JPH0478201B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmission circuit that can be switched between having and not having filter characteristics as required.

[Conventional technology]

Figure 4A shows an example of a so-called trap characteristic (band elimination characteristic) that attenuates a signal at a predetermined frequency _fO . filter) is generally known.

[Purpose of the invention]

However, depending on the application, for example in a satellite broadcasting receiver, etc., in order to remove irregular interference waves as necessary, there are two types of filters: one with the above-mentioned filter characteristics, and the other without the filter characteristics, for example, as shown in Figure 4. B
There are cases where it is necessary to switch to a state in which signals are passed in a wide band, such as in a wide band.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a transmission circuit that can be switched between having and not having filter characteristics as necessary.

[Means to achieve the purpose]

The transmission circuit of the present invention includes a resonant circuit connected to a transmission line, a negative resistance circuit having an active element that equivalently increases the Q of the resonant circuit connected to the resonant circuit, and the active element connected to the resonant circuit. The device is characterized in that it is configured so that it can be switched between an operating state and a non-operating state.

[Effect]

In the above transmission circuit, when the active element of the negative resistance circuit is activated, energy is supplied from the active element to the resonant circuit, and its Q
is equivalently significantly increased, thereby obtaining the desired filter properties. On the other hand, when the active element is switched to a non-operating state, the Q of the resonant circuit is significantly reduced and the filter function is significantly reduced. Therefore, by switching the active element between an operating state and a non-operating state, it is possible to switch between a state with filter characteristics and a state without filter characteristics.

〔Example〕

FIG. 1 is an equivalent circuit diagram of a transmission circuit according to an embodiment of the present invention. This circuit is an example of a case where the filter circuit has one stage, and the transmission lines 11, 1
A resonator 31 of λ/2 is coupled to the capacitor 2 by a capacitance 21, and an amplifier 41 and a phase adjustment line 51 are connected to the other end of the resonator 31.
2 and 23. 61 is a switch for turning on/off the DC power supply V _B for operation of the amplifier 41; Note that the amplifier 41 and the phase adjustment line 51 have a capacitance 2 of the resonator 31.
It may be coupled to the open end of the first side.

In the above transmission circuit, when the switch 61 is closed and the amplifier 41 is in operation, the amplifier 41 and the phase adjustment line 51 cooperate with each other to create a negative resistance circuit near the resonant frequency f _O of the resonator 31. Since it functions to supply energy to the resonator 31 side, the Q (no-load Q) of the resonator 31 is equivalently increased significantly. That is, the signal is rapidly attenuated at the resonant frequency _fO , and as a result, a predetermined filter characteristic (trap characteristic) as shown by the solid line in FIG. 2, for example, can be obtained.

On the other hand, when the switch 61 is opened to switch the amplifier 41 to a non-operating state, the resonator 31 is no longer supplied with energy from the amplifier 41, so the Q of the resonant circuit is the original (bare) state of the resonator 31. Q
It drops significantly to . Thereby the resonator 31
The function of the filter as a filter is significantly reduced, and a nearly flat frequency characteristic as shown by the broken line in FIG. 2, for example, is obtained. In that case, the original Q of the resonator 31
The smaller is, the smaller the insertion loss at frequency f _O when the amplifier 41 is inactive, so the switching of frequency characteristics (switch characteristics) becomes better.

In this way, according to the above transmission circuit, the amplifier 41
By switching between operating and non-operating states, it is possible to switch between states with and without filter characteristics, and thereby almost as shown in Figures 4A and B. Frequency characteristics can be realized.

Moreover, switching the frequency characteristics as described above,
Since this can be realized by simply switching the amplifier 41 between an operating state and an inactive state, the circuit configuration is simple and the transmission circuit can be made smaller and less expensive.

FIG. 3 is a diagram showing a specific example of a circuit that implements the transmission circuit of FIG. 1. The resonator 31 is
Although it is possible to use a transmission line resonator or the like, it is realized here by a series resonant circuit consisting of a capacitance 21 and an inductance 32. Further, the amplifier 41 is
A microwave IC or the like may also be used, but here it is realized by a transistor 42.

Note that the explanation above has been given using trap characteristics as an example of filter characteristics, but based on the same idea, even in the case of bandpass characteristics, there are two conditions in which the active element to equivalently increase the Q is operating and not operating. The filter characteristics can be turned on and off by switching to and .

〔Effect of the invention〕

As described above, according to the present invention, it is possible to switch between having and not having filter characteristics as necessary. Moreover, since the circuit configuration is simple, the device can be made smaller and lower in price.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of a transmission circuit according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of frequency characteristics obtained by the transmission circuit of FIG. 1. FIG. 3 is a diagram showing a specific example of a circuit that implements the transmission circuit of FIG. 1. FIGS. 4A and 4B are diagrams showing examples of frequency characteristics, respectively. 11, 12...Transmission line, 31...Resonator, 4
1...Amplifier, 51...Phase adjustment line.

Claims (1)

[Claims] 1 A state in which a resonant circuit is connected to the transmission line, a negative resistance circuit having an active element that equivalently increases the Q of the resonant circuit is connected to the resonant circuit, and the active element is operated. A transmission circuit characterized in that it is configured to be able to switch between an inactive state and an inactive state.