JPH0775327B2 - Induction radio band transceiver circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a transmission / reception circuit for an inductive radio band using a ferrite bar antenna, and in particular, it uses a toroidal core in a transmission / reception branch section to improve performance and simplify the configuration. It is intended to try.

[Conventional technology]

Since the transmission / reception circuit of the induction radio band (for example, 300KHz) that uses the ferrite bar antenna as the transmission / reception antenna is magnetic coupling, if you try to increase the transmission efficiency by class C amplification, interference with other equipment will occur due to spurious. Easy to do.

Fig. 2 shows an example of this type of transmitter / receiver circuit. 1 is a ferrite bar antenna for both transmission and reception, 2 is a power supply line, 3 is a housing containing the transmission / reception circuit, and Tr ₁ is a class C amplification transistor at the final stage of the transmission circuit. , + B are power supplies. The power supply line 2 is a 3-wire type,
The pair of l ₁ and l ₂ transmits, and the pair of l ₂ and l ₃ receives. A diode switch circuit for preventing the sneak of the transmission signal is provided on the path for branching the reception signal to the reception circuit, but it is omitted in the drawing.

[Problems to be solved by the invention]

In the circuit system shown in FIG. 2, since l ₁ and l ₂ of the power supply line ₂ are unbalanced, spurious emission during transmission becomes a problem. Further, since + B is supplied to the power supply line 2, there is a risk of short-circuiting between + B and the ground due to the disconnection of the power supply line 2 when mounted on a vehicle. Further, since the power feeding line 2 is a three-wire type, there is a problem that the wire diameter becomes large.

The present invention is intended to solve the above-mentioned problems by using a toroidal core in a transmitting / receiving branch portion.

[Means for solving problems]

The present invention, in a transmission / reception circuit of an induction radio band that also serves as a transmission / reception of a ferrite bar antenna, uses a toroidal core in a transmission / reception branch portion, and connects the core to each of the transmission circuit and the reception circuit of the transmission / reception circuit, A two-wire type feeder line is connected between the core and the ferrite bar antenna.

[Action]

Since the magnetic core of the toroidal core is closed, there is little leakage flux, and spurious effects are less likely to affect other devices. Further, since a balanced state can be achieved by connecting the core and the ferrite bar antenna with a two-wire type feed line, spurious emission can be mitigated even if the transmission efficiency is increased by class C amplification.
Also, since the power supply line is a two-wire type, the wire diameter can be reduced, and since it is not connected to the power supply, there is no fear of a short circuit accident.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention, 4 is a toroidal core, C _{1 to} C ₃ are capacitances, L _{1 to} L ₈ are inductances (L _{5 to} L ₈ are high frequency chokes), D ₁ , D ₂ is a switching diode, and Tr ₂ is a diode switch control transistor. The transmission circuit is magnetically coupled to the toroidal core 4 with the inductance L ₁ , and the capacitance C ₁ constitutes a parallel resonance circuit of the transmission frequency f ₁ together with the inductance L ₁ . The receiving circuit is magnetically coupled to the toroidal core 4 by the inductor L ₃ , and the capacitance C ₃ is the inductance L ₃
Together with this, a parallel resonant circuit having a reception frequency f ₂ is formed. on the other hand,
The power supply line 2 is a two-wire type and is magnetically coupled to the toroidal core 4 by the inductance L ₄ . The ferrite bar antenna 1 has its own inductance L ₂ and capacitance C _2, and a resonance circuit in which the inductance L ₄ is added to this is shared by the transmission and reception frequencies f ₁ and f ₂ .

The operation will be described. During transmission, the output of the transistor Tr ₁ (frequency f ₁ ) is radiated from the antenna 1 through the resonance circuit L ₁ C ₁ → toroidal core 4 → feed line 2. This frequency f ₁
Since the transmission output of is blocked by the resonance circuit L ₃ C ₃ of frequency f ₂ , it is prevented from sneaking into the reception circuit, but the control signal CTL is further set to L (low) to turn off the transistor Tr _2. This keeps the diodes D ₁ and D ₂ in a cut-off state and prevents them from wrapping around twice.

At the time of reception, the control signal CTL is set to H (high) to turn on the transistor Tr ₂ , and a bias current is supplied from + B to the diodes D ₁ and D ₂ . As a result, the diodes D ₁ and D ₂ are turned on, so that the received signal of the frequency f ₂ induced in the antenna 1 is fed line 2 → toroidal core 4 → resonance circuit L ₃ C ₃ → diode.
Input to the receiving circuit through D ₁ and D ₂ . At this time, frequency f ₁
The resonance circuit L ₁ C ₁ prevents the reception signal from sneaking into the transmission circuit side.

Note that the switch section formed by the diodes D ₁ and D ₂ may be a relay if high speed is not required for transmission / reception switching.

〔The invention's effect〕

As described above, according to the present invention, in a transmission / reception circuit of an induction radio band that also uses a ferrite bar antenna for transmission / reception, by using a toroidal core in a transmission / reception branch portion, a power supply line to the antenna is a two-wire balanced type. Therefore, it is possible to suppress spurious emission at the time of transmission and to simplify the configuration. In addition, there is no risk of accidents in the power supply system due to short circuits in the power supply line.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional transmission / reception circuit. In the figure, 1 is a ferrite bar antenna, 2 is a feeder line, and 4 is a toroidal antenna.

Claims (1)

[Claims] 1. In a transmission / reception circuit of an induction radio band for which a ferrite bar antenna is also used for transmission / reception, a toroidal core is used in a transmission / reception branch portion, and the core is connected to each of a transmission circuit and a reception circuit of the transmission / reception circuit. A transmission / reception circuit for an induction radio band, characterized in that the core and the ferrite bar antenna are connected by a two-wire power supply line.