To allow agreement on different resonance points of the series resonant circuit 1, it is possible to connect different capacitors 4a, 4b, 4c belonging to the unit 5 by means of one or more control wires 22 of a device 7 digital signal processing (DSP). The quality factor of the resonant circuit 1 can be reduced using a resistor 6 which can be connected by the intermediary of a control wire 21.

To produce the emission of a carrier wave field having a specific frequency f, the digital signal processing device 7 activates the resonant circuit 1 via a control stage 8, so that the resonance point of the resonant circuit 1 is tuned to f by connection of the appropriate capacitor 4a, 4b or 4c of the unit 5. For this purpose, it is for example possible to measure the amplitude of the voltage of the carrier wave.

A duplex responder transmits the data it contains while the carrier wave field is being transmitted by the transceiver. This operation is carried out by the fact that the transponder operating in duplex charges the field of the carrier wave by short-circuiting an inductance which it contains according to a particular time sequence and this charge of the field by inductive coupling is received by the transceiver in the form of a variation in amplitude of the signal of the resonant circuit 1. For this, it is naturally necessary that the frequency f of the carrier substantially coincide with the frequency for which the duplex responder is designed.

An example of time progression of a signal received in this manner, which contains the information to be read, is shown in Figure 2a. The frequency of the signal is f and the amplitude switches between the two values A1 and A2. The rectification of the received signal takes place in a rectifier 9 (see FIG. 1), the time constant of which is chosen so that the amplitude progression of the signal is not appreciably affected. The residues of the frequency f of the carrier wave as well as other parasites are removed from the signal by filtering in a bandpass filter 10, the transmission interval of which is a function of the frequencies to be detected, i.e., for example, a interval approximately between 1 and 70 kHz. The filtered signal is put in digital form by an analog-digital converter 11, after which it takes the form shown in FIG. 2b. It is also possible to decouple the DC component of the signal by capacitive means before the analog-digital conversion.

In order for the digital evaluation circuit contained in the signal processing device 7 to be able to carry out the evaluation, the type of data coding must first be determined. A simple and very quick way to determine the type of data encoding is to perform a Fourier analysis of the signal. This gives a Fourier spectrum having the frequency components of the signal. An example of the Fourier spectrum of a digital signal of the type of that presented in FIG. 2b is presented in FIG. 2c.

The comparison of the frequency components of the signal with characteristic frequencies relating to particular types of coding makes it possible to determine the type of coding which is present. The following examples show that the different types of coding contain unique characteristic frequency components.

To code signals, all the types of coding of duplex responders that are considered use the two amplitude values between which the responder can switch in a defined manner. In the simplest case, the amplitude itself is used as a characteristic of the coding. For a Manchester coding having the amplitude as a characteristic, a logic level 1 is represented by a low value of the amplitude during the first half of the duration "to" of a data bit and by a high value during the second half this time. A logic level 0 is represented by a high amplitude value during the first half and a low amplitude value during the second half of the data bit. Between two consecutive data bits, a transition between the two amplitude values takes place if identical bits follow one another; on the contrary, no transition takes place if the bits are different. The characteristic frequencies of this type of coding are therefore 1 / to and 2 / to.

In addition, it is possible to use as coding characteristic, not the amplitude itself, but rather the frequency at which the switching takes place between the two amplitudes. For example, a logic level 0 can be represented by a first frequency, for which the amplitude switches between two values, and a logic level 1 can be represented by a second frequency, for which the amplitude switches between two values. Figure 3b shows a Manchester encoding that uses two switching frequencies as characteristics, namely, in this example, f / 8 and f / 10. For logic level 1, the frequency switches, after to / 2, from f / 10 to f / 8, while, for logic level 0, it switches from f / 8 to f / 10 after to / 2. The frequency switches between two data bits if identical bits follow one another. The characteristic frequencies of the example in FIG. 3b are f / 8 and f / 10. As regards the phase coding of the data, which is presented in FIG. 3c, there is switching between the two amplitude values with a predefined frequency, for example half the value of the frequency of the carrier wave , ie f / 2, and the phase relation of the switching is used as coding. In FIG. 3c, for example, a logic level 0 is characterized by a low amplitude at the start of the data bit and by a high amplitude at the end of the data bit. However, a logic level 1 begins with a high amplitude value and ends with a low value. In a sequence of data bits having different logical values, the amplitude therefore remains at the ends of the data bit twice as long as for identical values as there are inside the data bit. The characteristic frequency associated with the phase coding presented in FIG. 3c is therefore f / 2.

Once the type of coding has been determined, various functions for evaluating the data are performed by the digital evaluation circuit of the signal processing device depending on the type of coding of the data.

If it is a Manchester coding having the amplitude as a characteristic (FIG. 3a), a digital bandpass filter operating on the appropriate interval, for example from 1 to 2 kHz, using from which the data is filtered, is performed, then a search is performed on the data to obtain the Manchester coding start code which identifies the beginning of the filtering of the actual data. For a Manchester coding having, as characteristic, the two switching frequencies between the two amplitude values, the data are first filtered by a bandpass filter within a transmission interval in which the switching frequencies are found. Then, a Fourier analysis of the entire data record is performed. Since, in the Manchester coding of the data, the two characteristics, namely f / 8 and f / 10 in the example of FIG. 3b, appear with the same frequency, in the case of a value different from the two components of Fourier of data recording for these two frequencies, a data correction factor can be specified to correct errors appearing in the data transmission or in the data.

To determine the starting point of the data bit in this type of coding, a Fourier analysis is carried out with a width corresponding to half a data bit, and the starting point of the Fourier analysis is delayed until 'so that a maximum appears in one of the two frequencies which are used as characteristics. Then, the half-bits of data are read, a Fourier analysis being carried out in each case for a width of half a bit of data, as well as the determination of that of the two frequencies used as characteristics which is present in the spectrum. of Fourier. To read the consecutive values, the starting point of the Fourier analysis is moved in each case by a quantity corresponding to the width of a half-bit of data. The values of the half data bits are then combined and read according to Manchester coding, so that the logical values of the different data bits are obtained. In the case of phase coding of the data, which is presented in FIG. 3c, one begins by filtering the data using a bandpass filter having a transmission interval within which the switching frequency enters the two amplitude values is found. To detect the starting point of a data bit, as shown in FIG. 4, after each switching time constant, the difference is produced between the two amplitude values 101 and 102 which are separated by half the switching time constant. Each of these differences is added to the sum of the previous differences. If the signal passes from a logical value to the other, the difference between the two amplitude values, for example 103, 104, changes sign, and the sum passes by an extreme value which locates the starting point of one bit of data. We can now read the data, since the sums are created for each bit using the differences indicated above and the signs of these sums are evaluated to determine the logical values of the data bits.

Since the different types of responders operate at generally different frequencies, it is advantageous for the transceiver to transmit different carrier wave frequencies in a time sequence. Such a time sequence of four frequencies f1 to f4 is presented in FIG. 5a. Each of the frequencies f 1 to f3 is activated for a particular duration. During this time, a Fourier analysis of the signal is performed to determine the type of coding of an answering machine operating in duplex at this frequency. If no responder is detected at this frequency, a transition to the next frequency is produced, after a time tl, by the fact that capacitors capable of modifying the resonance point of the resonant circuit 1 are connected using of unit 5 (see Figure 1).

During the transmission time of the carrier frequency f4, the signal from a transponder operating in duplex at this frequency can also be received. The carrier wave frequency f4 is also used for the case where a transponder operating in alternation is in the field of the transceiver, this frequency providing it with the energy necessary to charge its internal power supply source. Consequently, the carrier wave frequency f4 is transmitted in each case during the time t3 which is necessary for this operation.

In the case where, at one of the frequencies f1 to f4, a responder operating in duplex at one of these frequencies is received, this frequency is then transmitted until reception of a complete data record. The time t2 necessary for this operation again depends on the type of data encoding. Since the quality factor of the resonant circuit of a transponder is infinite, it may also happen that, during the transmission of one of the frequencies f1 to f4, a transponder operating in duplex at one of the adjacent frequencies is detected . If, for example, as shown in FIG. 5b, during the transmission of the frequency f1, a responder operating at the frequency f2 is detected, then, after the time tl, the frequency switches to f2, and the latter frequency is transmitted for a period t2.

During a pause P following the emission of the frequency f4, a check is carried out to determine whether a field returned by an answering machine operating in alternation is being received. To this end, it is advantageous to reduce the quality factor of the resonant circuit 1 (see FIG. 1) using the resistor 6, which is connected in the resonant circuit 1 via the control wire 21 of the signal processing device 7 using a switch 6a. Then, fields from answering machines operating in alternation in a relatively large frequency interval, approximately between 120 and 140 kHz, can be received.

If, during the pause P, no signal received from an answering machine operating in alternation is detected, the transmission of the carrier wave frequencies fl to f4 resumes immediately. However, if a signal from an answering machine operating alternately is received, the pause P is prolonged until reception of the complete data record.

To detect and evaluate any data arriving from an answering machine which operates in alternation mode, the switch 23a is activated during the pause P via the control wire 23 so that the data pass through the bandpass filter 12 and the comparator 13 The bandpass filter 12 has a transmission interval within which is the reception interval of the resonant circuit 1, preferably between approximately 120 and 140 kHz. The sinusoidal input signal is converted by the comparator 13 into a rectangular signal. To determine the respective frequency of this rectangular signal, the evaluation circuit of the signal processing device 7 counts the zero crossings of the rectangular signal. The data of an answering machine operating in alternation are usually coded in frequency. This means that a logic level 0 is represented by the emission of a frequency f1, while a logic level 1 is represented by the emission of a different frequency, ie f2, each emission taking place during a lapse of defined time. By determining the frequency sequence of the signal from a transponder operating alternately, the data can be read.

Another possibility making it possible to evaluate the data of an answering machine operating in alternation consists in using, instead of the comparator 13, an analog-digital converter, which puts the signal in digital form. Again, the frequency sequence of the digital signal is determined by the digital evaluation circuit of the signal processing device 7, thanks to the execution of a Fourier analysis of the data in each case, over the width of a data bit.

Since the cost of an analog-digital converter increases when its sampling frequency increases, it is advantageous to use an analog-digital converter whose sampling frequency fA is below the frequencies fl and, or, f2 signals. In the spectrum of Fourier, the components which belong to fl or f2 then appear at the image frequencies fl-fA or f2-fA.

The method of the invention is not limited to the examples of data coding which have been presented. Responders using other types of data encoding and, or, other frequencies can also be read using the method of the invention, in the same manner.

An additional advantage of the method of the invention lies in the fact that it is possible to incorporate simply in a transceiver currently existing the characteristics of future answering machines, or even answering machines which are not yet envisaged, by entering the data. necessary for the addition of a digital evaluation circuit suitable for these types of responders, this can be done in a simple manner from outside the transceiver, via an interface.

Of course, those skilled in the art will be able to imagine, from the method whose description has just been given by way of illustration only and in no way limitative, various variants and modifications not departing from the scope of the invention .

Claims

R E V E N D I C A T I O N S

1 - Method for reading, by means of a transceiver, data stored in transponders, where the data received from a transponder operating in duplex are put in digital form in the transceiver and a Fourier analysis of at least some of the data is carried out by a digital evaluation circuit (7), characterized in that, in order to read in various types of duplex responders, which employ different kinds of data coding, it is determined , in the Fourier spectrum, the values of frequency components which are characteristic of the various species of data coding, so as to detect the kind of data coding, and in that the digital evaluation circuit (7) constitutes different functions to evaluate the data, depending on the kind of data encoding that has been detected.

2 - Method according to claim 1, characterized in that the frequency of the carrier wave is extracted by filtering the data transmitted by an answering machine operating in duplex before the data is put in digital form.

3 - Method according to claim 1 or 2, characterized in that, for a form of coding of 'Manchester which uses the amplitude of the data as ^' characteristic of the coding, then, to evaluate the digitized data:

the data are filtered using a digital bandpass filter, the transmission interval of which is preferably within the range of 1 to 2 kHz, and

- the Manchester coding start code is sought to read the logical values of the respective data bits. 4 - Method according to claim 1 or 2, characterized in that, for a coding which represents a logic level 0 by a first frequency, at which the amplitude switches between two values, and which represents a logic level 1 by a second frequency , at which the amplitude switches between two values, then, to evaluate the digitized data: - the data is filtered using a digital bandpass filter, the transmission interval of which includes the two frequencies, and

- Fourier analyzes of the data are carried out using the width of a data bit to detect the starting point of the data bits and to read the data bits. 5 - Method according to claim 1 or 2, characterized in that, for a Manchester coding which uses the frequency with which the amplitude of data switches between two values as a characteristic of the code, then, to evaluate the digitized data:

- the data are filtered using a digital bandpass filter whose transmission interval contains the two frequencies, - a Fourier analysis of the entire data record is carried out to define a correction factor, and

- Fourier analyzes of the data are carried out using half the width of a respective data bit to detect the starting points of the data bits and to read the respective data bits. 6 - Method according to claim 1 or 2, characterized in that, for a phase coding of the data such that the amplitude level of the data switches between two values at a particular frequency and that between a logic level 0 and a level logic 1 there is a phase shift of half the time constant of the switching period, then, to evaluate the digitized data: - the data is filtered using a digital bandpass filter whose interval transmission contains the switching frequency,

- after each time constant in the switching period, the difference between two amplitude values is formed, these being separated from each other by a half time constant, and these differences are added together to form a sum,

the extreme values of this sum are detected to determine the beginnings of the data bits, and

- the sign of this sum is determined for each data bit in order to read the logical values of the data bits. 7 - Method according to claim 1, characterized in that, to read a responder, the transceiver transmits different frequencies of carrier waves according to a particular time sequence.

8 - Method according to any one of claims 1 to 7, caracté¬ ized in that, during a pause made in the emission of the frequency of the carrier wave, a check is made to know if a field returned by an answering machine that works alternately is or is not being received.

9 - Process according to claim 8, characterized in that, if it is established that a field is being received from an answering machine operating in alternation, the pause is extended until all the data sent by the alternator operating alternately has been received, while, in the case on the contrary, the transmission is carried out on the next carrier wave frequency after a pause, the length of which is correspondingly shorter.

10 - A method according to claim 8 or 9, characterized in that, for the reception of a field of an answering machine operating in alternation, the quality factor of the resonant transmission-reception circuit is reduced.

11 - Method according to claim 8 or 9, characterized in that, to read an answering machine operating in alternation, which emits a field at a first frequency to emit a logic level 0 and a field at a second frequency to emit a logic level 1 , - the signal received is filtered using a bandpass filter whose transmission interval contains the two frequencies,

the signal is converted into a rectangular signal using a comparator, and

- the zero crossings of the rectangular signal are counted by the digital evaluation circuit in order to determine the frequency of the signal. 12 - Process according to any one of claims 8 to 10, charac¬ terized in this, for reading an answering machine operating in alternation, which emits a field at a first frequency to emit a logic level 0 and a field at a second frequency for issue a logic level 1,

the data received by the transceiver are converted into digital form using an analog-digital converter, and

- a Fourier analysis of each bit of data is carried out in order to read the digitized form.

13 - Method according to claim 12, characterized in that the sampling frequency of the analog-digital converter is less than the two frequencies of the signal and, to read the data, the Fourier components of the data are determined and on evaluates them at the two image frequencies resulting from the combination of the signal frequencies with the sampling frequency.