RF SWITCH

Abstract: A radio frequency (RF) switch which is used in an RF unit of a communication apparatus and has a less insertion loss during a transmission. A strip line disposed in the RF switch is formed by combining first and second strip lines having different values of the characteristic impedance from each other.

Description: EF SWITCH TECHNICAL FIELD The present invention relates to a radio frequency (RF) switch used in an RF unit of various communication apparatuses. BACKGROUND ART A conventional radio frequency (RF) switch for switching an antenna over a transmitting circuit and a receiving circuit is descried in Japanese Patent Laid Open No. 7-312568. Fig. 5 illustrates an equivalent circuit of the conventional RF switch. As shown in Fig. 5, diode 524 is coupled between antenna 501 and transmitting circuit 502, and strip hne 540 is coupled between antenna 501 and receiving circuit 503. The cathode of diode 546 is coupled to strip line 540 at the receiving circuit 503 side, and the anode of the diode is grounded. Control voltage circuit 530 is coupled to the anode of diode 524. When a signal is received, namely, when diode 524, 546 are both turned off, a capacitor between both ends of diode 546 decreases a characteristic impedance of strip line 540 at receiving circuit 503 side. For compensating the decreasing, compensating capacitor 532 is couple to strip line 540 at the antenna 501 side. Capacitor 532 is disposed for receiving circuit 503. When a signal is transmitted, namely, when diodes 524, 546 are both turned on, capacitor 532 becomes an additional capacitor added on the signal path between antenna 501 and transmitting circuit 502. This increases a loss of the transmitted signal due to inserting the radio frequency switch. DISCLOSURE OF INVENTION A radio frequency (RF) switch not causing a less insertion loss during transmission is provided. A strip line disposed in the RF switch is formed by a combination of two strip lines having different characteristic impedances from each other. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is an equivalent circuit diagram of a radio frequency (RF) switch in accordance with an exemplary embodiment of the present invention. Fig. 2 is an equivalent circuit diagram of an RF switch module employing the RF switch in accordance with the exemplary embodiment of the present invention. Fig. 3 is a perspective view of a lamination-type RF switch module formed by laminating the RF switch modules in accordance with the exemplary embodiment of the present invention. Fig. 4 is an exposed perspective view of the lamination-type RF switch module shown in Fig. 3. Fig. 5 is an equivalent circuit diagram of a conventional RF switch. BEST MODE FOR CARRING OUT THE INVENTION An exemplary embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. Fig. 1 is an equivalent circuit diagram of a radio frequency (RF) switch used in an RF unit of a communication apparatus such as a portable telephone. The RF switch is a single-port-double-terminal (SPDT) type RF switch for selectively coupling antenna 101 to one of transmitting circuit 102 and receiving circuit 103. The RF switch comprises: (a) diode Ω x of which anode is coupled to transmitting circuit 102, and of which cathode is coupled to antenna 101; (b) controller 104 coupled to the anode of diode D x ; (c) strip line L of substantially 1/4 wavelength of a transmission frequency in transmitting circuit 102, the strip line of whose one end is coupled to the connection of diode Dj and antenna 101, and of which other end is coupled to receiving circuit 103; and (d) diode D 2 of which anode is coupled to a connection of strip line L and receiving circuit 103, and of which cathode is grounded. When a signal is transmitted, a positive voltage applied from controller 104 turns on both diodes Dj and D 2 . Thus, the receiving circuit 103 side of strip line L is grounded via the turned-on diode D 2 , and the receiving circuit 103 side observed from antenna 101 is opened. In addition, transmitting circuit 102 is coupled to antenna 101 via the turned-on diode D^ and the transmitted signal fed from transmitting circuit 102 are thus supplied to antenna 101. When a signal is received, a positive voltage is not applied from controller 104 to turn off both diodes D x and D 2 . Because the turned-off diode D j disconnects antenna 101 to transmitting circuit 102, the received signal fed from antenna 101 is supplied to receiving circuit 103. When a signal is received, i.e., when diode D 2 is turned off, a capacitor between both ends of diode D 2 makes a characteristic impedance of strip line L at the receiving circuit 103 side lower than that at the antenna 101 side. Capacitor Cj compensates a balance of characteristic impedances at both ends of strip line L. Strip line L is formed by series-interconnected two strip lines L : and L 2 having different characteristic impedances from each other. The combination of characteristic impedances of strip lines Lj and L 2 can determine a desired characteristic impedance of strip line L. Therefore, the balance of the characteristic impedances at both ends of strip line L is arbitrarily adjusted by deterrnining characteristic impedances of strip lines ^ and L 2 . As a result, the capacitance of compensating capacitor C x can be set to a value suitable for a transmission path during the transmission. And insertion loss of the RF switch during the transmission is thus suppressed. For example, when strip lines L 2 , L 2 are combined, and when the capacitance of compensating capacitor Cj is adequately selected, capacitor C x can cancel an inductance of diode D 1; the inductance which is contained in the transmission path during the transmission. Capacitor Cj also prevents the capacity between the ends of diode D x from decreasing the characteristic impedance of strip line L at the receiving circuit 103 side when diode D 2 is turned off during the reception. When the characteristic impedance of strip line L 2 at the receiving circuit 103 side is set higher than that of strip hne Lj at the antenna 101 side, the capacitance of capacitor Cj can be reduced. When the characteristic impedance of strip line L x is particularly set to substantially 50 ohms, compensating capacitor Cj can be omitted. When the characteristic impedance of strip line L 2 is set higher than that of strip line L 1? strip line L has a stepped impedance resonator (SIR) structure whose one end is short-circuited during the transmission. Therefore, a solid line length of strip line L is extremely reduced, the receiving path during the reception is shortened, and the insertion loss of the RF switch during the reception is accordingly suppressed. Capacitors C 2 at respective ends of antenna 101, transmitting circuit 102, and receiving circuit 103 cut a direct current (DC) component of the positive voltage applied from controller 104. Fig. 2 is an equivalent circuit diagram of an RF switch module in which low path filter (LPF) 201 is coupled to the transmitting circuit side of RF switch 202 discussed above. Fig. 3 is a perspective view of a lamination-type RF switch module formed by laminating the equivalent circuit of the diagram. As shown in Fig. 3, the lamination-type RF switch module includes antenna terminal electrode 2, transmitting terminal electrode 3, receiving terminal electrode 4, control voltage terminal electrode 5, and grounding terminal electrode 6 in the outer side-surfaces of layered body 1 made of dielectrics. Chip diodes 7, 8 and chip inductor 9 are disposed on the upper surface of layered body 1. Layered body 1, as shown in Fig. 4, comprises dielectric sheets 10a - 10k. Grounding electrodes 11a, lib are respectively disposed on the substantially entire surfaces of dielectric sheets 10a, 10c. Grounding electrode lie is disposed on the right part of dielectric sheet lOf. Capacitor electrodes 12, 13, 14, 15a, 15b for grounding are disposed on dielectric sheet 10b. Facing to grounding electrodes 11a and lib, electrode 12 forms capacitor C 4 in Fig. 2, electrode 13 forms capacitor C3 in Fig. 2, one of which ends connected to control voltage terminal electrode 5, electrode 14 forms capacitor Cj in Fig. 2, one of which ends connected to antenna terminal electrode 2, electrode 15a forms capacitor C 5 in Fig. 2, and electrode 15b forms capacitor C 6 in Fig. 2, one of which ends connected to transmitting terminal electrode 3, respectively. Strip line 16 as inductor L 3 in Fig. 2, one of which ends connected to transmitting terminal electrode 3, and strip line 17a as inductor L 2 in Fig. 2, one of which ends connected to receiving terminal electrode 4, are disposed on dielectric sheet lOd. Strip line 17b as inductor ~ X in Fig. 2, one of which ends connected to strip line 17a through via hole 18, is disposed on dielectric sheet lOe. Capacitor electrode 19 forming capacitor C 5 in Fig. 2, one of which ends connected to transmitting terminal electrode 3, is disposed at the left side of strip line 17b. Capacitor electrodes 20, 21, 22 are disposed on the left parts in dielectric sheets lOf, lOg, lOh. Facing to electrodes 20 and 22, electrode 21 forms capacitor C3 in Fig. 2. Facing to electrodes 19, electrode 20 forms capacitor C 4 in Fig. 2. Strip line 23 forming strip line L 4 in Fig. 2, one of which ends connected to grounding terminal electrode 6, is disposed on dielectric sheet lOi. Strip line 24 forming strip line L 5 in Fig. 2, one of which ends connected to control voltage terminal electrode 5, is disposed at the left side of strip line 23. Mounting electrodes 25a, 25b, 25c, 25d for mounting chip diodes 7, 8 and mounting electrodes 26a, 26b for mounting chip inductor 9 are formed on dielectric sheet 10k. The mounting electrode 25a side of chip diode 7, diode D 2 in Fig. 2, is coupled to connection electrode 28 through via hole 27, and to strip line 23 and capacitor electrode 12 through via hole 29. The mounting electrode 25b side of chip diode 7 is coupled to receiving terminal electrode 4 through via hole 30 and connection electrode 31. The mounting electrode 25c side of chip diode 8, diode D l in Fig. 2, is coupled to connection electrode 33 through via hole 32, and to strip line 24, capacitor electrode 22, capacitor electrode 20, strip line 16, and capacitor electrode 15b through via hole 34. The mounting electrode 25d side of chip diode 8 is coupled to antenna terminal electrode 2 through via hole 35 and connection electrode 36. Electrode 36 is coupled to an end of strip line 17b through via hole 37. The mounting electrode 26a side of chip diode 9, inductor L 6 in Fig. 2, is coupled to connection electrode 39 through via hole 38, and to capacitor electrode 21 through via hole 40. The mounting electrode 26b side of chip diode 9 is coupled to antenna terminal electrode 2 through via hole 41 and connection electrode 36. A respective thickness of dielectric sheets lOf, lOd shown in Fig. 4 differs from each other in order to make a respective characteristic impedance of strip lines L x and L 2 differs from each other. Strip line 17a, strip line L x in Fig. 2, is disposed on the lower surface of dielectric sheet lOf, and grounding electrode lie is disposed on the upper surface. Strip hne 17b, strip line L 2 in Fig. 2, is disposed on the upper surface of dielectric sheet lOd, and grounding electrode 1 lb is disposed on the lower surface. The characteristic impedance of strip hne 17a is determined by an interval between it and grounding electrode lib, and the characteristic impedance of strip line 17b is determined by an interval between it and grounding electrode lie. Accordingly, a desired characteristic impedance of each of strip lines 17a and 17b can be obtained by adjusting the thickness of each of dielectric sheets lOd and lOf. Actually, the thickness of dielectric sheet lOf is made thinner than that of dielectric sheet lOd, and the characteristic impedance of strip line 17a is accordingly set higher than that of strip line 17b. As discussed above, the capacitance of correcting capacitor Cj can be reduced, and an insertion loss of the RF switch during the transmission is thus suppressed. Characteristic impedances of strip lines 17a, 17b differing from each other are also obtained by making line widths thereof different from each other. The same effect can be obtained by forming strip lines 17a, 17b on a common layer, e.g. dielectric sheet lOd, and changing the line width in a single strip line such as strip line 17a at the intermediate portion the single strip line. Also, a combination of the changing of the line width and the differing of the thickness of dielectric sheets lOd, lOf can adjust the characteristic impedance. Strip lines 17a, 17b are connected through via hole 18. Because the electric characteristic of via hole 18, namely, Q value, is higher than that of an electrode pattern or the like formed on side surfaces of the layered product, the increasing of the insertion loss of the RF switch at this part is suppressed. INDUSTRIAL APPLICABILITY The present invention relates to a radio frequency (RF) switch used in an RF unit of various communication apparatuses and provides the RF switch with a less insertion loss during a transmission. The RF switch includes a strip line formed by combining two strip lines having different characteristic impedances.

Claims: CLAIMS 1. A radio frequency (RF) switch for coupling an antenna selectively to one of a transmitting circuit and a receiving circuit, comprising: a first diode coupled between said antenna and said transmitting circuit; a strip hne coupled between said antenna and said receiving circuit; a second diode coupled between said receiving circuit and a ground; and a controller for controlling turning on/off of said first and second diodes, wherein said strip line is formed by first and second strip lines, and each of said first and strip lines has a different characteristic impedance from each other. 2. The RF switch according to claim 1, wherein said first strip line is coupled to said antenna, said second strip line is coupled to said receiving circuit, and a characteristic impedance of said second strip line is higher than a characteristic impedance of said first strip line. 3. The RF switch according to claim 2, wherein the characteristic impedance of said first strip line is substantially 50 ohms. 4. A radio frequency (RF) switch comprising: a layered body formed by laminating a plurality of dielectric sheets; an antenna terminal electrode disposed on an outer surface of said layered body; a transmitting terminal electrode disposed on the outer surface of said layered body; a receiving terminal electrode disposed on the outer surface of said layered body; a grounding electrode disposed in said layered body; a first diode disposed on said layered body and coupled between said antenna terminal electrode and said transmitting terminal electrode; a strip line disposed in said layered body and coupled between said antenna terminal electrode and said receiving terminal electrode; and a second diode disposed on said layered body and coupled between said receiving terminal electrode and said grounding electrode, wherein said strip line is formed by first and second strip lines, and each of said first and strip lines has a different characteristic impedance from each other. 5. The RF switch according to claim 4, wherein line widths of said first and second strip lines differ from each other. 6. The RF switch according to claim 5, wherein said first strip line is coupled to said antenna terminal electrode, said second strip line is coupled to said receiving terminal electrode, and a characteristic impedance of said second strip line is higher than a characteristic impedance of said first strip line. 7. The radio frequency switch according to claim 4, wherein said first and second strip lines are respectively disposed on different dielectric sheets of said dielectric sheets in said layered body. 8. The RF switch according to claim 4, wherein line widths of said first and second strip lines differ from each other, and said first and second strip lines are respectively disposed on different dielectric sheets of said dielectric sheets in said layered body. 9. A radio frequency (RF) switch comprising: a layered body formed by laminating a plurality of dielectric sheets; an antenna terminal electrode disposed on an outer surface of said layered body; a transmitting terminal electrode disposed on the outer surface of said layered body; a receiving terminal electrode disposed on the outer surface of said layered body; a grounding electrode disposed in said layered body; a first diode disposed on said layered body, coupled between said antenna terminal electrode and said transmitting terminal electrode; a strip line disposed in said layered body, coupled between said antenna terminal electrode and said receiving terminal electrode; and a second diode disposed on said layered body, coupled between said receiving terminal electrode and said grounding electrode, wherein an interval between said first strip line and said grounding electrode differs from an interval between said second strip line and said grounding electrode. 10. The RF switch according to claim 9, wherein said first strip line is coupled to said antenna terminal electrode, said second strip line is coupled to said receiving terminal electrode, and a characteristic impedance of said second strip line is higher than a characteristic impedance of said first strip line. 11. The RF switch according to claim 10, wherei said first and second strip lines are respectively disposed on different dielectric sheets of said dielectric sheets in said layered body and coupled to each other through via hole.

Inventors: IWASAKI TOMOYUKI, NAKAKUBO HIDEAKI, IWASAKI, TOMOYUKI, NAKAKUBO, HIDEAKI
Applicants: IWASAKI TOMOYUKI, MATSUSHITA ELECTRIC IND CO LTD, NAKAKUBO HIDEAKI, IWASAKI, TOMOYUKI, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., NAKAKUBO, HIDEAKI
Application year: 2001
Main classification: H01P1
IPC codes: H01P1, H04B1, H05K3