JPH0775295B2 - High frequency transistor matching circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matching circuit for input / output of a transistor used in a high-frequency high-power amplifier, and in particular, impedance matching is performed and the impedance generated by the spatial size of the transistor is used. The present invention relates to a matching circuit for high-frequency and high-transistors that can eliminate a decrease in amplification efficiency due to a phase difference.

2. Description of the Related Art The input / output impedance of high frequency transistors does not generally match the characteristic impedance (50 ohms) of the main line microstrip line. In order to efficiently amplify the electric signal, it is preferable that the input / output impedance of the transistor and the impedance of the main line microstrip line for each input / output match as much as possible and the reflection at that point is as small as possible. Especially, the input / output impedance of the transistor for high frequency and high output 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 achieve impedance matching. Impedance of open 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 L is given by the length of the microstrip line.

Therefore, Zos becomes smaller as βL becomes π / 2, that is, L approaches λ / 4, and by choosing an appropriate value,
It can be matched with the transistor.

A typical configuration of a conventional high frequency amplifier by this method is
Shown in the figure.

In FIG. 3, 101 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 an input terminal, 105 is a main line composed of a microstrip line connected to an output terminal, 106 and 107 are provided on the transistor side of the main line, This is a so-called tapered portion in which the width of the electrode gradually increases. 112 is a wire connecting the transistor and the tapered portion,
Reference numeral 301 is an island-shaped electrode (pad) for input / output matching adjustment, and 302 is a wire for connecting the tapered portion and the adjustment pad. In this structure, adjustment of the input matching circuit and the output matching circuit is performed by connecting the 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 composed of a microstrip line connected to an input terminal, and 105 is Main lines composed of microstrip lines connected to the output terminals, and 106 and 107 are tapered parts provided on the transistor side of the main lines. 403 is an input impedance matching chip capacitor, 404 is an output impedance matching chip capacitor, the lower electrode is connected to the grounded pedestal, and the upper electrode is a wire and is the main part of the transistor and the input / output matching adjustment circuit board. The line is connected to the microstrip line tapered section. 40
Reference numerals 5 and 406 denote wires that connect the transistor, the chip capacitor, and the tapered portion. In this structure, the input / output matching is performed by the inductance of the chip capacitor and the wire connecting it.

DISCLOSURE OF THE INVENTION 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 the electric signal in the tapered portion, and particularly the signal. It is insufficient as a matching circuit for high-frequency and high-power FETs with a gate width that cannot be ignored compared to the wavelength.
For example, at 14 GHz, the length corresponding to 1/4 wavelength on the alumina substrate or GaAs substrate is about 2 mm, while
The gate width of GaAs FET for obtaining 3W output is about 4mm. Therefore, a considerable phase difference occurs between the electric signal passing through the central portion and the electric signal passing through the end portion of the tapered type portion shown in FIG. 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. The tapered section at the output further promotes its adverse effects.

With the matching method using the open stub shown in the first conventional example, it is quite difficult to match the high-frequency and high-output FETs with low input / output impedance, and 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.
Since the chip is mounted in the manufacturing process, the number of steps is increased, and since the chip mounting portion is separate, miniaturization and high integration are difficult, and as a result, the manufacturing cost is increased.

As a method of matching while eliminating the spatial phase difference, 1 /
So-called power dividers and power combiners using an impedance converter of four wavelengths are known, and are generally used in power amplifiers of several W or more. But at least 1/4
Since an impedance converter having a wavelength length 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 a transistor that uses a microstrip line as a main line, in which the transistor-side main line is tapered, and the taper-shaped portion and ground are provided. A thin film capacitor made of a dielectric material having a dielectric constant different from that of the substrate, and the length of the thin film capacitor part in the traveling direction of the high frequency signal is different in each part of the taper-shaped part, By compensating for the phase difference of the high-frequency signal at the position where the capacitor section exits, impedance matching with the transistor is achieved and at the same time the spatially generated phase difference is eliminated.

Operation The present invention has the above-described configuration and is capable of simultaneously performing impedance matching of a high-frequency and high-output transistor having a low impedance and a large size and compensating for a spatial phase difference. Further, the number of mounting steps is small, and the size and integration are small. The present invention provides a matching circuit for high-frequency and high-power transistors, which can be manufactured at low cost and is inexpensive to manufacture.

Embodiments Embodiments of a matching circuit for a high frequency transistor according to the present invention will be described below with reference to the drawings.

FIG. 1 shows one embodiment of the structure of a matching circuit for high-frequency transistors according to the present invention. In FIG. 1, 101
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 an input terminal, 105
Is a main line composed of a microstrip line connected to an output terminal, and 106 and 107 are tapered portions provided on the transistor side of the main line. Reference numeral 108 denotes an input matching thin film capacitor whose one electrode constitutes a part of the taper type portion, and 109 denotes an output matching thin film capacitor whose one electrode constitutes a part of the taper type portion, 110, 1.
Reference numeral 11 is a ground terminal connected to the other electrode of the thin film capacitors 108 and 109, and 112 is a wire connecting the tapered portion and the transistor 101.

The input / output matching circuit board uses an alumina ceramic board,
Cr-Au is used for the conductive parts such as the main line and the microstrip line, and the dielectric constant is about 4 as a thin film capacitor.
A thin film capacitor having a metal-dielectric-metal structure using silicon oxide as a dielectric was used. GaAs FET was used as the transistor and 14 GHz was used as the 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 this structure, impedance matching of input matching and output matching is performed by the thin film capacitors 108 and 109.

The matching method in this method will be described in more detail. As mentioned above, the input / output impedance of the high power FET is several ohms to less than 1 ohm, which is considerably lower than the impedance of the main line, 50 ohms. Therefore, in this embodiment, a thin film capacitor is inserted between the main line microstrip line and the ground in order to achieve the matching. Assuming that the length of the microstrip line to the ground is L, the impedance Zin of this series circuit is Zin = 1 / jωC + jZo · tanβL (2) = −j (1 / ωC−Zo · tanβL) (3) 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, and λ is the wavelength of the frequency to be matched in the substrate , L is the length of the microstrip line to ground.

It is represented by.

The effect of the microstrip line to the ground can be almost ignored if the width is sufficiently wide and the length is short, and it is substantially determined by the value of the electrostatic capacitance C, and by appropriately selecting it, It is easy to set the value of Zin to several ohms or less than 1 ohm.

Next, the operation of the spatial phase difference compensation of this embodiment will be described. The electric signal having the same phase up to the taper start portion spreads along the taper in the taper type portion and reaches the thin film capacitor portion. Usually, the end of the taper-shaped part has a longer distance than the center part, and in the case of the first embodiment,
Set so that the distance from the end to the thin film capacitor is longer. The electric signal that has entered the thin film capacitor is
Since the dielectric constant of thin film capacitors is different from that of the substrate,
Therefore, the phase velocity changes. Since the phase velocity is inversely proportional to the square root of the dielectric constant, the smaller the dielectric constant, the faster the phase velocity. The substrate on which the microstrip line is formed is an alumina substrate, and the dielectric constant of which is 9.8. On the other hand, the dielectric constant of the thin film capacitor is 4. Therefore, the phase velocity in the thin film capacitor is It is twice as fast as the phase velocity in the taper type part. Therefore, by making the length of the thin film capacitor part at the end appropriately longer than the length of the thin film capacitor at the center part, the taper type part can recover the phase delay at the end part that occurs before reaching the thin film capacitor. If the length of the microstrip line from the thin film capacitor to the transistor and the length of the connecting wire are the same, the phase difference of the electric signal can be completely eliminated at the input part of the transistor. . At that time, by setting the capacitance of the thin film capacitor to a value suitable for impedance matching,
Impedance matching can also be performed at the same time.

In the case of the output circuit, the reverse process is followed, but if there is no thin film capacitor as a result, the phase difference of the electric signal generated at the end and the center of the taper type part will be the same with the thin film capacitor. It is clear that we can compensate. The impedance matching can be considered in exactly the same way as the input circuit.

A GaAs FET having a gate width of about 4 mm and an output of 3 W class and having the same performance was used to compare the performance of the structure of this example with the structure of the second conventional example. In the method of 14), the power conversion efficiency was 15% and the linear gain was 4 dB at 14 GHz. However, by adopting the structure of this embodiment, the power conversion efficiency is 25% and the linear gain is 5 dB, which is a remarkable improvement in electrical characteristics. It was observed.

The second embodiment of the present invention is shown in FIG.

In FIG. 2, 101 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 microstrip lines connected to inputs, 105 is a main line composed of microstrip lines connected to output terminals, and 106 and 107 are tapers provided on the transistor side of the main lines. It is a mold part. 201 is a thin film capacitor for input matching, 202 is a thin film capacitor for output matching, 110 and 111 are ground terminals connected to the other electrode of the thin film capacitor, and 112 is a wire connecting the tapered portion and the transistor.

An alumina substrate with a permittivity of 9.8 was used for the input / output matching circuit substrate, Cr-Au was used for the conductive parts such as the main line and microstrip line, and titanium oxide with a permittivity of about 90 was used as the dielectric for the thin film capacitor. The metal-dielectric-metal thin film capacitor used as was used. Also, GaAs FET is used as a transistor, and the matching frequency is 14 GHz.
Was used.

In this structure, input / output impedance matching is performed by the thin film capacitors 201 and 202 as in the first embodiment.

The difference from the first embodiment is the dielectric constant of the thin film capacitor and the shape and size of the thin film capacitor portion. In this case, the dielectric constant of the thin-film capacitor is larger than that of the substrate, and therefore the difference speed in the thin-film capacitor part is And slow down. Therefore, in this case, contrary to the case of the first embodiment, the thin film capacitor portion has a structure in which the length closer to the end of the taper-shaped portion is shorter than that of the central portion. The phase of the electric signal in the part where the capacitor is exposed can be made the same in each part.

In this embodiment, impedance matching and spatial phase difference compensation are performed by a thin film capacitor. The thin film capacitor can be manufactured by a thin film forming technique such as chemical vapor deposition or sputtering, and can be easily integrated and manufactured on various substrates such as an alumina substrate. Therefore, unlike the conventional example, since the chip capacitor is not required, the number of mounting steps is small, the size and the degree of integration can be reduced, and the manufacturing cost can be reduced.

As described above, according to the present invention, in the transistor impedance matching circuit using the microstrip line for the main line, the transistor-side main line is tapered, and the substrate is provided between the tapered part and the ground. Having a thin film capacitor composed of dielectrics having different dielectric constants, the length of the thin film capacitor in the traveling direction of the high frequency signal,
By making each part of the taper-shaped part different, the phase difference of the high-frequency signal is compensated at the position where the thin-film capacitor part exits, and thereby impedance matching of a high-frequency high-power transistor with low impedance is achieved. At the same time, the phase difference between the signals caused by the spatial size of the transistor is eliminated, and the number of mounting steps is small, which enables small size and high integration. A matching circuit is provided.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention, FIG. 2 is a structural diagram of a second embodiment of the present invention, and FIGS. 3 and 4 are structural diagrams of a conventional example. . 101 …… transistor, 102 …… input matching circuit board, 103
Output matching circuit board, 104 Input main line, 105
Output side main line, 106, 107 ... tapered part, 108 ... input matching thin film capacitor, 109 ... output matching thin film capacitor, 110,111 ... ground terminal, 112 ... connection wire.

Claims (3)

[Claims] 1. In a transistor impedance matching circuit using a microstrip line as a main line, a transistor-side main line is tapered, and a dielectric material having a different dielectric constant from that of a substrate is provided between the taper-shaped portion and ground. Since the length of the thin film capacitor portion in the traveling direction of the high frequency signal is different in each part of the taper-shaped portion, the phase difference of the high frequency signal at the position where the thin film capacitor portion exits A matching circuit for high-frequency transistors, characterized in that 2. As the thin film capacitor, a dielectric having a dielectric constant smaller than that of the substrate is used, and the length of the thin film capacitor in the traveling direction of the high frequency signal becomes shorter as it gets closer to the central portion of the tapered portion. The matching circuit for a high frequency transistor according to claim 1, characterized in that: 3. A thin film capacitor having a dielectric constant larger than that of a substrate is used, and the length of the thin film capacitor in the traveling direction of a high frequency signal becomes longer as it gets closer to the central portion of the tapered portion. The matching circuit for a high frequency transistor according to claim 1, characterized in that: