Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing two electrode solid-state device
Reexamination Certificate
1995-12-04
2003-02-11
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing two electrode solid-state device
C333S103000, C333S104000, C327S493000
Reexamination Certificate
active
06518822
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency switch for changing signal paths in a high-frequency circuit, for example in a portable telephone, and more particularly to a high-frequency switch having four ports and utilizing diodes.
2. Background Art
In a portable telephone, in some cases, two antennas, or one antenna and one external terminal, are commonly used in a transmitter and a receiver. A conventional switch circuit having such a construction is illustrated in FIG.
7
.
A switch circuit
151
has a construction wherein 3-port switches
152
and
153
are connected to each other. The switch
152
has first, second and third ports P
21
, P
22
and P
23
. Similarly, the switch
153
has first to third ports P
31
, P
32
and P
33
. An antenna ANT is connected to the second port P
22
of the switch
152
and the third port P
23
is used as an external connection terminal EXT. A second antenna is sometimes connected to the third port P
23
. That is, in a portable telephone for use in a vehicle or the like, a second antenna which is mounted on the vehicle can also be connected. As another example of use of the external connection terminal EXT, there are cases where a prescribed signal is input through the external terminal when measuring electrical characteristics of the receiver in a portable telephone containing the switch circuit
151
therein.
In the switch
152
, the first port P
21
can be changed over to the second port P
22
or to the third port P
23
. The first port P
21
is connected to a first port P
31
of the switch
153
.
The first port P
31
of the switch
153
can be changed over between a second port P
32
and a third port P
33
. The second port P
32
is connected to the transmitter Tx and the third port P
33
is connected to the receiver Rx.
By using the above-mentioned switch
151
, either the antenna ANT or the external terminal EXT can be connected to either the transmitter Tx or the receiver Rx.
FIG. 8
shows a known type of high frequency switch using diodes which can constitute the 3-port switches
152
and
153
. A high frequency switch
161
has first to third ports P
61
to P
63
corresponding to either the first to third ports P
21
to P
23
or to the first to third ports P
31
to P
33
. The port P
61
is connected through a capacitor
164
to a cathode of a diode
165
a
. One end of a distributed constant line
167
a
is electrically connected to a point A of connection between an anode of the diode
165
a
and a capacitor
166
a
. Assuming that the wavelength of a high frequency signal flowing through this switch
161
is &lgr;, the distributed constant line
167
a
is composed of a transmission line having a length of &lgr;/4 or less. The other end of the distributed constant line
167
a
is connected through a capacitor
168
a
to ground potential. One end of a resistor
169
a
is connected to a point of connection between the distributed constant line
167
a
and a capacitor
168
a
and the other end thereof is connected to a control voltage terminal Vc
1
.
Also, the first port P
61
is connected through the capacitor
164
to a distributed constant line
171
constructed the same way as the distributed constant line
167
a
. The other end of the distributed constant line
171
is connected to ground potential.
Further, the cathode of a diode
165
b
is connected through the capacitor
164
to the first port P
61
. The anode of the diode
165
b
is connected through a capacitor
166
b to the third port P
63
. Also, as with the diode
165
a
, a series circuit consisting of a distributed constant line
167
b
and a capacitor
168
b
is connected between the anode side of the diode
165
b
and ground potential. One end of a resistor
169
b
is connected to a point of connection between the distributed constant line
167
b
and the capacitor
168
b
and the other end thereof is connected to a control voltage terminal Vc
2
.
In the high frequency switch
161
, by applying different control voltages to the control voltage terminal Vc
1
and the second control voltage terminal Vc
2
, it is possible to realize a state of connection wherein the port P
61
is connected to the second port P
62
or wherein the port P
61
is connected to the third port P
63
. For example, when a positive control voltage is applied to the control voltage terminal Vc
1
and, on the other hand, a negative control voltage is applied to the control voltage terminal Vc
2
, a forward bias voltage is applied to the diode
165
a
and a reverse bias voltage is applied to the diode
165
b
. That is, since the capacitors
166
a
,
168
a
,
164
,
166
b
and
168
b
block the flow of direct current, they block the control current supplied from the control voltage terminal Vc
1
which is thereby caused to flow through a circuit portion including the distributed constant line
167
a
, the diode
165
a
and the distributed constant line
171
. As a result, the diode
165
a
goes on. On the other hand, a reverse bias voltage is applied to the diode
165
b
, with the result that the diode
165
b
goes off.
Also, in order to guide the flow of a high frequency signal supplied from the second port P
62
, since the distributed constant line
167
a
is constructed as mentioned above, one end of the distributed constant line
167
a
can be set to have ground potential with respect to high frequencies by providing the capacitor
168
a
with a large capacitance. As a result, the impedance of a series circuit composed of the distributed constant line
167
a
and the capacitor
168
a
as viewed from the connection point A becomes infinite with respect to high frequencies by impedance inversion. Accordingly, a high frequency signal supplied from the second port P
62
is caused to flow into the first port P
61
.
On the other hand, when a negative control voltage is applied to the first control voltage terminal Vc
1
and a positive control voltage is applied to the second control voltage terminal Vc
2
, conversely to the above, a reverse bias voltage is applied to the diode
165
a
and a forward bias voltage is applied to the diode
165
b
. Accordingly, the diode
165
a
goes off and the diode
165
b
goes on. As a result, no signal flows between the second and first ports P
62
and P
61
and a signal flows between the first and third ports P
61
and P
63
. In this case as well, since the impedance of a series circuit composed of the distributed constant line
167
b
and the capacitor
168
b
becomes infinite with respect to high frequencies, no high frequency signal flows in the distributed constant line
167
b.
The distributed constant lines
167
a
and
167
b
respectively form the current paths for causing the control currents to flow through the diodes
165
a
and
165
b
and perform the function of increasing with respect to high frequency signals the impedances of the distributed constant lines
167
a
and
167
b
sides as viewed from the connection points A and B and thereby decreasing the insertion loss and reflection loss.
As mentioned above, in the high frequency switch
161
, by applying positive and negative control voltages to the control voltage terminals Vc
1
and Vc
2
, it is possible to terminate the connection between the first port P
61
and the second port P
62
and establish the connection between the first port P
61
and the third port P
63
, and vice versa.
The switch circuit
151
illustrated in
FIG. 7
is constructed using a pair of the high frequency switches
161
as the switches
152
and
153
. That is, in the switch circuit
151
, two 3-port high frequency switches are used and the first ports thereof are connected to each other.
As mentioned above, since the switch circuit
151
is constructed by connecting the two high frequency switches
152
and
153
, a high frequency signal passes through the two switches. For example, a transmission output supplied from the transmitter Tx passes through the two switches
153
and
152
before arriving at the antenna ANT. Similarly, a high frequency signal input from the a
Kato Mitsuhide
Tsuru Teruhisa
Keating & Bennett LLP
Le Dinh T.
Murata Manufacturing Co. Ltd.
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