JPH0376301A - Impedance conversion circuit - Google Patents

Abstract

PURPOSE:To obtain a small sized impedance conversion circuit with ease of manufacture and improved design performance by reducing the length of a transmission line and adding a capacitor to the line to increase its characteristic impedance. CONSTITUTION:The length of a transmission line (coplaner line) 1 (11) in an impedance conversion circuit converting the impedance between a 1st impedance Z0 and a 2nd impedance Z1 with use of the transmission line is selected shorter than a 1/4 wavelength of the operating frequency and its characteristic impedance Z is selected to be (Z0.Z1)<1/2> or over, and both ends of the line 1 are connected to a ground conductor via characteristics 2, 5 whose capacitance is identical to each other. Through the constitution above, since the length of the line 1 is shorter than the 1/4 wavelength of the operating frequency, the impedance Z is selected to be (Z0.Z1)<1/2> or over. Thus, the impedance Z is selected to be, e.g. 51OMEGA larger than a conventional impedance of 7OMEGA and a matching circuit section of various high frequency circuits is made small without incurring characteristic deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an impedance conversion circuit, and particularly to an impedance conversion circuit that performs impedance conversion between impedances ZO and 21 using a high frequency transmission line.

[Conventional technology]

FIG. 4 shows a conventional impedance conversion circuit used in high frequency communication equipment. In the figure, the line length of the transmission line 6 is a quarter wavelength at the operating frequency (90° if long),
Its characteristic impedance Z2 satisfies the following relationship.

Z2-FT7777 0) Here, 4 is a transmission line with characteristic impedance Zo or a connection terminal with impedance 20, and 5 is a transmission line with characteristic impedance Z1 or a connection terminal with impedance Z+, or a circuit with input impedance 21. It is element.

For example, if Zo is 500, Z + 4r IQ is 0, the characteristic impedance Z2 of the transmission line 6 is 0)
It is approximately 70 from the formula. As in this example, the same impedance variable circuit with an ultra-low impedance of 50Ω and about 1Ω is often required in a matching circuit inside a high-power amplifier. This is because, while the input/output impedance of a high-power amplifier is generally 500Ω, the real part of the input impedance of a high-power FET used therein is generally an extremely low impedance of about 1Ω.

[Problem to be solved by the invention]

However, it is not easy to design and manufacture a high frequency circuit using a transmission line whose characteristic impedance is 10Ω or less. For example, when designing a high-frequency circuit using microstrip lines, which are the most common transmission line,
The characteristic impedance range of a microstrip line that can be used to install a circuit using a transmission line model (a one-dimensional model that does not take into account the widthwise size of the line or its effects) is limited to 200 or more. Further, for Copley lines, the usable characteristic impedance range is usually 30Ω to 100Ω, and for slot lines, it is usually 40Ω to 150Ω.

It is not physically impossible to manufacture a microstrip line with a characteristic impedance of 10Ω or less, but since the width of the line is about the same as a quarter length, it is no longer possible It is no longer possible to design a circuit using a transmission line model, and the design becomes a planar circuit that extends two-dimensionally in the direction of the line wheels. In this case, circuit installation becomes extremely difficult and the design is poor. Therefore, in manufacturing a high-output amplifier using the impedance conversion circuit shown in FIG. 4 in the input/output matching circuit, it is generally necessary to adjust the characteristics by trial and error.

Furthermore, in the case of a monolithic microwave integrated circuit in which a high-power FEr and an input/output matching circuit are built together on two gallium arsenide substrates, the size of four chips is reduced because a quarter-wavelength impedance conversion circuit is used. It gets bigger.

For example, a quarter-wavelength transmission line in 10Gl-Iz is approximately 31111I when using a microstrip line or a coplanar line, and the size of the FET that is fabricated at the same time as the transmission line is usually 0.5 m square or less. The dimensions are relatively large in comparison.

The present invention has been made in view of the above points, and is a high output FE.
Installation of an impedance variable Jf path for matching between an ultra-low impedance circuit element of several Ω or so and a standard impedance of 500 for the input/output of a high frequency circuit.
It is an object of the present invention to provide a compact impedance conversion circuit that has improved uniformity, is easy to manufacture, and is easy to manufacture.

[Means to solve the problem]

FIG. 1 shows an original configuration diagram of the present invention. In the figure, 1 is a transmission line with characteristic impedance Z, 2 and 3 are capacitors each having the same capacitance IC, 4 is a transmission line with characteristic impedance Zo or a connection terminal with impedance Zo, and 5 is a transmission line with characteristic impedance z1. It is a line, a connection terminal with an impedance of Z+, or a circuit element with an input impedance of Z+.

The line length of the transmission line 1 is shorter than a quarter wavelength of the frequency used, and its characteristic impedance Z is set to be greater than or equal to f7. Each capacitor 2.5 is connected to a ground conductor.

[Effect]

Characteristic impedance of transmission line 1 2. and capacitor 2
The capacitances C of and 3 are respectively expressed by the following equations.

Z-F7:]]/ stn &
(2) C-=cos fl/ (2yr r rj'
:D:]]) ■Here, θ is the electrical length of the transmission line 1, and since the line length of the transmission line 1 is shorter than a quarter wavelength of the operating frequency f, 0°<θ<90°. Therefore, the characteristic impedance Z is equal to or larger than F-=ζ according to the equation 0.

Now, as an example, Zo is 50Ω and Z+ is 1Ω.

Consider the case where the frequency used is 10 GHz. First, let's consider the length of the transmission line as 1/45th of the wavelength3. In this case,
Since the electrical length θ is 8°, the characteristic impedance Z of the transmission line 1 is 510 from the equation 0, and the capacitance C of the capacitors 2 and 3 subtracted from the equation 0 is 2.23 OF. The length of the transmission line 1 being 1/45 wavelength corresponds to being shortened to 1/10th or less of the length of the transmission line 6 of the conventional impedance conversion circuit, which is 1/4 wavelength. Moreover, the characteristic impedance l of the transmission line 1 can be increased from 70 in the conventional example to 510, and this line impedance can be easily manufactured using a microstrip line or a coplanar line.

On the other hand, the characteristic impedance Z of the transmission line 1 to be used may be given first. For example, if the characteristic impedance Z of the transmission line 1 you want to use is 700, the electrical length θ should be 5.8°, and in this case, the capacitance C of the capacitor
is 2.24 pF.

In this way, in the present invention, the characteristic impedance of the transmission line 6 of the conventional quarter-wavelength impedance conversion circuit is 0).
Unlike the value determined by the formula, there is a degree of freedom in determining the characteristic impedance Z and line length.

As described above, the present invention miniaturizes the circuit by using a transmission line shorter than the length of the quarter-wave transmission line used in the conventional impedance conversion circuit, and adds a capacitor to improve the characteristics of the transmission line. By increasing the impedance, you can change the impedance using microstrip lines, coplanar lines, and slot lines! ! ! 5.It is different from conventional circuits in that it has a degree of freedom in which it can be manufactured within a line impedance range (generally 40Ω to 70Ω) that makes the installation and manufacturing of the circuit good and easy. Characteristics equivalent to those of a conversion circuit can be obtained.

The transmission line 1 is a cobrape line formed on a dielectric substrate such as a gallium arsenide substrate, and the capacitor 2
．． 3 may have a structure including a ground conductor of this coplanar line and a conductor facing this ground conductor with an insulator interposed therebetween. Further, the transmission line 1 is a slot line formed on a dielectric substrate such as a gallium arsenide substrate,
The above-mentioned shield 2.3 may have a structure consisting of two conductors of the slot line and a third conductor facing each other with an insulator interposed therebetween.

〔Example〕

2nd F! ! I shows a perspective view of a first embodiment of an impedance conversion circuit according to the present invention. This embodiment uses a coplanar line as a transmission line and has a configuration suitable for a monolithic microwave concentrator M circuit. In the figure, 10 is a dielectric substrate such as a gallium arsenide substrate, 11 is a prepped line constituting an impedance conversion circuit, 12 and 1
3 is a capacitor constituted by a ground conductor of the coplanar line and a conductor plate facing the ground conductor through an insulating film.

Further, 14 and 15 indicate a coplanar line for connection, a terminal for connection, or a circuit element such as a G1FET.

According to this embodiment, it is possible to easily manufacture an impedance conversion circuit between ultra-low impedance and 500 nm, which could not be achieved with a conventional quarter-wavelength impedance conversion circuit using a coplanar line.

FIG. 3 shows a perspective view of a second embodiment of the invention.

This example is an example in which a slot line is used as a transmission line.
20 is a dielectric substrate such as a gallium arsenide substrate, 21 is a slot line constituting an impedance conversion circuit, 22 and 23 are two conductors of the slot line 21, and a second conductor that faces these two conductors via an insulating film. This is a capacitor composed of three conductor plates. This third conductor plate has a potential equal to that of the ground conductor and behaves similarly to the ground conductor. Reference numerals 24 and 25 indicate connection slot lines, connection terminals, or circuit elements such as FETs.

According to this embodiment, one quarter of the conventional slot line
The wavelength impedance Ill conversion circuit can realize [! An impedance conversion circuit between ultra-low impedance and 50Ω can be easily produced.

Incidentally, since a capacitor has good H and L properties even at high frequencies, the impedance conversion circuit of the present invention can be used even in an ultra-high frequency band.

〔Effect of the invention〕

As explained above, according to the present invention, the transmission line of the impedance conversion circuit can be shortened to make the device more compact, and the characteristic impedance of the transmission line can be adjusted to a range that is easy to manufacture and has good circuit stage weight. In general, it has a degree of freedom in setting the resistance between 40Ω and 70Ω.

Further, since the capacitor has good performance even at high frequencies, the impedance conversion circuit of the present invention has the advantage that the number of circuits J1 can be made with high precision even in the high frequency band, and characteristics as designed can be obtained. By using the present invention, matching circuit sections of various high-frequency circuits can be downsized without causing characteristic deterioration. In particular, high-output amplifiers require a matching circuit between ultra-low input/output impedance transistors or FETs and the amplifier's input/output impedance (generally 500Ω), and if the matching circuit is constructed using the impedance conversion circuit of the present invention, It is possible to simultaneously reduce the size of the amplifier and improve its design. Furthermore, the present invention is suitable for integration and is effective in application to high frequency circuits that require small size and good acid resistance, such as monolithic microwave integrated circuits.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is a perspective view of the first embodiment of the present invention using a cobra loop line, and Fig. 3 is a perspective view of the second embodiment of the present invention using a slot line. 4 are diagrams showing an example of a conventional impedance conversion circuit. 1... Transmission line, 2.3.12.13.22゜23.
... Capacitor, 4.5... Connection transmission line, connection terminal or circuit element, 10.20... Dielectric substrate, 1...
・Cobrape line, 21...slot line. Figure Figure

Claims (1)

[Claims] In an impedance conversion circuit that performs impedance conversion between a first impedance Z_0 and a second impedance Z_1 using a transmission line, the line length of the transmission line is made shorter than a quarter wavelength of the operating frequency, and The characteristic impedance of the transmission line is √(Z_0・Z
_1) An impedance conversion circuit set as above and characterized in that both ends of the transmission line are connected to a ground conductor separately via first and second capacitors having the same capacitance.