JP2004072585A - High frequency device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency device which protects circuits connected downstream of an antenna terminal against the entry of high voltage noise of frequencies near a signal pass band such as static electricity into the device. <P>SOLUTION: The device comprises a switch 11 connected to the antenna terminal 10 and an SAW filter 12 connected to the switch 11. The switch has a capacitor 21 and an inductor 22 connected in parallel to a signal line between the antenna terminal 10 and the SAW filter 12. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency device that can be used for a mobile communication device such as a mobile phone, for example, and can protect a high-frequency component such as a filter from static electricity entering from an antenna terminal.
[0002]
[Prior art]
Recently, it has been recognized that in mobile communication devices such as mobile phones, there is a risk that internal electric circuits may be destroyed by static electricity entering from antenna terminals. This is because static electricity is applied at a speed of 1 nanosecond or less and a high voltage of several hundreds to several kilovolts.
[0003]
Therefore, in Japanese Patent Application Laid-Open No. 2001-127666, a high-pass filter 3 including a capacitor and an inductor is connected between the antenna terminal 1 and the switch circuit 2 to protect the circuit 2 as shown in FIG. ing.
[0004]
[Problems to be solved by the invention]
Mobile communication devices such as mobile phones have been miniaturized year by year, and high-frequency devices housed therein have also been required to be miniaturized.
[0005]
In the high-pass filter 3, if the amount of attenuation outside the pass band is to be increased, the capacitor and the inductor must be connected in multiple stages. Further, if the connection is made in multiple stages, not only the insertion loss becomes large, but also the high-frequency device becomes large. Therefore, within a limited size, only a certain characteristic can be obtained.
[0006]
However, if high-voltage noise having a frequency near the signal pass band such as static electricity enters, it may pass through the high-pass filter 3 and enter the circuit 2 connected to the antenna terminal 1 to be destroyed.
[0007]
Therefore, an object of the present invention is to provide a high-frequency device that can protect a circuit connected after an antenna terminal even if high-voltage noise having a frequency close to a signal pass band such as static electricity enters. Things.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following configuration.
[0009]
The invention according to claim 1 of the present invention particularly connects a capacitor and an inductor in parallel with a signal line between an antenna terminal and a filter in a high-frequency device, and bypasses static electricity invading from the antenna to the ground by the inductor. At the same time, the capacitor including the rising high-frequency component that cannot be completely removed by the inductor can protect the circuit including the filter.
[0010]
The invention described in claim 2 of the present invention particularly connects a capacitor and an inductor in parallel with a signal line between an antenna terminal and a switch, and can more reliably protect a circuit including a filter. it can.
[0011]
The invention described in claim 3 of the present invention particularly uses one element having both functions of a capacitor and an inductor, and can reduce the number of components, the mounting area, and the mounting cost. The range of use for mobile communication devices can be expanded.
[0012]
The invention according to claim 4 of the present invention provides an inductor function and a capacitor function inside a multilayer ceramic circuit board provided with various functions of a high-frequency device. The range of use for various mobile communication devices can be expanded.
[0013]
The invention described in claim 5 of the present invention particularly uses an inductor having an inductance of 50 nH or less, and can more reliably protect the circuit.
[0014]
In the invention according to claim 6 of the present invention, in particular, the capacitance of the capacitor is set to 10 pF or less, and the circuit can be protected more reliably.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
Hereinafter, the first embodiment of the present invention will be described with reference to the first embodiment.
[0016]
FIG. 1 is a block circuit diagram of a high-frequency device according to Embodiment 1, and can be used as, for example, an antenna duplexer in a GSM mobile phone conforming to the European mobile phone standard. In FIG. 1, reference numeral 10 denotes an antenna terminal, and reference numeral 11 denotes a switch connected to the antenna terminal 10, which has a function of switching a signal between a transmitting side and a receiving side. The switch 11 is composed of a semiconductor switch, and the switch 11 is connected to the transmitting terminal 31, the SAW filter 12 and the receiving terminal 32.
[0017]
Further, a capacitor 21 having a capacitance of 3 pF and an inductor 22 having an inductance of 18 nH are connected in parallel with the antenna terminal 10 and the signal line of the switch 11. The other ends of the capacitor 21 and the inductor 22 are connected to a ground terminal 23.
[0018]
When the capacitance of the capacitor 21 is as small as possible at 10 pF or less, it is possible to prevent an increase in insertion loss in the pass band without reducing the effect of removing static electricity. If it is larger than 10 pF, it is difficult to reduce the insertion loss in the pass band, which is not preferable. It is better to be as small as possible, but if it is 1 pF or less, it is not preferable because the static electricity resistance of the capacitor 21 itself becomes small and the durability of the circuit protection effect decreases. Therefore, it is preferable to use one having 2 to 5 pF.
[0019]
Further, by setting the inductance of the inductor 22 to 50 nH or less, the effect of removing static electricity is increased. If it exceeds 50 nH, high frequency components passing through the inductor increase, which is not preferable. In addition, since the insertion loss of the signal pass band can be reduced, it is preferable to set it to 3 nH or more.
[0020]
With the high-frequency device having such a configuration, the SAW filter 12 can be protected without increasing the insertion loss in the signal pass band.
[0021]
For comparison of the high-frequency device of the present embodiment, a high-frequency device using a high-pass filter 50 is prepared as shown in FIG. Other configurations are the same as those in FIG. In FIG. 4, the high-pass filter 50 needs to have an inductance of the inductor 51 of about 100 nH and a capacitance of the capacitor 52 of about 33 pF in consideration of the insertion loss in the signal pass band. However, when static electricity invades from the antenna terminal 10, high-frequency high-voltage components close to the pass band cannot be sufficiently removed. Also, if an inductor having a smaller inductance is used, the insertion loss in the pass band increases. Further, since the capacitance of the capacitor is as large as 33 pF, it is not possible to remove high-frequency components near the pass band.
[0022]
FIGS. 5 and 6 show voltages applied to the circuits after the switch 11 when 8 kV static electricity is contact-discharged to the antenna terminal 10 with respect to the high-frequency device of the present embodiment and the high-frequency device of the comparative example.
[0023]
In the high-frequency device of the present embodiment, as shown in FIG. 5, only a voltage of about 470 V is applied during several nanoseconds, but in the high-frequency device of the comparative example, as shown in FIG. Is applied with a voltage of about 950V.
[0024]
Compared with the high-frequency device of the comparative example, the high-frequency device of the present embodiment is applied with a voltage of about １ ／, which indicates that a sufficient voltage drop is performed.
[0025]
That is, by connecting the capacitor 21 and the inductor 22 in parallel with the antenna terminal 10 and the signal line of the switch 11, high voltage noise such as static electricity is reduced by the inductor 22 without increasing insertion loss in the pass band. At the same time, the capacitor 21 absorbs the rising high-frequency component that cannot be completely removed by the inductor 22, so that a high voltage is not applied to the switch 11 and the SAW filter 12, and only a necessary signal can be transmitted.
[0026]
Therefore, the switch 11 and the SAW filter 12, which are likely to be adversely affected by high-voltage noise, can be reliably protected, and a high-frequency device having excellent reliability can be obtained.
[0027]
(Embodiment 2)
Hereinafter, the second embodiment will be described in particular with respect to claims 1 to 3 of the present invention.
[0028]
FIG. 2 shows a cross-sectional view of the high-frequency device according to the second embodiment. The constituent circuit is the same as that shown in the first embodiment, and the description is omitted.
[0029]
In FIG. 2, reference numeral 40 denotes a laminated ceramic substrate, which is formed by alternately laminating a ceramic layer 41 and a conductor pattern 42 to form an antenna terminal 10, a transmission-side terminal 31, a reception-side terminal 32, and each element and terminal on the inner and outer peripheral surfaces. (Not shown) connecting the two. A switch 11, a SAW filter 12, a capacitor 21, and an inductor 22 each composed of a GaAs field effect transistor (hereinafter, FET) are mounted on the surface of the multilayer ceramic substrate 40 to realize the circuit shown in FIG.
[0030]
Therefore, as compared with the first embodiment, the size can be reduced by integrating the high-frequency device, and the range of application to mobile communication devices can be expanded.
[0031]
In addition, the capacitor 21 and the inductor 22 are integrally formed by laminating a ceramic layer and a conductor layer to form one element, thereby reducing the number of parts while maintaining the same protection effect from high-voltage noise. The mounting cost can be reduced.
[0032]
(Embodiment 3)
Hereinafter, the third embodiment of the present invention will be described with reference to the third embodiment.
[0033]
FIG. 3 is a cross-sectional view of the high-frequency device according to the third embodiment. The constituent circuits are the same as those shown in the first and second embodiments, and therefore the description is omitted.
[0034]
The difference between the third embodiment and the second embodiment is the shape of the capacitor 21 and the inductor 22.
[0035]
In the third embodiment, as shown in FIG. 3, the antenna terminal 10, the transmitting terminal 31, the receiving terminal 32 and the antenna terminal 10 are provided on the inner and outer peripheral surfaces of the laminated ceramic substrate 40 in which the ceramic layer 41 and the conductor pattern 42 are laminated. A circuit (not shown) for connecting each element to a terminal is formed. Further, when forming the multilayer ceramic substrate 40, the capacitor 22 is formed inside by forming the inductor 22 and simultaneously laminating the ceramic layer 44 formed of a dielectric material and the internal electrode 45. Then, the FET switch 11 and the SAW filter 12 are mounted on the surface of the multilayer ceramic substrate 40 to realize the circuit shown in FIG.
[0036]
Therefore, as compared with the second embodiment, not only can the high-frequency device be miniaturized and the application to mobile communication equipment can be expanded, but also, after the multilayer ceramic substrate 40 is formed, the capacitor and the inductor are bothersome. Since there is no need to mount it, productivity is excellent.
[0037]
In the first to third embodiments, the capacitor 21 and the inductor 22 are provided between the antenna terminal 10 and the switch 11. However, the capacitor 21 and the inductor 22 are provided in parallel between the SAW filter 12 and the antenna terminal 10 and one end is connected to the ground terminal. 23 may be formed. However, as shown in the above embodiment, by connecting the capacitor 21 and the inductor 22 at a position closer to the antenna terminal 10 when viewed in terms of a circuit, not only the SAW filter but also the circuit including the switch 11 is surely protected. It is desirable because it can be.
[0038]
In each of the above embodiments, the application to the GSM system has been described as an example. However, the present invention is not limited to this. For example, a PDC or AMPS system, a dual band or a triple band may be used. For a countermeasure against high voltage noise entering from the antenna terminal 10, a capacitor 21 and an inductor 22 are connected in parallel between the antenna terminal 10 and a circuit connected to the antenna terminal 10, and one end of the capacitor 21 and the ground is connected to the ground. A similar effect can be obtained by connecting to the terminal 23.
[0039]
Further, in each of the above-described embodiments, the switch 11 has been described by taking the FET as an example. However, a switch configured using a pin diode or the like may be used. Further, the SAW filter 12 has been described as an example configured only on the receiving side. However, the SAW filter 12 may be provided on the transmitting side, and a plurality of filters may be provided for improving accuracy. However, other filters, for example, a dielectric filter may be used.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a high-frequency device that can reliably protect a circuit connected later even if high-voltage noise having a frequency close to the signal pass band enters from the antenna terminal.
[Brief description of the drawings]
1 is a circuit block diagram of a high-frequency device according to Embodiments 1 to 3 of the present invention. FIG. 2 is a cross-sectional view of a high-frequency device according to Embodiment 2 of the present invention. FIG. 3 is a high-frequency device according to Embodiment 3 of the present invention. FIG. 4 is a circuit diagram of a high-frequency device for comparison. FIG. 5 is a graph showing static electricity removal characteristics of the high-frequency device according to the first embodiment of the present invention. FIG. 6 is static electricity of the high-frequency device shown in FIG. Graph showing removal characteristics [Fig. 7] Circuit diagram of conventional high-frequency device [Explanation of reference numerals]
REFERENCE SIGNS LIST 10 antenna terminal 11 switch 12 SAW filter 21 capacitor 22 inductor 23 ground terminal 31 transmitting terminal 32 receiving terminal 40 laminated ceramic substrate 41 ceramic layer 42 conductive pattern 44 ceramic layer 45 internal electrode 50 high-pass filter 51 inductor 52 capacitor

Claims (6)

A high-frequency device comprising an antenna terminal, a switch connected to the antenna terminal, and one or more filters connected to the switch, wherein a capacitor and an inductor are connected in parallel with a signal line between the antenna terminal and the filter. The high-frequency device according to claim 1, wherein the capacitor and the inductor are connected in parallel with a signal line between the antenna terminal and the switch. The high-frequency device according to claim 1, wherein the capacitor and the inductor are integrated elements. The high-frequency device according to claim 1, wherein the antenna terminal, the capacitor, and the inductor are each configured by a multilayer ceramic circuit board in which a conductor layer and a ceramic layer are laminated. The high-frequency device according to claim 1, wherein the inductance of the inductor is 50 nH or less. The high-frequency device according to claim 1, wherein the capacitance of the capacitor is 10 pF or less.

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