Wave transmission lines and networks – Attenuators
Reexamination Certificate
1999-10-14
2002-09-10
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Attenuators
C333S117000, C333S109000
Reexamination Certificate
active
06448866
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the variable attenuation circuit used for microwave communication device, for example. Microwave communication device is controlling high frequency characteristics, such as a power gain of apparatus and an output power level by using the variable attenuation circuit. As an attenuation circuit, a variable resistor network linked to the T type or I type is constituted, and a diode or a field effect transistor is used as a variable resistor.
However, it is necessary for realizing desired attenuation and desired impedance to decide each resistance of the variable resistor connected in series in parallel as any resistance according to attenuation, when above attenuation circuit is used, and the control circuit setting up resistor of a variable resistance becomes complicated.
Therefore, a circuit using the directivity coupler shown in
FIG. 1
or
FIG. 2
is used much as a circuit of microwave.
Referring now to the attenuation circuit shown in
FIG. 1
, a passage terminal
13
, and a coupling terminal
14
of a first directional coupler
10
connect to a coupling terminal
24
, and a passage terminal
23
of a second directional coupler
20
respectively. Field-Effect-Transistor (FET)
30
a,
30
b
are connected in parallel between the passage terminal
13
and the coupling terminal
24
, and the coupling terminal
14
and the passage terminal
23
respectively. An input terminal
11
of the first directional coupler
10
, and an input terminal
21
of the second directional coupler
20
are a signal input, and a signal output of this attenuation circuit respectively. And isolation terminals
12
and
22
of respective directional couplers
10
and
20
terminate in termination resistors
15
and
25
respectively.
Signals inputted from the input terminal
11
as signal input are distributed to the passage terminal
13
and coupling terminal
14
by first directional coupler
10
. After passing through the parallel circuit of the FETs
30
a
and
30
b,
the distributed signals are inputted into the coupling terminal
24
and the passage terminal
23
of the second directional coupler
20
respectively, is compounded, and is outputted from the input terminal
21
of the second directional coupler
20
as signal output. FET
30
a
and
30
b
that voltage between drain
31
a,
31
b
and source
32
a,
32
b
is 0 [V] are used as variable resistor by gate bias provided for gate
33
a,
33
b
through resistor
16
a,
16
b
from control terminal
41
. The power absorbed by FET
30
a
and
30
b
is changed, passage loss is controlled according to changing the resistance of FET
30
a
and
30
b
compared with the characteristic impedance (for example, 50 [&OHgr;]) of a directional coupler, as a result, the variable attenuation circuit is realized with it.
Moreover, Since the reflective power produced by the mismatching with the impedance of FET and the characteristic impedance of a directional coupler is absorbed by the terminus resistance
15
connected to the isolation terminal
12
, it can realize a matching state without returning to the input terminal
11
.
Next referring now to the attenuation circuit shown in
FIG. 2
, this circuit uses the mismatching with impedance of the directional coupler
10
and FET
30
a
or
30
b.
And, as a result, a variable attenuation circuit is realized by compounding the reflected signal, making it output from the isolation terminal
12
, changing the impedance of FET
30
a
and
30
b,
and controlling reflection.
Therefore, in the variable attenuation circuit using the directional coupler, the matching state is realized by using only gate bias of FET connected in parallel as control voltage, and using the character of a directional coupler. In the circuit shown in
FIG. 1
as mentioned above, in order to obtain the desired attenuation, the resistance of variable resistor, such as FET, is changed.
However, since reactance component of the impedance by influence of the parasitic capacity of FET or a parasitic inductance becomes large According frequency becomes high, even if gate bias changes, it is not able to change enough in the impedance of FET.
Referring now to
FIG. 3
,
FIG. 3
is a passage characteristic diagram of the variable attenuator in consideration of parasitic capacity of FET.
FIG. 3
shows the passage characteristic of the case, for example, in the composition of
FIG. 1
, used High-Electron-Mobility-Transistor (HEMT) that gate length is 0.3 micrometers and gate width is 300 micrometers. Moreover, it uses four fingers Lange couplers of main frequency 25 GHz as directional coupler. There is a problem that the variable range becomes small remarkably, in high frequency domain, as passage loss becomes large.
Accordingly, it is an object of the present invention to provide a microwave variable attenuation circuit. in the variable attenuation circuit using a coupler, preventing increase of the passage loss and decrease of the variable attenuation by the parasitic capacity of a variable resistor, and having good transmission characteristic.
REFERENCES:
patent: 4216445 (1980-08-01), Abajian
patent: 4837530 (1989-06-01), Kondoh
H. A. Watson, Editor, “Microwave Semiconductor Devices and their Applications”, Microwave Switches, Limiters and Phase Shifters, 1969, pp. 322-325.
Jones Stephen E.
Kabushiki Kaisha Toshiba
Pascal Robert
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