JPH0366207A - 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 the Invention The present invention relates to a high-frequency transistor matching circuit that can easily adjust the input/output matching state 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) However, 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 sixth section.
As shown in the figure. In FIG. 6, 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 601
is an open stub that forms a manual matching circuit, 602 is an open stub that forms an output matching circuit, 603.604
605 and 606 are island electrodes (pads) for adjusting the length of the open stub, and wires 605 and 606 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. 7, 101 is a field effect transistor (FET), 701 is an input matching adjustment circuit board, 702 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, 703 is a chip capacitor for human impedance matching, 704 is a chip capacitor for output impedance matching, and the lower electrodes of both chip capacitors 703 and 704 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. 705.706 is a wire connecting the transistor and the chip capacitor, 707.
70B is a wire connecting the chip capacitor and the main line microstrip line of the input/output matching adjustment circuit board. 709.710 is a pad for adjusting input/output matching, and 711.712 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.

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 by computer simulation.

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, the loss as a capacitor, such as dielectric loss, must be extremely small. becomes expensive. 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 an experimental determination or perform computer simulation, which requires a great deal of time and effort, and is a factor in increasing costs.

Means for Solving the Problems In order to solve the above problems, the present invention provides a transistor human output impedance matching circuit that includes a plurality of series circuits of thin film capacitors or interdigital capacitors and microstrip lines between the main line and the ground. ,
The susceptance formed by the thin film capacitor or interdigital capacitor and the microstrip line connected in series with it is larger as the capacitor is closer to the transistor, and the length of the microstrip line between each stage is shorter. , the matching state with the transistor can be adjusted over a wide band.

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, the present invention provides a matching circuit for high-frequency transistors that can reduce signal transmission loss due to the loss of matching capacitors, requires fewer mounting steps, can be integrated in a small size, is inexpensive to manufacture, and can be matched over a wide band. It is something.

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. 106 is a wire that connects the transistor and the manual matching circuit board; 107 is a wire that connects the transistor and the output matching circuit board; 108
．． 109.110 is a thin film capacitor for input matching, ILL
112 is a thin film capacitor for output matching, 113.11
4.115.116.117 is a microstrip line with one end connected to the electrode on the side of the thin film capacitor that is not connected to the main line, and the other end is a ground terminal.
Connected to 18.119.

The input/output matching circuit board uses a ceramic substrate such as alumina, the conductive parts such as the main line and microstrip line use Cr-Au, and the thin film capacitor uses a metal-dielectric-metal structure using silicon oxide as the dielectric. A thin film capacitor structure was used. Also, as a transistor, Ga
14G as the center frequency to match AsFET, also
Hz 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, input matching and output matching are adjusted by adjusting the capacitance of thin film capacitors 10B-112 and the length of microstrip lines 113-117 to appropriate values.

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 a microstrip line are inserted between the main line microstrip line and the ground in order to achieve the matching. The impedance of this series circuit is
Zin is Zin=1/jωc+jZo−tanBL (2)−
-j (1/ωc-Zo -tanBL) (3)
However, ω=2πf, β-2π/λf 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 internal resistance of the substrate at the frequency to be matched. The wavelength at , L is the length of the microstrip line to ground.

It is expressed as 1. Therefore, as shown in equation (3), by appropriately selecting the capacitance C and the length L of the microstrip line, the value of Zin can be adjusted to several ohms or 1 ohm.
It is easy to make it less than ohm.

In this embodiment, the number of stages of matching thin film capacitors and short-circuited microstrip lines is increased in order to widen the matching frequency range, that is, to widen the band. The effect will be explained using a so-called Smith chart shown in FIG. Figure 2 is a Smith chart, in particular, the atto is also displayed in tutance.

The normalized impedance is set at 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 O, is the impedance,
■In other words, respond openly. A circle A passing through points S and E in FIG. 2 represents a circle with a conductance of 1. Also, the curve E is a curve with a susceptance of 1, so that the left side represents a susceptance of 1 or more. The input/output impedance of a high-frequency, high-output transistor is 1 ohm or less, and usually takes a value near point S at a point inside A, for example, point X. When considered on the Smith 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 extend from point Y on circle A to point C. 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 C1 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 shorted tip microstrip line connected thereto. This is 1
This is an example of stage matching. However, this method cannot achieve broadband matching.

3 4 Generally, in order to achieve broadband matching, it is sufficient to increase the phase rotation (equivalent to rotating the phase on the chart) as much as possible before moving 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 assume that the input impedance of the transistor is at a point, X, and that point X is inside the equiconductance circle, Ml.

Ml is inside circle A and includes point X.

The wire 106 and the microstrip line connecting the transistor and the matching thin film capacitor 108 are phase-rotated, and the value thereof is set to be at the point X1 at the upper end of the circle M1. Therefore, the first stage matching thin film capacitor 1
08 and the value of the short-circuited microstrip line 113 are set so that it moves on the conductance circle l to the point x2. At this time, the point X2 is placed on the curve N2 having a smaller susceptance than the point X. Next, the length of the microstrip line is set so that the phase rotation of the interstage microstrip line between the first and second thin film capacitors brings the point X2 to the point X3 on the equiconductance circle M2. Next, the value is set using the second thin film capacitor 109 and the shorted microstrip line 114 so that the point X3 moves to the point X4. At this time, the point X4 is placed on the curve N3 having a smaller susceptance than the point X2. Then the second
By the phase rotation of the interstage microstrip line of the third thin film capacitor, the length of the microstrip line is set so that the point X4 is brought to the point X5 on the conductance circle A. Next, by moving the point X5 to the point C using the third thin film capacitor 110 and the shorted microstrip line 115, matching is achieved at the center frequency. As a result, the phase is rotated by two and a half revolutions, and broadband matching can be achieved at 5 6 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 formed by the matching thin film capacitor and the short-circuited microstrip line is larger in the previous stage. Assuming that the length of the short-circuited microstrip line is the same, 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, the length of the microstrip line can be increased within a range where the susceptance value does not become negative. In addition, the length of the interstage microstrip line is the same as that of the previous stage.
Since the diameter of the equiconductance circle is short and the amount of phase rotation is small, this corresponds to the fact that the earlier the equal conductance circle is, the shorter its length is. 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, just by adjusting that part, wideband matching can be achieved easily. In the description of this embodiment, it is assumed that the human power impedance of the transistor is within circle A. The input impedance of a high-frequency, high-output FET at 100 Hz to 20 GHz takes a vague value. 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, in the same way, matching can be achieved over a wide band using the circuit of this embodiment.

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 12-15GHz, and by the method of this embodiment, the matching frequency band can be extended from 0.3GHz to 3GHz.
It has been expanded 10 times to GHz.

Although the manual matching circuit has been described above, it is clear that the output matching circuit can 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 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), 1
= 1/ωC−ZOtanβL, and even if C is small,
It can be seen that the condition can be satisfied by increasing L.

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 determined only by the value of C when L is 0. As L increases from 0,
Zin becomes smaller and eventually becomes 1/ωC=Zotanβ
When it is L, it becomes O. Until then, Zin has a negative value, that is, it exists in the lower half of the Smith chart (region where the susceptance is positive). When L becomes larger than that, Zin becomes a positive value, and when L=1/4 wavelength, irrespective of the value of C, it becomes ■, and it no longer plays the role of impedance matching. Therefore, it is appropriate that the length of L is 1/4 wavelength or less9. Furthermore, in order to use it for matching low impedance transistors, the length of L should be within the range where C effectively acts as C, that is, 1/4 wavelength or less. ωC＞ZotanβL(
Zin is negative, or its reciprocal susceptance is positive)
It is preferable to take a value in the range of . 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.

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.

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

FIG. 3 shows a configuration in which the length of the short-circuited microstrip line at the tip can be adjusted, allowing matching adjustment to be made over a wider range. In FIG. 3, 102 is an input matching circuit board, 104 is a main line, and 10
6 is a wire 108.10 for connecting to the transistor
9.110 is a thin film capacitor for input matching, 118 is a ground terminal, 301.302.303 is a thin film capacitor,
Open-ended microstrip line connected to the electrode on the side to which the main line is not connected, 304.305.30
6 is a wire for adjusting the substantial length of the microstrip line to the ground. Further, 307 is a ground terminal.

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 any mismatching due to variations in transistor characteristics or variations in the manufacturing process of the thin film capacitor is corrected to the ground of the microstrip line. can be adjusted by changing the substantial length of the . In this embodiment, the actual length can be changed by connecting the microstrip line from an appropriate position to the ground terminal using a wire. Therefore, strictly speaking, the inductor 1 2 part of the wire will be connected in series, and the tip of the microstrip line will be connected in parallel as an open stub at the wire connection, so it is necessary to compensate for this. , it doesn't have that big of an effect, so basically you can make adjustments accordingly. In particular, regarding wires, adjustment can be made virtually without any trouble by shortening the length of the wires, increasing the number of wires, or using ribbons instead of wires.

Although only the input 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 that makes it easier to adjust the length of the microstrip line. In FIG. 4, 102 is an input matching circuit board, 104
is the main line, 106 is a wire for connecting to the transistor, 108.109.110 is a thin film capacitor for input matching, 118.307 is a ground terminal, 301.302.
303 is a microstrip line connected to the electrode of the thin film capacitor on the side to which the main line is not connected; 4
Numeral 01 is a pad for adjusting the substantial length of the microstrip line to the ground, and several pads are appropriately provided near each microstrip line. 4
02.403 is a wire for connecting the microstrip line, the pad, and the ground terminal. In this example, the length of the microstrip line to the ground is adjusted via the pad, reducing the influence of open stubs that are connected in parallel at the wire connection, as described in Example 2. be done. Therefore, there is less need for correction than in the case of the second embodiment.

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

FIG. 5 shows the structure of another embodiment of the type of capacitor used and the method of grounding. In FIG. 5, 102 is an input matching circuit board, 104 is a main line,
106 is the third wire for connecting to the transistor, 501. 502.503 is an input matching capacitor, and is a so-called interdigital capacitor that utilizes the capacitance between the opposing electrodes by arranging electrodes on a dielectric substrate in a complicated manner.
5.506 is a microstrip line connected to the electrode on the side where the main line of the interdigital capacitor is not connected, and 507.508.509 is a microstrip line connected to the electrode on the side where the main line is not connected, and 507.508. This is an electrically connected ground terminal called a via hole. In this example, by using a via-hole type ground terminal, a capacitor can be formed anywhere on the board, which increases the degree of freedom in designing an integrated circuit, simplifies mounting, and Useful for cost reduction, downsizing, etc.

Furthermore, although an interdigital capacitor was used in this example, an interdigital capacitor is easy to integrate like a thin film capacitor, and by reducing the area of the opposing electrode part, the loss of the capacitor can be reduced. The desired effect of the present invention 4 can be obtained.

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 a microstrip line between the main line and the ground, and the closer the susceptance of the series circuit is to the transistor, the larger the susceptance of the series circuit is. , 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 present invention provides a matching circuit for high-frequency transistors, which requires less mounting steps, can be integrated in a small size, has low manufacturing costs, and is capable of matching 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 FIG. 3 is a diagram illustrating its principle. To 101...transistor, 102...
Input matching circuit board, 103...Output matching circuit board, 104...Input end main line, 105...
... Output side main line, 106.107 ... Wire 108.109.110 ... Thin film capacitor for manual matching, 111 112 ... Thin film capacitor for output matching, 113. 114.115...
Microstrip line for manual alignment, 116.117
・・・・・・Microstrip line for output matching, 1
18, 119... Earth terminal.

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 a microstrip line are provided between the main line and the ground, and the susceptance of the series circuit is A matching circuit for high-frequency transistors, characterized in that the closer the transistor is to the transistor, the larger the microstrip line is, and the length of the microstrip line between each stage is shorter. (2) The high-frequency transistor matching circuit according to claim (1), wherein the capacitance of the thin film capacitor or the interdigital capacitor increases as it approaches the transistor. (3) The length of the microstrip line connected in series between the thin film capacitor or interdigital capacitor and ground is longer as it approaches the 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) Claim (1) characterized in that the matching state with the transistor can be adjusted by adjusting the substantial length of the microstrip line connected to the ground.
) matching circuit for the high-frequency transistor described. (6) An island-shaped electrode is provided near the microstrip line connected to the ground, the microstrip line is connected to the ground via the island-shaped electrode, and the number and position of the connected island-shaped electrodes are adjusted. 2. The high-frequency transistor matching circuit according to claim 1, wherein the substantial length of the microstrip line to the ground is adjusted by. (7) The high-frequency transistor matching circuit according to claim (1), wherein a ground terminal formed by a via hole is used as the ground.