JPH0522984Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial field of application> The present invention relates to a high frequency attenuator, in particular, it is equipped with a changeover switch, and when the changeover switch is not turned on, the attenuation is 0, and when the changeover switch is turned on, the attenuation amount is 0. , relates to a high frequency attenuator equipped with a changeover switch that provides a predetermined amount of attenuation.

<Prior Art> Conventionally, a high-frequency attenuator equipped with a changeover switch as described above is provided, for example, on the input side of a booster, and when the level of the input signal is lower than a predetermined level, the level is changed. Some devices allow the signal to pass through as is, and when the signal is large, operate a switch to attenuate the input signal by a predetermined attenuation amount. An example of such an attenuator is shown in FIG. In the same figure, 2 is an interlocking changeover switch, which has contacts 4a and 4b, and the contact 4a is the contact 6.
a, the contact 4b is switched to the contact 6b
When the contact 4a is switched to the contact 8a, the contact 4b is switched to the contact 8b. For example, a slide switch is used as the interlocking changeover switch 2. Contacts 6a and 6b of this interlocking changeover switch 2 are directly connected, and a π-type resistance attenuation circuit 10 is provided between contacts 8a and 8b. Note that the values of each of the resistors 10a to 10c constituting this resistance attenuation circuit 10 are set according to the required amount of attenuation.

In this high frequency attenuator, when the level of the signal supplied to the contact 4a is lower than a predetermined level, the contact 4a is switched to the contact 6a side, and the contact 4b is switched to the contact 6b side, and the signal is Contact 4a, contacts 6a, 6b, contact 4b
Through the booster high frequency amplification circuit (not shown)
supply to. That is, no attenuation takes place. Also,
When the level of the signal supplied to the contact 4a is higher than a predetermined level, the contact 4a is switched to the contact 8a side, and the contact 4b is switched to the contact 8b side, and the signal is passed through the contact 4a and the contact 8a. supplying it to the attenuation circuit 10 and attenuating it to a predetermined amount of attenuation;
It is supplied to the high frequency amplification circuit via the contact point 8b and the contactor 4b. That is, in this high frequency attenuator, the amount of attenuation can be switched in two stages.

<Problems to be Solved by the Invention> Such a high frequency attenuator has stray capacitance between the contacts 8a and 8b of the changeover switch 2 and between the contacts 6a and 6b. In FIG. 6, contacts 8a and 8b
The stray capacitance between them is indicated by 12. Contacts 6a, 6b
The stray capacitance between the contacts 6a and 6b can be ignored because they are directly connected, but the stray capacitance between the contacts 8a and 6b can be ignored.
Since the stray capacitance between 8b and 8b is connected in parallel to the resistor 10b of the resistance attenuation circuit 10, it affects the amount of attenuation. When the frequency band of the signal supplied to the contactor 4a is low, the reactance of stray capacitance is small, so the effect can be ignored. However, when the frequency band exceeds the UHF band, the reactance becomes large, so the effect is negligible. This is particularly noticeable when the amount of attenuation is increased. FIG. 7 shows the attenuation vs. frequency characteristic when the contacts 4a and 4b of the high-frequency attenuator shown in FIG. 6 are connected to the contacts 8a and 8b, respectively, and the target attenuation is -
Resistance attenuation circuit 10 so that it is 10dB to -20dB
If the design is designed so that the attenuation is -25 dB, the obtained attenuation will be approximately the same as the frequency increases. However, if the design is designed so that the attenuation is -25 dB, the target attenuation (- 25dB)
The amount of attenuation becomes smaller. That is, when the target attenuation amount is increased, the value of the resistor 10b becomes larger, so that the stray capacitance 12 becomes larger than the value of the resistor 10b.
The influence of reactance becomes large, and the amount of attenuation actually obtained becomes smaller than the target amount of attenuation.

The present invention has been developed in view of the above problems, and provides a high frequency attenuator in which the amount of attenuation is not affected by stray capacitance between contacts even when used in a relatively high frequency band. The purpose is to

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a high-frequency attenuator equipped with a changeover switch having at least the above-described configuration, in which a π-type or T-type attenuation circuit is connected. An inductor having an inductance that cancels out the stray capacitance in the used frequency band is provided between the contacts where the stray capacitance is generated. In this case, the inductor may form part of the component of the π-type attenuation circuit. Furthermore, the changeover switch may be modified so that it can be switched to another attenuation circuit having a smaller attenuation amount than the above-mentioned attenuation circuit.

<Operation> In the high frequency attenuator according to the present invention, the inductance of the inductor is set to a value that substantially cancels stray capacitance in the frequency band used. Therefore, when each contact is switched to the attenuation circuit side, the influence of stray capacitance does not appear, and attenuation amount almost as designed can be obtained.

<Example> A first example is shown in FIGS. 1 and 2. 1st
In the figure, 2 is a changeover switch, 4a and 4b are contacts, and 6a, 6b, 8a, and 8b are contacts, and since these are constructed in the same way as the conventional one shown in FIG. 6, a detailed explanation will be given. Omitted. Contacts 8a, 8
A π-type resistance attenuation circuit 10 is provided between B and B, as in the conventional one, and the values of the resistors 10a, 10b, and 10c constituting this resistance attenuation circuit 10 are determined by the influence of stray capacitance. The attenuation amount is -
It is selected to be 25dB.

An inductor 14 is provided between the contacts 8a and 8b where the stray capacitance 12 exists. As this inductor 14, for example, 420MHz to 820MHz
When using this high frequency attenuator in a frequency band of It can be used as follows.

In the high frequency attenuator configured in this way,
The contact 4a is used as a contact 8a, and the contact 4b is used as a contact 8b.
FIG. 2 shows the relationship between the attenuation amount and the frequency when the switch is switched to . As is clear from Figure 2, 470MHz
Then the attenuation is 25.30dB, and at 770MHz
25.20dB, almost no change, and,
At other frequencies during this period, the amount of attenuation is also approximately constant. This is because the inductor 14 is provided in parallel with the stray capacitance 12 to reduce the combined reactance of both, so that the stray capacitance 12 has almost no influence on the amount of attenuation of the resistive attenuation circuit 10.

Note that if the frequency band to be used can be very narrowly limited, the inductance of the inductor 14 can be set so that the stray capacitance 12 and the inductance of the inductor 14 resonate in parallel in that specific frequency band. As shown in FIG. 3, the amount of attenuation can be further increased in that specific frequency band. In addition, in Figure 3, 670MHz is selected as the resonant frequency, and at this frequency, the amount of attenuation is
It becomes 38.70dB.

A second embodiment is shown in FIGS. 4 and 5. In this embodiment, two attenuation circuits 16 and 18 are provided, and the changeover switch 2a has two states: one where the attenuation circuit 16 is connected between the contacts 4a and 4b, and the other where the damping circuit 16 is connected between the contacts 4a and 4b.
A damping circuit 16 is connected between the contacts 20a and 20b so that the damping circuit 18 can be switched between a state in which the contacts 4b are directly connected and a state in which the damping circuit 18 is connected between the contacts 4a and 4b.
are connected, the contacts 22a and 22b are directly connected, and the attenuation circuit 18 is connected between the contacts 24a and 24b. That is, it is configured such that the amount of attenuation can be changed in three stages. Of course, when the contact 4a is connected to the contact 20a, the contact 4b is connected to the contact 20.
b, and when the contact 4a is connected to the contact 22a, the contact 4b is connected to the contact 22b, and when the contact 4a is connected to the contact 24a, the contact 4b is connected to the contact 24b. Ru.

Stray capacitance exists between the contacts 20a and 20b, between the contacts 22a and 22b, and between the contacts 24a and 24b. However, since the contacts 22a and 22b are directly connected, there is no effect, and the contacts 22a and 22b are directly connected.
Even if there is stray capacitance between a and 24b, there is an attenuation that has almost no effect on the attenuation, for example -
Since the attenuation circuit 18 designed to provide attenuation of 20 dB to -10 dB is connected, the influence of stray capacitance can be ignored. The attenuation circuit 16 connected between the contacts 20a and 20b has an attenuation amount of -25 dB, and the influence of stray capacitance cannot be ignored. The stray capacitance between contacts 20a and 20b is denoted by 1
Shown as 2a. In the first embodiment, the attenuation circuit is a resistive attenuation circuit and an inductor is connected in parallel with the stray capacitance in order to cancel out the stray capacitance.
In the embodiment, some of the components of the π-type attenuation circuit,
That is, the contact 20 where the stray capacitance 12a exists
By using the inductor 16a as a component of the π-type attenuation circuit connected between a and 20b, the attenuation circuit 16
, and cancels the stray capacitance 12a. Note that this inductor 16a is the first inductor 16a.
Almost the same inductor 14 used in the embodiment can be used.

FIG. 5 shows a contactor 4a in the second embodiment.
is connected to the contact 20a, and the contact 4b is connected to the contact 20b.
This figure shows the relationship between the amount of attenuation and the frequency in a state where the contacts 4a and 4b are connected to each other, that is, when the attenuation circuit 16 is connected between the contacts 4a and 4b. It is clear from this figure that the attenuation amount is 25.00 dB at frequencies of 470 MHz and 770 MHz, and that the attenuation amount is approximately 25.00 dB between these frequencies as well. This is because the inductance 16a is connected in parallel with the stray capacitance 12a, and the combined inductance of both is set to a size that does not affect the amount of attenuation.

In each of the above embodiments, a π-type resistance attenuation circuit is used as the attenuation circuit, but a T-type attenuation circuit may also be used. In addition, in the first embodiment, the attenuation amount was switched to 0 dB state and the attenuation amount -25 dB state, but the changeover switch is the same as that shown in the second embodiment, and the state is changed from -10 dB to -25 dB. An attenuation circuit with an attenuation of 20 dB is provided, and the attenuation is 0 dB.
Attenuation is -10dB to -20dB and attenuation is -10dB to -20dB.
It may be possible to switch to a 25 dB state.

<Effects of the invention> As described above, according to the high-frequency attenuator of the invention as claimed in claim (1), the stray capacitance between the contacts of the changeover switch used therein can be canceled by the inductor. Even if the operating frequency becomes higher, it is possible to maintain an attenuation amount that is substantially close to a predetermined attenuation amount.

Further, according to the high frequency attenuator described in claim (2), the same effect as that described in claim (1) can be obtained, and the inductor for canceling stray capacitance is
Since it forms part of the component of the π-type attenuation circuit, the circuit configuration can be simplified.

Furthermore, according to the high-frequency attenuator described in claim (3), the same effects as those described in claim (1) or (2) can be obtained, and the amount of attenuation can be switched in three stages.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a first embodiment of a high frequency attenuator according to the present invention, Fig. 2 is a diagram of attenuation versus frequency characteristics of the same embodiment, and Fig. 3 is a diagram of attenuation versus frequency of a modified example of the same embodiment. A frequency characteristic diagram, FIG. 4 is a circuit diagram of the second embodiment, FIG. 5 is an attenuation vs. frequency characteristic diagram of the second embodiment, and FIG. 6 is a circuit diagram of a conventional high frequency attenuator.
FIG. 7 is an attenuation vs. frequency characteristic diagram of a conventional high frequency attenuator. 2, 2a...Switchover switch, 4a...First contact, 4b...Second contact, 6a, 22a...
First contact, 6b, 22b...Third contact, 8
a, 20a... Second contact, 8b, 20b... Fourth contact, 10, 16... Attenuation circuit, 12, 12
a... Stray capacitance, 14, 16a... Inductor,
18...Another attenuation circuit, 24a...Fifth contact,
24b...Sixth contact point.

Claims (1)

[Claims for Utility Model Registration] (1) It has first and second contacts and first to fourth contacts, and when the first contact is switched to the first contact, the second contact is configured such that when the first contact is switched to the third contact, the second contact is switched to the fourth contact, and the second contact is switched to the fourth contact; 3 contacts are directly connected, and the 2nd and 4th contacts are directly connected.
A π-type or T-type interlocking changeover switch with stray capacitance between the contacts, and a π-type or T-type switch with the input side between the second contact and the reference potential point and the output side between the fourth contact and the reference potential point. a first attenuation circuit, selected to have a value that almost cancels out the stray capacitance,
A high frequency attenuator comprising: an inductor provided between second and fourth contacts; (2) The high frequency attenuator according to claim 1, wherein the first attenuation circuit is a π type, and the inductor forms a part of a component of the π type attenuation circuit. (3) The changeover switch has a fifth and a sixth contact, and is configured such that when the first contact is switched to the fifth contact, the second contact is switched to the sixth contact. Claim 1, wherein another second attenuation circuit having a smaller attenuation amount than the first attenuation circuit is provided between the fifth and sixth contacts.
Or the high frequency attenuator described in 2.