Wave transmission lines and networks – Attenuators
Reexamination Certificate
2001-01-16
2003-04-01
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Attenuators
C327S309000
Reexamination Certificate
active
06542045
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a high-frequency variable attenuator for use in a radio communication circuit such as a portable telephone set and, more particularly, to a high-frequency variable attenuator including an attenuating circuit for attenuating an input high-frequency signal in response to a control voltage to produce an output high-frequency signal and a reference voltage generating circuit for supplying the attenuating circuit with a reference voltage.
In the manner which is well known in the art, a high-frequency variable attenuator of the type is for use in a radio communication circuit such as a portable telephone set and is implemented by a monolithic microwave integrated circuit. The high-frequency variable attenuator variably attenuates an input high-frequency signal in response to a control voltage to produce an output high-frequency signal. More specifically, the high-frequency variable attenuator comprises an attenuating circuit and a reference voltage generating circuit. The reference voltage generating circuit generates a reference voltage to supply the attenuating circuit with the reference voltage. The attenuating circuit has an input terminal supplied with the input high-frequency signal, an output terminal for producing the output high-frequency signal, and a control terminal supplied with the control voltage. On the basis of the control voltage, the attenuating circuit attenuates the input high-frequency signal in reference with the reference voltage to produce the output high-frequency signal.
The attenuating circuit includes an attenuator field effect transistor The attenuator field effect transistor has a gate terminal connected to the control terminal through a first attenuator resistor, a drain terminal connected to the input terminal through a first attenuator capacitor, a source terminal connected to the output terminal through a second attenuator capacitor. The reference voltage is supplied to the drain terminal and the source terminal of the attenuator field effect transistor through second and third attenuator resistors, respectively. Each of the second and the third attenuator resistors has a high resistance value. In addition, each of the first and the second attenuator capacitors plays a role for cutting off a direct current (DC) component.
In the manner which will later be described in conjunction with
FIG. 1. a
conventional high-frequency variable attenuator comprises a conventional reference voltage generating circuit for generating, as the reference voltage, a fixed reference voltage. In other words, a difference voltage between the control voltage and the reference voltage varies in dependency on only the control voltage. That is, the difference voltage is determined in response to the control voltage alone so as to have a constant variation amount.
More specifically, the conventional reference voltage generating circuit has a power-supply terminal supplied with a power-supply voltage and a ground terminal supplied with a ground voltage. The reference voltage generating circuit consists of a resistive potential divider. The resistive potential divider comprises first and second divider resistors which are connected in series between the power supply terminal and the ground terminal. The reference voltage generating circuit has a reference connection node between the first and the second divider resistors that generates a divided voltage as the fixed reference voltage.
Inasmuch as the difference voltage between the control voltage and the fixed reference voltage is determined so as to have the constant variation amount in the manner which is described above, in a case where the field effect transistor has a fixed structure, the conventional high-frequency variable attenuator has an attenuation amount having a slope which is uniquely determined in the manner which will later be described in conjunction with FIG.
2
. In addition, the conventional high-frequency variable attenuator is disadvantageous in that the attenuation amount has variations with respect to a threshold voltage of the attenuator field effect transistor in the manner which will later be also described in conjunction with FIG.
2
.
Various high-frequency variable attenuators of the type are already known. By way of example, Japanese Unexamined Utility Model Publication Jikkai No. Sho 59-134,928 or JP-U 59-134928 discloses a variable attenuator which comprises a first transistor connected between an input terminal and an output terminal, a first series circuit and a second series circuit. The first series circuit is connected between the input terminal and a common line and consists of a first resistor and a second transistor. The second series circuit is connected between the output terminal and the common line and consists of a second resistor and a third transistor. By varying direct current biases supplied to the first through the third transistors, an attenuation amount between the input terminal and the output terminal is varied.
Japanese Unexamined Patent Publication (JP-A) Tokkai No. Sho. 63-312,708 or JP-A 63-312708 discloses a variable attenuator which comprises first through third field effect transistors connected to each other in a &pgr;-shape fashion, and a plurality of resistors or diodes connected to gates sources, and drains of the first through the third field effect transistors. In the variable attenuator, two different negative control voltages are controlled by a positive fixed power source and a positive controllable power source. In other words, the variable attenuator disclosed in the JP-A 63-312708 is a &pgr;-type attenuator which has an attenuation amount control terminal, a constant voltage supplying terminal, a high-frequency signal input terminal, and a high-frequency signal output terminal.
Furthermore, Japanese Unexamined Patent Publication (JP-A) Tokkai No. Hei 6-69,754 or JP-A 6-69754 discloses a constant-resistance type variable attenuator in which a tertiary cross modulation distortion characteristic is improved by varying the gate width of a plurality of FETs applying control voltage on a gate so as to constitute the variable attenuator. More specifically, the bridged T type variable attenuator consists of a first field effect transistor (FET), first and second resistors, and a second FET. The first FET has a drain and a source connected to an input terminal and an output terminal for a microwave signal, and a gate connected to a first control terminal. The first resistor has one end connected to the drain of the first FET while the second resistor has one end connected to the source of the first FET. The first and the second resistors have other end connected to a common connection point in common. The second FET has a drain connected to the common connection point. a source grounded, and a gate connected to a second control terminal. The gate width of the second FET is enlarged so that the gate width of the first FET differs from that of the second FET. The saturated voltage of drain current upon the impression of the gate voltage around pinch-off increases as compared with the source voltage of the first FET, and the distortion characteristic of the second FET is improved.
Japanese Unexamined Patent Publication (JP-A) Tokkai No. Hei 6-77,762 or JP-A 6-77762 discloses a variable attenuator by incorporating a field effect transistor (FET) improved in mutual modulation distortion characteristics in a microwave integrated circuit concerning the variable attenuator for preparing the variable attenuating amount of microwaves by applying a control voltage to the gate of the FET The variable attenuator disclosed in JP-A 6-77762 comprises a field effect transistor (FET) and a choke coil. The FET has a source grounded, a drain connected to a signal line connecting between an input and an output, a gate connected to a control voltage terminal. A power source terminal is connected through the choke coil to the drain of the FET. When the control voltage is close to a threshold voltage of the FET and when the power su
Chang Joseph
NEC Compound Semiconductor Devices Ltd.
Pascal Robert
LandOfFree
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