JPH0961517A - Noncontact identification code-reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly read out an identification code even when noises exist in a frequency band in the vicinity of that of a data signal. SOLUTION: A transmission circuit 2 generates carrier signals in accordance with a switch signal Sf output from a control circuit 6. Accordingly, carrier signals switched in frequency every constant time are transmitted from an antenna 3. A noncontact identification tag modulates the received carrier signal by an identification code and transmits as a data signal. A receiving circuit 5 changes a demodulation characteristic in accordance with frequency change of the data signal subsequent to the switching of the carrier signal. The data signal can be correctly demodulated in accordance with the frequency change. Even when noises are present in the vicinity of frequency of one carrier signal, the identification code can be read by the other carrier signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contactless individual identification system, and more particularly to a contactless identification code reader for reading an identification code from a contactless identification tag.

[0002]

2. Description of the Related Art Conventionally, there has been a non-contact type individual identification system using a non-contact identification tag, which reads an identification code of a tag by a reading device to identify an individual. FIG. 5 is a block diagram of such a conventional non-contact type individual identification system, 10 is a non-contact identification code reader for transmitting a carrier signal for requesting a response to a non-contact identification tag described later, and 11 is a crystal oscillator. , 12 is a transmission circuit for generating a carrier signal, 13 is a transmission antenna for transmitting a carrier signal, 14 is a receiving antenna for receiving a data signal transmitted from a tag, and 15 is an identification code extracted from the data signal received by the antenna 14. The receiving circuit 16 is a control circuit for controlling the transmitting circuit 12. Also, 15a
Is a filter circuit for passing only the data signal, and 15b is P for demodulating the data signal passing through the filter circuit 15a.
It is an LL demodulation circuit.

Further, 20 is a contactless identification tag which returns a data signal containing an identification code when it receives a carrier signal, 21 is a transmitting / receiving antenna which receives a carrier signal and transmits a data signal, and 22 is an antenna 21 which receives the signal. A rectifier circuit that converts a carrier signal into electric power and supplies the electric power to a control circuit, which will be described later, and a control circuit 23 that modulates the carrier signal received by the antenna 21 with an identification code to generate a data signal.

Next, the operation of such a non-contact type individual identification system will be described. The transmission circuit 12 in the contactless identification code reader 10 generates a carrier signal of frequency fc based on the clock signal output from the crystal oscillator 11, and the transmission antenna 13 sends this carrier signal as an electromagnetic wave. When the carrier signal is received by the transmitting / receiving antenna 21, the control circuit 23 in the contactless identification tag 20 reads an identification code from an internal storage circuit (not shown), FSK-modulates the carrier signal with the identification code, and outputs a data signal. To generate.

At this time, the frequency of the data signal becomes fa and fb corresponding to the identification code "0" and "1" by the FSK modulation. Thus, the transmitting / receiving antenna 21
From, data signals of frequencies fa and fb are transmitted as electromagnetic waves. Then, the receiving circuit 15 in the reader 10
The identification code is extracted from the data signal received by the receiving antenna 14. That is, the filter circuit 15a, which is a bandpass filter, passes only the data signal, and the PLL demodulation circuit 15b FSK demodulates the data signal. With this, the identification code of the tag 20 is obtained, and the tag 20 (or the object with the tag 20) can be identified.

However, as shown in FIG. 6, if external noise is constantly present at the same frequency as the data signal or a frequency in the vicinity thereof, the filter circuit 15a having the pass frequency band characteristic as shown by the broken line in FIG. The noise cannot be removed, the S / N ratio is significantly reduced, and the data error rate is increased.

[0007]

As described above, in the conventional non-contact identification code reader, if the external noise having the same frequency as the data signal or a frequency in the vicinity thereof is constantly present, the external noise is removed. Therefore, there is a problem that a communication error occurs and the identification code cannot be read correctly. The present invention has been made to solve the above problems, and an object of the present invention is to provide a contactless identification code reader capable of correctly reading an identification code even when external noise is present in a frequency band near a data signal. And

[0008]

A contactless identification code reader according to the present invention switches a demodulation characteristic according to a switching signal, a control circuit for outputting a switching signal, a transmission circuit for generating a carrier signal according to the switching signal. However, it has a receiving circuit for demodulating a data signal. With such a configuration, carrier signals having different frequencies are output from the transmission circuit at regular intervals according to the switching signal from the control circuit,
Transmitted by the transmitting antenna. With the switching of the carrier signal, the frequency of the data signal sent from the contactless identification tag also changes. Then, the receiving circuit of the contactless identification code reading device demodulates the data signal and extracts the identification code while switching the demodulation characteristics according to the switching signal.

Further, the transmitting circuit is composed of a control voltage generating circuit for generating a control voltage and a voltage / frequency converter for generating a carrier signal, and the receiving circuit is a filter circuit for switching the pass band characteristic according to the switching signal. And a PLL demodulation circuit that switches the reference frequency for demodulation according to the switching signal. Then, the control voltage generation circuit generates a control voltage, and the voltage / frequency converter generates a carrier signal corresponding to this voltage, whereby carrier signals having different frequencies are generated at regular time intervals. Further, the filter circuit switches the pass band characteristic in accordance with the switching signal, and the PLL demodulation circuit switches the reference frequency, so that the demodulation characteristic becomes in accordance with the frequency change of the data signal due to the switching of the carrier signal.

[0010]

1 is a block diagram of a contactless identification code reader according to an embodiment of the present invention, and FIG. 2 is a timing chart for explaining the operation of the contactless identification code reader. . 1 is a crystal oscillator, 2 is a transmitting circuit for generating a carrier signal Rc, 3 is a transmitting antenna, 4 is a receiving antenna, 5 is a data signal R received by an antenna 4.
A receiving circuit for extracting the identification code D from d, and a control circuit 6 for outputting a switching signal Sf for switching the frequency of the carrier signal Rc at regular intervals.

Further, 2a is a control voltage generating circuit for generating a control voltage according to the switching signal Sf, 2b is a voltage / frequency converter for generating a carrier signal having a frequency according to the control voltage, and 2c is for amplifying the carrier signal. The driver circuit 5a performs switching of the pass band characteristic according to the switching signal Sf, the filter circuit 5b that passes only the data signal switches the reference frequency for demodulation according to the switching signal Sf, and demodulates the data signal passing through the filter circuit 5a. It is a PLL demodulation circuit.

Next, the operation of such a contactless identification code reader will be described. The control circuit 6 outputs the switching signal Sf as shown in FIG. Control voltage generation circuit 2a
Generates a control voltage corresponding to the switching signal Sf at the “H” level, and the voltage / frequency converter 2b receives the carrier signal Rc having the frequency fc1 according to the control voltage.
(This is designated as Rc1).

Thus, the carrier signal Rc1 is given to the transmitting antenna 3 via the driver circuit 2c, and the carrier signal Rc1 is transmitted from the antenna 3 as an electromagnetic wave.
Note that the carrier signal at the time of being output from the voltage / frequency converter 2b may be a rectangular wave, but in this case, the transmission antenna 3 constituting the LC circuit is formed.
When input to, it becomes a sine wave.

Since the contactless identification tag from which the identification code is read is exactly the same as that shown in FIG. 5, the contactless identification tag which has received the carrier signal Rc1 has a data signal Rd (which is obtained by FSK-modulating the carrier signal Rc1 with the identification code D). Rd
1) is returned. At this time, the frequency of the data signal Rd1 becomes fa1 and fb1 corresponding to the identification code D “0” and “1”, respectively.

Next, the filter circuit 5a in the reading device is
A bandpass filter including an operational amplifier (not shown) or the like, which can change the passband characteristic according to the switching signal Sf by switching an element connected to the operational amplifier that determines the passband characteristic with a switch or the like. It is like this.

By such an operation, when the switching signal Sf is at "H" level, the pass band characteristic is changed to the frequency fa.
It is set to a characteristic centered on 1 and fb1. Thus
Of the signals received by the receiving antenna 4, the frequency fa
Only the data signal Rd1 of 1 and fb1 is applied to the filter circuit 5a.
Pass through. Further, as shown in FIG. 3, the PLL demodulation circuit 5b has a well-known basic configuration such as a phase comparator 51 and a low-pass filter 52 for phase-comparing the data signal Rd passed through the filter circuit 5a and the output signal of the voltage controlled oscillator 50. Have.

Then, by switching the element that determines the reference oscillation frequency of the output signal of the voltage controlled oscillator 50 with a switch or the like, the voltage controlled oscillator 5 is responsive to the switching signal Sf.
The characteristics of the PLL can be changed by changing the reference oscillation frequency of 0. With such an operation, when the switching signal Sf is at "H" level, the frequencies fa1 and f
The characteristic is set so that the data signal Rd1 of b1 can be demodulated. In this way, the data signal Rd1 is demodulated and the identification code D is obtained. The reference oscillation frequency at this time is
It is a frequency at which fa1 and fb1 are substantially at the center.

Next, when the switching signal Sf becomes "L" level, the control voltage generating circuit 2a changes the control voltage according to the signal Sf, and the voltage / frequency converter 2b causes the frequency f to change.
c2 (fc1 ≠ fc2) carrier signal Rc (this is R
c2) is generated. In this way, the carrier signal Rc2 having the frequency fc2 is transmitted from the contactless identification code reader by the same operation as described above.

The contactless identification tag which has received the carrier signal Rc2 returns the data signals Rd2 of frequencies fa2 and fb2 corresponding to the identification code D "0" and "1", respectively. At this time, the data signal Rd2 is the carrier signal Rc.
2 is FSK modulated with the identification code D, so fa1
≠ fa2 and fb1 ≠ fb2. That is, the frequency of the data signal Rd also shifts as the frequency of the carrier signal Rc switches.

On the other hand, the filter circuit 5a in the reader is
When the switching signal Sf becomes the “L” level, the pass band characteristic is changed to a characteristic centered on the frequencies fa2 and fb2. As a result, only the data signal Rd2 passes through the filter circuit 5a. Subsequently, when the switching signal Sf becomes the “L” level, the PLL demodulation circuit 5b causes the frequencies fa2 and fb to be reached.
The reference oscillation frequency of the voltage controlled oscillator 50 is changed so that the two data signals Rd2 can be demodulated. In this way, the data signal Rd2 is demodulated. In addition, the reference oscillation frequency at this time is a frequency substantially at the center of fa2 and fb2.

As described above, the frequency of the carrier signal Rc transmitted to the contactless identification tag is switched at regular intervals, and the demodulation characteristics, that is, the pass band characteristic of the filter circuit 5a and the characteristic of the PLL demodulation circuit 5b are changed. Thus, the identification code D can be read by the carrier signals Rc1 and Rc2 having two frequencies.

Here, the control circuit 6 of the reading device sends the data signal Rd because the contactless identification tag is not nearby although the carrier signal Rc1 or Rc2 is transmitted as in case 1 of FIG. When the signal cannot be received, the transmission of the carrier signals Rc1 and Rc2 is stopped midway in order to suppress power consumption.

When the contactless identification tag is close and no external noise is present, the data signals Rd1 and Rd2 are sent from the tag with respect to the carrier signals Rc1 and Rc2 as in case 2 of FIG. Therefore, the identification code D can be correctly obtained for both carrier signals as shown in FIG. 2 (d).

However, as shown in FIG. 4, the frequencies fa1 and f
When external noise having a frequency near b1 is present, the PLL demodulation circuit 5b cannot demodulate the data signal Rd1 and a communication error occurs. This is the frequency fa1, fb1
This is because noise cannot be removed by the filter circuit 5a in the pass frequency band centered at. In this case, unlike the ERR in case 3 of FIG. 2, since the identification code D cannot be obtained correctly, the control circuit 6 stops the transmission of the carrier signal Rc1 on the way.

On the other hand, next, the switching signal Sf is "L".
When the level is reached, the carrier signal R is read from the reading device.
c2 is transmitted, and the pass band characteristic of the filter circuit 5a and the characteristic of the PLL demodulation circuit 5b are also changed. Thus, the external noise is removed by the filter circuit 5a having the characteristic shown by the broken line in FIG. 4, so that only the data signal Rd2 passes through the filter circuit 5a, and the identification code D can be obtained by the PLL demodulation circuit 5b.

The presence of noise in the vicinity of the carrier signal is fatal to the conventional reader, but according to the reader of the present invention as described above, noise is present in the vicinity of the frequency of one carrier signal. However, the identification code can be read by the other carrier signal whose frequency is different from that of noise. It should be noted that in the present embodiment, there are two types of frequency switching of the carrier signal, but it goes without saying that more than two types may be used.

[0027]

According to the present invention, the transmission circuit outputs carrier signals having different frequencies at regular time intervals, and the reception circuit demodulates the data signal while switching the demodulation characteristics so as to cope with the frequency change of the data signal. Therefore, even if external noise exists near the frequency of a certain carrier signal, the identification code can be correctly read by another carrier signal whose frequency is different from that of the external noise.

Further, by forming the transmission circuit from the control voltage generation circuit and the voltage / frequency converter, it is possible to realize a transmission circuit which generates carrier signals having different frequencies at regular intervals with a simple structure. Further, by configuring the reception circuit from the filter circuit and the PLL demodulation circuit, it is possible to realize a reception circuit that can correctly demodulate the data signal with a simple configuration even if the frequency of the data signal changes due to switching of the carrier signal. .

[Brief description of drawings]

FIG. 1 is a block diagram of a contactless identification code reader according to an embodiment of the present invention.

FIG. 2 is a timing chart diagram for explaining the operation of the non-contact identification code reader of FIG.

FIG. 3 is a block diagram showing one configuration example of the PLL demodulation circuit of FIG.

FIG. 4 is a diagram showing frequency spectra of a carrier signal, a data signal, and external noise in the contactless identification code reader of FIG.

FIG. 5 is a block diagram of a conventional non-contact type individual identification system.

6 is a diagram showing frequency spectra of a carrier signal, a data signal, and external noise in the non-contact type individual identification system of FIG.

[Explanation of symbols]

1 ... Crystal oscillator, 2 ... Transmission circuit, 3 ... Transmission antenna, 4
... reception antenna, 5 ... reception circuit, 6 ... control circuit, 2a ...
Control voltage generation circuit, 2b ... Voltage / frequency converter, 2
c ... Driver circuit, 5a ... Filter circuit, 5b ... PLL
Demodulation circuit.

Claims (2)

[Claims] 1. A contactless identification code that modulates a received carrier signal with an identification code for individual identification and transmits the carrier signal to a contactless identification tag that transmits this as a data signal to read the identification code. In the reading device, a control circuit that outputs a switching signal for switching the frequency of the carrier signal at regular time intervals, a transmission circuit that generates a carrier signal having a frequency corresponding to the switching signal and outputs the carrier signal to the transmitting antenna, and a carrier signal A receiving circuit that demodulates the data signal received by the receiving antenna and extracts the identification code while switching the demodulation characteristics according to the switching signal so that the characteristic has a characteristic according to the frequency change of the data signal due to the switching of Characteristic non-contact identification code reader. 2. The contactless identification code reader according to claim 1, wherein the transmitting circuit generates a control voltage generating circuit that generates a control voltage according to the switching signal, and a carrier signal having a frequency according to the control voltage. The receiving circuit is configured to generate a voltage / frequency converter, and the receiving circuit switches a pass band characteristic in accordance with a switching signal and passes a data signal only, and a reference frequency for demodulation in accordance with the switching signal.
A contactless identification code reading device comprising a PLL demodulation circuit for demodulating a data signal that has passed through a filter circuit.