WO2007032452A1

WO2007032452A1 - Variable resonance circuit, filter, communication apparatus and method for regulating temperature characteristics of variable resonance circuit

Info

Publication number: WO2007032452A1
Application number: PCT/JP2006/318306
Authority: WO
Inventors: Hiroshi Katta
Original assignee: Kyocera Corporation
Priority date: 2005-09-14
Filing date: 2006-09-14
Publication date: 2007-03-22
Also published as: JP4855407B2; JPWO2007032452A1; WO2007032452A9

Abstract

A variable resonance circuit having excellent resonance frequency and temperature characteristics of resonance frequency variation rate. The variable resonance circuit comprises a variable capacitance capacitor employing a thin film dielectric layer having a dielectric constant varying with a control voltage and a temperature coefficient X equal to variation in dielectric constant for temperature, and a transmission line obtained by forming a ground conductor and a line conductor on a dielectric layer having a dielectric constant varying with a control voltage and such a temperature coefficient Y that variation in dielectric constant for temperature has a polarity reverse to that of the temperature coefficient X. Since variation in equivalent capacitance of the transmission line serves to suppress variation in capacitance of the variable capacitance capacitor for temperature variation, variation in resonance frequency of the resonance circuit due to temperature variation can be suppressed, resulting in a variable resonance circuit excellent in temperature characteristics of resonance frequency.

Description

Specification

Variable resonance circuit, filter device, communication device, and temperature characteristic adjustment method for variable resonance circuit

Technical field

The present invention has a dielectric layer whose relative dielectric constant changes depending on an applied voltage as a resonance circuit used for communication equipment such as a mobile phone and high-frequency components such as a filter or an oscillator, and the capacitance changes. In particular, a variable resonance circuit using a variable capacitor whose resonance frequency can be varied by the variable resonance capacitor, in particular, a variable resonance in which a change in characteristics due to a temperature change of the resonance frequency and the resonance frequency variable rate is suppressed, that is, an excellent temperature characteristic. Regarding the circuit. Furthermore, the present invention relates to a filter device, a communication device, and a temperature characteristic adjustment method for the variable resonance circuit using the variable resonance circuit.

Background art

[0002] Conventionally, a variable resonance circuit in which an impedance element including an inductor component such as an inductor or a transmission line and a variable capacitor are combined is known. Such a variable resonance circuit is a voltage-controlled oscillator or a voltage-controlled variable circuit. It is used as a filter or a resonance circuit such as a notch circuit for removing unnecessary harmonic components and noise components. For example, Japanese Laid-Open Patent Publication No. 2003-110321 discloses that a ferroelectric oxide thin film having a velovskite structure such as strontium titanate or strontium barium titanate is used as a dielectric layer and sandwiched between them. By applying a predetermined control voltage between the upper electrode layer and the lower electrode layer, the resonance frequency can be changed by changing the relative dielectric constant of the dielectric layer and changing the capacitance. A variable resonance circuit using a capacitive capacitor has been proposed.

However, the relative dielectric constant of the variable capacitor proposed in Japanese Unexamined Patent Application Publication No. 2003-110321 also changes with temperature. Further, it is known that the variable capacitance of a variable capacitor generally increases as the relative dielectric constant increases. For this reason, temperature characteristics occur in the capacitance value and the capacitance variable rate due to the temperature dependence of the dielectric constant. For this reason, the resonance frequency and the common frequency of a variable resonance circuit using such a variable capacitor are used. The rate of change of the vibration frequency differs depending on the ambient temperature, and there is a problem that a desired resonance characteristic cannot be obtained stably. For example, when this variable resonance circuit is used for a filter, there is a problem that frequency selectivity, pass characteristics, attenuation characteristics, and the like change according to the ambient temperature.

Disclosure of the invention

The present invention has been devised in view of the problems in the prior art as described above, and its purpose is to suppress changes in resonance characteristics such as resonance frequency and resonance frequency change rate due to changes in ambient temperature. An object of the present invention is to provide a variable resonance circuit having excellent temperature characteristics, and to provide a filter device, a communication device, and a temperature characteristic adjusting method for the variable resonance circuit using the variable resonance circuit.

The present invention provides a variable capacitor using a first dielectric whose relative dielectric constant is a temperature coefficient X, and the relative dielectric constant is changed by application of a control voltage. A variable resonance circuit comprising: an inductor having a second dielectric whose change is a temperature coefficient Y having a polarity opposite to that of the temperature coefficient X.

In the present invention, the first dielectric has a relative permittivity that changes when a control voltage is applied, and the inductor includes a ground conductor and a line conductor formed on the second dielectric. It is a transmission line. That is, the relative permittivity changes with the application of the control voltage, and the change in the relative permittivity with respect to the temperature uses the first dielectric whose temperature coefficient is X, and the relative permittivity with the application of the control voltage. And a transmission line formed by forming a ground conductor and a line conductor on a second dielectric whose change in relative permittivity with respect to temperature is a temperature coefficient Y whose polarity is opposite to that of the temperature coefficient X. Is a variable resonance circuit characterized by

In the present invention, the product of the capacitance value of the variable capacitor and the absolute value of the temperature coefficient X (hereinafter referred to as IXI), the equivalent capacitance value of the transmission line, and the absolute value of the temperature coefficient Y ( In the following, the product of IYI is substantially equal.

In the present invention, the line conductor of the transmission line is characterized in that at least a part thereof is formed on a surface layer of the second dielectric and has a plurality of cutable branch portions. . In the present invention, the transmission line has a length that is an odd multiple of λg / 4 (λg: effective wavelength of a high-frequency signal propagating through the transmission line), and one end thereof is used for high-frequency grounding. The other end is connected to the signal input terminal together with the variable capacitor, and a control voltage is applied between the one end and the high-frequency grounding capacitor.

The present invention further includes a direct current limiting capacitor connected to at least one of the variable capacitor and the transmission line. In the present invention, the variable capacitor and The inductor is connected in parallel.

In the present invention, the variable capacitor and the inductor are connected in series.

In the present invention, the first dielectric and the second dielectric are barium strontium titanate forces.

Further, the present invention includes an input terminal, an output terminal, and a ground terminal, and the above variable on the input / output line connecting the input terminal and the output terminal or between the input / output line and the ground terminal. A filter device is provided with a resonance circuit.

According to another aspect of the present invention, there is provided a communication apparatus including at least one of a reception circuit and a transmission circuit having the filter device.

Further, according to the present invention, the relative dielectric constant varies depending on the control voltage, and the relative dielectric constant varies depending on the control voltage and the variable capacitor using the first dielectric whose change in the relative dielectric constant with respect to temperature is the temperature coefficient X. A variable resonance circuit including a transmission line formed by forming a ground conductor and a line conductor on a second dielectric having a temperature coefficient Y whose polarity is opposite to that of the temperature coefficient X. The product of the capacitance value of the variable capacitor and the absolute value of the temperature coefficient X, and the product of the equivalent capacitance value of the transmission line and the absolute value of the temperature coefficient Y are substantially equal to each other. The variable resonance circuit temperature is adjusted by adjusting one of the capacitance value of the variable capacitor, the temperature coefficient X, the equivalent capacitance value of the transmission line, and the temperature coefficient Y so as to be equal to each other. This is a characteristic adjustment method. In the present invention, at least a part of the line conductor of the transmission line is the first conductor.

The dielectric layer of 2 is formed so as to have a plurality of cutable branch portions, and the branch portions are cut to adjust the equivalent capacitance value of the transmission line. Brief Description of Drawings

[0004] Objects, features, and advantages of the present invention will become more apparent from the following detailed description and drawings.

FIG. 1 is an equivalent circuit diagram showing an embodiment of a variable resonance circuit according to an embodiment of the present invention.

FIG. 2 is a partially enlarged plan view showing an example of a line conductor of a variable transmission line having a plurality of cutable branch portions according to the present invention.

FIG. 3 is an equivalent circuit diagram showing a variable resonance circuit according to another embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram showing a variable resonance circuit of still another embodiment of the present invention. FIG. 5 is an equivalent circuit diagram showing the filter device of one embodiment of the present invention. FIG. 6 is an equivalent circuit diagram showing a filter device according to another embodiment of the present invention. FIG. 7 is a block diagram showing a communication apparatus according to an embodiment of the present invention.

FIG. 8 is a partially enlarged plan view showing another example of the line conductor of the variable transmission line having a plurality of cutable branch portions according to the present invention.

9A to 9C are sectional views showing examples of the transmission line of the present invention. 10A to 10C are a plan view and a cross-sectional view of the variable resonance circuit shown in FIG. 4, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the variable resonance circuit of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an equivalent circuit diagram showing a variable resonance circuit according to an embodiment of the present invention. Here, in FIG. 1, a variable capacitor having a thin film dielectric layer as a first dielectric is used, and a ground conductor and a line conductor are connected to the dielectric layer as a second dielectric as an inductor. An example using a transmission line that is formed will be described.

In the equivalent circuit diagram shown in FIG. 1, Ct is a variable capacitor, Tt is a λ gZ4 variable transmission line as a transmission line, and Cc is a high-frequency contact that forms a high-frequency grounding capacitor. Ground capacitors, LI and L2 are choke coils containing RF blocking inductor components for supplying control voltage, S is a signal input terminal, VI and V2 are voltage control terminals for applying control voltage, and Cd is This is a DC limiting capacitor that separates the voltage control terminals VI and V2 and limits the DC component to the signal input terminal S. Here, g is an effective wavelength when a high-frequency signal input from the signal input terminal S propagates through the λ gZ4 variable transmission line Tt.

In FIG. 1, a circuit in which a DC limiting capacitor element Cd and a variable capacitor Ct are connected in series between the signal input terminal S and the ground potential is connected to the DC limiting capacitor element Cd and the λ gZ4 variable transmission line Tt. A high-frequency grounding capacitor Cc is connected in parallel to the circuit connected in series. Furthermore, the voltage control terminal VI is connected between the DC limiting capacitor element Cd and the variable capacitor Ct via the choke coil L1, and the choke coil L2 is connected between the DC limiting capacitor element Cd and the λ gZ4 variable transmission line Tt. The voltage control terminal V2 is connected via.

In the example shown in FIG. 1, one DC limiting capacitor element Cd is provided in each of the variable capacitor element Ct side circuit and the gZ4 variable transmission line Tt side circuit, but the variable input element Ct is connected to the signal input terminal S. Side circuit and λ gZ4 variable transmission line Tt side circuit connected in parallel Signal input terminal When one DC limiting capacitive element Cd is provided on the S side, the variable capacitive element Ct side circuit or λ It may be provided in one of the circuits on the gZ4 variable transmission line Tt side.

When a control voltage is supplied from the voltage control terminal VI, the control voltage is applied from the voltage control terminal VI to the variable capacitor Ct via the RF blocking choke coil L1.

When a control voltage is supplied from the voltage control terminal V2, the current passes through the line conductor of the λ gZ4 variable transmission line Tt from the voltage control terminal V2 via the RF blocking choke coil L2, and passes through the high-frequency grounding capacitor Cc. Since it flows to the ground (ground potential), a control voltage is applied between the line conductor of the gZ4 variable transmission line Tt and the ground conductor.

In addition, the direct current limiting capacitive element Cd prevents the direct current component from leaking to the signal input terminal S side and can provide a potential difference between the control voltages VI and V2, so that the control voltages V1 and V2 are separated. be able to. Therefore, control voltages VI and V2 are controlled independently. It is possible to

The RF blocking choke coils LI and L2 are for blocking high frequency signals from the signal input terminal S from flowing directly to the control voltage terminals VI and V2.

The variable capacitor Ct is composed of an upper electrode layer and a lower electrode layer sandwiching a thin film dielectric layer whose relative dielectric constant varies with the control voltage and whose variation relative to temperature is a temperature coefficient X. By using the variable capacitor Ct having such a configuration, the thin film dielectric layer has a predetermined dielectric constant corresponding to the applied control voltage, and therefore the capacitance value of the variable capacitor Ct is controlled to a desired value. be able to. Any thin dielectric layer may be used as long as it is a high dielectric layer whose dielectric constant changes with application of voltage. Any material can be used for the upper electrode layer and the lower electrode layer as long as they have conductivity. For example, a sapphire R substrate is used as the support substrate for forming the variable capacitor Ct, and Pt is used as the lower electrode layer on this substrate, and (Ba Sr) Ti O (0≤x≤l, 0 < y≤l

) If a variable capacitor Ct with a structure using PtZAu (lower layer Z upper layer is shown below) is formed in the upper electrode layer, an element having a high Q value and suitable for a high-frequency circuit can be obtained. it can. The temperature coefficient X of the relative dielectric constant of the thin film dielectric layer can be changed by changing the composition ratio, film thickness, film forming temperature, etc. of the thin film dielectric layer. In addition, since each electrode layer has a GAP configuration, the lower electrode layer is not required, so that the device can be easily fabricated, integrated, and the like.

As shown in FIGS. 9A to 9C, the gZ4 variable transmission line Tt includes a microstrip line (FIG. 9A) and a coplanar line (FIG. 9B) configured by forming a ground conductor 12 and a line conductor 10 on a dielectric layer 11. ) And stripline (Fig. 9C). 9A, a line conductor 10 is formed on one main surface of the dielectric layer 11, and a ground conductor 12 is formed on the entire other main surface of the dielectric layer 11. In FIG. In FIG. 9B, a line conductor 10 is formed on one main surface of the dielectric layer 11, and two ground conductors 12 are formed on the one main surface so as to be spaced from each other with the line conductor 10 interposed therebetween. . In FIG. 9C, a ground conductor 12 is formed on the entire main surfaces of the dielectric layer 11, and a line conductor 10 is formed inside the dielectric layer 11. As described above, the configuration in which the dielectric layer 11 exists between the electric field generated between the line conductor 10 and the ground conductor 12 makes it possible to form the gZ4 variable transmission line Tt. Of this configuration By using the λ gZ4 variable transmission line Tt, the dielectric layer has a predetermined dielectric constant corresponding to the applied control voltage, so that the equivalent capacitance value of the λ gZ4 variable transmission line Tt can be controlled to a desired value. it can. The ground conductor and the line conductor are made of a conductive material, and the dielectric layer has a temperature coefficient X in which the change in relative dielectric constant with respect to temperature is opposite to that of the temperature coefficient X. A configuration using a material whose relative permittivity changes is used. For example, Pt for the ground conductor and (Ba Sr) Ti O (0≤x≤l, 0 <y≤ll -xy 3 for the dielectric layer

The temperature coefficient Y of the relative permittivity of the dielectric layer can be adjusted by changing the composition ratio of the dielectric layer, the film formation temperature, etc.

. Further, the dielectric layer may be composed of a plurality of layers using different compositions or materials.

Specifically, if the composition ratio is Ba-rich, for example (Ba Sr) Ti 2 O, the temperature coefficient

0. 85 0. 15 0. 85 3

Becomes positive, and if the composition ratio is Sr rich, for example (Ba Sr) Ti 2 O, the temperature coefficient is negative.

0. 2 0. 8 0. 85 3

It becomes.

In addition, the temperature coefficient can be controlled by applying strain to the thin film dielectric layer of the variable capacitor Ct and the dielectric layer of the λgZ4 variable transmission line Tt due to stress or the like. In other words, the temperature coefficient becomes negative when one of the cues is below the operating temperature range, and the temperature coefficient becomes positive when the Curie point exceeds the operating temperature range.

In addition to the above-mentioned barium strontium titanate, the dielectric layer and thin-film dielectric layer include Bi—Zr—Nb oxide (BZN), Sr—Bi—Ta oxide (SBT), Pb—La—. Ti-based oxide (PLT) can be used.

In the equivalent circuit diagram of Fig. 1, it can be seen that the variable transmission line Tt is a gZ4 short-circuited transmission line in the high-frequency region, and is equivalent to an LC parallel resonant circuit near the resonance frequency. Here, the equivalent inductor of the variable transmission line Tt is L, and the equivalent capacitance is C.

When the initial value of the equivalent capacitance C of the variable transmission line Tt at temperature T is C1 and the initial value of the capacitance value of the variable capacitor Ct is Ctl, the resonance frequency fl is ί1 = 1 / (2 π (L- (Cl + Ctl)) ^1/2 ). In addition, the capacitance value of the variable capacitor Ct when the control voltage (applied voltage) Va is applied from the voltage control terminal VI is Ct2, and the equivalent capacitance C of the variable transmission line Tt when the control voltage Vb is applied from the voltage control terminal V2. If the capacitance value of C2 is C2, the resonance frequency f2 is ί2 = 1 / (2π (L '(C2 + Ct2)) ^1/2 ). In other words, the resonance frequency of the variable resonance circuit can be changed to an arbitrary value by adjusting the capacitance value of the variable capacitor Ct and the capacitance value of the equivalent capacitance C of the variable transmission line Tt according to the applied voltage.

The capacitance and equivalent capacitance of such a variable capacitor Ct and variable transmission line Tt vary depending on the ambient temperature.

Where X is the temperature coefficient of the relative permittivity of the variable capacitor Ct, and = (e vc-e ve) / ((Τ'— Τ) · ε rc) (ε rc: temperature Τ of the thin film dielectric layer Relative dielectric constant, ε rc ': relative dielectric constant of the thin film dielectric layer at temperature T'), the capacitance value is proportional to the relative dielectric constant, so the capacitance value Ctl due to the temperature の of the variable capacitor Ct is the temperature At T ′, the capacitance value Ctl ′ = Ctl + Ctl−X− (T′−T).

Similarly, let Y be the temperature coefficient of the relative permittivity of the variable transmission line Tt, and Υ = (ε rt '-ε rt) / ((Τ'- Τ) · ε rt) (ε rt: Dielectric layer with temperature Τ ∈ rt ': dielectric constant of dielectric layer due to temperature T), the capacitance value C1 due to temperature 、 is the capacitance value C1' = C1 + C1-Y- (Τ , Ichigo).

Therefore, the resonance frequency fl at temperature Τ is f 1 = 1Z (2 π (L · (C1, + Ctl,)) ^1/2 ) = 1 / (2π (L- (Cl + Cl- Y- (Τ, one T) + Ctl + Ctl · Χ · (T, one T))) ^1/2 ). Here, since the polarities (signs) of the temperature coefficients X and Υ are opposite to each other, according to the variable resonance circuit of the present invention, the change in the capacitance value of the variable capacitor Ct with respect to the temperature change can be detected by the variable transmission line Tt. Since the change of the equivalent capacitance value is mitigated, the change of the resonance frequency of the variable resonance circuit due to the temperature change can be reduced.

Further, even if the control voltage is changed in the same range, the capacity change rate is different at different temperatures. This is because the capacitance is proportional to the relative dielectric constant, which is a function of temperature. In general, it is known that the capacity change rate increases as the relative dielectric constant increases. For example, if the relative dielectric constant of the variable capacitor Ct is reduced by the temperature coefficient X due to the temperature T ', the change rate of the capacitance is 1 I Ctl, 1 Ct2, I / Ctl, (Ctl ,: temperature Initial capacitance value at T ', Ct2': Capacitance value when control voltage is applied at temperature T, Ctl'-Ct2 ': Capacitance change amount) is also small, but the relative permittivity of variable transmission line Tt is polar Is increased due to the inverse temperature coefficient Y, the capacity change rate of the equivalent capacity C is increased. Therefore, temperature Even when the capacitance change rate decreases due to the change in the relative permittivity of the variable capacitor with respect to the change, the equivalent capacitance change rate due to the change in the relative permittivity of the transmission line increases. The decrease in frequency change rate can be reduced. Also, the product of the capacitance value of the variable capacitor ct and the absolute value IXI of the temperature coefficient X, the equivalent capacitance value of the transmission line Tt, and the absolute value of the temperature coefficient γ I γ I Is substantially equal to the resonance frequency fl '= 1 / (2 π (L- (C1 + C1 · Υ · (Τ'— Τ) + Ctl + C tl -X- (Τ 、一 Τ))) ^1/2 ) Ctl 'X + Cl' Y = 0, so ί1 '= 1 / (2 π (L • (ci + cti)) ^1/2 ), Which is equal to the resonance frequency fl at temperature T. Therefore, the change in the resonance frequency of the variable resonance circuit due to the temperature change can be further reduced.

To make Ctl 'X + Cl' Y = 0, adjust at least one of the initial capacitance value Ctl, temperature coefficient X of the variable capacitor Ct, the initial equivalent capacitance value C1 of the variable transmission line Tt, and the temperature coefficient Y. .

Here, in the example illustrated in FIG. 1, the force capacitor described in the example in which the variable capacitor Ct and the gZ4 variable transmission line Tt are connected in parallel may be connected in series. If both are connected in parallel, the impedance will increase at the resonance frequency, so that if the signal is used as a shunt, only signals near the resonance frequency can be passed. In addition, if both are connected in series, the impedance is reduced at the resonance frequency. Therefore, if the signal is used as a shunt, only the signal near the resonance frequency can be attenuated.

Here, it is preferable that at least a part of the line conductor constituting the variable transmission line Tt is formed on the surface layer of the dielectric layer and has a plurality of severable branch portions.

Here, a chip capacitor type may be used as the variable capacitor, or a thin film dielectric layer and a pair of electrodes sandwiching the thin film dielectric layer may be formed by a thin film forming method. You can also use a tip coil as the inductor.

FIG. 2 is a partially enlarged plan view showing an example of a line conductor of a variable transmission line that has a plurality of severable branch portions that constitute the variable resonance circuit of the present invention. In FIG. 2, the line conductor 10 includes a trunk portion 10a and an annular portion 10b protruding from the trunk portion 10a. It has bridging parts B and C so that it can be cut into pieces. Here, a part A of the portion where the trunk portion 10a and the annular portion 10b overlap, and the bridging portions B and C are defined as branch portions. In addition, the branch part A can open the annular part 10b if it is removed. In FIG. 2, the hatching different from the other line conductors 10 is given for easy understanding of the branch portions A to C.

In the line conductor 10, in the initial state, the high frequency signal flowing through the trunk portion 10a passes through the portion A which is the shortest distance. Here, by removing the A portion of the line conductor 10 using a laser or the like, the high-frequency signal enters the annular portion 10b from the trunk portion 10a and returns to the trunk portion 10a through the B portion. Therefore, since the line length of the line conductor 10 is longer than when passing through part A, the resonance frequency can be adjusted to be lower than the resonance frequency in the initial state. Also, if part B is removed in addition to part A, the high-frequency signal enters the annular part 10b from the trunk part 10a and returns to the trunk part 10a through the part C. The frequency can be adjusted even lower. Furthermore, if C part is removed in addition to A part and B part, the high-frequency signal returns from trunk part 10a to annular part 10b and returns to trunk part 10a, so that the line length becomes the longest and the resonance frequency can be adjusted to be lower. I can do it. In other words, the resonance frequency can be adjusted by cutting the branch portion.

It is desirable that at least a part of the line conductor 10 is formed on the surface layer of the dielectric layer so that the line conductor 10 can be easily removed from the outside by a laser or the like even when the variable resonance circuit is mounted.

By using the line conductor 10 having such branch portions A to C, the resonance frequency can be adjusted in a wide frequency range. For example, when a control voltage that maximizes the relative permittivity is applied to the variable capacitor Ct and the variable transmission line Tt, the resonance in the initial state is obtained so as to obtain the maximum value in the desired resonance frequency variable range. If the frequency is set by adjusting the length of the line conductor 10 of the variable transmission line Tt, the capacitance variable rate of the variable capacitance capacitor Ct and the equivalent capacitance value of the transmission line Tt by the applied voltage is maximized. I can make it. Since it is possible to resonate at a desired frequency using the variable capacitor Ct and the variable transmission line Tt having such a variable capacity variable rate as much as possible, the resonance frequency can be adjusted in a wide frequency range.

Also, by changing the length of the variable transmission line Tt as described above in the initial state, If the control voltage is not applied to the capacitance capacitor ct and the transmission line Tt, the control voltage required to obtain the desired resonance frequency is reduced by adjusting the state (OV) so that the desired resonance frequency can be obtained. Therefore, the power consumption of the variable resonance circuit can be reduced.

Furthermore, since the equivalent capacitance value of the variable transmission line Tt can be adjusted by changing the length of the variable transmission line Tt, the resonance frequency change due to the temperature change can be further reduced. In addition, since the equivalent capacitance value of the transmission line Tt can be adjusted after forming the variable resonance circuit, the change in the resonance frequency due to the temperature change can be easily reduced. Next, a variable resonance circuit according to another embodiment of the present invention will be described. FIG. 3 is an equivalent circuit diagram showing a variable resonance circuit according to another embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description thereof will be omitted.

In FIG. 3, a variable capacitor Ct is connected in parallel to a circuit in which a variable transmission line Tt and a high-frequency grounding capacitor Cc are connected in series between the signal input terminal S and the ground potential section. A voltage control terminal V3 is connected between the transmission line Tt and the high frequency grounding capacitor Cc. The DC voltage applied to the voltage control terminal V3 is applied to the variable transmission line Tt and the variable capacitor Ct. Also, in the high frequency range, the variable transmission line Tt can be viewed as a gZ4 tip short-circuited transmission line, so the impedance is sufficiently high, and the high frequency signal is sent from the signal input terminal S to the voltage control terminal V3 side. There is no leakage. Therefore, a voltage supply circuit such as a choke coil including an RF blocking inductor component for supplying the control voltage V3 is not required, and the variable resonance circuit can be reduced in size and can be easily handled as a variable resonance circuit.

Next, a variable resonance circuit according to still another embodiment of the present invention will be described. FIG. 4 is an equivalent circuit diagram showing a variable resonance circuit of still another embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description thereof is omitted. In FIG. 4, L4 and L5 include an RF blocking inductor component for supplying a control voltage. Choke coil, V4 and V5 are voltage control terminals for applying control voltage In FIG. 4, to the signal input terminal S, a direct current limiting capacitor element Cd, a variable capacitor Ct, and a gZ4 variable transmission line Tt are connected in series. Furthermore, the voltage control terminal V4 is connected between the variable capacitor Ct and the λ gZ4 variable transmission line Tt via the choke coil L4, and the choke coil L5 is connected between the DC limiting capacitor element Cd and the variable capacitor Ct. The voltage control terminal V5 is connected via In FIG. 4, the gZ4 variable transmission line Tt is an open-ended type.

A specific example of the circuit diagram shown in Figure 4 is shown in Figure 10A.

In addition, the same code | symbol is attached | subjected to the location similar to drawing shown to FIG. 9A-FIG. 9C.

The λ gZ4 variable transmission line Tt is a coplanar line, and a line conductor 10 and a ground conductor 12 arranged so as to sandwich it from both sides are formed on a dielectric layer 11 as a second dielectric. ing. On the dielectric layer 11, conductor portions 13a and 13b are formed on the extension lines of the line conductor 10. A chip capacitor as a variable capacitor is joined between the line conductor 10 and the conductor portion 13b. A chip capacitor as a direct current limiting capacitive element Cd is joined between the conductor portion 13b and the conductor portion 13a. The conductor portion 13a functions as the signal input terminal S. As a result, the DC limiting capacitive element Cd, the variable capacitor Ct, and the gZ4 variable transmission line Tt are connected in series. A choke coil L5 is joined between the conductor portion 13b and the ground conductor 12. As a result, the ground conductor 12 has a function as the voltage control terminal V5. Furthermore, a conductor portion 13 c is formed on the dielectric layer 11 so as to be spaced apart from the line conductor 10 and the ground conductor 12. The conductor 13c and the line conductor 10 are connected by a choke coil L4. The conductor 13c functions as the voltage control terminal V4. By adopting such a configuration, the resonance circuit shown in FIG. 4 can be made concrete.

FIG. 10B is a plan view showing a modification of FIG. 10A, and FIG. 10C is a cross-sectional view taken along line AA of FIG. 10B.

FIG. 10A differs from FIG. 10B and FIG. 10C in that a thin film formation method is formed on the dielectric layer 11 in place of the chip capacitor used as the variable capacitor Ct and the direct current limiting capacitor Cd. Specifically, a conductor portion 13d is formed on an extension line of the line conductor 10, and a thin film dielectric layer 14 is formed to cover both the line conductor 10 and one end side of the conductor portion 13d. Then, an electrode layer 15 is formed on the thin film dielectric layer 14. Thus, the variable capacitor Ct is formed by a configuration in which the thin film dielectric layer 14 is sandwiched between the line conductor 10 and the electrode layer 15. In addition, a direct current limiting capacitive element Cd is formed by a configuration in which the thin film dielectric layer 14 is sandwiched between the electrode layer 15 and the conductor portion 13d. Here, if the other end side of the conductor portion 13d is a signal input terminal S, a DC limiting capacitor element Cd, a variable capacitor Ct, and a gZ4 variable transmission line Tt are connected in series. Further, the choke coil L5 is connected between the electrode layer 15 and the ground conductor 12, and the choke coil L4 is connected between the line conductor 10 and the conductor portion 13c. With such a configuration, the resonant circuit shown in FIG. 4 can be realized.

When the control voltage is supplied from the voltage control terminal V4, the control voltage is applied from the voltage control terminal V4 via the choke coil L4 between the line conductor of the λgZ4 variable transmission line Tt and the ground conductor. At the same time, the control voltage is applied from the voltage control terminals V4 and V5 to the variable capacitor Ct via the choke coils L4 and L5. The voltage difference between the potentials of the voltage control terminals V4 and V5 is applied to the variable capacitor Ct. In FIG. 4, since the control voltage terminal V5 is grounded, a control voltage equal to the value of the voltage supplied to the control voltage terminal V4 is applied to the variable capacitor Ct.

As shown in Fig. 4, if a variable capacitor and a λ gZ4 variable transmission line Tt are connected in series, the impedance can be reduced at the resonance frequency, so if used as a shunt for the signal, the resonance frequency Next, an example in which a filter is formed using the variable resonance circuit of the present invention will be described. FIG. 5 is an equivalent circuit diagram showing the filter device of one embodiment of the present invention.

In FIG. 5, the signal input terminal S of the variable resonance circuit shown in FIG. 1 is connected to the input / output line connecting the input terminal In and the output terminal Out. The variable resonance circuit shown in Fig. 1 is connected to ground potential. For this reason, in the filter device shown in FIG. 5, a variable resonance circuit is connected between the input / output line and the dotted terminal. In this way, if the variable capacitor Ct and the gZ4 variable transmission line Tt are connected in parallel and used as a shunt for the signal, the impedance can be increased at the resonance frequency, so a signal in the vicinity of the resonance frequency can be obtained. It is possible to make a band pass filter that can only pass through. FIG. 6 is an equivalent circuit diagram showing a filter device according to another embodiment of the present invention.

In FIG. 6, the signal input terminal S of the variable resonance circuit shown in FIG. 4 is connected to the input / output line connecting the input terminal In and the output terminal Out. In the variable resonance circuit shown in FIG. 4, the ground electrode of the λgZ4 variable transmission line Tt is connected to the ground potential. Therefore, in the filter device shown in FIG. 6, a variable resonance circuit is connected between the input / output line and the ground terminal. In this way, when the variable capacitor Ct and gZ4 variable transmission line Tt are connected in series and used as a shunt for the signal, the impedance can be reduced at the resonance frequency. This can be a band rejection filter that can attenuate only the signal.

In FIGS. 5 and 6, an example in which a variable resonance circuit is connected between the input / output line and the ground terminal has been described. However, a bandpass filter is formed on the input / output line to form a band-pass filter. May be. For example, a variable resonance circuit shown in FIG. 6 may be provided on the input / output line. In this case, in addition to the signal input terminal S, the line conductor of the gZ4 variable transmission line Tt may be connected to the input / output line as a signal output terminal.

Next, an example in which a communication device is formed using the filter device of the present invention will be described. FIG. 7 is a block diagram showing a communication apparatus according to an embodiment of the present invention.

In FIG. 7, a transmitting circuit Tx and a receiving circuit Rx are connected to an antenna 140 via a duplexer 150. The high-frequency signal to be transmitted is removed from the unnecessary signal by the filter 210, amplified by the power amplifier 220, and then radiated from the antenna 140 through the isolator 230 and the duplexer 150. The high-frequency signal received by the antenna 140 passes through the duplexer 150, is amplified by the low-noise amplifier 160, the unnecessary signal is removed by the filter 170, and then re-amplified by the amplifier 180 and converted to a low-frequency signal by the mixer 190. Is done.

In Fig. 7, the filter device of the present invention is used for the! / And shift force of the duplexer 150, the finoleta 170, and the finoleta 210. High! Can be a communication device.

Note that although the communication device having the transmission circuit Tx and the reception circuit Rx has been described with reference to FIG. 7, the communication device may have one of the transmission circuit Tx and the reception circuit Rx! /. It should be noted that the present invention is not limited to the examples of the above-described embodiments, but is a summary of the present invention. It is possible to cover various changes without departing from the scope. For example, as shown in FIG. 8, it may be a line conductor of a variable transmission line formed so that a plurality of annular portions 10b 1, 10b2. In addition, a gZ2 open-ended transmission line may be used instead of the gZ4 short-circuited transmission line. Also, a λ gZ2 tip short-circuited transmission line may be used instead of the gZ4 tip-opened transmission line. Further, although FIGS. 10A to 10C have described the example in which the second dielectric is used as the substrate, a transmission line, a variable capacitor, or the like may be formed on the substrate by a thin film formation process.

The present invention can be implemented in various other forms without departing from the spirit or main characteristic power thereof. Therefore, the above-described embodiment is merely an example in all respects, and the scope of the present invention is shown in the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the scope of claims are within the scope of the present invention.

Industrial applicability

According to the present invention, the change of the equivalent capacitance value of the inductor works to suppress the change of the capacitance value in the entire variable resonance circuit with respect to the change of the capacitance value of the variable capacitor due to the temperature change. The change in the resonance frequency can be reduced.

Similarly, the change in the equivalent capacitance change rate of the inductor against the change in the capacitance change rate of the variable capacitor due to the temperature change works to suppress the change in the entire variable resonance circuit. It is possible to reduce the change in the resonance frequency change rate.

According to the present invention, the change in the equivalent capacitance value of the transmission line works to suppress the change in the capacitance value in the entire variable resonance circuit with respect to the change in the capacitance value of the variable capacitor due to the temperature change. It is possible to reduce the change in the resonance frequency due to.

Similarly, the change in the equivalent capacitance change rate of the transmission line suppresses the change in the entire variable resonance circuit with respect to the change in the capacitance change rate of the variable capacitor due to the temperature change. The change in the resonant frequency change rate of the circuit can be reduced. According to the present invention, since the change in the capacitance value of the variable capacitor due to the temperature change works so as to cancel the change in the equivalent capacitance value of the transmission line, the change in the resonance frequency of the variable resonance circuit due to the temperature change is further reduced. be able to.

Similarly, the change in the equivalent capacitance change rate of the transmission line cancels the change in the entire variable resonance circuit with respect to the change in the capacitance change rate of the variable capacitor due to the temperature change. The change in the resonant frequency change rate of the circuit can be further reduced.

According to the present invention, the impedance of the transmission line can be adjusted by cutting a part (branch part) of the transmission line and changing the line length of the line conductor, so that the resonance frequency of the variable resonance circuit can be adjusted. Can do.

In addition, by changing the length of the variable transmission line in the initial state as described above, a desired resonance frequency can be obtained in the state (ov) without applying a control voltage to the variable capacitor and the transmission line. Therefore, the control voltage required to obtain a desired resonance frequency can be reduced, and the power consumption of the variable resonance circuit can be reduced.

According to the present invention, it can be regarded as a short-circuited short-circuited line having an odd multiple of the length of gZ4 in terms of high frequency, and the impedance in the high frequency band with sufficient signal input terminal strength is sufficiently high, so that a control voltage is supplied. This eliminates the need for a voltage supply circuit such as a choke coil that includes an RF blocking inductor component to reduce the size of the variable resonance circuit and facilitates handling as a variable resonance circuit.

According to the present invention, the DC limiting capacitor element can separate the variable capacitor and the terminal for applying the control voltage to the transmission line, and can limit the DC component to the signal input terminal.

According to the present invention, since the impedance increases at the resonance frequency by connecting the variable capacitor and the inductor in parallel, when the signal is used as a shunt, only a signal in the vicinity of the resonance frequency can be passed. .

According to the present invention, when a variable capacitor and an inductor are connected in series, the impedance is reduced at the resonance frequency. Only the signal near the resonance frequency can be attenuated.

According to the present invention, the first dielectric and the second dielectric have a high capacitance change rate with a small dielectric loss. Therefore, a variable resonance circuit that can be adapted to a wide frequency range can be obtained. In addition, since the temperature coefficient can be adjusted by adjusting the composition, the first dielectric and the second dielectric can be formed using the same material system.

According to the present invention, it is possible to provide a filter device with little characteristic change due to temperature change.

According to the present invention, it is possible to provide a communication device with little filter characteristic change due to temperature change.

According to the present invention, the change in the resonance frequency due to the temperature change can be reduced by the temperature characteristic adjusting method for the variable resonance circuit of the present invention.

According to the present invention, since the equivalent capacitance value of the transmission line can be adjusted after forming the variable resonance circuit, the change in the resonance frequency due to the temperature change can be easily reduced. As described above, according to the present invention, it is possible to provide a variable resonance circuit excellent in temperature characteristics of the resonance frequency and the resonance frequency variable rate. In addition, since the voltage supply circuit can be simplified, it is possible to provide a variable resonance circuit that is small and easy to handle.

Claims

The scope of the claims

[1] The relative permittivity changes with the application of a control capacitor and the variable capacitor using the first dielectric whose change in relative permittivity with temperature is the temperature coefficient X, and the change in relative permittivity with respect to temperature A variable resonance circuit comprising: an inductor having a second dielectric material having a temperature coefficient X and a temperature coefficient Y having a polarity opposite to that of the temperature coefficient X.

[2] The first dielectric has a relative dielectric constant that changes when a control voltage is applied, and the inductor has a transmission line formed by forming a ground conductor and a line conductor on the second dielectric. A variable resonance circuit characterized by the above.

[3] The product of the capacitance value of the variable capacitor and the absolute value of the temperature coefficient X is substantially equal to the product of the equivalent capacitance value of the transmission line and the absolute value of the temperature coefficient Y. The variable resonance circuit according to claim 2.

[4] The line conductor of the transmission line is characterized in that at least a part thereof is formed on a surface layer of the second dielectric and has a plurality of severable branch portions. 2 or

3. The variable resonance circuit according to 3.

[5] The transmission line is λ g / 4 (λ g: effective wavelength of the high-frequency signal propagating through the transmission line.

), One end is grounded via a high frequency grounding capacitor, the other end is connected to the signal input terminal together with the variable capacitor, and between the one end and the high frequency grounding capacitor. 5. The variable resonance circuit according to claim 2, wherein a control voltage is applied to.

6. The variable resonance circuit according to claim 2, further comprising a direct current limiting capacitive element connected to at least one of the variable capacitor and the transmission line.

[7] The variable resonance circuit according to any one of [1] to [6], wherein the variable capacitor and the inductor are connected in parallel.

[8] The variable resonance circuit according to any one of [1] to [7], wherein the variable capacitor and the inductor are connected in series.

[9] The variable resonance circuit according to any one of [1] to [8], wherein the first dielectric and the second dielectric are made of barium strontium titanate.

[10] The input terminal, the output terminal, and the ground terminal, on an input / output line connecting the input terminal and the output terminal, or between the input / output line and the ground terminal. A filter device comprising the variable resonance circuit according to any one of the above.

11. A communication device comprising the filter device according to claim 10, comprising at least one of a reception circuit and a transmission circuit.

[12] A variable capacitance capacitor using a first dielectric whose relative dielectric constant changes according to the control voltage and whose change in relative dielectric constant with respect to temperature is a temperature coefficient X;

The transmission is made by forming a grounding conductor and a line conductor on the second dielectric whose relative dielectric constant changes with the control voltage, and whose relative dielectric constant changes with respect to temperature. A temperature characteristic adjusting method for a variable resonance circuit including a line, comprising: a product of a capacitance value of the variable capacitor and an absolute value of the temperature coefficient X; and an absolute value of an equivalent capacitance value of the transmission line and the temperature coefficient Y. Adjusting the capacitance value of the variable capacitor, the temperature coefficient X, the equivalent capacitance value of the transmission line, or the temperature coefficient Y so that the product with the value is substantially equal. Method for adjusting temperature characteristics of variable resonance circuit.

[13] The transmission line is formed such that at least a part of the line conductor of the transmission line has a plurality of cutable branch portions on a surface layer of the second dielectric, and the branch portions are cut to form the transmission line. 13. The method of adjusting a temperature characteristic of a variable resonance circuit according to claim 12, wherein an equivalent capacitance value of the path is adjusted.