Wave transmission lines and networks – Attenuators
Reexamination Certificate
1999-08-17
2002-07-02
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Attenuators
C333S116000, C333S08100R
Reexamination Certificate
active
06414565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to variable attenuators and mobile communication apparatuses.
2. Description of the Related Art
In general, a mobile communication apparatus such as a portable telephone is provided with a variable attenuating unit in which a plurality of attenuators having different attenuations are switched into use in
1
order to variably attenuate a high-frequency signal.
FIG. 8
shows a conventional variable attenuating unit used in the microwave band. A variable attenuating unit
70
includes an input terminal
71
, an output terminal
72
, field-effect transistors (hereinafter called FETs)
731
to
733
and
741
to
743
for permitting connection and disconnection from the input to output, and T-shaped resistor attenuators
751
to
753
having attenuations of A dB, B dB, and C dB, respectively. The drain electrodes D of the input-side FETs
731
to
733
, are connected to the input terminal
71
through a capacitor C
71
, and the drain electrodes D of the output-side FETs
741
to
743
, are connected to the output terminal
72
through a capacitor C
72
. The sources S of the FETs
731
to
733
are connected to ends of resistors R
71
to R
73
of the T-shaped resistor attenuators
751
to
753
through capacitors C
73
to C
75
, respectively, and the sources S of the FETs
741
to
743
are connected to ends of resistors R
74
to R
76
of the T-shaped resistor attenuators
751
to
753
through capacitors C
76
to C
78
, respectively. The other ends of the resistors R
71
to R
73
are connected to the other ends of the resistors R
74
to R
76
, respectively, in the T-shaped resistor attenuators, and the connection points are grounded through resistors R
77
to R
79
. The gate electrodes G of the FETs
731
to
733
and
741
to
743
are grounded through capacitors C
79
to C
84
, respectively, and connected to control terminals Vc
71
to Vc
76
through high-frequency blocking inductors L
71
to L
76
, respectively.
A negative voltage about equal to the pinch-off voltage of an FET to be controlled (e.g., ØV) is selectively applied to the control terminals Vc
71
to Vc
76
. When 0 V is applied to the control terminals Vc
71
and Vc
74
of FETs
731
and
741
, which are included in a first path, the channel resistances between the drains and sources of the FETs
731
and
741
become sufficiently lower than the characteristic impedance of the T-shaped resistor attenuator
751
. When negative voltages about equal to the pinch-off voltages of the FETs
732
,
742
,
733
, and
743
(which are included in second and third paths, respectively) are applied to the control terminals Vc
72
, Vc
75
, Vc
73
, and Vc
76
, the channel resistances between the drains and sources of the FETs
732
,
742
,
733
, and
743
become extremely high because the depletion layers extend in the channels. As a result, a microwave input into the input terminal
71
passes through only the first path, including the T-shaped resistor attenuator
751
. The second and third paths, including the T-shaped resistor attenuators
752
and
753
, respectively, are in cut-off states. Therefore, attenuation between the input terminal
71
and the output terminal
72
is A dB.
To switch the attenuation between the input terminal
71
and the output terminal
72
to B dB, 0 V is applied to the control terminals Vc
72
and Vc
75
of FETs
732
,
742
of the second path, and negative voltages about equal to the pinch-off voltages of the FETs
731
,
741
,
733
, and
743
are applied to the control terminals Vc
71
, Vc
74
, Vc
73
, and Vc
76
such that only the second path, including the T-shaped resistor attenuator
752
, is in a pass condition. The attenuation can be switched to C dB by a similar operation. With these operations, a plurality of attenuations can be variably controlled in a discontinuous manner.
In the above conventional variable attenuating unit, however, since a plurality of attenuators having different attenuations are switched using switches, the attenuation cannot be variably controlled in a continuous manner.
In addition, since the number of FETs required for the switches is double that of the attenuations to be variably controlled, the total number of components becomes large, and the structures of the switches become complicated. Thus, the structure of the variable attenuating unit itself becomes complicated and large, and its manufacturing cost increases.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide a compact variable attenuator and a compact mobile communication apparatus which allow attenuation to be variably controlled in a continuous manner.
One preferred embodiment of the present invention provides a variable attenuator comprising: a comb line comprising a first line and a second line electromagnetically coupled to each other; and a plurality of diodes connected to the first and second lines constituting the comb line; one end of each of the first and second lines being grounded; and the diodes being connected between the ground and the other ends of the first and second lines such that the anodes of the diodes are connected to the other ends of the first and second lines.
According to the above described variable attenuator, since the diodes are connected between the ground and the other ends of the first and second lines constituting the comb line, when a voltage applied to the diodes is variably controlled, the resistances of the diodes are variably controlled. As a result, the coupling degree of the first and second lines constituting the comb line is variably controlled. Therefore, the level of a high-frequency signal sent from the input port of the comb line to the output port is variably controlled. This means that the attenuation of the variable attenuator is variably controlled. In addition, the reflection loss is made to −13 dB or less when the voltage standing-wave ratio (VSWR) is 1.5 or less.
Since the diodes are connected between the ground and the other ends of the first and second lines constituting the comb line, the input terminal, the output terminal, and the diodes are connected to different ends of the first and second lines. Therefore, while the diodes are on or off, the impedance of the first line viewed from the input terminal and the impedance of the second line viewed from the output terminal can be made identical to the characteristic impedance of the high-frequency circuit section of a mobile communication apparatus on which the variable attenuator is mounted.
In addition, since the variable attenuator comprises the comb line and the diodes, its structure is simple. As a result, the variable attenuator can be made compact and its manufacturing cost can be reduced.
The above described variable attenuator may comprise a plurality of the comb lines. The plurality of the comb lines are connected to each other in cascade such that one end of a first line of the comb line is connected to one end of a second line of the adjacent comb line among the plurality of the comb lines.
According to the variable attenuator, since a plurality of comb lines are connected in cascade, the attenuation can be variably controlled in an extended range. Therefore, the number of components used in a mobile communication apparatus on which such a variable attenuator is mounted can be reduced. As a result, the mobile communication apparatus can be made compact.
The above described variable attenuator may further comprise a ceramic substrate formed by laminating a plurality of sheet layers made of ceramic, strip electrodes constituting the comb line being built in said ceramic substrate, and the diodes being mounted on said ceramic substrate.
According to the above described variable attenuator, since the ceramic substrate formed by laminating a plurality of sheet layers made of ceramic is provided and the ceramic substrate includes the strip electrodes constituting the comb line, a high-frequency band of 1 GHz or more can be handle
Nakajima Norio
Oida Toshifumi
Tanaka Koji
Jones Stephen E.
Murata Manufacturing Co. Ltd.
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