JPH0366210A - 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 a matching circuit for high-frequency transistors that can easily and inexpensively adjust the input and output impedances of transistors used in high-frequency, high-output amplifiers.

The human output impedance of conventional high frequency transistors generally does 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 input/output impedance of high-frequency, high-output transistors is 5
Since it is much lower than 0 ohm, a low impedance element is usually inserted in parallel with the input/output main line microstrip line to match the impedance. The impedance, Zos, of an open-terminated microstrip line (open stub) is: Zos--j-cot βL (1) However, β = 2π/λ λ is the wavelength on the microstrip line at the frequency to be matched ( Inner wavelength) L 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).
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 line, 106 is a wire connecting the transistor and the input matching circuit board, 107 is a wire connecting the transistor and the output matching circuit board, 301 is an open stub forming an input matching circuit, 302 is forming an output matching circuit 303.304 is an island-shaped electrode (pad) for adjusting the length of the open stub, 3
05.306 is a wire for connecting the open stub and the adjustment pad. In this structure, the manual matching circuit and the output matching circuit are adjusted by connecting an adjustment pad to the open stub with a wire, thereby substantially adjusting the length of the open stub.

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 a manual 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 a main line composed of a microstrip line connected to an input terminal. The main line consists of a microstrip line connected to the output terminal, 403 is a chip capacitor for human impedance matching, 404 is a chip capacitor for output impedance matching, and the lower electrodes of both chip capacitors 403 and 404 are grounded. The upper electrode is connected by a wire to the transistor and the main line microstrip line of the input/output matching adjustment circuit board. 405 and 406 are wire wires 407 connecting the transistor and the chip capacitor.
．． 408 is a wire connecting the chip capacitor and the main line microstrip line of the input/output matching adjustment circuit board. 409.410 is a pad for adjusting input/output matching, and 411412 is a wire for connecting the main line microstrip line and the adjustment pad. In this structure, input/output matching is performed primarily by the inductance of the chip capacitor and the wire connecting it, and is supplemented by connecting adjustment pads with wires on the input/output matching adjustment circuit board. Is going.

Problems to be Solved by the Invention However, with the adjustment method shown in the first conventional example, it is difficult to match high frequency, high output FETs with low impedance. The impedance of the main line is generally 50 ohms, whereas the impedance of high frequency, high output FETs is generally several ohms or less than 1 ohm.

Therefore, in order to match this, it is necessary to insert a capacitor with a considerably large capacitance between the main line and the ground. In order to achieve this with the open stub shown in Example 1, the length of the open stub must be very close to 1/4 wavelength of the frequency to be matched, as can be easily seen from equation (1). It needs to be long. However, the impedance of the open stub is cotβ
L, and in the vicinity of 1/4 wavelength, even if the stub length changes slightly, its value changes greatly, making actual adjustment extremely difficult. Therefore, the method of the first embodiment is not suitable for matching high frequency, high power FET (FET) transistors.

In addition, in the case of the configuration described in the second conventional example, since a large chip capacitor is connected, it is easier to match with a high frequency, high output FET with low impedance than in the first conventional example, but the capacitance of the chip capacitor Therefore, it is necessary to form an open stub on the input/output matching circuit board and finely adjust the matching by adjusting the length of the open stub. In addition, matching capacitors are inserted between the main line and the ground, so in order to reduce signal transmission loss, they must have extremely low dielectric loss and other losses as a capacitor, so they are inevitably expensive. Become something. Furthermore, mounting the chips during manufacturing increases the number of man-hours, and since a separate part is required for mounting the chips, it is difficult to achieve small size and high integration, resulting in high manufacturing costs.

Means for Solving the Problems In order to solve the above problems, the present invention has a transistor input/output impedance matching circuit that includes a series circuit of a thin film capacitor or an interdigital capacitor and an open-terminated microstrip line in parallel with the main line, By utilizing the fact that this open-terminated microstrip line can be considered to be electrically shorted at 1/4 wavelength of the frequency from the open end, that is, at the electrode end opposite to the main line connection electrode of the capacitor, the connection with the transistor is made. This allows the consistency state to be adjusted.

Effect The present invention has the above-described configuration, which makes it easy to match high-frequency, high-output transistors with low impedance.
Further, the present invention provides a high-frequency transistor matching circuit that can reduce signal transmission loss due to loss of a matching capacitor, requires fewer mounting steps, can be integrated in a small size, and is inexpensive to manufacture.

Embodiments Hereinafter, embodiments of a matching circuit for a high frequency amplifier 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. In Figure 1, 10
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 line connected to the output terminal. A main line constituted by a strip line; 106 is a wire connecting the transistor and the input matching circuit board; 1;
07 is a wire connecting the transistor and the output matching circuit board, (08 is a thin film capacitor for input matching, 1
09 is a thin film capacitor for output matching, 110.111 is an open-ended microstrip line whose one end is connected to the electrode on the side of the thin film capacitor that is not connected to the main line, and its length is 1/4 wavelength. There is. 112 is an island-shaped electrode provided near the open-ended microstrip line. The input/output matching circuit board uses a ceramic substrate such as Al5, the conductive parts such as the main line and microstrip line use the commonly used Cr-Au, and the thin film capacitor uses silicon oxide as the dielectric. A thin film capacitor with a metal-dielectric-metal structure was used.

Further, a GaAsFET was used as the transistor, and 14C; Hz was used as the matching frequency.

If the dielectric constant of the substrate Al≧ is 9.8, then 14GH2
The length of the microstrip line corresponding to 1/4 wavelength is approximately 2 mm.

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 series circuit of a thin film capacitor and an open-ended microstrip line is inserted in parallel with the main line microstrip line in order to achieve the matching. The impedance of this series circuit, Zin, is Z tn=1/jωc-jZo-co tβL(2
)=j(1/ωc+Zo-cotβL) (3)
However, ω-2πf β-2π/λ f is the frequency to be matched, 0C is the capacitance of the thin film capacitor, Zo is the characteristic impedance of the microstrip line, and λ is the substrate at the frequency to be matched. The wavelength within, L, is expressed by the length of the microstrip line.

Since L is 1/4 wavelength of the tube wavelength at the frequency to be matched, the second term in equation (3) becomes 0, so that only the value of the thin film capacitor can be seen as Zin. Therefore, by adjusting the capacitance C, it is easy to reduce the value of Zin to several ohms or 1 ohm or less.

Furthermore, by connecting the open-ended microstrip line to an island-shaped electrode provided nearby, the second term in equation (3) can be changed, resulting in the impedance of the series circuit of the open-ended microstrip line and the thin film capacitor. It is possible to adjust.

In this example, the value of the thin film capacitor is set from the beginning to a value that is considered to be closely matched, and the mismatching due to variations in transistor characteristics and variations in the manufacturing process of the thin film capacitor is corrected by using an open-terminated microstrip line. The impedance of the series circuit of the thin film capacitor and the open-terminated microstrip line as seen from the main line microstrip line can be changed by connecting the surrounding island-shaped electrodes, or it can be adjusted by setting an open stub on the main line microstrip line. be able to.

Furthermore, as can be seen from equation (3), by appropriately selecting the length of the microstrip line, the value of the capacitance of the matching capacitor can be selected to be extremely small. This means that the electrode area of the matching capacitor can be made extremely small, and therefore the loss of the capacitor that is proportional to the electrode area can be made extremely small. And vice versa,
This means that it can be used even if the loss characteristics of the capacitor are slightly worse than those of conventional capacitors, and in that case, the cost will be reduced. Another possibility is to ground the electrode end on the opposite side of the main line connection electrode 1 2 of the thin film capacitor, but in the case of a microstrip line board, there is no ground electrode on the board surface, so it is better to connect the strip line to ground at the end face of the board. , it is necessary to open a via hole, and there are restrictions on where to form the thin film capacitor. However, with this method, thin film capacitors can be formed anywhere within the substrate, which is thought to increase the degree of freedom in designing the impedance matching circuit.

In this embodiment, the input and output matching circuits are matched using the same method, but since the output impedance is generally higher than the human impedance, the method of this embodiment may be used only for input matching.

FIG. 2 shows another embodiment in which an interp or digital capacitor is used instead of a thin film capacitor. In this case, only the input end is shown, but it is obvious that the output side can also be configured in the same way.

In Figure 2, ・101 is a field effect transistor (F
ET), 102 is a manual matching circuit board, 104 is a main line composed of a microstrip line connected to an input terminal, 106 is a wire connecting the L transistor and the input matching circuit board, 201 is a manual matching interface. The digital capacitor 110 is an open-ended microstrip line whose one end is connected to the electrode of the interdigital capacitor on the side not connected to the main line, and its length is 1/4 wavelength. 112 is an island-shaped electrode provided near the open-ended microstrip line.

For the input/output matching circuit board, a ceramic board such as Algosu was used, and for the conductive parts such as the main line and the microstrip line, commonly used Cr-Au was used. Further, a 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 a microstrip line corresponding to 1/4 wavelength at 14 GHz is about 2M.

As in the first embodiment, it is easy to reduce the value of Zin to several ohms or 1 ohm or less by adjusting the capacitance of the interdigital capacitor. In addition, by installing an open-ended microstrip line nearby and connecting it to the cut-off island electrode, the second term in equation (3) can be changed, and as a result, the difference between the open-ended microstrip line and the interdigital capacitor can be changed. It is possible to adjust the impedance of the series circuit. Even if an interdigital capacitor is used as in the case of a thin (thin) imitation capacitor, integration is easy, and loss as a capacitor can be reduced by not reducing the area of the opposing electrode portion, and the present invention also The desired effect can be obtained.

Effects of the Invention As described above, the present invention provides a series circuit of a thin film capacitor or an interdigital capacitor and an open-terminated microstrip line in parallel with the main line, and connects the open end of the open-terminated microstrip line to 1/1 of the frequency. By utilizing the fact that an electrical short can be considered to occur at the fourth wavelength, that is, at the electrode end opposite to the main line connecting electrode of the main line microstrip line of the thin film capacitor or interdigital capacitor, this terminated open group 5 microstrip line can be By connecting it to an island-shaped electrode, the length can be changed and the matching state with the transistor can be adjusted.This makes it easy to match high frequency, high output transistors with low impedance, and is suitable for matching. Signal transmission loss due to capacitor loss can be reduced, and the number of mounting steps is reduced.
The present invention provides a high-frequency transistor matching circuit that can be integrated in a small size and is inexpensive to manufacture.

[Brief explanation of drawings]

FIG. 1 is a basic structural diagram showing one embodiment of the present invention, FIG. 2 is a structural diagram of another embodiment using the first basic configuration, and FIG.
FIG. 4 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, 106.107.114.115・
... wire, 108 ... thin film capacitor for input matching, 109 ... thin film capacitor for output matching, 110 ... open-terminated microstrip 6 pline for manual matching, 111... Open-terminated microstrip line for output matching, 112... Island electrode.

Claims (2)

[Claims] (1) In a transistor impedance matching circuit that uses a microstrip line as the main line, a series circuit of a thin film capacitor or an interdigital capacitor and an open-terminated microstrip line is installed in parallel with the main line, and this microstrip line matches the impedance. 1 of the channel wavelength at the frequency to be
A high-frequency transistor matching circuit characterized by having a /4 wavelength. (2) By providing an island-shaped electrode near the open-terminated microstrip line and connecting this island-like electrode to the open-terminated microstrip line, the impedance of the series circuit of the thin-film capacitor or interdigital capacitor and the open-terminated microstrip line can be reduced. 2. The high frequency transistor matching circuit according to claim 1, wherein the matching circuit can be changed.