JP2001167238A - Responsor for non-contact id tag system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a CMOS element, which is used for a responsor, from being broken down by a high voltage, and to suppress a radio receiver for an interrogator from being saturated by increase in reflected power from the responsor when the distance between the interrogator and the responsir is made short in a non-contact ID tag system. SOLUTION: A Zener diode 42 is added to the output of a rectifier part 41 of the responsor. Therefore, the output voltage of the rectifier part 41 is prevented from becoming higher than 3.5 V, and when received radio power is increased, the impedance of the Zener diode 42 is lowered. Thus, the circuit impedance of the rectifier part 41 is lowered and made close to the characteristic impedance of a reception antenna 13 and the reflection of radio waves is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact ID comprising an interrogator and a transponder having no power supply (also referred to as an ID tag).
The present invention relates to a transponder of a tag system.

[0002]

2. Description of the Related Art FIG. 1 shows a configuration of a non-contact ID tag system. The interrogator 11 has a power source and sends out radio waves or electromagnetically induced waves from the antenna 12. The following description is made as a radio wave. The interrogator 11 has a wireless transmission unit and a wireless reception unit. A radio wave is transmitted from the interrogator 11. The transmitted radio wave is transmitted to the antenna 13 of the transponder 14.
Received at. FIG. 2 shows a block diagram of the transponder 14. The transponder 14 rectifies a received radio wave to generate electric power, a detection unit 22 for detecting and receiving interrogation data transmitted by radio waves from the interrogator 11, and generates data for the received interrogation data. And a logic unit 23 for returning response data to the interrogator 11.

In order for the interrogator 11 to transmit interrogation data to the transponder, the transmission radio wave from the interrogator 11 is modulated by the interrogation data to the transponder. For example, the amplitude modulation is performed with a shallow modulation degree. The modulated signal is transmitted from the antenna 12, and is demodulated by the detector 22 via the antenna 13 of the transponder 14, and interrogation data is detected. From the detection unit 22, the clock is input to the Clock terminal of the logic unit 23, and the interrogation data is input to the In terminal of the logic unit 23. On the other hand, the radio wave from the interrogator 21 received by the antenna 13 is applied to the rectifier 21.
The rectifier 21 rectifies radio waves to create a DC voltage and supplies power to the Vdd terminal of the logic unit 23. The logic unit 23 operates with this power. Upon receiving the question data from the detection unit, the logic unit 23 analyzes the question data and creates necessary response data, and sends the response data to the interrogator 11 at a predetermined fixed timing after receiving the question data. This transmission method is performed by changing the voltage level of the Out terminal of the logic unit 23.

The rectifier 21 is designed so that the circuit impedance of the rectifier 21, that is, the input impedance when the rectifier 21 is viewed from the antenna 13, changes greatly when the voltage at the Out terminal of the logic unit is high and low. It is. When the Out terminal of the logic unit 23 is at a high voltage level (the same voltage level as the voltage applied to the Vdd terminal), the input impedance from the antenna 13 of the rectification unit 21 is high, and the Out terminal of the logic unit 23 is low. When the voltage level (0 volt) is reached, the antenna 1 of the rectifier 21
The input impedance from 3 is low. Although the rectifier 21 and the detector 22 are in parallel from the antenna 13, the input impedance of the detector 22 is always a high value, so the input impedance of the transponder 14 as viewed from the antenna is the input impedance of the rectifier 21. It is determined.

FIG. 3 shows a circuit diagram of the rectifier 21. The radio waves input from the antenna 13 are diodes 31, 34,
The voltage is double-rectified by the capacitor 36 and stored in the capacitor 39. The voltage rectified by the diodes 32 and 33 and the capacitor 37 is further applied to the voltage of the capacitor 39, and is stored in the capacitor 38 and applied to the Vdd terminal of the logic unit 23. In this state, the logic unit 23
Is applied to the capacitor 39 through the diode 35 when the same voltage is applied to the Out terminal of the Vdd terminal. As a result, the circuit impedance of the rectification unit 21 becomes high. That is, the input impedance of the rectifier 21 as viewed from the antenna 13 is high. Conversely, when the Out terminal of the logic unit 23 has a low voltage, for example, 0 V, the circuit impedance of the rectification unit 21 has a low value. Therefore, the input impedance seen from the antenna 13 becomes low. The value when the input impedance of the rectifier 21 is low is set so as to substantially match the characteristic impedance of the antenna.

When the input impedance from the antenna 13 is high, the characteristic impedance of the antenna 13 and the rectifier 2
Since the input impedance of No. 1 is in a mismatch state, the radio wave input from the antenna 13 is reflected and transmitted from the antenna 13. When the input impedance from the antenna 13 is low, since the characteristic impedance of the antenna 13 and the input impedance of the rectifier 21 are adjusted to match, the radio wave input from the antenna 13 is not reflected. The radio wave reflected from the antenna 13
It is received by the radio receiver of the interrogator 11,
When the voltage of the Out terminal of the third terminal is high, the interrogator 11
4 detects the radio wave reflected from the
When the voltage of the Out terminal is low, the interrogator 11 does not detect the radio wave reflected from the transponder 14, and receives response data from the logic unit 23 depending on the presence or absence of the reflected wave. That is, at the timing of sending the response data, the logic unit 23 applies a high voltage to the Out terminal when the response data is 1, and applies a low voltage when the response data is 0. Then, if there is a reflected radio wave from the transponder 14, it is determined that there is no reflected radio wave, or if the reflected radio wave is small, it is determined to be 0 and response data from the logic unit 23 is received.

[0007]

Although the ID tag system operates in this manner, some problems arise when the distance between the interrogator 11 and the transponder 14 is extremely short.
One is that the voltage obtained by rectifying the radio wave output from the rectifier 21 rises, a high voltage is applied to the Vdd terminal of the logic unit 23, and there is a risk of destroying the CMOS element used for the logic unit 23. It is. The maximum rated voltage of the CMOS element used in the logic unit 23 is usually 4 V. When the distance between the interrogator 11 and the transponder 14 approaches about 5 cm, the output voltage of the rectification unit 21 increases to 6 to 7 V. In addition, the CMOS device is broken by an overvoltage.

Another problem is that when the distance between the interrogator 12 and the transponder 14 becomes short, the power of the radio wave reflected from the transponder 14 increases, and the radio frequency amplifier circuit of the radio receiver of the interrogator 11 becomes saturated. , The reception of response data from the transponder 14 is disabled. In the interrogator 11, the amplification is increased in order to enable reception even when the transponder 14 is far away, so that if the response power from the transponder 14 is too strong, the received waveform will be distorted. As a countermeasure, there is a method of providing an automatic gain control circuit in the wireless receiver of the interrogator 11, but the automatic gain control circuit is complicated and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to economically reduce the problem of the prior art, that is, the overvoltage supplied to the CMOS and the saturation of the received waveform at the radio receiver of the interrogator at a point very close to the interrogator and the transponder. It is an object of the present invention to provide a non-contact ID tag system capable of performing a stable operation in a wide area.

[0010]

According to the present invention, there is provided a rectifier for receiving and rectifying a radio wave or an electromagnetically induced wave transmitted from an interrogator to generate a DC voltage; In a transponder of a non-contact ID tag system including a logic unit which operates by receiving a voltage, a zener diode is provided between an output terminal of the rectification unit and ground (ground). A transponder for an ID tag system is provided.

[0011]

Embodiments of the present invention will be described below in detail. FIG. 4 shows the transponder of the present invention. In FIG. 4, the rectifying unit 41 extracts DC power from the radio wave from the antenna 13 and supplies the DC power to the Vdd terminal of the logic unit 23. The detection unit 22 detects interrogation data from the interrogator from the radio wave received by the antenna 13 and sends it to the logic unit 23.
The logic unit 23 analyzes the received question data, and transmits response data by changing the voltage applied to the Out terminal at the timing of transmitting the response data. The rectifying unit 41 includes diodes 31, 32, 33, 34 and capacitors 36, 3
DC power is extracted from the radio wave at 7, 38, and 39 and supplied to the Vdd terminal of the logic unit 23. A zener diode 42 is inserted between the Vdd terminal and ground (ground). The voltage of the response data is applied to the diode 35 from the Out terminal of the logic unit 23. When no response data is sent, the voltage applied to the Vdd terminal is applied.

The operation of the present invention will be described below. The radio wave from the interrogator is received by the antenna 13 and applied to the rectifier 41, and operates in the same manner as described with reference to FIG.
1, 32, 33, 34 and the capacitors 36, 37, 38 become DC power and are applied to the Vdd terminal of the logic unit 23. A Zener diode 42 is inserted in this terminal in parallel with the capacitor 38. Zener diode 42
When the zener voltage of the capacitor is set to 3.5 V, the capacitor 3
8, the voltage applied to the Vdd terminal of the logic unit 23 cannot exceed 3.5V. Even if the distance between the interrogator 11 and the responder 14 becomes short in the circuit of FIG. 3 and the output of the rectifier 21 becomes as high as 6 V to 7 V,
Since the output of the rectification unit 41 of FIG. 4 is limited to approximately 3.5 V, the CMOS element having the maximum rating of 4 V used in the logic unit 23 is not destroyed.

Next, an operation of suppressing the reflected power of the radio wave received by the antenna 13 by the Zener diode 42 will be described. The terminal voltage of the capacitor 38 of the rectifier 41 is the Zener voltage of the Zener diode 42.
When the voltage is 5 V or less, no current flows through the Zener diode 42, and therefore, the same holds true with or without the Zener diode 42. When the distance between the interrogator and the transponder approaches, the high-frequency power received by the antenna 13 increases and the rectifier 41
The terminal voltage of the capacitor 38 rises. When this voltage exceeds the Zener voltage of the Zener diode 42, the impedance of the Zener diode 42 decreases, and a current exceeding the Zener voltage flows. Zener diode 42
, The impedance of the Zener diode decreases, and the circuit impedance of the rectifier 41 also decreases. Due to this impedance decrease, the antenna 1
By adjusting the circuit constants so as to approach the matching state with 3,
The reflected power of the radio wave received by the antenna 13 from the rectifier 41 is reduced. As a result, even when the interrogator and the transponder approach each other, the reflected power from the transponder does not increase, the saturation of the wireless receiver of the interrogator is eliminated, and stable reception of response data from the transponder becomes possible. That is, when the reception power of the radio wave received by the antenna 13 increases, the output of the rectifier 41 increases, the current flowing through the Zener diode 42 increases, and the impedance of the Zener diode 41 decreases. As a result, the circuit impedance of the rectifier 41 decreases and approaches the characteristic impedance of the antenna 13, so that the radio wave reflected from the antenna 13 decreases.
As described above, the simple addition of the Zener diode 42 to the output of the rectifier 41 reduces the reflected power from the transponder when the interrogator and the transponder, which has been a problem in the past, become extremely close. A transponder having an automatic control function can be realized.

[0014]

According to the present invention, the following effects can be obtained in a non-contact ID tag system having no power supply in the transponder. (1) Even if the interrogator and the transponder are close to each other, a transponder which does not destroy the CMOS element of the transponder due to an overvoltage can be obtained. (2) When the interrogator and the transponder are close to each other, the radio wave reflected from the transponder can be automatically reduced, so that it is not necessary to provide an expensive automatic gain control circuit in the interrogator. (3) The operating distance between the interrogator and the transponder is increased, and non-contact I
The application area of the D tag system is expanded.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a non-contact ID tag system.

FIG. 2 is a block diagram of a transponder.

FIG. 3 is a circuit diagram of a conventional rectifier.

FIG. 4 is a circuit diagram of a transponder according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 interrogator 12 interrogator antenna 13 transponder antenna 14 transponder 21 rectifying unit 22 detecting unit 23 logic unit 31, 32, 33, 34, 35 diode 36, 37, 38, 39 capacitor 41 rectifying unit 42 Zener diode

Continued on the front page (72) Inventor Shinichi Miyashita 3-14-20 Higashinakano, Nakano-ku, Tokyo Kokusai Electric Co., Ltd. (72) Inventor Yuzo Miura 3-14-20 Higashinakano, Nakano-ku, Tokyo Kokusai Electric Co., Ltd. F-term (reference) 2C005 MA35 NA09 TA22 5B035 AA00 BB09 CA12 CA23

Claims (1)

[Claims] 1. A non-contact device comprising: a rectifier for receiving and rectifying a radio wave or an electromagnetic induction wave transmitted from an interrogator to generate a DC voltage; and a logic unit which operates by receiving the DC voltage. A transponder for an ID tag system, wherein a zener diode is provided between an output terminal of the rectifier and ground (ground).