JP2000115018A - High frequency switch circuit and high frequency switch circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high frequency which circuit by which low pass filters on a reception route are eliminated or the number is reduced by grounding a strip line within the range of its line length through a capacitive component. SOLUTION: An antenna terminal 14 is connected to one end of the strip line 23 on a reception line through a capacitor 19 shared with a transmission line and the other end of the strip line 23 is connected to a reception terminal 16 through the capacitor 27. The anode side of a PIN diode 26 is connected to an intermediate point between the strip line 23 and the capacitor 27 and a cathode side is grounded. The strip line 23 is provided with the line length to be λ/4 as against the wave length λ of a transmission signal. Thus, the strip line 23 itself shows a low pass filter characteristic so that the low pass filter for coping with a high frequency is unnecessitated on the reception route. Then, whole communication equipment is made to be small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency switch circuit and a high-frequency switch circuit board, and more particularly to a high-frequency switch circuit for switching a signal path in a communication device such as a portable telephone.

[0002]

2. Description of the Related Art A high-frequency switch circuit is used in a mobile communication device such as a portable telephone as shown in FIG.
In order to share the same antenna ANT between the antenna and the receiving circuit Rx, it is used for switching between the antenna and the transmitting circuit and between the receiving circuit. As a configuration of a high-frequency switch circuit, a combination of a strip line SL and a switch element SW as shown in FIG.

An example of a circuit in which a PIN diode is used as the switch element SW will be described with reference to FIG. PIN
A high-frequency switch circuit using a diode has a transmission terminal 1
And a transmission line from the antenna terminal 2 to the reception terminal 3. On the transmission line, the transmission terminal 1 is connected via a capacitor 4 to the anode side of a PIN diode 5, and this diode 5
Is connected to the antenna terminal 2 via the capacitor 6. A control terminal 12 is connected to an intermediate point between the capacitor 4 and the diode 5 via a series circuit of a coil 10 and a resistor 11. On the other hand, on the reception line, the antenna terminal is connected to one end of the strip line 7 via the capacitor 6 shared with the transmission line, and the other end of the strip line 7 is connected to the reception terminal 3 via the capacitor 8. An intermediate point between the strip line 7 and the capacitor 8 is grounded via a PIN diode 9. The strip line 7 has a line length that is λ / 4 with respect to the wavelength λ of the transmission signal. Capacitors 4, 6, and 8 are connected to each PI
This is a coupling capacitor for preventing the bias current flowing through the N diode from flowing out of the high frequency switch circuit. Further, the coil 10 maintains a high impedance between the control terminal 12 and the transmission terminal 1 and prevents a transmission signal from flowing to the control terminal 12.

In the high-frequency switch circuit described above, at the time of transmission, a bias current flows through the diodes 5 and 9 due to the positive voltage applied from the control terminal 12, and the diodes 5 and 9 are turned on. Connected. Further, since the strip line 7 has a line length that is 1/4 of the wavelength of the transmission signal, the impedance between the antenna terminal 2 and the receiving terminal 3 becomes very high, and the antenna terminal 2 and the receiving terminal 3 are separated. State. Therefore, the transmission signal input to the transmission terminal 1 is transmitted to the antenna terminal 2 without flowing to the reception terminal 3 side.

On the other hand, at the time of reception, no voltage is applied to the control terminal 12 or a negative voltage is applied to turn off both the diodes 5 and 9 so that the transmission terminal 1 and the antenna terminal 2 are disconnected. I do. At this time, since the strip line 7 operates as a transmission line, the antenna terminal 2 and the receiving terminal 3 are connected with almost no loss. Therefore, the received signal input to the antenna terminal 2 is
The signal is transmitted to the receiving terminal 3 without flowing to the side. Thus, by controlling the voltage applied to the control terminal 12, transmission and reception can be switched.

[0006]

When the high-frequency switch circuit having the above configuration is actually used, as shown in FIG.
A low-pass filter (LPF) is provided between the transmission circuit Tx and the transmission terminal to prevent unnecessary spurious radiation.
In general, a band-pass (low-pass + high-pass) filter (BPF) is connected between the receiving circuit Rx and the receiving terminal for the purpose of preventing spurious reception. Therefore, between the antenna and the transmitting-side power amplifier and the receiving-side low-noise amplifier, in addition to the high-frequency switch circuit, 2
This required a number of low-pass filters, which hindered miniaturization of the communication device.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a high-frequency switch circuit and a high-frequency switch circuit board which can eliminate or reduce the number of low-pass filters on a receiving path.

[0008]

In order to achieve the object, a high-frequency switch circuit according to the present invention is provided between an antenna terminal and a reception terminal so that the same antenna can be switched to one of transmission and reception. In a high frequency switch circuit to which a strip line is connected, the strip line is grounded via a capacitance component within a range of the line length.

By adopting such a configuration, a distributed constant circuit is formed by the inductance L and the capacitance C on the receiving terminal side from the point where the capacitance component is connected to the entire length of the strip line, and the low frequency band is formed. Pass filter characteristics are exhibited.

It is preferable that the capacitance component comprises two small capacitances, a small capacitance formed at a first connection point of the strip line and a small capacitance formed at a second connection point of the strip line. Compared to the LPF characteristic equivalent to the two-stage Butterworth type when the connected capacitance is one, a steep attenuation equivalent to the three-stage Chebyshev type is obtained at the cutoff frequency,
This is because the frequency selection performance is excellent.

A circuit board suitable for the high-frequency switch circuit of the present invention is formed on a dielectric substrate on which a ground electrode is formed, and on the dielectric substrate with an interval in the thickness direction of the dielectric substrate with respect to the ground electrode. As an element of a high-frequency switch circuit that switches the same antenna to one of transmission and reception,
In a high-frequency switch circuit board including a strip line interposed between an antenna terminal and a receiving terminal, a capacitance forming electrode connected to a ground electrode and forming an interlayer capacitance with the strip line is provided on a dielectric substrate. It is characterized by being provided in.

According to the circuit board having this configuration, the strip line operates as a short stub during transmission so that the transmission signal does not flow to the reception circuit side. At the time of reception, the strip line operates as a transmission line. In particular, when operating as a transmission path, a filter having low-pass characteristics is obtained by adding a capacity to a part of the filter. As a result, the reception signal output to the reception circuit is only a signal of a predetermined frequency band in the transmission path, and the configuration of the reception circuit is simplified.

Further, this capacitance component can be achieved only by providing a capacitance forming electrode in the dielectric substrate so as to face a predetermined position of the strip line. That is, in the process of forming the dielectric substrate having the strip line, the capacitance forming electrodes can be formed at the same time, and there is no need to newly arrange another capacitor. Therefore, the number of components mounted on the dielectric substrate can be reduced without largely changing other wiring. As a result, high performance and miniaturization of the dielectric substrate having the strip line can be achieved at the same time.

Preferably, at least a part of the capacitance forming electrode is exposed on the surface of the dielectric substrate. This is because the capacitance value can be easily adjusted by trimming the exposed portion.

The circuit board of the present invention is not particularly limited as long as the dielectric substrate is provided with a predetermined strip line and a capacitance forming electrode. For example, a coupling capacitor, various resistors, a coil, and the like for preventing a current from flowing out of the circuit board may be provided on the dielectric substrate, or may be provided at another location.

[0016]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a high-frequency switch circuit according to the embodiment.

The high-frequency switch circuit includes a transmission line from the transmission terminal 13 to the antenna terminal 14 and an antenna terminal 1.
4 to the receiving terminal 16. On the transmission line, capacitors 18,
The PIN diode 20, the capacitor 19, and the antenna terminal 14 are connected in series. A control terminal 15 is connected to an intermediate point between the capacitor 18 and the diode 20 via a series circuit of a coil 21 and a resistor 22.
Therefore, the transmission line is the same as the conventional circuit configuration shown in FIG. 11, and each component functions as in the conventional circuit configuration.

On the other hand, on the receiving line, the antenna terminal 1
4 is connected to one end of a strip line 23 via a capacitor 19 shared with a transmission line, and the other end of the strip line 23 is connected to a reception terminal 16 via a capacitor 27. The anode side of the PIN diode 26 is connected to an intermediate point between the strip line 23 and the capacitor 27, and the cathode side is grounded. The strip line 23 has a line length that is λ / 4 with respect to the wavelength λ of the transmission signal. In this strip line 23, the antenna terminal 1
A capacitor 24 is provided between the ground electrode and a position closer to the receiving terminal 16 by a length 1 from the end on the fourth side. Further, a capacitor 25 is provided between a position closer to the receiving terminal 16 by a length m from the position and the ground electrode.

In the high-frequency switch circuit of this embodiment, at the time of transmission, a positive current applied from the control terminal 15 causes a bias current to flow through the diode 20, so that the diode 20 is turned on, that is, connected. At this time, the diode 26
Also turns on, the strip line 23 operates as a short stub having a line length such that the wavelength becomes 1/4 of the wavelength of the transmission signal, the impedance between the antenna terminal 14 and the receiving terminal 16 becomes extremely high, and the Terminal 1
6 is in a disconnected state. Therefore, the transmission signal input to the transmission terminal 13 is transmitted to the antenna terminal 14 without flowing to the reception terminal 16 side.

On the other hand, at the time of reception, no voltage is applied to the control terminal 15 or a negative voltage is applied so that the diodes 20 and 26 are both in the OFF state.
3 and the antenna terminal 14 are cut off. At this time, since the strip line 23 operates as a transmission line, the antenna terminal 14 and the receiving terminal 16 are connected. The reception frequency characteristic at this time is flat, and a good insertion loss between the antenna terminal 14 and the reception terminal 16 can be obtained in the pass band.

The length m of the strip line 23 near the receiving terminal 16 is determined by the inductance L and the capacitor 24.
The capacitors C1 and C2 of the capacitor 25 form a distributed constant type circuit as shown in FIG. 2, and functions as a three-stage Chebyshev type low-pass filter. Therefore, unnecessary high-frequency components at the time of reception are removed here. In order to obtain a desired frequency attenuation, the inductance determined by the length m and the added capacitance component may be adjusted and optimized. FIG. 3 shows transmission characteristics at both ends of the length m portion of the strip line 23. Since the reception frequency of GSM (GROUP SPECIAL MOBILE) is 925 to 960 MHz, C1, C2, and L are 2.7 pF, 2.7 pF, and 8.8 nH, respectively, so that the cutoff frequency is 1 GHz. It is necessary to design. In order to form this inductance with a strip line having a characteristic impedance of 50Ω on a dielectric substrate having a relative dielectric constant of 10 and a thickness of 0.1, the length m is about 13 mm.
Should be determined. Further, a capacitance of 2.7 pF can be easily formed on the same dielectric substrate.

In the above embodiment, the microstrip line is used as the transmission line on the receiving side. However, similar effects can be obtained by using another transmission line such as a strip line instead. The capacitors 24 and 25 may be discrete types, or may be interlayer capacitors obtained by providing a capacitor forming electrode in a layer between the transmission path and the ground. Further, the number of capacitors constituting the low-pass filter is not limited to two as described above, but may be one or three or more.

Next, an embodiment in which the high-frequency switch circuit of the above embodiment is applied to a substrate will be described with reference to the drawings.
FIG. 4 is a perspective view showing a first embodiment of the high-frequency switch circuit board, and FIG. 5 is a sectional view taken along line XX of FIG.

This high-frequency switch circuit board is composed of a dielectric substrate 32 formed by laminating a plurality of glass ceramic layers.
A strip line 28 linearly formed on the first main surface thereof, a ground electrode 29 formed substantially over the entire second main surface on the opposite side, and a strip line 28 formed inside the dielectric substrate 32. And two connection vias 31 that connect the ground electrode 29 and the capacitor formation electrodes 30 to each other.

The dielectric substrate 32 is formed by kneading a crystallized glass component and a ceramic component with an organic vehicle, forming a sheet, and printing conductors such as a strip line 28, a ground electrode 29, a capacitance forming electrode 30, and a connection via 31. It is obtained by laminating and firing. Strontium titanate or the like is added as a ceramic component in addition to alumina as a main component as a subcomponent for improving a dielectric constant. Its relative dielectric constant is 8 to 10 and the interlayer thickness is 50 to 100 μm
It is. Since the dielectric substrate 32 is made of a glass ceramic that can be fired at a low temperature, a low-resistance material such as gold, silver, copper, or a silver-platinum alloy can be used as the conductor material. Among them, copper is easily oxidized and must be fired in a reducing atmosphere, whereas silver and a silver-platinum alloy are preferable because they can be fired in the air. The capacitance value of 2.7 pF required for the three-stage Chebyshev low-pass filter is realized by setting the area where the strip line 28 and the capacitance forming electrode 30 face ^{each other} to about 9 to 18 mm ² .

Next, a second embodiment of the high-frequency switch circuit board will be described. FIG. 6 is a perspective view showing a high-frequency switch circuit board according to the second embodiment, and FIG. 7 is a sectional view taken along line YY of FIG. In this embodiment, a capacitance forming electrode 35 is provided on a first main surface of a dielectric substrate 33, a ground electrode 34 is provided on a second main surface opposite thereto, and a strip line 36 is provided inside the dielectric substrate 33. The capacitance forming electrode 35 and the ground electrode 34 are connected to the strip line 37 by a connection via 36 having a twisted positional relationship. When the capacitance forming electrode 35 is thus exposed on the surface of the dielectric substrate 33,
The interlayer capacitance value can be adjusted by trimming the capacitance forming electrode 35 after firing.

In the first and second embodiments,
Either the strip line or the capacitance forming electrode is exposed on the surface of the dielectric substrate. For example, ground electrodes 38 and 39 are formed on both main surfaces of the dielectric substrate 42 as shown in FIG. 8 as a third embodiment. Alternatively, both the strip line 41 and the capacitance forming electrode 40 may be provided inside the dielectric substrate 42.

[0028]

As described above, according to the present invention, since the strip line itself exhibits low-pass filter characteristics, a low-pass filter for high-frequency measures can be eliminated on the receiving path. The entire communication device can be reduced in size.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a high-frequency switch circuit according to an embodiment.

FIG. 2 is an equivalent circuit diagram of a region surrounded by a chain line in FIG.

FIG. 3 is a graph illustrating low-pass filter characteristics according to the circuit configuration of FIG. 2;

FIG. 4 is a perspective view showing a first embodiment of the high-frequency switch circuit board.

FIG. 5 is a sectional view taken along line XX of FIG. 4;

FIG. 6 is a perspective view showing a second embodiment of the high-frequency switch circuit board.

FIG. 7 is a sectional view taken along line YY of FIG. 6;

FIG. 8 is a sectional view showing a third embodiment of the high-frequency switch circuit board.

FIG. 9 is a conceptual diagram illustrating an application of the high-frequency switch circuit.

FIG. 10 is a conceptual diagram of a conventional high-frequency switch circuit.

FIG. 11 is a configuration diagram of a conventional high-frequency switch circuit.

FIG. 12 is a block diagram when a conventional high-frequency switch circuit is used for an actual transmission / reception block.

[Explanation of symbols]

 1,13 Transmission terminal 2,14 Antenna terminal 3,16 Receiving terminal 12,15 Control terminal 24,28,37,41 Strip line 30,35,40 Capacitance forming electrode 32,33,42 Dielectric substrate 29,34,38 , 39 Ground electrode

Claims (4)

[Claims] A high-frequency switch circuit in which a strip line is connected between an antenna terminal and a reception terminal so that the same antenna can be switched to one of transmission and reception. A high-frequency switch circuit which is grounded via a capacitance component within a range. 2. The capacitance component according to claim 1, wherein the capacitance component includes a small capacitance formed at a first connection point of the strip line and a small capacitance formed at a second connection point of the strip line. High frequency switch circuit. 3. A dielectric substrate on which a ground electrode is formed;
As an element of a high-frequency switch circuit formed on the dielectric substrate at an interval in the thickness direction of the dielectric substrate with respect to the ground electrode and for switching the same antenna to one of transmission and reception, an element between the antenna terminal and the reception terminal A high frequency switch circuit board including a strip line interposed therebetween, wherein a capacitance forming electrode connected to a ground electrode and forming an interlayer capacitance with the strip line is provided on the dielectric substrate. High frequency switch circuit board. 4. The high-frequency switch circuit board according to claim 3, wherein at least a part of the capacitance forming electrode is exposed on a surface of the dielectric substrate.