JP4134744B2 - Antenna switch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diode switch applied to a high-frequency switch circuit for switching a signal transmission path in a high-frequency circuit such as a digital cellular phone.
[0002]
[Prior art]
The antenna switch is used for switching the connection between the transmission circuit TX and the antenna ANT and the connection between the reception circuit RX and the antenna ANT in the mobile phone. As an example, FIG. 10 shows an equivalent circuit diagram of the antenna switch disclosed in Patent Document 1. This antenna switch is connected between a diode D201 having an anode connected to the transmitting circuit side and a cathode connected to the antenna side, a transmission line L201 connected to the anode of the diode, and between the antenna ANT and the receiving circuit RX. Transmission line L202 and a diode D202 having an anode connected to the receiving circuit side and a cathode connected to the ground side, and a low-pass filter circuit LPF connected between the diode D201 and the transmitting circuit TX. .
[0003]
FIG. 11 shows an equivalent circuit diagram of the antenna switch disclosed in Patent Document 2. This antenna switch is connected between a diode D301 having a cathode connected to the transmitting circuit side and an anode connected to the antenna side, a transmission line L301 connected to the cathode of the diode, and between the antenna ANT and the receiving circuit RX. Transmission line L302, and a diode D302 having a cathode connected to the receiving circuit side and an anode connected to the ground side, and a low pass filter circuit LPF connected between the diode D301 and the transmitting circuit TX. is there.
Here, the low-pass filter circuit is configured to attenuate the second and third harmonic spurious components of the transmission signal radiated from the antenna to prevent unnecessary interference with other mobile phones. Is common.
[0004]
In recent years, an antenna switch is rarely used as a single-function component of an antenna switch that switches a connection between a transmission circuit and an antenna or a connection between a reception circuit and an antenna, and a DAMPS ( Digital Advanced Mobile Phone System), GSM (Global System for Mobile Communication), DCS (Digital Cellular System) and PCS (Personal Communications Services) There is a need for higher functionality and smaller size, such as integration with a coupler. Along with this, it is necessary to increase the density of the transmission lines and laminated electrodes constituting the high-frequency circuit of the antenna switch, and to increase the functionality of the circuit configuration. Further, since the circuit becomes complicated due to the multiband or the like, the transmission distance of the signal tends to become long, and therefore, the loss of each circuit is required to be reduced.
In view of the above, a design is required in which the requirements for each of the above components affect the overall size, call time, and communication characteristics of the mobile phone, and no requirements can be ignored.
[0005]
[Patent Document 1]
JP-A-8-97743
[Patent Document 2]
JP 2002-246945
[0006]
[Problems to be solved by the invention]
The LPF of the antenna switch circuit shown in FIG. 10 is a five-stage π-type LPF composed of L204, L205, C207, C208, and C209, and there are three capacitor electrodes facing the GND electrode in the laminated structure. Become. As a result, the area occupied by the capacitor electrode of the LPF increases, which is disadvantageous for miniaturization. In addition, since the transmission lines L204 and L205 that connect these capacitors are connected in series, the resistance loss from the transmission circuit TX to the antenna ANT increases, which is disadvantageous in reducing the loss. Therefore, considering the case of a π-type three-stage LPF in which L205 and C209 are omitted instead of the five-stage π-type LPF, L205 is omitted, which is advantageous for reducing the loss, but the capacitor C209 is omitted. As a result, the harmonic attenuation characteristics deteriorate and the required characteristics cannot be satisfied. In addition, it is not possible to set a resonance frequency including a capacitor and an inductor at an arbitrary frequency, and it is not possible to set an attenuation pole using the resonance frequency.
[0007]
Next, the LPF of the antenna switch circuit shown in FIG. 11 is a modification of a three-stage π-type LPF composed of L303, L304, C305, C306, and C307. The characteristics of this LPF are L303 and C307. An attenuation pole can be obtained at an arbitrary frequency by the parallel resonant circuit configured and the series resonant circuit configured by L304 and C306. However, in order to adjust the frequency of the attenuation pole, the length and width of the transmission line as an inductor are adjusted, and the area of the electrode as a capacitor is adjusted. Since these adjustments are performed by manipulating the arrangement and size of the electrode pattern in a limited dielectric layer region, the adjustment of the attenuation pole frequency results in the capacitor C306 connected in series with the inductor in particular. There was a tendency to become smaller. As a result, an attenuation pole having an arbitrary frequency can be obtained, but the characteristic of attenuating the high-frequency component of the entire LPF has deteriorated.
[0008]
Accordingly, an object of the present invention is to provide a low-pass filter LPF capable of obtaining the two attenuation poles as described above, and to obtain a desired harmonic attenuation and to save the insertion loss characteristic without deteriorating. It is to provide a small antenna switch in space.
[0009]
[Problems to solve the problem]
The present invention is an antenna switch that is connected between a transmission circuit, a reception circuit, and an antenna, and that switches connection between the transmission circuit and the antenna, and connection between the reception circuit and the antenna. The switch has a low-pass filter in a signal path from the transmission circuit to the antenna, A first inductor and a second capacitor constituting a first series resonant circuit; and a path from a connection point between the first inductor and the second capacitor to a ground, and the first inductor and the second capacitor A first capacitor constituting a two-series resonance circuit, a second inductor constituting a parallel resonance circuit with the first series resonance circuit, and forming a first attenuation pole by the second series resonance circuit; The antenna switch forms a second attenuation pole by a parallel resonance circuit.
The antenna switch is configured as a laminate including a plurality of dielectric layers, and the first inductor and / or Above The second inductor is preferably a distributed constant line formed of an electrode pattern in a laminate made of dielectric layers.
In addition, a low-pass filter is provided in the signal path from the transmission circuit to the antenna, each A π-type filter including a resonance circuit is preferable.
Moreover, the low pass filter is configured. First inductor and second The inductor is a distributed constant line formed in a laminate composed of dielectric layers, and the series resonant circuit and Above It is preferable that a part of the distributed constant lines of the parallel resonant circuit is a common distributed constant line.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An equivalent circuit of one embodiment according to the present invention will be described with reference to FIG. 1, but the present invention is not limited to this antenna switch.
This antenna switch is connected between the first diode D11 connected between the transmission circuit TX and the antenna ANT, the cathode of the first diode D11 and the transmission circuit TX side, and the other end connected to the ground side. An inductor L11 to be connected, an inductor L12 connected between the receiving circuit RX and the antenna ANT, and a second diode whose cathode is connected to the receiving circuit RX side of the inductor L12 and whose other end is connected to the ground side. D12 is a main element of the switch circuit. DC cut capacitors C11, C12, and C13 are connected to input / output terminals of the transmission circuit TX, the reception circuit RX, and the antenna ANT, respectively.
[0011]
As shown in the broken line in FIG. 1, a low-pass filter LPF composed of inductors L1, L2, capacitors C1, C2, C3 between the first diode D11 and the inductor L11 whose other end is connected to the ground side. Has been inserted. In this low-pass filter LPF, a third capacitor C3 is connected between the transmission circuit TX and the ground from the transmission circuit TX side, and a second inductor L2 is provided between the transmission circuit TX and the cathode of the first diode D11. Also connected is a second capacitor C2 and a first inductor L1 connected in series. On the other hand, a first inductor L1 and a first capacitor C1 are connected in series between the cathode of the first diode D11 and the ground.
As a result, a first attenuation pole is formed by a series resonance circuit composed of the first inductor L1 and the first capacitor C1, and the first inductor L1 and the second capacitor C2 are connected in series to the second An antenna switch that forms a second attenuation pole by a parallel resonance circuit with the inductor L2 is configured.
The first attenuation pole and the second attenuation pole can arbitrarily change the attenuation frequency. The first attenuation pole is provided with an attenuation pole at a frequency twice as high as the transmission frequency, for example. A frequency that is three times the transmission frequency may be attenuated at the pole, or vice versa. Furthermore, for example, it is possible to set an attenuation pole with respect to the frequency of an arbitrary radio communication system with the first attenuation pole, and attenuate the harmonics of the transmission signal of the mobile phone with the second attenuation pole.
[0012]
In the equivalent circuit of FIG. 1, the control circuit VC1 is connected to the anode of the second diode D12 via the resistor R1. As shown in FIG. 2, the capacitor C15 may be connected between the inductor L11 and the ground, and the resistor R2 may be connected to the control circuit VC2 from the connection point between the transmission line L11 and the capacitor C15. In the circuit configuration of FIG. 1, only a forward bias voltage can be applied to the diodes D11 and D12 from the VC1, but in the case of the circuit configuration of FIG. 2, a reverse bias voltage can be applied and the diodes D11 and D12 are isolated. It is possible to increase.
[0013]
Inductors L11 and L12 that constitute the switch circuit shown in FIG. 1 are formed by transmission lines, and are formed by capacitor C1, C2, C3, C13, and C14 electrode patterns, and these are built in a laminate of dielectric layers, Further, by arranging chip elements such as diodes and resistors on the stacked body, the antenna switch can be configured in one stacked body. The chip elements arranged on the laminate can be appropriately set in relation to the circuit elements formed in the laminate.
Further, the first inductor L1 and the second inductor L2 constituting the low-pass filter are configured as transmission lines in the stacked body, and the transmission line L1 of the series resonant circuit and the transmission line L2 of the parallel resonant circuit are connected to each other in the stacked body. And if it arrange | positions so that it may pile up with respect to the lamination direction of a laminated body, a mutual inductance will generate | occur | produce between transmission lines, and the line length of a mutual transmission line can be shortened by the increase in the inductance, and an antenna switch is reduced in size. be able to.
[0014]
The first capacitor C1 constituting the series resonance circuit of the low-pass filter can be designed to be larger even if designed at the same resonance frequency as compared with the capacitor C306 constituting the series resonance circuit of FIG. . The first inductor L1 connected in series with the first capacitor C1 is connected to the second inductor L2, and is divided on the equivalent circuit, but is a continuous transmission line in the multilayer body. Therefore, the transmission line acting as a resonance circuit can be shortened in the case of the present invention, and as a result, the first capacitor C1 can be enlarged. As a result, the impedance of the path through which the high frequency passes to the ground potential can be lowered, and the characteristics of the LPF that obtains attenuation in the high frequency region can be improved.
[0015]
【Example】
In the present invention, a small antenna switch is configured by using a switch circuit and a low-pass filter circuit as a single component and having a laminated structure. Using this antenna switch, a small module component can be configured. For example, a duplexer circuit can be combined to support multiband, and a SAW filter, a coupler, a power amplifier, etc. can be modularized into a single laminate for high functionality.
Hereinafter, an embodiment of the present invention will be described in detail.
FIG. 5 is an exploded perspective view when the antenna switch shown as the equivalent circuit in FIG. FIG. 6 is a perspective view thereof. In this embodiment, only one antenna switch portion is extracted from the structure of a conventional multiband antenna switch module in order to avoid complication of the drawing. Therefore, as shown in FIG. 6, the laminated body 1 including the dielectric layer is composed of two diodes 2 and 3, capacitors 4, 5 and resistors 6, each of which has two components in FIG. Correspond to the diodes D11 and D12, the capacitors C11 and C12, and the resistor R1.
[0016]
In FIG. 5, in the laminate 1, the first ground electrode 61 and the back electrodes 23 to 29 are formed on the dielectric layer 11. The back electrode 29 is a terminal VC1, and the back electrode 28 is an ANT terminal.
Transmission lines are formed on the dielectric layers 12, 13, 14, 15 by electrode patterns. The transmission line L11 in the equivalent circuit is constituted by line electrodes 30, 32, 35, and 36, which are connected by through-hole electrodes, and the upper surface electrode 56 and the ground electrode 61 are connected. The transmission line L12 in the equivalent circuit is composed of line electrodes 33 and 34, which are connected by through-hole electrodes, and connect the upper surface electrodes 58 and 52.
[0017]
A second ground electrode 45 is formed on the dielectric layer 16 thereon, and is connected to the first ground electrode 61 by a through-hole electrode. The capacitor electrode 44 is opposed to the capacitor electrode 46 of the dielectric layer 17 to form a capacitor C13 in the equivalent circuit. The capacitor electrode 46 is connected to the back electrode 28 which is an ANT terminal by a through-hole electrode.
On the dielectric layer 17 thereabove, capacitor electrodes 49, 48, 47 that form capacitors C 14, C 3, C 1 in the equivalent circuit are formed facing the second ground electrode 45.
On the dielectric layer 18 thereabove, a capacitor electrode 51 is formed so as to face the capacitor electrodes 47 and 48, thereby constituting a capacitor C2 of an equivalent circuit. A third ground electrode 50 is formed and arranged to face the capacitor electrode 49, and becomes a part of the capacitance of the capacitor C14 on the equivalent circuit. The third ground electrode 50 is connected to the first and second ground electrodes by through-hole electrodes.
[0018]
Transmission lines are formed on the dielectric layers 19, 20, and 21, respectively. The transmission line L2 in the equivalent circuit is composed of 41 and 43, which are connected by through-hole electrodes and connect the upper surface electrodes 56 and 55. The transmission line L1 in the equivalent circuit is composed of 37 and 40 and is connected by through-hole electrodes, and the capacitor electrode 47, the transmission line 41, and the upper surface electrode 55 are connected.
The transmission line 38 on the dielectric layer 19 and the transmission line 31 on the dielectric layer 12 are connected by a through-hole electrode, and the top electrode 59 and the back electrode 29 are connected. The transmission line 39 on the dielectric layer 20 connects the upper surface electrode 58 and the capacitor electrode 44. The transmission line 42 on the dielectric layer 21 connects the upper surface electrode 53 and the capacitor electrode 49.
[0019]
On the dielectric layer 22, upper surface electrodes 52 to 60 for connecting mounting components such as a diode, a capacitor, and a resistor are formed. A capacitor C11 on an equivalent circuit is connected between the upper surface electrodes 56 and 57. The upper electrode 55 is connected to the cathode of the diode D11, and the upper electrode 58 is connected to the anode of the diode D11. The upper electrode 53 is connected to the anode of the diode D12, and the upper electrode 52 is connected to the cathode of the diode D12. A resistor R1 is connected between the upper surface electrodes 53 and 59. A capacitor C12 is connected between the upper surface electrodes 52 and 60. By mounting an appropriate capacitor and inductor between the upper surface electrodes 54 and 55 and between the upper surface electrodes 54 and 58, a series circuit of the capacitor and the inductor can be connected in parallel with the diode D11. When is OFF, the isolation between ANT and TX can be enhanced. The above capacitors and inductors can be mounted as necessary.
[0020]
This laminate uses a dielectric material having a dielectric constant of about 8 and forms a sheet with a doctor blade. On this sheet, an Ag electrode is formed by screen printing to form a pattern electrode. Fired at
[0021]
Here, FIG. 7 shows an exploded perspective view of an antenna switch configured by the equivalent circuit shown in FIG. The capacitor electrode corresponding to C306 in FIG. 11 is the electrode pattern 132 in FIG. The transmission lines corresponding to the inductor L303 are 138 and 141, and the transmission lines corresponding to the inductor L304 are 137, 140, and 143. On the other hand, the capacitor electrode corresponding to the capacitor C1 constituted by the equivalent circuit of FIG. 1 of the present invention is the electrode pattern 47 of FIG. Comparing the two, the capacitor electrode 47 according to the configuration of the present invention has a larger area than the ground electrode. The reason for this is that the inductors L303 and L304 in FIG. 11 are 138, 141 and 137, 140, and 143 in the transmission line on the dielectric layer, and they are connected through through-holes in the circuit, but can be seen in high frequency. For example, it becomes an independent transmission line and cannot be seen as a continuous transmission line as in the relation of the corresponding transmission lines 41, 43 and 37, 40 in FIG. Accordingly, the transmission lines 137, 140, and 143 in FIG. 7 corresponding to the inductor L304 in FIG. 11 are longer than the transmission lines 37 and 40 in FIG. 5, and the capacitors that form a series resonance circuit with the transmission lines 137, 140, and 143 The electrode 132 is configured to be small.
On the other hand, the transmission lines 41, 43, 37, and 40 corresponding in FIG. 5 are connected to the transmission lines 40 and 41 on the dielectric layer 20, and can be viewed as continuous transmission lines even in terms of high frequency. In other words, L1 and L2 in the equivalent circuit share a common transmission line. In the present invention, the transmission line acting as a series resonance circuit is shortened, and as a result, the capacitor electrode 47 connected in series can be made large.
[0022]
FIG. 8 shows the insertion loss characteristics between the input terminal TX and the antenna ANT of the antenna switch of the present invention (FIG. 1 for the equivalent circuit) and the conventional example (FIG. 11 for the equivalent circuit). In the figure, a solid line indicates the present invention, and a dotted line indicates a conventional example. Here, an improvement in attenuation of about 5 dB at the maximum is observed in the high frequency region of 2500 to 6000 MHz while minimizing the movement of the attenuation poles near 3500 MHz and 5500 MHz. As a result of enlarging the capacitor electrode to be grounded, it can be seen that the present invention has a greater attenuation in the harmonic band than the conventional example. This is due to the fact that the circuit configuration of the present invention is achieved and the capacitor provided in the laminated body can be made large, and the impedance is lowered and the high frequency component is easily passed to the ground electrode.
[0023]
Further, when the present invention (FIG. 1 in the equivalent circuit, FIG. 5 in the exploded exploded perspective view) and the conventional example (FIG. 11 in the equivalent circuit, FIG. 7 in the laminated exploded perspective view) are compared, the first inductor L1 in FIG. The second capacitor C2 (corresponding to 37, 40 and 51 in FIG. 5) is smaller than the corresponding inductor L304 and capacitor C307 (corresponding to 137, 140, 143 and 134 in FIG. 7) in FIG. In particular, the capacitor C2 in FIG. 1 is connected in series with the capacitance composed of the capacitor electrodes 48 and 51 and the capacitance composed of the capacitor electrodes 47 and 51 in FIG. When the influence of the inductor L1 and the capacitor C2 is reduced from FIG. 1, the equivalent circuit is a π-type low-pass filter including the capacitors C1 and C3 and the inductor L2. From this, it can be inferred that the attenuation is obtained in the high frequency region. The length of the inductor L1 as a transmission line is preferably ½ or less that of the inductor L2.
[0024]
Further, in FIG. 5, between the first ground electrode 61 and the second ground electrode 45, the first transmission line L 11 constituted by the line electrodes 30, 32, 35, and 36 and the line electrodes 33 and 34 are used. The configured second transmission line L12 is arranged. Capacitors C 3, C 1, C 2 and inductors L 2, L 1 constituting a low-pass filter are arranged above the mounting surface with respect to the second ground electrode 45. As a result, the ground electrode is disposed between the transmission line of the antenna switch circuit and the low-pass filter circuit, thereby preventing unnecessary interference.
[0025]
The low-pass filter LPF according to this embodiment includes a series resonant circuit including a first inductor L1 and a first capacitor C1, a first inductor L1 and a second capacitor C2 connected in series, and a second resonance filter LPF. A parallel resonance circuit with the inductor L2 is provided, and these resonance circuits are configured to have two attenuation poles. A low-pass filter composed of the resonance circuit and the third capacitor C3 is provided between the cathode of the first diode D11 and the inductor L11 in the switch circuit.
As another low-pass filter configuration, a series resonant circuit may be configured by the capacitor C3 and the inductor L3 as shown in FIG. 3, or an inductor is further added as shown in FIG. 4, and the inductor L3 and the capacitor C3. Two series resonant circuits may be configured by series connection and series connection of the inductor L1 and the capacitor C1. In the case of FIG. 3, the effect similar to that of the circuit of FIG. 1 can be obtained by the series connection of the inductor L3 and the capacitor C2, the parallel resonance circuit by the inductor L2, and the series resonance circuit by the inductor L3 and the capacitor C3. In the case of FIG. 4, a series connection of an inductor L1, a capacitor C2, and an inductor L3 and a parallel resonance circuit including an inductor L2, a series resonance circuit including an inductor L1 and a capacitor C1, a series resonance circuit including an inductor L3 and a capacitor C3, and the above three resonances. A circuit can be fabricated.
[0026]
It is also possible to configure a high-frequency switch module that handles a plurality of transmission / reception systems using the switch circuit incorporating the low-pass filter circuit in the above-described embodiment. As an example, FIG. 9 shows a block diagram in the case of handling two transmission / reception systems. The demultiplexing circuit connected to the antenna ANT demultiplexes into the first transmission / reception system and the second transmission / reception system, and includes the first switch circuit in the demultiplexed first transmission / reception system. The system has a second switch circuit. The first or second switch circuit switches between transmission TX and reception RX, and a low-pass filter circuit is provided in the transmission system. The antenna switch of the above embodiment can be used for the first or second switch circuit or both.
[0027]
【The invention's effect】
According to the present invention, two attenuation poles can be obtained, and at this time, the amount of harmonic attenuation can be increased without deteriorating the insertion loss characteristic. Therefore, it is possible to provide a small antenna switch that prevents unnecessary interference in a plurality of wireless systems and does not deteriorate the insertion loss characteristic. Further, it is possible to arbitrarily set a plurality of attenuation poles, and it is possible to avoid complication of the circuit and increase in insertion loss due to it.
[Brief description of the drawings]
FIG. 1 is an equivalent circuit diagram of a first embodiment of an antenna switch according to the present invention.
FIG. 2 is an equivalent circuit diagram of another embodiment of the antenna switch according to the present invention.
FIG. 3 is an equivalent circuit diagram of a low-pass filter according to another embodiment of the present invention.
FIG. 4 is an equivalent circuit diagram of a low-pass filter according to another embodiment of the present invention.
FIG. 5 is an exploded perspective view of the laminate of the first embodiment according to the present invention.
6 is a perspective view of the laminate of FIG. 5 according to the present invention.
FIG. 7 is an exploded perspective view of a conventional antenna switch laminate (FIG. 11).
FIG. 8 is a frequency characteristic diagram of an insertion loss between an embodiment according to the present invention and a conventional transmission circuit-antenna.
FIG. 9 is a block diagram of an embodiment of a high-frequency switch module using an antenna switch according to the present invention.
FIG. 10 is an equivalent circuit diagram of a conventional antenna switch.
FIG. 11 is an equivalent circuit diagram of another conventional antenna switch.
[Explanation of symbols]
L1: first inductor
L2: Second inductor
C1: first capacitor
C2: Second capacitor
C3: Third capacitor
D11: First diode
D12: Second diode
C11, C12, C13: DC cut capacitors
LPF: Low-pass filter
1: Laminated body
2, 3: Semiconductor element
4, 5: Capacitor
6: Resistance
11, 12, 13, 14, 15, 16: Dielectric layer
17, 18, 19, 20, 21, 22: Dielectric layer
61: First ground electrode
45: Second ground electrode
50: Third ground electrode
44, 46, 47, 48, 49, 51: Capacitor electrodes
30, 31, 32, 33, 34, 35: Line electrodes
36, 37, 38, 39, 40, 41: line electrode
42, 43: Line electrodes
23, 24, 25, 26, 27, 28, 29: Back electrode
52, 53, 54, 55, 56, 57, 58, 59, 60: Top electrode

Claims (4)

An antenna switch connected between a transmission circuit, a reception circuit, and an antenna for switching a connection between the transmission circuit and the antenna and a connection between the reception circuit and the antenna, the antenna switch being the transmission switch Has a low-pass filter in the signal path from the circuit to the antenna,
The low-pass filter is connected to a path from a connection point between the first inductor and the second capacitor constituting the first series resonant circuit, and the first inductor and the second capacitor to the ground, and 1 inductor and a first capacitor constituting a second series resonance circuit, and a second inductor constituting a parallel resonance circuit with the first series resonance circuit,
An antenna switch , wherein a first attenuation pole is formed by the second series resonance circuit, and a second attenuation pole is formed by the parallel resonance circuit. The antenna switch is composed of a laminate comprising a plurality of dielectric layers, said first inductor and / or the second inductor is a distributed constant line formed by electrode patterns in the laminate comprising a dielectric layer The antenna switch according to claim 1. A low-pass filter to the signal path from the transmitting circuit to the antenna, antenna switch according to claim 1 or 2 the low-pass filter, wherein the a π-type filter that includes the resonant circuit. It said first and second inductors that constitute the low-pass filter is a distributed constant line formed on the stack of dielectric layers, one of the first series resonant circuit and the distributed constant lines of the parallel resonant circuit 2. The antenna switch according to claim 1 , wherein the parts are common distributed constant lines.

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