JP3334004B2 - Moving object identification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving object identification apparatus for reading and writing data using electromagnetic waves.

[0002]

2. Description of the Related Art Generally, a moving object identification device includes an interrogator,
The interrogator emits a radio wave of 2.45 GHz, and transmits and receives data to and from the transponder. The transponder is attached to a moving body and moves, and includes a battery as a power source for operating an internal circuit. Therefore, it is necessary to reduce battery consumption.Conventionally, a transponder is provided with a detection circuit for detecting the presence or absence of a carrier or a data signal from the interrogator, and this detection circuit is always operated, and other circuits are operated by the interrogator. The operation is performed only when the detection circuit detects a carrier or a data signal.

FIGS. 8 and 9 show an example of a conventional detection circuit. FIG. 8 shows a comparison circuit 30 which compares the detection output of a 2.45 GHz carrier component obtained by a detection circuit with a direct or threshold level. However, when the detection output is larger, a power control signal for supplying the voltage of the battery to other parts of the circuit is output. In the circuit shown in FIG. 9, the signal amplified by the amplifier 31 is rectified by the diode 32, and the comparison circuit 35 compares the signal with the threshold. Capacitor 33 and resistor 3 4 is for determining the time constant is predetermined communication between transponders 2 to maintain the power control signal until the end.

[0004]

In the above-mentioned conventional mobile unit identification apparatus, in the system for detecting the carrier when the power supply voltage is supplied from the battery of the transponder to another circuit, the detection is performed by the receiving element. Since the level of the minute DC signal is directly compared, the speed of the circuit is not so high and the power consumption of the detection circuit can be reduced.However, when operating in a wide temperature range, the offset value of the circuit fluctuates. The circuit may malfunction. In the method of detecting data, a small data signal detected by the receiving element is subjected to AC amplification, and then the level comparison is performed. Thus, although the offset fluctuation does not pose a problem, as the data transmission speed increases, the data becomes higher. In order to amplify a signal, a high-speed amplifying element is required. As a result, the power consumption of the amplifying element increases, so that even when only the detection circuit is operated, the power consumption is large and the battery life becomes a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has no danger of a circuit malfunction due to an offset or the like, and can reduce power consumption of a transponder even at a high data transmission speed. It is intended to provide a device.

A mobile object identification device according to the present invention comprises an interrogator and a transponder, and transmits and receives data between the two by electromagnetic waves, and reads and writes data from and to the transponder.
The interrogator includes means for transmitting a signal having a frequency lower than the frequency component of the data to be transmitted, at least at the beginning of the transmission data, and transmitting the signal .
A detection circuit that detects the signal, and amplifies the detected signal.
An amplifier circuit for outputting the output to a demodulation circuit;
A rectifier circuit that receives the output of the amplifier circuit and rectifies it.
A comparison circuit that compares the output of the circuit with the reference level.
The output of the rectifier circuit corresponding to the low frequency signal is
When input to the comparison circuit, the comparison result of the comparison circuit
Supply power to the other circuits of the transponder in response to
At the same time, the bias current of the amplifier circuit is controlled .

[0007] In this mobile identification device, when data is transmitted from the interrogator to the transponder, a signal having a frequency lower than the frequency component of the data to be transmitted is attached to the head of the data to be transmitted. The transponder detects the signal from the interrogator.
The signal detected by this wave detection circuit is amplified by this wave detection circuit.
The signal is amplified by the circuit and output to the demodulation circuit. In addition, this amplification
The output of the path is rectified by a rectifier circuit and input to a comparison circuit. ratio
The comparison circuit compares the output of the rectifier circuit with the reference level.
You. Rectifier circuit output corresponding to the low frequency signal
Responds to the output of this comparison circuit when
Then, power is supplied to other circuits of the transponder. Also,
In response to the output of the comparison circuit of
The current is controlled to be high bias .

[0008]

The present invention will be described in more detail with reference to the following examples. FIG. 1 is a schematic diagram showing the overall configuration of a moving object identification apparatus according to one embodiment of the present invention. The mobile object identification device comprises an interrogator 1 fixedly mounted and a transponder 2 attached to a mobile body 3. The interrogator 1 emits a 2.45 GHz radio wave and communicates with the transponder 2. Send and receive data between

The transponder 2, as shown in FIG. 2, includes a transmitting / receiving antenna 4, a detection circuit 5, a level detection circuit 6, an amplifier 7, a demodulation circuit 8, a CPU 9, a memory 10,
A first modulation circuit 11, a transmitter 12, a second modulation circuit 13, a power supply battery 14, and a switch 15 that is turned on in response to the output of the level detection circuit 6 and supplies a power supply voltage to each circuit. And

In the transponder 2, the signal transmitted from the interrogator 1 is received by the antenna 4 and then detected by the detection circuit 5 using a diode or the like. As for the detection output, the detection level is detected by the level detection circuit 6. If the detection level is equal to or higher than a predetermined level, the transponder is assumed to have entered the communication area, the switch 15 is turned on, and power is supplied from the battery 14 to other circuits. I do. The detection output of the detection circuit 5 is amplified by the other amplifier 7, then demodulated by the demodulation circuit 8, and input to the CPU 9. The CPU 9 is provided with a memory 10 such as an E ² PROM as necessary.
Write data to Further, the CPU 9 reads the data from the memory 10, modulates the data with the subcarrier from the transmitter 12 by the modulation circuit 11, and then modulates the antenna 4 by the modulation circuit 13.
The data is returned to the interrogator 1 by performing modulation by impedance matching with the data, changing the path length, or the like.

FIG. 3 is a connection diagram showing a specific example of the level detection circuit 6 constituting the transponder. The level detection circuit 6 includes an amplification circuit 16 for amplifying an AC signal, a diode 17 for rectifying an AC component, a capacitor 18 and a resistor 19 constituting a time constant circuit, and a comparison circuit 20. In the level detection circuit 6, data in which a signal of a low frequency (100 HZ to 1 KHZ) is attached to the front of the data signal from the interrogator 1 is transmitted. Signal of frequency is amplifier circuit 1
6, and is half-waved by the diode 17. Then, the output is compared by the comparison circuit 20. When the input signal level is higher than a predetermined reference level, the comparison circuit 20 outputs a detection signal, and thereby the switch 15 of the circuit in FIG. 2 is turned on. Capacitor 1
8 and the resistor 19 are provided with a time constant for maintaining power supply to other circuits by power control until the predetermined communication between the interrogator 1 and the transponder 2 is completed even after the low frequency signal disappears. Is determined. For this connection, a timer IC or the like can be used. Amplifier circuit 16
It is sufficient that only low frequency signals can be amplified, so that low power consumption signals can be used.

FIG. 4 is a block diagram showing another example of the circuit of the transponder 2 according to another embodiment of the present invention. In each of the circuits in FIG. 4, the components denoted by the same reference numerals as those in the circuit in FIG. 2 indicate the same components. The feature of this transponder 2 is that an amplifying circuit 21 and a level detecting circuit 22 different from those in FIG.
Detection signal obtained by the detection circuit 5, amplified by the amplifier circuit 21, one to the demodulation circuit 8 and the other is that it has to be input to the level detecting circuit 2 2. Level detection circuit 22
Is equal to or higher than a predetermined level, it is determined that there is data from the interrogator 1, and power is supplied to other circuits,
The bias of the amplifier circuit 21 is changed.

FIG. 5 shows the amplifier circuit 2 of the transponder 2 shown in FIG.
FIG. 3 is a connection diagram illustrating a specific circuit example of a level detection circuit 1 and a level detection circuit 22. The amplifier circuit 21 includes an amplifier 23 that changes a bias current according to an applied voltage. The level detection circuit 22
A diode 24 for rectifying the alternating current signal inputted from the amplifier 21, the capacitor 25 constitute a time constant circuit for smoothing, a resistor 26, and a comparator circuit 2 7.

In the circuit shown in FIG. 5, the signal amplified by the amplifier 23 is rectified by the diode 24, and the comparison circuit 27 makes a comparison as to whether or not the threshold is exceeded. The capacitor 25 and the resistor 26 determine the time constant for connecting the power supply and the bias switching of the amplifier 22 until the predetermined communication between the interrogator 1 and the responder 2 is completed. FIG.
Is a voltage gain-frequency characteristic (hereinafter Af characteristic) of an open loop of the amplifier 23. Amplifier 2 3, using a low bias current consumption is equal to or less than several .mu.A, A
The -f characteristic is as shown in A (L) of FIG. When used with a high bias, the A-f characteristic is improved as shown by A (H) in FIG. 6, but the current consumption is several hundred μA to several mA.

When the data transmission speed from the interrogator 1 to the transponder 2 is set at a high speed of several tens of Kbps to several hundred Kbps, the amplifier 23 responds to this, so that a high bias is applied so that high frequency amplification can be performed. Need to work with
However, in this case, if the operation is always performed at a high bias, the power consumption is large and the battery life becomes a problem. Therefore, in the standby state, the amplifier 23 is operated with a low bias. From the interrogator 1, a low-frequency signal at which the amplification factor can be sufficiently obtained even when the amplifier 23 has a low bias is added to the head of the data, and after detecting this, the amplifier 23 is set to a high bias to correspond to the original data transmission speed. The following A-f characteristic is obtained. This enables low-consumption during standby and high-speed transmission during communication.

FIG. 6 is a timing chart for explaining data transmission and level detection in each of the above embodiments. A is the transmission data from the interrogator 1 to the responder 2, B
Indicates response data from the responder 2 to the interrogator 1. A signal having a low frequency component is added to the head of the data A as described above. Although the transmission efficiency is reduced, a signal having a low frequency component may be added to the head of the data every time, or may be inserted between the head and other middle points.

FIG. 6C shows a signal at point a in FIG. In order to reduce power consumption, the amplifier 16 can obtain a sufficient amplification factor only for low frequency components. Since data usually does not include low frequency components such as Manchester codes and FM codes, when the signal of the low frequency component ends and the data section starts, the output of the amplifier 16 decreases. Discharged at a constant. Until this value becomes equal to or less than the threshold, a signal D (point b in FIG. 3) for power supply control is output for t ₁ , during which the switch 15
Is turned on, and power is supplied to other circuits in the transponder 2.
The time constant of the capacitor 18 and the resistor 19 is selected so that t ₁ is output for a longer time than the time t ₂ during which normal communication is performed.

FIG. 6E shows a signal at point c in FIG. The amplifier 23 operates at a low bias in the standby state. However, when a signal of a low frequency component that provides a sufficient amplification factor is input even in this state, the signal of E rises and exceeds the threshold of the comparison circuit 27. Therefore, the signal E (point d in FIG. 5) for power supply control and bias switching becomes high, the switch 15 is turned on, power is supplied to other circuits in the transponder, and the amplifier 23 is set to high bias. Becomes
A predetermined amplification factor can be obtained even at the time of a data signal.
When there is no more data from the interrogator 1 to the responder 2, the data is discharged with the time constant of the capacitor 25 and the resistor 26. The holding time t ₃ of the signal F determined by this time constant is selected to be longer than the time t ₄ when the next data comes.

[0019]

According to the present invention, a signal having a frequency lower than the frequency component of the original transmission rate is added at least to the head of the data signal transmitted from the interrogator at first , and this is added to the comparison circuit of the transponder. The signal corresponding to the lower frequency signal
When added, the transponder responds to the output of this comparison circuit.
Power to the other circuits of the
Since the bias current is controlled, other circuits in standby state
Power supply to the amplifier and reduce the bias current of the amplifier circuit.
After receiving the low-frequency signal,
Supply power, and also set the amplifier circuit to high bias current,
Since the pressure gain-frequency characteristics can be made wide,
Long battery life with low power consumption and high speed for communication
The effect that transmission becomes possible is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing the entire configuration of a moving object identification device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a transponder of the moving object identification device of the embodiment.

FIG. 3 is a connection diagram showing a specific circuit example of a level detection circuit of the transponder.

FIG. 4 is a block diagram showing another example of the circuit configuration of the transponder.

FIG. 5 is a connection diagram showing a specific circuit example of a level detection circuit of the transponder.

FIG. 6 is a time chart for explaining the operation of the level detection circuit shown in FIGS. 3 and 5;

FIG. 7 is a diagram illustrating frequency-voltage gain characteristics of the amplifier circuit of FIG. 5;

FIG. 8 is a connection diagram showing a specific circuit of a level detection circuit of a transponder of the conventional mobile object identification device.

FIG. 9 is a connection diagram showing a specific circuit of another level detection circuit of the transponder of the conventional moving object identification device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Interrogator 2 Transponder 16 Amplification circuit 17 Diode 18 Capacitor 19 Resistance 20 Comparison circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H03F 1/02 H03G 3/30 C H03G 3/20 G01S 13/80 3/30 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 1/59 G01S 13/75 G01S 13/76 G01S 13/79 H03F 1/00 H03F 1/02 H03G 3/20 H03G 3/30

Claims (3)

(57) [Claims] 1. A mobile object identification device comprising an interrogator and a transponder, transmitting and receiving data between them by electromagnetic waves and reading / writing data from / to the transponder. Means for transmitting a signal having a frequency lower than the frequency component of the data to be transmitted and transmitting the signal to the transponder,
Detection circuit that detects the signal of the other, and amplifies the detected signal
And an amplifier circuit for outputting the output to a demodulation circuit;
A rectifier circuit for receiving and rectifying the output of the amplifier circuit;
A comparison circuit that compares the output of the rectifier circuit with the reference level
An output of a rectifier circuit corresponding to the low-frequency signal
Is input to the comparison circuit, the comparison result of the comparison circuit is
Power to each of the other circuits of the transponder in response to the
Control the bias current of the amplifier circuit.
A moving object identification device, characterized in that: 2. An output between the rectifier circuit and an input of a comparison circuit.
A time constant circuit for smoothing the output of the rectifier circuit,
The time constant circuit is shorter than the communication time between the interrogator and the transponder.
Time constant so that the level holding time at
2. The mobile object identification device according to claim 1, wherein: 3. The circuit between an output of the rectifier circuit and an input of a comparison circuit.
A time constant circuit for smoothing the output of the rectifier circuit,
The time constant of the time constant circuit is
Level retention time is longer than data and data time interval
2. The mobile object identification device according to claim 1 , wherein the mobile object identification device is set so as to be: