KR101993141B1 - Variable filter improved reflection loss and frequency suppression characteristic - Google Patents

Abstract

The present invention relates to a variable filter with an increased return loss characteristic and an increased frequency suppression characteristic which includes a variable resistance, a variable inductor, and a variable capacitor for limiting or permitting a frequency range desired by a user, and also includes an input unit (100) and an output unit (200). The variable filter including an input unit (100) and an output unit (200) comprises: two or more coupling circuits (300) which are connected in series between an input unit (100) and an output unit (200); one or more resonance circuits (400) of which one end units are connected between the coupling circuits (300) respectively, and the other end units are grounded; a first impedance matching circuit (500) of which one end unit is connected between the input unit (100) and the coupling circuit (300) and the other end unit is grounded; and a second impedance matching circuit (600) of which other one end unit is connected between the output unit (200) and the coupling circuit (300) and the other end unit is grounded.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a variable filter having improved reflection loss characteristics and frequency suppression characteristics,

And an impedance matching circuit is inserted in the input and output portions of the variable filter basic circuit, thereby improving the variable loss range of the variable filter and the reflection loss characteristic and the frequency suppression characteristic of the variable filter.

A filter is used in several ways. In light, a color filter is used to limit the wavelength range, and an interference filter is used to narrow the wavelength. An electric filter is used to limit the frequency range of electric waves or electric signals. It is also called a filter that interferes with the passage of particles and passes only gas, liquid, or fine particles of a certain size or smaller.

The term " filter " in the present invention means to limit a frequency band such as a radio wave or an electric signal. That is, a filter that restricts a frequency band and passes only a specific frequency is called a filter. The HI Pass Filter passes only high frequencies, while the Low Pass Filter passes only low frequencies. When these two are connected, it becomes Band Pass Filter (band filter).

A typical example of a bandpass filter is an RLC circuit. The RLC circuit is a circuit composed of resistors, coils, and capacitors in an electric circuit. It is characterized in that the current flowing at every point of the circuit is the same at every moment even if the intensity and direction of the current change with time as the alternating current flows. Here, the resistance effect of the entire circuit, which is represented by the ratio of the voltage to the current in the circuit, is called impedance, which is similar to the synthetic resistance in the current circuit. Band filters made up of RLC circuits can also be made by a combination of a low pass filter and a high pass filter. The range of frequencies that a bandpass filter passes is called a passband. An ideal bandpass filter must pass a perfect signal between certain frequencies and completely block the signal in other frequency bands. I can not. This is because the filter passes a little signal outside the passband. However, the signal outside the passband is not completely blocked, but the signal is much attenuated. This phenomenon is called a filter roll-off, and we try to make the filter closer to the ideal filter by designing the filter so as to minimize this roll-off. In a bandpass filter using such RLC, it is referred to as a variable filter in which L or C is varied so that only a desired signal is passed by the user.

Meanwhile, as shown in FIG. 1, the conventional variable filter structure is composed of a coupling circuit and a resonant circuit, and the characteristics of the filter are determined according to the number of the resonant circuit and the coupling circuit. However, when the frequency variable range is widened, the reflection loss and frequency suppression characteristics are poor.

KR 10-1274031 B1 KR 10-1818109 B1 KR 10-1614955 B1

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to solve the above-mentioned problems by providing an impedance matching circuit in an input unit and an output unit of a variable filter basic circuit, thereby improving a return loss characteristic and a frequency suppression characteristic of a variable filter, Thereby providing a variable filter.

The variable filter improved the reflection loss characteristic and the frequency suppression characteristic according to the present invention includes a variable resistor, a variable inductor, and a variable capacitor for limiting or allowing a frequency band desired by a user, and includes an input unit 100 and an output unit 200) comprising: at least two coupling circuits (300) connected in series between the input section (100) and the output section (200); At least one resonant circuit (400) connected between the coupling circuits (300) one by one and grounded at the other end; One end of the first impedance matching circuit 500 is connected between the input unit 100 and the coupling circuit 300 and the other end is grounded and the other end of the first impedance matching circuit 500 is connected between the output unit 200 and the coupling circuit 300 And a second impedance matching circuit 600 connected to the other end and grounded.

The present invention has an effect of inserting an impedance matching circuit in an input portion and an output portion of a variable filter basic circuit so as to have a smaller reflection loss and excellent frequency suppressing characteristic even when the variable range is wide, compared with a conventional variable filter without an impedance matching circuit have.

FIG. 1 is a filter circuit diagram composed of only a coupling and a resonant circuit, which are conventional techniques.
Fig. 2 is a circuit diagram of a variable filter in which an impedance matching circuit according to the present invention is additionally constructed.
3 is a circuit diagram showing an embodiment of a coupling circuit according to the present invention.
4 is a circuit diagram showing an embodiment of a resonant circuit according to the present invention.
5 is a circuit diagram showing an embodiment of a frequency variable filter according to the present invention.
6 is a circuit diagram showing an embodiment of a bandwidth variable filter coupling circuit according to the present invention.
7 is a circuit diagram showing an embodiment of an impedance matching circuit according to the present invention.
8A is a circuit diagram showing an embodiment in which a capacitor circuit according to the present invention is added.
FIG. 8B is a graph showing a waveform of a variable-type nut according to the present invention. FIG.
9A is a circuit diagram showing an embodiment in which a capacitor circuit according to the present invention is added and an additional capacitor is formed across the capacitor.
9B is a graph showing that the out-of-band suppression characteristic of the variable filter according to the present invention is improved.
10 is a circuit diagram of a resonant circuit capacitor bank of a frequency variable filter according to the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

When an element is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements as well, without departing from the spirit or scope of the present invention. Also, the terms "part," " module, "and the like described in the specification mean units for processing at least one function or operation, which may be implemented in hardware or software or a combination of hardware and software .

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between .

Prior to the description, numerous aspects and embodiments are set forth in this specification, which are intended to be illustrative only and not limiting.

After reading this specification, it will be understood by those skilled in the art that other embodiments and examples are possible without departing from the scope of the present invention.

Before dealing with the details of the embodiments described below, some terms will be defined or clarified.

A node is a point in a circuit where two or more circuit elements meet.

Resonance refers to the phenomenon of vibrating at a large amplitude at a specific frequency (frequency). The specific frequency at this time is called the resonance frequency, and it is possible to transmit a large amplitude and energy to the action of a small force at the resonance frequency. Every object vibrates with each unique frequency, and the frequency of the object is called the natural frequency. An object can have several natural frequencies, and the phenomenon that the external force of the same frequency as the natural frequency is periodically transmitted and the amplitude increases greatly is called resonance phenomenon. The frequency at this time is the resonance frequency. Vibration can be seen in many types of vibration systems such as mechanical systems, acoustics systems, and optical systems. Resonance in electrical and engineering vibration systems is also called resonance. When the vibrating bodies are connected to each other under the condition of resonance, the energy can be easily exchanged.

Coupled circuit means two or more circuits that can exchange energy.

FIG. 2 is a circuit diagram of a variable filter in which an impedance matching circuit according to the present invention is additionally constructed. FIG. 3 is a circuit diagram of a coupling circuit according to the present invention 4 is a circuit diagram showing an embodiment of a resonant circuit according to the present invention, FIG. 5 is a circuit diagram showing an embodiment of a frequency variable filter according to the present invention, and FIG. 6 is a circuit diagram showing a bandwidth variable filter Fig. 7 is a circuit diagram showing an embodiment of an impedance matching circuit according to the present invention, Fig. 8A is a circuit diagram showing an embodiment in which a capacitor circuit according to the present invention is added, and Fig. 8B FIG. 9A is a graph showing the waveform of a variable-type nut according to the present invention, 9B is a graph showing that the out-of-band suppression characteristic of the variable filter according to the present invention is improved, and FIG. 10 is a circuit diagram of a resonant circuit capacitor bank of the frequency variable filter according to the present invention .

Referring to FIG. 2, the variable filter improved the return loss characteristic and the frequency suppression characteristic according to the present invention includes a variable resistor, a variable inductor, and a variable capacitor to limit or allow a desired frequency band, ) And an output section (200), comprising: at least two coupling circuits (300) connected in series between the input section (100) and the output section (200); At least one resonant circuit (400) connected between the coupling circuits (300) one by one and grounded at the other end; One end of the first impedance matching circuit 500 is connected between the input unit 100 and the coupling circuit 300 and the other end is grounded and the other end of the first impedance matching circuit 500 is connected between the output unit 200 and the coupling circuit 300 And a second impedance matching circuit 600 connected to the other end and grounded.

More specifically, it is a variable filter that improves the reflection loss characteristic and the frequency suppression characteristic of the variable frequency range extension of the variable filter and the variable filter by inserting an impedance matching circuit in the input and output portions of the variable filter basic circuit. The variable filter in which the impedance matching circuit as shown in FIG. 2 is not inserted exhibits excellent reflection loss characteristics only in a region where the frequency variable range is narrow. However, when the impedance matching circuit is inserted, the variable loss filter exhibits excellent reflection loss characteristics even in a wide frequency variable range .

The first impedance matching circuit 500 and the second impedance matching circuit 600 may be formed of any one of an inductor, a capacitor, or a series combination of an inductor and a capacitor.

A node between the input unit 100, the coupling circuit 300 and the first impedance matching circuit 500 is referred to as a first node 10 and the coupling circuit 300, the second impedance matching A variable filter in which the node between the circuits 600 is referred to as a second node 20 has a capacitor circuit 700 having one end connected to the first node 10 and the other end connected to the second node 20, ), And the first impedance matching circuit (500) and the second impedance matching circuit (600) may be constituted by inductors.

A first additional capacitor 710 having one end connected between the capacitor circuit 700 and the first node 10 and the other end grounded and one end connected to the capacitor circuit 700 and the second node 20 And a second additional capacitor 720 connected between the other end and grounded.

3, the coupling circuit can be constituted by a series combination of an inductor L, a capacitor C, an inductor L and a capacitor C, and a parallel combination of an inductor L and a capacitor C .

Next, as shown in FIG. 4, the resonant circuit is composed of a parallel combination of the inductor L and the capacitor C. The frequency of the filter is determined by the resonance by the combination of the inductor (L) and the capacitor (C), and the resonance frequency equation is as follows.

<Formula 1.1>

In the above equation, the resonance frequency is determined by the value obtained by multiplying the inductor L and the capacitor C, and resonance characteristics are generated at a certain frequency when the inductor L and the capacitor C are combined. The resonance circuit can be variously configured by a combination of the inductor L and the capacitor C since the product of the inductor L and the capacitor C is constant even if the same resonance frequency is used.

Next, referring to FIG. 5, the frequency variable filter applies a fixed value to the coupling circuit and varies the frequency by changing the value of the capacitor C of the resonant circuit. The resonance frequency equation of the frequency variable filter is as follows.

<Formula 2>

Next, referring to FIG. 6, the bandwidth variable filter applies a fixed value to the resonant circuit and varies the bandwidth by changing the value of the inductor (L) or capacitor (C) of the coupling circuit. The inductor L, the capacitor C or the capacitor C and the inductor L may be connected in series or in parallel.

Next, referring to Fig. 7, the impedance matching circuit can be constituted by a series combination of an inductor L, a capacitor C, an inductor L and a capacitor C.

8A, the variable filter to which the capacitor circuit 700 is added includes a capacitor circuit 700 between the input unit and the output unit in the basic circuit of the variable filter, and an impedance matching circuit of the input unit and the output unit is configured as an L section Thereby forming a variable notch when the frequency of the variable frequency filter is variable. In FIG. 8B, it can be seen that the waveform of the variable-type nut is formed.

9A, a first additional capacitor 710 and a second additional capacitor 720 are further provided at both ends of the capacitor circuit 700 in addition to the variable filter to which the capacitor circuit 700 is added as described above can do. In this case, as shown in FIG. 9B, the out-of-band suppression characteristic of the variable filter is improved.

Next, with reference to FIG. 10, a method of varying the capacitance of the variable filter will be described in more detail. When the bias voltage exceeds the pin diode conduction voltage, the pin diode conducts. When the pin diode is conducting, the pin diode becomes a circuit having a small resistance value. Therefore, when all the pin diodes are conducting, the capacitor values are as follows.

<Equation 3.1>

The resonant frequency of the resonant circuit at the time of conducting all pin diodes is as follows.

<Equation 3.2>

When all pin diodes are connected, the capacitor value becomes C _T , and C _T becomes the largest value, so that the resonant frequency becomes the lowest frequency by (Equation 3.2).

If the bias voltage is applied below the pin diode conduction voltage, the pin diode will not conduct. If the pin diode is not conducting, then it has a very small capacitor value C _P. The capacitor value in the series combination of capacitors is less than C _P. Thus, the total capacitance value of the capacitor bank when all pin diodes are not conducting is approximately NC _P.

The resonant frequency of the resonant circuit when all pin diodes are not conducting is as follows.

<Equation 3.3>

Since the NC _P is very small at this time, the resonant frequency becomes the highest by (Eq. 3.3). Therefore, the frequency variable filter can change the frequency of the desired frequency by controlling the desired frequency to be the capacitance value of the desired frequency to change the total capacitance value of the capacitor bank circuit through ON / OFF control of the pin diode. The capacitor bank circuit is the most common example and can be composed of various circuits.

The types of capacitors used in the present invention include capacitors suitable for high frequency or low frequency that the user wants to restrict or allow such as electrolytic capacitors, tantalum electrolytic capacitors, ceramic capacitors, multilayer ceramic capacitors, Mylar capacitors, polypropylene capacitors, You will use it. In case of capacity, it can be used from 1pF to 1000μF according to the frequency that the user wants to limit or allow.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

10: First node
20: second node
100: Input unit
200: Output section
300: Coupling circuit
400: resonance circuit
500: first impedance matching circuit
600: second impedance matching circuit
700: capacitor circuit
710: first additional capacitor
720: second additional capacitor

Claims (4)

1. A tunable filter comprising an input (100) and an output (200), the variable filter comprising a variable resistor, a variable inductor and a variable capacitor to limit or allow a user to desire a frequency band,
At least two coupling circuits (300) connected in series between the input section (100) and the output section (200);
At least one resonant circuit (400) connected between the coupling circuits (300) one by one and grounded at the other end;
A first impedance matching circuit 500 having one end connected between the input unit 100 and the coupling circuit 300 and the other end grounded;
And a second impedance matching circuit 600 having one end connected between the output unit 200 and the coupling circuit 300 and grounded at the other end,
A node between the input unit 100, the coupling circuit 300 and the first impedance matching circuit 500 is referred to as a first node 10 and the coupling circuit 300, the second impedance matching circuit 600 is referred to as a second node 20,
Further comprising a capacitor circuit (700) having one end connected to the first node (10) and the other end connected to the second node (20)
Wherein the first impedance matching circuit (500) and the second impedance matching circuit (600) are constituted by inductors.
The method according to claim 1,
The first impedance matching circuit (500) and the second impedance matching circuit (600)
An inductor, a capacitor, or a series combination of an inductor and a capacitor.
delete The method according to claim 1,
A first additional capacitor 710 having one end connected between the capacitor circuit 700 and the first node 10 and the other end grounded;
Further comprising a second additional capacitor (720), one end of which is connected between the capacitor circuit (700) and the second node (20) and the other end of which is grounded. Variable filter.

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