JPH0366204A - Matching circuit for high frequency transistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an input/output matching circuit for transistors used in high-frequency, high-output amplifiers. The present invention relates to a high-frequency, high-transistor matching circuit that can eliminate a decrease in amplification efficiency due to phase difference.

Conventional technology The input/output impedance of a high frequency transistor is -g
does not match the characteristic impedance (50 ohms) of the main line microstrip line. In order to efficiently amplify electrical signals, it is preferable that the output impedance of the transistor and the impedance of the main line microstrip line of each output match as much as possible, so that reflection at that point is minimized. In particular, the input/output impedance of high-frequency, high-output transistors is
Since it is much lower than 50 ohms, a low impedance element is usually inserted in parallel with the input/output main line microstrip line to match the impedance. The impedance of the open-ended microstrip line (open stub), Zos, is: Zos--j-cot βL (1) Where, β = 2π/λ, λ is the wavelength on the microstrip line at the frequency to be matched. is given by the length of the microstrip line.

Therefore, Zos has βL of π/2, that is, L of λ
It becomes smaller as it approaches /4, and matching with the transistor can be achieved by selecting an appropriate value.

The typical configuration of a conventional high frequency amplifier using this method is shown in the third section.
As shown in the figure.

In FIG. 3, 101 is a field effect transistor (FE).
102 is an input matching circuit board, 103 is an output matching circuit board, 104 is a main line with a microstrip line connected to the input terminal, and 105 is a microstrisopline connected to the output terminal. The bottomed main lines 106 and 107 are so-called tapered portions, which are provided on the transistor side of the main line and have electrodes that gradually become wider. 112 is a wire connecting the transistor and the tapered part; 301 is an island-like electrode (pad) for input/output matching adjustment; and 302 is a wire connecting the tapered part and the adjustment pad. In this structure, the manual matching circuit and the output matching circuit are adjusted by connecting adjustment pads with wires.

As a further improvement of this method, one using a matching chip capacitor is known, and a typical structure thereof is shown in FIG. In FIG. 4, 101 is a field effect transistor (FET), 401 is an input matching adjustment circuit board, 402 is an output matching adjustment circuit board, 104 is a main line connected to the input terminal with a microstrip line at the bottom, 105 106 and 107 are tapered portions provided on the transistor side of the main line.

403 is a chip capacitor for input impedance matching,
404 is a chip capacitor for output impedance matching, the lower electrode is connected to the grounded pedestal, and the upper electrode is connected by wire to the transistor and the main line microstrip line tapered part of the input/output matching adjustment circuit board. has been done. 405 and 406 are wires connecting the transistor, the chip capacitor, and the tapered part.

In this structure, input/output matching is performed by the inductance of the chip capacitor and the wire connecting it.

Problems to be Solved by the Invention However, all of the methods shown in the conventional examples consider only impedance matching, and do not consider the phase difference of electrical signals in the tapered part. This is insufficient as a matching circuit for a high-frequency, high-output FET that has a gate width that is not negligible compared to the wavelength.

For example, in the case of 14 GHz, an alumina substrate or G
The length corresponding to 1/4 wavelength on the aAs substrate is approximately 2 mm.
and, on the other hand, a GaAsFET to obtain an output of 3W
The gate width is approximately 4 mm. Therefore, a considerable phase difference occurs between the electrical signals passing through the center of the tapered portion shown in FIG. 1 and the electrical signals passing through the ends. When a phase difference occurs in the input signal, a phase difference also occurs in the signal after being amplified by the FET, and as a result, the combined signal output is attenuated.
Amplification efficiency decreases. The tapered part in the output part is
It further aggravates the negative effects.

With the open stub matching method shown in the first conventional example, it is quite difficult to match high frequency, high output FETs with low input/output impedance, so the configuration of the second conventional example is usually adopted.

However, in the case of the configuration described in the second conventional example, it is necessary to separately connect a large chip capacitor, which makes impedance matching easier than in the first conventional example.
During manufacturing, mounting the chips increases the number of man-hours, and the chip mounting requires a separate section, making it difficult to achieve small size and high integration, resulting in high manufacturing costs.

As a method for achieving matching while eliminating spatial phase difference, 1
So-called power dividers and power combiners using impedance converters of /4 wavelength are known, and are generally used in power amplifiers of several watts or more. But at least 1
Since an impedance converter with a length of /4 wavelength is required, miniaturization is difficult.

Means for Solving the Problems In order to solve the above problems, the present invention provides an impedance matching circuit for transistors using a microstrip line as the main line, in which the main line on the transistor side is tapered, and the tapered part and the ground are connected to each other. There is a series circuit of a thin film capacitor and a short-circuited microstrip line in between, and the length of the shorted microstrip line to the ground is different in each part of the thin film capacitor section. By compensating for the difference in phase of the high-frequency signal at the position where the high-frequency signal appears, impedance matching with the transistor can be achieved while at the same time eliminating the phase difference that occurs spatially.

Effect The present invention has the above-described configuration, which enables impedance matching of high-frequency, high-output transistors with low impedance and large dimensions, and compensation of spatial phase difference at the same time.Furthermore, the number of mounting steps is small, and the device is compact and highly integrated. The present invention provides a matching circuit for high-frequency, high-output transistors that can be manufactured at low manufacturing cost.

Embodiments Hereinafter, embodiments of a matching circuit for high-frequency transistors according to the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the structure of a matching circuit for high frequency transistors according to the present invention. 101 in Figure 1
is a field effect transistor (FET), 102 is an input matching circuit board, 103 is an output matching circuit board, 104 is a main line composed of a microstrip line connected to the input terminal, and 105 is a microstrip connected to the output terminal. The main line constituted by a line, 106 and 107, is a tapered portion provided on the transistor side of the main line. 108 is an input matching thin film capacitor whose one electrode forms part of the tapered part; 109 is an output matching thin film capacitor whose one electrode forms part of the tapered part; 110 is the input matching thin film capacitor; An open-ended microstrip line connected between the other electrode of a thin-film capacitor and the ground, one each on the top and bottom. 1
Reference numeral 11 denotes short-circuited tapered microstrip lines connected between the other electrode of the output thin film capacitor and the ground, one each on the upper and lower sides. Reference numeral 112 indicates wires connecting the tapered portion and the transistor, and in this embodiment, there are three wires on the input side and three wires on the output side.

The input/output matching circuit board uses an Aruka Nasera ξ link board,
Cr-Au is used for conductive parts such as main lines and microstrip lines, and metal-dielectric material is used for thin-film capacitors, using silicon oxide with a dielectric constant of about 4 as a dielectric material.
A thin film capacitor with a metallic structure was used. Further, a GaAsFBT was used as a transistor, and 14GH2 was used as a matching frequency. When the dielectric constant of the alumina substrate is 9.8, the length of the microstrip line corresponding to 1/4 wavelength at 14 GHz is about 2 mm. In addition, the length of the open-ended microstrip line is 1/4 wavelength from the end of the thin film capacitor, and from the center,
The length is set to be 1/2 wavelength or less.

In this structure, impedance matching for input matching and output matching is performed by thin film capacitors and open-ended microstrip lines.

The matching method in this system will be explained in more detail. As mentioned above, the input/output impedance of the high output FET is from several ohms to less than 1 ohm, which is considerably lower than the impedance of the main line, which is 50 ohms. Therefore, in this embodiment, a thin film capacitor and an open-ended microstrip line are inserted in parallel to the main line microstrip line in order to achieve the matching. If the length of the microstrip line is L, the impedance of this series circuit, Zin, is: Zin=1/jωc+jZo-cotβL(2)--j
(1/ωC-Zo・cotβL) (3) However, ω=2π
f β = 2π/λ f is the frequency to be matched, C is the capacitance of the thin film capacitor Zo is the characteristic impedance of the microstrip line, λ is the wavelength within the substrate of the frequency to be matched, L is the length of the microstrip line to ground.

It is expressed as

Therefore, by appropriately selecting the length of the open-ended microstrip line and the capacitance value of the thin film capacitor, it is easy to reduce the value of Zin to several ohms or 1 ohm or less.

When L is 1/4 wavelength, cotβL becomes 0 and is determined only by the value of C.

Next, the operation of spatial phase difference compensation in this embodiment will be explained. The electrical signals that have the same phase up to the taper start portion spread along the taper and reach the thin film capacitor portion.

Usually, the distance at the end of the tapered part is longer than the center part, and in the case of this embodiment, the distance to reach the thin film capacitor is also longer at the end. The electrical signal that enters the thin film capacitor undergoes a change in phase velocity at the thin film capacitor section. If the opposing electrode of a so-called membrane capacitor is completely at ground potential, the phase velocity is inversely proportional to the square root of the dielectric constant. Therefore, the phase velocity at the thin film capacitor section is 1. /-'
JTT7r=1 2 1.57 times faster than the phase velocity at the tapered part.

However, as shown in this example, if the counter electrode is not completely at ground potential but forms part of an open-ended microstrip line, the phase velocity will depend on the length of this short-circuited microstrip line. Dependent. For example 1
If the length is /4 wavelength, that part is almost short-circuited at the frequency for which matching is to be achieved, and therefore, it can be considered that the other electrode of the thin film capacitor is almost at ground potential. In that case, the phase velocity is approximately the same as that of the thin film capacitor section. However, as the length approaches O or 1/2 wavelength, it gradually approaches an open state, and as a result, the phase velocity of that part becomes
The phase velocity approaches the phase velocity on the substrate Alξ, which is the substrate.

Therefore, in a configuration where the end of the tapered part is closer to the length of 1/4 wavelength than the center, as in this example, the end is close to the phase velocity in silicon oxide, and the center The phase velocity is close to that on the alumina substrate. therefore,
The phase velocity can be increased at the end, and by setting / to a value suitable for impedance matching, impedance matching can be performed at the same time.

Note that the length of the short-circuited microstrip line to the ground corresponds to a complete ground when it is O, and a complete open when it is 1/4 wavelength long, so a length of 1/4 wavelength or less is appropriate. By selecting a suitable length, the effects of this embodiment can be obtained.

In the case of the output circuit, the process is reversed to that of its input, but as a result, the phase difference of the electrical signal occurring in the tapered part can be compensated in the same way without the thin-film capacitor and the short-circuited microstrip line. is clear. Impedance matching can also be considered in exactly the same way as the input circuit.

GaAsFE with the same performance with a gate width of approximately 4 cylinders and an output of 3W class.
Using T, we compared the performance between the structure of this example and the structure of the second conventional example.
In the conventional method, the power conversion efficiency was 15% and the linear gain was 4 dB, which was 3 4 in H2, but with the structure of this embodiment, the power conversion efficiency was 20%, and the linear gain was 4.7 clB. A significant improvement in electrical properties was observed.

A second embodiment of the invention is shown in FIG.

In FIG. 2, 101 is a field effect transistor (FE).
T), 102 is an input matching circuit board, 103 is an output matching circuit board, 104 is a main line composed of a microstrip line connected to the input terminal, and 105 is composed of a microstrip line connected to the output terminal. Main lines 106 and 107 are tapered portions provided on the transistor side of the main line. 108 is an input matching thin film capacitor whose one electrode forms a part of the tapered part; 109 is an output matching thin film capacitor whose one electrode forms a part of the tapered part; 201
are short-circuited tapered microstrip lines connected between the other electrode of the input thin film capacitor and the ground, and are connected to the ground on the lower side of the board at the end of the board, one each on the top and bottom. Reference numeral 202 denotes a short-circuited tapered microstrip line connected between the other electrode of the output matching thin film capacitor and the ground 5. The end of the microstrip line 202 is connected to the ground on the bottom side of the board at the end of the board, and one each on the top and bottom. be. Reference numeral 112 indicates wires connecting the tapered portion and the transistor, and in this embodiment, there are three wires on the input side and three wires on the output side. 1
Reference numeral 13 denotes electrode bands for connecting the tapered part and the transistor 101 by wires 112, and these bands are provided at six locations in the front part.

108 is a thin film capacitor for input matching, 109 is a thin film capacitor for output matching, and 201 is a tapered ground terminal whose one end is connected to the electrode on the side of the thin film capacitor on the human power side that is not connected to the main line. There is one each. Reference numeral 202 denotes a tapered ground terminal whose one end is connected to the electrode of the output side thin film capacitor on the side not connected to the main line, and there is one each on the upper and lower sides. 112 is a wire connecting the tapered part and the transistor;
Reference numeral 113 denotes electrode pads for connecting the output section of the thin film capacitor by wires 112, and there are six electrode pads in total.

For the input/output matching circuit board, an aluminum substrate with a dielectric constant of 9.8 is used, Cr-Au is used for the conductive parts such as the main line and microstrip line, and as a thin film capacitor, an oxidized substrate with a dielectric constant of about 90 is used. A thin film capacitor with a metal-dielectric-metal structure using titanium as a dielectric was used. Further, a GaAsFET was used as the transistor, and 14 GHz was used as the matching frequency.

In this structure, impedance matching for input matching and output matching is performed by a thin film capacitor and a short-circuited microstrip line, as in the first embodiment.

The difference from the first embodiment is the shape and dimensions of the short-circuited microstrip line section. In this case, the dielectric constant of the thin film capacitor is larger than that of the substrate, so the phase velocity in the thin film capacitor part is as slow as r''tE7(1)=0.33 times that in the tapered part. Therefore, in this case, contrary to the case of the first embodiment, the structure is such that the length of the tip short-circuited microstrip line part is longer in the part near the end of the tapered part than in the center part. By setting it as , it is possible to make the phase of the electric signal at each part the same at the part where the thin film capacitor exits.

In this embodiment, impedance matching and spatial phase difference compensation are performed using a thin film capacitor and a short-circuited microstrip line. Thin film capacitors can be created using thin film forming techniques such as chemical vapor deposition and sputtering, and can be easily fabricated on various substrates such as Al≧S substrates. Therefore, as shown in the conventional example,
Since a chip capacitor is not required, the number of mounting steps is small, and it is possible to achieve small size and high integration, and therefore, the manufacturing cost can be reduced.

Effects of the Invention As described above, the present invention provides an impedance matching circuit for transistors using a microstrip line as the main line, in which the main line on the transistor side is tapered, and a thin film capacitor is connected between the tapered part and the ground. and a tip short-circuited microphone 7, which has a series circuit of loss strip lines, and the length of the tip short-circuited microstrip line to the ground is different in each part of the thin film capacitor section, so that the position where the tip exits from the thin film capacitor section is different. This system is designed to compensate for the phase difference in high-frequency signals in the circuit, thereby matching the impedance of high-frequency, high-output transistors with low impedance, and at the same time eliminating the phase difference in the signals caused by the spatial size of the transistors. The present invention also provides a matching circuit for high-frequency, high-output transistors that requires fewer mounting steps, can be made compact and highly integrated, and is inexpensive to manufacture.

[Brief explanation of drawings]

Figure 1 is a structural diagram showing one embodiment of the present invention, Figure 2 is a structural diagram of a second embodiment of the present invention, and Figures 3 and 4 are structural diagrams of a conventional example. . 101...Transistor, 102...
Input matching circuit board, 103...Output matching circuit board, 104...Input side main line, 105...
...Output side main line, 106.107...Tapered part, 108...Thin film capacitor for manual matching 9, 109...Thin film capacitor for output matching, 1
10.111...Tip short circuit microstrip line, 112...Connection wire, 113.
...Electrode pad.

Claims (3)

[Claims] (1) In a transistor impedance matching circuit that uses a microstrip line as the main line, the main line on the transistor side is tapered, and a series circuit of a thin film capacitor and a short-circuited microstrip line is connected between the tapered part and the ground. Since the length of the short-circuited microstrip line to the ground is different in each part of the thin film capacitor section, the difference in phase of the high frequency signal at the position exiting the thin film capacitor section can be compensated for. A high-frequency transistor matching circuit characterized by: (2) As a thin film capacitor, a dielectric material with a larger dielectric constant than the substrate is used, and the length of the short-circuited microstrip line to the ground is 1/4 wavelength or less, and the closer it is to the center of the thin film capacitor, the shorter it becomes. The matching circuit for high frequency transistors according to claim 1, characterized in that: (3) As a thin film capacitor, a dielectric material with a dielectric constant smaller than that of the substrate is used, and the length of the tip short-circuited microstrip line to the ground is 1/4 wavelength or less, and the closer to the center of the thin film capacitor, the longer it is. A matching circuit for high frequency transistors according to claim 1, characterized in that: