JPH05136607A - Micro wave transistor for electric power amplification - Google Patents

Abstract

PURPOSE:To obtain the improve structure for which the effect of the resistance insertion can be stably expected and to realize a stable micro wave amplifier even when the impedance is fluctuated by the dispersion of the capacitance value, etc., of an FET chip, an Au wire and a chip capacitor which are components, at an internal matching type FET. CONSTITUTION:In an envelope 101, an electric field-effect type transistor chip and a matching circuit to convert so as to match the impedance of the said transistor chip to the desired resistance are provided. The matching circuit includes a distribution constant circuit to provide a good conductivity thin metallic film on insulation substrates 14 and 104. At least two places of micro strip lines 14a and 104a to constitute the distribution constant circuit are constituted of the thin resistor film and the electric length of the micro strip line between the thin resistor films is about 1/4 of the wavelength at the frequency to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a microwave transistor for power amplification, especially a so-called internally matching type transistor having an impedance conversion circuit in an envelope.

[0002]

2. Description of the Related Art A GaAs field effect transistor for power amplification (hereinafter referred to as GaAs) is used as a device for amplifying microwaves.
The FET is abbreviated as “FET”, and is widely used in place of the conventionally used traveling-wave tube type amplifier. A power amplification GaAs FET is generally an input / output lead in which a fine GaAs semiconductor chip having a source electrode, a drain electrode, and a gate electrode is mounted on an envelope made of metal or ceramic, and each electrode is provided on the envelope. It is connected to the terminals and the base metal for grounding with thin metal wires. Normally, a plurality of such GaAs FETs for power amplification are connected and used, but the input and output impedances of each FET have their respective impedances. Therefore, simply connecting them maximizes the ability of the FET. I can't pull it out. Therefore, the FE of the previous stage is placed between each FET stage.
A matching circuit is required to match the output impedance of T with the input impedance of the subsequent stage. Also, the impedance of the input / output terminals of the microwave amplifier itself is generally adjusted to 50 ohms.
It is necessary to convert the input impedance of T and the output impedance of the final stage FET to 50 ohms. From such a situation, the input / output impedance of the FET itself should be 5
A power amplification GaAs FET called an internal matching type FET set to 0 ohm has been developed.

The internal matching type FET is a FET in which a matching circuit is provided inside the envelope so that the input output impedance is approximately 50 ohms. A plan view of the structure of a conventional internal matching type FET will be described below with reference to FIG. Reference numeral 101 in the figure is a container called a metal wall type envelope in which all parts including a semiconductor chip are stored. This envelope is usually an input / output terminal 101b used for connecting a metal base 101a such as copper to an external circuit, a ceramic piece 101c for supporting this terminal, and a metal frame provided with a cap for hermetically sealing. It consists of 101d. A GaAsFET chip 102 has a source electrode, a drain electrode, and a gate electrode on the surface. Reference numeral 103 denotes a capacitive element called a chip capacitor, in which gold electrodes are provided on the front and back of a high dielectric substrate. Reference numeral 104 denotes an insulating substrate (alumina substrate) provided with a distributed constant circuit, and the distributed constant circuit includes a microstrip line 104a, an open stub 104b, and the like. Then, these parts are connected by a gold (Au) wire and the internal matching type FET functions. FIG. 4 shows an equivalent circuit of this internal matching type FET. Inductance by Au wire, capacitance by chip capacitor,
The microstrip line and the open stub provided on the alumina substrate convert the low impedance of the GaAsFET chip itself, such as several ohms, into an impedance of nearly 50 ohms. FIG. 5 shows, as an example, a Smith chart representation of the input / output impedance of an internally matched FET having an output of 5 W in the X band.
5 (a) shows the impedance on the input side, and FIG.
Shows the impedance on the output side. In these figures, the frequency is changed from 9 GHz to 12 GHz. The points indicated by fL, fM, and fH in the figure are the band edges f = of the low frequency band to be used by this FET.
9.5 GHz, band center frequency f = 10 GHz, and high band edge f = 10 GHz. In the case of a power FET, it is preferable that the output impedance is not necessarily set to 50 ohms, but the output impedance is converted to the maximum impedance. On the other hand, it is preferable to convert the input impedance to 50 ohms, but it is not possible to make it 50 ohms over the entire frequency band due to the interaction between the input and output (feedback effect) and the limitation caused by the size of the envelope. is there. Due to such a reason, the actual internal matching type FET
The impedance of FIG. 5 can be traced the impedance locus as shown in FIGS. 5 (a) and 5 (b). In this example, f
The impedance at L, fM, and fH is ZL = 70 +
j0Ω, ZM = 30 + j0Ω, and ZH = 50−j25Ω.

[0004]

FE as described above
When T is connected, impedance mismatch occurs between the front FET and the rear FET, and microwaves are reflected between the FETs. In this case, the reflected microwave influences the operation of the preceding FET, and not only the characteristics expected from simply connecting the FET cannot be obtained, but also the oscillation phenomenon or the gain is improved by increasing the input. Abnormal phenomena of input / output characteristics may be seen. As one of the measures for suppressing such a phenomenon, there is a method of inserting a resistor in the input circuit. If this method is adopted, the input impedance of the FET becomes a value obtained by adding this resistance value to the impedance when the resistor is not inserted (impedance as seen from the FET side from the position where the resistor is inserted). For example, in the above example, assuming that a resistance of 10 ohm is inserted at the root of the lead terminal of the envelope for the sake of simplicity, ZL is fL.
= 80 (= 70 + 10) + j0Ω, ZM = 40 for fM
(= 30 + 10) + j0Ω, fH at ZH = 60 (= 5
0 + 10) -j25Ω, and the maximum value in the band of the standing wave ratio r is from rmax = 1.67 when no resistor is inserted to rmax = 1.6. Since the standing wave ratio r is thus reduced, the microwaves are less reflected between the FETs, and more stable operation is possible. However, in a high frequency band such as the X band among the microwave bands, the impedance locus also differs among individual FETs due to variations in the length of the FET chip and the Au wire forming the inductance. Therefore, for example, as shown in FIG.
FETs (ZL = 80 + j0Ω, ZM = 50 + j0Ω, which have impedance loci as shown in FIG.
ZH = 40-j20Ω), assuming a similar resistance, the impedances at fL, fM, and fH are ZL = 90 + j0Ω and ZM = 60 +, respectively.
Since j0Ω and ZH = 50−j20Ω, the maximum value in the band of the constant pressure wave ratio r is rmax = 1.8, which is worse than rmax = 1.64 when no resistance is added. The present invention has been made in order to eliminate the above-mentioned drawbacks, and it is an object of the present invention to provide an internal matching type power amplification microwave transistor capable of stable operation even when there are variations in individual FETs. To aim.

[0005]

A microwave transistor for power amplification according to the present invention is for converting a field effect transistor chip in an envelope and an impedance of the transistor chip to match a desired resistance. In the internally matched power field effect transistor having the matching circuit, the matching circuit includes at least a distributed constant circuit in which a thin metal film having good conductivity is provided on an insulating substrate, and a microstrip line forming the distributed constant circuit. Is formed of a resistance thin film, and the electrical length of the microstrip line between the two resistance thin films is about ¼ of the wavelength at the frequency used.

[0006]

In the internal matching type FET according to the present invention, even if the impedance varies due to variations in the capacitance value of the FET chip, Au wire, and chip capacitor, the effect of stable resistance insertion can be expected, and stable microwave amplification can be expected. Provide the device.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing the structure of an internal matching type FET according to an embodiment. In the figure, parts that are the same as those of the prior art are designated by the same reference numerals and the description thereof is omitted. Figure 14
Is an insulating substrate (alumina substrate) provided with a distributed constant circuit. This distributed constant circuit includes a matching circuit including a microstrip line 14a and an open stub 14b. Further, the resistor 14 which is a feature of the present invention
c and 14d are formed in two places. The tantalum nitride thin film is formed by selectively removing gold (Au), which is the uppermost layer of the metallized film on the alumina substrate forming the microstrip line having the characteristic impedance of the resistance value of 50Ω. The resistance value of each of these two resistors is set to 5Ω, and they are provided at a distance of about ¼ of the effective wavelength of the microwave of the frequency to be used. FIG. 2 shows an equivalent circuit of this internal matching type FET.

In order to see the effect of the FET according to the present invention,
A case similar to the case described in the conventional example will be described. First, the impedance looking into the FET side from the microstrip line immediately before the resistance on the FET side is the frequency f
ZL = 70 + j0Ω, ZM = for L, fM, and fH, respectively.
30 + j0Ω and ZH = 50−j25Ω. These impedances are ZL = 75 + j0Ω, ZM = 35 + j0Ω, ZH = 55 due to the inserted 5Ω resistors.
Converted to -j25Ω. Furthermore, it is converted by a microstrip line with an electrical length of 1 / 4λ, and ZL = 33 + j
It is converted into 0Ω, ZM = 71 + j0Ω, and ZH = 38 + j17Ω. Furthermore, ZL is inserted by the inserted 5th resistance in the second stage.
= 38 + j0Ω, ZM = 76 + j0Ω, ZH = 43 + j
Converted to 17Ω. That is, the maximum value of the standing wave ratio r in the band in this case is rmax = 1.5. Next, a trial calculation will be made for the second case described in the conventional example.
That is, A forming the FET chip and the inductance
Although the circuit is similar due to the variation in the length of the u wire, the impedance of the FET side from the microstrip line immediately before the resistance on the FET side is ZL = 100 + j0 at frequencies fL, fM, and fH, respectively.
Ω, ZM = 50 + j0Ω, and ZH = 40−j20Ω. In this case, two resistors, 1 /
ZL converted by 4λ microstrip line
= 29 + j0Ω, ZM = 50 + j0Ω, ZH = 51 + j
Converted to 21Ω. That is, the maximum value of the standing wave ratio r in this case in the band is rmax = 1.7. In summary, the conventional internal matching type F that does not use resistors
In ET, the standing wave ratio values for the two cases are

[0010]

[Table 1]

[0011] and

[0012]

[Table 2]

(Standing wave ratio for expressing the effect of the present invention, taking the FET having the input impedance shown in FIGS. 5a and 6 as an example), the maximum constant in two cases is obtained. The standing wave ratio rmax is 1.7 and 2.0. Similarly, in the conventional resistance insertion type internal matching FET in which a resistance of 10Ω is simply inserted, the maximum standing wave ratio rmax in the two cases is 1.6 and 2.2. Further, in the case of the novel resistance insertion type internal matching FET according to the present invention in which two resistors are provided at a distance of ¼λ, the maximum standing wave ratio rmax in the two cases is 1.5 and 1.7, as in the conventional case. It has no adverse effect.

[0014]

According to the internal matching type FET of the present invention, even if the impedance varies due to variations in the capacitance value of the FET chip, Au wire, chip capacitor, etc.,
A stable effect of resistance insertion can be expected, and thus a stable microwave amplification device can be realized.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of an internal matching type power FET according to the present invention,

2 is an equivalent circuit diagram of the internal matching type FET shown in FIG. 1;

FIG. 3 is a plan view of an internal matching type power FET of a conventional example,

FIG. 4 is an equivalent circuit diagram of the internal matching type FET shown in FIG.

5 (a) and 5 (b) are respectively Smith chart display diagrams of the input and output impedances of the internal matching type FET,

FIG. 6 is a Smith chart display diagram of the input impedance of another internal matching type FET.

[Explanation of symbols]

 14 ... Insulating substrate 14a ... Microstrip line 14b ... Open stubs 14c, 14d ... Resistor 101 ... Envelope 102 ... GaAsFET chip 104 ... Distributed constant circuit

Claims (1)

[Claims] 1. An internal matching type power field effect transistor having a field effect transistor chip in an envelope and a matching circuit for converting the impedance of the transistor chip to match a desired resistance, The matching circuit includes a distributed constant circuit in which a thin metal film having good conductivity is provided on an insulating substrate, and at least two microstrip lines forming the distributed constant circuit are formed of resistive thin films, and between the resistive thin films. The electrical length of the microstrip line is about 1 / wavelength at the frequency used.
4. A microwave transistor for power amplification, which is 4.