JPH0366841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microwave semiconductor switch that switches a propagation path depending on whether the power of an incident radio wave is high or low.

[Conventional technology]

Figure 3 shows, for example, the symposium "IEEE1982Microwave and Mili" held in June 1982 in the United States.
−meter Wave Monolithic Circuits
1 is a diagram showing an example of the structure of a conventional microwave semiconductor switch shown in a collection of papers of ``Symposium''.

In the figure, 1 is a metal base, 2 is a semiconductor substrate,
3 is a first input/output line, 4 is a second input/output line,
5 is a third input/output line, 6 is a low impedance line with a length of 1/2 wavelength, and 7 is a high impedance line with a length of 1/2 wavelength, and these microstrip lines are connected to the semiconductor substrate. It consists of 2.

Further, 8 is a first field effect transistor (hereinafter abbreviated as the first FET), 9 is a drain electrode of the first FET, 10 is a source electrode of the first FET, 1
1 is the gate electrode of the first FET. first
The source electrode 10 of the FET is connected to the metal base 1 using a gold wire 12 or the like, and the drain electrode 9 of the first FET is connected to the low impedance line 6.

On the other hand, 13 is a second field effect transistor (hereinafter abbreviated as second FET), 14 is a drain electrode of the second FET, 15 is a source electrode of the second FET,
16 is the gate electrode of the second FET. second
The source electrode 15 of the FET is connected to the metal base 1 using a gold wire 12 or the like, and the drain electrode 14 of the second FET is connected to the high impedance line 7.

A bias voltage is applied to the gate electrode 11 of the first FET 8 from a first bias terminal 18 via a bias circuit 17 made of a microstrip line. Similarly, a bias voltage is applied to the gate electrode 16 of the second FET 13 from the second bias terminal 19 via the bias circuit 17.

Furthermore, if the point where the first input/output line 3 is connected to the low impedance line 6 and the high impedance line 7 is called a connection point 20, then this connection point 2
A first wire is connected to a low impedance line 6 and a high impedance line 7 at positions 1/4 wavelength from 0, respectively.
In this configuration, the source electrodes of the FET 8 and the second FET 13 are connected.

Note that in order to have the source electrode and drain electrode of both FETs at the same potential, a high impedance grounding line 21 whose tip is connected to the metal base 1 is connected to the first input/output line 3.

Next, the operation will be explained.

FIG. 4 shows an equivalent circuit to explain the operation of the conventional microwave semiconductor switch shown in FIG. 3. In this equivalent circuit representation, the bias circuit 17 and the grounding high impedance line 21 are not shown.

In explaining the operation using FIG. 4, we will first explain the operation separately for the case where a low power microwave is incident from the first input/output line 3, and then the case where a high power microwave of about several W is incident. Let's do it.

First, consider a case where a low-power microwave enters from the first input/output line 3 and propagates to the third input/output line 5.

At this time, the second bias terminal 19 has _{a negative bias voltage V BIAS (} |
V _BIAS |>|V _P |) is applied, and the second FET 13 exhibits high impedance. At the same time, the first bias terminal 18 is set to OV, and the first FET 8 presents a low impedance line. This impedance
Let it be R ₁ . Since this R ₁ is sufficiently smaller than the characteristic impedance Z ₁ of the low impedance line 6, the impedance when looking from the connection point 20 to the second input/output line 4 side becomes a high impedance that is almost in an open state. Therefore, the microwave incident from the first input/output line propagates on the high impedance line 7 side and appears on the third input/output line 5. At this time, since the second FET exhibits high impedance, it does not affect the propagating microwave.

Next, consider a case in which high-power microwaves enter from the first input/output line 3 and are supplied to the second input/output line 4. At this time,
The bias conditions applied to the FET are as follows. That is, the second bias terminal 19 is
OV, the first bias terminal 18 is the pinch-off voltage
Negative bias voltage V _BIAS (｜V _{BIAS ｜}
> |V _P |). Under this bias condition,
The second FET 13 has a low impedance R ₂ , the first
FET8 becomes high impedance. For this reason,
The impedance seen from the connection point 20 from the third input/output line 5 side is a high impedance close to an open state, and the microwave incident from the first input/output line propagates on the low impedance line 6 side and passes through the second input/output line 5.
appears on the input/output line 4.

Here, the first FET 8 exhibits high impedance and does not affect the microwave propagating through the low impedance line 6 having the characteristic impedance _Z1 .

In the switch in this bias state, since high-power microwaves propagate, the RF current flowing through the second FET 13 and the RF voltage applied to the first FET 8 each have large values. Therefore, it is necessary to use an FET with performance that can withstand this value.

Now, considering the case where a microwave with a power of P Watts is incident, the RF current I flowing through the second FET 13 is expressed by the following equation.

I=2Z ₂ √2Z ₀ P/R ₂ Z ₀ +2Z ₂ ² ...(1) Here, R ₂ is the resistance of the second FET 13 in the OV bias state, and Z ₂ is the characteristic impedance of the high impedance line 7. .

On the other hand, the RF voltage V applied to the first FET 8 can be expressed by the following equation.

V=Z ₁ /Z ₀ √2 ₀ (2) Here, Z ₁ is the characteristic impedance of the low impedance line 6.

For example, input and output power is 5W, Z ₀ = 50Ω, R ₂ =
3Ω, and if Z ₂ is 75Ω and Z ₁ is 40Ω,
Current I and voltage V are I=0.23A and V=14V, respectively.
becomes. Of these, the current value of 0.23 A is the drain current that can be passed through a normal FET with a gate value of 1 mm class, and there is no problem, but the voltage value V = 14 V is a value that may exceed the permissible value for the FET. In other words,
Assuming that the gate bias voltage of the first FET 8 is V _BIAS , the pinch-off voltage is V _P , and the gate breakdown voltage is V _BR , the following relationship is required.

｜V _BR ｜≧V+｜V _P ｜… (3) ｜V _BIAS ｜=1/2V+｜V _P ｜ Pinch-off voltage ｜V _P ｜Assuming = 2V, the breakdown voltage ｜V _BR ｜ is 16V bias voltage ｜ 9V is required as V _BIAS |. This breakdown voltage of 16V cannot be easily obtained with FETs designed for mass production, and there was a problem in that it was difficult to reduce the allowable input power of this type of microwave semiconductor switch to about 3W.

Furthermore, in order to lower the voltage applied to the FET, the electrical length of the low-impedance line 6 needs to be 1/2 wavelength, which poses the problem of increasing the area of the semiconductor substrate 2 that constitutes this microwave semiconductor switch. Ta.

[Problem that the invention seeks to solve]

Conventional microwave semiconductor switches are configured as described above, so in order to increase the allowable input power to several watts, it is necessary to use a manufacturing method for FETs with high breakdown voltage through a special process, resulting in a decrease in yield and There was a problem that it was not suitable for mass production. Also, at the same time,
In order to avoid applying high voltage to the FET as much as possible, a 1/2 wavelength low impedance line was used, which resulted in the problem of an increase in the size of the semiconductor substrate.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a high-power-resistant microwave semiconductor switch for switching the microwave path.

[Means for solving problems]

The microwave semiconductor switch according to the present invention includes:
Near the connection of three input/output lines, one
A FET is inserted in series in one input/output line, and the other FET is connected in parallel to the other input/output line at a position 1/4 wavelength from the connection point.

[Effect]

In the microwave semiconductor switch of this invention, when a microwave with a power of several watts is incident, an FET inserted in series in the input/output line that becomes the output side
Both the FET and the FET immediately connected in parallel to the input/output line on the cut-off side are brought into a low impedance state. Therefore, the RF voltage applied to the FET is low, and even if the FET has a low breakdown voltage, it can handle several watts of power.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the structure of an embodiment of the present invention. A first FET 8 is installed near the connection point 20 between the first, second, and third input/output lines 3, 4, and 5.
is inserted in series between the connection point 20 and the second input/output line 4, and 1/ is inserted from the connection point 20 to the third input/output line 5.
This is a configuration in which second FETs 13 are connected in parallel at the length of four wavelengths. The first inserted in series
FET8 connects the source electrode 9 of the first FET to point 2
0, the drain electrode 10 of the first FET is connected to the second input/output line 4, and the second FET 13 inserted in parallel connects the source electrode 14 of the second FET to the third input/output line 5. The drain electrode 15 of the second FET is connected to the metal base 1 via a gold wire 12.

Further, 21 is a high impedance line for grounding, which is used to ground the drain electrodes and source electrodes of the first and second FETs 8 and 13, one end of which is an input/output line, and the other end of which is made of metal. Base 1
connected to.

Next, the operation of this invention will be explained. FIG. 2 shows an equivalent circuit representation of the embodiment shown in FIG.

In this microwave semiconductor switch, the high power microwave incident from the first input/output line 3 is transferred to the second input/output line 3.
The first input/output line 3
The bias voltage is controlled so that the low power microwave incident from the input/output line 5 is passed through the third input/output line 5.

First, consider the case where high-power microwaves are incident from the first input/output line 3. In this case, the first
FET8 is connected to OV via the first bias terminal 18.
A gate bias voltage of is applied to the first FET.
The impedance between the source electrode and the drain electrode of No. 8 is a low impedance _R1 . On the other hand, the second
A gate bias voltage of OV is similarly applied to the FET 13 via the second bias terminal 19, and the impedance between the source electrode and the drain electrode of the second FET 13 becomes a low impedance _R2 . At this time, the impedance seen from the connection point 20 to the second FET 13 becomes a high impedance close to an open state, so the high power microwave incident from the first input/output line 3 passes through the first FET 8. and propagates to the second input/output line 4. In this state, if we consider the case where a microwave with a power of P watts is incident, the first and second FETs 8,
The RF currents I ₁ and I ₂ flowing through 13 are given by the following equations, respectively.

I ₁ =2√Z ₀ P/2Z ₀ +R ₁ …(4) I ₂ =2√Z ₀ P/2Z ₀ +R ₂ …(5) For example, input power is 3W, Z ₀ =50Ω, R ₁ =
If R ₂ = 3Ω, the first FET8, the second FET
The RF current flowing through 13 is equal to I=0.34A.
At this time, it is added to the first and second FETs 8 and 13.
The RF voltage is equally approximately 1V.

Next, consider a case where low power microwaves are incident from the first input/output line 3.

In this case, the negative gate bias voltage V _BIAS of both the first FET 8 and the second FET 13 is set to a value smaller than the pinch-off voltage _VP , and (|V _BIAS |>|
V _P |) The impedance between the source electrode and the drain electrode exhibits high impedance. Therefore, the microwave incident from the first input/output line 3 propagates toward the third input/output line 5 because the second input/output line 4 side has a high impedance. At this time, the RF voltage applied to both FETs in a high impedance state is sufficiently small to cause no problem with respect to the FET's performance limit, since the propagating microwave is at a low voltage.

In other words, in a microwave semiconductor switch with this configuration, when a microwave with a large current area is incident, the two FETs are biased so that they both present a low impedance line, so an RF voltage exceeding the breakdown voltage of the FET is applied. never be done. Furthermore, 2 exhibiting low impedance
The RF current flowing through one FET increases as the power of the incident microwave increases;
This can be solved by increasing the FET gate width.

〔Effect of the invention〕

As described above, according to the present invention, when high-power microwaves are incident, both FETs are biased so that they have low impedance.
RF applied between the drain and source electrodes of the FET
The voltage will be lower and will not cause damage to the FET.
Therefore, there is no need for FETs with high breakdown voltages, which greatly contributes to improving the yield of switches. Furthermore, since there is no need to lower the RF voltage applied to the FET by using a 1/2 wavelength low impedance line as in the past, there is an effect that miniaturization can be achieved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a microwave semiconductor switch according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of the microwave semiconductor switch shown in FIG. 1, and FIG. 3 is a diagram showing a conventional microwave semiconductor switch. FIG. 4 is an equivalent circuit diagram of FIG. 3. 2 is a semiconductor substrate, 3 is a first input/output line, 4 is a second input/output line, 5 is a third input/output line, 8 is a first field effect transistor, and 9 is a first field effect transistor. A source electrode, 10 a drain electrode of the first field effect transistor, 11 a gate electrode of the first field effect transistor, 13 a second field effect transistor
14 is a source electrode of the second field effect transistor, 15 is a drain electrode of the second field effect transistor, 16 is a gate electrode of the second field effect transistor, 17 is a bias circuit, and 20 is a connection point. It is. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. By integrally configuring a circuit element consisting of a field effect transistor and a microstrip line on a semiconductor substrate, setting the drain electrode and source electrode of the above field effect transistor to the same potential, and changing the bias voltage applied to the gate electrode. In a microwave semiconductor switch that switches the propagation path of microwaves propagating through a microstrip line,
The first input/output line, the second input/output line, and the third input/output line.
The drain electrode and the source electrode of the first field effect transistor are connected in series to the connection point and the second input/output line in the vicinity of the connection point of the input/output line, and approximately 1/2 from the connection point. The configuration is such that the drain electrode of a second field effect transistor whose source electrode is grounded is connected to the position of the third input/output line having a length of four wavelengths in parallel to the third input/output line. Features of microwave semiconductor switch.