JPH0590852A - Microwave amplifier - Google Patents

Abstract

PURPOSE:To enable a microwave amplifier using a multifinger type FET to act as a series negative feedback inductor by adding a source inductor to the FET so that the inductor can ideally function as a source inductor for each unit FET. CONSTITUTION:In a microwave amplifier consisting of a multifinger type FET 7 using coplanar line or microstrip line, inductor 3 is connected to the source electrode 2 of FET 7. Further, the source electrode 2 and inductor 3 are laid such that lengths of lines from section 4 connecting the source electrode and the inductor to the source electrodes 2a, 2b, ..., 2h of individual unit FETs become equal to one another. With this, the influence of the parasitic line 6 formed in the source electrode 2 can be made equivalent to each unit FET and is made small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave amplifier, and more particularly to a microwave amplifier capable of obtaining a good gain / noise characteristic and a good input / output VSWR characteristic of the amplifier over a wide band.

[0002]

2. Description of the Related Art Conventionally, as one of methods for stabilizing a high frequency field effect transistor (hereinafter referred to as "FET") and flattening a gain, an appropriate series connection is provided between a source electrode of a source-grounded FET and ground. A method of forming a negative feedback circuit by inserting a source inductance is known as a known technique. This method not only stabilizes the FET to flatten the gain, but also allows S11 * (complex conjugate of S11) of the FET and the input minimum noise reflection coefficient ΓOPT to be close to each other, thus increasing the noise figure of the FET amplifier. Without doing so, it is possible to reduce the voltage standing wave ratio (hereinafter abbreviated as VSWR) of the input and output of the amplifier, and to widen the band of the amplifier.

On the other hand, with the development of advanced ion implantation technology, epitaxial growth technology and ultrafine processing technology, GaA
MESFET (Metal Semiconductor)
ducter Field Effect Trans
of high performance and heterojunction HEMT (High Electr) composed of AlGaAs / GaAs
on Mobility Transistor is being put to practical use, and the cutoff frequency of these FETs (hereinafter referred to as “ft”)
Has a performance in the millimeter wave band of 50 GHz or more. Furthermore, monolithic microwave integrated circuits (hereinafter "MMIC") using these FETs.
Development) is progressing.

By the way, using these FETs in which ft has a millimeter wave band, a frequency of 1 to 15 GH is relatively low.
When constructing an amplifier that operates near z, the reduction in gain due to the source inductance is not important. Rather, the stabilization index (K) of the FET is usually smaller than 1, so that an external circuit with a loss or a negative feedback circuit is added so that the K value becomes 1 or more so that the input / output impedance does not become negative. There is a need. If the K value is 1 or more, it is absolutely stable and does not oscillate even if any power source or load is connected to the input / output terminal, so perfect matching can be achieved.

In recent years, in MMICs, a coplanar line having a ground conductor formed on the front surface of a dielectric substrate and a microstrip line formed on the back surface are mainly used to form a circuit. For these two types, the method of inserting a proper series source inductance between the source electrode of the source-grounded FET and the ground conductor to form a negative feedback circuit is mainly realized by a microstrip line. It has been.

3A and 3C and FIGS. 4A and 4C,
It is a structural example of the microwave amplifier which comprises the negative feedback circuit using the conventional microstrip line. In this microwave amplifier, the ground conductor is formed on the back surface of the dielectric substrate 50 as described above, and the FET 7 is formed on the front surface of the dielectric substrate 50.
Alternatively, the FET 17 is arranged and the input matching circuit 11 is connected to the FETs 7 and 17. In the microwave amplifier shown in FIG. 3, a gate feeding part 8 and a multi-finger type FET 7 having a plurality of π-shaped gate feeding structures of gate electrodes 1 are generally arranged on the surface of the dielectric substrate 50. There is. The inductor 3 is connected to the source electrode 2 of the FET 7 on one side (FIG. 3A) or both sides (FIG. 3C) of the source electrode 2. Reference numeral 4 in the drawing denotes a connection portion between the source inductor 3 and the source electrode 2. Further, as shown in FIGS. 4A and 4C, the multi-finger type FET 1 in which the gate electrode 1 and the feeding portion 18 of the gate electrode have a comb shape
Also in No. 7, F having the π-shaped gate feeding structure
Similar to the ET7, the inductor 3 is connected to one side (FIG. 4A) or both sides (FIG. 4C) of the source electrode 2.

[0007]

However, the inductor 3 is connected to the source electrodes 2 of the multi-finger type FETs 7 and 17 as shown in FIGS. 3A, 3C and 4A, 4C of the conventional example. Then, FIG. 3 (B) (D) and FIG.
(B) As shown in (D), the connection portion 4 of the inductor 3 and the source electrode 2 and the source electrode portion 2a of the unit FET of each portion,
2b ,. ． ． A parasitic line 6 having a certain impedance is generated up to 2 h. Because of this parasitic line 6,
The source electrode portions 2a, 2b ,. ． ． Two
Even if the potentials of h are different and they are formed to have the same characteristics, the individual unit FETs will not operate the same. As a result, a circuit configured using such an FET differs from the ideal high frequency operation when the inductor 3 is connected to the source, resulting in a significant decrease in gain and an increase in noise. There is a point.

In view of the above, the present invention provides a microwave amplifier comprising a coplanar line or a microstrip line using a multi-finger type FET.
When a source inductance is added to ET, such an FET having a plurality of gate electrodes is ideally operated as a single FET, and the source inductor is operated as a series negative feedback inductor.

[0009]

To achieve the above object, in a microwave amplifier comprising a multi-finger type FET using a coplanar line or a microstrip line, an inductor is connected to the source electrode of the FET, and The source electrode and the inductor are arranged so that the line lengths from the connection portion of the source electrode and the inductor to the source electrode portion of each unit FET of the FET are substantially the same.

In the microwave amplifier, a gate electrode and a multi-finger type FET in which a power feeding portion of the gate electrode has a comb shape are provided, and a plurality of unit source electrode portions have respective gate electrodes and drain electrodes. Is formed so as to be surrounded by a closed line from four directions to form a source electrode, and an inductor is connected to one end or a plurality of ends of the source electrode.

[0011]

In a circuit in which a source inductor is added to the source electrode of a multi-finger type FET, the source inductor is connected in the above arrangement to form a parasitic line having a certain impedance in the source electrode. Influence of each unit FET becomes equal and small, and the potentials of the source electrode portions of each unit FET are equalized, and the above inductor is made an ideal source inductor for each unit FET. Can be operated. That is, the multi-finger type FET can ideally operate as a single FET, and the source inductor can operate as a series negative feedback inductor. As a result, the gain of the FET can be flattened and the FET can be stabilized without significantly decreasing the gain of the FET, and the S11 * (complex conjugate of S11) of the FET and the input minimum noise reflection coefficient ΓOPT must be close to each other. Therefore, the noise figure of the microwave amplifier is not increased, and VSWR (voltage standing wave ratio) of the input and output of the amplifier can be reduced to broaden the band of the amplifier.

[0012]

1 and 2 are views for explaining the first and second embodiments of the present invention. The same parts as those of FIGS. 3 and 4 for explaining the conventional example are designated by the same reference numerals.

FIGS. 1A, 1B, 1C and 1D are circuit pattern diagrams showing a main part of a microwave amplifier according to a first embodiment of the present invention. FIG. 1A shows a microstrip line 1 in which a ground conductor is formed on the back surface of a dielectric substrate 50.
FIG. 2B is an enlarged view of the FET 7 portion of the microwave amplifier. On the other hand, Fig. 1
(C) shows a microwave amplifier including a coplanar line 30 in which a ground conductor 31 is formed on the surface of a dielectric substrate 50. FIG. 3D is an enlarged view of the FET7 portion of the microwave amplifier. Since the ground conductor 31 is divided in the portion where the coplanar line 30 branches, the ground conductors are connected to each other by the air bridge 32 so that the ground potential becomes the same in high frequency.

1A and 1C, the FET 7 is arranged on the surface of the dielectric substrate 50, and the input matching circuit 11 and the output matching circuit 12 are connected to the FET 7 in the first stage. The FET 7 is configured as a multi-finger type FET having a structure including a plurality of π-shaped gate electrodes 1 and a gate feeding portion 8. In the FET 7 of the microwave amplifier of the present embodiment, the inductor 3 is connected to each side of the source electrode 2 divided by the input signal line 13, and the positions of these connecting portions 4 are the positions of the source electrode 2 and the inductor 3. Unit FET from connection part 4 to each part
Source electrode portions 2a, 2b ,. ． ． The line lengths 6 up to 2h are selected to be substantially the same. For example, the inductor 3 is connected near the center of the source electrode 2 on each side divided by the input signal line 13.
In this embodiment, from the connection point 4 of the inductor to the source electrode portions 2a, 2b ,. ． ． The line lengths 6 up to 2h are not completely equal, but the difference between the line lengths 6 is negligible with respect to the signal wavelength in terms of the used frequency. In the present embodiment, the above-mentioned line lengths 6 have a difference of at most 50 μm,
This length is almost negligible in comparison with the signal wavelength in the dielectric substrate 50 of 9.7 mm at the operating frequency of 12 GHz.

Depending on the operating frequency and the gate width of the FET 7, the above-mentioned inductor 3 may be connected to each line only by connecting the inductor 3 to the vicinity of the center of each source electrode 2 divided by the input signal line 13. When the lengths 6 cannot be made substantially the same, the area of the source electrode 2 is widened or a plurality of inductors are further added to make the respective line lengths 6 substantially the same. It is possible. In the figure, reference numeral 20 denotes a via hole for grounding a signal, which is formed at the other end of the inductor 3.

Next, the characteristics of the present microwave amplifier will be described. When a two-stage MMIC low noise amplifier is constructed using two FETs on a GaAs wafer, the microwave band of the microstrip type of this embodiment (FIG. 1A) is a conventional microstrip in the frequency band of 11 to 13 GHz. Type microwave amplifier (Fig. 3 (A))
Compared with, the noise figure was reduced by 30%, the gain was improved by 30%, the characteristics of input / output VSWR2 or less were obtained, and the characteristics closer to the calculated value were obtained.

2A, 2B, 2C and 2D are circuit pattern diagrams showing the main part of the microwave amplifier according to the second embodiment of the present invention. FIG. 2A shows a microstrip line 1 in which a ground conductor is formed on the back surface of the dielectric substrate 50.
FIG. 2B is an enlarged view of the FET 27 portion of the microwave amplifier. On the other hand, FIG. 2C shows a microwave amplifier including a coplanar line 30 in which a ground conductor 31 is formed on the surface of a dielectric substrate 50. FIG. 2D shows FET2 of the microwave amplifier.
It is an enlarged view of 7 parts. Since the ground conductor 31 is divided in the part where the coplanar line 30 branches, the air bridge 32 is arranged so that the ground potential becomes the same in high frequency.
The ground conductors are connected to each other by.

2A and 2C, the FET 27 is arranged on the surface of the dielectric substrate 50, and the input matching circuit 11 and the output matching circuit 1 are provided in the FET 27 of the first stage.
2 are connected. The FET 27 is a multi-finger type FET in which the gate electrode 1 and its gate feeding portion 18 are formed in a comb shape. The source electrode 28 of the FET 27 in the first stage is composed of a plurality of unit source electrode portions 2a, 2b, 2
c and 2d are the gate electrode 1 and the drain electrode 5, respectively
Are arranged so as to be surrounded by a closed line from four directions, and the inductor 3 is connected from arbitrary portions on both sides of the source electrode 28.

The difference between the conventional microwave amplifier shown in FIG. 4A and the microwave amplifier of this embodiment shown in FIG. 2A will be described below. In these two microwave amplifiers, the shapes of the source electrodes of the FET 17 and the FET 27 are different. The FET 17 having the comb-shaped gate feeding structure shown in the conventional example is different from the FET 7 having the π-shaped gate feeding structure as in the above-described embodiment in the gate feeding structure 18.
Since the source electrode 2 and the drain electrode 5 have different structures and arrangements, and the source electrode 2 and the drain electrode 5 also have a comb shape, the potential inside the source electrode easily floats at high frequencies and the potential inside the source electrode is unlikely to be the same potential. It has a structure.

Therefore, in the FET 27 of this embodiment, as shown in FIG.
As shown in (B) (or (D)), the plurality of source electrode portions 2a, 2b, 2c, 2d surround the respective gate electrodes 1 and drain electrodes 5 with closed lines from four directions by air bridge wiring. The potentials in the source electrodes can be made the same. The inductor 3 is connected from an arbitrary portion on both sides of the source electrode 28 of the FET thus configured. In this embodiment, the gate power supply unit 18
The inductor 3 is connected from the source electrode 28 in the vicinity of.

Next, the characteristics of the microwave amplifier of this embodiment will be described. When a two-stage MMIC low noise amplifier is constructed by using two FETs on a GaAs wafer, the microwave band of the microstrip type of this embodiment (FIG. 2A) is a conventional microstrip in the frequency band of 11 to 13 GHz. Type microwave amplifier (Fig. 4
Compared to (A)), the noise figure was reduced by 30%, the gain was improved by 30%, the input / output VSWR was 2 or less, and a characteristic closer to the calculated value was obtained.

In the first and second embodiments, the frequency f = 11 to 13
Although the GHz amplifier has been described, the present invention is not limited to this frequency band but can be widely applied to microwave band amplifiers. Although the first-stage FET has been described in the first and second embodiments, the present method can be applied to the second-stage and subsequent FETs.

[0023]

As is apparent from the above description, the microwave amplifier of the present invention is a multi-finger type FE.
An FET having a plurality of gate electrodes can be ideally operated as a single FET and a source inductor can be operated as a series negative feedback inductor simply by changing the arrangement of the inductors connected to T and the shape of the source electrode. It will be possible. As a result, the FET can be stabilized, and the gain of the microwave amplifier can be flattened without significantly lowering it. Further, it is possible to widen the band of the amplifier by increasing the input / output VSWR of the amplifier without increasing the noise figure of the microwave amplifier. Further, not only the characteristics can be improved, but also the design of the MMIC can be remarkably facilitated and the yield of the MMIC can be improved.

[Brief description of drawings]

FIG. 1 is a substrate surface view for explaining a first embodiment according to the present invention.

FIG. 2 is a substrate surface view illustrating a second embodiment according to the present invention.

FIG. 3 is a substrate surface view illustrating Conventional Example 1.

FIG. 4 is a substrate surface view illustrating a second conventional example.

[Explanation of symbols]

1 gate electrode 2 source electrode 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h source electrode of each unit FET 3 source inductor 4 connection between source inductor and source electrode of FET 5 drain electrode 6 in source electrode Main parasitic line 7 π-shaped multi-finger type FET 8 Gate feed part of FET 7 10 Microstrip line signal line 11 Input matching circuit 12 Output matching circuit 13 Input signal line 17 Comb-shaped multi-finger type FET 18 FET 17 or FET 27 gate feed unit 20 Via hole for grounding a signal 27 Multi-finger type FET 28 having a comb-shaped gate feed structure 28 Source electrode consisting of a closed line surrounding a gate electrode and a drain electrode in four directions 30 Coplanar line Contact A signal line 32 coplanar line conductor 31 coplanar line, air bridge 50 dielectric substrate for connecting the divided grounding conductor

Claims (2)

[Claims] 1. A microwave amplifier having a coplanar line having a ground conductor formed on the front surface of a dielectric substrate or a microstrip line having a ground conductor formed on the back surface of the dielectric substrate, wherein a plurality of gate electrodes are provided on the front surface of the substrate. Forming a multi-finger type field effect transistor having an inductor connected to the source electrode of the transistor, and the arrangement of the inductor and the source electrode is from the connection portion of the source electrode and the inductor to the source electrode of each unit transistor of the transistor. A microwave amplifier characterized in that the line lengths up to the section are formed to be substantially the same. 2. A multi-finger having a plurality of gate electrodes in a microwave amplifier having a coplanar line having a ground conductor formed on the front surface of a dielectric substrate or a microstrip line having a ground conductor formed on the back surface of the dielectric substrate. Type field effect transistor is formed, a gate electrode of the field effect transistor and a power feeding part of the gate electrode have a comb shape, and a plurality of unit source electrode parts close respective gate electrodes and drain electrodes from four directions. A microwave amplifier, characterized in that it is wired in a shape surrounded by a line, and an inductor is connected to one end or a plurality of ends of the source electrode.