Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2000-03-09
2002-11-12
Maung, Nay (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C333S08100R
Reexamination Certificate
active
06480708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable attenuator, a composite variable attenuator and mobile communication apparatus.
2. Description of the Related Art
Generally, in mobile communication apparatus such as mobile telephones, variable attenuators have been used to variably attenuate high frequency signals by using switches to select among a plurality of attenuators having different attenuation values.
FIG. 8
shows a prior art variable attenuator for use in a microwave band. A variable attenuator
70
includes an input terminal
71
, an output terminal
72
, field effect transistors (FET)
731
to
733
and
741
to
743
for switching conduction and cutoff between input and output, and T-type resistance attenuators
751
to
753
, each having losses of A (dB), B (dB) and C (dB), respectively. In this configuration, each of the drain electrodes D of the FETs
731
to
733
, which work as switches at the input end, is connected to the input terminal
71
via a capacitor C
71
, while each of the drain electrodes D of the FETs
741
to
743
, which work as switches at the output end, is connected to the output terminal
72
via a capacitor C
72
. Also, the source electrodes S of the FETs
731
to
733
are connected to one end of respective resistors R
71
to R
73
of the T-type resistance attenuators
751
to
753
via capacitors C
73
to C
75
, respectively; while the source electrodes S of the FETs
741
to
743
are connected to one end of respective resistors R
74
to R
76
of the T-type resistance attenuators
751
to
753
via capacitors C
76
to C
78
, respectively. Further, the other ends of the resistors R
71
to R
73
of the T-type resistance attenuators
751
to
753
, respectively, are connected to the other ends of the resistors R
74
to R
76
, respectively, to connect their nodes to a ground via resistors R
77
to R
79
, respectively. Further, the gate electrodes G of the FETs
731
to
733
and
741
to
743
are connected to the ground via capacitors C
79
to C
81
and C
82
to C
84
, respectively, and are connected to control terminals Vc
71
to Vc
73
and Vc
74
to Vc
76
, respectively, via inductors L
71
to L
73
and L
74
to L
76
, respectively, for cutting-off high frequencies.
A negative voltage at the same level as the pinch-off voltage of the respective FET to be controlled or 0 V is selectively applied to each of the control terminals Vc
71
to Vc
76
: If 0 V is applied to the control terminals Vc
71
and Vc
74
in the first route and a negative voltage at the same level as the pinch-off voltage of the FETs
732
,
742
,
733
and
743
to be controlled is applied to the control terminals Vc
72
, Vc
75
, Vc
73
, and Vc
76
in the second and third routes, respectively, the channel resistance between the drain and the source of the FETs
731
and
741
becomes sufficiently lower than the characteristic impedance of the T-type resistance attenuator
751
. On the other hand, the channel resistances between the drains and the sources of the FETs
732
,
742
,
733
and
743
becomes extremely high due to expansion of depletion layers within the channels. As a result, microwaves input from the input terminal
71
pass through only the first route including the T-type resistance attenuator
751
, while the second and third routes including the T-type resistance attenuators
752
and
753
, respectively, are disabled. Accordingly, attenuation between the input terminal
71
and the output terminal
72
becomes 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
in the second route and a negative voltage at the same level as the pinch-off voltage of the FETs
731
,
741
,
733
and
743
to be controlled is applied to the control terminals Vc
71
and Vc
74
in the first route, and Vc
73
and Vc
76
in the third route, to enable only the second route including the T-type resistance attenuator
752
. Switching the attenuation to C (dB) is also achieved by a similar operation to the above. The above operations allow variable control of a plurality of attenuations, but discontinuously.
However, the conventional variable attenuator described above has a problem in that the attenuation can not be variably controlled in a continuous manner due its configuration in which it uses switches to select among a plurality of attenuators having different attenuation values.
Also, it tends to require many component parts because the number of FETs that compose a switch in each channel is a number that is a multiple of the number of attenuation steps to be provided. This results in a more complex construction of switches and, further, a more complex configuration of the variable attenuator itself, making the size of the variable attenuator larger and its production cost higher.
SUMMARY OF THE INVENTION
To overcome the above problems, embodiments of the present invention provide a compact variable attenuator, a composite variable attenuator and mobile communication apparatus capable of variably controlling attenuation continuously in order to solve the problems described above.
One embodiment of the present invention provides a variable attenuator which comprises a first comb line consisting of first and second lines which are electromagnetically coupled, and a second comb line consisting of third and fourth lines which are electromagnetically coupled. First and second diodes are connected to the third and fourth lines of the second comb line, the first diode being connected between the third line and a ground with its anode connected to one end of the third line, the second diode being connected between the fourth line and a ground with its anode connected to one end of the fourth line, and the other ends of the first and third lines being connected and the other ends of the second and fourth lines, respectively, which are connected. A first terminal is connected to one end of the first line, and a second terminal is connected to one end of the second line. A first control terminal for turning the first diode on and off is connected to the junction of the other end of the first line and the other end of the third line and a second control terminal for turning the second diode on and off is connected to the junction of the other end of the second line and the other end of the fourth line.
Also, the variable attenuator of the present invention is characterized by being provided with a laminated ceramic substrate comprising a plurality of sheet layers made of ceramic, the ceramic substrate having strip-electrodes which form the first and second lines of the first comb line and the third and fourth lines of the second comb line, wherein the first and second diodes are mounted on the ceramic substrate.
A composite variable attenuator of the present invention is characterized by comprising a plurality of the above variable attenuators, wherein a plurality of variable attenuators are connected in cascade by connecting one end of the second line of a variable attenuator to one end of the first line of an adjacent variable attenuator.
Mobile communication apparatus of the present invention is characterized by using the above variable attenuator.
Also, it is characterized by using the above composite variable attenuator.
According to the variable attenuator of the present invention, since the first and second diodes are connected between one end of each of the third and fourth lines of the second comb line and the ground, it is possible to variably control the resistance of the first and second diodes by variably controlling the voltage being applied to the first and second diodes from the first and second control terminals. As a result, the loss in the first and second lines of the first comb line and that in the third and fourth lines of the second comb line can be variably controlled.
According to the composite variable attenuator of the present invention it is possible to expand the range of attenuation that can be va
Oida Toshifumi
Tanaka Koji
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Vuong Quochien B.
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