JP2005260806A - High frequency switch circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency switch circuit capable of ensuring high isolation characteristics in a plurality of frequency bands while reducing the number of components as little as possible. <P>SOLUTION: An inductor 9 and switches 5-8 are arranged and a capacity component at the time of turning off the switches 1-4 and the inductor 9 are resonated in parallel to improve isolation characteristics. Furthermore, all the switches 5-8 are turned off to ensure isolation characteristics other than a resonance point. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency switch circuit comprising a plurality of field effect transistors.

  A conventional high-frequency switch circuit will be described below.

  FIG. 11 and FIG. 12 are circuit diagrams showing an example of the prior art of a high-frequency switch circuit using FETs.

(Prior art 1)
In the high-frequency switch circuit of FIG. 11, reference numeral A denotes a first high-frequency signal input / output terminal. The first high-frequency signal input / output terminal A is connected to, for example, an antenna. Reference numerals B to E respectively denote second high-frequency signal input / output terminals. Reference numerals 1 to 4 denote switches having a configuration in which a plurality of FETs are connected in multiple stages. Reference numerals 10 to 13 denote switches having a configuration in which a plurality of FETs are connected in multiple stages. The switches 10 to 13 are arranged to drop a high-frequency signal leaking from the switch path in the OFF state among the switches 1 to 4 to the ground. Reference numerals 14 to 17 denote capacitors.

  In the switch circuit of FIG. 11, most of the high-frequency signals input from the first high-frequency signal input / output terminal A are output to the second high-frequency signal input / output terminal B through the switch 1. The high frequency signal passes through the off switches 2 to 4 and leaks to the second high frequency signal input / output terminals C to E. At this time, by turning on the switches 11 to 13, a path is provided for dropping the leaked signal passing through the off switches 2 to 4 to the ground. As a result, it is possible to reduce signal leakage to the second high-frequency signal input / output terminals C to E.

(Prior art 2)
In the configuration of FIG. 11 described above, the isolation characteristic is uniquely determined by the frequency characteristic of the device, and thus it may be difficult to ensure sufficient isolation characteristic in a desired frequency band. A technique devised to solve this problem is a technique in which an inductor is arranged in parallel with a switch section between high-frequency signal input / output terminals. The prior art 2 will be described below with reference to FIG.

  In the switch circuit of FIG. 12, symbol A indicates a first high-frequency signal input / output terminal. The first high-frequency signal input / output terminal A is connected to, for example, an antenna. Reference numerals B to E denote second high-frequency signal input / output terminals. Reference numerals 1 to 4 denote switches having a configuration in which a plurality of FETs are connected in multiple stages. Reference numerals 10 to 13 denote switches having a configuration in which a plurality of FETs are connected in multiple stages. The switches 10 to 13 are arranged to drop a high-frequency signal leaking from the switch path in the off state among the switches 1 to 4 to the ground. Reference numerals 14 to 17 denote capacitors. Reference numerals 18 to 21 denote inductors for resonating in parallel with off capacitances of individual FETs when the switches 1 to 4 are in an off state.

  When the switch circuit of FIG. 12 does not have an inductor, most of the high-frequency signal input from the first high-frequency signal input / output terminal A is the second high-frequency signal input / output terminal B through the switch 1 as in the prior art 1. However, some high-frequency signals leak to the second high-frequency signal input / output terminals C to E via the switches 2 to 4 in the off state. For this reason, the inductors 18 to 21 are arranged in parallel with the switches 1 to 4 made of FET, respectively, and the off capacitance of the FET in the off state and the inductors 18 to 21 are caused to resonate in parallel to leak a high frequency signal at a desired frequency. Reduce. As a result, the insertion loss between the first high-frequency signal input / output terminal A and the second high-frequency signal input / output terminal B can be reduced.

Here, the “switch” is configured around a semiconductor switch element such as a field effect transistor or a bipolar transistor, and is hereinafter abbreviated as “switch”.
Japanese Patent Laid-Open No. 08-204530

  In the case of the prior art 2, when there are a plurality of second high-frequency signal output terminals as in the high-frequency switch circuit having the above-described configuration, in order to improve the isolation characteristics in all the paths and reduce the insertion loss, The same number of inductors 18 to 21 as the two high-frequency signal input / output terminals B to E are required. Thus, by arranging the inductors 18 to 21 for all the paths, problems such as an increase in the size and cost of the high-frequency switch circuit arise.

The inductance values of the inductors 18 to 21 arranged in parallel with the switches 1 to 4 are f = 1 / 2π√ (LC) with respect to one resonance frequency f with the off-capacitance C of the FETs in the switches 1 to 4.
In the case of switching operation in multiple frequency bands, the isolation characteristics in one frequency band are improved, but in other frequency bands, the isolation characteristics due to resonance are determined. However, the isolation characteristics may deteriorate in a certain frequency band.

  The present invention solves the above-mentioned problems of the prior art, secures the isolation characteristics as in the prior art 2 after reducing the number of parts, and has high isolation characteristics and low insertion loss in a plurality of frequency bands. An object of the present invention is to provide a high-frequency switch circuit capable of ensuring characteristics.

  In order to solve the above problems, a high-frequency switch circuit according to the present invention divides a plurality of transmission / reception signals having different pass frequency bands into transmission / reception systems, and includes at least one first high-frequency signal input / output terminal and a plurality of transmission / reception signals. A plurality of second high-frequency signal input / output terminals, one end connected to at least one first high-frequency signal input / output terminal, and the other end connected to a plurality of second high-frequency signal input / output terminals. A first switch, an inductor having one end connected to at least one first high-frequency signal input / output terminal, and a plurality of second high-frequency signal input terminals commonly connected to the other end of the inductor And a plurality of second switches each having the other end connected thereto.

  According to the configuration of the present invention, it is possible to improve the isolation characteristic while reducing the number of parts by sharing the inductor used in the parallel resonant circuit in all paths. Further, with respect to a certain pass frequency band, the isolation characteristic can be enhanced by using resonance by the inductor, and the isolation characteristic can be enhanced by not using the resonance by the inductor with respect to another pass frequency band.

  In the high-frequency switch circuit of the present invention, at least one first high-frequency signal input / output terminal is connected to the antenna side of the mobile communication device.

  The high-frequency switch circuit of the present invention includes a laminated body in which an inductor is built in a plurality of dielectric layers, and a chip element that constitutes the first and second switches and is disposed on the laminated body. By doing so, it may be combined and integrated.

  The present invention reduces the number of components by sharing an inductor used for a parallel resonant circuit in all paths, and also has high isolation characteristics in multiple frequency bands by changing the logic of a switch arranged in series with the inductor. Switch circuit can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.

  FIG. 1 is a circuit diagram showing a configuration of a high-frequency switch circuit according to the present embodiment. In FIG. 1, symbol A indicates a first high-frequency signal input / output terminal. The first high-frequency signal input / output terminal A is connected to, for example, an antenna. There may be a plurality of first high-frequency signal input / output terminals. Reference numerals B to E denote second high-frequency signal input / output terminals. Reference numerals 1 to 4 denote switches having a configuration in which a plurality of FETs are connected in multiple stages. Reference numerals 5 to 8 denote switches having a configuration in which a plurality of FETs are connected in multiple stages. Reference numeral 9 denotes an inductor.

  The operation of the high-frequency switch circuit of the present embodiment configured as described above will be described below.

  When the switch 1 is turned on and the high frequency signal is transmitted from the first high frequency signal input / output terminal A to the second high frequency signal input / output terminal B, the switches 2 to 5 are turned off to turn on the second. The high-frequency signal is not leaked to the high-frequency signal input / output terminals C to E. At this time, the switches 6 to 8 are turned on, and the inductor 9 and the off capacitances of the switches 2 to 4 are connected in parallel between the first high-frequency signal input / output terminal A and the second high-frequency signal output terminals C to E. By providing the resonance circuit, it is possible to improve the isolation characteristic at a certain frequency as in the conventional technique, and it is possible to reduce the value of the insertion loss at this frequency.

  The frequency at which the isolation characteristic is improved by resonance is determined by the inductance value of the inductor 9 when the off-capacitance of the switches 1 to 4 is fixed. By changing the inductance value of the inductor 9, it is possible to improve the isolation characteristics in a desired frequency band.

  Further, by setting all the switches 5 to 8 to the off state, it is possible to ensure the isolation characteristics other than the resonance point.

  In the present embodiment, an RF simulation is performed on the assumption that the high-frequency switch circuit is used as an antenna switch circuit of a mobile phone. The first high-frequency signal input / output terminal A is an antenna-side terminal, and the second The high frequency signal input / output terminal B is connected to the PCS system (transmission Tx: 1850 to 1910 MHz, reception Rx: 1930 to 1990 MHz), and the second high frequency signal input / output terminal C is connected to the CDMA system (transmission Tx: 824 to 849 MHz, reception Rx: 869 to 894 MHz), the second high-frequency signal input / output terminal D is a GPS system (1545: 42 ± 1 MHz), and the second high-frequency signal input / output terminal E is a GSM system (transmission Tx: 880-915 MHz, reception Rx: 925-960 MHz). It corresponds to.

  The insertion loss of the high-frequency switch circuit has frequency characteristics, and generally the insertion loss increases as the frequency increases. Therefore, the PCS system using the highest frequency band among the above communication methods. Then, the isolation characteristic and the insertion loss characteristic were verified by RF simulation.

  FIG. 2 shows a circuit diagram in the embodiment of the present invention at the time of transmission / reception of the PCS system, and FIG. 3 shows a circuit diagram in the case where a resonance circuit using an inductor is not used (prior art 1). 4 shows isolation characteristics between the first high-frequency input / output terminal A and the second high-frequency signal input / output terminal C (or the second high-frequency signal input / output terminals D and E), and FIG. The insertion loss characteristics between the high frequency signal input / output terminal A and the second high frequency signal input / output terminal B are shown. 4 and 5, schematic 1 indicates each characteristic of the prior art 1 that does not use an inductor-based resonance circuit, and schematic 2 indicates each characteristic when resonance is used in the embodiment of the present invention.

  The simulation result of the isolation characteristic of FIG. 4 will be described. The switch 1 and the switches 6 to 8 in FIG. 1 are turned on and the switches 2 to 5 are turned off, thereby causing parallel resonance between the inductor 9 and the off capacitances of the switches 2 to 4. As a result, it is possible to improve the isolation characteristics in the PCS system (see schematic 2) as compared to the case where the resonance circuit by the inductor 9 is not used (see schematic 1). That is, when the resonance circuit using the inductor 9 is not used, it is −42.85 dB at 1.91 GHz, whereas when the resonance circuit using the inductor 9 is used, −71.54 dB is obtained at 1.91 GHz. As can be seen from FIG.

  The simulation result of the insertion loss characteristic in FIG. 5 will be described. By improving the isolation characteristics in the PCS system, leakage of high-frequency signals to other paths is reduced. As a result, it was confirmed that the insertion loss in the PCS system is reduced (see schematic 2) as compared with the case where the resonance circuit by the inductor 9 is not used (see schematic 1). In other words, when the resonance circuit using the inductor 9 is not used, it is -0.6896 dB at 1.91 GHz, whereas when using the resonance circuit using the inductor 9, it is -0.6767 dB at 1.91 GHz. It can be seen that the loss is decreasing.

  FIG. 6 shows a circuit diagram of the embodiment of the present invention at the time of transmission / reception of the GSM system. FIG. 7 shows the isolation characteristics between the first high-frequency input / output terminal A and the second high-frequency signal input / output terminal D (or the second high-frequency signal input / output terminals B and C), and FIG. The insertion loss characteristic between the signal input / output terminal A and the second high-frequency signal input / output terminal E is shown. 7 and 8, schematic 2 indicates each characteristic when resonance is used in the embodiment of the present invention (same as in FIGS. 4 and 5), and schematic 3 uses resonance in the embodiment of the present invention. Each characteristic is shown when not. That is, when the resonance circuit using the inductor 9 is used, it is −26.76 dB at 0.915 GHz, whereas when the resonance circuit using the inductor 9 is not used, it is −34.45 dB at 0.915 GHz. As can be seen from FIG.

  The simulation result of the isolation characteristic of FIG. 7 will be described. The high-frequency signal is prevented from leaking to the inductor 9 by turning on the switch 4 in FIG. As a result, parallel resonance in the frequency band of the PCS system (transmission Tx: 1850 to 1910 MHz, reception Rx: 1930 to 1990 MHz) is not performed. Therefore, it is possible to improve the isolation characteristics in the frequency band of the GSM system (transmission Tx: 880 to 915 MHz, reception Rx: 925 to 960 MHz) as compared with the switching operation (see schematic 2) at the time of transmission / reception of the PCS system. (See schematic3).

  The simulation result of the insertion loss characteristic in FIG. 8 will be described. The improvement of the isolation characteristic in the GSM system described above reduces the leakage of high frequency signals to other paths. From this, it was confirmed that the insertion loss in the GSM system is reduced (see schematic 3) compared with the switching operation (see schematic 2) during transmission and reception of the PCS system. That is, when the resonance circuit using the inductor 9 is used, it is -0.7203 dB at 0.915 GHz, whereas when the resonance circuit using the inductor 9 is not used, it is -0.6929 dB at 0.915 GHz. It can be seen that the loss is decreasing.

  Even when the first high-frequency signal input / output terminal is composed of a plurality of high-frequency signal input / output terminals, the same effect as in the case where the first high-frequency signal input / output terminal is single can be obtained. In the embodiment shown in FIG. 9, the two first high-frequency signal input / output terminals indicated by reference numerals A1 and A2 are made common via switches 30 and 31 connected to the respective terminals, and a plurality of second high-frequency signal input / output terminals are connected. Are connected to switches 1-4 arranged in series with respect to the high-frequency signal input / output terminals B-E.

  As shown in FIG. 10, in the above-described high-frequency switch circuit of the present invention, a laminated body in which an inductor is built in a plurality of dielectric layers, and first and second switches are configured and arranged on the laminated body. It is also possible to take a composite and integrated form by being constituted by the chip elements. In FIG. 10, reference numeral 51 denotes a chip element including a switch portion in the circuit of the present invention, reference numeral 52 denotes a dielectric layer made of a dielectric substrate, reference numeral 53 denotes a spiral inductor formed on the dielectric substrate, and reference numeral 54 denotes a dielectric. This is a through hole provided to electrically connect the body substrate. It is possible to obtain the same effect as that of the present invention by electrically connecting the chip element indicated by reference numeral 1 and the spiral inductor using bonding wires and through holes.

  The high-frequency switch circuit according to the present invention secures the isolation characteristics as in the prior art 2 after reducing the number of components, and also ensures high isolation characteristics and low insertion loss characteristics in a plurality of frequency bands. It is effective as a mobile communication device such as a mobile phone terminal.

It is a circuit diagram which shows the structure of the switch circuit for high frequencies in embodiment of this invention. It is a circuit diagram which shows the high frequency switch circuit at the time of transmission / reception of the PCS system in embodiment of this invention. It is a circuit diagram which shows the high frequency switch circuit when not using the resonance by an inductor (prior art 1). It is a characteristic view which shows the simulation result of the isolation characteristic in embodiment and prior art 1 of this invention. It is a characteristic view which shows the simulation result of the insertion loss in embodiment and prior art 1 of this invention. It is a circuit diagram which shows the switch circuit at the time of transmission / reception of the GSM system in embodiment of this invention. It is a characteristic view which shows the simulation result of the isolation characteristic in embodiment of this invention. It is a characteristic view which shows the simulation result of the insertion loss in embodiment of this invention. FIG. 4 is a circuit diagram showing a configuration of a high-frequency switch circuit when there are a plurality of first high-frequency signal input / output terminals in the embodiment of the present invention. In an embodiment of the present invention, a schematic diagram showing a model in a case where a switch circuit is constituted by a multilayer body in which inductors are built in a plurality of dielectric layers and a chip element arranged on the multilayer body, and is integrally integrated. It is a perspective view. It is a circuit diagram which shows the structure of the prior art 1 of the switch circuit for high frequency. It is a circuit diagram which shows the structure of the prior art 2 of the switch circuit for high frequency.

Explanation of symbols

A 1st high frequency signal input / output terminal B-E 2nd high frequency signal output terminal 1-4 1st switch 5-8 2nd switch 9 Inductor 31,32 Switch 51 Chip element 52 Dielectric layer 53 Spiral inductor 54 Through hole

Claims (3)

A high frequency switch circuit that divides a plurality of transmission / reception signals having different pass frequency bands into each transmission / reception system,
At least one first high-frequency signal input / output terminal and a plurality of second high-frequency signal input / output terminals;
A plurality of first switches each having one end connected to the at least one first high-frequency signal input / output terminal and the other end connected to the plurality of second high-frequency signal input / output terminals;
An inductor having one end connected to the at least one first high-frequency signal input / output terminal;
A high-frequency switch circuit comprising: a plurality of second switches having one end connected in common to the other end of the inductor and the other end connected to the plurality of second high-frequency signal input terminals.   The high-frequency switch circuit according to claim 1, wherein the at least one first high-frequency signal input / output terminal is connected to an antenna side of the mobile communication device.   The inductor is incorporated in a plurality of dielectric layers, and the chip elements arranged on the laminate constituting the first and second switches are combined and integrated. The high-frequency switch circuit according to claim 1.

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