JPH0366203A - Matching circuit for high frequency transistor - Google Patents

Abstract

PURPOSE:To avoid the spatial phase difference and also to take impedance matching of a transistor(TR) while differentiating the length up to the tip of a tip open microstrip line from each part of thin film capacitors by forming a tapered main line at a TR side and providing a series circuit comprising a thin film capacitor and the tip open microstrip line. CONSTITUTION:TR side main lines 104, 105 are formed to be taper lines 106, 107 in an impedance matching circuit of a TR using a microstrip line to a main line, and a series circuit comprising a thin film capacitor 108 and the tip open microstrip line 111 is provided in parallel with the tapered parts and the length up to the tip of the tip open and short-circuit microstrip line is differentiated from each part of the thin film capacitor. Thus, the difference from the phase of a high frequency signal is compensated at a position after the said thin film capacitor and then the impedance matching of a high frequency high output TR with a low impedance is taken and also the phase difference caused by the physical size of the TRs is eliminated.

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 and output impedances of high frequency transistors generally do not match the characteristic impedance (50 ohms) of the main line microstrip line. In order to efficiently amplify electric 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 reduced as much as possible. In particular, the human 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) However, 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 second section.
As shown in the figure.

In FIG. 2, 101 is a field effect transistor (FE).
T), 102 is a manual matching circuit board, 103 is an output matching circuit board, 104 is a main line composed of a microstrip line connected to an input terminal, and 105 is composed of a microstrip line connected to an output terminal. 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; 201 is an island-shaped electrode (pad) for input/output matching adjustment; and 202 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. 3, 101 is a field effect transistor (FET), 301 is an input matching adjustment circuit board, 302 is an output matching adjustment circuit board, 104 is a main line composed of a microstrip line connected to an input terminal, and 105 is a main line composed of a microstrip line connected to an input terminal. A main line constituted by a microstrip line connected to an output terminal, 106 and 107 is a tapered portion provided on the transistor side of the main line.

303 is a chip capacitor for input impedance matching,
304 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. 305 and 306 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 Al5 substrate or a G
The length corresponding to 1/4 wavelength on the aAs substrate is approximately 2ni
m, and on the other hand, G a A to obtain an output of 3 W
The gate width of sFET is approximately 4 cabinets. 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 and the amplification efficiency is reduced. A tapered section at the output section further exacerbates this negative effect.

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 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 that uses a microstrip line as the main line. The thin film capacitor part has a series circuit of a thin film capacitor and an open-ended microstrip line, and the length to the tip of the open-ended microstrip line is different in each part of the thin film capacitor part. By compensating for the difference in phase of the high frequency signal at the position, impedance matching with the transistor can be achieved and at the same time phase difference that occurs spatially can be eliminated.

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 the high frequency transistor matching circuit of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the structure of a matching circuit for a high frequency transistor 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.

Reference numeral 111 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. 112 is a wire connecting the tapered part and the transistor;
In this example, the input (!l!l 3 trees, the output (!l!)
There are 3 trees.

The input/output matching circuit board uses an aluminum alloy 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 GaAsFET was used as a transistor, and 14GH2 was used as a matching frequency. If the dielectric constant of the substrate to which aluminum is attached 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 the tree method will be explained in more detail. As mentioned above, the output impedance of a 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
-2πf 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 174 wavelengths, cotβL becomes O 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. The phase velocity is inversely proportional to the square root of the dielectric constant if the opposing electrode of the thin film capacitor is completely at ground potential. Therefore, the phase velocity at the thin film capacitor section is 1. r King 17T; 1 2 1.57 times faster than the phase velocity in the tapered part.

However, as shown in this example, if the counter electrode is not at perfect ground potential (and forms part of an open-ended microstrip line), the phase velocity is determined by the length of this short-circuited microstrip line. Depends on, 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 0 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 that on an alumina substrate, which is a hollow substrate.

Therefore, in a tank bottom where the length of the tapered part end is closer to 1/4 wavelength than the center part as in this example, the end part is close to the phase velocity in silicon oxide. The phase velocity at the center is close to that on the alumina substrate. therefore,
The end portion can have a higher phase velocity, thereby recovering the phase lag at the tapered portion. By making the length of the microstrip line from the thin-film capacitor to the transistor the same as the length of the connecting wire, it is possible to completely eliminate the phase difference in the electrical signal at the input of the transistor. At this time, by setting the impedance of the series circuit of the thin film capacitor and the open-ended microstrip line to a value suitable for impedance matching, impedance matching can be achieved at the same time.

Note that when the length of the open-end microstrip line is 0 or 1/2 wavelength, it is completely open, and when it is 1/4 wavelength, it is completely short. By selecting an appropriate length, the effects of this embodiment can be obtained.

In the case of the output circuit, the course is reversed as in the case of its input, but as a result, without thin film capacitors and open-ended microstrip lines, the phase difference of the electrical signal produced in the tapered section can be kept the same. It is clear that compensation is possible. Impedance matching can also be considered in exactly the same way as the input circuit.

GaAs with the same performance with a gate width of approximately 4rMl and an output of 3W class.
When we compared the performance using FETs using the structure of this embodiment and the structure of the second conventional example, we found that the conventional method achieved a power conversion efficiency of 15% at 14GH2. , the linear gain was 4 dB, but by using the structure of this example, the power conversion efficiency was 21% and the linear gain was 4.8 dB, which was a significant improvement in terms of electrical characteristics.

When a material having a higher dielectric constant than the substrate, such as titanium oxide, is used as the dielectric for the thin film capacitor, the relationship between the phase velocities is opposite to that of the first embodiment. In this case, the phase velocity in the thin film condenser part is 33 times slower than that in the tapered part. To,
The length of the open-ended microstrip line is close to 1/4 wavelength in the part near the center of the tapered part, and the length is close to 0 in the part near the end of the tapered 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 example, only examples of characteristics are shown as structures of a thin film capacitor and an open-ended microstrip line, but it is clear that there are various other modified structures that can obtain the effects of the present invention. .

The structure of this embodiment is advantageous for integration, since it is not necessary to ground the thin film capacitor and it can be formed almost anywhere on the substrate. In addition, the dimensions and shape of the tapered part, the location where the thin film capacitor is formed, and the film thickness are adjusted so that the capacitance of the thin film capacitor required for matching and the length of the open-ended microstrip line at the exit of the thin film capacitor are set to appropriate values. You can choose.

In this embodiment, impedance matching and spatial phase difference compensation are performed using a thin film capacitor and an open-ended microstrip line. The thin film capacitor 5 6 can be produced by a thin film forming technique such as chemical vapor deposition or sputtering, and can be easily fabricated integrally on various substrates such as an alumina substrate. therefore,
Since a chip capacitor as shown in the conventional example is not required, the number of mounting steps is small, and compactness and high integration are possible, resulting in low manufacturing costs.

Effects of the Invention As described above, the present invention provides an impedance matching circuit for a transistor 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 in parallel to the tapered part. It has a series circuit of open-ended microstrip lines,
The length to the tip of the open-ended short-circuited microstrip line is different in each part of the thin film capacitor section, so that the difference in phase of the high frequency signal at the position exiting the thin film capacitor section is compensated for. This achieves impedance matching for high-frequency, high-output transistors with low impedance, and at the same time eliminates signal phase differences caused by the spatial size of the transistors.It also requires fewer mounting steps and is highly integrated. The present invention provides a matching circuit for high-frequency, high-output transistors that can be manufactured at low manufacturing cost.

[Brief explanation of drawings]

Figure 1 is a structural diagram showing one embodiment of the present invention, Figures 2 and 3 are
The figure shows a structural diagram of a conventional example. 101...Transistor, 102...
Manual 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 input matching, 109 ... Thin film capacitor for output matching, 11
0.111...Open-ended microstrip line, 112...Connection wire.

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 an open-ended microstrip line is connected in parallel to the tapered part. and the length to the tip of the open-ended microstrip line is different in each part of the thin film capacitor section, so that a difference in phase of the high frequency signal at a position exiting the thin film capacitor section is compensated for. A high-frequency transistor matching circuit characterized by: (2) As a thin film capacitor, a dielectric material having a larger permittivity than the substrate is used, and the length to the tip of the open-ended microstrip line is closer to the length of a quarter wavelength as it is closer to the center of the thin film capacitor; 2. The high frequency transistor matching circuit according to claim 1, wherein the value becomes closer to 0 closer to the end. (3) As a thin film capacitor, a dielectric material with a dielectric constant smaller than that of the substrate is used, and the length to the tip of the open-ended microstrip line approaches the length of a quarter wavelength as it approaches the end of the thin film capacitor. , Claim (1) characterized in that the closer to the center, the closer the length is to 1/2 wavelength.
) matching circuit for the high-frequency transistor described.