JPH0652845B2 - Transmission line - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a line used in a high-frequency circuit, which is a coplanar type transmission line that maintains a constant impedance.

[Prior Art] Conventionally, when the input circuit having the configuration using the FET Q ₁ as shown in FIG. 6 is configured by a coplanar type transmission line, it is realized by the configuration as shown in FIG. 7. In FIG. 6, I
Is an input terminal, C ₁ is a capacitor, Q ₁ is a FET, and R ₁ is a terminating resistor. Further, in FIG. 7, the same reference numerals as those in FIG. 6 indicate the same parts, 1 is a center conductor serving as the input end I, 2 is a ground conductor serving as a ground end, 4 is a connecting wire, and 5 is a dielectric substrate. is there.

In the input circuit of FIG. 6, the signal input to the input terminal I has its DC component cut by the capacitor C ₁ , then terminated by the terminating resistor R ₁ and input to the gate of the FET Q ₁ .

In the coplanar type transmission line of FIG. 7 (hereinafter simply referred to as a transmission line), a signal is input to the center conductor 1, and the pattern width of the center conductor 1 and the center conductor 1 and the ground conductor 2 The spacing is mainly determined by the impedance of the transmission line. And here, a part of the pattern of the central conductor 1 is cut, the capacitor C ₁ is mounted, and the terminating resistor R
₁ is formed at the right end of the center conductor 1.

That is, the transmission line is interrupted in a DC manner (conducted in an AC manner) on the way and then AC terminated by the terminating resistor R ₁ . Then, the FET is bonded by bonding from the central conductor 1 near the terminating resistor R ₁ of this transmission line.
Connecting to Q ₁ . In addition, the hatched portion in FIG. 7 where no reference numeral is given indicates an insulating member. The same applies to each of the following figures.

[Problems to be Solved by the Invention] A conventional transmission line for realizing the above-described input circuit shown in FIG. 6 has a configuration in which a terminating resistor R ₁ is inserted after a capacitor C ₁ . Therefore, it can be used in the case of an AC amplifier or the like that does not require DC termination, but cannot be used in the case where a pulse waveform cannot be faithfully transmitted unless it is DC terminated, such as a pulse circuit. For this reason, it is necessary to realize a circuit having a configuration in which the terminating resistor R ₁ is placed in front of the capacitor C ₁ by a coplanar type transmission circuit, but conventionally, there was no transmission line that realized this in a wide band and with good high frequency characteristics. .

That is, a transmission line having the configuration shown in FIG. 9 is conceivable as a transmission line that realizes the input circuit shown in FIG.
There were the following problems.

A transmission line terminated with two termination resistors R ₁ (each having a resistance value twice that of R ₁ in FIG. 8) and a capacitor C
Another transmission line for connecting ₁ and the connecting wire 4 is required. Although this transmission line has a short line length, it cannot be said to be integral with the terminated transmission line in terms of high frequency, and thus causes various deterioration in performance.
Specifically, ringing occurs in the pulse waveform and the input impedance deteriorates in the high frequency range.

The present invention has been made to solve such a problem, and an object thereof is to obtain a coplanar type transmission line having a circuit configuration in which a terminating resistor is brought before a capacitor and having a wide band and good high frequency characteristics. To do.

[Means for solving problems]

A transmission line according to the present invention is a coplanar type transmission line in which a terminating resistor is connected between a center conductor and a ground conductor, and an input signal is transmitted while maintaining a constant impedance, and an island-shaped conductor is formed in the center conductor. The terminal resistor side of this island-shaped conductor is connected to the electrode of the capacitor whose other electrode is connected to the center conductor, and the other side is also connected to the center conductor, and the other side is smaller than the capacitor. It is connected to the electrodes of a capacitor having good high-frequency characteristics formed in the above.

That is, according to the present invention, the impedance of the coplanar type transmission line (hereinafter, simply referred to as a transmission line) is determined by the pattern width of the center conductor and the distance between the center conductor and the ground conductor as described above. The intent is that the high frequency impedance of the transmission line is not affected even if an island-shaped conductor that is cut off in terms of direct current but is conductive in high frequency is formed.

The capacitors connected to both ends of the island-shaped conductor electrically connect the center conductor and the island-shaped conductor with each other at high frequencies.

With such a configuration, in addition to the terminated transmission line,
This avoids providing another transmission line, which is a problem in the past.

[Action]

In the present invention, after the signal input from the center conductor is terminated by the terminating resistor, the low frequency signal passes through the capacitor and the island conductor connected to the center conductor, and the high frequency signal is transmitted from the center conductor. The signal is transmitted through a capacitor having a small size and a small residual inductance, that is, a high frequency characteristic.

〔Example〕

FIG. 1 is a diagram showing the configuration of an embodiment of the transmission line of the present invention.

In FIG. 1, the same symbols as in FIG. 7 indicate the same parts,
Reference numeral 3 is an island-shaped conductor formed in the central conductor 1, C _2a is a capacitor having a small capacity but good high frequency characteristics, and C _2b wave is a multilayer type capacitor having a large high capacity but not good high frequency characteristics. If it is large, it is not limited to the laminated type). 2 is an equivalent circuit diagram of the coplanar type transmission line shown in FIG.

Here, the pattern width of the central conductor 1 is narrowed in the middle and then widened again, and is connected to the terminating resistor R ₁ and the multilayer capacitor C _2b whose other end is connected to the island-shaped conductor 3 and is connected to the transmission line. The impedance is set so that a constant value can be maintained mainly by the ratio of the distance between the center conductor 1 and the ground conductor 2 surrounding the center conductor 1. This is connected with the conductor 3, FETs Q ₁ of the capacitor C _2a and islands are connected by the connection wires 4 from the capacitor C _2a, narrowing the width of Nearby central conductor 1 capacitor C _2a is small in size This is because the FET Q ₁ can be mounted near to the FET Q ₁ .
Therefore, the length of the connecting wire 4 can be short, and high frequency characteristics can be improved.

The high frequency signal is mainly transmitted from the central conductor 1 to the FET Q ₁ via the capacitor C _2a , and the low frequency signal is mainly the central conductor 1, the multilayer capacitor C _2b , the island-shaped conductor 3, and the like.
It is transmitted to the FET Q ₁ via the electrode of the capacitor C _2a . At this time, the distance between the capacitor C _2a and the multilayer capacitor C _2b does not matter at low frequencies. Further, here, the upper limit frequency is extended by making the capacitor C _2a smaller than the multilayer capacitor C _2b to reduce the residual inductance and the like.

Further, FIG. 3 is a diagram showing the structure of another embodiment in which the capacitance of the multilayer capacitor C _2b is increased in the transmission line shown in FIG. 1, and in this embodiment two terminating resistors are branched. R
_Two multilayer capacitors C _2b are mounted together with No. 2, and by doing so, it is possible to design with an arbitrary layout.

The embodiment shown in FIG. 4 prevents the embodiment of FIG. 1 from resonating at a certain frequency because the distance between the island-shaped conductor 3 between the capacitor C _2a and the laminated capacitor C _2b becomes too long. In order to do so, the resistor R ₃ is inserted into the island-shaped conductor 3.

Furthermore, the embodiment shown in FIG. 5 is realized by using only one large-capacity multilayer capacitor C _2b, and can be used only when the high frequency characteristics are not a serious problem. Further, although the central conductor 1 has the curved portion in the above-described embodiment, the present invention is not limited to this.

〔The invention's effect〕

As described above, according to the present invention, in a coplanar type transmission line in which a terminating resistor is connected between a center conductor and a ground conductor and an input signal is transmitted while maintaining a constant impedance, an island-shaped conductor is formed in the center conductor. The terminal resistor side of this island-shaped conductor is connected to the electrode of the capacitor whose other electrode is connected to the center conductor, and the other electrode is connected to the center conductor of the other side and is smaller than the capacitor. Since it is connected to a capacitor having good high-frequency characteristics in size, that is, having a small residual inductance, there is an advantage that a transmission line having a wide band and good high-frequency characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the transmission line of the present invention, FIG. 2 is an equivalent circuit diagram of the transmission line shown in FIG. 1, and FIGS. 3, 4, and 5 show the present invention. FIGS. 6 and 8 are diagrams showing the configuration of another embodiment, respectively, and FIGS. 7 and 9 are diagrams showing the configuration of a conventional coplanar transmission line. . In the figure, 1 is a central conductor, 2 is a ground conductor, 3 is an island-shaped conductor,
4 is a connecting wire, 5 is a dielectric substrate, C _2a is a capacitor,
C _2b is a multilayer capacitor, Q ₁ is a FET, R ₁ and R ₂ are termination resistors, and R ₃ is a resistor.

Claims (1)

[Claims] 1. In a coplanar type transmission line in which a terminating resistor is connected between a center conductor and a ground conductor and which transmits an input signal while maintaining a constant impedance, an island-shaped conductor is formed in the center conductor, The terminal resistor side of this island-shaped conductor is connected to the electrode of the capacitor whose other electrode is connected to the center conductor, and the other electrode is connected to the same center conductor on the opposite side, and is smaller than the capacitor. A transmission line characterized in that the frequency range is widened by connecting to an electrode of a capacitor having a good high-frequency characteristic formed in dimensions.