High-frequency switch circuit, high-frequency switch module and wireless communication device

A high-frequency switch circuit common to a plurality or frequency bands comprises a first high-frequency switch connected to first high-frequency signal input and output terminals and adapted to pass transmission signals of a first or a second frequency band and block received signals of the first and second frequency band; and a demultiplexer has a first high-frequency circuit which consists of a first phaser connected to the first terminal and a first bandpss filter succeeding to the first phaser, and a second high-frequency circuit which consists of a second phaser connected to the first terminal and a second bandpass filter succeeding to the second phaser. The transmission line in the first phaser has a line length such that the input impedance of the first high-frequency circuit is substantially open in the pass band of the second bandpass filter, whereas the transmission line in the second phaser has a line length such that the input impedance of the second high-frequency circuit is substantially open in the pass band of the first bandpass filter. Thus, the high-frequency switch circuit passes one of thc received signals of the first and second frequency bands and blocks the other.

FIELD OF THE INVENTION

The present invention relates to a branching circuit used in high-frequency bands such as microwave bands, particularly to a branching circuit for branching high-frequency signals of a plurality of frequency bands, and a high-frequency switch circuit comprising such a branching circuit for switching signal transmission lines in high-frequency circuits in digital mobile phones (cell phones), etc., and a high-frequency switch module comprising such parts contained in or mounted onto an integral laminate and further to a wireless communications device such as a mobile phone comprising these parts.

BACKGROUND OF THE INVENTION

Wireless communications devices, for instance, mobile phones have become popular remarkably in recent years with their functions and services improved increasingly. Explanation will be made on a mobile phone as an example. There are various systems for mobile phones, for instance, GSM (Global System for Mobile Communications) and DCS 1800 (Digital Cellular System 1800) systems widely used mostly in Europe, a PCS (Personal Communications Services) system used in the U.S., and a PDC (Personal Digital Cellular) system used in Japan. According to recent rapid expansion of mobile phones, however, a frequency band allocated to each system cannot allow all users to use their mobile phones in major cities in advanced countries, resulting in difficulty in connection and thus causing such a problem that mobile phones are sometimes disconnected during communication. Thus, proposal was made to permit users to utilize a plurality of systems, thereby increasing substantially usable frequency, and further to expand serviceable territories and to effectively use communications infrastructure of each system.

As a mobile phone having this new system, dual-band mobile phones (see Japanese Patent 2,983,016), triple-band mobile phones, etc. are proposed. While a usual mobile phone comprises only one transmitting/receiving system, the dual-band mobile phone comprises two transmitting/receiving systems, and the triple-band mobile phone comprises three transmitting/receiving systems. With these structures, users can choose and utilize available transmitting/receiving systems among a plurality of systems.

Such a mobile phone comprises a high-frequency switch module comprising a branching circuit (diplexer) for directing a received signal to either one of a low-frequency system and a high-frequency system depending on a frequency band of each system, and a high-frequency switch circuit for switching signal paths of a reception line and a transmission line. Usable as a means for separating reception and transmission in place of the high-frequency switch for switching lines is a branching circuit (duplexer) comprising a bandpass filter utilizing frequency difference between reception frequency and transmission frequency. For instance, Japanese Patent Laid-Open No. 8-321738 discloses a duplexer comprising a combination of a first bandpass filter and a first phase shifter with a second bandpass filter and a second phase shifter for branching signals of different frequencies, without comprising the high-frequency switch. However, Japanese Patent Laid-Open No. 8-321738 fails to refer to a combination of such duplexer with the high-frequency switch to provide a high-frequency switch circuit adapted to larger numbers of frequency bands, and the formation of these circuits to a module to provide small and lightweight wireless communications devices.

OBJECT OF THE INVENTION

Accordingly, an object of the present invention is to provide a branching circuit suitable for miniaturizing a multiband high-frequency switch module for handling signals of a plurality of frequency bands.

Another object of the present invention is to provide a high-frequency switch circuit comprising such a branching circuit, thereby having a simple and low-cost circuit structure with small electricity consumption.

A further object of the present invention is to provide a high-frequency switch module formed by integrally laminating a plurality of dielectric green sheets having electrode patterns for the high-frequency switch circuit.

A still further object of the present invention is to provide a wireless communications device such as a small mobile phone, etc. comprising the high-frequency switch module.

DISCLOSURE OF THE INVENTION

As a result of intense research on high-frequency switch circuits for use in high-frequency circuits such as a triple-band, high-frequency switch module, etc. for handling signals in a plurality of frequency bands, the inventions have come to conceive a high-frequency switch module for triple-band mobile phones as shown inFIG. 15. This high-frequency switch module is adapted to three systems comprising a DCS 1800 system (transmission TX: 1710–1785 MHz, reception RX: 1805–1880 MHz) as a first transmitting/receiving system, a PCS system (transmission TX: 1850–1910 MHz, reception RX: 1930–1990 MHz) as a second transmitting/receiving system and a GSM system (transmission TX: 880–915 MHz, reception RX: 925–960 MHz) as a third transmitting/receiving system, an antenna ANT and transmission/reception circuits of the GSM system, the DCS system and the PCS system being switched in the triple-band mobile phone.

This triple-band, high-frequency switch module comprises a branching circuit block103composed of a high-pass filter HPF and a low-pass filter LPF for branching a terminal connected to ANT to first and second transmitting/receiving systems (for instance, DCS and PCS) on a high-frequency side and a third transmitting/receiving system (for instance, GSM) on a low-frequency side. Disposed downstream of this branching circuit block103on the side of the low-pass filter is a second switch circuit block102for switching a line connecting a transmission circuit GSM TX of the third transmitting/receiving system GSM to the branching circuit block, and a line connecting a reception circuit GSM RX of the third transmitting/receiving system to the branching circuit block. Disposed downstream of the branching circuit block103on the side of the high-pass filter is a first switch circuit block101for switching a line for connecting a reception circuit DCS RX of the first transmitting/receiving system to the branching circuit block, a line for connecting a reception circuit PCS RX of the second transmitting/receiving systems to the branching circuit block, and a line for connecting a transmission circuit DCS/PCS TX of the first and second transmitting/receiving systems to the branching circuit block.

The first switch circuit block101is constituted by a high-frequency switch of an SPDT (Single Pole Dual Throw) type comprising a terminal501, a terminal504connected to the transmission circuit DCS/PCS TX and a terminal505connected to the reception circuits DCS RX and PCS TX, and an SPDT-type high-frequency switch disposed downstream of the terminal505for switching an output terminal502connected to the first reception circuit GSM RX and an output terminal503connected to the second reception circuit (PCS RX). When a diode switch circuit comprising a plurality of diodes as disclosed by for instance, Japanese Patent Laid-Open No. 6-197040, etc. is used as the above switch circuit, the first switch circuit block101encircled by a chain line inFIG. 15is constituted by a high-frequency switch comprising four diodes as shown inFIG. 16.

What is necessary to connect the terminal501to the terminal503in the first switch circuit block101is to turn diodes201,202off by applying positive voltage from a voltage control circuit VC1for switching the switch circuit, and by applying zero voltage to a voltage control circuit VC2, and to turn diodes203,204on by applying positive voltage from a voltage control circuit VC4for switching the switch circuit, and by applying zero voltage to a voltage control circuit VC3. Namely, a high-frequency signal input to the terminal501does not appear at the terminal504because the diode202is in an OFF state with high impedance, but appears at the terminal505because the diode201is in an OFF state with high impedance, thereby connecting the terminal505to the terminal501via a transmission line401. Further, because the diode203is in an ON state with low impedance, the transmission line403is grounded at a high frequency, so that the transmission line403has high impedance viewed from the terminal505, resulting in no high-frequency signal appearing at the terminal502, while a high-frequency signal input to the terminal501appears at the terminal503because the diode204is in an ON state with low impedance.

However, when the terminal501is connected to the terminal503in the above circuit, in other words, when a mobile phone is in a state of receiving a signal, electric current of at least about 1 mA should flow between the voltage control circuits VC3–VC4, consuming a battery accordingly. Therefore, the mobile phone has a shortened reception-waiting time, having difficulty in lowering electric consumption. Also, because each of the above high-frequency switches comprises three so-called SPDT-type switches each having two output terminals per one input terminal, it has a complicated structure. Further, the high-frequency switch module needs a large circuit and thus a large laminate comprising it, disadvantageous particularly for triple band or more.

Accordingly, a high-frequency switch module further miniaturizing the mobile phone is desired. Paying attention to the impedance characteristics of bandpass filters, the inventors have found that a combination of a branching circuit comprising a phase shifter and a bandpass filter with high-frequency switch can provide a high-frequency switch circuit and its module with good insertion loss characteristics and a simple overall circuit structure as well as reduced electric consumption, thereby having completed the present invention.

Thus, the high-frequency switch circuit common to high-frequency signals of a plurality of frequency bands according to the first embodiment of the present invention comprising:

a first high-frequency switch connected to a first terminal for inputting and outputting high-frequency signals for passing a transmitting signal of a first frequency band or a transmitting signal of a second frequency band but blocking a received signal of the first frequency band and a received signal of the second frequency band; and

a branching circuit comprising a first high-frequency circuit comprising a first phase shifter connected to the first terminal and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the first terminal and a second bandpass filter disposed downstream thereof, a transmission line for constituting the first phase shifter having such a line length that the impedance of the first high-frequency circuit viewed from the input side is substantially open at a passband frequency of the second bandpass filter, a transmission line for constituting the second phase shifter having such a line length that the impedance of the second high-frequency circuit viewed from the input side is substantially open at a passband frequency of the first bandpass filter, whereby one received signal in the first and second frequency bands is permitted to pass while the other received signal is shut off.

When part of transmission/received signals of the first and second frequency bands overlap with each other, a transmitting signal of the second transmitting/receiving system (for instance, PCS) should be blocked to flow into the first high-frequency circuit on the side of a reception circuit (GSM RX) of the first transmitting/receiving system (for instance, DCS). For this purpose, it is effective that the second high-frequency switch for passing a received signal of the first frequency band or a received signal of the second frequency band but blocking a transmitting signal of the first frequency band and a transmitting signal of the second frequency band is disposed between the first terminal and the branching circuit.

The high-frequency switch circuit common to high-frequency signals of a plurality of frequency bands according to the second embodiment of the present invention comprising:

first and second filter circuits connected to an antenna terminal and having different passbands from each other;

a first high-frequency switch connected to the second filter circuit for passing a transmitting signal of the first frequency band or a transmitting signal of the second frequency band but blocking a received signal of the first frequency band and a received signal of the second frequency band;

a second high-frequency switch connected to the second filter circuit for passing a received signal of the first frequency band or a received signal of the second frequency band but blocking a transmitting signal of the first frequency band and a transmitting signal of the second frequency band;

a branching circuit connected to the second high-frequency switch for passing one received signal in the first and second frequency bands but blocking the other received signal, comprising a first high-frequency circuit comprising a first phase shifter connected to a terminal on the side of the second high-frequency switch and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the terminal and a second bandpass filter disposed downstream thereof; and

a high-frequency switch circuit connected to the first filter circuit for switching a transmitting signal and a received signal of the third transmitting/receiving system.

The high-frequency switch circuit common to high-frequency signals of a plurality of frequency bands according to the third embodiment of the present invention comprising:

first and second filter circuits connected to an antenna terminal and having different passbands from each other;

a first high-frequency switch connected to the second filter circuit for switching a signal path for passing a transmitting signal of the first frequency band and a transmitting signal of the second frequency band, and a signal path for passing a received signal of the first frequency band and a received signal of the second frequency band;

a branching circuit connected to the first high-frequency switch for passing one received signal of the first or second frequency band but blocking the other received signal, comprising a first high-frequency circuit comprising a first phase shifter connected to a terminal on the side of the first high-frequency switch and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the terminal and a second bandpass filter disposed downstream thereof; and

a high-frequency switch circuit connected to the first filter circuit for switching a transmitting signal and a received signal of the third transmitting/receiving system.

The high-frequency switch circuit common to high-frequency signals of a plurality of frequency bands according to the fourth embodiment of the present invention comprising:

first and second filter circuits connected to an antenna terminal and having different passbands from each other;

a first high-frequency switch connected to the second filter circuit for passing a transmitting signal of the first frequency band or a transmitting signal of the second frequency band but blocking a received signal of the first frequency band and a received signal of the second frequency band;

a second high-frequency switch connected to the second filter circuit for passing a received signal of the first frequency band or a received signal of the second frequency band but blocking a transmitting signal of the first frequency band and a transmitting signal of the second frequency band;

a branching circuit connected to the second high-frequency switch for passing one received signal of the first or second frequency band but blocking the other received signal, comprising a first high-frequency circuit comprising a first phase shifter connected to a terminal on the side of the second high-frequency switch and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the terminal and a second bandpass filter disposed downstream thereof;

a third high-frequency switch connected to the first filter circuit for passing a transmitting signal of the third frequency band or a transmitting signal of the fourth frequency band but blocking a received signal of the third frequency band and a received signal of the fourth frequency band;

a fourth high-frequency switch connected to the first filter circuit for passing a received signal of the third frequency band or a received signal of the fourth frequency band but blocking a transmitting signal of the third frequency band and a transmitting signal of the fourth frequency band; and

a branching circuit connected to the fourth high-frequency switch for passing one received signal of the third or fourth frequency band but blocking the other received signal, comprising a first high-frequency circuit comprising a first phase shifter connected to a terminal on the side of the fourth high-frequency switch and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the terminal and a second bandpass filter disposed downstream thereof.

The high-frequency switch circuit common to high-frequency signals of a plurality of frequency bands according to the fifth embodiment of the present invention comprising:

first and second filter circuits connected to an antenna terminal and having different passbands from each other;

a first high-frequency switch connected to the second filter circuit for switching a signal path for passing a transmitting signal of the first frequency band and a transmitting signal of the second frequency band, and a signal path for passing a received signal of the first frequency band and a received signal of the second frequency band;

a branching circuit connected to the first high-frequency switch for passing one received signal of the first or second frequency band but blocking the other received signal, comprising a first high-frequency circuit comprising a first phase shifter connected to a terminal on the side of the first high-frequency switch and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the terminal and a second bandpass filter disposed downstream thereof;

a second high-frequency switch connected to the first filter circuit for switching a signal path for passing a transmitting signal of the third frequency band and a transmitting signal of the fourth frequency band, and a signal path for passing a received signal of the third frequency band and a received signal of the fourth frequency band; and

a branching circuit connected to the second high-frequency switch for passing one received signal of the third or fourth frequency band but blocking the other received signal, comprising a first high-frequency circuit comprising a first phase shifter connected to a terminal on the side of the second high-frequency switch and a first bandpass filter disposed downstream thereof, and a second high-frequency circuit comprising a second phase shifter connected to the terminal and a second bandpass filter disposed downstream thereof.

The above are the structures of high-frequency switch circuits for dual band, triple band and quarto band in this order. In triple-band or quatro-band, high-frequency switches, it is preferable that the former is constituted by an SPST-type, high-frequency switch, while the latter is constituted by an SPDT-type, high-frequency switch.

In the branching circuit of the present invention, because a phase shift angle of a phase circuit in one high-frequency circuit is properly adjusted such that the input impedance in a passband of a filter in the other high-frequency circuit becomes high, there is substantially no leak in both frequency components corresponding to the respective passband filters. Therefore, output can be withdrawn only by transmission loss of the filter, resulting in low insertion loss. Incidentally, the phase circuit, which may also be called phase shift circuit, functions to adjust the phase shift angle to turn the input impedance substantially open. Because this branching circuit is used in place of the high-frequency switch, the number of diodes decreases, resulting in low electricity consumption. In addition, the SPST-type high-frequency switch makes the circuit structure simpler, and even in the case of using an SPDT-type, one high-frequency switch can be omitted as compared with the circuit shown inFIG. 15, thereby providing less expensive, high-frequency switch modules. This is more effective as the number of frequency bands handled increases from a dual band to a triple band and to quarto band.

One feature of the present invention is that a transmission circuit is shared by the first, second, third and fourth transmitting/receiving systems, resulting in simple and small overall structure of the high-frequency switch circuit. Also, the first and second phase shifters may be constituted by transmission lines and capacitors, and the transmission lines preferably have a line length of λ/10–λ/4. The line length is an actual length of a line in a spiral or meander form, etc.

The first and second bandpass filters are surface acoustic filters, laminate-type dielectric filters, coaxial resonator filters and bulk-wave filters, and preferable among them is the surface acoustic filter (including a balanced output-type surface acoustic filter and an unbalanced output-type surface acoustic filter).

In the present invention, it is preferable that the transmission lines or the capacitors for the phase shifters are constituted by electrode patterns formed on a plurality of green sheets made of dielectric materials, and that these green sheets are laminated and sintered to an integral laminate, thereby forming a branching circuit having a one-chip structure. Also, the bandpass filters (for instance, surface-mounted surface acoustic filters) are preferably mounted onto a top surface of the integral laminate.

In the high-frequency switch circuit for each band, an unbalanced output-type surface acoustic filter preferably constitutes the bandpass filter for the branching circuit, with a balun connected to the output of this surface acoustic filter. With a balun circuit for unbalance-balance conversion connected to the output of a surface acoustic filter of an unbalanced input-unbalanced output type, there is no need to provide an additional conversion circuit when circuits and electronic parts downstream of the unbalanced output-type surface acoustic filter are of a balanced input type. Particularly when the balun circuit is contained in the integral laminate, the number of parts and the area for mounting parts can be reduced. Of course, when a surface acoustic filter of an unbalanced input-balanced output type is used, such means is unnecessary. Preferable switch elements for these high-frequency switch circuits are diodes and transistors, and the diode switch is most effective.

The branching circuit module for handling a plurality of transmitting/receiving systems of different passbands according to the present invention comprises a first phase shifter connected to a first terminal for inputting and outputting high-frequency signals, a first bandpass filter disposed downstream thereof, a second phase shifter connected to the first terminal, and a second bandpass filter disposed downstream thereof, the first phase shifter and the second phase shifter being contained in a sintered laminate of dielectric green sheets, and the first passband filter and the second passband filter being mounted onto the laminate.

In the above branching circuit module, the first phase shifter is constituted by a transmission line having such a line length that the impedance viewed from the input side is substantially open at a passband frequency of the second bandpass filter, and the second phase shifter is constituted by a transmission line having such a line length that the impedance viewed from the input side is substantially open at a passband frequency of the first bandpass filter.

In the high-frequency switch module for handling a plurality of transmitting/receiving systems of different passbands according to the present invention, the phase shifters of the above high-frequency switch circuit, the bandpass filters and the first and second filter circuits are constituted by transmission lines and capacitors.

In the above high-frequency switch module, at least part of transmission lines and capacitors in the phase shifter, the bandpass filter and the first and second filter circuits and at least part of transmission lines in the first to fourth high-frequency switches are constituted by electrode patterns formed on a plurality of green sheets made of a dielectric material, the green sheets being laminated and sintered to an integral laminate containing the electrode patterns, with diodes constituting the high-frequency switch mounted onto the integral laminate.

With phase shifters constituted by transmission lines, elements including bandpass filters can be constituted by electrode patterns contained in an integral laminate, thereby forming a high-frequency switch module of a one-chip structure, which is small and lightweight with high freedom of design as high-frequency parts. The electrode patterns of the transmission lines for the phase shifters arc preferably formed on lower layers than those constituting the bandpass filters. With the electrode patterns of the transmission lines for the phase shifters arranged lower than those of the bandpass filters, insertion loss characteristics and isolation characteristics can be improved.

The wireless communications device of the present invention comprises the above high-frequency switch module. The wireless communications device is preferably a mobile phone.

In the preferred embodiment of the present invention, the mobile phone comprises the above high-frequency switch circuit, and a voltage control circuit for applying voltage for determining the operation mode of the high-frequency switch circuit.

Because the mobile phone of the present invention comprises a small, lightweight, high-frequency switch module of a low electricity consumption type having good insertion loss characteristics, it has high reception sensitivity and long reception-waiting time.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are explained in detail below referring to the attached figures. For simplicity of explanation, a DCS (transmission TX: 1710–1785 MHz, reception RX: 1805–1880 MHz) system as the first signal frequency band f1, a PCS (transmission TX: 1850–1910 MHz, reception RX: 1930–1990 MHz) system as the second signal frequency band f2, a GSM (transmission TX: 880–915 MHz, reception RX: 925–960 MHz) system as the third signal frequency band f3, and a DAMPS (Digital Advanced Mobile Phone Service, transmission TX: 824–849MHz, reception RX: 869–894MHz) system as the fourth signal frequency band f4are taken as examples, though the present invention, of course, is applicable to other communications systems.

FIG. 1is a block diagram showing one example of the branching circuit of the present invention. This branching circuit is a dual-band branching circuit for branching the received signals of DCS (f1) and PCS (f2), which comprises (a) a first high-frequency circuit of a DCS system comprising a first phase shifter3connected to a common terminal10and a first bandpass filter5disposed downstream thereof, and (b) a second high-frequency circuit of a PCS system comprising a second phase shifter4similarly connected to the terminal10and a second bandpass filter6disposed downstream thereof.

FIG. 4is a block diagram showing another example of the branching circuit of the present invention. This branching circuit comprises capacitors31,32connected upstream and downstream of the first phase shifter3and capacitors41,42connected upstream and downstream of the second phase shifter4. The branching circuit in this embodiment is advantageous in that the transmission line can be made short.

Each of the phase shifters3and4is constituted by a transmission line having an actual line length of about λ/10–λ/4 at a frequency band f1, f2. As shown in the Smith chart ofFIG. 2, the first bandpass filter5comprises a surface acoustic filter (SAW) having input impedance of substantially 50 Ω in a reception frequency band of DCS system, resulting in substantially a short-circuited state in a reception frequency band of the PCS system. As shown in the Smith chart ofFIG. 3, the second bandpass filter6comprises a surface acoustic filter (SAW) having input impedance of substantially 50 Ω in a reception frequency band of the PCS system, resulting in substantially a short-circuited state in a reception frequency band of the DCS system.

As described above, the first bandpass filter5has attenuation characteristics necessary for a system in which the reception band of DCS is a passband f1, the impedance characteristics of the first bandpass filter5viewed from the input side being such that it is substantially in a short-circuited state in a reception passband f2of PCS. On the other hand, the second bandpass filter6has such impedance characteristics as to exhibit attenuation characteristics necessary for a system in which the reception band of PCS is a passband f2, the impedance viewed from the side of the second bandpass filter6being substantially in a short-circuited state in a reception passband of DCS.

This branching circuit is constituted such that it meets the following conditions: With a phase shifter3disposed upstream of the first bandpass filter5, the impedance characteristics of the first high-frequency circuit viewed form the side of the terminal10are in a substantially open state in a reception band f2of PCS. Also, with the phase shifter4disposed upstream of the second bandpass filter6, the impedance characteristics of the second high-frequency circuit viewed form the side of the terminal10are in a substantially open state in a reception band f1of DCS. Accordingly, without the second phase shifter4, a signal of the reception band f1of DCS sent to the first reception circuit would be absorbed by the second bandpass filter6, because the input impedance of the second bandpass filter6in a reception band f1of DCS is substantially in a short-circuited state. However, with the second phase shifter4, the impedance of the second high-frequency circuit in a reception band f1of DCS viewed form the side of the terminal10is phase-reversed to a substantially open state, a high-frequency signal flows into the first reception circuit via the first high-frequency circuit.

The same is true when a signal of reception band f2of PCS is sent to the second reception circuit. With the first phase shifter3, the impedance of the first high-frequency circuit in a reception band f2of PCS viewed form the side of terminal10is phase-reversed to a substantially open state, causing a high-frequency signal to flow into the second reception circuit via the second high-frequency circuit.

The term “substantially open state” means a case where the real number part R is adjusted to 150 Ω or more, and a case where an absolute value of the imaginary number part X is adjusted to 100 Ω or more, in the impedance Z expressed by Z=R+jX. Expressed in Smith charts of FIGS.2and3, for instance, this “substantially open state” corresponds to hatched regions on the right side. Accordingly, when a signal of the reception band f1of DCS is sent to the first reception circuit, the line length of the second transmission line4should be adjusted, such that the impedance of the second high-frequency circuit in the reception band f1of DCS viewed form the side of the terminal10is included in a hatched region on the Smith chart ofFIG. 3. Also, when a signal of the reception band f2of PCS is sent to the second reception circuit, the line length of the first transmission line3should be adjusted, such that the impedance of the first high-frequency circuit in the reception band f2of PCS viewed form the side of the terminal10is included in a hatched region on the Smith chart ofFIG. 2.

FIG. 5is a block diagram showing a dual-band, high-frequency switch circuit common to both systems of DCS and GSM according to the first embodiment of the present invention. This high-frequency switch circuit comprises a branching circuit as a means for branching the received signals of DCS and GSM, a circuit common to a transmitting system of a DCS system and a transmitting system of a GSM system, and a common terminal. A first high-frequency switch SW1disposed in a signal path is a switch of an SPST (Single Pole Single Throw) type for preventing the received signals of DCS and GSM from entering into the transmission circuit.

FIG. 6is an equivalent circuit of the dual-band, high-frequency switch circuit SW1in the embodiment shown inFIG. 5. A common terminal10is connected to an antenna ANT to switch a transmission TX of DCS/GSM and a reception RX of DCS or GSM to the antenna ANT. The first switch circuit SW1comprises as main elements a diode202and a transmission line402, and the diode202has a cathode connected to an input/output terminal10and an anode connected to a transmitting system TX for both DCS and GSM via a capacitor303, and connected to a transmission line402connected to a ground via a capacitor304. Also, a voltage control circuit VC2for controlling the diode is connected between the transmission line402and the capacitor304.

The branching circuit shown inFIG. 1is inserted between the common terminal10and each receiving system RX for DCS and GSM, and this branching circuit passes one of received signals of DCS and GSM without regard to voltage control of the diode while blocking the other received signal, so that it is operated without leak of both received signals. Accordingly, there is no need of a switch circuit comprising a diode, resulting in a simple circuit structure.

FIG. 7shows a high-frequency switch circuit according to the second embodiment of the present invention. In this circuit, a high-frequency switch SW2is disposed upstream of the phase shifters3,4shown inFIG. 5. Such structure can be used even when a reception band of DCS and a transmission band of PCS partially overlap with each other as in a combination of DCS and PCS. In this embodiment, the high-frequency switches SW1, SW2are of an SPST type, though they may be SPDT-type, high-frequency switches as shown inFIG. 8.

FIG. 9shows an equivalent circuit of high-frequency switch circuit ofFIG. 8, in which a high-frequency switch1and a high-frequency switch2are constituted by diode switches. What differs from the circuit ofFIG. 6are that a transmission line401is connected between a common terminal10on the antenna side and a branching circuit on the side of reception, that a diode201is connected such that its anode is connected to the reception side, that a capacitor302is connected between the cathode of the diode201and a ground, and that a voltage control circuit VC1for diode control is connected between the diode201and the capacitor302. Inserted between the anode of the diode201and each reception RX of DCS and PCS is a branching circuit shown inFIG. 1. Because a diode is omitted in a switch circuit for switching DCS RX and PCS RX in this embodiment, too, the high-frequency switch circuit has a simple structure.

FIG. 10shows a high-frequency switch circuit according to the third embodiment of the present invention. This circuit is a triple-band, high-frequency switch circuit common to three systems of DCS, PCS and GSM. In this high-frequency switch circuit, too, the same branching circuit as above is used as a means for branching the received signals of DCS and PCS. Connected to an antenna ANT are first and second filter circuits F1, F2. The first filter circuit F1is a low-pass filter LPF, to which a high-frequency switch SW5for switching a reception circuit RX and a transmission circuit TX of GSM is connected. The second filter circuit F2is a high-pass filter HPF, to which the above high-frequency switch circuit for DCS and PCS is connected. Incidentally, a low-pass filter7is connected between the SPDT-type, high-frequency switch SW4and the transmission TX of DCS/PCS, and a low-pass filter8for sending a transmitting signal is connected between the high-frequency switch SW5and the transmitting system TX of GSM.

FIG. 12shows one example of an equivalent circuit of the triple-band, high-frequency switch module explained in detail below.

FIG. 11shows a high-frequency switch circuit according to the fourth embodiment of the present invention. This high-frequency switch circuit is a quatro-band, high-frequency switch circuit common to four systems of DCS, PCS, GSM and DAMPS. This high-frequency switch circuit, too, comprises branching circuits as means for branching the received signals of DCS and PCS and the received signals of GSM and DAMPS, respectively. Also, it comprises a transmission circuit common to GSM and DAMPS, additionally with a low-pass filter8and a high-frequency switch SW6. Because the other structures are the same as in the triple-band, high-frequency switch circuit shown inFIG. 10, their explanations will be omitted.

In the high-frequency switch circuit in the above each embodiment, a balun circuit (BAL), which is an unbalance-balance conversion circuit, may be connected downstream of the surface acoustic wave (SAW) filter. Because the surface acoustic filter is of an unbalanced input-unbalanced output type, the connection of the balun circuit in the high-frequency switch circuit makes additional conversion circuits unnecessary, as long as circuits or electronic parts downstream of the surface acoustic filter are of a balanced-input type. Particularly when the balun circuit is contained in an integral laminate, the number of parts and the area for mounting parts can be reduced.

An equivalent circuit of the triple-band, high-frequency switch circuit shown inFIG. 10will be explained in detail referring toFIG. 12. Each of the first and second filter circuits F1, F2connected to the antenna ANT is constituted by a transmission line and a capacitor. The equivalent circuit shown inFIG. 12comprises a low-pass filter as a first filter F1for passing the transmission/received signals of GSM while attenuating the transmission/received signals of DCS and PCS, and a high-pass filter as a second filter F2for passing transmission/received signals of DCS and PCS while attenuating the transmission/received signals of GSM. The first filter F1has a structure in which a transmission line LF1and a capacitor CF1are connected in parallel, with a capacitor CF3connected between them and a ground. The second filter F2has a structure in which a transmission line LF2and a capacitor CF2are connected in parallel with a transmission line LF3connected between them and a ground, and a capacitor CF4is connected to the transmission line LF2and the capacitor CF2in series. With such structure, the received signals of the first transmitting/receiving system and the second and third transmitting/receiving system can be separated. The first and second filters F1, F2may have other structures a–h:a. A structure in which the first filter circuit is constituted by a low-pass filter, and the second filter circuit is constituted by a notch filter;b. A structure in which the first filter circuit is constituted by a notch filter, and the second filter circuit is constituted by a bandpass filter;c. A structure in which the first filter circuit is constituted by a low-pass filter, and the second filter circuit is constituted by a bandpass filter;d. A structure in which the first filter circuit is constituted by a notch filter, and the second filter circuit is constituted by a notch filter;e. A structure in which the first filter circuit is constituted by a notch filter, and the second filter circuit is constituted by a high-pass filter;f. A structure in which the first filter circuit is constituted by a bandpass filter, and the second filter circuit is constituted by a bandpass filter;g. A structure in which the first filter circuit is constituted by a bandpass filter, and the second filter circuit is constituted by a notch filter; andh. A structure in which the first filter circuit is constituted by a bandpass filter, and the second filter circuit is constituted by a high-pass filter.

A third high-frequency switch circuit SW5for switching a transmission circuit TX and a reception circuit RX of GSM, a high-frequency switch circuit SW4for switching a transmission circuit TX of DCS/PCS, a reception circuit DCS RX of DCS and a reception circuit PCS RX of PCS, and a branching circuit for passing one received signal but blocking the other received signal to switch a reception circuit DCS RX of DCS and a reception circuit PCS RX of PCS, all connected downstream of the first and second filters F1, F2, comprise transmission lines as main constituents.

The third high-frequency switch circuit SW5is an upper switch circuit inFIG. 12, which switches a transmission circuit TX and a reception circuit RX of GSM. The switch circuit SW5comprises two diodes DG1, DG2and two transmission lines LG1, LG2as main constituents, and the diode DG1is disposed between an input/output terminal IP1of a transmission/received signal of GSM and GSM TX, such that the anode of the diode DG1is connected to the input/output terminal IP1, with the transmission line LG1connected between the cathode of the diode DG1and the ground. The transmission line LG2is connected between the input/output terminal IP1and GSM RX, and the end of the transmission line LG2on the side of GSM RX is connected to a cathode of the diode DG2. A capacitor CG6is connected between the anode of diode DG2and the ground. A voltage control circuit Vg is connected between the anode of the diode DG2and the capacitor CG6via a resistor RG and a capacitor CG5having one end ground.

Each of the transmission line LG1and the transmission line LG2has such a line length that its resonance frequency is within a frequency band region of the transmitting signal of GSM. Particularly when their resonance frequencies are substantially equal to an intermediate frequency (897.5 MHz) of a transmitting signal frequency of GSM, excellent insertion loss characteristics can be achieved within a desired frequency band region. The low-pass filter circuit inserted between the first filter F1and GSM TX is constituted by a transmission line and capacitors. In the equivalent circuit shown inFIG. 12, a π-type, low-pass filter constituted by a transmission line LG3and capacitors CG3, CG4, CG7is inserted between the diode DG1and the transmission line LG1.

The high-frequency switch circuit SW4is a lower switch circuit inFIG. 12for switching a reception circuit DCS RX of DCS, a reception circuit PCS RX of PCS and a transmission circuit DCS/PCS TX of DCS and PCS. This switch circuit comprises two diodes DP1, DP2, the above branching circuit, and two transmission lines LP1, LP2as main constituents. The diode DP1is disposed between the input/output terminal IP2of the transmission/received signal of DCS/PCS and DCS/PCS TX, with its anode connected to the input/output terminal IP2and with the transmission line LP1connected between its cathode and a ground. A transmission line LP2is connected between the input/output terminal IP2and the branching circuit, and a diode DP2having a cathode connected to the transmission line LP2is disposed between one end of the transmission line LP2on the side of the branching circuit and the ground. A capacitor CP6is connected between the anode of the diode DP2and the ground. A voltage control circuit Vd is connected between the anode of the diode DP2and the capacitor CP6via a resistor RP and a capacitor CP5having one end grounded. A first high-frequency circuit on the side of DCS RX comprising the transmission line LP5and the bandpass filter DCS SAW connected to the transmission line LP5, and a second high-frequency circuit on the side of PCS RX comprising the transmission line LP6and the bandpass filter PCS SAW connected to the transmission line LP6are connected to the cathode of DP2in parallel, constituting a branching circuit.

The transmission lines LP1and LP2have such a line length as to provide resonance frequency within a frequency band region (1710 MHz–1910 MHz) between a lower-limit frequency and an upper-limit frequency of the transmitting signals of DCS and PCS. More preferably, the resonance frequency of the transmission lines LP1and LP2is substantially an intermediate frequency (1810 MHz) of the transmitting signal frequencies of DCS and PCS, to obtain excellent electric characteristics in cach mode, so that two transmitting signals can be treated by one circuit.

With such a structure, the circuit can be made simpler with fewer circuit parts to provide a miniaturized high-frequency switch module with excellent electric characteristics, as compared with a case where the transmitting systems of DCS and PCS are handled separately. Also, some parts such as amplifiers can be made common to the transmission circuits of the first and second transmitting/receiving systems, thereby further making mobile phones comprising high-frequency switch modules smaller and lighter in weight.

A low-pass filter circuit inserted between the second filter F2and DCS/PCS TX is constituted by a transmission line and a capacitor. In the equivalent circuit shown inFIG. 12, a π-type, low-pass filter circuit constituted by the transmission line LP3and the capacitors CP3, CP4and CP7is inserted between the diode DP1and the transmission line LP1. In this low-pass Filter circuit, its transmission line LP3has a line length corresponding to an intermediate frequency of the transmitting signals of the transmitting/receiving systems of DCS and PCS, specifically λ/8–λ/12. Here, assuming that the first transmitting/receiving system is DCS, and the second transmitting/receiving system is PCS, for instance, the “intermediate frequency” of the transmitting signal is a middle of the transmitting signal of DCS (1710–1785 MHz) and the transmitting signal of PCS (1850–1910MHz), namely 1810 MHz. If the line length of the transmission line LP3is λ/8 or more relative to this intermediate frequency, passband characteristics are narrow band, failing to obtain desired insertion loss characteristics near the lower-limit frequency of the transmitting signal of DCS and near the transmitting signal of PCS. Also, if it is less than λ/12, there is less attenuation in high-frequency regions such as a second harmonic wave, a third harmonic wave, etc. In any case, the characteristics of a high-frequency switch module are undesirably deteriorated.

The high-frequency switch circuit of the present invention selects any one of the first, second and third transmitting/receiving systems, by supplying voltage from the voltage control circuit to control ON/OFF of the diode switches. The operation of the high-frequency switch circuit having thc equivalent circuit shown inFIG. 12will be explained in detail below.

To connect the first and second transmission circuits DCS/PCS TX to the second filter F2, positive voltage is supplied from the voltage control circuit Vd. The positive voltage supplied from the voltage control circuit Vd is removed of a DC component by capacitors CB2, CP3, CP4, CP5, CP6, CF4and bandpass filters of DCS SAW and PCS SAW, and applied to the circuit including the diodes DP1, DP2, so that the diodes DP1, DP2are turned on. With the diode DP1in an ON state, impedance is low between the first and second transmission circuits DCS/PCS TX and the connection point IP2. Also, the diode DP2in an ON state and the capacitor CP6has the transmission line LP2grounded at a high frequency to cause resonance, thereby making the impedance of the first and second reception circuits DCS RX and PCS RX viewed from the side of the connection point IP2extremely large. Accordingly, the transmitting signal from the first and second transmission circuit DCS/PCS TX is transmitted to the second filter without leak to the first reception circuit DCS RX and the second reception circuit PCS RX.

(2) GSM RX Mode

To connect the first reception circuit DCS RX to the second filter F2, zero voltage is applied from the voltage control circuit Vd to turn the diodes DP1, DP2off. With the diode DP1in an OFF state, impedance between the connection point IP2and the first and second transmission circuit DCS/PCS TX is large. Thus, the diode DP2in an OFF state has the connection point IP2connected to the connection point IP3via the transmission line LP2. Also, the second high-frequency circuit comprising a combination of the transmission line LP6and the bandpass filter PCS SAW is adjusted to have such impedance is substantially open in a reception band f1of the first frequency band DCS viewed from IP3to the side of the second reception circuit PCS RX. Accordingly, a received signal from the second filter F2in a reception band f1of the first frequency band DCS is transmitted to the first reception circuit DCS RX without leaking to the first and second transmission circuits DCS/PCS TX and the second reception circuit PCS RX.

(3) PCS RX Mode

Because it is the same as the GSM RX mode, explanation is omitted.

(4) GSM TX Mode

To connect the third transmission circuit GSM TX to the first filter F1, positive voltage is applied from the voltage control circuit Vg. With a DC component removed from the positive voltage applied from the voltage control circuit Vg by capacitors CB1, CG6, CG5, CG4, CG3and CG1and the bandpass filter of GSM SAW, the positive voltage is applied to a circuit including diodes DG2, DG1to turn the diodes DG2, DG1on. With the diode DG1in an ON state, impedance between the third transmission circuit GSM TX and the connection point IP1is low. Also, the diode DG2turned on and the capacitor CG6have the transmission line LG2grounded at a high frequency to cause resonance, resulting in extremely increased impedance viewed from the connection point IP1to the third reception circuit GSM RX. Accordingly, the transmitting signal from the third transmission circuit GSM TX is transmitted to the first filter without leaking to the third reception circuit GSM RX.

(5) GSM RX Mode

To connect the third reception circuit GSM RX to the first filter F1, zero voltage is applied to the voltage control circuit Vg, to turn the diodes DG1, DG2off. With the diode DG2in an OFF state, the connection point IP1is connected to the third reception circuit GSM RX via the transmission line LG2. Also, with the diode DG1in an OFF state, impedance between the connection point IP1and the third transmission circuit GSM TX is large. Accordingly, a received signal from the first filter F1is sent to the third reception circuit GSM RX without leaking to the third transmission circuit GSM TX1.

Another feature of the present invention is that at least part of transmission lines and capacitors constituting the phase shifters, the bandpass filters, the first and second filter circuits, the low-pass filters, etc., and at least part of transmission lines constituting the high-frequency switches in each of the above embodiments are formed by electrode patterns on a plurality of green sheets made of a dielectric material, and that green sheets with electrode patterns are laminated and sintered to an integral laminate, so that these elements arc contained in the laminate, while the diodes for constituting the high-frequency switches are mounted onto the integral laminate, thereby providing a small high-frequency switch module.

The appearance of the laminate according to one embodiment of the present invention is shown in a perspective view ofFIG. 14, and the inner structure of the laminate is shown inFIG. 13. In this embodiment, the transmission lines of the first and second filter circuits, the low-pass filter circuit and the switch circuits are formed in the laminate, while diodes, bandpass filters and high-capacitance capacitors that cannot be contained as chip capacitors in the laminate are mounted onto the laminate, thereby providing a one-chip-type, triple-band, high-frequency switch module.

The laminate of the high-frequency switch module is produced by preparing green sheets of 50 μm–200 μm in thickness made of dielectric ceramic materials that can be sintered at low temperatures, printing a conductive paste based on Ag on each green sheet to form a desired electrode pattern, properly laminating the electrode pattern-formed green sheets and integrally sintering the laminated green sheets. Each line electrode is mostly formed with a width of 100–400 μm.

The inner structure of the high-frequency switch module will be explained in the order of lamination. First, a ground electrode41is formed on a substantially entire surface of a lowermost green sheet20. Through-holes for connecting to terminal electrodes formed on a rear surface are formed in peripheral portions on four sides of the green sheet20.

Next, four capacitors (constituting a capacitance with a ground) connected between the voltage control circuits Vg, Vd and the diodes DG2, DP2are printed in electrode patterns on the green sheet21, which is then laminated. Laminated thereon is a green sheet22having a ground electrode42formed on a substantially entire surface, and then a green sheet23formed with five capacitor electrodes and four line electrodes for constituting a low-pass filter, etc. Further laminated thereon is a green sheet24having two capacitor electrodes and five line electrodes formed thereon. Further laminated is a green sheet25formed with eight line electrodes, two of which constitute transmission lines LP5and LP6, a green sheet26having seven line electrodes, two of which constitute transmission lines LP5and LP6, and then a green sheet27having four line electrodes formed thereon and a green sheet28having two line electrodes formed thereon.

These line electrodes are properly connected via through-holes to form transmission lines for the first, second and third switch circuits SW1, SW2, SW5, transmission lines for the phase shifters3,4, and transmission lines for the first and second filter circuits and the low-pass filters. The line electrodes43and44are connected to each other via through-hole electrodes to form the transmission line LP5in the equivalent circuit, and the line electrodes45and46are connected to each other via through-hole electrodes to form the transmission line LP6in the equivalent circuit. The other line electrodes are connected via through-hole electrodes to form transmission lines LG2, LP2, LG3, LP3in the equivalent circuit.

The laminate is provided with steps for mounting SAW filters as bandpass filters in a green sheet29laminated on the green sheet28and its overlying green sheets, and three SAW filters for DCS, PCS and GSM are mounted thereon. Also, a half of this green sheet29is provided with a ground electrode. Green sheets30,31,32laminated thereon are formed with proper electrodes for capacitors. A green sheet33laminated thereon has only a through-hole. Line electrodes for constituting transmission lines LF1, LF2constituting the first and second filter circuits F1, F2, and line electrodes for constituting LP1, LG1are formed between a green sheet34laminated on the green sheet33and a green sheet35. A green sheet36laminated thereon and an uppermost green sheet37are formed with lands for connecting elements mounted thereon, and diodes DG1, DG2, DP1, DP2, a capacitor CG1and resistors RG, RP are mounted onto the lands.

These green sheets were compressed and integrally sintered to form a laminate of 6.7 mm×5.0 mm×1.0 mm in outer dimension. Mounted on this laminate were diodes DG1, DG2, DP1, DP2, a chip capacitor CF3, chip resistors RP, RG and bandpass filters GSM SAW, DCS SAW, PCS SAW.FIG. 13shows a state where these elements are mounted onto the laminate.

The control logic of each voltage control circuit Vg, Vd in the high-frequency switch module of this embodiment is shown in Table 1. With this control logic, each mode of GSM, DCS and PCS is changed.

Using this high-frequency module for a multiband mobile phone, it has been found that it enjoyed low electricity consumption in a battery, providing a low-electricity consumption mobile phone.

Though the systems of DCS, PCS and GSM are used in the above explanation, the same effects can be obtained in a combination of other systems (for instance, GPS, D-AMPS, TD-SCDMA), too.

According to the present invention, the high-frequency switch circuit having a simple circuit structure with low electricity consumption, the small, lightweight, inexpensive, high-frequency switch module capable of handling signals of a plurality of frequency bands, and the wireless communications device such as a mobile phone comprising such high-frequency switch module can be obtained.