JPH075707Y2 - Input protection circuit device for signal receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an input protection circuit device for a signal receiver such as a wireless receiver.

[Prior Art] FIG. 3 is a block diagram of an input protection circuit for a wireless receiver which is a first conventional example. In FIG. 3, the signal received by the antenna 1 is input to the common side of the switch 2a. The a side of the switch 2a is connected to the a side of the switch 2b,
On the other hand, the b side of the switch 2a is connected to the b side of the switch 2b via an attenuator 3 having an attenuation amount of 20 dB, for example. Further, the common side of the switch 2b is the high frequency amplifier 4 of the radio receiver.
Connected to the input terminal of. Where switches 2a and 2b
Are switched to the a side or the b side in conjunction with each other.

In the input protection circuit of the first conventional example configured as described above, when the antenna 1 is receiving a signal of a predetermined level that is less than or equal to the maximum input level that this receiver can receive, the switches 2a and 2b are turned on. Switch to side a, antenna 1
The signal received in 1 is input to the high frequency amplifier 4 of the receiver and received. On the other hand, when a level exceeding the maximum input level (hereinafter referred to as an excessive input level) is input to the antenna 1 during reception of the signal of the predetermined level and two signal interference may occur, the switches 2a and 2b are turned on. After switching to the b side, the predetermined signal received by the antenna 1 and the interference signal having an excessive input level are attenuated by the attenuator 3 and then output to the high frequency amplifier 4 to prevent the two signal interference. It is possible to prevent the high-frequency amplifier 4 from being damaged by a signal having an excessive input level.

FIG. 4 is a block diagram of an input protection circuit for a second conventional wireless receiver. In FIG. 4, the signal received by the antenna 1 is output to the high-frequency amplifier 4 via the connection point 10 of the input protection circuit composed of, for example, six diodes D1 to D6. Connection point 10 is a diode circuit in which three diodes D1 to D3 are cascaded in the same direction.
It is connected to ground via 21 and is connected to ground via a diode circuit 22 in which three diodes D4 to D6 are cascaded in the same direction. Here, the connection point 10 is connected to the cathode of the diode D1 and the anode of the diode D4.

In the input protection circuit of the second conventional example configured as described above, when the antenna 1 is receiving a signal of a predetermined level or less which is the maximum input level receivable by the receiver, the signal is protected by the input protection circuit. The signal can be input to the high frequency amplifier 4 of the receiver through the circuit and can be received by the receiver, while a signal having an excessive input level can be received by the antenna 1.
Input to the positive excess input level voltage is terminated by the diode circuit 22 and the negative excess input level voltage is terminated by the diode circuit 21, thereby terminating the excessive input level signal. It is possible to prevent the signal of the excessive input level from being input to the high frequency amplifier 4, and to prevent the destruction of the high frequency amplifier 4 due to the excessive input level.

FIG. 5 is a block diagram of an input protection circuit for a wireless receiver which is a third conventional example. In FIG. 5, this input protection circuit includes diodes D21, D22 and a constant voltage diode Dz.
It is provided with two diode series circuits in which 1, Dz2 are connected in series in opposite directions, and two NPN type transistors Q1 and Q2. The output terminal of the antenna 1 is connected to the base of the transistor Q1 via the diode series circuit, and is also connected to the collector of the transistor Q1 and the emitter of the transistor Q2. The base of the transistor Q2 is connected to ground via another diode series circuit described above.
The emitter of the transistor Q1 and the collector of the transistor Q2 are connected to the ground. Further, the output terminal of the antenna 1 is connected to the high frequency amplifier 4.

In the input protection circuit of the third conventional example configured as described above, when the antenna 1 is receiving a signal of a predetermined level which is lower than the maximum input level receivable by this receiver, the signal is protected by the input protection circuit. The signal can be input to the high frequency amplifier 4 of the receiver through the circuit and can be received by the receiver, while a signal having an excessive input level can be received by the antenna 1.
Input to the diode, the diode series circuit composed of the diodes D21 and Dz1 becomes conductive due to the voltage of the positive excessive input level, and at this time, the transistor Q1 turns on, while the voltage of the negative excessive input level causes the diode D22 to rise. And the diode series circuit composed of Dz2 become conductive, and at this time, the transistor Q2 is turned on.
As a result, the output terminal of the antenna 1 is terminated, the signal of the excessive input can be terminated, the signal of the excessive input level is prevented from being input to the high frequency amplifier 4, and the high frequency amplifier 4 based on the excessive input level is prevented. Can be prevented from being destroyed.

[Problems to be Solved by the Invention] However, in the above-described first conventional example, when the signal of the excessive input level is input, the operator interlocks the switches 2a and 2b in advance with each other to the B side. When the signal of the excessive input level is abruptly input, the switches 2a and 2b cannot be switched to the b side, and the high frequency amplifier 4 cannot be protected, which may lead to destruction. There was a problem.

Further, in the above-mentioned second and third conventional examples, for a signal having an instantaneous excessive input level, the signal is terminated,
The high frequency amplifier 4 can be protected, but when a signal having a steady excessive input level that is continuously input for a relatively long time is input to the antenna 1, the power consumed by the diode and the transistor is There is a problem that the diode or the transistor may be destroyed by exceeding a predetermined maximum power of the diode or the transistor. Further, if a diode or transistor that can withstand this electric power is selected, the diode or transistor becomes expensive.

The object of the present invention is to solve the above-mentioned problems, and even if a signal of an excessive input level is input, the elements of the protection circuit are not destroyed and the signal of, for example, a high-frequency amplifier 4 connected to the subsequent stage of the protection circuit. An object of the present invention is to provide an input protection circuit device for a signal receiver capable of protecting the input stage circuit of the receiver.

[Means for Solving Problems] An input protection circuit device for a signal receiver according to the present invention comprises:
An input protection circuit device for a signal receiver for receiving an input signal, the attenuator for attenuating the signal by a predetermined attenuation amount and outputting the signal to the signal receiver, and the attenuator connected in parallel with the attenuator. A thermal reed switch that is turned on from being turned on by heating and a thermal reed switch that is provided close to the thermal reed switch, terminates the signal and generates heat when the signal that exceeds a predetermined level is input, and the thermal reed switch. And a diode means for heating and holding the thermal reed switch in an off state.

[Operation] In the input protection circuit device configured as described above, when the signal that does not exceed the predetermined level is input, the thermal reed switch is in the ON state, so the signal is attenuated by the attenuator. Without being output to the signal receiver.

On the other hand, when the signal above the specified level is input,
When the thermal reed switch connected in parallel with the attenuator is heated, the thermal reed switch is turned from an on state to an off state, and the attenuator attenuates the signal by a predetermined attenuation amount and then outputs the signal to the signal receiver. However, the diode means terminates the signal and generates heat to heat the thermal reed switch and hold it in the off state. Therefore, even if a signal having an excessive input level is input, the circuit of the input stage of the signal receiver such as the high frequency amplifier 4 connected to the subsequent stage of the protection circuit can be protected without destroying the elements of the protection circuit. it can. Further, it is not necessary to use a fragile or expensive semiconductor element for the protection circuit.

[Embodiment] FIG. 1 is a block diagram of an input protection circuit for a radio receiver according to an embodiment of the present invention. In FIG. 1, the same parts as those in the above-mentioned drawings are designated by the same reference numerals. ing.

In the input protection circuit of this embodiment, (1) the output terminal of the antenna 1 is directly connected to one end of the resistor R2, and (2) the diodes D11 and D12 are connected to the thermal reed switch SW together with the resistor R2. Provided in close proximity, diode D11
And a large current flows through D12, the diode D
The feature is that 11 and D12 heat the thermal reed switch SW. Therefore, since a resistor is not connected between the output terminal of the antenna 1 and the resistor R2, the resistor has an advantage that the input signal is not attenuated even when a small signal is input.

In FIG. 1, the output terminal of the antenna 1 is a resistor R2 of, for example, 4.7 kΩ (maximum power consumption 1 W) for attenuating the signal of the above-mentioned excessive input level, and a coupling capacitor of, for example, 0.1 μF for blocking a DC component. It is connected to the input terminal of the high frequency amplifier 4 via C. In parallel with the resistor R2, the diodes D11 and D12 and the resistor R2 are always turned on.
A thermal reed switch SW, which is provided close to and is turned off by being heated, is connected. Further, the input terminal of the high frequency amplifier 4 is connected to the anode of the diode D11 and the cathode of the diode D12. The cathode of the diode D11 is, for example, +1
It is connected to the DC power supply Vcc of 2V and connected to the ground via the bypass capacitor Cb, while the diode D1
The second anode is connected to ground. Here, the diodes D11 and D12 are, for example, MI-402 type diodes manufactured by Mitsubishi Electric, and the diodes are high frequency switching diodes with a maximum power consumption of 1 W.

The thermal reed switch SW is in an on state at room temperature, and when the temperature of the thermal reed switch SW exceeds a predetermined off temperature Toff, the thermal reed switch SW is turned on.
The SW is turned off, and when the temperature of the thermal reed switch SW is lowered to be equal to or lower than the on temperature Ton lower than the off temperature Toff in the off state, the thermal reed switch SW is turned on. Therefore, it is assumed that the thermal reed switch SW has the above-described hysteresis specification with respect to temperature.

Regarding the operation of the input protection circuit configured as above,
According to the following two cases, FIG. 1 and FIG.
This will be described with reference to the timing chart of (B). Note that the heat generation amount of the diodes D11 and D12 and the heat generation amount of the resistor R2 in the following description and the timing charts of FIGS. 2A and 2B are the heat generation amount due to the current flowing through each element and the current. It includes the amount of heat that cannot be completely radiated after the flow stops.

(A) When the resistance value of the resistor R2 is relatively small and the heat generation of the resistor R2 contributes to the on / off of the thermal reed switch SW when a signal having an excessive input level flows through the resistor R2.

(B) When the resistance value of the resistor R2 is relatively large and the heat generation of the resistor R2 does not contribute to the on / off of the thermal reed switch SW even when a signal having an excessive input level flows to the resistor R2.

In both cases (a) and (b), the resistance value of the resistor R2 can be sufficiently attenuated so that the excessive input level signal received by the antenna 1 does not destroy the high frequency amplifier 4 in the subsequent stage. Set to resistance.

(A) Operation when the resistance value of the resistor R2 is relatively small (second
(Refer to the timing chart of FIG. (A)) When a signal with an excessive input level is received by the antenna 1 as shown in FIG. 2 (A), the signal passes through the thermal reed switch SW and the capacitor C and becomes high frequency. It is input to the amplifier 4. At this time, the diodes D11 and D12 generate heat,
As a result, the thermal reed switch SW is heated, and when the temperature of the thermal reed switch SW exceeds the off temperature Toff, the thermal reed switch SW is changed from the on state to the off state. As a result, the signal of the excessive input level is attenuated by the resistor R2 and output to the high frequency amplifier 4. At this time, the amount of heat generated by the diodes D11 and D12 decreases,
The temperature of the thermal reed switch SW is kept above the ON temperature as long as the signal of the excessive input level is input to the resistor R2 due to the heat generated by the signal of the excessive input level flowing to the resistor R2. SW is held off. After that, when the signal of the excessive input level is no longer received by the antenna 1, the temperature of the thermal reed switch SW is set to the on temperature To.
When the value becomes n or less, the thermal reed switch SW changes from the off state to the on state.

Therefore, in the case of the above (a), the thermal reed switch SW is switched from the ON state to the OFF state each time a signal having an excessive input level is input.

(B) Operation when the resistance value of the resistor R2 is relatively large (second
(Refer to the timing chart of FIG. 2B.) When a signal having an excessive input level is received by the antenna 1 as shown in FIG. 2B, the high frequency signal is passed through the thermal reed switch SW and the capacitor C. It is input to the amplifier 4. At this time, the diodes D11 and D12 generate heat,
As a result, the thermal reed switch SW is heated, and when the temperature of the thermal reed switch SW exceeds the off temperature Toff, the thermal reed switch SW is changed from the on state to the off state. As a result, the signal of the excessive input level is attenuated by the resistor R2 and output to the high frequency amplifier 4. At this time, the resistor R2 receives the excessive input level signal and heats the resistor R2, but as described above, the amount of heat generation is extremely small and does not contribute to the on / off of the thermal reed switch SW. Further, since the signal level input to the diodes D11 and D12 is reduced by turning off the thermal reed switch SW, the heat generation amount of the diodes D11 and D12 is reduced, which lowers the temperature of the thermal reed switch SW and turns on the above. When the temperature falls below the temperature Ton, the thermal reed switch SW changes from the off state to the on state. At this time, when a signal having an excessively high input level is still being received by the antenna 1, the signal is input to the high frequency amplifier 4 via the thermal reed switch SW and the capacitor C as described above, and at this time, the diode D11 is supplied. And D12 generate heat,
As a result, the thermal reed switch SW is heated, and when the temperature of the thermal reed switch SW exceeds the off temperature Toff, the thermal reed switch SW is changed from the on state to the off state. As a result, the signal of the excessive input level is attenuated by the resistor R2 and output to the high frequency amplifier 4.

Therefore, in the case of the above (b), when the signal of the excessive input level is received by the antenna 1,
The above-described operation of switching the thermal reed switch SW from the ON state to the OFF state and from the OFF state to the ON state is repeated. After that, when the signal of the excessive input level is not received by the antenna 1, the thermal reed switch SW is held in the ON state.

In the case of performing the operation (b) in the input protection circuit of FIG. 1, when the signal of the excessive input level is continuously input, the thermal reed switch SW repeatedly turns on and off. Even if a signal having an excessive input level is input, the thermal reed switch SW is turned off for a short time, and the signal is output to the high frequency amplifier 4 side via the capacitor C. However, the power of the signal having the excessive input level only for a short time can be absorbed by the diodes D11 and D12 as in the conventional example. Therefore, by operating as described above, it is possible to prevent the signal of the excessive input level from being input to the high frequency amplifier 4 and prevent the destruction of the high frequency amplifier 4 due to the signal of the excessive input level.

In the above cases (a) and (b), the diodes D11 and D12 generate heat and receive the thermal reed switch when a signal of a predetermined level below the excessive input level is received.
The amount of heat heated to the SW is the thermal reed switch SW
Temperature does not exceed the off temperature Toff, the thermal reed switch SW remains in the on state, and the signal is output to the high frequency amplifier 4 via the thermal reed switch SW and the capacitor C to be received.

As described above, the input protection circuit of the present invention protects the high frequency amplifier 4 connected to the subsequent stage of the protection circuit without destroying the elements of the protection circuit even when a signal having an excessive input level is input. There is an advantage that you can. Further, since the diodes D11 and D12 terminate the signal of the above-mentioned excessive input level for a short time as described above, the diodes whose rated power consumption is smaller than those of the second conventional example are used as the diodes D11 and D12. There is an advantage that you can.

Other EmbodimentsIn the above embodiments, the resistor R2 is used for attenuating a signal having an excessive input level, but the present invention is not limited to this, and various types for attenuating the signal having an excessive input level with a predetermined attenuation amount. Attenuator may be used.

In the above embodiment, in order to terminate a signal having a very large level for a short time, the diode D11
Although D12 and D12 are used, the present invention is not limited to this, and means for terminating other types of surge signals composed of transistors, Zener diodes, etc. may be used.

[Advantages of the Invention] As described in detail above, according to the present invention, a thermal reed switch that is connected in parallel with an attenuator and changes from an on state to an off state by heating, and is provided close to the thermal reed switch. , A diode means for terminating the signal when the signal exceeding a predetermined level is input and generating heat to heat the thermal reed switch to hold the thermal reed switch in the off state, so that an excessive input level Even if a signal is input, the signal can be terminated, and the thermal reed switch is kept in the OFF state to continue to attenuate the signal. Therefore,
It is possible to prevent the above-mentioned thermal reed switch from turning on when a signal with an excessive input level is input, without destroying the elements of the protection circuit as in the conventional example, and yet at a high frequency connected to the subsequent stage of the protection circuit. The advantage is that the signal receiver including the amplifier 4 can be protected.

[Brief description of drawings]

1 is a block diagram of an input protection circuit according to an embodiment of the present invention, FIGS. 2 (A) and 2 (B) are timing charts showing the operation of the circuit of FIG. 1, and FIGS. It is a block diagram of the input protection circuit which is the 1st thru | or the 3rd prior art example. 1 ... Antenna, 4 ... High-frequency amplifier, R2 ... Resistor, SW
...... Thermal reed switch, D11, D12 …… Diode.

Claims (1)

[Scope of utility model registration request] 1. An input protection circuit device for a signal receiver that receives an input signal, the attenuator outputting the signal to the signal receiver after attenuating the signal with a predetermined attenuation amount, and the attenuator. A thermal reed switch that is connected in parallel with the thermal reed switch to turn from an on state to an off state by heating, and is provided close to the thermal reed switch, terminates the signal when a signal exceeding a predetermined level is input, and heats up. An input protection circuit device for a signal receiver, comprising: diode means for heating the thermal reed switch to hold the thermal reed switch in an off state.