JPH04298127A - Transmission reception circuit for induction radio equipment - Google Patents

Abstract

PURPOSE:To improve the reception sensitivity by setting a time constant to that offering a slow response when a positive half cycle is rectified by a voltage doubler rectifier circuit and setting a time constant to that offering a fast response when a negative half cycle is rectified by the voltage doubler rectifier circuit so as to bias a detection voltage with an envelope voltage of a reception signal. CONSTITUTION:A time constant of one detection circuit comprising a diode 33, a resistor 35 and a capacitor 37 connecting to a transmission coil 31 is set slow and a time constant of the other detection circuit comprising a diode 34, a resistor 36 and a capacitor 38 is set fast so as to have a sufficient band with respect to a band rate of an ASK signal. A nearly mean value of a half wave rectifier signal of the signal received by the transmission reception coil 31 is outputted from the one detection circuit and envelope detection signal of the ASK signal is outputted from the other detection circuit. The DC component from the ASK envelope detection signal is cut off by the capacitor 40 and the result is inputted to a CMOS buffer 42 and the CMOS buffer 42 is biased by using the mean value voltage via a resistor 39 to allow even a small level signal to exceed a threshold level thereby improving the reception sensitivity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitting/receiving circuit for an induction radio that performs communication using induced electromotive force generated in a coil by an alternating magnetic field.

0002

[Prior Art] Among devices that perform communication using induced electromotive force, there is a device that requires low power consumption due to battery operation, etc., as disclosed in U.S. Patent No. 3,299,424. . This allows a master station and a slave station to communicate by guided radio, and is effective in reducing the power consumption of slave stations, and is currently used in data carrier systems and the like.

FIG. 4 shows a transmitting and receiving circuit of a slave station. this is,
The ASK signal received by the transmitting/receiving coil 1 is detected by a detection diode 2, and then shaped by a CMOS buffer 6 into digital data, which is input to a microcomputer 8. At the time of transmission, data from the microcomputer 8 is transmitted by changing the load condition of the transmitting/receiving coil 1 by substantially short-circuiting/opening the transmitting/receiving coil 1 using the transmitting transistor 7. By detecting this on the master station side, data is transmitted from the slave station to the master station. 3 and 4 are capacitors, and 5 is a resistor.

0004

[Problems to be Solved by the Invention] However, in the above method, the transmitting/receiving coil 1 must receive a signal sufficient for the signal detected by the detection diode 2 to exceed the threshold voltage of the CMOS buffer 6, resulting in poor sensitivity. Ta. As shown in Fig. 5, the method of improving the sensitivity is to separate the coil from the coil side via a capacitor 9, and connect it to the coil side using resistors 10 and 11.
How to bias the MOS buffer 6, two diodes 2A, 2B, two resistors 5A, 5B as shown in Figure 6
It is also possible to double the voltage and rectify the electromotive force generated in the coil 1 using the two capacitors 4A and 4B, but in the biasing method, a through current flows to the CMOS buffer 6, which increases current consumption and reduces power consumption. cannot be converted into Further, when voltage doubler rectification is used, while the receiving sensitivity is improved, there is a problem in that it becomes difficult to connect the transmitting transistor 7. That is, even if the drain is connected to a in FIG. 6, the transmitting/receiving antenna 1 cannot be effectively short-circuited, and if connected to b, a reverse voltage will be applied between the drain and the source. Another problem is the following. When a slave station moves, communication between the master station and the slave station takes place when the slave station enters the master station's communication area, but since the slave station moves, it does not remain in the master station's communication area until communication is completed. There is a risk. In order to prevent this, it is desirable that the communication area be designed to be a little narrow at the start of communication, and then expand a little once communication has started, but conventionally there has been no easy way to achieve this.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a transmitting/receiving circuit for an inductive radio device which solves the above-mentioned problems.

[0006]

Means for Solving the Problems In order to achieve the above object, the present invention provides a transmitting/receiving circuit for an induction radio that performs communication by utilizing the fact that an alternating current change in a magnetic field generates an induced electromotive force in a receiving coil. One side of the receiving coil is grounded, and the other side of the receiving coil is connected to a voltage doubler rectifier circuit, and the time constant of the circuit that rectifies the positive half cycle of the voltage doubler rectifier circuit is a signal received by the receiving coil. The time constant of the circuit that rectifies the negative half cycle of the voltage doubler rectifier circuit is set to be slow compared to the baud rate of the circuit, and the time constant of the circuit that rectifies the negative half cycle of the voltage doubler rectifier circuit is set to be fast enough to pass the baud rate, and the time constant of the circuit that rectifies the negative half cycle of the voltage doubler rectifier circuit is set to be fast enough to pass the baud rate. The method is characterized in that the circuit output for rectifying the negative half cycle is biased by the output voltage of the circuit.

[0007]

According to the present invention, the detection voltage of the received signal is biased by the envelope voltage of the received signal, thereby improving the receiving sensitivity. Further, since no bias is generated when there is no received signal, low power consumption is maintained.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a transmitting/receiving circuit according to the present invention. In this circuit, the diode 3 connected to the transmitter/receiver coil 31
3, the time constant of one of the detection circuits consisting of a resistor 35 and a capacitor 37 is set to be slow, and as shown in the time chart of FIG. Output voltage. 32 is a capacitor, and 43 is a microcomputer.

On the other hand, the time constant of the other detection circuit consisting of the diode 34, resistor 36, and capacitor 38 is designed to be fast enough to have a bandwidth sufficient for the baud rate of the ASK signal. Output. Here, if the direct current component is cut from this signal by the capacitor 40 and input to the CMOS buffer 42, and if the CMOS buffer 42 is biased via the resistor 39 with the previous average value voltage, the CMOS buffer 42 can be used even if the signal is smaller.
can exceed the threshold value of , and the sensitivity can be improved. In this circuit, if there is no signal in the transmitter/receiver coil 31, no bias is applied, so sensitivity can be improved without increasing current consumption during standby. (connection between

Next, FIG. 3 shows an embodiment of a transmitting/receiving circuit that expands the communication area when it enters an operating state. A diode 45 is inserted in series with the power supply 44 of the slave station. When the slave station is not in a communication state, the microcomputer 43 etc. are in a stopped state, so almost no current flows from the power supply 44 of the slave station, so almost no forward voltage drop occurs in the diode 45, and the CMOS buffer A voltage of Vcc=V (voltage of power supply 44) is applied to Vcc of 42. Here, since the threshold voltage of the CMOS buffer 42 is approximately Vcc/2, the detected voltage must reach V/2 in order for the slave station to enter the operating state. here,
If the received voltage now exceeds V/2 and the slave station enters the operating state, a current necessary for operation flows from the power supply 44, and a forward voltage drop occurs in the diode 45. If this voltage is ΔV, the voltage applied to Vcc is V-ΔV,
As a result, the threshold voltage of the CMOS buffer 42 is 1/
2(V-ΔV) and ΔV/2. As a result, the signal level that must be received by the transmitting/receiving coil 31 can be lower than when the threshold value is required to be V/2, and the communication area can be expanded.

0012

[Effects of the Invention] According to the present invention, the receiving sensitivity can be improved without increasing the current consumption when there is no communication state, that is, the stopped state, and there is no problem in connecting the transmitting transistor. can be realized. Furthermore, since the communication area expands slightly after communication starts, it is possible to prevent the user from leaving the communication area easily even when moving, for example, once communication has started, and it is possible to improve the reliability of communication.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing signal waveforms of various parts in the same embodiment.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional example.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is a circuit diagram of a conventional example.

[Explanation of symbols]

31 Transmitting/receiving coil 33, 34 Diode 40 Capacitor 42 CMOS buffer

Claims (2)

[Claims] 1. A transmitting/receiving circuit for an induction radio that performs communication by utilizing the fact that an alternating current change in a magnetic field generates an induced electromotive force in a receiving coil, wherein one side of the receiving coil is grounded;
A voltage doubler rectifier circuit is connected to the other side of the receiving coil, and a time constant of a circuit for rectifying a positive half cycle of the voltage doubler rectifier circuit is set to be slower than a baud rate of a signal received by the receiving coil. The time constant of the circuit that rectifies the negative half cycle of the voltage doubler rectifier circuit is set to be fast enough to pass the baud rate, and the output voltage of the circuit that rectifies the positive half cycle is used to A transmitting/receiving circuit for an induction radio, characterized by biasing the output of a circuit that rectifies a half cycle. 2. A CMOS buffer is used as a data shaper for the output of the circuit that rectifies the negative half cycle, a diode is inserted in series with a power supply circuit including at least the CMOS buffer, and when the receiving circuit is in operation, the diode is connected to the CMOS buffer. 2. The transmitting/receiving circuit for an induction radio according to claim 1, wherein the power supply voltage of the CMOS buffer is lowered by a forward voltage drop caused by the flow of current.