JPS63290401A - Active filter - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the attenuation characteristic at a high frequency region by providing an electromagnetic wave absorbing body near the resonator so as to increase the suppression ratio of the spurious radiation. CONSTITUTION:A ferrite rubber 11 as the electromagnetic wave absorbing body is arranged at the upper part in a shield case 9 of an active filter 1. Thus, the electromagnetic wave in the spurious mode is absorbed, then the case 9 does not act like a cavity thereby absorbing the spurious radiation. As a result, the deterioration in the attenuation characteristic by the spurious mode is prevented. In this case, when each resonator 3 is in the resonance state, an amplifier 7 acts like a negative resistor, the energy is supplied to a resonator 3 at the center thereby improving the sharpness Q equivalently.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an active filter in which a plurality of resonators are disposed in a case, and an active element such as an amplifier is combined with the resonators, and in particular, the present invention relates to an active filter in which a plurality of resonators are arranged in a case and an active element such as an amplifier is combined with the resonators. The present invention relates to the structure of an active filter that can increase the spurious suppression ratio without lowering the sharpness Q of the filter and prevent deterioration of the attenuation characteristics in a high frequency region.The present invention relates to an active filter that uses a dielectric resonator. Since it is suitable for this, this will be explained below as an example.

[Conventional technology]

Multiple dielectric resonators (hereinafter referred to as resonators) are arranged on a dielectric substrate, and a positive feedback circuit including an active element is coupled to one of the resonators to add negative resistance. Conventionally, there are active filters shown in FIGS. 2 and 3 that equivalently increase the sharpness Q by .

In the figure, 1 is an active filter, and three cylindrical resonators 3 are arranged at predetermined intervals on the upper surface of a dielectric substrate 2 with spacers 6 made of a low dielectric constant material such as forsterite interposed therebetween. As a result, the adjacent resonators 3 are inductively coupled to each other. Further, an input electrode 8a and an output electrode 8b are formed on the left and right edges in the drawing of the upper surface of the dielectric substrate 2, and this input electrode FIi8
The resonator 3 adjacent to the output electrode 8b and the resonator 3 adjacent to the output electrode 8b are also twi-coupled. Further, a positive feedback circuit 4 is formed on the upper surface of the dielectric substrate 2, and this includes coupling electrodes 5a and 5b formed to sandwich the central resonator 3.
and an amplifier 7 as an active element formed by connecting one ends of the coupling electrodes 5a and 5b. and,
The active filter 1 is housed in a box-shaped shield case 9 made of, for example, metal or metallized plastic in order to obtain electrical and mechanical stability. In addition, 10a and 10b are the above-mentioned people, and the output electrode 8a
, 8b is a connector for leading out to the outside.

In the active filter 1, when each resonator 3 is in a resonant state, energy is supplied from the amplifier 7, so that the sharpness Q is equivalently increased.

[Problem that the invention seeks to solve]

However, in the conventional active filter 1 described above,
There is a problem in that the attenuation characteristics deteriorate in a frequency range considerably higher than the intended passband frequency. This is considered to be due to the fact that since the filter I is housed in the case 9, the case 9 itself operates as a cavity, and its electromagnetic waves generate spurious on the output side.

The present invention was made in order to solve the above-mentioned conventional problems, and it increases the spurious suppression ratio and
The purpose of the present invention is to provide an active filter that can prevent deterioration of attenuation characteristics in

[Means for solving problems]

The present invention provides an active filter in which a plurality of resonators are arranged in a case, and an active element is combined with the resonators, in the vicinity of the resonators. It is characterized by the provision of a 1UF wave absorber.

(Function) According to the active filter according to the present invention, since the electromagnetic wave absorber is disposed near the resonator, the electromagnetic waves are absorbed by the magnetic wave absorber, so that the case does not operate as a cavity. The spurious suppression ratio can be increased accordingly, and as a result, deterioration of the attenuation characteristics in the high frequency range can be prevented.

By the way, for the purpose of suppressing spurious waves, for example, it has been conventionally adopted to arrange a magnetic wave absorber in high frequency filters, etc., but in this case,
The problem was that the Q of the basic mode also decreased along with the spurious mode.

Therefore, even in the present invention, there is a concern that the Q of the fundamental mode may also decrease due to the provision of the electromagnetic wave absorber. On the other hand, in the present invention, by supplying energy from an active element, it is possible to compensate for the above Q. Therefore, only the Q of the spurious mode can be significantly lowered without lowering the Q of the fundamental mode, and the spurious It can be suppressed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an active filter according to an embodiment of the present invention. In FIG. 0, the same reference numerals as in FIGS. Since it is the same as that of , detailed explanation thereof will be omitted.

In the upper part of the shield case 9 of the active filter 1 of this embodiment, for example, ferrite rubber 11 is disposed as an electromagnetic wave absorber. The ferrite rubber 11 extends along both upper corner edges of the case 9 in a direction perpendicular to the plane of FIG. 1, and is attached with an adhesive. The size and position of the ferrite rubber 11 may be determined depending on the degree of spuriousness. For example, if the spurious mode is large, it may be placed on the ceiling inside the case 9.

Next, the effects of this embodiment will be explained.

In the active filter 1 of this embodiment, when each resonator 3 enters a resonant state, the amplifier 7 becomes a negative resistance, thereby supplying energy to the central resonator 3, and the sharpness Q becomes equivalent to can be enhanced.

In this case, as shown in FIGS. 2 and 3, in the conventional active filter 1, when an input signal is applied to the input electrode 8a, the case 9 itself becomes a cavity due to the electromagnetic waves excited by the end effect of the input electrode 8a. There was a problem in that the damping characteristics were deteriorated due to the generation of spurious signals.

In contrast, in this embodiment, since the ferrite rubber 11 as an electromagnetic wave absorber is disposed inside the case 9, the electromagnetic waves in the spurious mode are absorbed by the ferrite rubber 11, so that the case 9 operates as a cavity. This eliminates the need for spurious signals to be generated and suppresses spurious signals. As a result, deterioration of damping characteristics due to spurious modes can be prevented.

Further, as mentioned above, if an electromagnetic wave absorber such as the ferrite rubber 11 was simply provided, there was a problem that the Q of the fundamental mode would also decrease, but in this embodiment, the energy is supplied from the amplifier 7, so The above-mentioned decrease in Q can be compensated for, and as a result, only the spurious can be suppressed without substantially lowering the Q of the fundamental mode.

In the above embodiments, an active filter employing a dielectric resonator was explained as an example, but the present invention is of course applicable to other resonators, such as a microstrip line resonator or a lumped constant resonator. It can also be applied to active filters.

〔Effect of the invention〕

As described above, according to the active filter according to the present invention, since the electromagnetic wave absorber is disposed near the resonator, it is possible to absorb electromagnetic waves and suppress spurious waves, which has the effect of preventing deterioration of the attenuation characteristics. and in this case,
Since the reduction in Q is compensated for by the active element, there is an effect that only the Q of the spurious mode can be suppressed without substantially lowering the Q of the fundamental mode.

[Brief explanation of drawings]

FIG. 1 is a partially sectional front view showing an active filter according to an embodiment of the present invention, FIG. 2 is a partially sectional plan view showing a conventional active filter, and FIG. 3 is a partially sectional front view thereof. In the figure, 1 is an active filter, 2 is a dielectric substrate, 3 is a dielectric resonator, 7 is an amplifier (active element), and 11 is ferrite rubber (electromagnetic wave absorber). Patent applicant Murata Manufacturing Co., Ltd. Representative Patent attorney Tsutomu Shimofu Figure 1 1 (Ja, <bba bb6 Figure 2 1 Figure 3

Claims (1)

[Claims] (1) An active filter comprising a plurality of resonators arranged in a case and an active element combined with the resonators, characterized in that an electromagnetic wave absorber is arranged near the resonators.