JPH08110378A - Method and equipment for interogating remote transponder - Google Patents

Abstract

PURPOSE: To discriminate an adjacent transponder by changing the period of a response on detecting a signal from an adjacent another transponder. CONSTITUTION: Two transponders 12, 12a exist in a range of a coil 38 for transmitting a question pulse of an interrogator. A power 1 transmitting circuit 300 drives a coil 38 and the coil 38 operates as a transmit/receive antenna. A question pulse is sent from the interrogator, and the question pulse is received by the first and second transponders 12, 12a. Subsequently, when the question pulse is ended, the first transponder 12 detects the end of question pulses and initializes the response having a designated period. When a signal from the second transponder 12a is detected by the first transponder 12, the period of response by the first transponder 12 is changed. The period of the response received by the interrogator is analyzed to judge whether both of the first and second transponders 12, 12a are near the interrogator or not.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to methods and apparatus for detecting adjacent transponders.

[0002]

BACKGROUND OF THE INVENTION The preferred embodiment of the present invention provides for measuring the duration of response signals from multiple transponders.
It detects the presence of adjacent transponders.
US Patent No. 5,053,774 and Patent Application No. 07 / 981,635 (both Joseph H. Schue
(assigned to Texas Instruments Incorporated by rmann)), a typical response period to an RF interrogation pulse is about 20 ms during which the transponder typically generates a 128-bit response message. Can operate After this 20 ms period, the transponder output is squelched. The squelching of the response signal is performed by the transponder timer triggered by the end of the burst (when the excitation signal ends). This timer counts up to 128 (bits) and then discharges the transponder charging capacitor.

[0003]

A device or an apparatus which can identify or detect an object provided with the device or the apparatus at a predetermined position in a non-contact state and at a predetermined distance from each other. The demand is great. There is also another need to be able to determine if two or more transponders are adjacent to each other.

[0004]

The present invention provides for determining if two or more transponders are adjacent.
It is the first to utilize the coupling between adjacent transponders. When two transponders are adjacent, they are both charged up and respond to RF interrogation pulses separately. Thus, one transponder sends a response signal and the other transponder enters this signal field. This radiation signal interferes with the vibrations maintained in the resonant circuit of the other transponder. The interference of this cross-coupled response causes a beat in each resonant circuit of the transponder.
This beat phenomenon is similar to the phenomenon that musicians hear when tuning an out-of-tune instrument. When the frequencies of the musical instruments are different, cooperative interference (the acoustic signals are in phase with each other, the sound intensity increases) and destructive interference (the acoustic signals are 180 degrees out of phase, and the sound intensity decreases). You can hear patterns that change over time. like this,
A pattern that changes with time is called a beat.

Such a beat effect can occur in both transponders. During the period of destructive interference, both transponders stimulate the end effect of the burst and cause the timer to be reset repeatedly (because the end of the burst resets the timer). New one for logic and transponder to send data signal by resetting timer
The 28ms window opens. Therefore, the discharging function of the transponder is repeatedly disabled by this beat effect, and the transponder transmits until the charging capacitor is completely discharged.

A beat effect also occurs between the transponder of the preferred embodiment and other transponders, such as those manufactured by manufacturers other than the applicant of the present invention. Interference with other types of transponders causes a beat in the resonant circuit, causing the timer to reset repeatedly.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the transponder device to be described comprises an interrogator 10 and a transponder 12.
The interrogator 10 is preferably held by the operator's hand and manufactured to transmit an RF interrogation pulse when the key 14 is pressed. The interrogator 10 can receive the RF signal and detect the information contained in the signal. An RF signal is transmitted from the transponder 12, which transponder 12 in this embodiment preferably has the same frequency as the interrogation pulse R.
It is adapted to respond to the transmission of the RF interrogation pulse by returning the F signal. The RF signal is data modulated by the transponder 12 using frequency shift keying (FSK) modulation. A base unit 16 manufactured as a fixed unit is linked to the interrogator 10. The functions of interrogator 10, transponder 12 and base unit 16 and their interaction will be described in more detail later. First, the configuration of these units will be described.

The interrogator 10 includes as a central control unit a microprocessor 18 which controls the functional sequences. The RF oscillator 20 produces an RF oscillating signal as soon as it is set to the active state by the signal at the output 22 of the microprocessor 18. The output signal of the RF oscillator 20 passes through the switch 24 and the amplifier 26,
Alternatively, it can be supplied to the coupling coil 32 via the switch 28 and the amplifier 30. Switch 24
And 28 are respectively controlled by the microprocessor with the aid of signals generated at the outputs 34 and 36 of the microprocessor. Coupling coil 32
A coil 38 of a resonance circuit including a coil 38 and a capacitor 40 is coupled to the. A resistor 44 that can be bridge-connected by a switch 42 is connected in series to the coil 38 and the capacitor 40, and another switch 46 is provided between the resistor 44 and ground. Switches 42 and 46 are controlled by a microprocessor which produces control signals corresponding to its outputs 48 and 50. When switch 46 is closed, the resonant circuit consisting of coil 38 and capacitor 40 acts as a parallel resonant circuit, while when switch 46 is open it acts as a series resonant circuit. Coil 38 acts as a transmit and receive coil, which transmits the RF interrogation pulse supplied to it by oscillator 20 and which receives the RF signal sent back by transponder 12.

The RF signal received by the resonant circuit is fed to two amplifiers 52, 54 adapted to amplify the received RF signal and limit these signals for pulse shaping. A parallel resonance circuit 56 that guarantees the required reception sensitivity is connected to these amplifiers. The output terminal of the amplifier 54 is connected to the clock generator 48, which generates a clock signal from the supplied signal and which outputs the clock signal to the input terminal 6 of the microprocessor 18.
Supply to 0.

Further, the output signal of the amplifier 54 is the demodulator 6
2 and the demodulator 62 demodulates the signal applied to it and the demodulated signal to the microprocessor 18
To the input terminal 64 of the.

The information contained in the received RF signal is
After demodulation by demodulator 62, it is provided via microprocessor 18 to random access memory 66, which can store this information. Microprocessor 18
A bidirectional connection circuit 68 is disposed between the random access memory 66 and the random access memory 66, and this circuit also enables input of information from the microprocessor 18 to the random access memory 66 and transfer of information in the reverse direction. ing. The information stored in the random access memory 66 can be retrieved by the jack 70.

The display unit 72, which is signaled by the microprocessor 18, allows the operator to view the data contained in the received RF signal. Since the interrogator 10 is a portable device, a rechargeable battery 74 is provided as a power source.
After the switch 76 is closed, the output voltage of the battery 74 is
It is supplied to the terminal labeled "+" among the predetermined chips in the interrogator 10. However, this supply voltage is supplied to the two amplifiers 52, 54, the clock generator 58 and the demodulator 62 via a separate switch 78 controlled by the microprocessor 18.

The battery 74 can be charged with a voltage induced in the coil 80, rectified in the rectifier 82 and smoothed by the capacitor 84. This voltage is preferably induced in coil 80 via coil 112 in base unit 16. The charging sensor 86 detects that a charging voltage has been induced in the coil 18, that is to say that the battery 74 is being charged, and the input 88 of the microprocessor 18 then generates a corresponding message signal.

Another switch 90, controlled by a signal from the output 92 of the microprocessor 18, RF's to the coupling coil 96 via the amplifier 94 in the closed state.
The output signal of the oscillator 20 can be supplied. The switch 90 is generally used to energize the transponder 12 to transmit RF interrogation pulses to initiate data transfer to and from the transponder 12. .

The RF oscillator 20 can be modulated by a modulator 98. The modulation signal required for this purpose can be provided by the microprocessor 18 via the switch 100 to the modulator 98, which is connected to the output 10 of the microprocessor.
It is controlled by the signal from 2. Microprocessor 1
The modulation signal from 8 is supplied to the coupling coil 104 when the switch 100 is also closed.

The base unit 16 also shown in FIG.
Is a fixed unit, which is connected to the mains power network via a jack 106.
The power supply 108 generates an operating voltage for the charging voltage generator 110, and the output signal of the generator is supplied to the coil 112. A switch 114 is inserted between the power supply 108 and the charging voltage generator 110, and the switch 11 is installed whenever the interrogator 10 is installed in the base unit 16.
4 is closed. This switch is shown in FIG. 1 as a type of activation button 116 located at the border of the interrogator 10. When the interrogator 10 is installed in the base unit 16, the coils 112 and 80 are spaced within the base unit and the interrogator 10 such that the coils 112 and 80 cooperate like primary and secondary windings of a transformer. It is arranged in a way. In this way, the battery 74 can be contactlessly charged when needed. The coils 96 and 104 in the interrogator 10 connect the interrogator 10 to the base unit 16
When it is installed in the above position, it is arranged so as to be extremely close to the coil 118 in space. Thus one coil 96
Further, a signal can be transmitted in a non-contact state between the coil 104 and the other coil 118. Demodulator 120 serves to demodulate the signal produced by coil 118.

The preferred embodiment transponder 12 shown in FIG. 2 includes a parallel resonant circuit 1 having a coil 132 and a capacitor 134 for receiving RF interrogation pulses.
30. A capacitor 136 that operates as an energy storage device is connected to the parallel resonant circuit 130. Further, the parallel resonant circuit 130 is also connected to the RF bus 138. This resonant circuit 130 is well known to those skilled in the art,
Works as both receiver and transmitter. The clock recovery circuit receives the RF signal from the RF bus 138 and recovers the clock signal 139 having a substantially square waveform. RF bus 138
The burst end portion detector 142 connected to has a function of monitoring the power level of the RF carrier on the RF bus 138. Upon receiving the RF interrogation pulse from interrogator 10, such RF carrier is generated on RF bus 138. The burst end part detector 142 is connected to the RF bus 1
As soon as the power level of the RF carrier at 38 drops below a predetermined threshold value, it produces an RF threshold signal of a predetermined value at its output. This RF carrier is rectified by connecting diode 144 to RF bus 138, resulting in charging capacitor 136. The energy stored in this capacitor 136 is proportional to the energy contained in the RF interrogation pulse. Therefore, the DC voltage can be extracted from the capacitor 136 after receiving the RF interrogation pulse. Capacitor 136
The function of the Zener diode 146 connected to is to ensure that the DC voltage that can be taken out from the tap does not exceed the value determined by the actual configuration, for example, the Zener voltage of the diode 146 in the integrated circuit. The function of is voltage limiting and can be accomplished by a number of circuits well known to those skilled in the art. Zener diode 146 performs a similar function to prevent the voltage on RF bus 138 from becoming too large. First, when the transponder 12 is queried, the interrogator 10 sends an RF signal to the transponder to charge the transponder 12. This operation is called a charging phase.

Power-on reset (referred to as POR,
The circuit (not shown) sends a POR signal to the start detection circuit 154. The POR signal monitors the Vcc level and is activated when the Vcc level rises from a level below the predetermined DC threshold to a level above the predetermined DC threshold. Generally, this POR signal occurs within the charging phase of the transponder. PO
R circuits are well known to those skilled in the art and are commonly used in almost all classes of circuits known as "state machines" so that they can be initialized to a known state. When the start detection circuit 154 receives the POR signal, the output end 150 of the end of the burst detection circuit 142 is received.
To monitor. At the output terminal 150, the end portion (EOB) of the burst signal is generated. When the positive state EOB is detected after the positive state power-on reset signal, the start detection circuit 154 switches the switch 156.
The power is switched to the clock recovery circuit 140 via the. The clock recovery circuit 140 is the resonance circuit 130.
It is preferred to clean up the signal from and generate the recovered RF clock. The reproduced RF clock is preferably a rectangular wave. The output signal of start detect circuit 154 remains positive until a subsequent POR is received. All components of the transponder except the clock regenerator 140 are continuously supplied with Vcc, but by utilizing low power CMOS technology, they are inactive (ie the clock regenerator 140 is active). It is preferable to consume only a negligible amount of power when there is no power).

Referring to FIG. 2, frequency divider 158 receives clock signal 139 and divides its frequency by eight. The pluck circuit 192 preferably sends a short pulse each time it is triggered by the divided clock signal received from the divider 158. This pluck circuit 192 is a field effect transistor or FET1.
The resonance circuit 130 is formed by forming a conduction path between the resonance circuit 130 and the ground via the RF bus 138 so that the resonance circuit 90 instantaneously becomes conductive and the resonance circuit obtains the electric energy from the charging capacitor 136. Maintain the vibration of. The pluck circuit 192 is metaphorically named because it describes that the resonance circuit 130 is vibrated in the same manner as the guitar string is vibrated by tracking the guitar string. is there. This plucking operation is temporarily performed on the RF bus 1.
The width of the pulse is not sufficient for a given channel resistance of FET 190 to drop the voltage on 38 below the threshold and trigger the end 142 of the burst detection circuit to energize this circuit. . 2nd frequency divider 16
A value of 0 further divides the frequency of the clock signal 139 into two so that the clock frequency at the output end of the frequency divider 160 becomes 1/16 of the original clock frequency.

The read circuit of the preferred embodiment will now be described with further reference to FIG. The shift clock input signal of the output shift register 172 is input to the output terminal of the second frequency divider 160, and data is passed through this register 172 at a frequency 1/16 of the original clock frequency. The output shift register 172 shifts / loads the “load” signal from the output end of the start section detection circuit 154.
Upon receipt at load input 174, it receives a parallel load from memory 168 or other source via data bus 220. After this loading of the output shift register 172, the signal from the start detection circuit 154 will be positive so that the shift signal is received at the shift / load input 174 of the register 172. While this shift signal is positive, the data is clocked at the shift clock input 176 by 16 clocks of the original clock frequency.
It is shifted one-half through the output shift register. As shown, the data is recirculated through the output shift register 172 through the data path 182 and sends a signal through the data path 182 to the FET or gate of the modulator 200. The data of the output shift register has a predetermined time (pre-bit time, pre-bit-ti
During me), it is preferably low, and either high or low depending on the data loaded internally. In this embodiment, during this pre-bit time, the receiver coil 38 of the interrogator is powered by the power burst overload (pow).
er burst overload (charging phase) and is used to separate read and write functions, as described below. The FET 200 is not conducting while the output signal of the output shift register 172 is low. While the output of the output shift register 172 is high, the FET 200 is in the conductive state, so that the capacitor 198 is connected to the resonance circuit 1.
32 to reduce its resonance frequency. In essence, FET 200 operates as a switch under the control of output shift register 172, connecting capacitor 198 or leaving it unconnected to modulate the frequency of resonant circuit 130. In this way, FET2
In response to the data applied to 00, frequency modulation of the resonance frequency of the resonance circuit 130, that is, the carrier frequency is performed. When the original resonant frequency of the resonant circuit 130 is maintained for 1 bit period, a low level or zero signal is displayed and the original resonant circuit 1 in parallel with the capacitor 198.
When 30 parallel new resonant frequencies occur within one bit period, a high level or "1" signal is displayed.

Next, referring to FIG. 2, the operation of the discharge logic circuit will be described. The timer 184 has an input terminal 1
At 86, the output signal of divider 160 is received and the frequency of the clock signal is divided into some other 128 minutes. Since the preferable data transmission bit length is 128, the timer 8
The division ratio of 4 is some 128 minutes in this example.
When changing the bit length, it is preferable to change the frequency division ratio of the timer 184 correspondingly. Diode 21
0 maintains a unidirectional current from the timer 184 to the parallel RC circuit of the field effect transistor, ie, the capacitor 212 and the resistor 214, which maintains the charge on the gate of the FET 216 for a known period. The capacitor 212 is
It can be charged by timer 184 via diode 210, but must be discharged via resistor 214. When the gate of FET 216 is maintained above the threshold voltage by the parallel circuit of resistor 214 and capacitor 216, FET 216 acts to provide a low impedance discharge path to ground for charging capacitor 136. In this way, after the entire data frame (128 bits (reading phase) in this example) is transmitted from the transponder 12 to the interrogator 10, the residual energy in the transponder 12 is changed to the charging capacitor 136.
Excluded by a short circuit across. Such an operation ensures that the transponder is properly initialized during the next charging phase and does not remain indefinite, i.e. incorrect, so that subsequent charging can be blocked. Furthermore, due to this function, each transponder 12 in the field of the interrogator 10 has the same activation condition.

Next, a circuit (writing function) capable of writing data to the transponder 12 will be described with further reference to the circuit of the transponder 12 shown in FIG.
In the preferred embodiment of the invention, the interrogator 10 pulse pauses the RF interrogation pulse as shown in FIG.
pause podulation (PPM). This signal is displayed on the RS bus 138. As is well known to those skilled in the art, pulse-pause modulation systems operate by alternately activating and deactivating carrier waves. During the period when the carrier is deenergized, the burst end detector 142 detects the drop in RF energy and is energized. After the start part detection circuit 154 is activated by the POR signal, the start part detection circuit 15
4 is the first EO generated by the start bit (see FIG. 4)
It is activated by the B signal. As will be described later, since each data bit status is transmitted depending on the presence or absence of phase shift of the carrier wave, the start bit is used in this preferred embodiment, but another start bit is not required to be transmitted. Examples are also possible. The period during which the carriers are energized, known as the phase shift, is shorter than the pre-bit time of the read phase. Since the output shift register 172 starts shifting while the phases are out of phase, this specific condition is used in this embodiment. However, since the pre-bit time is longer than the phase shift time, none of the output shift registers can shift, and they shift zero, so that F is actually
The ET 198 is neither energized nor inverted and no unwanted modulation of the carrier 138 occurs. The EOB signal is de-energized when the carrier returns. By activating and deactivating the EOB signal, the start detection circuit 154 keeps the output active until a new POR signal is received, regardless of the switching of the EOB signal, so that the clock recovery circuit 140 is switched through the switch 156. To keep the power supply to.

A fourth frequency divider 162 is provided. The frequency divider receives the clock signal from the second frequency divider 160, divides the clock signal again into 1/16, and inputs it to the input shift register. An input clock signal is supplied to the clock input terminal 227 of 228. In the preferred embodiment, the percentage of write data is at the resonant frequency, or 1/265 of the receive clock frequency. Steps must be taken to shift the data into the input shift register 228 while the data is stable. This can be guaranteed as follows. The fourth frequency divider 162 is AN
It is energized by the start detection circuit 154 via the D gate 155. Each successive zero bit, or low bit, received by the burst end detection circuit 142 drives the burst detection circuit output 150 positive. This positive signal is received at the negative logic input of AND gate 155. This negative logic input terminal is ANDed as well known to those skilled in the art.
It is displayed as a circle at the input end of the gate 155. Since the output signal of the AND gate 155 is made negative by the definition of the AND function, the fourth frequency divider 162 is cleared and the input clock is synchronized with the input data.

The end detection circuit 234 detects the end of the data frame when a bit combination in the input shift register 228 is received, and if the programming command has been received by the command recorder 230, the programming logic 232 is detected. Energize. This data is then transferred from input shift register 228 to memory 168 or other memory via parallel data bus 220. A memory for transferring data is an electrically erasable programmable read only memory (EEP).
ROM) is preferred.

Burst end detector 142 generally operates as a pulse pause modulation (PPM) demodulator. Many other modulation methods are known in the field of wireless communication,
It is also possible to use another demodulator for such another modulation method instead of the burst end detector.

In the preferred embodiment, provision is also made to initialize the test sequence via test logic 236. The test logic 236 includes a signal and data bus 22 from the command recorder 230.
It can receive data from zero and initialize a number of test routines such as are commonly practiced in logic circuit design. The result of these test routines is the data bus 2
20 and can be output to the modulation circuit through the field effect transistor 200 by the shift register 172.

In the preferred embodiment of the present invention, a programmable tuning network 238 is provided. The programmable tuning network 238 operates by switching a network of parallel capacitors 240, each capacitor 240
Is grounded through a field effect transistor, or FET 240. Each field effect transistor is connected to a latch 244, which receives data from the memory 168 or the command recorder 230 via the data bus 220 under the control of the latch signal 246 from the command recorder 230 and latches it. To do.
By switching the field effect transistor 242 to the conducting on-state, the associated capacitor 240 is connected in parallel with the parallel resonant circuit 130. By increasing the capacitance in this way, the resonance frequency of the parallel resonant circuit 130 is lowered. When the field-effect transistor 242 is switched to the non-conducting off-state, the capacitor associated therewith floats and does not affect the parallel resonant circuit 130. The network 238 of FET and capacitor pairs 240, 242 can provide many different values of increased capacitance, depending on the combination of relative values of each capacitor 240, as is well known to those skilled in the art. Alternatively, the latch 244 can be a one-time programmable (OTP) memory so that the data is stored fixedly therein, and the device has a programmable tuning network (programmable tuning network).
(work) 238 can be permanently programmed to set the value.

The divider ratios of the dividers in the embodiments described herein are selected to suit the details of each design. This division ratio must in each case be chosen to optimally perform the work for which they were designed.

Referring to FIG. 3 in conjunction with FIGS. 1-2, assume there are at least two transponders 12, 12a within the range of the coil 38 transmitting the RF interrogation pulse. The power / transmission circuit 300 is provided to drive the coil 38. Alternatively, a separate antenna 39 may be provided as the transmitting antenna and the coil 38 may be used as the receiving antenna 38. However, the coil 38 preferably operates as a transmit and receive antenna. Power / transmit circuit 300 preferably comprises oscillator 20 and amplifier 26 of interrogator 10 of the preferred embodiment of FIG. Transponder 1
Coil 13 of parallel resonant circuit 130 (FIG. 2) of 2, 12a
2 receives this RF interrogation pulse so that the resonant circuit 130 is stimulated and vibrates. The RF oscillation in the portion 138a of the RF bus 138 is rectified by the rectifier diode 144, and the capacitor 136 is charged with direct current. After that, only the energy charged in the capacitor 136 is used for the energy supply of the transponders 12, 12a. The read circuit 302 is arranged to receive the transponder response. The read circuit 302 preferably comprises a clock generator 58 capable of generating a carrier detect (CD) signal to the microprocessor, ie the microprocessor 18
Can interpret the presence or absence of a clock signal as carrier detection. The timer 304 is preferably provided within the microprocessor 18 of the interrogator 10. Timer 30
4 measures the period during which the clock signal is present. When the data signal is obtained from the output terminals of the reading circuit 302 and the timer 304, the decoder 304 determines whether the data is a) good reading with CD ≤ 20 ms, or b) the CD is not detected. It was possible to determine if c was not performed, c) CD ≧ 20 ms, and thus more than two transponders were present close to the interrogator. The functionality of the decoder 306 is preferably within the microprocessor 18 of the preferred interrogator 10.

Referring now to FIG. 4, the RF level on RF bus 138 begins to drop when the reception of RF interrogation pulses is complete. The burst end section detector 148 is
As soon as the level increase is detected and the power level drops below a predetermined level, an EOB signal of a predetermined value is generated at its output terminal 150. The timer 184 is reset by EOB.

In the pluck circuit 192, the field effect transistor 190 becomes non-conductive after the end of the excitation pulse, so that no more current can flow through the coil 132. However, since the parallel resonant circuit 130 is of high quality, the vibration of the RF carrier does not immediately stop, and the resonant circuit continues to vibrate while being damped.
Frequency divider 158 that halves the frequency of the RF carrier wave
Is a monoflop after the second oscillation period.
p) 192, which causes the flop 190 to be triggered. The monoflop 192 applies a sustain pulse to the field effect transistor 190 during the holding time. A holding pulse from the pluck circuit 192 causes a current to flow through the coil 132 during the holding time. This means pumping energy to the RF carrier wave generator for a short period of time. Since the frequency divider 158 is used, this pumping effect (pu
The mpping effect) occurs after the oscillation period of 1 / n of the RF carrier wave.

It is assumed that the data is permanently stored in the memory 168 and that these data are uniquely assigned to the transponders 12, 12a. This data can be composed of 128 bits, for example. At the timing of the clock signal applied to the clock input terminal 176, the information in the memory 168 is transferred to the output shift register 172. 128 pulses are required to perform this transfer operation. The reason is that the shift register 172 contains all the information of 128 data bits. The timer 184 determines that the data transfer is completed by counting the clock pulses.
After receiving the 128 pulses, the timer 184 generates a signal at its output 188 which is sent to the FET 216 via the diode 210. Since the preferable data transmission bit length is 128, the dividing ratio of the timer 184 is 1/128 in this example. If this bit length has to be changed, the third timer 1 is correspondingly
It is also preferable to change the division ratio of 84. Diode 21
0 maintains a unidirectional current from timer 184 to the parallel RC circuit of the field effect transistor, capacitor 212212 and resistor 214, which maintains the charge on the gate of FET 216. Capacitor 2
12 can be charged by timer 184 via diode 210, but must be discharged via resistor 214. The FET 216 is a resistor 214 and a capacitor 21.
When the gate of FET 216 is maintained above the threshold voltage by a parallel circuit with 2, it acts to form a bottom impedance discharge path for charging capacitor 136 to ground. After the entire data frame (128 bits (reading phase) in this example) from the transponder 12 to the interrogator 10 is transmitted in this way, the remaining energy in the transponder is charged by the charging capacitor 136.
Usually eliminated by a short circuit across. This action ensures that during the next charging phase the transponder is properly initialized and does not remain in an indeterminate or incorrect state so that the next charging is not blocked.

When two or more transponders 12 and 12a are adjacent to each other, the interrogator 10 includes the transponders 12 and 12a.
It is preferable to detect such a condition so as to prevent the interfering signal from a from being considered as valid data. By utilizing the result of the cross coupling between the adjacent transponders 12 and 12a, the interrogator 10 can detect that the transponders 12 and 12a are adjacent to each other. When such a condition is detected, the interrogator 10 determines the transponder 1
Actions can be taken, such as more powerful or selective addressing of 2, 12a, or notification to the user. If the two transponders 12 and 12a are adjacent, they are both charged and respond separately. For example, because of the tight coupling between the two, one transponder 1
2 answers and the other transponder 12a goes into its electric field. Such tight coupling causes beats in each of the transponder resonant circuits 130 because their frequencies are slightly different. Such destructive interference (ie, the signal in the resonant circuit 132 of one transponder 12 is combined with the combined signal from the other transponder 12a 18
The burst end detector 142 resets the timer 184 due to a 0 degree phase shift). Resetting timer 184 causes a new 12
An 8-bit window opens. This occurs continuously within each transponder 12, 12a. Therefore, the signal vibration energy in the resonance circuit 130 is 20 ms.
Instead of being damped later, natural vibrations can be damped by the usual parasitic damping effects. In the example, this new time is about 40 ms.

It can be determined whether there is another type of transponder, that is, a transponder that is not the type of transponder of the type described herein as the preferred embodiment adjacent to the preferred transponder 12. In such a case, the other transponders are more lossy (ie, operate at a lower Q factor and dissipate more energy during the function from the preferred transponder 12), so that the transponders consume more energy from their vibrations. Send to adjacent transponder and discharge faster than adjacent transponder. Thus, in the exemplary embodiment, the transponder can be discharged in about 30 ms instead of 40 ms. In either case, the discharge time is longer than 20 ms and the vibrations decay during normal interrogation cycles.

Although a few preferred embodiments have been described above, it should be understood that the scope of the present invention is within the scope of the claims and includes embodiments different from those described above.

Microcomputers are used in some contexts to mean, for example, that microcomputers are those that require memory, while microprocessors are those that do not. As used herein, such terms are synonymous and are meant to mean equivalents. Phrases or processing or control circuits may be ASIC (special purpose integrated circuit), PAL (programmable array logic), PL
A (programmable logic array), decoder, memory, non-software based processor or other circuit, or microprocessor and microcomputer digital computer of any kind of architecture, or a combination thereof. The memory device is SRAM (static random access memory), DRAM (dynamic random access memory), pseudo static RAM, latch, EEPROM
(Electrically erasable programmable read only memory), EPROM (erasable programmable read only memory), register or other memory device known to those skilled in the art. It is to be understood that the terms including these are not limiting in interpreting the present invention.

It is also possible to construct a full-duplex transponder structure or a half-duplex structure. Frequency shift keying (FS
The K) modulation method is considered to be a possible data modulation method, but is not limited to this, but also pulse pause modulation, amplitude shift keying (ASK), quadrature AM (QAM) modulation, quadrature phase shift keying (QPSK) or other modulation. Law is also possible. It can be implemented to prevent different types of multiplexing, eg cross-signal interference of time or frequency modulation. Not only can it be made up of discrete components or fully integrated circuits made of silicon, gallium arsenide or other electronic material families, but also in light-based or other technology-based forms Is also possible. Also, it should be understood that various embodiments of the present invention can use, or be embodied in, hardware, software or microcoded hardware.

Although the invention has been described with reference to the illustrated embodiments, this description should not be construed as limiting. Given this description, those skilled in the art will be able to contemplate not only various variations of the illustrated embodiments and combinations thereof, but also other embodiments of the present invention. Therefore, the appended claims are to cover such variations or embodiments.

With respect to the above description, the following items will be further disclosed. (1) a) sending an RF interrogation pulse from the interrogator, b) receiving the RF interrogation pulse by first and second transponders, c) terminating the RF interrogation pulse, and d) the RF interrogation by the first transponder. Detecting the end of the interrogation pulse, e) RF with a predetermined period in the first transponder
Initializing a response, f) detecting the RF signal from the second transponder with the first transponder, and g) determining the period of the RF response in the first transponder when detecting the RF signal from the second transponder. How to ask a remote transponder with a change.

(2) receiving the RF response by the interrogator and analyzing the duration of the RF response to determine if both the first and second transponders are near the interrogator. The method of claim 1, further comprising: (3) The method of claim 2 further comprising the step of selectively addressing one of the first and second transponders by the interrogator. (4) The method according to claim 1, wherein the first transponder is a half-duplex transponder. (5) The method according to claim 1, wherein the second transponder is a half-duplex transponder.

(6) The method according to claim 1, wherein the second transponder is a full-duplex transponder. (7) The method of claim 1, wherein the first transponder has a resonant circuit for receiving the RF interrogation pulse and oscillating in response to the RF interrogation pulse. (8) Detecting the RF signal from the second transponder in the first transponder includes detecting the oscillation generated in the resonance circuit of the first transponder and the second transponder.
8. The method of claim 7 performed by detecting destructive interference with the RF signal from the transponder. (9) The method according to item 1, wherein the period is selected by a counter that counts a predetermined number of oscillations in the resonant circuit.

(10) a) send an RF interrogation pulse from the interrogator, and b) near the interrogator, first and second transponders (each of the first and second transponders comprises a parallel circuit of a coil and a capacitor). Including a resonant circuit), c) receiving the RF interrogation pulse by each coil of the transponder, and d) generating an oscillation caused by coupling of signal energy from the RF interrogation pulse to the resonant circuit to the transponder. E) terminating the RF interrogation pulse from the interrogator, f) detecting the end of the RF interrogation pulse in the first transponder, and g) in the first transponder. RF with a predetermined period at
Initializing a response, h) detecting destructive interference between the oscillation generated in the resonant circuit of the first transponder and the RF signal from the second transponder, and i) the RF response in the first transponder. Changing the period, j) receiving the RF response by the interrogator,
A method for interrogating a remote transponder, comprising the steps of analyzing a period of response to determine if the first and second transponders are in the vicinity of the interrogator.

(11) a) an interrogator operable to transmit an RF interrogation pulse and receive an RF response; and b) first and second transponders approaching said interrogator, said at least said first transponder. A transponder has the resonant circuit operable to receive the RF interrogation pulse from the interrogator and to oscillate with the signal energy in the RF interrogation pulse); and c) to receive the end of the RF interrogation pulse. A transponder burst end detector electrically coupled to the resonant circuit; d) a transponder transmitter electrically coupled to the burst end detector for transmitting an RF response to the RF interrogator; e) The transponder's power to determine that the response message from the transponder is complete and to disable the transmitter. Device for interrogating a remote transponder, comprising: a counter, and f) a response signal detector provided on the transponder so as to detect a response from an adjacent transponder and reset the counter of the transponder.

(12) The apparatus according to claim 11, wherein the burst end detector of the transponder and the transmitter of the transponder have an intervention control circuit for controlling them. (13) The device according to item 11, wherein the interrogator has an antenna for receiving the RF response. (14) The apparatus according to claim 13, wherein the interrogator further includes a readout circuit electrically coupled to the antenna for detecting valid data returned from the transponder.

(15) The interrogator further comprises a timer circuit electrically coupled to the antenna for measuring the period of the RF response from the first transponder.
The transponder according to item 4. (16) The interrogator further includes a decoder electrically coupled to the read circuit and the timer circuit.
Transponder according to the item.

(17) The RF interrogation pulse from the interrogator is 2
An interrogator for determining whether it has been received by one or more transponders, comprising: a) a transmitting antenna for transmitting RF interrogation pulses to the transponders, and b) an RF response from at least one of the transponders. A) a receiving antenna for receiving, c) a readout circuit electrically coupled to the receiving antenna and operable to extract a data signal from the RF response, and d) electrically coupled to the receiving antenna, A timer operable to measure the duration of the RF response, and e) whether it has received a valid response from a single transponder without being electrically coupled to the readout circuit and the timer and without interfering with other transponders. A decoder operable to interpret a signal received from the readout circuit and the timer Question equipped with a. (18) The interrogator according to Item 17, wherein the transmitting antenna is the same antenna as the receiving antenna.

(19) The method of interrogating the remote transponder is to send an RF interrogation pulse from the interrogator (10),
The RF interrogation pulse is received by the first and second transponders (12, 12a), and the transponders (12, 12a) are received.
a) There is a step of causing vibration in each resonance circuit (130). Said vibration is caused by the coupling of signal energy from the RF interrogation pulse into the resonant circuit (130).
When the RF interrogation pulse ends, the first transponder (1
2) detects the end of the pulse and has a first period of time
Initialize the RF response. The first transponder (12) also detects the second RF response from the second transponder (12a), but the response of this first transponder is the second R
It is affected by the F response. The response time difference in the first transponder (12) for the response affected and the response unaffected by the adjacent transponder can be detected in the interrogator so that the interrogator can detect when the RF response it receives does not match.

Reference to Related Patents The following US patents and patent applications assigned by the applicant of the present application are incorporated by reference. U.S. Patent and Application Number Filing Date TI Company Case No. 5,053,774 February 13, 1991 TI-12797A 07 / 981,635 November 25, 1992 TI-16688

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a preferred interrogator and base unit.

FIG. 2 is a block circuit diagram of a preferred transponder.

FIG. 3 is a more general block diagram of the preferred device showing the most salient features.

FIG. 4 is a signal waveform diagram of an antenna signal according to a normal transponder that is not affected by a transponder in close proximity and a transponder with respect to another transponder in close proximity.

[Explanation of symbols]

 10 Interrogator 12 First Transponder 12a Second Transponder 130 Resonant Circuit

Claims (2)

[Claims] 1. A) sending an RF interrogation pulse from an interrogator, b) receiving the RF interrogation pulse by first and second transponders, c) terminating the RF interrogation pulse, and d) at the first transponder. Detecting the end of the RF interrogation pulse, e) RF having a predetermined period in the first transponder
Initializing a response, f) detecting the RF signal from the second transponder with the first transponder, and g) determining the period of the RF response in the first transponder when detecting the RF signal from the second transponder. How to ask a remote transponder with a change. 2. An interrogator operable to transmit an RF interrogation pulse and receive an RF response; and b) first and second transponders approaching said interrogator, said at least said first transponder. Has a resonant circuit operable to receive the RF interrogation pulse from the interrogator and oscillate with the signal energy in the RF interrogation pulse; c) the resonant circuit to receive the end of the RF interrogation pulse. A transponder burst end detector electrically coupled to: d) a transponder transmitter electrically coupled to the burst end detector for transmitting an RF response to the RF interrogator; e) A transponder counter for determining that the response message from the transponder is complete and disabling the transmitter; ) Detecting a response from an adjacent transponder, to reset the counter of the transponder device for interrogating the remote transponder and a response signal detector provided in the transponder.