JPH0366206A - High frequency transistor matching circuit - Google Patents

Abstract

PURPOSE:To device the circuit such that the matching state with a transistor(TR) is adjusted over a wide range by increasing each stage susceptance of circuits connected in series toward the TR and decreasing the length of a microstrip line between the stages toward the pre-stage. CONSTITUTION:The circuit consists of input matching thin film capacitors 108, 109, 110, output matching thin film capacitors 111, 112, and tip open microstrip lines 113, 114, 115, 116, 117 connecting to an electrode of the thin film capacitors not connecting to a main line, and the susceptance comprising the matching thin film capacitors and the capacitance of the tip open microstrip lines is increasing toward the pre-stage. Moreover, the length of each inter-stage microstrip line is decreasing toward the pre-stage. The input matching and the output matching are adjusted by selecting the static capacitance of the thin film capacitors 108-112 and the length of the tip open microstrip lines 113-117.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a matching circuit for high-frequency transistors that can easily adjust the matching state of the human output of transistors used in high-frequency, high-output amplifiers over a wide band, with little loss, and at low cost. It is something.

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 an electric signal, it is preferable that the input/output impedance of the transistor and the impedance of the input/output main line microstrip line match as much as possible so that reflection at that point is minimized. In particular, the human output impedance of high-frequency, high-output transistors is
Since it is much smaller 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. , L is 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 fifth section.
As shown in the figure. In FIG. 5, 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, and 105 is an output terminal. 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; 501
502 is an open stub that forms an input matching circuit, 502 is an open stub that forms an output matching circuit, 503.504 is an island electrode (pad) for adjusting the length of the open stub, and 505.506 is an open stub and for adjustment. This is the wire for connecting the pads. In this structure,
The input matching circuit and output matching circuit can be adjusted by connecting the adjustment pad to the open stub with a wire.
This is essentially done by 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. 6, 101 is a field effect transistor (FET), 601 is an input matching adjustment circuit board, 602 is an output matching adjustment circuit board 104 is a main line composed of a microstrip line connected to the input terminal, and 105 is an output The main line consists of a microstrip line connected to the terminal, 603 is a chip capacitor for input impedance connection, 604 is a chip capacitor for output impedance matching, and the lower electrodes of both chip capacitors 603 and 604 are grounded. It is connected to the top of the pedestal, and 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. 605.606 are wires connecting the transistor and the chip capacitor, 607.
608 is a wire connecting the chip capacitor and the main line microstrip line of the input/output matching adjustment circuit board.

609.610 is a pad for adjusting input/output matching,
611 and 612 are wires 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.

Adjustment becomes even more complex when attempting to extend the range of matching frequencies even further. Generally, in order to widen the matching frequency band, according to the method of the first embodiment, a plurality of open stubs are provided at appropriate positions. In the case of the method of the second embodiment, the number of matching chip capacitors is increased to widen the band. In reality, the optimum value is determined experimentally, or the optimum value is determined by a computer using nihon rayon or the like.

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, as can be easily seen from equation (1), the length of the open stub must be set to approximately 1/4 wavelength of the frequency to be matched. It needs to be close in length. 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 becomes thick (changes), making actual adjustment extremely difficult.Therefore, the method of the first embodiment is not suitable for matching transistors (high-frequency, high-output FETs).

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 ground, so in order to reduce signal transmission loss, the capacitor must have extremely low loss such as dielectric loss, and as a result, it is inevitably expensive. becomes. 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.

Furthermore, when attempting to widen the band, it is necessary to make decisions experimentally or perform computer simulations, which requires a great deal of time and effort, leading to an increase in costs.

Means for Solving the Problems In order to solve the above problems, the present invention provides a series circuit of a thin film capacitor or an interdigital capacitor and an open-ended micros I lip line in parallel to the main line in a transistor input/output impedance matching circuit. There are multiple sets, and the susceptance of the series circuit is larger as it is closer to the transistor, and the length of the microstrip line between each stage is shorter, so that the matching state with the transistor can be adjusted over a wide band. This is how it was done.

Effect The present invention has the above-described configuration, which makes it easy to match high-frequency, high-output transistors with low impedance.
In addition, it is possible to reduce the signal transmission loss due to the loss of the matching capacitor, and it also requires fewer mounting steps, allows for compact integration, and has low manufacturing costs. It provides:

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 (F B "F'), 102
is an input matching circuit board, 103 is an output matching circuit board, 10
4 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 is a wire connecting the transistor and the input matching circuit board. , 107 is a wire 10B connecting the transistor and the output matching circuit board, 109.110 is a thin film capacitor for input matching, 111 and 112 are thin film capacitors for output matching,
113.114.115.116.117 is an open-ended microstrip line connected to the electrode on the side of the thin film capacitor that is not connected to the main line.

The input/output matching circuit board uses Alkusuna's ceramic board, Cr-Au is used for the conductive parts such as the main line and microstrip line, and the thin film capacitor is made of metal using silicon oxide as the dielectric. A thin film capacitor with a dielectric-metal structure was used. Also, as a transistor, Ga
14 as the center frequency to also match the As FET.
GHz was used. When the dielectric constant of the substrate ξ is 9.8, the length of the microstrip line corresponding to 1/4 wavelength at 14 GHz is about 2 mm.

In this structure, the input matching and output matching adjustments are
The size of the capacitance of the thin film capacitors 108-112,
This is done by setting the length of the open-end microstrip line 113117 to an appropriate value.

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 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: 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, and λ is the frequency within the substrate to be matched. The wavelength, L, is the length of the microstrip line.

It is expressed as Therefore, as can be seen from equation (3), by appropriately selecting the capacitance C and the length L of the microstrip line, it is easy to reduce the value of Zin to several ohms or 1 ohm or less. be. Note that cotβ is 0 when the length is 1/4 wavelength, and Zin
is determined only by the capacitance C.

In this implementation series, in order to widen the matching frequency range, that is, to widen the band, the number of stages of matching thin film capacitors and open-ended microstrip lines is increased. The effect will be explained using the so-called progress chart shown in FIG. Figure 2 is a Smith chart, especially displayed in terms of attrition. The normalized impedance is set to 50 ohms. Therefore, the center point C of the circle corresponds to an impedance of 50 ohms, and therefore matching is achieved when the impedance of the matching circuit reaches this point, that is, 50 ohms. The left end of the circle, point S, corresponds to 0 ohm, or in other words, a short circuit. The right end of the circle, point 0, corresponds to the impedance, ■, in other words, the oven. A circle A passing through points S and E in FIG. 2 represents a circle with a conductance of 1. Also, the song vAE is susceptance, l
The left side of this curve represents a susceptance of 1 or more. The input/output impedance of a high frequency, high power transistor is 1 ohm or less, and is usually a circle A.
A value near point S is taken at a point inside , for example, point X1. When considered on the schedule chart, matching is equivalent to moving point X to point C using a matching circuit. A typical example is a matching method corresponding to curves Pl and C1 that reach point C via point Y on the circular hole. Pl is the amount of phase rotation and corresponds to the length of the microstrip line connected in series between the transistor and the matching capacitor, and CI corresponds to the susceptance connected in parallel to the main line. The characteristics corresponding to Pl can also be approximately obtained by a wire connecting a transistor and a matching circuit. The value corresponding to C1 corresponds to the susceptance of the thin film capacitor and the open-ended microstrip line connected thereto. This is an example of one-stage matching. However, this method cannot achieve broadband matching.

Generally, in order to achieve broadband matching, it is sufficient to increase the phase rotation (equivalent to rotation on a scale chart) as much as possible before moving 3 4 to point C. This is because phase rotation allows a wider frequency range to be concentrated at one point on the Smith chart. For this purpose, in this embodiment, the number of stages of matching elements is increased. Furthermore, by giving a constant relationship to the constants of the matching elements, wideband matching can be achieved with almost no need for adjustment. The operation will be further explained using FIG.

Now the input impedance of the transistor is at point X,
Assume that point X is inside the equiconductance circle, Ml. M
l is inside circle A and includes point X.

The phase is rotated by the wire 106 and the microstrip line connecting the transistor and the matching thin film capacitor 108, and the value thereof is set to be at the point X1 at the upper end of the circle M1. Therefore, the alignment of the first-stage matching thin film capacitor 108 and the open-end microstrip line 113 is set so as to move on the conductance circle Ml to the point X2.

At this time, the point X2 is placed on the curve N2 having a smaller sesaptance than the point X.

Next, by rotating the phase of the microstrip line between the stages of the first and second thin film capacitors, the length of the microstrip line is set so that point X2 is brought to point X3 on the equiconductance circle M2. Next, the second thin film capacitor 109 and the open-ended microstrip line 11
4, the value is set so that point x3 moves to point X4. At this time, the point x4 is placed on the curve N3 having a smaller sesaptance than the point X2.

Next, by rotating the phase of the microstrip line between the stages of the second and third thin film capacitors, the length of the microstrip line is set so that point x4 comes to point X5 on the conductance circular hole.

Next, by moving the point X5 to the point C using the third thin film capacitor 110 and the open-ended microstrip line 115, matching is achieved at the center frequency. As a result, the phase is rotated by two and a half revolutions, and wideband matching can be achieved near the frequency to be matched.

At this time, as shown in this example, the method of determining the constant of the matching circuit is that the first equiconductance circle is within circle A, and as the number of stages of the matching circuit increases, it approaches circle A and the susceptance is By setting it to be small, it is possible to focus on the matching point C while repeating phase rotation. This corresponds to the fact that the susceptance of the matching thin film capacitor and the open-ended microstrip line is larger in the earlier stages. If the length of the open-ended microstrip line is the same, this corresponds to the fact that the value of the thin film capacitor in the previous stage is larger. Further, if the value of the thin film capacitor is the same, this corresponds to making the length of the microstrip line closer to the length of 1/4 wavelength within a range where the susceptance value does not become negative. Furthermore, the length of the interstage microstrip line corresponds to the fact that the earlier the interstage microstrip line is, the shorter the diameter of the equiconductance circle is and the smaller the amount of phase rotation is required. The maximum length of the interstage microstrip line is when the phase is rotated within circle A, and the angle of view from point C is 180 degrees or less, that is, the length of the microstrip line required for that much phase rotation. is less than 1/4 wavelength.

The movement adjustment from point X to point X1 shown in this example is as follows:
The length, thickness, and number of wires connecting the transistor and matching circuit can be easily adjusted. Therefore, by adjusting that part, broadband matching can be easily achieved. In the description of this embodiment, it is assumed that the input impedance of the transistor is within circle A. The input impedance of the high-frequency, high-output FET at IOG Hz - 20 GHz takes a vague straight line. Also, even if it is outside circle A, depending on the values of the initial connecting wire and the microstrip line, a fairly wide range of phase rotation is possible and it can be brought substantially into circle A. Therefore, similarly, the circuit of this embodiment can perform matching over a wide band.

At 7 8 14 GHz, the matched frequency range was 13.8-14.1 GHz when matching was done with one stage, but when matching was done with three stages as in this example, can be matched at 12.5-14.5 GHz, and by the method of this example, the matching frequency band can be adjusted to 0.3 GHz.
The frequency has been expanded approximately seven times from Hz to 2GHz.

Although the input matching circuit has been explained above, it is clear that the output matching circuit can also be constructed in the same manner and the same objectives and effects can be obtained. Note that FIG. 1 shows an embodiment in which the output matching circuit has a two-stage configuration. Even if the number of stages changes, the method of setting the circuit constants of each stage in this embodiment is as described above. As the number of stages increases, the amount of phase rotation in the matching circuit increases, enabling matching over a wide band.

Furthermore, as can be seen from equation (3), by appropriately selecting the length of the open-ended microstrip line, the value of the capacitance of the matching capacitor can be selected to be extremely small.

For example, if you want Zin=-jl (1 ohm), (
From formula 3), it is sufficient to determine the values of L and C so as to satisfy the condition of 1-1/ωC+ZocotβL. Specifically, L
This can be achieved by choosing the length of around 1/4 wavelength. Even if C is small, L is around 1/4 wavelength, 1/4
If a value slightly longer than the wavelength is taken, the value of ZocotβL takes a negative and small value, which shows that Zin can be made small.

This means that the electrode area of the matching capacitor can be made extremely small, and therefore the loss of the capacitor, which is proportional to the electrode area of the capacitor, can be made extremely small. Conversely, the capacitor can be used even if its loss characteristics are slightly worse than the conventional capacitor, and in that case, the cost will be reduced.

Further, there is a preferable range for the length of L.

As can be seen from equation (3), the value of Zin is ■ when L is 0, gradually becomes smaller as L approaches the length of 1/4 wavelength, and eventually becomes smaller when l/ωC−ZocotβL. , becomes 0. Until then, Zin has a positive value, that is, it exists in the upper half 9 0 plane (region where the susceptance is negative) on the graph. When L becomes larger than that, Zin becomes a negative value, and when L=1/2 wavelength, irrespective of the value of C, it becomes ■, and does not play the role of impedance matching. Therefore, the length of L must be within the range in which C effectively acts as C for use in matching low impedance transistors, that is, 1 /arc>-z o co tβL(Z
It is preferable to take a value in the range of (in is negative, or its reciprocal, susceptance, is positive). If the conditions are within these conditions, the susceptance of the series circuit can be reduced by increasing the length of L. Therefore, as in this example, if the susceptance is set to be lower as the side closer to the transistor is set, the length of the short-circuited microstrip line on the side closer to the transistor is made longer, even if the value of C is almost the same. If this is done, the effects of the present invention can be obtained.

Also, the length of the open-ended microstrip line is reduced to 1/4.
When it is set to the wavelength, in equation (3), the term due to the open-ended microstrip line becomes 0, and Zin in equation (3) is determined only by the capacitance of the thin film capacitor.

The tank bottom of this embodiment allows the thin film capacitor to be grounded at almost any location without being subject to too many restrictions on the substrate, so it is useful for integration and miniaturization.

In this embodiment, matching was performed using the same method for both input and output matching circuits, but since the output impedance is generally higher than the input impedance, the method of this embodiment may be used only for manual matching.

Another embodiment with a wider adjustment range is shown in FIG.

In FIG. 3, the length of the microstrip line with an open end can be adjusted, so that alignment can be adjusted over a wider range. In Fig. 3, 102 is the input matching circuit board, 104 is the main line, 106 is the wire 10B for connecting to the transistor, 109.110 is the input matching thin film capacitor, 113.114.115 is the main line of the thin film capacitor. An open-ended microstrip line connected to the electrode on the side to which it is not connected, 30
Reference numeral 1 denotes an island-shaped electrode (pad) provided near each of the open-end microstrip lines, and 302 represents a wire for adjusting the substantial length of the open-end microstrip line.

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 caused by variations in transistor characteristics and manufacturing process of the thin film capacitor is corrected by using an open-ended microstrip line. Adjustment can be made by changing the substantial length.

In this embodiment, the actual length can be changed by appropriately connecting the open-ended microstrip line and the island-shaped electrode with a wire. Therefore, strictly speaking, the inductance of the wire will be added in series, and it will be necessary to compensate for that amount, but it will not have a large effect, so basically it is possible to adjust by that amount. In particular, by shortening the length of the wires, increasing the number of wires, or using ribbons or the like instead of wires, adjustment can be made virtually without any trouble.

Although only the manual matching circuit is shown in this embodiment, it is clear that the output matching circuit can be constructed in the same manner.

FIG. 4 shows the structure of another embodiment in which the types of capacitors used are different. In Figure 4, 102
is an input matching circuit board, 104 is a main line, 106 is a wire for connecting to a transistor, 401.402.4
03 is a human matching capacitor, which is a so-called interdigital capacitor that utilizes the capacitance between the opposing electrodes by arranging electrodes facing each other in a complicated manner on a dielectric substrate. 113, 114, and 115 are the interdigital This is a microstrip line connected to the electrode on the side where the main line of the capacitor is not connected. Although an interdigital capacitor was used in this example, an interdigital capacitor is easy to integrate like a thin film capacitor, and the loss of the capacitor can be reduced by reducing the area of the opposing electrode. 3 4 It is possible to obtain the desired effect of the invention.

Effects of the Invention As described above, the present invention has a plurality of series circuits of a thin film capacitor or an interdigital capacitor and an open-ended microstrip line in parallel to the main line, and the closer the susceptance of the series circuit is to that of the transistor, the more The microstrip line is large and the length of the microstrip line between each stage is short, making it easy to match high-frequency, high-output transistors with low impedance, and reducing signal transmission loss due to loss in matching capacitors. The purpose of the present invention is to provide a matching circuit for high-frequency transistors that can be reduced in size, requires fewer mounting steps, can be integrated in a small size, is inexpensive to manufacture, and can be matched over a wide band.

[Brief explanation of drawings]

Fig. 1 is a basic structural diagram showing one embodiment of the present invention, Fig. 2 is an explanatory diagram of its operation and principle, and Figs.
Structural diagrams of other embodiments using the basic configuration of FIGS. 5 and 6
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 ... Wire, 108.109.110 ... Thin film capacitor for input matching, 111.112 ... Thin film capacitor for output matching, 113.114.115...
Open-ended microstrip line for input matching, 11
6, 117...Open-ended microstrip line for output matching.

Claims (7)

[Claims] (1) In a transistor impedance matching circuit using a microstrip line as the main line, a plurality of series circuits of a thin film capacitor or an interdigital capacitor and an open-ended microstrip line are connected in parallel to the main line, and the susceptance of the series circuit is is larger as the microstrip line is closer to the transistor, and the length of the microstrip line between each stage is shorter. (2) The matching circuit for high-frequency transistors according to claim (1), wherein the electrostatic capacitance of the thin film capacitor or the interdigital capacitor increases as it approaches the transistor. (3) The length of the open-ended microstrip line connected in series to the thin film capacitor or interdigital capacitor is as long as that of a transistor, and the susceptance of the series circuit is positive. A matching circuit for high frequency transistors according to claim (1). (4) The high-frequency transistor according to claim (1), wherein the maximum length of the microstrip line between each stage is equal to or less than 1/4 wavelength of the frequency to be matched. matching circuit. (5) The high-frequency transistor matching circuit according to claim (1), wherein the length of the open-ended microstrip line is approximately 1/4 wavelength of the frequency to be matched. (6) The high-frequency transistor matching circuit according to claim (1), wherein the matching state with the transistor can be adjusted by adjusting the substantial length of the open-ended microstrip line. (7) By providing island-shaped electrodes near the open-ended microstrip line and adjusting the number and position of the island-shaped electrodes connected to the open-ended microstrip line,
2. The high-frequency transistor matching circuit according to claim 1, wherein the substantial length of the microstrip line is adjusted.