TECHNICAL FIELD

Communications, electrical selective (e . g. , remote control) information on demand/ transponder.

BACKGROUND ART Heretofore/ in identification device systems/ there is usually found some sort of an exciter which is associated with an interrogator which feeds a combined alternating current clock signal and power supply sig¬ nal to a responder device via an inductive coupling. The responder may be implanted in an animal or on some¬ thing whose identity is to be ascertained/ such as a freight car and the responder produces a coded identi¬ fication signal which is fed back through the inductive coupling to a detector and demodulator which produces an output signal characteristic of the particular animal or thing that is being identified. Many coded data transmission systems have been used. In some the responder entails a resonant circuit which varied in frequency according to the encoded signal peculiar to the animal or thing being identified. In Kaplan et al. U.S. Pat. 3/689/885/ coded information was returned from a responder to an interrogator in the form of spaced bursts of alternative current of a fixed fre¬ quency. In Begle U.S. Pat. 4/333,072/ for example/ the responder or tag circuit produced an alternating current signal which varied in amplitude according to the encoded signal characteristic of the animal or thing being identified. All of these systems were sub¬ ject to certain drawbacks/ the resonant circuit signals being subject to variations in resonance produced by, for example/ changes in temperature which/ in some

instances/ could produce spurious variations in fre¬ quency which were difficult if not impossible to dif¬ ferentiate from variations produced by the encoding de¬ viceT and in a system wherein the code signal was re- presented by variations in amplitude of an oscillating circuit/ such variations in amplitude are difficult to accurately detect.

DISCLOSURE OF INVENTION

As in most of its predecessor systems the subject device is supplied with a combined clock and power sig¬ nal from an interrogating unit which is inductively coupled to a transponder device which is implanted on the thing to be identified and detected/ which device produces an encoded signal which is fed back through the inductive coupling to the interrogating unit/ but in a different form than that incorporated in the pre¬ decessor devices. In this system/ the clock signal derived via the inductive coupling from the interrogat¬ ing unit is reduced in frequency and then caused to . shift in frequency. In particular an incoming clock signal of 400 KHz is fed to a variable modulus counter followed by a divide-by-two circuit which/ in one state/ -divides the clock signal by eight and/ in another state/ divides the clock signal by ten. Thus, the output of the variable modulus counter produces an alternating current signal of either 40 KHz or 50 KHz, a shift from one of which frequencies/ generally stated, is representative of a "zero" and from the other is representative of a "one". The "ones" or "zeros" are produced by the encoding device-, and these identifying signals of either 40 KHz or 50 KHz are re¬ turned to the interrogating device via the inductive coupling and detected; and it is an easy task for the interrogator-detector to recognize a shift from a

40 KHz signal to a 50 KHz signal and vice-versa. The foregoing represents a simplification of the encoding system. In practice, an array of logic gates is used to control the insertion of a sync word in the data- stream. This logic also creates a Manchester encoding on the datastream. The result is a serial composite including sync and data information.

The composite stream controls the modulus (divide ratio) of the variable modulus counter which is clocked by the input clock (400 KHz). The output of the vari¬ able modulus counter is either 80 KHz or 100 KHz, de¬ pending on the data value. This counter drives a divide-by-two flip flop which results in output fre¬ quencies of 40 KHz or 50 KHz which vary as a function of the data.

The primary object of this invention is to provide a system for identifying an object, animal or person consisting essentially of two units, one being a pas¬ sive integrated transponder (PIT) which is carried by or embedded in the thing or animal to be identified and which responds to interrogation with an identifying code, and the other unit being an interrogator-reader separate from the PIT. .

BRIEF DESCRIPTION OF DRAWINGS More specific objects will be apparent from the following specification and drawings in which:

Fig. 1 is a block diagram of the overall system: Fig. 2 is a circuit diagram of the exciter: Fig. 3 is a circuit diagram of the signal con- ditioner:

Fig. 4 is a circuit diagram of the passive in¬ tegrated transponder (PIT) :

Fig. 5 is a diagram of a typical data stream wave;

Fig. 6 is a circuit diagram of the demodulator; and,

Fig. 7 and 7A are a diagram of the control logic and encoding circuit.

MODES FOR CARRYING OUT THE INVENTION

Overall Operation

Figure 1 shows the overall system consisting of a reader/exciter 2 and the passive integrated transpσnder (PIT) 18.

The reader/exciter unit 2 includes three main functional units: The exciter 4, signal conditioner 6 and the demodulation and detection circuits 8. The exciter 4 consists of an AC signal source 10, followed by a power driver 12 which provides a high current, high voltage signal to the interrogator coil 14 through a capacitor 16. The interrogator coil 14 and the capa¬ citor 16 are selected to resonate at the exciter signal frequency so that the voltage across the coil is much greater than the voltage output from the driver.

The signal conditioner 6 connects to the inter¬ rogator coil 14 and serves to amplify the signal re¬ turned from the PIT 18 while filtering out the exciter signal frequency as well as other noise and undesired signals outside of the frequency range used by the PIT signals.

The amplified output of the signal conditioner 6 is fed to the demodulation and detection unit 8 which includes a low pass filter 20 to further reduce exciter signal energy, a frequency shift keyed (FSK) demodula¬ tor 22 and a microcomputer 24. The FSK demodulator 22, is a phase-locked loop circuit configured as a tone de¬ coder which gives a digital output as the signal from the PIT 18 shifts between two frequencies. The micro-

computer 24 extracts the identification code from this digital output by observing the timing of transitions between the two logic levels. The identification code obtained by the microcomputer 24 can be transferred to a display or printer, sent over communication lines to a remote point, stored on tape, disk or other storage medium, or sent to another computer.

The PIT 18 consists of an induction coil 26 which is located such that the magnetic flux generated by the interrogator coil 14 couples energy at the exciter .fre¬ quency into the PIT. This energy is converted to a DC voltage using a full-wave rectifier bridge 28 and a smoothing capacitor 30 as is commonly used in power supply circuits. This DC voltage supplies the power to the control logic and ID memory circuit 32.

The control logic consists of counters and gates which sequentially read out the contents of the ID memory. The logic also inserts a sync word into the signal data stream to allow the reader/exciter to syn- chronize to the data. The exciter signal which appears on the PIT coil 26 is connected into the control logic to provide a clock signal for the counters. The logic circuits convert the serial data and sync stream into a frequency shift keyed (FSK) waveform which is connected to the PIT coil 26 through complementary current sinks to place a time varying load on the PIT coil 26 which, appears at the interrogator coil 14 (due to the mutual inductance) as a time varying voltage. It is this vol¬ tage which is amplified by the signal conditioner and detected.

The following detailed description of the system, the different components, e.g., the exciter 4, the sig¬ nal conditioner 6, etc., are different units which, except for the passive integrated transponder PIT 18, plug into a connect with one another through standard

connection as indicated. It should be understood, how¬ ever/ that/ except for the PIT/ they may all be wired together. in the following description of the circuits/ the 5 number prefix denotes the drawing figure in which the designated element resides. Thus/ "2C1" or "2L1" means that "Cl" and "Ll" are in the circuit shown in Fig. 2.

Detailed Description Exciter 4

10 A schematic diagram of the exciter 4 is shown in

Figure 2. The exciter consists of a crystal controlled oscillator 34 formed by gate 2U.B and crystal 2X_ . In this example the crystal frequency is 4 MHz. The crystal oscillator output is buffered by 2U.C and

15 then divided in frequency by 5 using 2ϋ A, 2U_B/ 2U A. The output of 2U A, which is now at 800 KH/ is divided in frequency by another factor of 2 in 2U B to create a square wave output at 400 KH. This square wave output then drives a high power switch

20 driver 36 which in turn will drive the coil. The func¬ tion of gate 2U..A in this circuit is to allow the exciter to be remotely enabled and disabled via the enable input line from TSI-5.

The high power switch driver 36 is formed by VMOS

25 transistors 2Q, and 2Q_. 2Q is switched on by a positive going signal from pin 14 of U_B. This turns 2Q« on with a low resistance to ground. When the output pin 14 is at a low logic level/ 2Q is turned fully off. 20. performs the same func-

30 tion being turned on between a positive DC voltage and off in a high impedance state. Where transistors 2Q_ and 2Q perform a voltage translation required to take the output of 2U1D/ pin 11, and convert it to the required voltage levels to drive the gate of 2Q..

In operation transistor 2Q_ is on when transistor 2Q- is off and visa versa. This timing of 2Q_ and 2Q- sets up an alternating voltage which is im¬ pressed upon the coil via terminals TSI-7 and TSI-8 through capacitors 2C. and 2C . Resistors 2R. through 2R_ and 2R._ through 2R. → serve to reduce the dissipation of ^' 2Q and 2Q during the switching transitions and also define the Q of the circuit formed by 2C. and 2C_ and the coil. The voltage across the coil is much greater than the DC voltage at the drain of 2Q-. This is due to the resonance of 2C. and 2C_ with the coil induc- tance/ at the exciter frequency, in this case 400 KHz. The connections to and from exciter 4 are generally as indicated by the legends. TP 1 and TP 2 are test points. Enable connection TSI-5 and TSI-6 need not be used. They do, however, provide for remote control of the exciter. Open circuit, at these points, enables the exciter. TSI-9 and TSI-10 connect to the signal conditioner.

Signal Conditioner 6

The signal conditioner 6 is shown in Figure 3 and consists of a conventional power supply 38 formed by transformer 3T1, , diodes 3CRJ_ through 3CRo-/ capacitors 3C._ through C. → and voltage regula- tors 3VR and 3VR_. This power supply provides a positive 15 volt and negative 15 volt DC output to power the signal conditioning circuits. The signal conditioning circuit consists of a bandpass filter 40 tuned to the frequencies used by the PIT 18. The band- pass filter 40 consists of inductances 3L. 3L- ₇ 3L- and capacitors 3C. and.3C-. In this case the PIT frequency is shifted between 40 and 50 kilohertz. Resistor 3R. sets the bandwidth of the

filter at 10 kilohertz. In addition 3I__ through 3L_ appear as a high impedance to the exciter fre¬ quency of 400 kilohertz; and the series combination of 3L. and 3C. and 3C_ serve as a very low impedance at 400 kilohertz to reject the exciter fre¬ quency. Amplifier 3U.. is a unity gain amplifier which acts as a buffer to drive a bandpass filter 42 formed by 3C-, 3L _g , 3L _g and 3C_. This is again a bandpass filter of 40 to 50 kilohertz. The output of this filter is amplified in 3U- and 3U_ to create the filtered amplified ^* output of the signal conditioner circuit. The connection for the signal conditioner are generally as indicated in that "SIGNAL" and "SIGRTN" " connect to exciter connections TSI-9 and TSI-10, respectively, "AC-10" and "AC-9" are connec¬ tions to a power line, 110 volts , 60 HZ, "+ 15 v" is a positive voltage output and connects to TSI-3 of ex¬ citer 4, "GROUND 6" is a return for the supply voltages and connects to exciter TSI-4. The "- 15 v" connection 5 is not presently used, TPI is a test point and the jack 44 in the output of the conditioning 6 which con¬ nects to the J→ input of the demodulator circuit (Fig. 6).

Passive Integrated Transponder The PIT, Fig. 4, consists of the inductance wind¬ ing 26, the full-wave rectifier bridge 46, programmable matrix array 4U2 and the control logic 4U1 necessary to provide a frequency shift keyed modulated waveform serially encoded with the data programmed into the matrix 4U2. The circuit is powered by an alternating current excitation signal resulting from the mutual in¬ ductance between the interrogator coil 14 and the PIT winding 26. This is converted to a DC voltage by the full-wave rectifier bridge formed by 4CR., 4CR-,

4CR_ and 4CR. and the ripple filtering capaci¬ tor 4C.,. This filtered DC level provides the power to the control logic circuits. The zener diode 4VR1 protects the circuit from excessive DC voltage. The control logic 4U1 provides the signals to scan the. matrix array 4U2, convert the data to serial format and insert sychronization information, and generate an FSK modulated output. The array 4U2 of Fig. 4 is a fusible link diode matrix model HM-0186 manufactured by Harris Semiconductor., into which the ID data characterizing the particular PIT transponder is programmed prior to incorporation of 4U2 into the circuit. The array is scanned at a rate determined by the AC excitation sig¬ nal which is low pass filtered by 4R and 4C _~ and then injected into the circuit. Within 4U the clock signal is divided in frequency by 100 and then further divided by eight and decoded to provide eight row select outputs to scan the array. A divide by six counter with associated gating multiplexes the five column outputs of the array into a serial format. Synchronization information is inserted during one phase of the divide by six operation. The resulting serial composite waveform controls a variable modulus counter (divide by 4/divide by 5) which is clocked at a rate set by the winding 26 produce an FSK modulated waveform. This waveform is divided by 2 and connected back to the AC excitation input via open drain comple¬ mentary drivers and current limiting resistors"4R. ^* and 4R-. Referring to Fig. 7A, 7B the incoming 400 KHz clock signal is fed through a series of flip flop units, being first divided by two, then by five, again by five, again by two and again by 8 and the output ^* signal of this series of flip flops, then at 500 hz, is used to generate eight row strobes via NAND gates DM

to scan the array 4U2 whose output pins 1 , 14, 8, 13 and 9 are respectively connected to the input pins 13, 14 _/ 15, 16 and 17 of the column select gate array. While these input pins 13, 14/ 15, 16 and 17 are des- cribed as being connected to positive voltage supply by 100 k resistors/ in actual practice the actual devices are FETs/ the net result being the same as if resistors -were used to bias the incoming circuits to the column select gates. Reverting momentarily to the NAND gates DM/ the - outputs of the UK counter are decoded by eight, three input NAND gates to generate the eight row strobes. These row strobes connect to the row inputs of the diode matrix. During the operation the row strobes are sequentially set to a "low" output. With a 400 KHz clock input a row output is low for 250 milliseconds and it takes 2 milliseconds for all the row inputs to sequence through the low state. The process repeats every 2 milliseconds. The column input pins 13 through 17 are sequen¬ tially enabled by the outputs of the LMN counters and five, four-input NAND gates of the column select matrix. A given column input is enabled for the time it takes to strobe all eight row outputs (2 milli- seconds in the present case). Then the next column is enabled and so on. When the LMN counter is in the 0-0-0 state/ no column inputs are enabled and the sync word is inserted.

An array LG of logic gates is used to control the insertion of a sync word in the data stream. This logic also creates a Manchester encoding on the data- stream. The result is a serial composite including sync and date information which is fed to the variable modules counter UMC as a composite stream. The com- posite stream controls the modulus (divide ratio) of a

variable modulus counter. The counter (OPQ) is clocked by the input clock (400 KHZ). The output of this coun¬ ter is either 80 KHZ or 100 KHZ depending on the data value. This counter drives a divide-by-2 (flip-flop R) 5 which results in output frequencies of 40 KHZ or 50 KHZ which vary as a function of the data.

The output drivers of the divide by two counter are open-drain transistors which are connected through resistors to the transponder coil (Pit coil 26). Thus,

10. when a driver is "on" it "sinks" current from the coil. Since the drivers are driven out of phase, and con¬ nected to opposite sides of the coil, they create an alternating current at the coil with a frequency of 40 KHz or 50 KHz. The Manchester encoded signal is illus-

15 trated in Fig. 5. Manchester encoding is well-known.

In this instance, a shift from low to high state, pro- ^~ duced by a shift from 40 KHz to 50 KHz represents a zero and a descending shift from 50 KHz to 40 KHz re¬ presents a one. 0 -A representation of the serial digital data stream which controls the variable modulus counter is shown in figure 5. The data stream consists of a total of 48 bit periods. Data is encoded using a Manchester en¬ coding technique commonly employed in serial data 5 transmissions. In the Manchester technique, data values are represented by transitions from a low to high level or high to low level in the middle of the bit period. In the present representation, a logical zero data is represented by a low to high transition in 0 the middle of the bit period. A logical 1 of the data is represented by a transition from a high to a low in the middle of the bit period. Sync information is con¬ tained in the first 8 bit periods of the data stream. The sync consists of 4 bit periods of preamble informa-

tion followed by a constant low level for one and a half bit periods/ a constant high level for one and a half bit periods and a bit period appearing as a zero data bit. Each preamble bit period also appears as a zero data bit. The eight sync bit periods are followed by 40 bit periods containing the actual ID data. The circuit runs continuously such that an endless stream of sync followed by data followed by sync and a re¬ peating sequence appears.

Demodulation

The input J2 which connects to output 44 of the signal conditioner (Fig. 3) for the demodulation cir¬ cuits/ Fig. 6/ has a low ,pass filter 48 which functions to further reduce the undesired exciter signal frequen- cies/ followed by a tone decoder 6U2 which tracks the excursions of the frequency shift key waveform output from the passive integrated transponder. 6U2 is an FSK demodulator manufactured by EXAR Corporation/ model XR-2211. The low pass filter is a three pole unity gain design formed by 6U..a in combination with 6R_ through 6R. and 6C. through 6C _fi . The output of this low pass filter drives the tone decoder 6U2. The ^• tone decoder itself consists of a voltage controlled oscillator and a phase detector arranged such that the phase detector output provides a control voltage into the voltage controlled oscillator to track the fre¬ quency excursions of the input signal. The free- running frequency of the voltage controlled oscil¬ lator is set by 6C and 6R_ plus 6R_. The phase detector output, at pin 11, provides a control voltage to the oscillator through 6Ro_ so that the oscillator tracks the frequency of the incoming signal and phase-locks to it. The output of the phase detec¬ tor is filtered by 6C..-/ 6R and 6C... and input to a

comparator circuit. The comparator thresholds in the center of the tracking range between the two frequen¬ cies. Therefore, as the frequency shifts between its lower value and its upper value, the data output at pin 7 of 642 alternates between two logic levels. Thus,

6U2 demodulates the FSK waveform at pin 2 into a digi¬ tal waveform at pin 7. This digital waveform may be processed by the microcomputer using the sync and timing information within the waveform to actually de- code the final identification number.

The output connection for demodulation (Fig. 6) are as follows:

"Carrier Detect A is a connection to a computer to indicate that a carrier signal from the transponder 18 is present.

Carrier Detect B is the same as "Carrier Detect A", but with opposite logic sense.

"Demod Data" supplies the demodulated ends data to the computer.