JP3362189B2 - Wireless IC card - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a wireless IC with an interrogator.
The present invention relates to a wireless IC card that constitutes a card system and performs non-contact communication.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 4, a wireless IC card system includes a wireless line between an interrogator 1 and a wireless IC card (responder) 2 which is mounted on or attached to a moving body to move. 3, the non-contact communication is performed using the microwave of 2.45 GHZ, for example. The wireless IC card used in this type of system conventionally uses a diode detection circuit in the reception circuit, and detects the reception voltage by extracting the voltage across the detection diode through a terminating resistor having a constant value. .

[0003]

SUMMARY OF THE INVENTION The above-mentioned conventional wireless I
In the C card, in order to improve the receiving sensitivity and increase the transmission speed at the same time, the bias current of the detection diode must be increased. Therefore, if it is attempted to secure the sensitivity during standby, a large bias current will continue to flow even during standby, and there is a problem that the battery life is shortened.

The present invention has been made in view of the above-mentioned problems, and has a low power consumption during standby, good sensitivity, a high transmission rate during communication, and a good sensitivity.
The purpose is to provide a card.

[0005]

A radio IC card of the present invention includes an antenna, a detection element for detecting a radio wave received by the antenna, and a bias current circuit for supplying a bias current to the detection element. A circuit having a load resistance for deriving the detection output of the detection element, wherein the bias current value of the bias current circuit and / or the resistance value of the load resistance is changed depending on whether the standby state or the communication state. It is equipped with a means to make it.

In this wireless IC card, the resistance of the load resistance is increased during standby, and is decreased during communication, and the current value of the bias current circuit is decreased or zero during standby, and bias is applied during communication. Since the current is increased, low power consumption and improved sensitivity can be achieved during standby, and transmission speed and sensitivity can be improved during communication.

[0007]

The present invention will be described in more detail with reference to the following examples. FIG. 1 is a wireless IC showing an embodiment of the present invention.
It is a circuit diagram of a card. This wireless IC card includes an antenna 11 for transmission / reception, a matching circuit 12, a diode 13 for detection, a power supply 18 for supplying a bias current to the diode 13, a current limiting resistor 19, a high impedance line 20, and a diode 13. The switching signal 1 to the terminating resistor 14 connected in parallel to the terminating resistor 14 and the terminating resistor 14 according to the detection output 17.
A control circuit 15 for sending 6 is provided.

In this wireless IC card, the antenna 1
The signal input from 1 passes through the matching circuit 12 and is detected by the detection diode 13. At this time, the voltage across the diode 13 is derived as the detection output 17 via the terminating resistor 14. The bias current to the diode 13 passes from the bias source 18 through the current limiting resistor 19 and the high impedance line 20 in order to eliminate the influence of high frequency. During communication, signal 1 from control circuit 15
6, the resistance of the terminating resistor 14 is set small, and conversely, when the detection output 17 becomes zero, that is, the control circuit 15
Signal 16 increases the resistance value of the terminating resistor 14 so that the standby sensitivity does not become too small. This will be described further with reference to FIG. 5. FIG. 5 is a graph showing the relationship between the DC bias current value to the diode (horizontal axis) and the demodulation voltage (vertical axis) at the time of carrier input.

As can be seen from this graph, the demodulation sensitivity is relatively poor when the bias current is small. There is a problem when the wireless IC card performs carrier detection during standby. FIG. 6 is a graph showing the relationship between the termination resistance value of the detection output (horizontal axis) and the demodulation voltage when the carrier wave is input (vertical axis). It can be seen from this graph that the demodulation voltage increases as the terminating resistance increases. Therefore, from the graphs of FIGS. 5 and 6, it is possible to improve the carrier detection sensitivity by increasing the terminating resistance with no or almost no bias current in order to suppress the power consumption during standby. it can.
The embodiment circuit shown in FIG. 1 is a circuit having such a device.

FIG. 7 is a graph showing the relationship between the frequency of the signal wave (horizontal axis) and the detected output signal wave amplitude (vertical axis).
The broken line shows the case where the terminating resistance is 10 kΩ, and the solid line shows the case where the terminating resistance is 100 Ω. From this graph, it can be seen that when the signal frequency is high, the smaller the terminating resistance, the better the detection sensitivity. The transmission speed can be increased by reducing the terminating resistance.

FIG. 2 shows a radio I according to another embodiment of the present invention.
It is a circuit diagram of a C card. The circuit of this embodiment is almost the same as that shown in FIG. 1 in the basic configuration, but in the embodiment of FIG. 1, the resistance value of the terminating resistor 14 is changed by a command from the control circuit 15. In the example, the resistance value of the current limiting resistor 19 is changed by the signal 21 from the control circuit 15, and the bias current flowing through the detection diode 13 is changed. Signal input from the antenna 11 passes through the integer case circuit 12, is detected by the detection diode 13. At this time, the voltage across the detection diode 13 is derived as the detection output 17 via the terminating resistor 14. In this respect, there is no difference from the circuit of FIG. The bias current to the diode 13 flows from the bias input source 18 through the current limiting resistor 19, but passes through the high impedance line 20 in order to eliminate the influence on the high frequency. The current limiting resistance 19 is changed by the signal 21 of the control circuit 15 in order to change the bias current of the diode during standby and during communication. The reason is clear from the graph of FIG. 5 described above. The bias current is increased to increase the sensitivity during communication, and is decreased to achieve low power consumption during standby.

FIG. 3 is a circuit diagram of a wireless IC card showing still another embodiment of the present invention. The basic configuration of this embodiment circuit is the same as that shown in FIGS. 1 and 2,
In the embodiment of FIG. 1, the terminating resistor 14 is changed by a command from the control circuit 15 during communication and during standby, and the circuit of FIG. 2 is changed by a signal from the control circuit 15 during communication and during standby. While the bias current is controlled by changing the resistance value of the current limiting resistor 19, the wireless IC card of this embodiment sets the resistance values of both the terminating resistor 14 and the current limiting resistor 19 during communication. It is changed by a signal from the control circuit 15 during standby. From the antenna 11 as a basic operation, the input signal passes through the integer case circuit 12,
It is detected by the detection diode 13. At this time, the voltage across the detection diode 13 is derived as a radio wave output 17 via the terminating resistor 14. On the other hand, the bias current to the diode 13 flows from the bias source 18 through the current limiting resistor 19, but passes through the high impedance line 20 to eliminate the influence on the high frequency. The terminating resistance to the diode and the bias current are changed during standby and during communication. For the same reason as in the embodiments shown in FIGS. 1 and 2, by performing this simultaneously, it is possible to improve the transmission speed and sensitivity during communication, and to improve the sensitivity with low power consumption during standby.

[0013]

According to the invention described in claim 1 , the bias is provided.
The current value of the current circuit is made small or zero during standby and communication
Achieves low power consumption during standby because it is sometimes large
Therefore, the sensitivity can be improved during communication. Claim
According to the invention of Item 2, the resistance value of the load resistance is
Since it is set to a large value and set to a small value during communication,
It can improve the sensitivity and increase the transmission speed during communication.
You can get it. According to the invention of claim 3,
The current value of the ass current circuit is made small or zero during standby,
Increase the value during communication and wait for the resistance value of the load resistance.
Sometimes it is big and when communicating it is small, so when waiting
Can achieve low power consumption and improved sensitivity, and is suitable for sensitivity during communication.
It is possible to realize higher transmission speed and higher transmission speed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a wireless IC card showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a wireless IC card showing another embodiment of the present invention.

FIG. 3 is a circuit diagram of a wireless IC card showing still another embodiment of the present invention.

FIG. 4 is a perspective view showing an outline of a wireless IC card system in which the present invention is implemented.

FIG. 5 is a graph showing a relationship between a diode DC bias and a demodulation voltage in the wireless IC card of the embodiment.

FIG. 6 is a graph showing the relationship between the terminal resistance and the demodulation voltage of the wireless IC card of the example.

FIG. 7 is a graph showing a relationship between a signal wave frequency and a detection output signal wave amplitude of the wireless IC card of the example.

[Explanation of symbols]

13 Detection diode 14 Terminator 15 Control circuit 19 Current limiting resistor

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G06K 19/00-19/18 G06K 17/00 H04B 5/02

Claims (3)

(57) [Claims] 1. An antenna, a detection element for detecting a radio wave received by the antenna, a bias current circuit for supplying a bias current to the detection element, and a load resistance for deriving a detection output of the detection element. In a wireless IC card including a circuit having the bias current circuit,
A wireless IC card characterized by having a means of setting it to zero and enlarging it at the time of communication . 2. An antenna, a detection element for detecting a radio wave received by the antenna, a bias current circuit for supplying a bias current to the detection element, and a load resistance for deriving a detection output of the detection element. In a wireless IC card including a circuit having the load resistance, the resistance value of the load resistance is increased during standby and during communication.
A wireless IC card having means for reducing the size . 3. An antenna, a detection element for detecting a radio wave received by the antenna, a bias current circuit for supplying a bias current to the detection element, and a load resistance for deriving a detection output of the detection element. In a wireless IC card including a circuit having the bias current circuit,
It is set to zero, and it is increased during communication, and the resistance of the load resistance is
A wireless IC card comprising means for increasing the resistance value during standby and decreasing it during communication .