IL112442A

IL112442A - Process for reading out data stored in transponders by means of a transceiver

Info

Publication number: IL112442A
Application number: IL112442A
Authority: IL
Original assignee: Allflex Sa
Priority date: 1994-01-26
Filing date: 1995-01-25
Publication date: 1998-02-22
Also published as: IL112442A0; UY23897A1; TNSN95006A1; EP0741888A1; CO4340583A1; WO1995020797A1; ATA13994A; ZA95634B; MA23437A1; AT401211B; AU1581395A

Description

Process for the reading out data stored in transponders by means of a transceiver ALLFLEX S.A.

C. 96317 A PROCESS FOR READING OUT DATA STORED TRANSPONDERS BY MEANS OF A TRANSCEIVER The invention concerns a process for reading out data stored in transponders by means of a transceiver.

Wireless identification systems consisting of a transceiver and associated transponders in which data are stored, which data can be read out by the transceiver, are used in various fields, for example, for identification of animals in a livestock husbandry operation.

The various known systems use different types of data coding and operate at different frequencies of fields for data transmission. Also, there are distinctions between the full-duplex process and the half-duplex process for data communication: Transponders which operate in full duplex are activated by the transceiver by transmission of a carrier field and transmit the data stored in them during activation by the carrier field. Transponders which operate in half duplex use the energy of the carrier field to load an internal power source and return their data after activation by the carrier field at frequencies which generally differ from the carrier f equency.

Because of the large number of systems used, it can happen, for example, in cattle breeding operations through the purchase of animals with transponders already implanted or by switching to a new system, that a plurality of systems are simultaneously in use. Until now, in this situation, it has been disadvantageously necessary to use a plurality of transceivers in order to be able to read out the desired data from the different transponders.

An object of the invention is to provide a process whereby different coding types and possibly even different frequencies can be read out by a single transceiver. Furthermore, the additional capability of also being able to read out half-duplex transponders would be advantageous. It is a further object of the invention to provide a device for performance of this process.

This is accomplished according to the invention in that for the reading out of various transponders operating in full duplex, whose data are coded differently, the data received by the transceiver are converted into a digital form, the type of data coding is determined, and the data are evaluated by a digital evaluation circuit which performs different functions for evaluation of the data depending on the type of data coding.

A significant advantage of the digitization of the data consists in that the data can be evaluated in many different ways, for which, otherwise, a plurality of different analog circuits would be necessary.

In a preferred embodiment of the invention, the type of data coding is determined through the performance of a Fourier analysis of the data and the magnitude of characteristic frequency components is examined in the Fourier spectrum of the data. With each of the currently used types of coding, characteristic frequencies, occur, such as those listed in the descriptions of the figures using various examples.

Since the response frequencies of the various types of transponders may be different, it is advantageous to transmit a plurality of carrier frequencies in a specific temporal sequence. To also be able to read out half-duplex transponders, it is advantageous to check, during a pause in the transmission of the carrier frequencies from the transceiver, whether a field returned by a half-duplex transponder is being received. If not, the pause is advantageously terminated and the sequence of carrier frequencies is again transmitted; whereas otherwise, the pause is extended until a complete data record is read out.

The accurate evaluation of the digitized data and additional details and advantages of the invention are explained in the following with reference to the accompanying drawings.

The drawings depict: Figure 1 is a simplified basic circuit diagram of a transceiver according to the invention; Figure 2a is a schematic temporal progression of an input signal of the transceiver with a full-duplex transponder; Figure 2b illustrates the rectified, filtered, and digitized signal ; Figure 2c is the associated Fourier spectrum; Figure 3 is a representation of temporal amplitude progressions with different types of coding of amplitudes, with Manchester coding of the amplitude levels (Figure 3a), with Manchester coding of the switching frequency of the amplitude levels (Figure 3b), and with phase coding of the amplitude levels (Figure 3c); Figure 4 is a schematic representation of the procedure for evaluation of a phase coded signal; Figures 5a and 5b are representations of two temporal sequences of the carrier frequencies transmitted by the transceiver; and Figure 6 is a frequency coded signal.

A simplified basic circuit diagram of the transceiver according to the invention in Figure 1 shows the series-resonant circuit 1 with the capacitor 4 and the antenna coil 2, onto which the antenna 3 is coupled. To tune different resonance points of the series-resonant circuit 1, different capacitors 4a, 4b, 4c can be connected in the unit 5 by means of the control wire(s) 22 of the digital signal processor 7. The Q-factor of the resonant circuit 1 can be reduced by the resistor 6 connectable by means of the control wire 21.

In order to transmit a carrier field with a specific frequency f, the resonant circuit 1 is activated via the driver stage 8 from the digital signal processor 7, whereby the resonance point of the resonant circuit 1 is tuned by connection of suitable capacitors 4a, 4b, 4c of the unit 5 to f. For this, for example, the amplitude of the carrier voltage can be measured.

A transponder which operates in full duplex transmits the data stored in it while the carrier field is being transmitted from the transceiver. This is achieved in that the full-duplex transponder loads the carrier field by shorting an inductance contained in it in a specific temporal sequence and this load of the field through inductive coupling is receiving by the transceiver as a change in the amplitude of the signal of the resonant circuit 1. For this, the carrier frequency f and the frequency for which the full-duplex transponder is designed must, of course, substantially coincide.

An exemplary temporal progression of a signal received in this manner, which contains the information to be read out, is depicted in Figure 2a. The frequency of the signal is f and the amplitude switches between the two values Al and A2.

Rectification of the signal received occurs in the rectifier 9 (see Figure 1) whose time constant is designed such that the amplitude progression of the signal is not significantly affected. Remnants of the carrier frequency f as well as other interference are filtered out of the signal in the bandpass filter 10, which has a transmission range based on the frequencies to be detected, for example, approximately l-70kHz. The filtered signal is converted by an analog-to-digital converter 11 into a digital form and then has the form depicted in Figure 2b. It is also possible to decouple the direct current component of the signal capacitively before the analog-to-digital conversion.

For evaluation of the digitized evaluation circuit contained in the signal processor 7, the type of data coding is first determined. A simple and very rapid method for determination of the type of data coding consists in a Fourier analysis of the signal. Through it, a Fourier spectrum with the frequency components of the signal is obtained. An exemplary Fourier spectrum of a digital signal of the type in Figure 2b is depicted in Figure 2c.

A comparison of the frequency components of the signal with characteristic frequencies for specific coding types enables determination of the type of coding present. The fact that the different types of coding contain unique characteristic frequency components is demonstrated in the following using some examples.

To code signals all full-duplex transponder coding types under consideration use the two values of the amplitude between which the transponder can switch in a defined manner. In the simplest case, the amplitude itself is used as the characteristic for coding. With Manchester coding with the amplitude as the characteristic, a logical 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. A logical 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 occurs if identical bits follow each other; in contrast, no transition occurs if the bits are different. The characteristic frequencies of this type of coding are thus 1/to and 2/to.

Also, not the amplitude itself but rather the frequency at which the switch between the two amplitudes is made may be used as the coding characteristic. For example, a logical 0 can be represented by a first frequency at which the amplitude is switched between two values, and a logical 1 can be represented by a second frequency at which the amplitude is switched between two values. In contrast, Figure 3b depicts Manchester coding which uses two switching frequencies as characteristics, f/8 and f/10 in this example. With a logical 1, the frequency switches after to/2 from f/10 to f/8, whereas with a logical 0 it switches from f/8 to f/10 after to/2. The frequency switches between two data bits if identical bits follow each other. Characteristic frequencies in the example of Figure 3b are f/8 and f/10.

With phase coding of the data, as depicted in Figure 3c, there is switching between the two amplitude values at a predefined frequency, eg., half the value of the carrier frequency f/2, and the phasing of the switching is used for coding. In Figure 3c, for example, a logical 0 is characterized by the low amplitude at the beginning of the data bit and the high amplitude at the end of the data bit. A logical 1, however, begins with the high amplitude value and ends with the low one. With a sequence of data bits with differing logical values, the amplitude thus remains on the ends of the data bit twice as long with the identical values as within the data bit. A characteristic frequency with the phase coding in Figure 3c is thus f/2.

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

If there is Manchester coding with the amplitude as the characteristic (Figure 3a), a digital bandpass filter in the appropriate range, eg. l-2kHz, with which the data are filtered, is provided, then a search is performed in the data for the beginning code of the Manchester coding, which identifies the beginning of the actual data filtering.

With Manchester coding with the two switching frequencies between the two amplitude values as a characteristic, the data are first filtered by a bandpass filter within whose transmission range both switching frequencies fall. Then, a Fourier analysis of the entire data record is performed. Since, with Manchester coding of the data, both characteristics, ie., f/8 and f/10 in the example of Figure 3b, appear with equal frequency, in the case of a different value of the two Fourier components of the data record at these two frequencies, a correction factor for the data can be specified to correct errors in data transmission or data.

To determine the starting point of the data bit, with this type of coding a Fourier analysis is performed with the width of half a data bit, and the starting point of the Fourier analysis is delayed until a maximum appears at one of the two frequencies being used as characteristics. The half data bits are then read, with a Fourier analysis performed in each case with the width of half a data bit and a determination as to which of the two frequencies being used as characteristics is present in the Fourier spectrum. For reading out the consecutive values, the starting point of the Fourier analysis is in each case shifted by the width of half a data bit. The values for the half data bits are subsequently combined and read in the sense of the Manchester coding, whereby the logical values of the individual data bits are obtained.

With phase coding of the data, as depicted in Figure 3c, the data are first filtered with a bandpass filter within whose transmission range are switching frequency between the two amplitude values falls. To detect the starting point of a data bit, as shown in Figure 4, after each switching time constant, the difference between the two amplitude values 101, 102, which are separated by one-half the switching time constant, is generated. Each of these differences is added to the sum of the previous differences. If the signal changes between two logical values, the difference between the two amplitude values changes, eg., 103, 104, changes its sign and the sum feeds through an extreme value which marks the starting point of a data bit. The data can now be read since the sums are created for each data bit using the above-described differences and the signs of these sums are evaluated to determine the logical values of the data bits.

Since the different types of transponders are operated at generally differing frequencies, it is advantageous of the transceiver transmits different carrier frequencies in a temporal sequence. Such a temporal sequence of four frequencies fl through f4 is depicted in Figure 5a. Each of the frequencies fl through f3 is activated for a specific period of time. During this time, a Fourier analysis of the signal is performed to detect the coding type of a full-duplex transponder operating at this frequency. If no such transponder is detected at this frequency, after tl the transition to the next frequency occurs, by capacitances to change the resonance point of the resonant circuit 1 being connected with the help of the unit 5 (see Figure 1).

During the time that the carrier frequency f4 is being transmitted, a signal of a full-duplex transponder operating at this frequency can also be received. The carrier frequency f also serves the purpose that if a half-duplex transponder is in the field of the transceiver, this frequency provides it the energy to load its internal power source. Consequently, the carrier frequency f4 is transmitted in each case for the period t3 required for this.

If at one of the frequencies fl through f4 a full-duplex transponder operating at this frequency is received, this frequency is transmitted until a complete data record is received. The time t2 necessary for this again depends on the type of data coding. Because of the infinite Q-factor of the resonant circuit of a transponder, it may also occur that during the transmission of one of the frequencies fl through f4, a full-duplex transponder operating at one of the adjacent frequencies is detected. If, for example, as depicted in Figure 5b, during transmission of frequency fl a transponder operating at the frequency f2 is detected, after tl the frequency is switched to f2 and this is transmitted for a period t2.

During a pause P after transmission of f4, a check is performed to determine whether a field returned from a half-duplex transponder is being received. For this , the Q-factor of the resonant circuit 1 (see Figure 1) is advantageously reduced by means of the resistor 6, which is connected into the resonant circuit 1 via the control wire 21 of the signal processor 7 using a switch 6a. Thus, fields from half-duplex transponders in a relatively large frequency range between approximately 120 and 140kHz can be received.

If during the pause P, no reception of a signal of a half-duplex transponder is detected, transmission of the carrier frequencies fl through f4 is immediately resumed. If, however, a signal from a half-duplex transponder is received, the pause P is extended until reception of the complete data record.

For detection and evaluation of possible data arriving from a half-duplex transponder, the switch 23a is operated during the pause P via the control wire 23 such that the data travel through the bandpass 12 and the comparator 13. The bandpass 12 has a transmission range in which the reception range of the resonant circuit 1 falls, preferably from approximately 120 and 140kHz. The sine input signal is converted by the comparator 13 into a rectangular signal. To determine the respective frequency of this rectangular signal, the zero-passes of the rectangular signal are counted by the evaluation circuit of the signal processor 7.

The data of a half-duplex transponder are usually frequency coded. That means that a logical 0 is represented by the transmission of a frequency fl, a logical 1 by the transmission of a different frequency f2, each for a defined period of time. By determining the sequence of frequencies of the signal of a half-duplex transponder, the data can be read.

An alternative possibility for evaluating the data of a half-duplex transponder consists in using an analog-to-digital converter instead of the comparator 13, which converter changes the signal to a digital form. The sequence of frequencies of the digital signal is again determined by the digital evaluation circuit of the signal processor 7, by performing a Fourier analysis of the data in each case over the width of a data bit.

Since analog-to-digital converters with increasing sampling frequency become increasingly more expensive, it is advantageous to use an analog-to-digital converter with a sampling frequency fA below the signal frequencies fl and/or f2. In the Fourier spectrum, the components which belong to fl or f2, then appear at the image frequencies fl-fA or f2-fA.

The process of the invention is not restricted to the examples of data coding presented. Transponder types which use other types of data coding and/or other frequencies can also be read out using the process according to the invention in the same manner.

An additional advantage of the process according to the invention consists in that future transponder types or those not yet considered can be incorporated into an existing transceiver simply, by entering the necessary data for addition of a digital evaluation circuit suitable for these types of transponders into the existing transceiver simply from the outside via an interface. 11

Claims

1. A process for reading out data stored in transponders by means of a transceiver, where the data received from a full-duplex transponder is transformed into digital form in the transceiver and a Fourier analysis of at least some of the data is carried out by a digital evaluation circuit, characterized in that for reading out from various types of full-duplex transponders which employ different kinds of data coding, in the Fourier spectrum the values of frequency components characteristic of the various kinds of data coding are determined, thereby detecting the kind of data coding, and in that the digital evaluation circuit builds up different functions for evaluating the data, depending on the kind of data coding detected.

2. The process according to claim 1, wherein the carrier frequency is filtered out of data transferred by a full-duplex transponder before the data is converted to digital form.

3. The process according to claim 1 or 2, wherein with a form of Manchester coding which uses the amplitude of the data as the characteristic of the coding in order to evaluate the digitized data, - the data is filtered by means of a digital band-pass filter the transmission range of which is preferably in the range from l-2kHz, - the starting code of the Manchester coding is searched in order to read the logical values of the individual data bits.

4. The process according to claim 1 or 2, wherein with a coding which represents a logical 0 by a first frequency, with which the amplitude is switched between two values, and which represents a logical 1 by a second frequency, with which the amplitude is switched between two values, in order to evaluate the digitized data - the data is filtered by a digital band-pass filter, the transmission range of which includes both frequencies, - Fourier analyses of the data is performed with the width of a data bit for detection of the beginning point of the data bits and for reading the data bits.

5. The process according to claim 1 or 2, wherein with a Manchester coding which uses the frequency with which the amplitude of the data is switched between two values as a characteristic of the code, in order to evaluate the digitized data - the data is filtered by a digital band-pass filter the transmission range of which includes both frequencies, a Fourier analysis of the entire data record is performed to define a correction factor, - Fourier analyses of the data is performed with half the width of an individual data bit for detection of the starting points of the data bits and for reading the individual data bits.

6. The process according to claim 1 or 2, wherein with a phase coding of the data whereby the amplitude level of the data is switched between two values at a specific frequency and between a logical 0 and a logical 1, there is a phase shift of half a time-constant of the switching period, in order to evaluate the digitized data - the data is filtered by a digital band-pass filter the transmission range of which includes the switching frequency, - after each time-constant of the switching period the difference between two amplitude values is formed, these being a half time-constant apart and these differences are added together to make a sum, - to determine the beginnings of the data bits extreme values of this sum are detected, and - in order to read out the logical value of the data bits the digit sign of this sum is determined for each data bit.

7. The process according to claim 1, wherein for reading out of a transponder the transceiver transmits different carrier frequencies in a specific temporal sequence.

8. The process according to any one of claims 1 to 7, wherein in a pause in the transmission of the carrier frequency a check is made whether a field returned from a transponder operating in half-duplex is being received.

9. The process according to claim 9, wherein if it is established that a field is being received from a half-duplex transponder, the pause is extended until all data sent by the half-duplex transponder has been received, while otherwise transmission is made on the next carrier frequency after a correspondingly shorter pause.

10. The process according to claim 8 or 9, wherein for reception of a field of a half-duplex transponder, the Q-factor of the send/receive resonant circuit is reduced.

11. The process according to claim 8 or 9, wherein for reading out of a half-duplex transponder, which transmits a field at a first frequency to transmit a logical 0 and a field at a second frequency to transmit a logical 1 - the received signal is filtered by a band-pass filter the transmission range of which includes both frequencies, - the signal is converted by means of a comparator into a rectangular signal, and - the zero-passes of the rectangular signal are counted by the digital evaluation circuit to determine the signal frequency.

12. The process according to any one of claims 8 to 10, wherein for reading out of a half-duplex transponder, which transmits a field at a first frequency to transmit a logical 0 and a field at a second frequency to transmit a logical 1 - the data received by the transceiver is converted by an analog-to-digital converter into a digital form, and - a Fourier analysis of each data bit is performed for reading the digitized form.

13. The process according to claim 12, wherein the sampling frequency of the analog-to-digital converter is lower than the two signal frequencies, and for reading the data, the Fourier components of the data are determined and evaluated at the two image frequencies which result from the signal frequencies in combination with the sampling frequency. For the Applicants DR. REINHOLD COHfc ND PARTNERS