JPH05218797A - Variable attenuator - Google Patents

Abstract

PURPOSE:To suppress deterioration in the distortion characteristic by providing an inductive bias line through which a signal controlling a drain voltage of a field effect transistor(TR) passes to the attenuator. CONSTITUTION:The attenuator is provided with a FET 3 inserted to a path between signal lines having a signal input terminal 1 receiving a high frequency signal and a signal output terminal 2 and a gate resistor 4 being a resistor with a high resistance through which a signal used to control a gate voltage of the FET 3 passes and with an inductive drain bias line 7 through which a signal used to control the drain voltage of the FET 3 passes. Then the high frequency signal is fed between a drain and a source of the FET 3. The distortion characteristic is not deteriorated by applying a DC voltage between the drain and the source to apply a high frequency voltage only at a straight line part of a drain voltage versus drain current curve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low distortion variable attenuator using field effect transistors.

[0002]

2. Description of the Related Art Generally, in a communication system constructed by using electric / electronic circuits, a system is provided in the system for the purpose of adjusting the level diagram in the line configuration and stabilizing the fluctuation of the signal level in the system due to temperature characteristics. A variable attenuator is provided.
A PIN diode is generally well known as the variable resistance element. This utilizes the characteristic that the high frequency resistance changes when the current flowing through the PIN diode is changed, and the variable attenuator using the PIN diode has a high input level at which the distortion characteristics deteriorate, so it is an effective variable attenuator. is there.

Recently, development of a monolithic integrated circuit in which a large number of circuit elements are integrated on a semiconductor substrate to form a high frequency circuit has been actively pursued, and gallium arsenide is suitable for an ultra high frequency operation of an integrated circuit operating in a microwave band or higher. In many cases, it is formed on a semiconductor substrate such as. At the same time, it is necessary to construct a variable attenuator on a semiconductor substrate such as gallium arsenide, but the technology for making a P-type semiconductor on a gallium arsenide substrate is still immature, and a P-type semiconductor with good characteristics is available. Since no semiconductor has been obtained, it is difficult to realize a PIN diode. Therefore, a variable attenuator that uses a field effect transistor as a variable resistance element and is connected in parallel to a signal line has been realized. This changes the channel resistance of the field effect transistor by controlling the gate voltage.

[0004]

In the conventional variable attenuator using such a field effect transistor, since a high frequency signal flows between the drain and source, the distortion characteristic of the variable attenuator has a drain-source voltage vs. drain-source voltage. Although it depends on the linearity of the source current characteristic, the characteristic is essentially non-linear, and the distortion characteristic of the variable attenuator using the field effect transistor is higher than that of the variable attenuator using the PIN diode. It is extremely inferior, does not satisfy the level of distortion characteristics required in the communication system, and has not been put to practical use.

An object of the present invention is to eliminate such drawbacks and to provide a variable attenuator having means for suppressing deterioration of distortion characteristics.

[0006]

According to the present invention, a field-effect transistor inserted in a path between a signal line having a terminal for inputting a high-frequency signal and a terminal for outputting a high-frequency signal and a common potential,
A variable attenuator having a high resistance resistor through which a signal for controlling the gate voltage of the field effect transistor passes, and an inductive bias line through which a signal for controlling the drain voltage of the field effect transistor passes. Is characterized by.

Here, it may be formed on the gallium arsenide semiconductor substrate.

[0008]

The drain voltage is controlled via the bias line of the drain electrode of the field effect transistor connected in parallel between the signal input / output terminals. This suppresses the deterioration of distortion characteristics.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of this embodiment. In this embodiment, as shown in FIG. 1, a signal line having a signal input terminal 1 and a signal output terminal 2, in which DC blocking capacitors 5 and 6 are inserted, a DC blocking capacitor 5 and a DC blocking capacitor 6 are provided. The drain electrode is connected to the signal line between them, the source electrode is connected to a common potential, and the gate is connected to the gate bias terminal 12 via the gate resistance 4, and the field effect transistor 3 and the DC blocking capacitor 5. The drain bias line 7 connects the signal line between the DC blocking capacitor 6 and the drain bias terminal 8. That is, in this embodiment, as shown in FIG. 1, the field effect transistor 3 inserted in the path between the signal line having the signal input terminal 1 for inputting the high frequency signal and the signal output terminal 2 for outputting and the common potential. And a gate resistor 4 which is a high resistance resistor through which a signal for controlling the gate voltage of the field effect transistor 3 passes. Further, as a feature of the present invention, the drain voltage of the field effect transistor 3 is An inductive drain bias line 7 through which a control signal passes is provided.

Next, the operation of this variable attenuator will be described.
As the variable resistance element of this variable attenuator, the channel resistance of the field effect transistor 3 is used by controlling the gate voltage. The high frequency signal is applied between the drain and source of the field effect transistor 3. FIG. 2 is an example of a drain voltage-drain current curve of a normally-on type N-channel field effect transistor. When only a high frequency signal is applied without applying a DC voltage between the drain and source, the non-linearity in the negative drain voltage region is observed at a smaller drain voltage than the non-linearity in the positive drain voltage region. It deteriorates the distortion characteristics of the attenuator. Therefore, if a high-frequency voltage is applied only to the linear portion of the drain voltage-drain current curve of FIG. 2 by applying a DC voltage between the drain and the source, the distortion characteristic will not deteriorate. FIG. 3 shows an example of the difference between the output of the desired wave of the high frequency signal and the third-order distortion component with respect to the attenuation amount when a constant high frequency signal is input to this variable attenuator and the drain voltage is changed. It is possible to change the amount of attenuation when the difference between the desired wave and the third-order distortion component is minimized by adding a drain voltage, and the distortion characteristics are deteriorated by adding an appropriate drain voltage to the required amount of attenuation. Can be suppressed.

[0011]

As described above, according to the present invention, the drain voltage of the field effect transistor can be controlled.
There is an effect that an attenuator with less distortion can be realized by appropriately selecting the drain voltage with respect to the required attenuation amount. Further, since it can be formed on a gallium arsenide semiconductor, it has the effect of enabling miniaturization and cost reduction.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing drain voltage-drain current characteristics of a field effect transistor.

FIG. 3 is a diagram showing a difference between a desired wave and an output of a third-order distortion component with respect to an attenuation amount when a signal input is constant.

[Explanation of symbols]

 1 signal input terminal 2 signal output terminal 3 field effect transistor 4 gate resistance 5, 6 DC blocking capacitor 7 drain bias line 8 drain bias terminal 12 gate bias terminal

Claims (2)

[Claims] 1. A field-effect transistor inserted in a path between a signal line having a terminal for inputting a high-frequency signal and a terminal for outputting a high-frequency signal and a common potential, and a signal for controlling a gate voltage of the field-effect transistor pass therethrough. A variable attenuator having a high resistance value, comprising an inductive bias line through which a signal for controlling a drain voltage of the field effect transistor passes. 2. The variable attenuator according to claim 1, which is formed on a gallium arsenide semiconductor substrate.