Programmable memory for an encoding system.

0001This invention relates to a system which includes a reader and a transponder displaced from the reader for identifying the transponder to the reader in accordance with a code individual to the transponder and transmitted to the reader at the command of the reader. The system is able to provide such identification without interference from extraneous noise, even at high levels, or small obstacles in the path of data transmission between the transponder and the reader. More particularly, the invention relates to a system for initially transmitting an identifying code from the reader to the transponder and programming this code into the transponder to identify the transponder.

0002As our society becomes increasingly complex, it becomes increasingly important to be able to identify different objects. For example, in an aircraft plant for manufacturing a jet airplane, thousands, and even tens of thousands, of different tools are required to manufacture the different parts incorporated into the airplane. It is accordingly important to be able to identify the individual tools quickly and reliably. One reason is that a fast and reliable identification of each individual tool is cost-efficient because it minimizes the time needed to identify such tool. Another reason is that a fast and reliable identification of each individual tool minimizes the possibility that the wrong tool will be selected and used on a workpiece, thereby causing the workpiece to be ruined or damaged.

0003It has been known for an extended period of time that it would be desirable to provide a system for obtaining a fast and reliable indication of objects such as tools. An extensive effort has accordingly been made by a wide variety of different parties to provide a satisfactory system. Such efforts have not been productive for a number of reasons. As a result, a satisfactory system still does not exist for identifying objects such as tools.

0004The systems now in use are undesirable for a number of reasons. They are not fast. For example, some of the systems use a transponder which stores energy received from a displaced reader and which then generates a code after such storage of energy. The energy is stored by charging a capacitance at the transponder. Other systems sweep a range of frequencies and detect the perturbations produced at individual frequencies in such frequency range. As will be appreciated, both types of systems are relatively slow.

0005The systems now in use have other severe limitations. The systems are not self synchronous. In other words, the systems do not operate on the basis of clock signals internally generated in the system. As a result, the systems sometimes provide the reader with false and inaccurate indications of the code identifying the object at the transponder. This causes an improper object to be identified sometimes at the reader.

0006The systems now in use also have other critical limitations. For example, the systems now in use are sometimes responsive to extraneous signals. Furthermore, in the systems now in use, members in the path between the transponder and the reader sometimes block the reception by the reader of the identifying signals transmitted by the transponder. This blockage has occurred even when the members in the path are relatively small. These problems have been exacerbated by the fact that the systems now in use are not self-synchronous. This has caused the systems now in use to identify objects improperly.

0007The systems now in use are also relatively complicated. This has caused the systems now in use to be excessively large from the standpoint of the space occupied by such systems. It has also prevented the systems now in use from taking advantage of integrated circuit technology. For example, it would be desirable to dispose the transponder on a single integrated circuit chip and to dispose all, or at least substantially all, of the reader components on another integrated circuit chip.

0008Co-pending application Serial No. 840,318 relating to an "Identification System" filed by me on March 14, 1986, and assigned for record to the assignee of record in this application discloses and claims a system which overcomes the above disadvantages. The system is fast, accurate and reliable. It operates on a self-synchronous and passive basis. It is immune to extraneous signals and it is effective even when small members are disposed between the transponder and the reader. It is simple and compact such that the transponder is disposed on a single integrated circuit chip and all, or substantially all, of the reader circuit is disposed on another single integrated circuit chip. It is quite tolerant of variations in the values of components so that it can be produced economically in quantity.

0009In one embodiment of the system disclosed and claimed in co-pending application Serial No. 840,318, a reader (which can also be considered to be an interrogator) identifies information, such as the identity of an object at a transponder, provided in binary form at the transponder. The reader initially generates a pulse which activates the transponder into transmitting a series of signals, such as by magnetic induction, to the reader. Upon each count of a particular number of signals in the reader, the reader generates a new pulse which causes the transponder to produce a new series of signals. The generation of the pulses by the reader may occur through the charge and discharge of energy in a storage member such as a capacitance.

0010The series of signals produced by the transponder in co-pending application Serial No. 840,318 may have either a first frequency or second frequency. The signals may be generated at the first and second frequencies in each sequence in an order dependent upon (a) the binary code provided at the transponder and (b) the polarity of the pulse produced by the reader in such sequence. The signals may be generated at the second frequency by connecting a capacitance across a coupling coil at the transponder. The reader then identifies the information by demodulating the signals received by it at the first and second frequencies.

0011The reader in co-pending application Serial No. 840,318 is able to interrupt at any time the generation of the sequences of signals at the transponder when it does not receive the signals transmitted by the transponder. The reader then operates on a free running basis to generate pulses of opposite polarity at a relatively low frequency. In this way, the reader is constantly prepared to activate the transponder when the transponder becomes subsequently disposed within the effective range of the reader.

0012The memory storing the code in the transponder may be programmable. This invention provides a system operable at the reader for programming a binary code into such memory from the reader to constitute the binary information thereafter identifying the object. The code is transmitted from the reader to the object by sequences of pulses similar to the pulses described above as being transmitted from the reader to the transponder to interrogate the transponder as to the code in the transponder.

0013To program the memory with such a code, the reader in this invention generates, and transmits to the transponder, sequences of pulses, each sequence coding for a programmable item of information (e. g. binary "1", binary "0" and reset). Depending upon the individual programmable item, the coded sequence may have pulses of the same polarity or pulses of opposite polarity. At a time related to each each such sequence, the reader produces a sequence different from the coded sequence and indicating that pulses coding for a programmable item follow.

0014The transponder in this invention demodulates and decodes the transmitted pulses to to recover the identifying code. This code is then recorded in the programmable memory and is used thereafter to identify the transponder when the reader interrogates the transponder as described above.

0015In the drawings: <ul id="ul0001" list-style="none"><li>Figure 1 is a simplified block diagram of a system constituting one embodiment of this invention for generating at a transponder information such as the identification of an object, transmitting this information to a reader and identifying the information at the reader;</li><li>Figure 2 is a circuit diagram, partly in block form, of the reader included in the system shown in Figure 1;</li><li>Figure 3 is a circuit diagram schematically illustrating the construction of additional features in the reader shown in Figure 1;</li><li>Figure 4 is a circuit diagram, partly in block form, of the transponder included in the system shown in Figure 1;</li><li>Figure 5 is a sectional view, in front elevation, illustrating the construction of one of the members, including cores and coils with magnetic properties, which are included in the reader and transponder to provide a magnetic coupling between the reader and the transponder;</li><li>Figure 6 is a view in side elevation of the magnetic member shown in Figure 5;</li><li>Figure 7 is one form of truth table illustrating the operation of a format generator included in the transponder shown in Figure 4;</li><li>Figure 8 illustrates wave forms of signals generated by the reader and the transponder;</li><li>Figure 9 illustrates the characteristics of signals generated in the reader;</li><li>Figure 10 schematically illustrates an integrated circuit chip which incorporates substantially all of the components of the reader; and</li><li>Figure 11 schematically illustrates an integrated circuit chip which incorporates substantially all of the components of the transponder;</li><li>Figure 12 is a circuit diagram, partially in block form, of one embodiment of a system at the reader for transmitting pulses to the transponder to program the programmable memory in the transponder;</li><li>Figure 13 illustrates sequences of signals for programming individual items (e. g. binary "1", binary "0" and reset) in the programmable memory in the transponder);</li><li>Figure 14 illustrates the voltages produced at strategic terminals in the system of Figure 12 when the system is operating to program a particular sequence of programmable items into the memory at the transponder;</li><li>Figure 15 is a schematic circuit diagram illustrating how an identifying code for a transponder is produced at the reader;</li><li>Figure 16 is a circuit diagram, partially in block form, schematically illustrating a system at the transponder for demodulating and then decoding the programmable pulses received at the transponder and for recording the decoded information in the memory in the transponder; and</li><li>Figure 17 is a table illustrating the operation of the transponder of Figure 16 in responding to the programmable pulses to record the decoded information in the memory in the transponder.</li></ul>

0016Figure 1 shows a simplified diagram of one embodiment of a system constituting this invention. The embodiment shown in Figure 1 includes a pulse generator 10 connected to a coil 12 at a reader generally indicated at 14. A frequency detector and demodulator 16 is coupled to the coil 12 and output indications from the frequency detector and demodulator are introduced to a line 18. A transponder generally indicated at 20 includes a coil 22 magnetically coupled to the coil 12. A capacitance 24 exists across the coil 22. A switch 26 and a capacitance 28 are also connected in series across the coil 22. The system shown in Figure 1 and further shown in Figures 2-6 is fully disclosed and claimed in co-pending application Serial No. 840,318.

0017The coils 12 and 22 are constructed so that they are magnetically coupled to each other through a finite distance. This distance may be in the order of a few milliinches to a few feet. The coils 12 and 22 are further constructed so that they will not be responsive to magnetic signals extraneous to those generated by the coils 12 and 22.

0018To initiate the operation of the system shown in Figure 1, the pulse generator produces a pulse indicated at 30 in Figure 8. This pulse is coupled as by magnetic induction through the coil 12 to the coil 22 which produces a plurality of signals 32. These signals are limited in amplitude to produce signals 38 having rectangular characteristics. When the switch 26 is open, the coil 22 and the capacitance 24 form a resonant circuit which causes the signals 34 to have a first frequency such as three (3) megahertz. However, when the switch 26 becomes closed, the capacitance 28 becomes connected in parallel with each of the coil 22 and the capacitance 24. As a result, the signals generated by the transponder 20 have a second frequency such as two (2) megahertz.

0019The information, such as the identification of the object, is transmitted in the form of a binary code constituting a plurality of bits each represented by a binary "1" or a binary "0". For each binary bit, a sequence of signals at both the first and second frequencies is generated at the transponder 20. The order of generating the signals at the first and second frequencies in each sequence relative to the pulses such as the pulse 30 is dependent, at least in part, on the value of the binary bit being identified in that sequence.

0020The signals, such as the signals 32, generated in each plurality are magnetically coupled by the coil 22 to the coil 12 as by magnetic induction. The reader 14 then counts these signals. When the count reaches a particular value such as ten (10), the pulse generator 10 in Figure 1 generates a new pulse such as that indicated at 34 in Figure 8. This pulse has a polarity opposite to that of the pulse 30. This causes a plurality of signals, such as those indicated at 36 in Figure 8 to be produced. The signal 36 correspond to the signals 32 except that they have a frequency different from the frequency of the signals 32. For example, the signals 36 have the second frequency if the signals 32 have the first frequency. Similarly, the signals 36 have the first frequency if the signals 32 have the second frequency.

0021The signals 36 are then transmitted to the reader 14 and are counted at the reader. When the count reaches the particular value such as ten (10), the pulse generator 10 generates a pulse 40 (Figure 8) in the coil 12. This pulse has the same polarity as the pulse 30. The generation of the pulse 40 causes the transponder 20 to generate a plurality of signals at one of the first and second frequencies. In this way, the reader 14 and the transponder 20 interact to provide for the generation of pulses, such as the pulses 30, 34 and 40, at the reader 14 and the generation of a plurality of signals at the transponder 20 in response to each of these pulses.

0022As will be appreciated, each sequence of signals is formed from a particular number (such as ten (10)) of signals at the first frequency and the particular number of signals at the second frequency. This means that the time required to produce each of the successive sequences is constant. In each sequence, the particular order of the signals at the first frequency and the signals at the second frequency controls the value of the binary bit represented by the sequence. This order is determined by the frequency detector 16 which demodulates the signals produced in the coil 12 at the first and second frequencies. The demodulated signal is indicated at 42 in Figure 8. As will be seen, the demodulated signal in each sequence has two time portions of unequal duration. The duration of the time portion corresponding to the signals at the first frequency (e. g. 3 megahertz) is shorter than the duration of the time portion corresponding to the signals at the second frequency (e. g. 2 megahertz).

0023Figure 2 indicates additional details of the reader 14 shown in Figure 1. The reader 14 shown in Figure 3 includes a power source 50, such as a battery, constructed to provide a direct voltage. One terminal of the power source 50 may be connected to a reference potential such as ground. The stationary contacts of a switch 52 are connected to the opposite terminals of the power source 50. A connection is made from the movable arm of the switch 52 through a resistance 53 to one terminal of a capacitance 54. Although the switch 52 is shown as being mechanical, it will be appreciated that the switch 52 may be formed from electronic components such as semi-conductors, as will be seen in Figure 3.

0024The coil 12 is connected in Figure 2 between the second terminal of the capacitance 54 and the grounded terminal of the power source 50. The coil 12 and the resistance 53 may be constructed to damp any pulses, following the pulses, such as the pulses 30, 34 and 40, produced in the coil 12. The coil 12 is also constructed to direct to the coil 22 magnetic flux produced in the coil 12 with a minimal leakage of flux in any other direction than in the direction toward the coil 22. By limiting the leakage of flux from the coil 12 to occur substantially only in a direction toward the coil 22, the coil 12 is substantially immune to stray magnetic fields. The coil 12 is also "immune" to interaction with magnetic or electrically conductive material which is not disposed in the path of the flux produced by the coil.

0025The two terminals of the coil 12 are connected to input terminals of a limiting amplifier 56. The output signals from the amplifier 56 are introduced to one input terminal of an "exclusive or" network 57, another input terminal of which receives signals from an output terminal of an astable multivibrator generally indicated at 60. The output signals from the "exclusive or" network 57 pass to the input terminal of a counter 58, the output from which passes to the input terminals of the clocked astable multivibrator 60. The multivibrator 60 has two (2) substantially identical inputs and a clock input, one of the identical inputs may be designated as a "set" input ("S") and the other of such identical inputs may be designated as a "reset" input ("R"). The signals introduced to each input in the multivibrator 60 control the operation of an associated stage in the multivibrator.

0026First terminals of resistances 62 and 64 are respectively connected from the output terminal of each stage in the multivibrator 60 to the input terminal of the other stage in the multivibrator. Connections are respectively made from the second terminals of the resistances 62 and 64 to first terminals of capacitances 66 and 68, second terminals of which receive the reference potential such as ground. The signals on the output terminals of the two stages in the multivibrator control the position of the movable arm of the switch 52. The movable arm of the switch 52 is moved alternately upwardly and downwardly in accordance with the signals produced on the output terminals of the two stages in the multivibrator 60.

0027The transponder 20 is shown in additional detail in Figure 4. It includes the coil 22 which is also shown in Figure 1. The capacitance 24 (also shown in Figure 1) is shown in broken lines as being connected across the coil 22. The capacitance is shown in broken lines because it may be considered to be formed from distributed capacitances in the coil 22 and in other elements in the circuitry shown in Figure 4. If necessary, a discrete capacitance can be connected across the coil 22 and can be considered to be included in the distributed capacitance 24. The coil 22 and the capacitance 24 form a circuit which is resonant at the first frequency such as three (3) megahertz. This resonant circuit generates signals on a ringing basis in response to each pulse from the coil 12.

0028The drain of a transistor 72 is connected to a first terminal of the coil 22 and the source of the transistor 72 is connected to one terminal of a capacitance 74, the other terminal of which is common to the second terminal of the coil 22. The first terminal of the coil 22 is also common with the gate of a transistor 76 and the drain of a transistor 78. Connections are made from the second terminal of the coil 22 to the drain of the transistor 76 and the gate of the transistor 78. The sources of the transistors 74 and 76 are common with the reference potential such as ground. The transistors 74 and 76 may be field effect transistors.

0029A voltage limiter 80 is connected across the coil 22. The signals from the voltage limiter 80 are respectively introduced through lines 81 and 83 to the two (2) input terminals of a clock separator 82. The clock separator 82 has a first output alternately providing first clock signals representing a positive polarity in the excitation pulses such as the pulses 30, 34 and 40 and has a second output alternately producing second signals representing a negative polarity in such excitation pulses. The signals from the clock separator 82 are introduced to input terminals of a format generator 84 and a multiplexer 86. The output from the format generator 84 is introduced to the gate of the transistor 72. The format generator 84 also receives input signals from the multiplexer 86. Binary input information identifying the object to be identified may be introduced to input terminals of the multiplexer 86 and may be stored in the multiplexer.

0030When the movable arm of the switch 52 in Figure 2 engages the upper stationary contact of the switch as shown in Figure 2, a circuit is established which includes the power source 50, the switch 52, the resistance 53, the capacitance 54 and the coil 12. This causes a surge of current to flow through the coil 12 to produce the pulse 30. The pulse is considerably damped, as indicated at 90 in Figure 8, because of the construction of the coil 12 and the inclusion of the resistance 53.

0031The generation of the pulse 30 in the coil 12 causes the signals 32 to be produced in the transponder 20. These signals, in turn, cause signals to be coupled magnetically back into the coil 12. These signals are limited in amplitude by the amplifier 56 and are then introduced through the "exclusive or" network 57 to the counter 58. When the count in the counter 58 reaches a particular value such as ten (10), the counter produces a signal to trigger the multivibrator 60 from one state of operation to the other. This causes a signal to be introduced to the switch 52 to actuate the movable arm of the switch from engagement with the upper stationary contact of the switch to engagement with the lower stationary contact of the switch.

0032When the movable arm of the switch 52 engages the lower stationary contact of the switch, the capacitance 54 becomes discharged through a circuit including the capacitance, the coil 12, the switch 52 and the resistance 53. As will be seen, the current through the coil 12, as a result of the discharge of the capacitance 54, is in an opposite direction from the current flowing through the coil 12 as a result of a charging of the capacitance. The pulse 34 generated in the coil 12 as a result of the discharge of the capacitance 54 accordingly has a polarity opposite to the polarity of the pulse 30. In this way, the pulses generated by the coil 12 alternately have one polarity and then the opposite polarity. This is indicated in Figure 8 by a positive polarity for the pulses 30 and 40 and a negative polarity for the pulse 34.

0033The transponder 20 produces a pulse, as by magnetic induction, corresponding to each of the pulses, such as the pulses 30, 34 and 40, produced in the reader 14. As previously discussed, the transponder 20 also generates a plurality of signals every time that the reader 14 generates a pulse such as the pulse 30 or the pulse 34. Since the successive pulses such as the pulses 30 and 34 have opposite polarities, the pluralities of signals, such as the signals 32 and the signals 36, generated by the transponder 20 also have opposite polarities.

0034The transistor 78 in Figure 4 operates to pass to ground the negative swings of the signals produced on the upper terminal of the coil 22 in Figure 4 so that only the positive swings of these signals pass to the voltage limiter 80 through the line 81. In like manner, the transistor 76 operates to ground the negative portions of the signals produced on the lower terminal of the coil 22 in Figure 4 so that only the positive swings of such signals pass to the voltage limiter 80 through the line 83.

0035The amplitudes of the signals introduced to the voltage limiter 80 are limited to produce signals such as the signals 38 in Figure 8 and are then introduced to the clock separator 82. The clock separator 82 determines the polarity of the reader pulse associated with each plurality of the signals produced in the coil 22, such as the signals 32 or the signals 36, and generates a clock signal on a particular one of its outputs in synchronism with the occurrence of such pulse. As will be seen, each successive clock signal coincides in time with the pulse from the coil 22 and the polarity of this pulse is opposite to the polarity of the previous pulse since the pulses 30, 34 and 40 have alternate polarities. Clock signals, such as a clock signal 96 in Figure 8, coincident in time with a positive polarity in the pulse from the coil 22 are introduced from one output line of the clock separator 82 to the format generator 84. Clock signals, such as a clock signal 98 in Figure 8, coincident in time with a negative polarity in the pulse fronl the coil 22 are introduced from the other output line of the clock generator 82 to the format generator 84.

0036In addition to receiving the clock signals from the clock separator 82, the format generator 84 also receives signals from the multiplexer 86. The multiplexer 86 stores a plurality of binary signals each having first and second logic levels respectively coding for a binary "1" and a binary "0". The binary signals in the plurality have a unique code to identify each individual object. For example, the code may have a pattern such as 011010110101 to identify an individual tool from thousands of other tools, the least significant bit in the plurality being at the right.

0037The successive bits of information stored in the multiplexer 86 are introduced by the multiplexer to the format generator 84 in synchronism with the clock signals of a particular polarity from the clock separator 82. For example, when the first pulse in each sequence, such as the pulse 30 or the pulse 40, has a positive polarity, the next bit in the code from the multiplexer 86 is introduced to the format generator 84 upon the generation of a pulse of positive polarity in the coil 12. Since the multiplexer 86 operates at the beginning of each sequence to shift into the format generator 84 the next bit of the code identifying the object, the multiplexer 86 operates, in effect, as a shift register.

0038The format generator 84 produces signals in accordance with the truth table illustrated in Figure 7. Under certain sets of conditions as specified in the truth table, the format generator 84 generates a signal which causes the transistor switch 72 to become opened (or non-conductive). This will cause the coil 22 to generate signals at the first frequency such as three (3) megahertz. Under other sets of conditions as specified in the truth table, the format generator 84 will generate a signal which will cause the transistor switch 72 to become closed (or conductive). This will connect the capacitance 74 across the coil 22. As a result, the coil 22 will generate signals at the second frequency such as two (2) megahertz.

0039Figure 7 illustrates one form of a truth table to show how the format generator 84 responds to the polarity of the clock signals from the clock generator 82 and the binary bits of information from the multiplexer 86 to determine the order in which the signals are generated at the first and second frequencies in each sequence. For example, as indicated in Figure 7, when a binary "1" is provided by the multiplexer 86 and the polarity of the first clock signal in each sequence is positive, the format generator 84 initially opens the switch 72 in the sequence for times following a positive clock signal. This is indicated by the letter "O" in Figure 7 to show that the switch 72 is initially opened in the sequence. This causes the signals at the first frequency to be generated in the sequence before the signals at the second frequency are generated in the sequence. Similarly, if a binary "0" is to be generated in a sequence and the polarity of the first clock signal in the sequence is negative, the switch 72 is initially opened in the sequence and is subsequently closed in the sequence. This is indicated by the letter "O" in Figure 7 for this set of conditions. In Figure 7, the letter "C" for a set of conditions indicates that the switch 72 is initially closed in a sequence and is then opened in the sequence.

0040As previously described, the successive pluralities of signals generated by the transponder 20 are received by the reader 14. These signals are demodulated by the frequency detector and demodulator 16 and the demodulated signals are introduced to the line 18. The pattern of the binary 1's and binary O's in the multiplexer 86 can accordingly be detected by determining the relative time duration of the positive and negative portions of the demodulated signals in each sequence and the polarity of the pulses such as the pulses 30 and 40 at the beginning of each sequence. In effect, the truth table shown in Figure 7 is reconstructed.

0041The demodulated signals (also shown at 42 in Figure 8 for one sequence) are illustrated at 97 in Figure 9 in relation to the excitation pulses such as the pulses 30, 34 and 40. The detection by the frequency detector and demodulator 16 of the pattern of the binary 1's and binary O's in the multiplexer 86 is facilitated by the fact that the duration of time between successive pulses of the same polarity, such as the pulses 30 and 40, is substantially constant regardless of the order in which the signals at the first and second frequencies is generated. For example, the sum of the duration of time between the pulses 30 and 34 and between the pulse 34 and the successive pulse 40 (all constituting one sequence) is equal to the sums of the duration of time between the initial pulses in successive sequences.

0042It may sometimes happen that the magnetic coupling between the coil 12 in the reader 14 and the coil 22 in the transponder 20 may be interrupted in the middle of the generation of the sequences of signals to identify the object associated with the transponder. This may occur for several reasons. For example, the transponder 20 may be moved out of the effective range of the reader 14 or a member of relatively large size may be disposed between the reader and the transponder to block any magnetic induction between the reader and the transponder. The circuitry shown in Figure 3 is included in the reader 14 to operate under such circumstances. The circuitry shown in Figure 3 includes a resistance 106, the resistance 53, the capacitance 54 and the coil 12 shown in Figure 2.

0043The system shown in Figure 3 also includes a pair of transistors 100 and 102 which may collectively comprise the switch 52. The transistor 100 may comprise a p-channel field effect transistor and the transistor 102 may comprise an n-channel field effect transistor. The source of the p-channel transistor 100 is connected to the power source 50. The drain of the transistor 100 and the drain of the transistor 102 have common connections with the resistance 53 and with one terminal of the resistance 106, the other terminal of which receives the reference potential such as ground. The source of the transistor 102 also receives the reference potential such as ground.

0044A connection is made from the gate of the transistor 100 to the output terminal of one stage in the astable multivibrator 60. The gate of the transistor 102 receives the output signals from an "and" gate 108. One input terminal of the "and" gate 108 receives the voltage on the same output terminal of the multivibrator 60 as introduces signals to the gate of the transister 100. A second input terminal of the "and" gate 108 receives signals produced on a line 110.

0045When a signal having a logic level representing a binary "1" is produced on the line 110, the system described above operates to detect at the reader 14 the binary code provided in the multiplexer 86 at the transponder 20. However, when the generation of the sequences of signals from the transponder 20 to the reader 14 is interrupted as by an interruption in the magnetic coupling between the coils 12 and 22, the multivibrator 60 starts to operate on a free running basis at a relatively low frequency. For example, when the signal on the output line from the multivibrator 60 is low, the transistor 100 becomes conductive. This causes a current to flow through a circuit including the voltage source 50, the transistor 100, the resistance 53, the capacitance 54 and the coil 12. This current charges the capacitance 53.

0046After the capacitance 54 has become charged, it discharges slowly through a circuit including the capacitance, the resistance 53, the resistance 106 and the coil 12. When the signal on the output line from the multivibrator 60 becomes high, this signal passes through the "and" gate 108 and causes the transistor 102 to become conductive. The remaining charge in the capacitance 54 is then discharged through a circuit including the capacitor, the resistance 53, the transistor 102 and the coil 12. In this way, the multivibrator 60 operates on a free running basis at a relatively low frequency. This causes the coil 12 to generate pulses at the relatively low frequency to activate the transponder 20 when the transponder is moved relative to the reader within magnetically inductive range relative to the reader 14.

0047It may sometimes be desired to interrupt the dialog between the reader 14 and the transponder 20 while the reader and the transponder are in the middle of this dialog. To provide such an interruption, a signal having a logic level of "0" is produced on the line 110. This inactivates the "and" gate 108. This causes the charge produced in the capacitance 54 to discharge slowly through the circuit including the coil 54, the resistances 53 and 106 and the coil 12. Because of this slow discharge, negative pulses corresponding to the pulse 34 in Figure 8 are not produced in the coils 12 and 22.

0048A reset generator 99 is connected between the clock separator 82 and the multiplexer 86 in Figure 4. The reset generator 99 is responsive to the production of clock signals of alternate polarity by the clock separator 82. Thus, when a negative pulse such as the pulse 34 is not generated by the coils 12 and 22 for a particular period of time such as a period greater than the period between the pulses 30 and 40 (but less than twice this period), the reset generation 99 operates to reset the multiplexer 86. In this way, a new operation in identifying the object individual to the code in the multiplexer 86 can be initiated.

0049The coil 12 produces a pulse every time that the capacitance 54 charges or discharges through the coil as discussed in the previous paragraph. These pulses interrogate the area within the effective range of the coil 12. If there is any transponder within this area and the coil 12 in the reader 14 points toward this transponder, an electronic dialog is instituted between the reader and such transponder, as discussed in detail above, to determine the identity of the object at such transponder. In this way, by producing pulses at a relatively low frequency as discussed above, the circuitry shown in Figure 4 is ready at any instant to initiate an identification of the object at the transponder 14 in accordance with the unique code provided in the multiplexer 86. This identification is initiated by providing on the line 110 a signal having a logic level coding for a binary "1".

0050Figures 5 and 6 illustrate the construction of the magnetic members, including the coil 12, at the reader 14. A similar construction may be provided for the magnetic members, including the coil 22, at the transponder 20. At the reader 14, the coil 12 is wound on a core 130 having an E-shape in section. The coil 12 is disposed on the middle leg of the core 130 and is shielded within the end legs. In this way, when the coil 12 is energized, it produces leakage flux indicated at 132 in Figure 5. This leakage flux extends from the core 130 in a controlled direction. This leakage flux is magnetically coupled to the coil 22 at the transponder 20 to induce signals in the coil 22 when the coil 22 at the transponder is within the effective range of the coil 12 at the reader 14.

0051The reader coil 12 is included in a circuit which includes the resistance 53. This causes the pulses, such as the pulses 32 and 36, produced in the coil 22 to be damped. On the other hand, the coil 22 is connected in a resonant circuit which includes the capacitance 24 (and an additional capacitance if necessary) to generate the signals at the first frequency and which includes the capacitances 24 and 74 to generate the signals at the second frequency. Furthermore, the signals produced by the coil 22 are not damped by any added resistance. The coil 22 is also loosely coupled to the coil 12. For these reasons, the coil 22 is able to generate a plurality of signals every time that the coil 12 generates a pulse.

0052The system described above is self synchronous. This results from the fact that the reader 14 produces clock signals, such as the clock signals 96 and 98 in Figure 8, at a particular time in each of the pluralities of signals generated by the coil 22. It also results from the fact that each sequence of signals generated at the first and second frequencies has the same time duration. It also results from the fact that the coil 12 responds to the signals produced in the coil 22 to produce a new pulse after each particular count of such signals and that the coil 22 responds to each pulse generated by the coil 12 to generate the plurality of signals. The system is accordingly self synchronous even though no clock signals are externally generated.

0053The system shown in the drawings and described above also has other important advantages. For example, the transponder 20 does not require an external source of energy since it receives its energy from the pulses generated by the coil 12. Furthermore, the reader 14 receives a minimal amount of energy since the pulses such as the pulses 32, 36 and 40 have a relatively short duration compared to the relatively long interval between successive pairs of pulses.

0054The system is also advantageous because it is relatively immune to extraneous noises and to small obstacles in the transmission path. This results from several factors. For example, the coils 12 and 22 are responsive only to magnetic signals emanating directly toward the openings in the cores upon which they are wound. Furthermore, the information is generated in the form of frequency modulated codes at specific frequencies such as the first and second frequencies. Another factor is that the reader 14 generates each pulse only after it has counted a particular number of signals generated at each of the first and second frequencies by the coil 22.

0055The system shown in the drawings and described above is also relatively fast. This results partly from the fact that the transponder 20 responds instantaneously to the pulses generated in the reader 14. It also results from the fact that the reader 14 responds instantaneously to the signals generated by the transponder 20. It further results from the fact that substantially all of the components in the reader 14 can be disposed on a first integrated circuit chip 100 (Figure 10) and that this chip is of relatively small size. Another contributing factor is that substantially all of the components in the reader 20 can be disposed on an integrated circuit chip 102 (Figure 11) and that this chip is of relatively small size.

0056The system described above is also quite tolerant of variations in component values. This facilitates the relative ease with which the reader 12 and the transponder 22 can be manufactured in quantity. The relative ease of manufacture is enhanced by the manufacture of the reader 14 on the integrated circuit chip 100 (Figure 10) and the manufacture of the transponder 22 on the integrated circuit chip 102 (Figure 11).

0057Although the system has been described above with reference to identifying an object, the system can be used to generate any type of information. This can be accomplished by eliminating the multiplexer 86 and introducing directly to the format generator 84 signals generated externally to the transponder in binary coded form to represent the information to be identified. Alternatively, the externally generated information can be introduced to the multiplexer 86, which stores such information and then introduces such information to the format generator 84 by operating as a shift register.

0058The system shown in the drawings and described above is also advantageous because virtually all of the components in the reader can be disposed on the integrated circuit chip 100 in Figure 10. The integrated circuit chip 100 in Figure 10 is illustrated only schematically and can be considered to include all of the components in Figures 2 and 3 except for the coil 12 and, in some cases, the capacitance 54. The capacitance 54 may not be considered to be included in the integrated circuit chip 100 because it is a charging capacitor and accordingly has a relatively high value.

0059Similarly, virtually all of the components in the transponder 20 can be disposed on the integrated chip 102 in Figure 11. The integrated circuit chip 102 in Figure 11 is also illustrated schematically. All of the components shown in Figure 4 (except for the coil 22) are included in the integrated circuit chip 102.

0060By disposing virtually all of the components in the reader 14 on the integrated circuit chip 100 and all of the components in the transponder 20 on the integrated circuit chip 102, the reader and the transponder can occupy minimal spaces. This allows the transponder 20 to be disposed inconspicuously on an object to be identified. It also allows the reader 14 to be carried conveniently in a pocket until it is desired to be used. The disposition of the reader 14 and the transponder 20 on integrated circuit chips also allows the reader and the transponder to be duplicated with substantially identical characteristics and to operate at relatively high frequencies.

0061The system described above is disclosed and claimed in application Serial No. 840,318 assigned of record to the assignee of record in the application. This system may include a read-only memory in which signals pre-programmed into the memory cannot be changed. The system may be also used with a programmable memory 102 in the chip 102 in Figure 11. Under such circumstances, the memory 14 in the transponder may be preprogrammed by pulses generated in the reader and transmitted by the reader to the transponder for demodulation and decoding by the transponder and for recording by the transponder of the decoded information in the programmable memory. The programmable memory 104 may be of different types. For example, it may be an electrically programmable read-only memory, an electrically erasable programmable read-only memory or a write once-read many programmable memory. All of these are well known in the art.

0062A system at the reader for programming the programmable information in the transponder memory 104 is shown in Figure 12. The system shown in Figure 12 may include a pair of transistors 200 and 202. The transistor 200 may be a pnp transistor and the transistor 202 may be an npn transistor. The emitter of the transistor 200 may receive a positive voltage from a power supply 204 and the emitter of the transistor 202 may receive a reference voltage such as a ground 206.

0063The collectors of the transistors 200 and 202 may be connected to a resistor 208 which is in series with a capacitance 210 (which may be the capacitance 54 in Figure 1). A coil 212 (which may be the coil 12 in Figure 1) is connected between the capacitance 210 and the reference potential such as ground. A connection is made from the ungrounded terminal of the coil 212 to one terminal of a resistance 216. The other terminal of the resistence 216 is common with the anode of a diode 218 and the cathode of a diode 220. The cathode of the diode 218 and the anode of the diode 220 are common with the reference potential such as the ground 206.

0064The voltage on the anode of the diode 218 and the cathode of the diode 220 is introduced to one input terminal of a comparator 222. A second input terminal of the comparator 222 receives the reference potential such as the ground 206. The output from the comparator 222 is introduced to one input terminal of an exclusive "or" network 224. A second input terminal of the exclusive "or" network 224 receives the voltage on the output terminal of one stage (designated as the "false" stage) in a bistable member such as a flip-flop generally indicated at 226.

0065The signals from the exclusive "or" network 224 are introduced to a counter 228. The counter 228 may be programmed at each instant to count to a particular value dependent upon the programmable item to be inserted into the programmable memory in the transponder. Upon each count of the particular count in the counter 228, a signal is introduced to the input terminals in the flip-flop 226 to trigger the flip-flop from one state of operation to the other. The output terminals of the true and false stages in the flip-flop 226 are respectively connected to the bases of the transistors 220 and 202.

0066Figure 13 illustrates the sequence (or pattern) of signals produced in the reader for each different type of programmable information. In Figure 13, the pulses move from right to left at progressive instants of time so that the most recent pulse in a sequence is at the right. For example, to program a binary "0" in the programmable memory in the transponder, a sequence of signals generally indicated at 230 is produced. This sequence includes a first pair of pulses 230a and 230b alternately with positive and negative polarities. The sequence also includes a second pair of pulses 231a and 231b of positive and negative polarities. The second pair of pulses 231a and 231b indicates that programmable information is contained in the preceeding sequence. The preceeding pair of pulses 231a and 231b indicates a binary "0".

0067In like manner, a binary "1" is indicated in Figure 13 by a second pair of pulses 233a and 233b alternately of positive and negative polarities. This indicates that signals representing a programmable item is contained in the preceeding sequence. The programmable item constituting a binary "1" is indicated by a pair of pulses 234a and 234b, both of negative polarity. The pulses of positive and negative polarity preceeded by two pulses of negative polarity are generally indicated at 235 in Figure 13.

0068A sequence of pulses to initialize a code sequence identified as "Reset" is generally indicated at 236 in Figure 13. This sequence includes a pair of pulses 237a and 237b, first of positive polarity and then of negative polarity, to indicate that a programmable item is contained in the preceeding sequence. This pair of pulses follows a single pulse 238a of positive polarity. When a programmable item constituting a reset is produced, it may indicate that the following sequences individually represent binary "1's" and binary "0's" to be programmed into the memory 104 (Figure 11).

0069The system shown in Figure 12 operates to produce the sequences of pulses indicated at 230, 235 and 236 in Figure 13. When the flip-flop 226 is in the false state of operation, a voltage of relatively low polarity is introduced to the gate of the transistor 200 to make the transistor conductive. A pulse of current accordingly flows through a circuit including the power supply 204, the transistor 200, the resistance 208, the capacitance 210 and the coil 212 to charge the capacitance. This current produces a voltage pulse, such as a pulse 240 in Figure 14, in the coil 212. The coil 212 is coupled to the transponder which incorporates a tuned circuit so as to produce ringing signals as indicated at 244 in Figure 14.

0070When the true state of the flip-flop 226 becomes operative, voltage of a relatively high polarity is produced on the output terminal of the left stage in the flip-flop. This causes the transistor 202 to become conductive. The capacitance 210 accordingly discharges through a circuit including the capacitance, the resistance 208, the transistor 202 and the coil 212. This flow of current produces a pulse of a negative polarity in the coil 212, as indicated at 242 in Figure 14. This pulse is followed by ringing signals as indicated at 246 in Figure 14.

0071The diode 218 operates to limit the amplitude of the positive pulses, such as the pulse 240, produced by the coil 212 and the diode 220 operates to limit the amplitude of the pulses of negative polarity, such as the pulse 242, produced by the coil. The pulses of limited amplitude are indicated at 247 in Figure 14. Because of this limitation in the amplitude of the pulses such as the pulses 240 and 242, the amplitudes of the ringing signals 244 and 246 more nearly approach those of the pulses 240 and 242.

0072The pulses, such as the pulses 247, of limited amplitude are introduced to the comparator 222 which operates to saturate the pulses such as the pulses 240 and 242 and the ringing signals such as the ringing signals 244 and 246. The resultant pulses from the comparator 222 are as indicated at 248 in Figure 14. As will be appreciated, all of the pulses now have substantially the same amplitude.

0073The saturated pulses from the comparator 222 and the voltage on the output terminal of the false stage in the flip-­flop 226 are introduced to the exclusive "or" network 224. The network 224 is constructed in a conventional manner to pass a pulse only when one of the input voltages introduced to the network is low and the other input voltage introduced to the network is high. The pulses passing through the exclusive "or" network 224 are indicated at 250 in Figure 14.

0074The pulses passing through the network 224 are introduced to the counter 228. As will be seen from the subsequent discussion, the counter 228 is set at each instant to count to a value dependent upon the programming operation at that instant. When the particular count is reached in the counter 228, the counter becomes reset to start a new count. This causes a triggering signal to be introduced to the flip-flop 226 to set the flip-flop from its previous state of operation to the other state of operation. The triggering signals introduced to the flip-flop 226 are indicated at 252 in Figure 14.

0075In the representations shown in Figure 14, the first pulse in a sequence appears at the left and successive pulses appear progressively toward the right. In Figure 14, the pulses 240 and 242 constitute a pair for synchronizing the operation of the system shown in Figure 12. These pulses are separated by a particular number such as ten (10) ringing cycles. A reset is then programmed by the production of pulses 260, 262, 264 and 266. The pulses 264 and 266 indicate that a programming item is contained in the preceeding pulses in time and the pulse 260 indicates that the programming item constitutes a reset. The pulses 260 and 262 provide such an indication since there is the particular separation of one (1) ringing cycles between these two (2) pulses. In this way, only the pulse 260 is considered at the transponder in providing the initialization reset and the pulse 262 is disregarded at the transponder.

0076In like manner, pulses such as the pulses 282 and 284 separated by the particular number such as ten (10) ringing cycles and having opposite polarities indicate that a programmable item is contained in the preceeding pulses. This programmable item is indicated by pulses 276, 278 and 280. The pulses 276 and 280 are separated by the particular number such as ten (10) clock signals to indicate that the programmable item is a binary "1". The pulse 278 is accordingly disregarded at the transponder in a manner similar to the way that the transponder disregards the pulse 262 in the previous paragraph.

0077In Figure 14, the pulses 264 and 266 also represent a binary "0". The reason is that the pulses 264 and 266 are followed by the pulses 274 and 276 respectively having a positive and negative polarity. Thus, as will be seen it is not necessary to send a separate pair of pulses for each programmable item, such as the pulses 264 and 266, respectively having positive and negative polarities. Specifically, the pulses 264 and 266 indicate that a reset is represented by the pulses 260. The pulses 264 and 266 also represent a binary "0" since they are followed by the pulses 274 and 276.

0078In considering Figure 14 in relation to Figure 16, it will be seen that the letter "A" through "F" are shown at strategic terminals in Figure 16. The voltages or signals produced at these terminals are shown in the rows "A" through "F" in Figure 17. Figure 14 also indicate the value for the letter "N" indicated in Figure 12. This indicates a preselected number of ringing cycles to be produced at each instant.

0079Figure 15 is a schematic diagram of how the system shown in Figure 14 operates at the reader to obtain the generation by the circuitry shown in Figure 12 of the patterns of signals for programming the programmable memory 104 at the transponder. The system shown in Figure 15 includes a microcomputer 300 which generates an individual code to be recorded in the memory 104 at the transponder. This code controls at each instant the count to be provided in the counter 228 (also shown in Figure 12). As will be appreciated, every time that a count has been completed, a signal is introduced from the counter to the flip-flop 226 in Figure 12 to obtain the generation of a pulse which is transmitted by the coil 212 to the transponder 20.

0080Figure 16 schematically illustrates a system at the transponder 20 for demodulating and detecting the programming pulses from the reader 12. The programming pulses from the reader 12 are received by a coil 302 at the transponder 20. The coil 302 may be the same as the coil 22 in Figure 1. The pulses in the coil 302 are introduced to a clock separator 304 which determines whether a pulse is derived from a positive or negative signal in the coil 302. The positive pulses from the clock separator 304 are introduced on one line to a shift register 306 and the negative pulses are introduced on another line to the shift register. The pulses representing each programmable item are then shifted through the shift register 306 to obtain an identification of the programmable item (e. g. binary "1", binary "0" and reset) in accordance with the relative polarities of the pulses in the shift register 306. This identification is provided by a decoder 308 in accordance with a truth table in Figure 17. The programmable items (e.g. binary "1" or binary "0") may then be recorded in the appropriate positions in the programmable memory 104. It will be appreciated that the clock separator 304, the shift register 306 and the decoder 308 may be included in a microprocessing unit at the transponder 20.

0081Figure 17 constitutes a table illustrating how signals are produced in the shift register 306 for the different programmable items constituting a binary "1", a binary "0" and a reset. In Figure 17, the successive stages in the shift register 306 are respectively illustrated at A, B, C and D to correspond to the designations for the shift registers in Figure 16. As will be seen, the signals are shifted progressively from the stage A to the stage B, then to the stage C and finally to the stage D. The decoder 308 examines the four (4) signals in parallel in the stages A, B, C and D in the shift register 306. A positive signal in the stage A and a negative signal in the stage B indicate that a programmable item is represented by the signals in the stages C and D. A positive signal in the stage C indicates a reset. When a reset is produced, this indicates that the following individual sequences represent binary "1's" or binary "0's" which may be recorded in the programmable memory 104 (Figure 11) in a pattern represented by such signals. Two negative signals in the stages C and D represent a binary "1". A positive signal in the stage C and a negative signal in the stage D represent a binary "0".

0082The apparatus disclosed above and shown in Figures 12-16 has certain important advantages. One advantage is that it is able to program the memory 104 in the transponder 20 by using the same types of pulse transmission as are used subsequently in identifying the transponder in accordance with the operation of the circuitry and apparatus shown in Figures 1-6.

0083Another advantage to the programming system and method of this invention is that the communication between the reader and the transponder is substantially foolproof during the programming of the transponder. This results in part from the characteristics of the coils 12 and 22 as shown in Figures 5 and 6. It also results in part from the inclusion of the pair of pulses of opposite polarity following the pair of pulses identifying each programmable item. By including this pair of pulses, the transponder is able to identify that the preceeding pair of pulses represents a programmable item and is able to identify such programmable item from such preceeding pair of pulses.

0084There is another important advantage to the programming system and method of this invention. This results from the fact that the programming pulses are produced on a self synchronizing basis at the reader and that the pulses are produced after particular counts in the counter 228. This facilitates the identification and decoding of the programming pulses at the transponder 20.

0085The programming is also relatively fast. This results in part from the use of integrated circuit chips for the reader 12 and the transponder 20. It also results in part from the generation of the programming pulses at the reader 12 in accordance with the counts provided in the counter 228.

0086Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.