multiband high-frequency switching module

Abstract: A multiband high-frequency switching module in the form of a laminate body for use in a communication system utilizing a plurality of transmit-receive systems includes a band-separating circuit (2) and switching circuits (SW1, SW2) for the plurality of transmit-receive systems. The band-separating circuit (2) is constituted by filter circuits each comprising an LC circuit. One end of the band-separating circuit (2) is connected to a common antenna. One end of each switching circuit is connected to the band-separating circuit and the other end is connected in parallel to a receiving circuit and a transmitting circuit. Each switching circuit (SW1, SW2) comprises a switching element (DG1, DG2; DP1, DP2) and a transmission line (LG1, LG2; LP1, LP2). The laminate body comprises a plurality of dielectric layers, pattern electrodes printed on the dielectric layers, and chip elements mounted on a top surface of the laminate body. The switching elements (DG1, DG2; DP1, DP2) include a first switching element (DG1, DP1) having an anode connected to a line directed to a common antenna terminal (CAT) side and cathode connected to a line directed to the transmission circuit (TX1, TX2) side, and a second switching element (DG2, DP2) having an cathode connected to a line directed to the receiving circuit (RX1, RX2) side and a anode connected to a line directed to a ground terminal (GRD: 89).

Description: BACKGROUND OF THE INVENTION The present invention relates to a high-frequency composite circuit part, more specifically, to a multiband high-frequency switching module used in a communication system utilizing a plurality of transmit-receive systems having different passbands. A digital cellular radiotelephone uses a high-frequency switch to alternately and electrically connect an antenna (ANT) to a transmitting circuit (TX) or a receiving circuit (RX). Fig. 15 is a schematic circuit diagram showing a conventional single-band high-frequency switch circuit disclosed in Japanese Patent Laid-Open No. 6-197040. In Fig. 15, the high-frequency switch alternately connects an antenna ANT to a transmitting circuit TX or a receiving circuit RX, and comprises a first diode D1, the anode thereof being connected to the transmitting circuit TX and the cathode thereof being connected to the antenna ANT, a strip line SL connected between the antenna ANT and the receiving circuit RX, and a second diode D2, the anode thereof being connected between the strip line SL and the receiving circuit RX and the cathode thereof being grounded. The high-frequency switch is made into a dielectric laminate body having a plurality of substrates, in which the strip line SL is disposed on an inner substrate and the diodes D1, D2 are mounted on the top surface of the dielectric laminate body. With the recent striking spread of the cellular radiotelephone, there has been increased demand for improving the performance thereof, expanding the service area, etc. As a radiotelephone of new type, a dual-band radiotelephone has been proposed. In contrast to the conventional radiotelephone which utilizes a single transmit-receive system, the dual-band radiotelephone uses two transmit-receive systems having different passbands. A user may communicate by suitably selecting a desired transmit-receive system. If the respective transmit-receive systems are constituted by different circuits, the resultant dual-band radiotelephone would become large in its size and expensive. Therefore, the parts for the dual-band radiotelephone, as many as possible, should be shared between the transmit-receive systems in view of reducing the size and the production cost. A high-frequency switching module with the features included in the first part of claim 1 is known from EP-A-0 797 312 A2 and, similarly, US-A-5,473,293. These modules are operable in a single frequency band. EP-A-0 567 766 discloses a circuit including frequency filters for switching an automobile antenna so as to associate different frequency ranges separately to different receivers. OBJECT AND SUMMARY OF THE INVENTION It is an object of the present invention is to provide a multiband high-frequency switching module for alternately and electrically connecting a common antenna to a transmitting circuit or a receiving circuit of any one of two or more transmit-receive systems having different passbands. Another object of the present invention is to provide a multiband high-frequency switching module made into a small laminated structure. These objects are met by the high-frequency switching module defined in claim 1. In an embodiment of the present invention, there is provided a multiband high-frequency switching module in the form of a laminate body for use in a communication system utilizing a plurality of transmit-receive systems having different passbands, a circuit of the multiband high-frequency switching module comprising: (a) a band-separating circuit, one end thereof being connected to a common antenna terminal for connecting a common antenna; and (b) switching circuits for the transmit-receive systems, one end of each switching circuit being connected to the band-separating circuit and the other end being connected in parallel to a receive terminal for connecting a receiving circuit and a transmit terminal for connecting a transmitting circuit so as to alternately connect the common antenna to the receiving circuit or the transmitting circuit; and the laminate body comprising a plurality of dielectric substrates, pattern electrodes printed on the dielectric substrates, terminal electrodes formed on surfaces of the laminate body, and chip elements mounted on a top surface of the laminate body. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block schematic diagram showing a preferred embodiment of the multiband high-frequency switching module according to the present invention; Fig. 2 is a schematic circuit diagram showing an equivalent circuit of the multiband high-frequency switching module of Fig. 1; Fig. 3 is a plan view of a laminate body of the multiband high-frequency switching module according to the present invention; Fig. 4 is a perspective view of a laminate body of the multiband high-frequency switching module according to the present invention; Fig. 5 is a plan view showing each substrate constructing the laminate body of Figs. 3 and 4; Fig. 6 is a block schematic diagram showing a first preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 7 is a block schematic diagram showing a second preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 8 is a block schematic diagram showing a third preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 9 is a block schematic diagram showing a fourth preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 10 is a block schematic diagram showing a fifth preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 11 is a block schematic diagram showing a sixth preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 12 is a block schematic diagram showing a seventh preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 13 is a block schematic diagram showing a eighth preferred circuit of the multiband high-frequency switching module according to the present invention; Fig. 14 is a block schematic diagram showing a ninth preferred circuit of the multiband high-frequency switching module according to the present invention; and Fig. 15 is a schematic circuit diagram showing a conventional single-band high-frequency switch circuit. DESCRIPTION OF THE PREFERRED EMBODIMENTS The multiband high-frequency switching module of the present invention comprises a band-separating circuit, switching circuits each alternately connecting a common antenna to a receiving circuit or a transmitting circuit of any one of a plurality of transmit-receive systems having different passbands, and terminals for connecting the common antenna, the receiving circuit, or the transmitting circuit. The present invention will be described while taking a high-frequency switching module for a dual-band system as an example. However, it should be noted that the present invention is equally applicable to a communication system including three or more transmit-receive systems having different passbands, regardless of the following description of preferred embodiments. In a preferred embodiment of the present invention, the multiband high-frequency switching module may comprise a band-separating circuit, a first switching circuit for a first transmit-receive system and a second switching circuit for a second transmit-receive system. Such a multiband high-frequency switching module is suitable for use in an dual-band cellular radiotelephone. The band-separating circuit separates a communication signal into two bands for the first and second transmit-receive systems. The band-separating circuit is constituted by two filter circuits, each comprising an inductor component and a capacitor component and corresponding to each of the first and second transmit-receive systems. The circuits for the band-separating circuit may be notch filter circuits, low PASS filter circuits, high PASS filter circuits, band PASS filter circuits, or any combination of these circuits. For example, the band-separating circuit may be constituted by first and second notch filter circuits, each comprising parallel-connected inductor and capacitor. One end of each notch filter circuit is respectively connected to the corresponding switching circuit, and the other end thereof is connected to a common antenna terminal for connecting the common antenna. Between one of the notch filter circuits and its corresponding switching circuit, a capacitor being grounded may be connected in a shunt configuration. Between the other notch filter circuit and its corresponding switching circuit, a capacitor may be connected and an inductor being grounded may be further connected in a shunt configuration between the notch filter circuit and the capacitor. Each of the first and second transmit-receive systems includes one switching circuit, one end thereof being connected to the band-separating circuit which is connected to the common antenna terminal for connecting the common antenna terminal, another end thereof being connected to a receive terminal for connecting the receiving circuit, and still another end thereof being connected to a transmit terminal for connecting the transmitting circuit. Thus, the first switching circuit alternately connects the common antenna to a first transmitting circuit or a first receiving circuit, and the second switching circuit alternately connects the common antenna to a second transmitting circuit or a second receiving circuit. The switching circuit may be a diode switching circuit which is connected to a control circuit through a control terminal to apply a voltage of a predetermined level to the diodes, thereby controlling the switching operation. For example, the multiband high-frequency switching module may have first and second control terminals for controlling the transmitting circuits of the first and second transmit-receive systems, and third and fourth control terminals for controlling the receiving circuits of the first and second transmit-receive systems. The receiving circuits of the first and second transmit-receive systems may be controlled by the same control terminal A low PASS filter circuit comprising an inductor component and a capacitor component may be incorporated into the switching circuit to provide the transmit system (a path from the common antenna terminal to the transmit terminal through the band-separating circuit and the switching circuit) of each transmit-receive system with a low PASS filtering function. Thus, the multiband high-frequency switching module of the present invention may include the following various circuit constructions. (A) As shown in Fig. 6, in a first preferred circuit, the band-separating circuit 2 is constituted by a low PASS filter circuit LPF for the first transmit-receive system and a notch filter circuit NF for the second transmit-receive system, and a low PASS filter circuit LPF2 is incorporated into the second switching circuit SW2. (B) As shown in Fig. 7, in a second preferred circuit, the band-separating circuit 2 is constituted by a low PASS filter circuit LPF for the first transmit-receive system and a high pass filter circuit HPF for the second transmit-receive system, and a low PASS filter circuit LPF2 is incorporated into the second switching circuit SW2. (C) As shown in Fig. 8, in a third preferred circuit, the band-separating circuit 2 is constituted by a notch filter circuit NF for the first transmit-receive system and a band pass filter circuit BPF for the second transmit-receive system, and a low PASS filter circuit LPF1 is incorporated into the first switching circuit SW1. (D) As shown in Fig. 9, in a fourth preferred circuit, the band-separating circuit 2 is constituted by a low pass filter circuit LPF for the first transmit-receive system and a band pass filter circuit BPF for the second transmit-receive system. No low PASS filter circuit is incorporated into the switching circuits, because the band pass filter circuit BPF has a function of low pass filter. (E) As shown in Fig. 10, in a fifth preferred circuit, the band-separating circuit 2 is constituted by a first notch filter circuit NF1 for the first transmit-receive system and a second notch filter circuit NF2 for the second transmit-receive system. A first low PASS filter circuit LPF1 and a second low PASS filter circuit LPF2 are respectively incorporated into the first switching circuit SW1 and the second switching circuit SW2. (F) As shown in Fig. 11, in a sixth preferred circuit, the band-separating circuit 2 is constituted by a notch filter circuit NF for the first transmit-receive system and a high pass filter circuit HPF for the second transmit-receive system. A first low PASS filter circuit LPF1 and a second low PASS filter circuit LPF2 are respectively incorporated into the first switching circuit SW1 and the second switching circuit SW2. (G) As shown in Fig. 12, in a seventh preferred circuit, the band-separating circuit 2 is constituted by a first band pass filter circuit BPF1 for the first transmit-receive system and a second band pass filter circuit BPF2 for the second transmit-receive system. No low pass filter circuit is incorporated into the switching circuits, because the band pass filter circuits BPF1 and BPF2 have a function of low pass filter. (H) As shown in Fig. 13, in an eighth preferred circuit, the band-separating circuit 2 is constituted by a band pass filter circuit BPF for the first transmit-receive system and a notch filter circuit NF for the second transmit-receive system, and a low PASS filter circuit LPF2 is incorporated into the second switching circuit SW2. (I) As shown in Fig. 14, in a ninth preferred circuit, the band-separating circuit 2 is constituted by a band pass filter circuit BPF for the first transmit-receive system and a high pass filter circuit HPF for the second transmit-receive system, and a low PASS filter circuit LPF2 is incorporated into the second switching circuit SW2. Fig. 1 is a block schematic diagram showing a preferred embodiment of the multiband high-frequency switching module according to the present invention. The multiband high-frequency switching module 1 surrounded by broken line is used in a communication system utilizing two transmit-receive systems having different passbands, and suitable for alternately connecting a common antenna ANT to a transmitting circuit (TX1, TX2) and a receiving circuit (RX1, RX2) of each transmit-receive system in a dual-band radiotelephone. For example, a first transmit-receive system may be (Global System for Mobile Communication (GSM) and a second transmit-receive system may be Digital Cellular System (DCS)1800 system. The multiband high-frequency switching module 1 of Fig. 1 comprises a first switching circuit SW1 for switching a transmitting circuit TX1 and a receiving circuit RX1 of the first transmit-receive system (GSM), a first low pass filter circuit LPF1 incorporated into the first switching circuit SW1, a first transmit terminal TT1 for connecting the transmitting circuit TX1, a second switching circuit SW2 for switching a transmitting circuit TX2 and a receiving circuit RX2 of the second transmit-receive system (DCS), a second low PASS filter circuit LPF2 incorporated into the second switching circuit SW2, a second transmit terminal TT2 for connecting the transmitting circuit TX2, and a band-separating circuit 2 for separating the bands of communication signals to the respective transmit-receive systems. The switching circuits SW1, SW2 may have control terminals CT1, CT2 for respectively connecting control circuits VC1, VC2. The band-separating circuit comprises first and second notch filter circuits NF1, NF2, one end of each notch filter circuit being connected to a common antenna terminal CAT for connecting a common antenna ANT, and the other end thereof being connected to respective switching circuit. The receiving circuits RX1, RX2 are respectively connected to the switching circuits SW1, SW2 through receive terminals RT1, RT2. Fig. 2 is a schematic circuit diagram showing an equivalent circuit of the multiband high-frequency switching module of. Fig. 1. The band-separating circuit connected to the common antenna terminal CAT includes first and second notch circuits, the first notch circuit comprising parallel-connected inductor LF1 and capacitor CF1 and the second notch circuit comprising parallel-connected inductor LF2 and capacitor CF2. One of the ends of the first notch circuit is connected to the common antenna terminal CAT and the opposite end is grounded through a capacitor CF3 for enhancing the low pass filtering operation of the band-separating circuit. One of the ends of the second notch circuit is connected to the common antenna terminal CAT and the opposite end is connected to a capacitor CF4 and an inductor LF3 being grounded. The inductor LF3 and the capacitor CF4 enhance the high pass filtering operation of the band-separating circuit. The first switching circuit SW1 comprises diodes DG1, DG2 and transmission lines LG1, LG2. The anode of the diode DG1 is connected to the common antenna terminal CAT through a capacitor CG1. The anode is further connected, through the transmission line LG2, to a receive terminal RT1 for connecting the receiving circuit RX1 through a capacitor CG5. The cathode of the diode DG2 is connected between the transmission line LG2 and the receive terminal RT1, and the anode is grounded through a capacitor CG6. Between the diode DG2 and the capacitor CG6, the control terminal CT1 for connecting the control circuit VC1 through series-connected resistor RG and inductor LG is connected in a shunt configuration. The cathode of the diode DG1 is connected, through a low pass filter circuit LPF1, to a transmit terminal TT1 for connecting the transmitting circuit TX1 through a capacitor CG2. The low pass filter circuit LPF1 comprises an inductor LG3 and capacitors CG3, CG4, CG7. Between the low PASS filter circuit LPF1 and the transmit terminal TT1, the transmission line LG1 being grounded is connected in a shunt configuration. The second switching circuit SW2 comprises diodes DP1, DP2 and transmission lines LP1, LP2. The anode of the diode DP1 is connected to the common antenna terminal CAT through a capacitor CP1 which may be omitted. The anode is further connected, through a transmission line LP2, to a receive terminal RT2 for connecting the receiving circuit RX2 through a capacitor CP5. The cathode of the diode DP2 is connected between the transmission line LP2 and the receive terminal RT2, and the anode is grounded through a capacitor CP6. Between the anode and the capacitor CP6, a control terminal CT2 for connecting the control circuit VC2 through series-connected resistor RP and inductor LP is connected in a shunt configuration. The cathode of the diode DP1 is connected, through a low pass filter circuit LPF2, to a transmit terminal TT2 for connecting the transmitting circuit TX2 through a capacitor CP2. The low pass filter circuit LPF2 comprises an inductor LP3 and capacitors CP3, CP4, CP7. Between the low PASS filter circuit LPF2 and the transmit terminal TT2, the transmission line LP1 being grounded is connected in a shunt configuration. Series-connected inductor LP4 and capacitor 8 is connected to the diode DP1 in parallel. This LC series circuit is optional, and improves the isolation characteristics when the diode DP1 is in off-state. The multiband high-frequency switching module of the above circuit is made into a form of laminate body comprising a plurality of dielectric substrates, pattern electrodes formed on the dielectric substrates, terminal electrodes made on the side surfaces of the laminate body, and circuit elements mounted to the top surface of the laminate body. In the present invention, the common antenna terminal to which a plurality of transmit-receive systems are connected through the band-separating circuit, the transmit terminals for connecting the transmitting circuit of respective transmit-receive systems, and the receive terminals for connecting the receiving circuits of respective transmit-receive systems are made on the side surfaces of the laminate body, thereby enabling to mount the multiband high-frequency switching module to a circuit board through the bottom surface thereof. Each terminal may extend to the top or bottom surface. On each of the four side surfaces, at least one ground terminal is preferably formed to reduce the insertion loss of the multiband high-frequency switching module. At least one ground terminal or control terminal for controlling the switching circuit, preferably the ground terminal, is disposed between the high-frequency terminals (the common antenna terminal, the transmit terminals and the receive terminals) on the side surface to prevent the high-frequency terminals from being positioned directly adjacent to each other. With such a configuration, the interference between the high-frequency terminals is minimized and the insertion loss is reduced. Also, the isolation between the signal terminals is made good. In a more preferred embodiment, each of the high-frequency terminals is disposed between two ground terminals. With this configuration, the leakage of signals and the interference between the high-frequency terminals are more securely avoided and the isolation between the high-frequency terminals are enhanced. The transmit terminals are preferred to be collectively positioned while being separated by the intervening ground terminal or control terminal as mentioned above. The receive terminals are also preferred to be collectively positioned. The transmit terminals and the receive terminals are preferably disposed on the opposite sides with respect to a vertical plane, perpendicular to the side surface having the common antenna terminal, dividing the laminate body into two equal parts. More preferably, the transmit terminals and the receive terminals are located symmetrically with respect to the vertical plane. Such a construction makes it easy to respectively connect the transmit terminals and the receive terminals to the respective transmitting circuits and the receiving circuits on the circuit board to which the multiband high-frequency switching module is to be mounted. In addition, the common antenna terminal and the other high-frequency terminals (the transmit terminals and receive terminals) are preferably disposed on the opposite sides with respect to another vertical plane, preferably perpendicular to the above vertical plane and parallel to the side surface having the common antenna terminal, dividing the laminate body into tow equal parts. Since the multiband high-frequency switching module is disposed between the common antenna and the transmitting and receiving circuits, with such a configuration, the multiband high-frequency switching module can be connected to the common antenna and the transmitting and receiving circuits by the shortest lines, thereby to avoid an additional insertion loss. As described above, it is preferable that the common antenna terminal is disposed on one of the two parts formed by dividing the laminate body with a first vertical plane parallel to the side surface having the common antenna terminal, and the transmit and receive terminals on the other. Assuming that the other half opposite to the common antenna terminal is further equally divided into two quadrisect parts by a second vertical plane perpendicular to the first plane, it is preferable that the transmit terminals is disposed on one of the quadrisect parts and the receive terminals on the other. In this configuration, the transmit terminals are collectively disposed on one quadrisect part and the receive terminals are collectively disposed on the other. Therefore, as described above, the connection of the multiband high-frequency switching module to the common antenna, the transmitting circuits and the receiving circuits is made by a short line to avoid an additional insertion loss. In the laminate body, the circuit of the multiband high-frequency switching module is formed by the pattern electrodes formed on the dielectric substrates and the chip elements mounted on the top surface of the laminate body. The band-separating circuit and the transmission lines of the switching circuits are preferably formed by the pattern electrodes on the inner substrates between the top substrate and the bottom substrate. More specifically, the transmission lines of the switching circuits are preferably formed by the pattern electrodes on the substrates between the substrates having the ground electrode patterns. The pattern electrodes for the band-separating circuit comprising a capacitor component and an inductor component are formed on the substrates laminated on the substrate having the upper ground electrode pattern. The pattern electrode for the inductor component is formed on the substrate being laminated above the substrate having the pattern electrode for the capacitor component. In the present invention, it is preferable that the transmit system of at least one transmit-receive system has a low pass filtering function. This can be achieved by constituting the band-separating circuit from at least one low PASS filter circuit as described above. Another method is to incorporate a low PASS filter circuit into at least one switching circuit. For example, as shown in Fig. 2, the low PASS filter circuit LPF1 comprising the inductor LG3 and the capacitors CG3, CG4, CG7 is incorporated into the first switching circuit SW1, namely between the diode DG1 and the transmission line LG1 each constituting the first switching circuit SW1. Such an incorporation of the low PASS filter circuit into the switching circuit makes the overall circuit symmetrical, thereby to reduce the insertion loss and secure high characteristics in broad band. The pattern electrodes for the low pass filter circuit to be incorporated into the switching circuit is preferably formed on the substrates to be laminated above the substrates having the pattern electrodes for the switching circuits. Specifically, the pattern electrodes for the capacitor component of the low pass filter circuit are formed on the substrates above the substrate having the upper ground pattern electrode, and the pattern electrode for the inductor component is formed on the substrate being laminated above the substrates having the capacitor pattern electrodes. The pattern electrodes for the inductor components and the pattern electrodes for the capacitor components are preferably formed on the different substrates. The capacitor pattern electrodes of the low pass filter circuit being incorporated into the switching circuit and the capacitor pattern electrodes of the band-separating circuit are preferred to be formed on the same substrate separately. Also, the inductor pattern electrodes of the low pass filter circuit and the band-separating circuit are preferably formed on the same substrate separately. The band-separating circuit and the low pass filter circuit may be connected to the switching circuit via through holes made on the substrates intervening therebetween. As described above, the laminate body of the present invention preferably comprises, from the bottom surface (mounting surface), the substrate having the lower ground electrode, the substrates having the transmission lines of the switching circuits, the substrate having the upper ground electrode, the substrates having the capacitor components of the band-separating circuit and the low pass filter circuit, and the substrates having the inductor components of the band-separating circuit and the low pass filter circuit. On the top surface of the laminate body, chip elements of the diodes and the capacitors other than those constituting the band-separating circuit, the switching circuits and the low pass filter circuits are mounted. A metal cover for covering the chip elements may be disposed on the top surface of the laminate body while maintaining the terminal electrodes on the side surfaces exposed to the atmosphere. The metal cover may be fixed to the laminate body by soldering or a mounting device. A plan view and a perspective view of a laminate body of the multiband high-frequency switching module having the equivalent circuit of Fig. 2 are shown in Fig. 3 and Fig. 4, respectively. Fig. 5 is a plan view showing each substrate constructing the laminate body of Figs. 3 and 4. In this embodiment, the band-separating circuit, the low PASS filter circuits and the transmission lines of the switching circuits were formed on the inner substrates of the laminate body. On the top surface of the laminate body, the diodes and chip capacitors were mounted. The laminate body was produced as described below. A green sheet made of a dielectric ceramic material sinterable at low temperatures was used as the substrate. The pattern electrodes for each circuit elements were formed by printing an electrically conductive paste mainly comprising Ag on the green sheets. The green sheets with pattern electrodes and, if desired, a green sheet with no pattern electrode (dummy layer) were stacked and sintered to produce the integral laminate body. As best shown in Fig. 5, green sheets 11 to 22 were stacked in turn with the green sheet 11 disposed lowermost and with the green sheet 22 disposed uppermost. A ground electrode 31 was formed on nearly entire surface of the lowermost green sheet 11. The ground electrode 31 had ports for connecting the ground terminals (GRD) 81, 83, 85, 87, 89, 91, 93, 94 and 95 to be formed on the side surfaces of the resultant laminate body. On the lowermost green sheet 11, stacked was the dummy green sheet 12 with no pattern electrode. On the green sheet 13, line electrodes 41, 42, 43 were printed. On the green sheet 14, line electrodes 44 to 47 were formed. Each of the line electrodes 45-47 had at one end thereof a through hole electrode shown by a circle with a cross. The green sheet 15 had only two through hole electrodes. The green sheet 16 having a ground electrode 32 was stacked on the green sheet 15. The line electrodes disposed between the ground electrodes 31 and 32 constitute the transmission lines of the first and second switching circuits, SW1, SW2. Specifically, the line electrodes 42 and 46 are connected to each other by the through hole electrode to constitute the transmission line LG1. Likewise, the line electrodes 41 and 45 constitute the transmission line LG2, and the line electrodes 43 and 47 constitute the transmission line LP1. The line electrode 44 constitutes the transmission line LP2. On the green sheets 17 to 19, printed were the pattern electrodes 67 to 71 for constituting capacitors. The pattern electrodes 61 to 65 respectively constitute the capacitors CG4, CG3, CP4, CP3 and CF3, each with the ground electrode 32. Further, the electrodes 66 and 70, the electrodes 64 and 69, the electrodes 62 and 67, the electrodes 70 and 71 and the electrodes 68 and 71 respectively constitute the capacitors CF4, CP7, CG7, CF2 and CF1. The ground electrode 32 is partly cut out so that the electrode 66 opposes only to the electrode 70. In the cut out portion of the ground electrode 32, formed were two through hole electrodes communicated to the line electrodes 44 and 45. On the green sheet 19, the green sheet 20 having line electrodes 48, 49, 56 was disposed. Line electrodes 50 to 55 were formed on the green sheet 21. On the uppermost green sheet 22, were formed lands 23 to 29 and 33 to 37 for connecting the chip elements, such as diodes and chip capacitors, being mounted thereon. The line electrodes 48 and 55 were connected to each other via the through hole electrode to constitute LF1. Likewise, the line electrodes 54 and 56 constitute LF2, and the line electrodes 49 and 53 constitute LF3. The line electrodes 50 and 52 respectively constitute LG3 and LP3. The line electrode 51 is a DC line for the control circuit. The above green sheets 11 to 22 were stacked, pressed and then sintered in a known manner to obtain an integral laminate body. On the side surfaces of the laminate body, the terminal electrodes 81 to 96 were formed as shown in Fig. 4. Then, diodes DG1, DG2, DP1, DP2, chip capacitors CG1, CG6, CP1, CP6, CP8, and a chip inductor LP4 were mounted to the respective lands on the top surface of the laminate body to obtain a multiband high-frequency switching module of the present invention in the form of laminate body. Of the circuit elements shown in Fig. 2, CP2, CP5, CG2, CG5, RG, LG, RP and LP are formed on the circuit board to which the multiband high-frequency switching module is mounted. In the above embodiment, the transmission lines 41 to 47 of the first and second switching circuits are disposed between the ground electrodes 31, 32 to effectively prevent the interference between the switching circuits and the band-separating circuit and/or the low pass filter circuits. Since the ground electrodes are disposed lower in the laminate body, the grounding is easily secured. The capacitors CG3, CG4, CP3, CP4, CF3 being grounded are formed by opposing the upper ground electrode 32 to the pattern electrodes 61 to 65 on the substrate just above the upper ground electrode 32. Also, since the terminal electrodes are formed on the side surface of the laminate body, the multiband high-frequency switching module can be mounted through its bottom surface. The high-frequency terminals (common antenna terminal CAT, transmit terminals TT1, TT2, receive terminals RT1, RT2) are located separately by the intervening ground terminal GRD and control terminal CT1, CT2. At least one ground terminal is disposed between the high-frequency terminals. In other words, any one of the high-frequency terminals is disposed between the ground electrodes. Further, at least one ground terminal is disposed on any of the side surfaces of the laminate body. As shown in Fig. 3, the common antenna terminal CAT and the other high-frequency terminals (transmit terminals TT1, TT2 and receive terminals RT1, RT2) are located on opposite sides with respect to a vertical plane X parallel to the side surface having the common antenna terminal CAT and dividing the laminate body into two equal parts. Also, the transmit terminals TT1, TT2 and the receive terminals RT1, RT2 are located on opposite sides with respect to another vertical plane Y, perpendicular to the plane X, dividing the laminate body into equal two parts. As described above, the multiband high-frequency switching module of the present invention alternately connects the common antenna to the transmitting or receiving circuit of a first transmit-receive system or the transmitting or receiving circuit of a second transmit-receive system. The first and second transmit-receive systems may be GSM system and DCS1800 system. However, the present invention is not limited to the above embodiment, and equally applicable to switching the transmitting circuits and the receiving circuits of a plurality of transmit-receive systems having different passbands. The multiband high-frequency switching module of the present invention is suitable for use in a dual-band cellular radiotelephone, etc. Since the multiband high-frequency switching module can be made into a small chip with laminated structure, the present invention is effective for reducing the size of the dual-band cellular radiotelephone, etc.

Claims: A high-frequency switching module in the form of a laminate body for use in a communication system utilizing a transmit-receive system, the module comprising: a switching circuit (SW1, SW2) for said transmit-receive system, one end of the switching circuit being connected to an antenna terminal (CAT) for connection to an antenna (ANT) and the other end being connected in parallel to a receive terminal (RT1, RT2) for connection to a receiving circuit (RX1, RX2) and a transmit terminal (TT1, TT2) for connection to a transmitting circuit (TX1, TX2), the switching circuit (SW1, SW2) comprising a transmission line (LG2; LP2) and switching elements (DG1, DG2; DP1, DP2) connected in series via the transmission line, a first one (DG1, DP1)of said switching elements having an anode connected to a line directed to the antenna terminal (CAT) side and a cathode connected to a line directed to said transmitting circuit (TX1, TX2) side, and the second switching element (DG2, DP2) having a cathode connected to a line directed to said receiving circuit (RX1, RX2) side and an anode connected to a line directed to a ground terminal (GRD; 89), wherein said laminate body comprises a plurality of dielectric layers, pattern electrodes printed on said dielectric layers, and chip elements mounted on a top surface of said laminate body, characterised in that the module further comprises a band-separating circuit (2) constituted by filter circuits (NF1, NF2) each including an LC circuit, the band-separating circuit (2) having a first end connected to said antenna terminal (CAT) and second ends each connected to a said switching circuit (SW1, SW2) for a separate frequency band, and said first and second switching elements (DG1, DG2; DP1, DP2) in each said switching circuit (SW1, SW2) are continuously connected in series flow and are both controlled to their ON/OFF states by a control voltage (VC1, VC2) applied to the anode side of said second switching element (DG2, DP2). The module of claim 1, wherein a transmit system comprising said common antenna terminal (CAT), said band-separating circuit (2), said switching circuit (SW1, SW2) and said transmit terminal (TT1, TT2) of at least one transmit-receive system (GSM, DCS) has a low pass filter function provided by a low pass filter circuit (LPF1, LPF2) incorporated in said switching circuit (SW1, SW2).

Inventors: KEMMOCHI SHIGERU, TAI HIROYUKI, TAKETA TSUYOSHI, TANAKA TOSHIHIKO, WATANABE MITSUHIRO, KEMMOCHI, SHIGERU, TAI, HIROYUKI, TAKETA, TSUYOSHI, TANAKA, TOSHIHIKO, WATANABE, MITSUHIRO
Applicants: HITACHI METALS LTD, HITACHI METALS, LTD.
Application year: 1998
Main classification: H04B1
IPC codes: H05K1, H05K3, H04B1