U.S. patent application number 11/077346 was filed with the patent office on 2005-07-21 for switch apparatus and mobile communications terminal apparatus.
This patent application is currently assigned to Sony Corporation. Invention is credited to Iida, Sachio.
Application Number | 20050159113 11/077346 |
Document ID | / |
Family ID | 18904363 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050159113 |
Kind Code |
A1 |
Iida, Sachio |
July 21, 2005 |
Switch apparatus and mobile communications terminal apparatus
Abstract
A small-sized switch apparatus for switching between signal
paths of at least first, second and third frequency bands is
capable of handling high-powered high-frequency signals with a
relatively low control voltage and is useful in a mobile terminal
apparatus. A first signal terminal of a diplexer is connected to an
antenna terminal, and a second signal terminal is connected to a
high-frequency switch via a filter. A third signal terminal of the
diplexer is connected to a high-frequency switch via a second
filter. The high-frequency switch has PIN diodes as switching
devices, and performs switching between a global system for mobile
communications transmission signal and a global system for mobile
communications reception signal. The high-frequency switch has
three sets of serially connected multi-staged FETs as switching
devices, and performs switching between wide-band code division
multiple access transmission/reception signals, a digital cellular
system transmission signal and a digital cellular system reception
signal.
Inventors: |
Iida, Sachio; (Chiba,
JP) |
Correspondence
Address: |
Jay H. Maioli
Cooper & Dunham
1185 Avenue of the Americas
New York
NY
10036
US
|
Assignee: |
Sony Corporation
|
Family ID: |
18904363 |
Appl. No.: |
11/077346 |
Filed: |
March 10, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11077346 |
Mar 10, 2005 |
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10239940 |
Sep 26, 2002 |
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10239940 |
Sep 26, 2002 |
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PCT/JP02/01370 |
Feb 18, 2002 |
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Current U.S.
Class: |
455/78 ;
455/552.1 |
Current CPC
Class: |
H04B 1/005 20130101;
H04B 1/406 20130101; H04B 1/48 20130101; H04B 1/006 20130101 |
Class at
Publication: |
455/078 ;
455/552.1 |
International
Class: |
H04B 001/44; H04M
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2001 |
JP |
P2001-042003 |
Claims
1. A switch apparatus for switching between signal paths
comprising: a diplexer having a first signal terminal forming a
transmission/reception signal terminal shared by signals of at
least said first, second and third frequency bands, a second signal
terminal for outputting a signal of said first frequency band
separated from a received signal, a third signal terminal for
outputting a remaining signal after said signal of said first
frequency band is separated, wherein said received signal inputted
to said first signal terminal is divided between said second and
third signal terminals, and transmission signals to be inputted to
said second and third signal terminals are combined and outputted
to said first signal terminal; a first high-frequency switch
connected to said second signal terminal of said diplexer; a second
high-frequency switch connected to said third signal terminal of
said diplexer, wherein said first high-frequency switch includes a
plurality of switching means respectively configured with diodes
for selectively switching between two signal terminals for
connection to said second signal terminal of said diplexer, and
said second high-frequency switch includes at least three switching
means respectively configured with FETs for selectively switching
between at least three signal terminals for connection to said
third signal terminal of said diplexer; and short circuit means
having serially connected FETs connected between one of said three
signal terminals and electrical ground and having a terminal for
receiving a control signal for controlling said serially connected
FETs to connect said one of said three signal terminals to
electrical ground.
2. The switch apparatus according to claim 1, wherein each
switching means of said second high-frequency switch includes a
plurality of serially connected FETs.
3. The switch apparatus according to claim 1 or 2, wherein said
signals of said first, second and third frequency bands are global
system for mobile communications, wide-band code division multiple
access, and digital cellular system signals, respectively.
4. The switch apparatus according to claim 3, wherein said first
high-frequency switch includes PIN diodes as said switching means
and performs switching between a global system for mobile
communications transmission signal and a global system for mobile
communications reception signal, and said second high-frequency
switch includes three sets of serially connected multi-staged FETs
as said switching means, and performs switching between wide-band
code division multiple access transmission/reception signals, a
digital cellular system transmission signal and a digital cellular
system reception signal.
5. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a mobile communications
terminal apparatus, and more specifically, to a switch apparatus
for use in a mobile communications terminal apparatus for a
multi-system, in which various frequency bands and communications
schemes are used, and for switching between signal paths of at
least three frequency bands.
BACKGROUND ART
[0002] In recent years, mobile communications has developed
significantly, and in Europe, mobile communications terminal
apparatuses (hereinafter referred to simply as mobile terminals)
using several frequency bands and several communications schemes
are proposed. For instance, there is UMTS (Universal Mobile
Telecommunication System) which combines GSM (Global System for
Mobile Communications) using a frequency band of 900 MHz band, DCS
(Digital Cellular System) using a frequency band of 1.8 GHz and
WCDMA (Wideband Code Division Multiple Access) using a frequency
band of 2 GHz.
[0003] Because UMTS needs to operate as a mobile terminal of a
multi-system with differing frequency bands as well as
communications schemes, the circuitry thereof becomes complex, and
the increase in the number of components causes the apparatus to
become larger and an increase in cost. For this reason, there is a
need to reduce the number of components by integrating the
circuitry, and to proactively share the components. In particular,
since facilitating the sharing of an antenna, which is large in
size, greatly contributes to the miniaturization of a terminal, the
development of a small-sized switch apparatus is now an important
issue in order to switch an antenna between systems.
[0004] As a conventional example, there is a switch apparatus for
sharing an antenna using a diplexer and a high-frequency switch in
a mobile terminal in which GSM and DCS are integrated. Switch
apparatuses of this sort include the switch apparatus disclosed in
Unexamined Japanese Patent Application No. 2000-183780, for
instance.
[0005] The configuration of such a switch apparatus of the
conventional example is shown in FIG. 4. An antenna, which
resonates with the frequency bands of both GSM and DCS, is
connected to an antenna terminal T.sub.ant. A GSM reception circuit
is connected to a GSM reception signal terminal T.sub.gsmrx. A GSM
transmission circuit is connected to a GSM transmission signal
terminal T.sub.gsmtx. A DCS reception circuit is connected to a DCS
reception signal terminal T.sub.dcsrx. A DCS transmission circuit
is connected to a DCS transmission signal terminal T.sub.dcstx. A
diplexer 1 has the combined characteristics of a high-pass filter
and a low-pass filter, and mutually separates signals of GSM and
DCS with an isolation of approximately 20 dB. A filter 2 attenuates
the higher harmonics of a GSM transmission signal. A high-frequency
switch 4 switches between transmission and reception of GSM. A
filter 3 attenuates the higher harmonics of a DCS transmission
signal. A high-frequency switch 5 switches between transmission and
reception of DCS.
[0006] Here, PIN diodes are used for the high-frequency switches 4
and 5. The PIN diodes come to be in an on state when forward-biased
and the impedance drops to approximately several .OMEGA., and comes
to be in an off state of high impedance with an inter-terminal
capacitance on the order of several hundred fF. In general, in
handling large power with a PIN diode, there is a higher
probability of causing distortion in signals during transmission
when it is in the off state.
[0007] In transmitting with GSM, a voltage of 3V is applied to
control terminals T.sub.ctl2 and T.sub.ctl3, and 0V is applied to
T.sub.ctl1 and T.sub.ctl4. As a result, PIN diodes D1 and D2 come
to be in the on state, and D3 and D4 come to be in the off state.
Thus, it is turned on between the GSM transmission signal terminal
T.sub.gsmtx and the filter 2, and the GSM transmission signal is
transmitted to the antenna terminal T.sub.ant via the
high-frequency switch 4, the filter 2 and the diplexer 1. Although
part of the GSM transmission signal reaches the high-frequency
switch 5, because it is attenuated by 20 dB or more from 33 dB of
the GSM standards, only approximately 13dBm is applied to the PIN
diodes D3 and D4 both in the off state, and no distortion occurs
even with a reverse-bias potential of a low voltage. In
transmitting with DCS, a voltage of 3V is applied to the control
terminals T.sub.ctl1 and T.sub.ctl4, and 0V is applied to the
control terminals T.sub.ctl2 and T.sub.ctl3, but otherwise an
explanation of the operation would be the same as GSM
transmission.
[0008] Thus, the switch apparatus of the conventional example
prevents the occurrence of distortion at the PIN diodes in the off
state by mutually separating the transmission signals of GSM and
DCS with the diplexer 1. It may be said that this is a
configuration realizable with a small-sized diplexer by virtue of
the fact that the frequencies are widely separated, GSM being in
the 900 MHz band, and DCS in the 1.8 GHz band.
[0009] However, in order to make it possible to switch between
WCDMA in addition to GSM and DCS, because WCDMA is in the 2 GHz
band and DCS is in the 1.8 GHz band, and the frequencies are close
to each other, there arises a problem in that these two signals
cannot be separated with a small-sized diplexer.
[0010] Although a method of suppressing the occurrence of
distortion by applying a reverse-bias potential of a high voltage
to a PIN diode is also conceivable, it would become necessary to
provide a voltage transformer apparatus such as a DC-DC converter,
and there arises a problem in that the number of components and the
cost increase. Therefore, this method is not suitable for a
small-sized mobile terminal.
[0011] In addition, high-frequency switches such as the
high-frequency switches 4 and 5 which use PIN diodes have a problem
in their structure such that they are difficult to expand for use
in switching between signals of 3 or more systems.
[0012] The present invention is provided in order to solve the this
problem, and its object is to provide a small-sized switch
apparatus capable of handling high-powered high-frequency signals
with a relatively low control voltage, which switches between
signals paths of at least a first, second and third frequency
bands, and a mobile terminal apparatus using same.
DISCLOSURE OF THE INVENTION
[0013] A switch apparatus according to the present invention is a
switch apparatus for switching between signal paths of at least a
first, second and third frequency bands, and comprises a diplexer
having a first signal terminal, which is a transmission/reception
signal terminal common to the signals of at least the first, second
and third frequency bands mentioned above, a second signal terminal
for outputting the signal of the first frequency band separated
from a received signal, and a third signal terminal for outputting
the remaining signal after the signal of the first frequency band
mentioned above is separated, wherein the received signal to be
inputted to the first signal terminal mentioned above is divided
between the second and third signal terminals mentioned above, and
transmission signals inputted to the second and third signal
terminals mentioned above are combined and outputted to the first
signal terminal, a first high-frequency switch connected to the
aforesaid second signal terminal of the diplexer, and a second
high-frequency switch connected to the aforesaid third signal
terminal of the diplexer, and is characterized in that the first
high-frequency switch mentioned above has a plurality of switching
means respectively configured with diodes, and is configured such
that two signal terminals are selectively switched and connected to
the aforesaid second signal terminal of the diplexer, and the
second high-frequency switch has at least three switching means
respectively configured with FETs, and is configured such that at
least three signal terminals are selectively switched and connected
to the third signal terminal of the diplexer mentioned above.
[0014] As described above, in handling signals of at least three
frequency bands, first, a signal of one frequency band and signals
of other frequency bands are divided, and the signal in which
signals of several frequency bands coexist are handled with at
least three switching means in the second high-frequency switch,
without increasing the size of the diplexer. The second
high-frequency switch comprising at least the three switching means
can be made a simple circuit configuration employing a relatively
small number of components by being configured with FETs instead of
diodes.
[0015] In addition, by connecting each of the switching means of
the second high-frequency switch in series and in multiple stages,
even when a transmission signal of a different frequency band,
which does not pass through the diplexer in the second
high-frequency switch, is applied without being attenuated, the
FETs in the off state are not turned on even with low reverse-bias
potentials, and the occurrence of distortion may be prevented.
[0016] On the other hand, by having the first high-frequency switch
comprise diodes, when switching between the two signal terminals,
both diodes are simultaneously turned on at signal transmission.
(Both diodes are simultaneously turned off at signal reception.)
Thus, the problem of distortion during the off state of the
switching devices does not arise at signal transmission in the
first high-frequency switch. As regards the relation with the
second high-frequency switch, because the diplexer comes in
between, the problem of distortion, again, does not arise.
[0017] In the switch apparatus above, the signals of the first,
second and third frequency bands, for example, are GSM, WCDMA and
DCS signals, respectively.
[0018] The mobile communications terminal apparatus according to
the present invention may be configured by connecting the first
signal terminal of the diplexer of the switch apparatus having the
configuration mentioned above to the antenna, connecting the
transmission/reception circuit for the signal of the first
frequency band mentioned above to the two signal terminals of the
first high-frequency switch mentioned above, and connecting the
transmission/reception circuit for the signals of the second and
third frequency bands mentioned above to at least the three signal
terminals of the second high-frequency switch mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a block diagram showing the configuration of a
switch apparatus which is one mode for carrying out the present
invention;
[0020] FIG. 2 is a diagram which illustrates as a table the status
of the control signal of each switching device of the switch
apparatus of FIG. 1 and the corresponding switching status;
[0021] FIG. 3 is a block diagram showing the configuration of a
switch apparatus of a second mode for carrying out the present
invention; and
[0022] FIG. 4 is a block diagram showing the configuration of a
switch apparatus of a conventional example.
BEST MODES FOR CARRYING OUT THE PRESENT INVENTION
[0023] Modes for carrying out the present invention will now be
described in detail below.
[0024] FIG. 1 shows the configuration of a switch apparatus of one
mode for carrying out the present invention. In this drawing, like
elements shown in FIG. 4 are designated by like reference numerals.
An antenna, which resonates with the frequency bands of WCDMA, DCS
and GSM, is connected to an antenna terminal T.sub.ant. A GSM
reception circuit is connected to a GSM reception signal terminal
T.sub.gsmrx. A GSM transmission circuit is connected to a GSM
transmission signal terminal T.sub.gsmtx. A DCS reception circuit
is connected to a DCS reception signal terminal T.sub.dcsrx. A DCS
transmission circuit is connected to a DCS transmission signal
terminal T.sub.dcstx. A WCDMA transmission/reception circuit is
connected to a WCDMA transmission/reception signal terminal
T.sub.wcdma. The reason only WCDMA is transmission/reception is
because transmission and reception are simultaneously performed
since the duplex operation scheme of WCDMA is FDD (Frequency Domain
Duplex).
[0025] As described above, a diplexer 1 has the combined
characteristics of a high-pass filter and a low-pass filter. In the
configuration of FIG. 1, the diplexer 1 has a first signal terminal
which is connected to the antenna terminal T.sub.ant, a second
signal terminal which is connected to a filter 2 and a third signal
terminal connected to a filter 3. WCDMA and DCS signals pass
through the high-pass filter of the diplexer 1, GSM signals pass
through the low-pass filter of the diplexer 1, both signals are
mutually separated with an isolation of approximately 20 dB. The
filter 2 attenuates the higher harmonics of the GSM transmission
signal. The filter 3 attenuates the higher harmonics of the WCDMA
and DCS transmission signals. A high-frequency switch 4 is
controlled such that it conducts one of the GSM transmission signal
and a reception signal. A high-frequency switch 50 is controlled
such that it conducts one of the DCS transmission signal, reception
signal and the WCDMA transmission/reception signal.
[0026] The high-frequency switch 4 as used herein has the same
configuration as the high-frequency switch 4 shown in FIG. 4 and
uses PIN diodes as switching devices. As described above, when the
PIN diodes are forward-biased, the impedance falls to approximately
several .OMEGA. and they come to be in an on state, and when
reverse-biased, they come to be in an off state of a high impedance
with an inter-terminal capacitance on the order of several hundred
fF.
[0027] On the other hand, for the high-frequency switch 5, field
effect transistor FETs, more specifically in this case, GaAs
(gallium arsenide) FETs, are used as the switching devices. In
other words, serially connected FETs 31, 32 and 33, serially
connected FETs 21, 22 and 23 and serially connected FETs 11, 12 and
13 are respectively inserted between the filter 3 and each of the
signal terminals the WCDMA transmission/reception signal terminal
T.sub.wcdma, the DCS transmission signal terminal T.sub.dcstx and
the DCS reception signal terminal T.sub.dcsrx. A control voltage is
applied from a control terminal T.sub.ctl5 to each of the FETs 31,
32 and 33 via resistances Rg. A control voltage is applied from a
control terminal T.sub.ctl4 to each of the FETs 21, 22 and 23 via
resistances Rg. Similarly, a control voltage is applied from a
control terminal T.sub.ctl3 to each of the FETs 11, 12 and 13 via
resistances Rg. In addition, a bias voltage terminal T.sub.bias is
connected to each of the terminals (source or drain) of the FETs
33, 23 and 13 on their transmission/reception circuit sides via
resistances R5, R4 and R3. Further, the bias voltage terminal
T.sub.bias is connected to terminals (drain or source) of the FETs
31, 21 and 11 on the filter 3 side via a resistance Rb.
[0028] An FET in a non-saturation region behaves like a resistance,
and the fact that the resistance value thereof changes with a gate
voltage is made use of. Near a turn-on voltage Vf, the impedance
falls to approximately several .OMEGA. and it comes to be in the on
state, and at or below a pinch-off voltage Vp, it comes to be in
the off state of a high impedance with a capacitance of several
hundred fF. Although occurrences of distortion are likely even in
handling large power with the FET when it is in the off state, by
multi-staging and connecting several FETs in series as shown in
drawing, it is possible to expand the handling power in proportion
to the square of the number of stages.
[0029] Incidentally, in the case of PIN diodes, when connected in
multiple stages, a reverse bias potential is divided, and the
handling power thus cannot be increaesd. The difference between a
diode and an FET mainly lies in the fact that FETs are
three-terminal devices, where as diodes are two-terminal devices,
and that a gate voltage for on/off control is applied to FETs. By
connecting FETs in multiple stages, because the input signal
voltage can be divided between several FETs, while on the other
hand the same gate voltage as that In the case of using a single
FET can be maintained for each of the FETs, it becomes possible to
increase the handling power without having the reverse-bias
potential voltage divided. Thus, FETs are advantageous in that they
can easily be multi-staged such that the handling power may be
increased.
[0030] Incidentally, although the high-frequency switch 4 may have
an FET configuration like the high-frequency switch 50, because a
control voltage of 5V would currently be required to handle GSM
signals (more high-powered than others) with an FET configuration
like the high-frequency switch 50, in the present mode, a diode
configuration, which can handle GSM signals with a control voltage
of 3V, is adopted. In addition, diodes D1 and D2 in the
high-frequency switch 4 are turned on at the time of transmission
of the GSM signal, as described later, and hence, the problem of
distortion occurring does not arise during signal transmission.
[0031] In FIG. 2, the status of a control signal of each of the
switching devices of the switch apparatus of FIG. 1 and the
corresponding switching status are illustrated altogether as a
table. As can be understood from this table, when transmitting with
GSM on the high-frequency switch 4 side, a voltage of 3V is applied
to the control terminal T.sub.ctl2, and 0V is applied to
T.sub.ctl1. As a result, both of the PIN diodes D1 and D2 come to
be in the on state. Therefore, it is now turned on between the GSM
transmission signal terminal T.sub.gsmtx and the filter 2, and the
GSM transmission signal is transmitted to the antenna terminal
T.sub.ant via the high-frequency switch 4, the filter 2 and the
diplexer 1. Incidentally, on the high-frequency switch 50 side,
when no transmission is performed, by applying a voltage of 3V to
the control terminal T.sub.bias and by applying 0V to T.sub.ctl3,
T.sub.ctl4 and T.sub.ctl5, all of the FETs may be turned off. At
this point, although part of the GSM transmission signal reaches
the high-frequency switch 50, because it is attenuated to
approximately 13dBm at the diplexer 1, the FETs in the off state do
not give rise to distortion.
[0032] When transmitting with DCS on the high-frequency switch 50
side, a voltage of 3V is applied to the control terminals
T.sub.bias, T.sub.ctl1 and T.sub.ctl4, and 0V is applied to
T.sub.ctl2, T.sub.ctl3 and T.sub.ctl5. As a result, the FETs 21, 22
and 23 come to be in the on state, and the other FETs come to be in
the off state. When GSM transmission is not performed
simultaneously with DCS, the PIN diodes D1 and D2 also come to be
in the off state. At this point, it is turned on between the DCS
transmission signal terminal T.sub.dcstx and the filter 3, and the
DCS transmission signal is transmitted to the antenna terminal
T.sub.ant via the high-frequency switch 50, the filter 3 and the
diplexer 1. Since the maximum transmission power of DCS is assumed
to be 30dBm, this signal may be applied to the other FETs 11, 12
and 13, as well as the FETs 31, 32 and 33 in the high-frequency
switch 5 without being attenuated. Therefore, although occurrences
of distortion at the switching devices may be anticipated, because
the handled power is expanded by multi-staging the FETs in the
present mode as mentioned above, it is possible to suppress the
occurrences of distortion. Incidentally, although part of the DCS
transmission signal reaches the high-frequency switch 4, because it
is attenuated by 20 dB or more at the diplexer 1, only
approximately 10dBm is applied to the PIN diodes D1 and D2 even
when these diodes are in the off state, and no distortion occurs
even with reverse-bias potentials of a low voltage (3V or less in
the present mode).
[0033] When transmitting with WCDMA on the high-frequency switch 50
side, a voltage of 3V is applied to the control terminals
T.sub.bias, T.sub.ctl1 and T.sub.ctl5, and 0V is applied to the
control terminals T.sub.ctl2, T.sub.ctl3 and T.sub.ctl4. As a
result, the FETs 31, 32 and 33 come to be in the on state, and the
other FETs come to be in the off state. If GSM is not operated at
the same time, the PIN diodes D1 and D2 also come to be in the off
state. Thus, it is turned on between the WCDMA
transmission/reception signal terminal T.sub.wcdma and the filter
3, and the WCDMA transmission signal is transmitted to the antenna
terminal T.sub.ant via the high-frequency switch 50, the filter 3
and the diplexer 1. In this case, although occurrences of
distortion at the FETs 11, 12 and 13, and the FETs 21, 22 and 23
may be anticipated because the maximum transmission power of WCDMA
is assumed to be 24dBm, it is possible to suppress the occurrence
of distortion because, as in the case mentioned above, the handling
power is expanded by multi-staging the FETs. In addition, although
part of the WCDMA transmission signal reaches the high-frequency
switch 4, because it is attenuated at the diplexer 1 by 20 dB or
more, only approximately 4dBm is applied to the PIN diodes D1 and
D2 in the off state, and no distortion occurs even with reverse
bias potentials of a low voltage.
[0034] When receiving with GSM on the high-frequency switch 4 side,
a voltage of 3V is applied to the control terminal T.sub.ctl3, and
0V is applied to T.sub.ctl2. As a result, the PIN diodes D1 and D2
come to be in the off state. Thus, it is turned on between the GSM
reception signal terminal T.sub.gsmrx and the filter 2, and the GSM
reception signal, which entered from the antenna terminal
T.sub.ant, is transmitted to the GSM reception signal terminal
T.sub.gsmrx via the diplexer 1, the filter 2 and the high-frequency
switch 4.
[0035] When receiving with DCS on the high-frequency switch 50
side, a voltage of 3V is applied to the control terminals
T.sub.bias and T.sub.ctl3, and 0V is applied to the control
terminals T.sub.ctl4 and T.sub.ctl5. As a result, the FETs 11, 12
and 23 come to be in the on state. Thus, it is turned on between
the DCS reception signal terminal T.sub.dcsrx and the filter 3, and
the DCS reception signal, which entered from the antenna terminal
T.sub.ant, is transmitted to the DCS reception signal terminal
T.sub.dcsrx via the diplexer 1, the filter 3 and the high-frequency
switch 50.
[0036] When receiving with WCDMA on the high-frequency switch 50
side, a voltage of 3V is applied to the control terminals
T.sub.bias and T.sub.ctl5, and 0V is applied to the control
terminals T.sub.ctl3 and T.sub.ctl4. As a result the FETs 31, 32
and 33 come to be in the on state. Thus, it is turned on between
the WCDMA transmission/reception signal terminal T.sub.wcdma and
the filter 3, and the WCDMA reception signal, which entered from
the antenna terminal T.sub.ant, is transmitted to the WCDMA
transmission/reception signal terminal T.sub.wcdma via the diplexer
1, the filter 3 and the high-frequency switch 50.
[0037] By a relatively simple circuit configuration of a switch
apparatus as described above, a small-sized switch apparatus, which
performs switching between signals of three or more systems, and
which is capable of handling high-powered high-frequency signals
with a relatively low control voltage, may be realized. In
addition, since an antenna may be shared among three or more
different communications schemes such as GSM, DCS and WCDMA, it
becomes possible to configure a small-sized mobile terminal
apparatus. Further, in each of the communications schemes GSM, DCS
and WCDMA, since the PIN diodes D1 and D2 are in the off state
during reception, a reduction in electric current consumption may
be realized.
[0038] FIG. 3 shows another mode for carrying out the present
invention. This is the switch apparatus shown in FIG. 1, wherein
the high-frequency switch 50 is replaced with a high-frequency
switch 51. The high-frequency switch 51 is the high-frequency
switch 50 to which serially connected FET 41 through FET 43 are
added between the T.sub.dcsrx signal terminal and the ground as
short circuit means. One end of the serially connected FET 41
through FET 43 is connected to the T.sub.dcsrx signal terminal, and
the other end is connected to a connection point between the
resistances Rb and R3 via a resistance R6, while being grounded via
a capacitor C4. Isolation may be improved by applying 3V to the
gates of the FET 41 through FET 43 via the resistances Rg only
during DCS transmission, while applying 0V to the others.
[0039] Preferred modes for carrying out the present invention are
described above, however, various modifications and changes other
than those mentioned above are possible. For example, the control
voltages of 0V and 3V applied to the respective control terminals
are not necessarily limited to these values. Further, the number of
stages of the serially connected FETs is not limited to three
stages, and the method of connecting the FETs is not limited to
those illustrated in drawing.
[0040] According to the present invention, a small-sized switch
apparatus, which is capable of handling high-powered high-frequency
signals with a relatively low control voltage, and which switches
between signal paths of at least a first, second and third
frequency bands, may be realized with a relatively simple circuit
configuration without increasing the size of a diplexer. In
addition, since the antenna may be shared among three or more
different communications schemes such as GSM, DCS and WCDMA, it
becomes possible to configure a small-sized mobile terminal
apparatus. Further, it is possible to simultaneously operate both
of the sides (for instance, GSM and WCDMA or DCS and GSM) divided
by the diplexer, and hence, a variety of system operations may be
accommodated.
* * * * *