WO2010044503A1

WO2010044503A1 - Band balanced filter

Info

Publication number: WO2010044503A1
Application number: PCT/KR2008/006287
Authority: WO
Inventors: Chung-Seok Lee; Jong-Soo Ha; Hee-Seok Song; Young-Ki Kim; Soon-Young An; Jin-Wuk Seo; Jung-Woo Kang
Original assignee: SAMYOUNG ELECTRONICS CO Ltd
Current assignee: SAMYOUNG ELECTRONICS CO Ltd
Priority date: 2008-10-17
Filing date: 2008-10-24
Publication date: 2010-04-22
Anticipated expiration: 2011-04-17
Also published as: KR20100042949A

Abstract

A band balanced filter is disclosed. The band balanced filter includes an input port through which an unbalanced signal is input, a band pass filter (BPF) passing a signal at a certain band, a Balun converting the unbalanced signal into a balanced signal, and a first output port and a second output port outputting the balanced signal. The BPF and the Balun have structures in which a plurality of layers are laminated. Circuits are laminated so that a small sized band balanced filter can be designed. Since a fundamental resonant frequency and a first harmonic frequency of a resonator is very large, a band balanced filter of a wide pass band having a wide upper stopband property can be manufactured.

Description

BAND BALANCED FILTER

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a band balanced filter and, more particularly to a band balanced filter to which an imbalanced signal is applied through an input terminal and is filtered by a laminated resonant filter such that a balanced signal is output through an output terminal via a balanced line .

2. Description of the Related Art

A general band pass filter circuit consisting of lumped elements includes a T-type band pass filter circuit as illustrated in FIG. 1 and a Jl -type band pass filter circuit as illustrated in FIG. 2. Each of the band pass filter circuits in FIGS. 1 and 2 is constructed by combining a resistor 110 of a prototype low pass filter circuit with networks of a serial resonator 140 and parallel resonators 150 each of which includes inductors 120 and capacitors 130. In the band pass filters as illustrated in FIGS. 1 and 2, there are several difficulties in designing a filter such that unique parameters of the respective lumped elements are determined when the respective prototype lumped elements are arranged in the form of resonators using a frequency conversion function, characteristics of the filters are suddenly changed by a minute change of the parameter, and it is hard to implement the serial resonators 140 and the parallel resonators 150 simultaneously.

Thus, the band pass filter is practically implemented by only one type of a resonator using an inverter with emittance conversion characteristics. That is, there is an existing band pass filter having J- inverters 200 (admittance inverter 210) as illustrated in FIG. 3 or K-inverters 220 (impedance inverter 230) as illustrated in FIG. 4.

In order to combine the networks of the serial resonators 140 and the parallel resonators 150 as illustrated in FIGS. 1 and 2 with each other, a phase of voltage must be the same as that of current when applying AC voltage 100. However, since, in the band pass filter, the parameters of lumped elements are already determined and the characteristic of the filter is changed due to the minute change of the parameters of the lumped elements, the band pass filter must be implemented by an inverter having only one type having the emittance conversion characteristics of the serial resonators 140 and the parallel resonators 150 as illustrated in FIGS. 3 and 4.

On the other hand, in the practice of implementing a band pass filter consisting of the lumped elements, resonators and inverters of the band pass filter must be implemented using a distributed constant circuit such as a transmission line. In other words, the resonators using a transmission line can implement a serial resonance circuit using a λ /2 transmission line with a short end or a parallel resonance circuit using a λ. /4 transmission line with a short end and a λ /2 transmission line with an open end.

However, the above-mentioned band pass filter has the following disadvantages.

First, when the λ. /2 and λ /4 resonators are applied to a single sided circuit and a double sided circuit, it is difficult to design a small filter because of a length of the transmission line. That is, there are restrictions such that the λ. /2 resonator must be λ. /2 in length and the λ. /4 resonator must be λ. /4 in length. Thus, since the resonators increase in size, it is technically difficult to design a small filter.

Second, in view of frequency characteristics of the resonator, there is a technical restriction that resonance is generated at a desired reference frequency f and (2n+l) times the reference frequency, for example, 3f, 5f, etc. In a case of designing a filter using the frequency characteristics of a resonator, a designer feels difficulty of forming a diplexer having broad pass band because of harmonic pass band occurring at integer times a desired pass band. Thus, performance of overall circuit deteriorates.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an aspect of the present invention to provide a broad pass band balanced filter with a wide upper stop band by laminating circuits to miniaturize the band balanced filter and by increasing a difference between a fundamental resonant frequency and a first order harmonic resonant frequency. It is another aspect of the present invention to provide a very small band balanced filter applicable to a front-end of a receiver module of a digital video broadcasting-handheld (DVBH) device as a digital-TV broadcasting standard.

It is still another aspect of the present invention to provide a very small band balanced filter to which low temperature co-fired ceramic (LTCC) technology is applied to obtain a small and light communication terminal. In accordance with an aspect of the present invention, the above and other objects may be accomplished by the provision of a band balanced filter including: an input port through which an unbalanced signal is input; a band pass filter (BPF) passing a signal at a certain band; a Balun converting the unbalanced signal into a balanced signal; and a first output port and a second output port outputting the balanced signal; wherein the BPF and the Balun have structures in which a plurality of layers are laminated; wherein the BPF receives a signal from the input port, and in the BPF, first capacitors (509a, 510a, 511a) laminated on certain layers to be electrically connected to each other and first inductors (413a and 514a) laminated on certain layers to be electrically connected to each other form an input end of the BPF, second inductors (513b, 513d, 514b, 514d, 515a, and 515c) laminated on certain layers to be electrically connected to each other form a resonant line of the BPF, the second inductors (513b, 513d, 514b, 514d, 515a, and 515c) and second capacitors (509a and 509b) on certain layers make resonance, and third capacitors (509b, 510b, and 511b) laminated on certain layers to be electrically connected to each other and third inductors (513e and 514e) laminated on certain layers to be electrically connected to each other form an output end of the BPF; and wherein, in the Balun, a fourth inductor (507) on a certain layer receives an unbalanced signal output from the output end of the BPF, a balanced line on a certain layer (503) that is uncoupled with an unbalanced line on a certain layer (506) outputs a part of the balanced signal (first balanced signal) through the first output port, and a balanced line on a certain layer (505) that is coupled with an unbalanced line on the layer (506) outputs the rest (second balanced signal) of the balanced signal through the second output port, an input port through which an unbalanced signal is input; a band pass filter (BPF) passing a signal at a certain band; a Balun converting the unbalanced signal into a balanced signal; and a first output port and a second output port outputting the balanced signal; wherein the BPF and the Balun have structures in which a plurality of layers are laminated; wherein the BPF receives a signal from the input port, and in the BPF, first capacitors (509a, 510a, 511a) laminated on certain layers to be electrically connected to each other and first inductors

(413a and 514a) laminated on certain layers to be electrically connected to each other form an input end of the BPF, second inductors (513b, 513d, 514b, 514d, 515a, and 515c) laminated on certain layers to be electrically connected to each other form a resonant line of the BPF, the second inductors (513b, 513d, 514b, 514d, 515a, and 515c) and second capacitors (509a and 509b) on certain layers make resonance, and third capacitors (509b, 510b, and 511b) laminated on certain layers to be electrically connected to each other and third inductors

(513e and 514e) laminated on certain layers to be electrically connected to each other form an output end of the BPF; and wherein, in the Balun, a fourth inductor (507) on a certain layer receives an unbalanced signal output from the output end of the BPF, a balanced line on a certain layer (503) that is uncoupled with an unbalanced line on a certain layer (506) outputs a part of the balanced signal (first balanced signal) through the first output port, and a balanced line on a certain layer (505) that is coupled with an unbalanced line on the layer (506) outputs the rest (second balanced signal) of the balanced signal through the second output port. Moreover, in the BPF, fifth inductors (513c, 514c, and 515c) laminated on certain layers to be electrically connected to each other adjust a pass bandwidth.

In the BPF, fourth capacitors (512, 511a, and 511b) laminated on certain layers to be electrically connected to each other adjust an interval between poles of return loss.

According to the present invention, since circuits are laminated to miniaturize a size of a band balanced filter, a small sized filter can be designed. Since a difference between a fundamental resonant frequency and a first harmonic frequency of a resonator is very large, a band balanced filter of wide pass band having a wide upper stopband property can be manufactured.

In particular, according to the present invention, a band balanced filter can applied to a front-end of a receiver module of a digital video broadcasting -handhelds as a European digital TV standard. Moreover, low temperature co- fired ceramics (LTCC) are applied to a very small sized band balanced filter to suit to a small and light communication terminal .

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a circuit of an existing T-type band pass filter consisting of lumped elements;

FIG. 2 is a circuit of an existing Jt -type band pass filter consisting of lumped elements;

FIG. 3 is a circuit of an existing band pass filter consisting of J-inverters (admittance inverters) ;

FIG. 4 is a circuit of an existing band pass filter consisting of K-inverters (impedance inverters);

FIG. 5 is a block diagram illustrating a band balanced filter according to an embodiment of the present invention; FIG. β is a circuit of the band balanced filter according to the embodiment of the present invention;

FIG. 7 is a partial enlarged view of a transmission line used in the circuit of FIG. 6;

FIG. 8 is a perspective view of the band balanced filter according to the embodiment of the present invention;

FIG. 9 is an exploded perspective view of the band balanced filter according to the embodiment of the present invention;

FIGS. 10 to 26 are pattern views illustrating respective layers of the band balanced filter according to the embodiment of the present invention; and FIGS. 27 to 30 are graphs illustrating frequency characteristics of the band balanced filter according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to accompanying drawings. The same reference symbols are used throughout the drawings to refer to the same or like parts. FIG. 5 is a block diagram illustrating a band balanced filter according to an embodiment of the present invention.

A band balanced filter according to the embodiment of the present invention includes an input (unbalanced) port 310 into which an unbalanced signal is input, a band pass filter (BPF) 340 passing a UHF signal, a balun 350 as a circuit converting the unbalanced signal from the filter into a balanced signal, and output (balanced) ports 1 and 2 320 and 330 outputting balanced signals.

Since a general filter outputs a filtered signal in the form of an unbalanced signal but the filtered unbalanced signal must be converted into a balanced signal when the filter is connected to parts such as a mixer including balanced lines, the balun 350 is added to the filter for the conversion.

When the unbalanced signal is applied to the input port

310, the unbalanced signal is filtered by a λ. /4 laminated resonator filter and then a balanced signal is output through the output ports 320 and 330 via the balance line while the respective ports 310, 320, and 330 are processed by side printing.

FIG. 6 is a circuit of the band balanced filter according to the embodiment of the present invention, and

FIG. 7 is a partial enlarged view of a transmission line (TL) used in the circuit of FIG. β. The TL represents a line through which an electromagnetic wave travels and may be a microstrip or a stripline. As illustrated, TIl to TL8 401, 402, 403, 404, 405, 406, 407, and 408 are inductors, in which inductor devices are implemented on a plane. In more detail, as illustrated in FIG. 7, the inductors have a stripline configuration 440 in which an inductor is sandwiched by ground plates (GND) 441. Cl to C5 411, 412, 413, 414, and 415 are capacitors, in which capacitor devices are implemented on a plane.

Since a resonator which has TL2, TL4, C2 and C4 and is applied to a circuit of the band balanced filter according to the embodiment of the present invention has a λ/4 laminated resonator configuration and is a stepped impedance resonator (SIR), the resonator has band rejection characteristics. Moreover, a parallel resonator TLl and Cl is applied to an input end of the filter and a parallel resonator TL5 and C5 is applied to an output end of the filter such that notch characteristics are improved. A filtered unbalanced signal is converted into a balanced signal by passing through balanced lines TL7 and TL8 of a balun TLβ, TL7, and TL8 and is outputted through output terminals 320 and 330. Hereinafter, functions of the respective inductors and capacitors which are illustrated in the drawings will be described.

TLl 401 is a resonator line of a notch filter located in an input unit and determines a position of notch to improve attenuation characteristics. TL2 402 and TL4 404 are resonator lines of a band pass filter (BPF) 340 and determine positions of frequency of a pass-band of a signal. TL3 403 is a part for inductance coupling of the BPF 340 and adjusts a width of the pass band. TL5 405 is a resonator line of a notch filter located at an output unit and determines a position of notch to improve attenuation characteristics. TL6 406 is an unbalanced line of the balun 350 and affects phase and amplitude characteristics. TL7 407 is a balanced line coupled with TL6 406 and affects phase and amplitude characteristics. TL8 408 is a balanced line separated from TL6 406 and affects phase and amplitude characteristics.

In more specific, the unbalanced line (TL6) of the balun 350 is grounded to the GND to a length of λ/4. Balance lines TL7 and TL8 are transmission lines having a length of λ/2 wherein the balanced line TL7 having a length of λ/4 is coupled with the unbalanced line TL6 and the balanced line TL8 having a length of λ/4 is not coupled with the unbalanced line TL6.

Thus, a signal passed through the balance line TL8 is outputted to a first output (balance) port 320 and a signal passed through the balance line TL7 is outputted to a second output port 330. The signals outputted to the two output

(balance) ports 320 and 330 have amplitudes such as a sine waveform and their phases are different from each other by 180 degrees . Cl 411 is a capacitance component of the notch filter located at the input unit and determines the notch position to improve the attenuation characteristics. C2 and C4 412 and 414 are loading capacitors of the resonator of the BPF 340, determine a frequency position of a signal pass band, and control a harmonic component. C3 413 is a capacitance coupling part of the BPF 340 and adjusts a pole distance of the return loss. C5 415 is a capacitance component of a notch filter located at the output unit and determines a notch position to improve attenuation characteristics. FIG. 8 is a perspective view illustrating a band balanced filter 500 according to an embodiment of the present invention and FIG. 9 is an exploded perspective view illustrating the band balanced filter 500 according to the embodiment of the present invention.

In the band balanced filter 500 according to the embodiment of the present invention, a total of 17 layers are laminated and TLs on the respective layers are interconnected through via-holes 530.

A wide area is required to achieve high inductance and capacitance. However, according to the band balanced filter 500 of this embodiment of the present invention, a pattern is formed in the form of a laminated structure so that desired parameters may be achieved by a small sized filter 500. Since the band balanced filter 500 according to the embodiment of the present invention has a size of 2.5 mm * 2.0 mm * 1.2 mm (L * W * T) , a very small sized laminated band balanced filter 500 may be manufactured.

In the band balanced filter 500 according to the embodiment of the present invention, various laminating technologies may be applied to manufacture a filter. Particularly, the band balanced filter 500 may be applied to a filter using a multi-layer printed circuit board (PCB) , a filter using low temperature co-fired ceramic (LTCC) technology, and other laminated structure using other materials. Moreover, the band balanced filter 500 is employed in an RF module using the laminating technology so that the RF module may be designed.

Meanwhile, the LTCC technology is a technique of manufacturing a multi-layer laminated semiconductor device using a ceramic dielectric with a thick layer (thickness: tens to hundreds micrometers) , manufactured by tape casting and a conductive metal paste for implementing several circuit devices . In more detail, FIG. 9 shows a connection between respective layers used in the band balanced filter according to the embodiment of the present invention. The respective layers are electrically connected to each other through coupling and a via-hole 530. On the other hand, the via-hole 530 is made by making a hole in a dielectric material and filling the hole with metal to transmit an electric signal. Some of the layers are electrically connected to each other through the via-hole 430 and others are connected to each other by the coupling. In this embodiment, inductance components are connected to each other through the via-hole 530 while capacitance components are connected to each other through the coupling. The inductance components are connected to each other through the via-hole 530 to obtain a high inductance and to reduce a size. When the inductance components are implemented in a plane, an area where the inductance components are implemented is wide and a size of a product increases. Thus, the present invention is made to overcome this problem. For example, a thirteen to fifteen layers 513 and 514 have the same structure as those of the inductance components of TLl to TL5 in FIG. 6. When the structure is implemented in a plane, it needs a wide area and a size of a product increases. Since a distance between the respective layers is very short as long as 30 micrometers when the layers are laminated according to the embodiment of the present invention, a desired small size of an inductance may be obtained when the layers are connected to each other through the via-hole 530.

Moreover, in the band balanced filter 500 according to the embodiment of the present invention, the layers are connected in a laminated structure so that the capacitance components are connected to each other through the coupling. Like, the connection between the inductance components through the via-hole 530, the capacitance components are connected to each other through the coupling so that the capacitance increases and a size of the filter is reduced. For example, in order to obtain the capacitances, namely, Cl and C5 411 and 415 in FIG. 6, capacitors are implemented on a ninth layer 509, a tenth layer 510, and eleventh layer 511 in the laminated form such that capacitors with the same structure are patterned on the upper and lower layers. Therefore, the laminated structure of multiple layers is formed to obtain the capacitances of Cl and C5 411 and 415 so that an area of a pattern implemented in a plane is reduced and a size of a product is reduced.

FIGS. 10 to 26 are pattern views illustrating respective layers of the band balanced filter 500 according to the embodiment of the present invention.

In this embodiment of the present invention, seventeen layers are laminated in the band balanced filter 500 and the respective layers are electrically connected to each other through the via-hole 530. Hereinafter, the respective layers will be described.

FIG. 10 shows a first layer 501 that is a pattern to recognize a direction of a port.

FIG. 11 shows a second layer 502 that is a GND pattern breaking an external signal transmitted to an upper ground plane and serving as a ground.

FIG. 12 shows a third layer 503 that is a balance line of a balun with a length of λ/4 and is not coupled with an unbalanced line. The third layer 503 serves as an inductor of TL8 408 in FIG. 6 and is connected to an output (balance) port

1 320.

FIG. 13 shows a fourth layer 504 that is a ground plane to separate the third layer 503.

FIG. 14 shows a fifth layer 505 that is a balanced line of the balun with a length of λ/4 to be coupled with the unbalanced line. The fifth layer 505 serves as an inductor of

TL7 407 in FIG. 6 and is connected to an output (balanced) port 2 330.

FIG. 15 shows a sixth layer 506 that is an unbalanced line of the balun with a length of λ/4 to serve as an inductor of TL6 406 in FIG. 6 and to be coupled with the balanced line of the fifth layer 505.

FIG. 16 shows a seventh layer 507 that is an unbalanced line input of the balun to serve as an inductor of TL6 in FIG. 6 and to input an output signal from the filter to the unbalanced line of the balun 350.

FIG. 17 shows a eighth layer 508 that is a GND pattern breaking an external signal transmitted to an intermediate ground plane and serving as a ground.

FIG. 18 shows a ninth layer 509 that is a loading capacitor of the BPF 340 in which a nine-first capacitor 509a and a nine-second capacitor 509b serve as the capacitors C2 412 and C4 414 in FIG. 6, respectively. The ninth layer 509 forms a capacitance in association with the eighth layer 508. This directly relates to a resonance frequency and spurious emission of a resonator forming a filter. Moreover, the nine- first capacitor 509a and the nine-second capacitor 509b serve as the capacitors indicated by Cl 411 and C5 415 in FIG. 6, adjust an input/output coupling, and determine a position of notch.

FIG. 19 shows a tenth layer 510 that is an input/output capacitor in which a ten-first capacitor 510a and a ten-second capacitor 510b serve as the capacitors indicated by Cl 411 and C5 415 in FIG. 6, respectively. The ten-first capacitor 510a and the ten-second capacitor 510b adjust an input/output coupling and serve as capacitors of a notch filter to determine a position of notch.

FIG. 20 shows an eleventh layer 511 that is an input/output capacitor of a filter, wherein an eleven-first capacitor 511a and an eleven-second capacitor 511b serve as the capacitors indicated by Cl 411 and C5 415 in FIG. 6, respectively and determine a position of notch. Moreover, the eleven-first capacitor 511a and the eleven-second capacitor 511b adjust an input/output coupling, serve as the capacitor indicated by C3 413 in FIG. 6, and are in associated with the capacitance coupling to adjust an interval of poles.

FIG. 21 shows a twelfth layer 512 that serves as the capacitor indicated by C3 413 in FIG. β, relates to the capacitance coupling, and adjusts poles and position of notch to influence the insertion loss and attenuation.

FIG. 22 shows a thirteen layer 513 in which a thirteen- first inductor 513a and a thirteen-fifth inductor 513e are inductors indicated by TLl 401 and TL5 405 in FIG. 6 respectively and lines serving as inductors of the notch filter positioned in an input/output unit of the filter. A thirteen-second inductor 513b, a thirteen-third inductor 513c, and a thirteen-fourth inductor 513d are inductors indicated by TL2 402, TL3 403, and TL4 404 in FIG. 6 respectively and form a line of the resonator of the filter and a line of the inductance coupling.

FIG. 23 shows a fourteen layer 514 in which a fourteen- first inductor 514a and a fourteen-fifth inductor 514e are inductors indicated by TLl 401 and TL5 405 in FIG. 6 respectively and are lines serving as inductors of the notch filter positioned in the input/output unit of the filter. A fourteen-second inductor 514b, a fourteen-third inductor 514c, and a fourteen-fourth inductor 514d are inductors indicated by TL2 402, TL3 403, and TL4 404 in FIG. 6 respectively to form the line of the resonator of the filter and the line of the inductance coupling. FIG. 24 shows a fifteenth layer 515 in which a fifteen- first inductor 515a, a fifteen-second inductor 515b, and a fifteen-third inductor 515c are inductors indicated by TL2 402, TL3 403, and TL4 404 in FIG. 6, respectively and form the line of the resonator of the filter and the line of the inductance coupling.

FIG. 25 shows a sixteenth layer 516 that is a GND pattern breaking an external signal transmitted to a lower ground plane and serving as a ground.

FIG. 26 shows a seventeenth layer 517 that is mounted on a PCB or a module and through which a signal is input and output .

The band balanced filter according to the embodiment of the present invention includes an input (unbalanced) port 310 through which an unbalanced signal, a BPF 340 through a UHF signal passes, a Balun 350 converting the unbalanced signal of the filter into a balanced signal, and an output (balanced) port 1 320 and an output (balanced) port 2 330 through which a balanced signal is output. The BPF 340 and the balun 350 have a structure in which a plurality of layers are laminated.

In the BPF 340, the nine-first capacitor 509a, the ten- first capacitor 510a, and the eleven-first capacitor 511a connected to each other by the coupling and the thirteen-first inductor 513a and the fourteen-first inductor 514a connected to each other through the via-hole form the input end notch filter.

The thirteen-second inductor 513b, the thirteen-fourth inductor 513d, the fourteen-second inductor 514b, the fourteen-fourth inductor 514d, the fifteen-first inductor 515a, and the fifteen-third inductor 515c are laminated and connected to each other through the via-hole to form the resonant line of the BPF. The thirteen-second inductor 513b, the thirteen-fourth inductor 513d, the fourteen-second inductor 514b, the fourteen-fourth inductor 514d, the fifteen-first inductor 515a, and the fifteen-third inductor 515c make resonance with the loading capacitor, that is, the nine-first capacitor 509a and the nine-second capacitor 509b.

At the output end of the BPF, the nine-second capacitor 509b, the ten-second capacitor 510b, and the eleven-second capacitor 511b connected to each other by the coupling and the thirteen-fifth inductor 513e and the fourteen-fifth inductor 514e connected to each other through the via-hole are laminated to form an output end notch filter. Moreover, in the BPF 340, the thirteen-third inductor 513c, the fourteen-third inductor 514c, the fifteen-second inductor 515b are laminated and connected to each other through the via-hole to form the inductance coupling, to adjust a pass band width, and to be grounded to the GNDs 502, 504, 508, and 516.

Moreover, the capacitor on the twelfth layer 512, the eleven-first capacitor 511a, and the eleven-second capacitor 511b are laminated to form the capacitance coupling and to adjust an interval between poles of the return loss. In the balun 350, the balanced line, that is, the third layer 503 which is not coupled with the sixth layer 506 outputs a balanced signal to the output (balanced) port 1 320 when an input unit of the unbalanced line, that is, the seventh layer 507 receives an unbalanced signal passing through the BPF, and another balanced line of the fifth layer 505 coupled with the unbalanced line of the sixth layer 506 outputs a balanced signal to the output (balanced) port 2 330.

As described above, although the embodiment of the present invention is described by taking the band balanced filter having a structure in which seventeen layers are laminated, the band balanced filter needs various capacitances and inductances in accordance with a desired frequency range. It is appreciated to those skilled in the art that the band balanced filter according to the embodiment of the present invention may be designed to have seventeen or less layers.

FIGS. 27 to 30 are graphs illustrating frequency characteristics of the band balanced filter 500 according to the embodiment of the present invention. The band balanced filter according to the embodiment of the present invention is manufactured to satisfy the specifications as listed in the following Table. [Table 1 ]

In FIGS. 27 to 30, horizontal axes indicate frequency ranged from 0 (zero) to 1.2 GHz. The vertical axis of FIG. 27 indicates the return loss in the form of a standing wave ratio. The return loss is a loss generated when a signal input into the input (unbalanced) port 310 is returned. As illustrated in the drawing, the standing wave ratio in the pass band indicated by the vertical axis is less than 2 and satisfies the specifications as listed in Table 1 .

In FIG. 28, the vertical axis indicates the input loss in the unit of dB. The input loss is an input loss generated when an unbalanced signal is input through the input (unbalanced) port 310 and a balanced signal is output through the output (balanced) port 1 320 and the output (balanced) port 2 330. It is understood that a desired signal is passed since the input loss is small in the pass band.

For example, the frequency range of a pass band of Table 1 is 470 to 750 MHz and FIG. 28 satisfies the range. The attenuation must be equal to or greater than 20 dB in the frequency range of 174 to 240 MHz in the attenuation item.

Since a value of the vertical axis in FIG. 28 is equal to or less -20 dB in the frequency range of 174 to 240 MHz, FIG. 28 satisfies the specification.

The vertical axis of FIG. 29 represents a difference between an input loss which is generated when an unbalanced signal is input through the input (unbalanced) port 310 and a balanced signal is output through the output (balanced) port 1 320 and an input loss which is generated when an unbalanced signal is input through the input (unbalanced) port 310 and a balanced signal is output through the output (balanced) port 2 330 in the unit of dB.

In the specifications as listed in Table 1, amplitude balance must not exceed ±1 in the pass band. Since the value indicated in the unit of dB is near 0 (zero), the amplitudes of the balanced signals output from the output ports 320 and 330 are the same and satisfy the specifications as listed in Table 1.

The vertical axis of FIG. 30 represents a phase difference between a balanced signal output from the output (balanced) port 1 320 and a balanced signal output from the output (balanced) port 2 330. In other words, when the phase difference between the output ports 320 and 330 is 180 + A, the vertical axis of FIG. 30 represent a value of A in the unit of dB. In the specifications as listed in Table 1, the phase balance in the pass band must not exceed 180 ±10 degrees and FIG. 30 satisfies this condition.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims .

Claims

WHAT IS CLAIMED IS:

1. A band balanced filter comprising: an input port through which an unbalanced signal is input; a band pass filter (BPF) passing through a signal at a certain band; a Balun converting the unbalanced signal into a balanced signal; and a first output port and a second output port outputting the balanced signal; wherein the BPF and the Balun have structures in which a plurality of layers are laminated; wherein the BPF receives a signal from the input port, and in the BPF, first capacitors (509a, 510a, 511a) laminated on certain layers to be electrically connected to each other and first inductors (513a and 514a) laminated on certain layers to be electrically connected to each other form an input end of the BPF, second inductors (513b, 513d, 514b,

514d, 515a, and 515c) laminated on certain layers to be electrically connected to each other form a resonant line of the BPF, the second inductors (513b, 513d, 514b, 514d, 515a, and 515c) and second capacitors (509a and 509b) on certain layers make resonance, and third capacitors (509b, 510b, and 511b) laminated on certain layers to be electrically connected to each other and third inductors (513e and 514e) laminated on certain layers to be electrically connected to each other form an output end of the BPF; and wherein, in the Balun, a fourth inductor (507) on a certain layer receives an unbalanced signal output from the output end of the BPF, a balanced line on a certain layer (503) that is uncoupled with an unbalanced line on a certain layer (506) outputs a part of the balanced signal (first balanced signal) through the first output port, and a balanced line on a certain layer (505) that is coupled with the unbalanced line on the layer (506) outputs the rest (second balanced signal) of the balanced signal through the second output port.

2. The band balanced filter as set forth in claim 1, wherein, in the BPF, fifth inductors (513c, 514c, and 515b) laminated on certain layers to be electrically connected to each other adjust a pass bandwidth.

3. The band balanced filter as set forth in claim 1, wherein, in the BPF, fourth capacitors (512, 511a, and 511b) laminated on certain layers to be electrically connected to each other adjust an interval between poles of return loss.