U.S. patent application number 11/592218 was filed with the patent office on 2007-05-10 for switch circuit and high-frequency composite part.
This patent application is currently assigned to Hitachi Metals, Ltd.. Invention is credited to Keisuke Fukamachi, Shigeru Kemmochi, Hiroyuki Tai, Mitsuhiro Watanabe.
Application Number | 20070105506 11/592218 |
Document ID | / |
Family ID | 27654473 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070105506 |
Kind Code |
A1 |
Kemmochi; Shigeru ; et
al. |
May 10, 2007 |
Switch circuit and high-frequency composite part
Abstract
A switch circuit for selectively switching connection of an
antenna side circuit with a reception circuit and a transmission
circuit of two communication systems one of which has a reception
frequency band partially overlapped with a transmission frequency
of the other. The switch circuit includes (a) a first switch unit
for switching connection to the antenna side circuit with the
transmission circuit side of the first and the second communication
systems and the reception circuit side of the first and the second
communication system and (b) a second switch unit connected between
the first switch unit and the reception circuit of the first end
and the second communication system for switching connection of the
antenna side circuit with the reception circuit of the first and
the second communication system. (c) The transmission circuit side
of the first and the second communication system of the first
switch unit is connected to a transmission circuit shared by the
first and the second communication system. (d) When the
transmission circuit of the first and the second communication
system is connected to the antenna side circuit, the second switch
unit cuts off the connection between the reception circuit of the
first communication system and the first switch unit.
Inventors: |
Kemmochi; Shigeru;
(Meerbusch, DE) ; Watanabe; Mitsuhiro;
(Saitama-ken, JP) ; Fukamachi; Keisuke;
(Saitama-ken, JP) ; Tai; Hiroyuki; (Tottori-ken,
JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Hitachi Metals, Ltd.
|
Family ID: |
27654473 |
Appl. No.: |
11/592218 |
Filed: |
November 3, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10502982 |
Nov 1, 2004 |
7167687 |
|
|
PCT/JP03/00952 |
Jan 31, 2003 |
|
|
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11592218 |
Nov 3, 2006 |
|
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Current U.S.
Class: |
455/78 |
Current CPC
Class: |
H01P 1/15 20130101; H04B
1/005 20130101; H04B 1/44 20130101; H04B 1/48 20130101; H04B 1/406
20130101 |
Class at
Publication: |
455/078 |
International
Class: |
H04B 1/44 20060101
H04B001/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2002 |
JP |
2002-24029 |
Claims
1. A switch circuit for selectively switching the connection of a
receiving circuit or a transmitting circuit in two communication
systems, in which a receiving frequency bandwidth in a first
communication system partially overlaps a transmitting frequency
bandwidth in a second communication system, and an antenna circuit,
comprising: two switches, including a first switch switching the
connection of said antenna circuit to said transmitting circuit of
first and second communication systems and the connection of said
antenna circuit to receiving circuits of first and second
communication systems, and a second switch being connected between
said first switch and said receiving circuit of said first and
second communication systems to switch the connection of said
antenna circuit to said receiving circuit of the first
communication system via said first switch, and the connection of
said antenna circuit to said receiving circuit of the second
communication system via said first switch; a transmitting circuit
common to said first and second communication systems being
connected to said transmitting circuit of the first and second
communication systems in said first switch; and said second switch
disconnecting said receiving circuit of said first communication
system from said first switch, while said transmitting circuit of
said first and second communication systems are connected to said
antenna circuit.
2. (canceled)
3. The switch circuit according to claim 1, wherein there is a
capacitor between said first switch and said second switch.
4.-21. (canceled)
22. The switch circuit according to claim 1, wherein the operation
current of said second switch is lower than that of said first
switch.
23. The switch circuit according to claim 1, wherein the operation
current of said second switch is 2.5 mA or less.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a switch circuit for a
multi-band mobile phone, which has a capable of making
communications in plural systems, and a high-frequency composite
part comprising it.
BACKGROUND OF THE INVENTION
[0002] There are various systems for mobile phones, for instance,
EGSM (extended global system for mobile communications) and DCS
(digital cellular system) widely used mostly in Europe, GSM 850
(global system for mobile communications 850) and GSM 1900 (global
system for mobile communications 1900) widely used in the U. S.,
and 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 frequencies, and
further to expand serviceable territories and to effectively use
communications infrastructure of each system.
[0003] To utilize a plurality of systems, a user should
conventionally have a mobile phone capable of communicating in
plural systems. As a high-frequency part used in such a mobile
phone, the inventors proposed a high-frequency switch module for
switching transmitting circuits and receiving circuits in different
communication systems (WO 00/55983).
[0004] The high-frequency switch module of WO 00/55983 comprises
first and second filter circuits having different passbands, a
switch circuit connected to the first filter circuit for switching
a transmitting circuit and a receiving circuit of a communication
system A, and a switch circuit connected to the second filter
circuit for switching transmitting circuits of communication
systems B, C, a receiving circuit of a communication system B and a
receiving circuit of a communication system C.
[0005] The first and second filter circuits function as circuits
for branching a received signal of the communication system A and
received signals of the communication systems B, C. The switch
circuit is a diode switch comprising a diode and a transmission
line as main elements, and any one of pluralities of communication
systems A, B, C is selected by controlling the diode in an ON or
OFF state by applying voltage from a control circuit, thereby
switching the antenna and transmitting circuits and receiving
circuits of the communication systems A, B, C.
[0006] Specific examples of the communication systems A, B, C
disclosed by WO 00/55983 are GSM, DCS 1800 and PCS, respectively.
GSM corresponds to the EGSM, DCS 1800 corresponds to the GSM 1800,
and PCS corresponds to the GSM 1900. Table 1 shows transmitting
frequency and receiving frequency of each communication system.
TABLE-US-00001 TABLE 1 Communication Transmitting Receiving
Frequency System Frequency (MHz) (MHz) EGSM 880 to 915 925 to 960
GSM 1800 1710 to 1785 1805 to 1880 GSM 1900 1850 to 1910 1930 to
1990
[0007] JP 2000-165288 A, JP 2001-44885 A and JP 2002-171195 A
disclose high-frequency composite parts used in pluralities of
different communication systems.
[0008] With respect to GSM 1800 and GSM 1900 among communication
systems handled by such high-frequency composite parts, it is
appreciated that the transmitting frequency of GSM 1900 overlaps
the receiving frequency of GSM 1800 in a range of 1850 MHz to 1880
MHz.
[0009] Problems in a case where the receiving frequency of the
first communication system (GSM 1800) partially overlaps the
transmitting frequency of the second communication system (GSM
1900) in the conventional high-frequency switch module for handling
GSM 1800 and GSM 1900 described in WO 00/55983 will be explained
using the equivalent circuit shown in FIG. 21.
[0010] This high-frequency switch module selects a transmitting
mode of GSM 1800/GSM 1900, a receiving mode of GSM 1800, and a
receiving mode of GSM 1900, by controlling voltage applied from
control terminals as shown in Table 2. TABLE-US-00002 TABLE 2 Mode
VC2 VC3 GSM 1800 TX V+ 0 (Transmitting) GSM 1900 TX V+ 0
(Transmitting) GSM 1800 RX 0 0 (Receiving) GSM 1900 RX 0 V+
(Receiving)
(A) GSM 1800/GSM 1900 Transmitting Mode
[0011] In the transmitting mode of GSM 1800 or GSM 1900, positive
voltage (V+) is applied to a control terminal VC2, and zero voltage
is applied to a control terminal VC3, to control diodes DD1, DD2 in
an ON state. A transmission line ld3 has such proper length that
its resonance frequency is in a frequency range (1710 MHz to 1910
MHz) of transmitting signals of GSM 1800 and GSM 1900, and grounded
through the diode DD2 in an ON state and a capacitor cd4 for
resonance. As a result, impedance is large (ideally infinitive)
when the receiving circuits of GSM 1800 and GSM 1900 are viewed
from the connection point IP2. Accordingly, transmitting signals
sent from the transmitting circuit of GSM 1800 and GSM 1900 are
sent to an antenna via the second filter circuit without leaking to
the receiving circuit. At this time, the diodes DP1, DP2 are
controlled in an OFF state.
[0012] However, because impedance is practically not sufficiently
large in other frequencies than the resonance frequency when the
receiving circuits of GSM 1800 and GSM 1900 are viewed from a
connection point IP2, part of the transmitting signals of GSM 1800
and GSM 1900 (hereinafter referred to as "leak signals") leak to
the receiving circuits of GSM 1800 and GSM 1900 via the
transmission line ld3. In addition, the resonance frequency may be
changed by the unevenness of the capacitance of the capacitor cd4
and a capacitance component parasitic to the transmission line ld3,
resulting in further increase in a signal leaking to the receiving
circuits of GSM 1800 and GSM 1900.
[0013] Specifically, because the diodes DP1, DP2 are in an OFF
state in the case of transmitting mode in GSM 1800, the leak signal
does not appear in the receiving circuit of GSM 1900 by isolation
when the diode DP1 is in an OFF state. On the other hand, the leak
signal appearing in the receiving circuit of GSM 1800 via the
transmission line lp2 is removed by a filter circuit (not shown)
disposed upstream of the receiving circuit, resulting in
substantially no leakage to the receiving circuit of GSM 1800. In
the case of transmitting mode in GSM 1900, however, a leak signal
of 1850 MHz to 1880 MHz overlapping the receiving frequency of GSM
1800 among those in a transmitting frequency of GSM 1900 appearing
in the receiving circuit of GSM 1800 is supplied to the receiving
circuit of GSM 1800 without being removed by the filter circuit,
entering into analog-processing ICs constituting an LNA (low-noise
amplifier)and a mixer in the receiving circuit and a
modulator/demodulator, and thus causing the malfunction of these
circuit parts.
(B) GSM 1800 Receiving Mode
[0014] In a receiving mode in GSM 1800, the diodes DP1, DP2, DD1
and DD2 are controlled in an OFF state by applying zero voltage to
the control terminals VC2 and VC3. With the diode DD1 in an OFF
state, impedance is large between the connection point IP2 and the
transmitting circuit of GSM 1800/GSM 1900. With the diode DP1 in an
OFF state, impedance is large between the connection point IP3 and
the receiving circuit of GSM 1900. The connection point IP2 is thus
connected to the receiving circuit of GSM 1800 via transmission
lines ld3 and lp2.
(C) GSM 1900 Receiving Mode
[0015] In the receiving mode in GSM 1900, positive voltage is
applied to the control terminal VC3, and zero voltage is applied to
the control terminal VC2, to control the diodes DD1, DD2 in an OFF
state and the diodes DP1, DP2 in an ON state. With the diode DD1 in
an OFF state, impedance is large between the connection point IP2
and the transmitting circuit of GSM 1800/GSM 1900. The transmission
line lp2 has such length that it is resonated at 1930 MHz to 1990
MHz in a frequency range of the received signal of GSM 1900.
Accordingly, it is grounded through the diode DP2 in an ON state
and the capacitor CP1 for resonance, resulting in large impedance
when the receiving circuit of GSM 1800 is viewed from the
connection point IP3. The connection point IP2 is thus connected to
the receiving circuit of GSM 1900.
[0016] The diodes DP1, DP2 for switching the receiving circuits of
GSM 1800 and GSM 1900 usually have low power consumption and small
insertion loss. Such diodes are generally more likely subjected to
distortion than diodes with large power consumption in an OFF
state. Accordingly, the diodes DP1, DP2 in an OFF state are likely
to distort the transmitting signals of GSM 1800, GSM 1900 leaking
via the transmission line ld3, thereby generating harmonics having
frequencies corresponding to integral multiples of those of these
transmitting signals. These harmonics, which are added to the
transmitting signals of GSM 1800, GSM 1900, are radiated from the
antenna. With respect to such problems, none of WO 00/55983 JP
2000-165288 A, JP 2001-44885 A and JP 2002-171195 A provides any
solutions.
OBJECTS OF THE INVENTION
[0017] Accordingly, an object of the present invention is to
provide a switch circuit for a high-frequency composite part for
use in a mobile phone with a capable of handling pluralities of
communication systems, which suffers from extremely small leakage
of transmitting signals to receiving circuits, thus having
extremely large isolation, when handling communication systems
having partially overlapping transmitting/receiving signals.
[0018] Another object of the present invention is to provide a
switch circuit with suppressed generation of harmonics without
suffering from increase in power consumption.
DISCLOSURE OF THE INVENTION
[0019] The first switch circuit of the present invention
selectively switches the connection of a receiving circuit or a
transmitting circuit in two communication systems, in which a
receiving frequency bandwidth in a first communication system
partially overlaps a transmitting frequency bandwidth in a second
communication system, and an antenna circuit; [0020] (a) it
comprising two switches, a first switch switching the connection of
the antenna circuit to transmitting circuit of first and second
communication systems and the connection of the antenna circuit to
receiving circuits of first and second communication systems, and a
second switch being connected between the first switch and the
receiving circuit of the first and second communication systems to
switch the connection of the antenna circuit to the receiving
circuit of the first communication system via the first switch, and
the connection of the antenna circuit to the receiving circuit of
the second communication system via the first switch; [0021] (b) a
transmitting circuit common to the first and second communication
systems being connected to the transmitting circuit of the first
and second communication systems in the first switch; and [0022]
(c) the second switch disconnecting the receiving circuit of the
first communication system from the first switch, while the
transmitting circuit of the first and second communication systems
is connected to the antenna circuit.
[0023] The switch circuit preferably comprises switching elements,
inductors and capacitors. There is preferably a capacitor between
the first switch and the second switch.
[0024] The switching element of the present invention is
constituted by semiconductor elements performing switching
operations by changing impedance, such as field-effect transistors,
bipolar transistors, PIN diodes, etc. The field-effect transistor
is made conductive or non-conductive by changing impedance between
a source and a drain by control voltage applied from a gate. The
PIN diode is made conductive or non-conductive by changing
impedance between an anode and a cathode by control voltage. The
inductor is, for instance, a transmission line such as a strip line
electrode, a microstrip line electrode, etc., a coil, a chip
inductor, etc. The capacitor is, for instance, a laminate capacitor
constituted by capacitor electrodes, a chip capacitor, etc. These
elements may properly be selected depending on demanded
requirements.
[0025] The second switch circuit of the present invention
selectively switches the connection of a receiving circuit or a
transmitting circuit for two communication systems, in which a
receiving frequency bandwidth in the first communication system
partially overlaps a transmitting frequency bandwidth in the second
communication system, and an antenna circuit; [0026] (a) the switch
circuit, which comprises switching elements, inductors and
capacitors, being constituted by a first switch and a second
switch, the first switch comprising a first port connected to the
antenna circuit, a second port connected to the transmitting
circuit of the first and second communication systems, and a third
port connected to the second switch, and the second switch
comprising a fourth port connected to the first switch via a
capacitor, a fifth port connected to the receiving circuit of the
first communication system, and a sixth port connected to the
receiving circuit of the second communication system; [0027] (b) a
first inductor being disposed between the fourth port and the fifth
port; [0028] (c) a first switching element being disposed between
the fifth port and the ground; [0029] (d) a second switching
element being disposed between the fourth port and the sixth port;
and [0030] (e) the first and second switching elements being
controlled in an ON state while the transmitting circuit of the
first and second communication systems is connected to the antenna
circuit.
[0031] The first inductor is preferably a transmission line having
such length that resonance occurs in a receiving frequency range of
the second communication system. With such structure, the first
inductor is grounded at high frequencies through the first
switching element in an ON state for resonance, and impedance is
relatively large in a receiving frequency of the second
communication system, when the fifth port connected to the
receiving circuit of the first communication system is viewed from
the fourth port. Because impedance is also high in a transmitting
frequency of the second communication system, a leak signal from
the first switch, which appears in the fourth port, is attenuated,
thereby making it possible to suppress leakage to the receiving
circuit of the first communication system.
[0032] Though a leak signal having a frequency close to the
receiving frequency of the second communication system may appear
in the sixth port via the second switching element, the leak signal
is removed by a filter circuit disposed downstream between the
sixth port and the receiving circuit of the second communication
system. Accordingly, the leak signal substantially does not leak to
the receiving circuit of the second communication system. Also,
because the switching element of the second switch is in an ON
state, the generation of harmonics can be prevented.
[0033] The third switch circuit of the present invention
selectively switches the connection of a receiving circuit or a
transmitting circuit for two communication systems, in which a
receiving frequency bandwidth in the first communication system
partially overlaps a transmitting frequency bandwidth in the second
communication system, and an antenna circuit; [0034] (a) the switch
circuit, which comprises switching elements, inductors and
capacitors,.being constituted by a first switch and a second
switch, the first switch comprising a first port connected to the
antenna circuit, a second port connected to the transmitting
circuit of the first and second communication systems, and a third
port connected to the second switch, and the second switch
comprising a fourth port connected to the first switch via a
capacitor, a sixth port connected to the receiving circuit of the
first communication system, and a fifth port connected to the
receiving circuit of the second communication system; [0035] (b) a
first inductor being disposed between the fourth port and the fifth
port; [0036] (c) a first switching element being disposed between
the fifth port and the ground; [0037] (d) a second switching
element being disposed between the fourth port and the sixth port;
and [0038] (e) the first and second switching elements being
controlled in an OFF state, while the transmitting circuit of the
first and second communication systems is connected to the antenna
circuit.
[0039] With such structure, the second switching element has
isolation characteristics in an OFF state, preventing the leak
signal from leaking to the receiving circuit of the first
communication system. Though the first inductor is designed to
resonate in a receiving frequency range of the first communication
system, the leak signal may appear in the fifth port via the first
inductor. However, the leak signal is removed by a downstream
filter circuit disposed between the fifth port and the receiving
circuit of the second communication system, so that it does not
leak to the receiving circuit of the second communication
system.
[0040] In the second and third switch circuits, the first switch
comprises a third switching element disposed between the first port
and the second port, a second inductor disposed between the first
port and the third port, and a fourth switching element disposed
between the third port and the ground, and when the transmitting
circuit of the first and second communication systems is connected
to the antenna circuit, the third and fourth switching elements are
preferably controlled in an ON state.
[0041] More preferably, the fourth switching element comprises a
diode, and a first capacitor is disposed between the diode and-the
ground. The diode generally has an inductance component because of
lead terminals, etc. It also has parasitic inductance because of
line patterns for connecting the diode to other circuit elements,
etc., so that a completely short-circuited state is not necessarily
achieved even when the diode is turned on.
[0042] This makes impedance smaller when the third port is viewed
from the first port, resulting in poor isolation and insertion loss
characteristics. Accordingly, the first capacitor is disposed in
series to the fourth switching element for series resonance in the
present invention, such that impedance is large when the third port
is viewed from the first port, thereby reducing a transmitting
signal leaking to the second switch and thus improving isolation
and insertion loss characteristics.
[0043] In the second and third switch circuits, the operation
current of the switching element of the second switch is preferably
lower than that of the switching element of the first switch. Using
a switching element operable with current of 2.5 mA or less,
particularly 1 mA or less at a temperature of 0.degree. C. to
+85.degree. C., power consumption can be reduced at the time of
transmitting and receiving, resulting in reduced battery
consumption of mobile phones.
[0044] In the second and third switch circuits, the first switch
and the second switch can be made composite by making the
characteristic impedance of the first inductor higher than that of
the second inductor, thereby making it easy to achieve impedance
matching in the production of the switch circuit.
[0045] The high-frequency composite part of the present invention
comprises either of the first to third switch circuits, switching
elements, inductors and capacitors being contained in or mounted
onto a multi-layered ceramic substrate obtained by laminating
pluralities of ceramic sheets, and connected by connection means
formed in or on the multi-layered substrate.
[0046] In the high-frequency composite part, transmission lines
constituting the first and second inductors are preferably
contained in the multi-layered substrate, and these transmission
lines are preferably formed in horizontally different regions in
the multi-layered substrate. Such structure not only prevents their
interference, but also prevents the resonance frequency and
characteristic impedance of these transmission lines from changing
due to parasitic capacitance, etc., thereby improving isolation
characteristics, and making it easy to achieve impedance matching
between the first switch and second switch. Further, when the
transmission lines are formed as strip line electrodes in a region
sandwiched by ground electrodes formed in the multi-layered
substrate, their interference with electrode patterns constituting
other circuit elements can preferably be prevented. Impedance may
be changed by forming the first inductor and/or the second inductor
by connecting transmission lines formed on two layers or more
through viaholes, and by making the width of a transmission line
formed on one layer different from the width of transmission lines
formed on other layers.. Such structure makes it easy to achieve
impedance matching with circuits disposed upstream or downstream of
the transmission lines.
[0047] It is preferable that the fourth switching element is a
diode, that the first capacitor disposed between this diode and the
ground is contained in the multi-layered substrate, and that a
hot-side electrode constituting the first capacitor is disposed
above an upper ground electrode among those sandwiching
transmission lines constituting the first and second inductors. The
capacitor electrodes are connected to diodes through viaholes
formed in the multi-layered substrate, and the diodes are mounted
onto an upper surface of the multi-layered substrate. Accordingly,
the above structure can make the distances between the diodes and
the capacitor electrodes smaller, thereby reducing parasitic
inductance and thus obtaining high isolation characteristics.
[0048] In the second switch, too, the first switching element may
be a diode, and the second capacitor may be disposed between this
diode and the ground to obtain high isolation characteristics. If a
hot-side electrode constituting the first capacitor and a hot-side
electrode constituting the second capacitor are formed on the same
layer via a common ground electrode and a ceramic layer, they are
less affected by lamination discrepancy in a horizontal direction,
thereby making it possible to produce capacitors with uniform
capacitance and thus provide stable isolation characteristics.
[0049] If one of the ground electrodes sandwiching the transmission
line is a common ground electrode, the step of forming ground
electrodes can be decreased, thereby making the multi-layered
substrate thinner. Also, the interference of the capacitor
electrode with electrode patterns constituting other circuit
elements, the switching elements such as diodes mounted onto the
multi-layered substrate, etc. and other mounted parts is reduced by
sandwiching the capacitor electrode on the hot side by the ground
electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a block diagram showing a high-frequency circuit
comprising a switch circuit according to one embodiment of the
present invention;
[0051] FIG. 2 is a view showing an equivalent circuit of the switch
circuit according to one embodiment of the present invention;
[0052] FIG. 3 is a view showing an equivalent circuit of a switch
circuit according to another embodiment of the present
invention;
[0053] FIG. 4 is a view showing an equivalent circuit of a switch
circuit according to a further embodiment of the present
invention;
[0054] FIG. 5 is a view showing an equivalent circuit of a switch
circuit according to a still further embodiment of the present
invention;
[0055] FIG. 6 is a graph showing isolation characteristics between
TX1, TX2 and RX1 in a GSM 1800/GSM 1900 transmitting mode in the
switch circuit according to one embodiment of the present
invention;
[0056] FIG. 7 is a graph showing isolation characteristics between
TX1, TX2 and RX1 in a GSM 1800/GSM 1900 transmitting mode in a
comparative switch circuit;
[0057] FIG. 8 is a view showing an equivalent circuit of a switch
circuit according to a still further embodiment of the present
invention;
[0058] FIG. 9 is a view showing an equivalent circuit of a switch
circuit according to a still further embodiment of the present
invention;
[0059] FIG. 10 is a view showing an equivalent circuit of a switch
circuit according to a still further embodiment of the present
invention;
[0060] FIG. 11 is a block diagram showing another example of a
high-frequency circuit comprising the switch circuit according to
one embodiment of the present invention;
[0061] FIG. 12 is a block diagram showing a further example of a
high-frequency circuit comprising the switch circuit according to
one embodiment of the present invention;
[0062] FIG. 13 is a plan view showing a high-frequency composite
part comprising the switch circuit according to one embodiment of
the present invention;
[0063] FIG. 14 is a squint view showing a multi-layered substrate
for use in the high-frequency composite part shown in FIG. 13;
[0064] FIG. 15 is an exploded plan view showing a laminate
structure of the multi-layered substrate for use in the
high-frequency composite part shown in FIG. 13;
[0065] FIG. 16 is a view showing an equivalent circuit of the
high-frequency composite part shown in FIG. 13;
[0066] FIG. 17 is a plan view showing another high-frequency
composite part comprising the switch circuit according to one
embodiment of the present invention;
[0067] FIG. 18 is a perspective view showing a multi-layered
substrate for use in the high-frequency composite part shown in
FIG. 17;
[0068] FIG. 19 is an exploded plan view showing a laminate
structure of the multi-layered substrate for use in the
high-frequency composite part shown in FIG. 17;
[0069] FIG. 20 is a view showing an equivalent circuit of the
high-frequency composite part shown in FIG. 17; and
[0070] FIG. 21 is a view showing an equivalent circuit of a
conventional switch circuit.
BEST MODE FOR CARRYING OUT THE INVENTION
[1] First Embodiment
[0071] FIG. 1 shows a high-frequency circuit comprising a switch
circuit according to one embodiment of the present invention, and
FIG. 2 shows the equivalent circuit of the switch circuit. It is
assumed below for the simplification of explanation without
intention of restricting the present invention that among
pluralities of communication systems, a first communication system
f1 is GSM 1800 (transmitting frequency: 1710 to 1785 MHz, receiving
frequency: 1805 to 1880 MHz), and a second communication system f2
is GSM 1900 (transmitting frequency: 1850 to 1910 MHz, receiving
frequency: 1930 to 1990 MHz).
[0072] This switch circuit is constituted by a first switch 100 and
a second switch 105 both comprising switching elements, inductors
and a capacitor. The first switch 100 comprises a first port 100a
connected to an antenna circuit; a second port 100b connected to
transmitting circuit of GSM 1800 and GSM 1900, and a third port
100c connected to a second switch 105. The second switch 105
comprises a fourth port 105a connected to the first switch 100 via
a capacitor CP, a fifth port 105b connected to the receiving
circuit of GSM 1800, and a sixth port 105c connected to the
receiving circuit of GSM 1900. The second switch 105 comprises a
transmission line lp2 as a first inductor disposed between the
fourth port 105a and the fifth port 105b, a diode DP2 as a first
switching element disposed between the fifth port 105b and the
ground, a capacitor CP1, as a second capacitor disposed between the
first diode DP2 and the ground, a diode DP1 as a second switching
element disposed between the fourth port 105a and the sixth port
105c, and a transmission line or inductor lp1 disposed between the
sixth port 105c and the ground.
[0073] The second switch 105 switches the receiving circuit RX1 of
GSM 1800 and the receiving circuit RX2 of GSM 1900, and the first
switch 100 switches the transmitting circuit TX1, TX2 of GSM
1800/GSM 1900 and the second switch circuit 105. The second switch
105 has as main elements two diodes DP1, DP2 as switching elements,
and transmission lines lp1, lp2 as inductors (or an inductor in
place of the transmission line lp1). The diode DP1 having an anode
connected to the fourth port 105a and a cathode connected to the
receiving circuit RX2 of GSM 1900, and a grounded transmission line
lp1 is disposed on the cathode side.
[0074] A transmission line lp2 is connected between the fourth port
105a and the fifth port 105b, and the fifth port 105b is connected
to a diode DP2 connected to the ground via the capacitor CP1. A
control circuit VC3 is connected between the diode DP2 and the
capacitor CP1 via an inductor LP and a resistor RP1.
[0075] Disposed upstream of the second-switch 105 is the first
switch 100 for switching the transmitting circuit TX1, TX2 of GSM
1800/GSM 1900 and the second switch. The first switch 100 has two
diodes DD1, DD2 and two transmission lines ld2, ld3 (or an inductor
in place of the transmission line ld2) as main elements.
[0076] A diode DD1 disposed between the second port 100b and the
first port 100a has an anode connected to the first port 100a and a
cathode connected to a transmission line ld2 connected to the
ground. A transmission line ld3 is connected between the first port
100a and the third port 100c, and a diode DD2 connected to the
ground via a capacitor cd4 is disposed on the side of the third
port 100c. A control circuit VC2 is connected between the diode DD2
and the capacitor cd4 via an inductor LD and a resistor RD.
[0077] The control logic of the control circuits VC2, VC3 for
causing the switch circuit in this embodiment to perform the
predetermined operation is shown in Table 3. Voltage is applied
from the control circuits to control the switching elements in an
ON or OFF state, thereby selecting a transmitting mode of GSM
1800/GSM 1900, a receiving mode of GSM 1800, and a receiving mode
of GSM 1900. TABLE-US-00003 TABLE 3 Mode VC2 VC3 GSM 1800 TX V+ V+
(Transmitting) GSM 1900 TX V+ V+ (Transmitting) GSM 1800 RX 0 0
(Receiving) GSM 1900 RX 0 V+ (Receiving)
[0078] The operation of the switch circuit will be explained below
in detail.
(A) GSM 1800/GSM 1900 Transmitting Mode
[0079] To connect the transmitting circuit TX1, TX2 of GSM 1800 and
GSM 1900 to the antenna circuit ANT, positive (high) voltage is
applied from the control circuit VC2 and the control circuit VC3.
Positive voltage applied from the control circuit VC2 is deprived
of a DC component by the capacitors C1, C2, cd4, CP, and supplied
to the first switch 100 including the diodes DD1, DD2. As a result,
the diodes DD1, DD2 are turned on. When the diode DD1 is in an ON
state, there is small impedance between the second port 100b and
the first port 100a. In addition, the transmission line ld3 is
grounded at high frequencies through the diode DD2 in an ON state
and the capacitor cd4, causing resonance, and thus making impedance
high when the third port 100c is viewed from the first port
100a.
[0080] Further, positive voltage applied from the control circuit
VC3 is deprived of a DC component by capacitors CP, C20, C21, CP1,
and supplied to the switch circuit 105 including the diodes DP1,
DP2. As a result, the diodes DP1, DP2 are turned on. The
transmission line lp2 grounded at high frequencies through the
diode DP2 in an ON state and the capacitor CP1, causing resonance,
so that there is large impedance when the fifth port 105b is viewed
from the fourth port 105a.
[0081] With the above structure, there is extremely large impedance
in a line from the first port 100a to the receiving circuit RX1 of
GSM 1800 when the transmitting signal of GSM 1900 is sent to the
antenna circuit. Accordingly, the leakage of the transmitting
signal of GSM 1900 to the receiving circuit RX1 of GSM 1800 can be
reduced.
[0082] FIG. 6 shows isolation characteristic of TX1, TX2 to RX1 in
a transmitting mode of GSM 1800/GSM 1900, when voltage (V+) of 2.6
V is applied from the control circuit VC2 and the control circuit
VC3 in the switch circuit in this embodiment. FIG. 7 shows
isolation characteristic of TX1, TX2 to RX1 in the same switch
circuit as in FIG. 6 in a transmitting mode of GSM 1800/GSM 1900,
when voltage (V+) of 2.6 V is applied from the control circuit VC2,
and when voltage (0) of 0 V is applied from the control circuit VC3
(Comparative Example).
[0083] As shown in FIG. 6, the receiving circuit of the first
communication system is disconnected from the first switch to
obtain excellent isolation characteristics in a desired frequency
bandwidth in the second switch, in a case where the transmitting
circuit of the first and second communication systems are connected
to the antenna circuit. Improvement in the isolation
characteristics resulted in improved insertion loss characteristics
between the transmitting circuit TX1, TX2 of GSM 1800 and GSM 1900
and the antenna circuit ANT. In addition, because the second switch
105 is operated with low operation current, the operation current
of the first switch 100 and the second switch 105 was a little
higher 8.8 mA than 8.0 mA in Comparative Example. It was further
confirmed that by operating the second switch 105, harmonics
radiated from the antenna were reduced by about 2 dB to 5 dB.
(B) GSM 1800 Receiving Mode
[0084] When the receiving circuit RX1 of GSM 1800 is connected to
the antenna circuit ANT, zero voltage is applied from the control
circuits VC2 and VC3, resulting in the diodes DP1, DP2, DD1, DD2 in
an OFF state. With the diode DD1 in an OFF state, there is large
impedance between the first port 100a and the second port 100b.
Also, with the diode DP1 in an OFF state, there is large impedance
between the fourth port 105a and the sixth port 105c. As a result,
a receiving signal of GSM 1800 taken through the antenna is
transmitted to the receiving circuit RX1 of GSM 1800 via the
transmission lines ld3, lp2 with low loss without leaking to the
transmitting circuit TX1, TX2 of GSM 1800/GSM 1900 and the
receiving circuit RX2 of GSM 1900.
(C) GSM 1900 Receiving Mode
[0085] When the receiving circuit RX2 of GSM 1900 is connected to
the antenna circuit ANT, zero voltage is applied from the control
circuit VC2, and positive voltage is applied from the control
circuit VC3. The positive voltage applied from control circuit VC3
is deprived of a DC component by capacitors, and supplied to the
second switch 105 including the diodes DP1, DP2. As a result, the
diodes DP1 and DP2 are turned on. With the diode DP1 in an ON
state, there is low impedance between the fourth port 105a and the
sixth port 105c. The diode DP2 in an ON state and the capacitor CP1
have the transmission line lp2 grounded at high frequencies,
causing resonance in a frequency bandwidth of the receiving signal
of GSM 1900, so that there is extremely large impedance in the
bandwidth of the receiving signal of GSM 1900 when the fifth port
105b is viewed from the fourth port 105a. Further, with the diode
DD1 in an OFF state, there is large impedance between the first
port 100a and the second port 100b. As a result, the receiving
signal of GSM 1900 taken through the antenna is transmitted to the
receiving circuit RX2 of GSM 1900 with low loss without leaking to
the transmitting circuit TX1, TX2 of GSM 1800/GSM 1900 and the
receiving circuit RX1 of GSM 100.
[0086] This embodiment provides the switch circuit with extremely
small leakage of the transmitting signal to the receiving circuit
(extremely large isolation). In this embodiment, transmission
lines, capacitors, etc. may be constituted in a multi-layered
substrate made of dielectric materials, etc. by a low-temperature
cofirable ceramic (LTCC) technology. The. transmission lines ld2
and lp1 may be mounted onto the laminate as inductors such as chip
inductors, coils, etc. together with other circuit elements
(diodes, resistors, etc.).
[0087] FIGS. 3 to 5 shows other examples of the first switch 100
and the second switch 105. The embodiment shown in FIG. 3 uses
diodes as switching elements, and the embodiments shown in FIGS. 4
and 5 use transistors as switching elements.
[0088] These embodiments will be explained below taking use in the
second switch 105 for example, though the first switch 100 may
also-be constituted by a similar equivalent circuit. The second
switch 105 comprises a diode DP1 between the fourth port 105a and
the sixth port 105c. The cathode of the diode DP1 is connected to
the fourth port 105a, and the transmission line lp1 connected to
the ground via a capacitor CP5 is disposed on the rode side of the
diode DP1. Because the transmission line lp1 functions as a choke
coil, an inductor or a coil may be used instead. The transmission
line lp2 is connected between the fourth port 105a and the fifth
port 105b, and a diode DP2 connected to the ground via a capacitor
CP1 is disposed on the side of the fifth port 105b. A resistor R is
connected in parallel with the capacitor CP1. In place of this
resistor R, an inductor (coil) with sufficiently large impedance
may be used. A control circuit VC3 is connected between the
transmission line lp1 and the capacitor CP5. Such switch circuit
can also exhibit excellent effects as above.
[0089] The second switch shown in FIG. 4 comprises a transistor
FET1 between the sixth port 105c and the fourth port 105a, the
transistor FET1 having a drain connected to the fourth port 105a
and a source connected to the sixth port 105c. The gate of the
transistor FET1 is connected to a control terminal VC3 via a
resistor R. A transmission line lp2 is disposed between the fourth
port 105a and the fifth port 105b. A transistor FET2 is disposed on
the side of the fifth port 105b, a drain is connected to the fifth
port 105b and a source connected to the ground electrode. The gate
of the transistor FET2 is connected to the control terminal VC3 via
a resistor R.
[0090] This switch circuit can switch signal lines by voltage
applied to the control terminal VC3, like other switch circuits.
Incidentally, a control logic is different between a depression
type and an enhancement type in the transistors FET1, FET2. Used in
the operation according to the control logic shown in Table 3 is
the enhancement type FET, in which impedance between the source and
the drain becomes low when voltage is applied to the gate. Even
with such switch circuit, excellent effects can be obtained like
above.
[0091] The second switch shown in FIG. 5 comprises a transistor
FET1 between the sixth port 105c and the fourth port 105a, and a
transistor FET2 between the fourth port 105a and the fifth port
105b, the gates of the transistors FET1, FET2 being connected to
the control terminals VC3, VC4, respectively, via resistors R.
[0092] This switch circuit can switch signal lines by voltage
applied from the control terminals VC3, VC4, like other switch
circuits. The series connection of pluralities of transistors can
preferably suppress the generation of distortion even in an OFF
state. Even with such switch circuit, excellent effects can be
obtained like above.
[2] Second Embodiment
[0093] With respect to a switch circuit according to a second
embodiment of the present invention, detailed explanation will be
made below in a case where a first communication system is GSM 1800
(transmitting frequency: 1710 to 1785 MHz, receiving frequency:
1805 to 1880 MHz), and a second communication system is GSM 1900
(transmitting frequency: 1850 to 1910 MHz, receiving frequency:
1930 to 1990 MHz), like the first embodiment. Incidentally, because
the equivalent circuit- of the switch circuit in this embodiment
shares many common parts with that of the first embodiment,
explanation will be concentrated on different parts for
simplification.
[0094] The equivalent circuit of this switch circuit is shown in
FIG. 8. Though it does not differ from the switch circuit of the
first embodiment in an equivalent circuit, it is opposite to the
first embodiment in the connection of the receiving circuits of GSM
1900 and GSM 1800 and the fifth and sixth ports in the second
switch; the receiving circuit RX2 of GSM 1900 being connected to
the fifth port 105b, and the receiving circuit RX1 of GSM 1800
being connected to the sixth port 105c. To have such circuit
structure, the constants of the circuit elements, the length of the
transmission lines, etc. are properly set in each switch circuit,
and they may of course be different from those in the first
embodiment.
[0095] The control logic of the control circuits VC2, VC3 for
subjecting the switch circuit in this embodiment to the
predetermined operation is shown in Table 4. TABLE-US-00004 TABLE 4
Mode VC2 VC3 GSM 1800 TX V+ 0 (Transmitting) GSM 1900 TX V+ 0
(Transmitting) GSM 1800 RX 0 V+ (Receiving) GSM 1900 RX 0 0
(Receiving)
(A) GSM 1 800/GSM 1900 Transmitting Mode
[0096] To connect the transmitting circuit TX1, TX2 of GSM 1800/GSM
1900 to the antenna circuit ANT, positive voltage (V+) is applied
from the control circuit VC2, and zero voltage is applied from the
control circuit VC3. With zero voltage applied from the control
circuit VC3, the diode DP1 is in an OFF state, resulting in large
impedance between the fourth port 105a and the sixth port 105c. As
a result, as in the first embodiment, the transmitting signals of
GSM 1800/GSM 1900 are sent to the first port 100a with low loss
without leaking to the receiving circuit RX1 of GSM 1800, and
radiated from the antenna.
(B) GSM 1800 Receiving Mode
[0097] To connect the receiving circuit RX1 of GSM 1800 to the
antenna circuit ANT, zero voltage is applied from the control
circuit VC2, and positive voltage is applied from the control
circuit VC3. The positive voltage applied from the control circuit
VC3 is deprived of a DC component by capacitors C20, C21, CP, CP1,
and sent to the second switch 105 including the diodes DP1, DP2. As
a result, the diodes DP1 and DP2 are turned on. With the diode DP1
in an ON state, impedance is low between the sixth port 105c and
the fourth port 105a. Also, with the diode DP2 in an ON state and
the capacitor CP1, the transmission line lp2 is grounded at high
frequencies, resulting in resonance in a frequency bandwidth of the
receiving signal of GSM 1800, and thus extremely large impedance in
the bandwidth of the receiving signal of GSM 1800 when the fifth
port 105b is viewed from the fourth port 105a. Further, with the
diode DD1 in an OFF state, impedance is large between the first
port 100a and the second port 100b. As a result, the receiving
signal of GSM 1800 taken through the antenna is transmitted to the
receiving circuit RX1 of GSM 1800 with low loss without leaking to
the transmitting circuit TX1, TX2 of GSM 1800/GSM 1900 and the
receiving circuit RX2 of GSM 1900.
(C) GSM 1900 Receiving Mode
[0098] To connect the receiving circuit RX2 of GSM 1900 to the
antenna circuit ANT, zero voltage is applied from the control
circuits VC2 and VC3 to turnoff the diodes DP1, DP2, DD1, DP2. With
the diode DD1 in an OFF state, impedance is large between the first
port 100a and the second port 100b. Also, with the diode DP1 in an
OFF state, impedance is large between the fourth port 105a and the
sixth port 105c. As a result, the receiving signal of GSM 1900
taken through the antenna is transmitted to the receiving circuit
RX2 of GSM 1900 via the transmission lines ld3, lp2 with low loss
without leaking to the transmitting circuit TX1, TX2 of GSM
1800/GSM 1900 and the receiving circuit RX1 of GSM 1800.
[0099] This embodiment can also provide the switch circuit with
extremely small leakage of the transmitting signal to the receiving
circuit (extremely large isolation).
[3] Third Embodiment
[0100] A switch circuit according to a third embodiment of the
present invention will be explained below. Because the equivalent
circuit of the switch circuit in this embodiment shares many parts
with that of the second embodiment, explanation will be
concentrated on different parts for simplification.
[0101] The equivalent circuit of this switch circuit is shown in
FIG. 9. The equivalent circuit of this switch circuit differs from
that of the second embodiment in that a capacitor CP5 is disposed
between the transmission line lp1 of the second switch 105 and the
ground, and that a control circuit VC2 is connected between this
transmission line lp1 and the capacitor CP5 via an inductor and a
resistor.
[0102] When the switch circuit in this embodiment is operated
according to the same control logic of the control circuits VC2,
VC3 as in the second embodiment, reverse voltage is applied to the
diodes DP1, DP2 of the second switch 105 in the transmitting mode
of GSM 1800/GSM 1900, resulting in excellent isolation
characteristics and attenuated harmonics radiated from the antenna.
Incidentally, the control circuit VC2 may be connected between a
diode and a capacitor in place of the resistor R, such that reverse
voltage is applied to the diodes DP1, DP2 by the switch circuit as
in FIG. 3 as the second switch 105, thereby obtaining the same
effects.
[4] Forth Embodiment
[0103] A switch circuit according to a fourth embodiment of the
present invention will be explained below. Because the equivalent
circuit of the switch circuit in this embodiment shares many parts
with that of the first embodiment, explanation will be concentrated
on different parts for simplification.
[0104] The equivalent circuit of this switch circuit is shown in
FIG. 10. The equivalent circuit of this switch circuit differs from
that of the first embodiment in that the second switch 105 is a
GaAs switch comprising transistors. The control logic is different
between the depression-type transistor and the enhancement-type
transistor. For instance, these control logics are shown in Table 5
below. This embodiment can also provide the switch circuit with
extremely small leakage of the transmitting signal to the receiving
circuit (extremely large isolation). In this embodiment, it is
possible to suppress the generation of distortion by connecting
pluralities of transistors in series, even when there is leakage in
a transmitting signal from the first switch to the second switch.
TABLE-US-00005 TABLE 5 Mode VC2 VC3 VC4 Depression Type GSM 1800 TX
V+ 0 V- (Transmitting) GSM 1900 TX V+ 0 V- (Transmitting) GSM 1800
RX 0 V- 0 (Receiving) GSM 1900 RX 0 0 V- (Receiving) Enhancement
Type GSM 1800 TX V+ V+ 0 (Transmitting) GSM 1900 TX V+ V+ 0
(Transmitting) GSM 1800 RX 0 0 V+ (Receiving) GSM 1900 RX 0 V+ 0
(Receiving)
[5] Fifth Embodiment
[0105] The fifth embodiment provides a high-frequency composite
part (multiband antenna switch module) comprising a branching
circuit (diplexer) 300 and filter circuits 120, 125 integrated in a
multi-layered substrate, and the switch circuit 10 of the present
invention in a high-frequency circuit handling three communication
systems shown in FIG. 11. FIG. 13 is its plan view, FIG. 14 is a
squint schematic view showing the multi-layered substrate, FIG. 15
is a development view showing each layer constituting the
multi-layered substrate shown in FIG. 14, and FIG. 16 shows the
equivalent circuit of the high-frequency composite part.
[0106] In this embodiment, the inductors, capacitors and switching
elements in the switch circuit 10 are formed in the multi-layered
substrate, together with the inductors, capacitors and switching
elements constituting the diplexer 300 comprising the first and
second filter circuits, the lowpass filter circuits 120, 125 and
the switch circuit 15 in the high-frequency circuit shown in FIG.
11. Transmission lines are formed as the inductors in the
multi-layered substrate, and diodes as the switching elements and
high-capacitance capacitors that cannot be contained in the
multi-layered substrate as chip capacitors are mounted onto the
multi-layered substrate, thereby constituting a one-chip,
triple-band, high-frequency composite part.
[0107] The multi-layered substrate constituting this high-frequency
composite part may be produced from a low-temperature-cofirable,
dielectric ceramic material, by forming green sheets of 20 .mu.m to
26 .mu.m in thickness, printing an Ag-based conductive paste on
each green sheet to form a desired electrode pattern, integrally
laminating pluralities of green sheets with desired electrode
patterns, and firing the multi-layered substrate. The width of most
line electrodes is preferably 100 .mu.m to 400 .mu.m. The
low-temperature-cofirable, dielectric ceramic materials may be, for
instance, (a) Al.sub.2O.sub.3-based ceramics containing at least
one of SiO.sub.2, SrO, CaO, PbO, Na.sub.2O and K.sub.2O as an
additional component, (b) Al.sub.2O.sub.3-based ceramics containing
at least one of MgO, SiO.sub.2 and GdO as an additional component,
or (c) ceramics based on Al.sub.2O.sub.3, SiO.sub.2, SrO,
Bi.sub.2O.sub.3, TiO.sub.2, etc.
[0108] These laminate green sheets are integrally pressure-bonded,
and fired at a temperature of about 900.degree. C., to obtain a
multi-layered substrate having an outer size of 6.7 mm.times.5.0
mm.times.1.0 mm, for instance. Terminal electrodes are formed on
the side surfaces of this multi-layered substrate. Incidentally,
the terminal electrodes may be formed on the bottom surface of the
multi-layered substrate, and the positions of the terminal
electrodes may be properly selected.
[0109] The internal structure of the multi-layered substrate is
shown in FIG. 15. The reference numerals in the figure are the same
as in the equivalent circuit shown in FIG. 16. The second
transmission line ld3 and the first transmission line lp2
constituting the inductors of the switch, circuit 10 of the present
invention are formed in a region sandwiched by the ground electrode
G formed on the tenth layer and the ground electrode 15 formed on
the 15-th layer, together with other transmission lines lp1, ld2
constituting the switch circuit 10 and transmission lines lg2, lg3
constituting the switch circuit 15 of SPDT. Electrode patterns
constituting the second transmission line ld3 and the first
transmission line lp2 are respectively formed on the 12-th to 14-th
layers and connected through viaholes (shown by black circles in
the figure). Transmission lines are formed in horizontally
different regions, such that they do not overlap in a lamination
direction. Such structure can prevent interference between
electrode patterns constituting the other circuit elements and
transmission lines, thereby improving isolation
characteristics.
[0110] Impedance matching can be achieved by making the electrode
pattern constituting the second transmission line ld3 wider than
the electrode pattern constituting the first transmission line lp2,
and by making the characteristic impedance of the second
transmission line ld3 lower than that of the first transmission
line lp2, when the first switch 100 and the second switch 105 are
integrated into one multi-layered substrate. In this embodiment,
the width of the second transmission line ld3 is 0.25 mm, about two
times that of the first transmission line lp2.
[0111] The first capacitor cd4 arranged between the diode DD2, the
fourth switching element, and the ground is constituted by the
ground electrode G formed on the eighth layer and an opposing
capacitor electrode formed on the seventh layer, above the ground
electrode G formed on the tenth layer. The capacitor electrode
preferably does not overlap the other electrode patterns
(particularly capacitor electrode patterns) to prevent
interference. However, in the case of forming a multi-layered
composite part, it is sometimes difficult to prevent the capacitor
electrodes from overlapping other electrode patterns. In this
embodiment, accordingly, the capacitor electrodes are separate from
the other electrode patterns (a line connected to the control
terminal VC2 formed on the third layer, and a line connected to the
receiving terminal RX1) by at least 100 .mu.m in a lamination
direction to prevent interference. The second capacitor CP1 of the
second switch 105 is similarly formed on the same layer as the
first capacitor cd4, sharing the ground layer G on the eighth
layer. With such structure, the high-frequency composite part with
excellent isolation and insertion loss characteristics were
obtained.
[6] Sixth Embodiment
[0112] In the sixth embodiment, the switch circuit 10 of the
present invention is integrated in a multi-layered substrate
together with the diplexer 300 and the filter circuits 120, 125,
130, 140 in a high-frequency circuit handling three communication
systems shown in FIG. 11, to constitute a high-frequency composite
part (multi-band antenna switch module). FIG. 17 is a plan view
showing the high-frequency composite part, FIG. 18 is a squint
schematic view showing a multi-layered substrate portion of the
high-frequency composite part, FIG. 19 is a development view
showing the structure of each layer constituting the multi-layered
substrate of FIG. 18, and FIG. 20 is a view showing the equivalent
circuit of the high-frequency composite part.
[0113] In this embodiment, a second transmission line ld3 is formed
in a region sandwiched by the ground electrode G formed on the
12-th layer and the ground electrode G formed on the fifth layer,
and part of the ground electrode G formed on the fifth layer that
overlaps the second transmission line ld3 is cut off. Accordingly,
the second transmission line ld3 has higher characteristic
impedance than when the ground electrode G is not cut off, thereby
making it possible to achieve impedance matching when the first
switch 100 and the second switch 105 are integrated into one
multi-layered substrate. Also, an electrode pattern formed on the
eighth layer to constitute the second transmission line ld3 does
not overlap electrode patterns constituting other circuit elements
in a lamination direction. In this embodiment, the electrode
pattern is separate from connection lines formed on the second
layer by at least 100 .mu.m, to prevent interference.
[0114] Further, the first capacitor cd4 disposed between the diode
DD2, the fourth switching element, and the ground is constituted by
the capacitor electrode patterns formed on the fourth layer, in a
region sandwiched by the ground electrode G formed on the fifth
layer and the ground electrode G formed on the third layer. Such
structure prevents interference with the connection lines on the
second layer. This embodiment provides the high-frequency composite
part with excellent isolation and insertion loss
characteristics.
[0115] The switch circuit of the present invention has been
explained in detail without intention of restricting the present
invention thereto, and various modifications may be added unless
they deviate from the scope of the present invention. Also,
communication systems used in the switch circuit of the present
invention are not restricted to those in the above embodiments, and
the present invention is applicable to combinations of different
communication systems having partially overlapping transmitting
frequencies and receiving frequencies [for instance, GSM 850
(transmitting frequency: 824 MHz to 849 MHz, receiving frequency:
869 MHz to 894 MHz) and EGSM (transmitting frequency: 880 MHz to
915 MHz, receiving frequency: 925 MHz to 960 MHz)]. For instance,
the present invention is applicable to high-frequency circuit
blocks handling four different communication systems shown in FIG.
12.
[0116] The present invention provides the switch circuit which has
a capable of switching transmitting circuits and receiving circuits
with extremely small leakage of transmitting signals to the
receiving circuits (extremely large isolation) in pluralities of
communication systems which the frequency bandwidth of transmitting
signals and the frequency bandwidth of receiving signals partially
overlap, and the high-frequency composite part comprising such
switch circuit.
* * * * *