JPH11122067A - Lc filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LC filter circuit capable of applying the laminated LC ceramic filter good in mass productivity and coping with the channel multiplication of a portable telephone or the like. SOLUTION: IC parallel resonance circuits 1 in which a variable capacitor Vc is connected in parallel an inductor L1 are respectively connected between the respective coupling elements of an input/output line and a specified voltage from a variable DC voltage generator DC is applied to the LC parallel resonance circuits 1. Thus, the capacitance of the variable capacitors Vc of the respective LC parallel resonance circuits is changed, a resonance frequency required for the LC parallel resonance circuits is generated, a passing band width is practically widened and the band width can be set without depending on the characteristics of a filter. Thus, even in the case of applying the laminated LC ceramic filter composed by laminating the dielectric layers of a low Q-value, a wide frequency band is secured and the realizing channel multiplication is coped with.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LC filter circuit used for a mobile communication device such as a mobile phone and a mobile phone.

[0002]

2. Description of the Related Art Among filters used in mobile communication equipment, those requiring a steep attenuation generally use a dielectric filter. On the other hand, it is easy to manufacture,
As a filter having excellent mass productivity, a laminated LC filter formed by laminating dielectric layers made of a dielectric ceramic material such as a glass ceramic, a composite material of glass and a dielectric ceramic material, or a low melting point oxide has been proposed. .

[0003]

When the filter is applied to a cellular phone or the like, the bandwidth of the center frequency requires a wide range due to the increase in the number of channels, and this is divided into several parts to secure the number of channels. Therefore, a device having an output waveform having a wide bandwidth is required.

[0004] Incidentally, the dielectric filter has an advantage that a wide frequency bandwidth can be taken and steep attenuation can be ensured, but there is a problem that the shape is large, the mass productivity is poor, and the manufacturing cost is high. .

On the other hand, the laminated LC filter is small and excellent in mass productivity, but has a low Q value, so that the attenuation outside the band becomes slow to obtain a wide pass band, and the S / N ratio decreases. Cause problems.

SUMMARY OF THE INVENTION An object of the present invention is to provide an LC filter circuit which can be applied to a multi-layered LC filter having good mass productivity and which can cope with multi-channel operation of a cellular phone or the like.

[0007]

According to the present invention, a plurality of coupling elements C ₁ , C ₂ and C ₁ are arranged in series on an input / output line, and a variable capacitor VC and an inductor L are arranged between the coupling elements. ₁ is connected in parallel with the LC parallel resonance circuit, and the voltage control device specifies and controls the voltage generated from the variable DC voltage generator, and applies the specified voltage to the LC parallel resonance circuit. An LC filter circuit characterized in that a capacitance value of a variable capacitor VC of each LC parallel resonance circuit is controlled so that a required resonance frequency is generated from the LC parallel resonance circuit. Here, as the variable capacitance capacitor, one using a pn junction diode as a voltage-dependent capacitor (voltage variable capacitance diode) or the like is proposed.

As the variable DC voltage generator, an amplifier or the like built in a cellular phone or the like can be used, and a required voltage is generated from the variable DC voltage generator by a voltage control device including a central control unit CPU and the like. Is controlled as follows.

[0009] Here, from the variable DC voltage generator, FIG.
As shown in the figure, a voltage in the range of, for example, 0 to 0.3 V is generated. When this LC filter circuit is used as a transmitting filter of a mobile communication device, the LC parallel resonance circuit generates a center frequency lower than this by about 80 MHz based on the center frequency of the received signal. Thus, the voltage controller determines the designated voltage value, and further controls the variable DC voltage generator to generate the designated voltage.

Here, the capacitance value of the variable capacitor changes according to the applied voltage, and when the value of the applied voltage increases,
The capacitance value decreases. When the capacitance value changes, LC
The resonance frequency of the parallel resonance circuit changes, and accordingly, the attenuation pole f _N2 of the high frequency side changes while maintaining the attenuation pole f _N1 of the low frequency side of the filter. For this reason, the center frequency changes with a change in the designated voltage of the variable DC voltage generator, and it is possible to arbitrarily generate a frequency of a waveform corresponding to the designated voltage, and cover a wide bandwidth. It is possible to cope with a multi-channel of a mobile phone or the like.

Since the filter circuit itself does not need to have a wide bandwidth frequency characteristic, the Q value is low,
Even when a laminated LC filter having a narrow frequency bandwidth is applied, a wide frequency band W shown in FIG. 3 can be covered, and it is possible to cope with multi-channels.

[0012] Therefore, at least provided with a circuit portion of the LC parallel resonance circuit formed by connected in parallel with an inductor L ₁ variable capacitor VC, be composed of a stacked LC filter comprising a dielectric layer laminating a plurality it can. Further, a plurality of coupling elements C arranged in series on the input / output line
₁ , C ₂ , C _1, and a circuit portion including an LC parallel resonance circuit formed by connecting an inductor L ₁ in parallel with a variable capacitor VC connected between the coupling elements C ₁ , C ₂ , C _1. Can be constituted by a laminated LC filter formed by laminating a plurality of dielectric layers.

Although the present invention makes it possible to apply a multilayer LC filter, it can produce a frequency bandwidth W only by changing the designated voltage of the variable DC voltage generator. Even in a configuration in which a filter is not applied, various applications are expected for bandwidth control.

[0014]

FIG. 1 is an equivalent circuit diagram of an LC filter circuit showing one embodiment of the present invention. Here, a plurality of coupling capacitors (coupling elements) C ₁ , C ₂ , C ₁ are arranged in series on the input / output line M to which the high-frequency voltage is applied, and each coupling capacitor C ₁ , C ₂ and coupling capacitor C ₂
, Between C _3, LC parallel resonance circuit 1 is connected. still,
An inductor may be used as the coupling element.

[0015] The LC parallel resonance circuit 1 includes a series line made of a variable capacitor VC and the read inductor L ₃ Prefecture, in which the series line made of a capacitor C ₃ and the inductor L ₁ Metropolitan formed by connecting in parallel is there. Here, the wide-range attenuation pole f of the output waveform of the filter shown in FIG.
_N2 is dependent on the capacitance value of the variable capacitor VC, the low frequency side attenuation pole f _N1 is dependent on the inductance of the inductor L _1. As this variable capacitance capacitor, one using a pn junction diode as a voltage-dependent capacitor (voltage variable capacitance diode) is proposed.

[0016] Here, the LC parallel resonance circuit 1, in relation to the object of the invention, may be constituted by only the variable capacitor VC and the inductor L _1. Moreover, the fundamental frequency waveform is adjusted by a capacitance setting of the capacitor C _3.

On the other hand, in each LC parallel resonance circuit 1, a variable DC voltage generator DC including a rectifier and the like is connected to an inductor L.
It is connected via a _2, L _2. The variable DC voltage generator DC is designated and controlled by a voltage control device including a central control device CPU and the like so that a required voltage is generated. The inductor L ₂ is a choke coil for an AC blocking,
Since a large inductance is required, a chip inductor is used to prevent a high-frequency voltage from flowing into the variable DC voltage generator DC from the input / output line M. further,
When the capacitor C ₄ is connected in parallel with the variable DC voltage generator DC, and a high-frequency voltage leaks from the inductor L ₂ ,
So that flow into the capacitor C ₄ side.

In such a configuration, based on the center frequency of the received signal, the voltage controller CPU determines a designated voltage value such that the LC parallel resonance circuit generates a center frequency about 80 MHz lower than this, Further, control is performed so that the variable DC voltage generator generates the specified voltage. Then, a specified voltage in the range of 0 to 0.3 V is generated from the variable DC voltage generator DC and applied to the LC parallel resonance circuit 1. As a result, the capacitance value of the variable capacitance capacitor VC changes due to the relationship that the capacitance value decreases as the value of the applied voltage increases. As shown in the waveform diagram of FIG.
The high-frequency attenuation pole f _N2 changes while the low-frequency attenuation pole f _N1 is maintained. For this reason, the required center frequency f ₀ can be generated.

Thus, a wide frequency bandwidth W can be covered, and the frequency bandwidth is substantially widened. For this reason, when applied to a mobile phone or the like, the bandwidth of the center frequency is required to be about 60 MHZ (variably set according to the specification) to increase the number of channels, but this condition can be satisfied as a result. It will be. The setting of the cover band can be easily handled by setting the voltage change width of the variable DC voltage generator DC.

FIG. 2 shows a laminated LC filter F constituting a circuit portion X of the LC filter circuit. here,
The laminated LC filter has six square dielectric layers 10 in the figure.
a to 10f are laminated, and an electrode pattern such as a conductive layer 11, linear electric circuits 13, 13 and various capacitor electrodes, which will be described later, is formed on the laminated surface of each of the dielectric layers 10a to 10f by screen printing or the like. , And are integrally sintered to form a one-chip structure. These dielectric layers 10 a to 10 f are stacked on the base layer 25.

Each of the dielectric layers 10a to 10f is made of a dielectric material such as glass ceramic, a composite material of glass and dielectric ceramic material, or a low melting point oxide.

Here, the dielectric layer 10a has a surface
A conductive layer 11 is formed so as to cover almost the entirety, and a connection end 12 connected to an external earth electric circuit extends to the edge.

In the dielectric layer 10b, on both left and right sides, linear electric circuits 13, 13 are extended inward from edges connected to the earth electric circuit, and the inductors L are formed by the linear electric circuits 13, 13.
Constitute the _1, L _1.

In the dielectric layer 10c, rectangular capacitor electrode layers 14, 14 are formed in the left and right regions, respectively, and the via 1
5 and 15 are connected to the linear electric circuits 13 and 13.

Square capacitor electrode layers 16, 16 are also formed on the left and right regions of the dielectric layer 10d.
Through the thickness of d, the capacitor electrode layers 14, 16, 14,
16 face each other up and down, so that the capacitors C ₃ and C _3
Make up _three . The capacitor electrode layers 16, 16
Has connection edges 17, 17 extending to the edges of the dielectric layer 10d. The edges 17, 17 have external chip inductors L ₂ , L ₂ , a designated voltage generator DC and a capacitor C _4.
Is connected.

On the left and right sides of the upper surface of the dielectric layer 10e, the capacitor electrode layers 16 and 16 are vertically opposed to each other via the thickness of the dielectric layer 10e. 18 capacitor electrode layer 1
9 is formed. The capacitor electrode layers 18, 18 have input / output ends 20, 21 extending to both side edges. The electric path between the input / output terminals 20 and 21 is an input / output line M.
Here, the capacitor electrode layers 16, 18 facing up and down,
The 16 and 18, coupling capacitors C _1, C ₁ are formed, coupling capacitor C ₂ is formed so as to face the capacitor electrode layer 18,19,18 is the respective surface direction.

Further, on the dielectric layer 10f, variable capacitance capacitors VC, VC are provided on both the left and right sides along the front-rear direction. These variable capacitors VC, VC are connected to conductive paths formed before and after, and lead inductors L ₃ , L ₃ are formed at these connection portions. Connection front end 2 of this conductive path
2 is connected to an earth electric circuit, and the connection end 23 is connected to the edge 1.
7, 17 are connected.

Thus, the circuit portion X is configured as described above, and the circuit portion Y composed of an external line is connected to the circuit portion X via the edges 17 and 17.

Since the electrode patterns on the dielectric layers 10a to 10f can be easily formed by means such as screen printing, mass productivity is improved.

In the above-described configuration, a circuit part X including a plurality of coupling elements C ₁ , C ₂ , C ₁ arranged in series on the input / output line M and the LC parallel resonance circuit 1 is formed by a dielectric layer. 10a
1 to 10f, and an appropriate circuit portion including at least the LC parallel resonance circuit 1 in the equivalent circuit of FIG.
It can be constituted by the filter F.

[0031]

According to the present invention, as described above, between each coupling element of the input and output lines, and the variable capacitor VC, the LC parallel resonance circuit 1 and an inductor L ₁ becomes connected in parallel with respectively connected Applying a specified voltage from the variable DC voltage generator DC to the LC parallel resonance circuit 1,
This is because the capacitance of the variable capacitor VC of each LC parallel resonance circuit is changed so that a required resonance frequency can be generated in the LC parallel resonance circuit, and the pass bandwidth is substantially widened. The bandwidth can be set without depending on the characteristics of the filter, which has an excellent effect.

For this reason, the dielectric layer 10a having a low Q value
Even when a laminated LC filter formed by laminating 10 to 10f is applied, a wide frequency band W can be secured, and it is possible to cope with multi-channels. Produce benefits. 1) The entire structure can be formed into a simple and uniform shape, which enables downsizing and space saving. In addition, mechanical stiffness is improved because of simple sintering of the laminate. 2) Since the circuit portion X has a structure that is confined in the dielectric layers 10a to 10f, the circuit portion X is isolated from the external atmosphere, is less susceptible to external influences such as humidity and mechanical shock, and is stable in characteristics. 3) Since an electrode pattern is formed on the laminated surface of the dielectric layers 10a to 10f and the circuit portion X is formed by connecting the electrode patterns, an arbitrary circuit constant can be easily formed only by setting the pattern. This gives flexibility in filter design. 4) Since each dielectric layer is formed of the same material in the form of a sheet, the required conductive layers are formed and laminated, and then sintered together, it is easy to manufacture and mass-produced. Rich in

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing one embodiment of the present invention.

FIG. 2 is an exploded perspective view of a laminated LC filter F constituting a circuit portion X of the present invention.

FIG. 3 is a waveform chart graph showing a change in an output waveform of a filter.

[Explanation of symbols]

1 LC parallel resonance circuit 10a~10g dielectric layer C ₁ -C ₃ capacitor L _1, L ₂ inductor M output line DC variable DC voltage generator VC variable capacitor X, Y circuit portion F laminated LC filter

Claims (3)

[Claims] 1. A plurality of coupling elements C ₁ , C ₂ ,
C ₁ is arranged in series, and a variable capacitance capacitor VC and an inductor L ₁ are connected in parallel between each coupling element.
Each of the C parallel resonance circuits is connected, and the voltage generated by the variable DC voltage generator is specified and controlled by the voltage control device, and the specified voltage is applied to the LC parallel resonance circuits to thereby adjust the variable capacitance of each LC parallel resonance circuit. An LC filter circuit wherein a required resonance frequency is generated from an LC parallel resonance circuit by controlling a capacitance value of a capacitor VC. 2. A variable capacitor VC and an inductor L _1.
And a circuit portion having at least an LC parallel resonance circuit formed by connecting
2. The LC filter circuit according to claim 1, wherein the LC filter circuit comprises a C filter. 3. A plurality of coupling elements C ₁ , C ₂ , C ₁ arranged in series on an input / output line, a variable capacitor VC and an inductor L connected between the coupling elements C ₁ , C ₂ , C _{1. 1}
3. The LC part according to claim 1, wherein a circuit portion including an LC parallel resonance circuit formed by connecting a plurality of dielectric layers is formed by a laminated LC filter formed by laminating a plurality of dielectric layers. Filter circuit.