Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-03-25
2003-11-25
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S275000
Reexamination Certificate
active
06653697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-input, four-output high frequency switch circuit as a switch semiconductor integrated circuit formed on a semiconductor substrate. The invention also relates to a communications terminal, such as a portable telephone terminal, constructed using a high frequency switch circuit. The present invention is particularly suited to a two-input, four-output high frequency switch circuit of which low insertion loss and high isolation are required, and a communications terminal constructed using the same.
2. Description of the Related Art
Mobile communications business, including car telephones and portable telephone terminals, has been developing rapidly in recent years. Nowadays, a variety of mobile communications systems are in operation all over the world. In these mobile communications systems, many portable telephone terminals use semiconductor field-effect transistors in their signal processing sections.
For portable telephone terminals for which portability is particularly important, monolithic microwave ICs using GaAs field effect transistors have been vigorously developed as semiconductor integrated circuit devices that can simultaneously achieve smaller size, lower operating voltage, and lower power consumption. Among others, the development of high frequency switch circuits to be used in portable telephone terminals to switch high frequency signals has become a pressing need.
When using a field effect transistor as a switching device, the bias voltage to be applied to the gate terminal of the field effect transistor must be controlled. For example, the field effect transistor can be put in the ON state by applying to the gate terminal a gate bias sufficiently higher than the pinch off voltage and thereby putting the drain-source channel in a low impedance state in a controlled manner. Conversely, the field effect transistor can be put in the OFF state by applying to the gate terminal a gate bias sufficiently lower than the pinch off voltage and thereby putting the drain-source channel in a high impedance state in a controlled manner.
When using a GaAs field effect transistor alone as described above, there arises the problem that high isolation cannot be achieved, though the insertion loss is small. If high isolation is to be achieved with a field effect transistor alone, the gate width of the field effect transistor should be reduced. Reducing the gate width, however, results in increased ON resistance, and hence the problem of increased insertion loss. It is therefore difficult to achieve low insertion loss and high isolation at the same time.
In this way, when using a field effect transistor alone, it is difficult to achieve low insertion loss and high isolation at the same time. In view of this, a plurality of field effect transistors are used in combination to overcome this problem.
As an example of a switch circuit employing such a configuration, there is a single pole dual throw switch constructed using one series field effect transistor and one shunt field effect transistor in combination for each signal path. With this configuration, since a radio frequency signal leaking via a capacitive component of the series field effect transistor in the OFF state can be flown to ground through the shunt field effect transistor in the ON state, high isolation can be achieved.
On the other hand, in a digital portable telephone terminal using a time division multiple access communications scheme, a dual pole dual throw switch is used to switch between the attached antenna and an external antenna, i.e., a test antenna, and also switch between the transmitter and receiver sections built in the portable telephone terminal. A dual pole dual throw switch is a switch that has first and second input terminals and first and second output terminals, and that switches signals from the first and second input terminals to the first and second output terminals, respectively, or conversely to the second and first output terminals, respectively.
As an example of equipment using such a dual pole dual throw switch, a communications terminal will be described below.
FIG. 5
shows the RF section, i.e., the radio frequency signal processing section, of the communications terminal which uses the dual pole dual throw switch. This communications terminal is constructed to be able to switch connections between two antennas
1
,
2
and transmitter and receiver sections
3
,
4
.
For this purpose, the dual pole dual throw switch
7
is provided with four signal terminals RF
2
, RF
4
, RF
5
, and RF
6
. A switch S
3
is inserted, that is, connected in series, in a signal path connecting between the signal terminal RF
2
and the signal terminal RF
4
. A switch S
4
is inserted, that is, connected in series, in a signal path connecting between the signal terminal RF
4
and the signal terminal RF
5
. A switch S
5
is inserted, that is, connected in series, in a signal path connecting between the signal terminal RF
5
and the signal terminal RF
6
. A switch S
6
is inserted, that is, connected in series, in a signal path connecting between the signal terminal RF
6
and the signal terminal RF
2
. The receiver section
4
is connected to the signal terminal RF
2
, and the transmitter section
3
is connected to the signal terminal RF
5
. The antenna
1
is connected to the signal terminal RF
6
, and the antenna
2
is connected to the signal terminal RF
4
.
Using the above configuration, signals to be input to the receiver section
4
can be input by switching between the two antennas
1
and
2
. Likewise, output signals from the transmitter section
3
can be transmitted by switching between the two antennas
1
and
2
.
However, today's portable telephone terminals use two antennas, i.e., a whip antenna as a transmitting/receiving antenna and a built-in antenna as a receiving antenna, for diversity reception. Further, to inspect such portable telephone terminals at the factory, two test antennas, one corresponding to the whip antenna and the other to the built-in antenna, are used.
To serve the purpose, the high frequency switch circuit is provided with four signal terminals as antenna terminals connected to the first, second, third, and fourth antennas, respectively. The first antenna is the whip antenna. The second antenna is the built-in antenna. The third antenna is the test antenna corresponding to the first antenna. The fourth antenna is the test antenna corresponding to the second antenna. The antenna terminals connected to the third and fourth antennas are called the test terminals, which are connected to the test antennas at the time of factory testing but are left open during normal use.
Therefore, the high frequency switch circuit has three switching functions, one for switching between transmission and reception, another for switching between the first and second antennas and the third and fourth antennas, and the other for switching between the receiving antennas for diversity reception, and is constructed so that any switch path can be connected within the high frequency switch circuit.
As an example of equipment using such a high frequency switch circuit, a communications terminal will be described below.
FIG. 6
shows the RF section, i.e., the radio frequency signal processing section, of the communications terminal which uses the high frequency switch circuit. This communications terminal uses a two-input, four-output switch
8
as the high frequency switch circuit, instead of the dual pole dual throw switch
7
shown in FIG.
5
. The two-input, four-output switch
8
differs from the dual pole dual throw switch
7
shown in
FIG. 5
by the addition of two signal terminals RF
1
and RF
3
. A switch S
1
is inserted, that is, connected in series, in a signal path connecting between the signal terminal RF
2
and the signal terminal RF
1
. A switch S
2
is inserted, that is, connected in series, in a signal path connecting between the signal terminal RF
2
and the signal terminal RF
3
. An antenna
Hidaka Kenichi
Nakatsuka Tadayoshi
Tara Katsushi
Nelms David
Nguyen Thinh T
Stevens Davis Miller & Mosher LLP
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