JPH09162602A - High frequency single pole double throw switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single pole double throw switch with a simple configuration in which the scale of the circuit is made small and the power consumption is reduced while keeping conventional switching functions. SOLUTION: This high frequency single pole double throw switch has a common terminal 10 and a couple of distribution terminals 11, 12 each connecting to the common terminal 10 via a distributed constant line 1 (2), and a semiconductor switching element such as a PIN diode 13 is interposed between either of the distribution terminals 11, 12 and a ground point (GND). Lines with a characteristic impedance having a multiple of the 4th root of 2 with a characteristic impedance of a high frequency transmission synchronizing signal connecting to the common terminal 10 and a couple of the distribution terminals 11,12 and whose transparent phase angle is 90 deg. are used for the distributed constant lines 1, 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency single pole double throw switch used in a microwave band and a millimeter wave band.

[0002]

2. Description of the Related Art Conventionally, a single-pole double-throw switch using a semiconductor switching element (hereinafter referred to as SPDT switch)
It has been known. This type of SPDT switch is excellent in high-speed switching performance, and is therefore widely used for switching between transmission waves and reception waves in, for example, wireless communication devices. 9 and 10 are both examples of SPDT switches using pin diodes as switching elements.

The SPDT switch shown in FIG. 9 is, for example,
A pair of distributed constant lines 41, 42 having the same characteristic impedance as the characteristic impedance of the high frequency transmission system and a transmission phase angle of 90 degrees are input to the common terminal 10 for inputting a high frequency signal.
One end of each of these is connected to form a three-terminal circuit network. The branch terminals 11 and 12 at the other ends of the distributed constant lines 41 and 42 are respectively provided with the diode 13 which is a semiconductor switching element.
a and 13b are shunted (branched) from the signal line to the ground portion (GND). Such a connection form is generally called a "shunt type".

In the shunt type SPDT switch, by applying a negative voltage to the bias terminal 15a of one diode 13a through the choke coil 14a, the diode 13a is turned off and the impedance between the branch terminal 11 and GND is opened. Set a close value. The other diode 13
By applying a positive voltage to the bias terminal 15b of b through the choke coil 14b, the diode 13b is turned on, and the impedance between the branch terminal 12 and GND becomes a value close to a short circuit. Observing this state at branch point A,
On one branch terminal 11 side, the line state of the distributed constant line 41 is preserved as it is, and the switch functions as a conductive state. Further, the distributed constant line 42 is opened on the other branch terminal 12 side, and the switch function is cut off. The above state is reversed by switching between positive and negative bias. This is the operating principle of the shunt type SPDT switch.

Further, the SPDT switch shown in FIG.
A forward end of each of the pair of diodes 13a and 13b is connected to a common terminal 10 for inputting a high frequency signal,
The opposite ends of the diodes 13a and 13b are connected to the branch terminals 11 and 12, respectively. A DC bias return choke coil 43 is connected between the branch point A and GND. Such a connection form is used for each diode 1
Since 3a and 13b are connected in series between the common terminal 10 and the branch terminals 11 and 12, they are generally called "series type".

In the series type SPDT switch, each of the bias terminals 15a and 15b has a choke coil 14a,
The diodes 13a and 13b are turned on or off by applying mutually opposite positive and negative voltages via 14b. Observing this state at the branch point A, one branch terminal 11 side connected to the diode 13a in the ON state becomes conductive, and the other branch terminal 12 side connected to the diode 13b in the OFF state is opened. Become. If the positive and negative of the bias are reversed, the above state is reversed. This is the operating principle of the series type SPDT switch.

In actual use, the SPDT switch may be constructed by combining the "shunt type" and the "series type" depending on the operating frequency band and the required performance.

[0008]

As described above, in the conventional SPDT switch composed of "shunt type", "series type", or a combination thereof, it is necessary to have at least two switching elements and their driving circuits. Becomes
Also, the insertion loss of the switching element during conduction,
Isolation characteristics at the time of interruption are usually designed to be equal in each branch path.

However, when the SPDT switch is actually incorporated in a wireless communication device or the like, depending on the purpose of use, the insertion loss during conduction and the isolation characteristics during interruption do not necessarily have to be equal in both branch paths. There is. For example, in the case where the condition that the loss and the isolation of the receiving system are emphasized and the characteristic of the loss and the isolation of the transmitting system is not important as long as there is a switching function, as in the conventional SPDT switch, It is not necessary to have the same characteristics with respect to. Even in a limited application under such a condition, the SP having the above-mentioned structure is conventionally used.
I had no choice but to adopt a DT switch. Therefore, the circuit scale including the switching element and its drive circuit becomes larger than necessary, resulting in high cost, and extra power consumption.

Therefore, an object of the present invention is to solve the conventional SPDT.
An object of the present invention is to provide an SPDT switch having a simple structure that can reduce the circuit size and power consumption while maintaining the switch function.

[0012]

In order to solve the above problems, the present invention provides an improved shunt type SPDT switch and series type SPDT switch. The shunt type SPDT switch of the present invention has one common terminal and a pair of branch terminals respectively connected to the common terminal via a distributed constant line, and one of the pair of branch terminals and a ground portion are connected. A semiconductor switching element is interposed between the distributed constant lines, and the distributed constant line has a characteristic impedance that is a square root of 2 times the characteristic impedance of a high-frequency transmission system connected to the common terminal and the pair of branch terminals. And the transmission phase angle is 90 degrees.

The series type SPDT switch of the present invention has one common terminal and a pair of branch terminals respectively connected to the common terminal via a distributed constant line, and any one of the pair of branch terminals. A semiconductor switching element is connected in series between the terminal and the common terminal, and the distributed constant line is 2 with respect to the characteristic impedance of the high frequency transmission system connected to the common terminal and the pair of branch terminals.
It is characterized by having a characteristic impedance that is four times the root power of and having a transmission phase angle of 90 degrees.

As the semiconductor switching element, a pin diode or a field effect transistor can be used depending on the application. Further, instead of the distributed constant line, a lumped constant line equivalent to the distributed constant line can be used.

(Principle of Operation) Next, the principle of operation of each SPDT switch will be described. First, the operation of a general distributed constant line will be described with reference to FIG. In FIG. 1A, the normalized characteristic impedance Z is the square root of 2 and the transmission phase angle θ
Indicates that the power source E having the characteristic impedance Zo is connected to one end a of the 90 ° distributed constant line and the load impedance Zo is connected to the other end b thereof. In this case, the impedance seen from the end a toward the load side can be defined by the square of the normalized characteristic impedance Z of the distributed constant line. Here, the normalized characteristic impedance Z is the characteristic impedance of the distributed constant line,
Characteristic impedance of the system, that is, characteristic impedance Z of the high frequency transmission system connected to the input and output ends of the distributed constant line
It is divided by o. FIG. 1 (b) shows a state in which one distributed constant line shown in FIG. 1 (a) is connected, and FIG. 1 (c) shows two similar lines connected in parallel from the a end as a base point. It shows the state. The reflection coefficient Γa at the end a in FIGS. 1B and 1C is expressed by the equation (1). Γa = (√2-1) / (√2 + 1) (1)

Based on the above points, the semiconductor switching element is connected in a shunt type or a series type to the distributed constant line whose normalized characteristic impedance Z is the fourth root of 2 and whose transmission phase angle θ is 90 degrees. The operation principle in the case will be described.

(1) Case of shunt type FIG. 2 is an explanatory view of the principle of the case of shunt type. Referring to FIG. 2, the power source E having the characteristic impedance Zo and the first and second distributed constant lines 1 and 2 are connected to the end a corresponding to the common terminal. A semiconductor switching element is shunt-connected to the end b between the first distributed constant line 1 and the load Zo. In the figure, the broken line is an equivalent circuit when the pin diode 3 is used as the semiconductor switching element. The pin diode 3 has an equivalent impedance (Rs) that is 1/10 or less of the characteristic impedance of the high frequency transmission system when forward biased. On the other hand, at the time of reverse bias, due to the junction capacitance Cj,
The equivalent impedance is 10 times or more the characteristic impedance of the high frequency transmission system. Therefore, at the time of forward bias, the end b is in a state close to a short circuit. At this time, a
From the end, it is approximated that the first distributed constant line 1 is almost open and only the second distributed constant line 2 is connected. On the other hand, when reverse bias is applied, pi is added to the end b.
Since there is almost no effect of connecting the n-diode 3, it is approximated as if the first and second distributed constant lines were connected at the same time.

If this is made to correspond to the function of the SPDT switch, at the time of forward bias, the a end and the c end become conductive, and a low insertion loss characteristic can be obtained. At this time, the a end and the b end are in a cutoff state, and high isolation characteristics are obtained. This is the same performance as a conventional SPDT switch. Further, the reflection coefficients at the a-end and the c-end, which are in conduction, are both the values of the above equation (1), which poses no practical problem. On the other hand, when a reverse bias is applied to the pin diode 3, both the a terminal and the b terminal and the a terminal and the c terminal become conductive, so that the signal input to the a terminal is branched into two.
It is led to the edge and the edge c. At this time, the reflection coefficient at the a end has the value shown by the equation (1), and the reflection coefficient Γb at the b end and the c end has the value shown by the equation (2). Γb = 1 / (1 + √2) ・ ・ ・ (2)

(2) Case of series type FIG. 3 is an explanatory view of the principle in the case of series type. Referring to FIG. 3, a power source E having a characteristic impedance Zo, a first distributed constant line 1 in which semiconductor switching elements are connected in series, and a second distribution in which no semiconductor switching elements are present are provided at an end a corresponding to a common terminal. The constant line 2 is connected. In the figure, the broken line is an equivalent circuit when a pin diode is used as the semiconductor switching element.
The equivalent impedance value of the pin diode 3 at the time of forward bias and reverse bias is the same as that of the shunt type described above. That is, at the time of reverse bias, the first distributed constant line 1 is in a substantially open state as viewed from the end a,
The end and the end b are in a disconnected state, and high isolation characteristics can be obtained. Further, a conduction state is established between the a end and the c end, and a low insertion loss characteristic is obtained. At this time, the reflection coefficients at the a-end and the c-end in the conductive state both have the values shown by the equation (1), which poses no practical problem. On the other hand, at the time of forward bias, the first and second distributed constant lines are simultaneously connected, and the signal input to the a terminal is branched into two and guided to the b terminal and the c terminal. At this time, the reflection coefficient at the end a has the value shown by the equation (1), and the reflection coefficient at the ends b and c has the value shown by the equation (2).

As described above, by setting the characteristic impedance of the distributed constant lines 1 and 2 and the transmission phase angle θ to specific values, the function of the SPDT switch can be realized by only one semiconductor switching element and its drive circuit. You can

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the SPDT switch of the present invention will be described with reference to FIGS. FIG.
(A) is a shunt type SPDT switch using a pin diode as a semiconductor switching element, and corresponds to the principle explanatory diagram shown in FIG. 2. In the figure, components having the same functions as those shown in FIG. 2 are designated by the same reference numerals.

In the SPDT switch having the configuration shown in the figure, the normalized characteristic impedance Z of each of the distributed constant lines 1 and 2 is the fourth root of 2, and the transmission phase angle θ is 90 degrees. Therefore, a forward bias is applied to the bias terminal 15. Then, the common terminal 10 and the first branch terminal 11 are cut off from each other, and high isolation characteristics are obtained. Therefore, the signal input to the common terminal 10 is led to only the second branch terminal 12 with low loss. Reference numeral 14 is a choke coil. On the other hand, when the reverse bias is applied to the bias terminal 15, the first and second branch terminals 1 are connected to the common terminal 10.
Since both 1 and 12 are in a conductive state, the signal input to the common terminal 10 is branched into two and is guided to each branch terminal 11 and 12. In any of the above cases, each terminal 10, 11,
The reflection coefficient at 12 does not pose a practical problem.

The electrical characteristics of the SPDT switch thus constructed are shown in FIG. FIG. 8A shows circuit constants of the constituent elements of FIG. Further, FIG. 7B is a loss characteristic diagram between the common terminal 10 and the second branch terminal 12, and FIG. 7C is a loss characteristic diagram between the common terminal 10 and the first branch terminal 11. 6D is a diagram showing the return loss characteristic of the common terminal, and FIG. 8E is a diagram showing the return loss characteristic of the first and second branch terminals 11 and 12. As is clear from these figures, it is proved that, for a limited purpose, an SPDT switch having characteristics practically no problem can be obtained.

FIG. 4B shows a shunt type SPDT switch using a field effect transistor (FET) as a semiconductor switching element, and corresponds to the principle explanatory diagram shown in FIG. This SPDT switch is connected to the gate G of the FET 16 from the control terminal 18 through the high resistance 17.
By applying the control voltage (0v and negative voltage) to
It realizes the same function as in the case of the configuration shown in FIG. When 0v (same potential as GND) is applied as the control voltage, F
The drain D and the source S of the ET16 have low resistance.
The pin diode 13 shown in (a) is replaced with the same state as when the forward bias is applied. Further, when a negative voltage, that is, a voltage about the same as the pinch-off voltage of the FET 16 is applied as the control voltage, the drain D of the FET 16 is
There is only parasitic capacitance between the source and the source S, and the state is replaced with the same state as when the reverse bias is applied to the pin diode 13 shown in FIG. Other operations are similar to those in the case of FIG. The remarkable difference between the configurations shown in FIGS. 4A and 4B is that the former is for high power operation in which distortion characteristics (eg, intermodulation distortion) pose a problem due to the nature of a semiconductor switching element, and the latter is for switching speed. It is suitable for low power operation that requires high speed and low power consumption.

FIG. 5A shows a series type SPDT switch using a pin diode as a semiconductor switching element, and corresponds to the principle explanatory diagram shown in FIG. In the figure, components having the same functions as those of the components shown in FIG. 3 are designated by the same reference numerals.

In the SPDT switch having the configuration shown in the figure, the normalized characteristic impedance Z of each of the distributed constant lines 1 and 2 is the fourth root of 2, and the transmission phase angle θ is 90 degrees. Therefore, a reverse bias is applied from the bias terminal 15. Then, the pin diode 13 is turned off. Therefore, the common terminal 10 and the first
A high isolation characteristic is obtained when the connection between the branch terminal 11 and the branch terminal 11 is cut off. Therefore, the signal input to the common terminal 10 is guided to the second branch terminal 12 only with low loss. On the other hand, when a forward bias is applied to the bias terminal 15, the signal input to the common terminal 10 is branched into two and is guided to the first and second branch terminals 11 and 12. At this time, the reflection coefficients at the terminals 10, 11, and 12 are values that do not pose a problem in practical use.

FIG. 5B shows a series type SPDT switch using an FET as a semiconductor switching element, and corresponds to the principle explanatory view shown in FIG. In the figure, components having the same functions as the components shown in FIG. 4B are designated by the same reference numerals. The on / off relationship between the control voltage applied from the control terminal 18 and the FET 16 is shown in FIG.
The description in the configuration of (b) is valid as it is.

6 (a) and 6 (b) are shown in FIG.
In each SPDT switch shown in (b), the distributed constant lines 1 and 2 are replaced with lumped constant lines 100 and 200 equivalent to the distributed constant lines 1 and 2. The illustrated element values L and C are expressed by the following equations (3) and (4), respectively. L = (1 / 2πf) ・ Z ・ sinθ ・ ・ ・ (3) C = (1 / 2πf ・ Z) ・ tanθ / 2 ・ ・ ・ (4)

In the above equations, Z is the normalized characteristic impedance, the 4th root of 2, f is the operating frequency (Hz), θ
Is the transmission phase angle. The SPDT switch having the configuration shown in the figure can maintain all the above-mentioned switching functions and can make all the constituent elements, particularly the transmission lines, lumped constants.
It becomes easy to convert to C (monolithic maicrowave integrated circuit).

7 (a) and 7 (b) are shown in FIG.
In each SPDT switch shown in (b), the distributed constant lines 1 and 2 are replaced with lumped constant lines 100 and 200 equivalent to the distributed constant lines 1 and 2. The illustrated element values L and C are represented by the above equations (3) and (4), respectively.
As in the case of FIG. 6, the advantage of using such a configuration is that it is useful in the MMIC implementation.

The present invention has been described above based on a plurality of embodiments. However, the semiconductor switching element used in the present invention may be any one as long as it has excellent switching characteristics between the conductive state and the cutoff state. It is not limited to the FET.

[0032]

As is apparent from the above description, according to the present invention, since only one semiconductor switching element and its driving circuit are required, the circuit scale becomes about half as compared with the SPDT switch having the conventional structure. It is possible to simultaneously achieve downsizing, low power consumption, and cost reduction. In addition, for example, because the distortion characteristics are important for high power operation, pin diodes are used, and for low power operation, FETs that have high switching speed and low power consumption are used. The element can be arbitrarily selected, and the SPDT switch having a wide range of applications can be realized. Further, by making the constituent elements into MMICs, smaller SPDT switches can be mass-produced, so that the practical effects thereof are immense.

[Brief description of the drawings]

1 (a), (b) and (c) are SPDTs of the present invention.
The principle explanatory drawing of a switch.

FIG. 2 is an explanatory view of the principle of the shunt type SPDT switch according to the present invention.

FIG. 3 is an explanatory view of the principle of a series type SPDT switch according to the present invention.

FIG. 4A is an explanatory view of an embodiment of a shunt type SPDT switch of the present invention using a pin diode,
(B) is explanatory drawing of one Embodiment of the shunt type SPDT switch of this invention which used FET.

5A is an explanatory view of an embodiment of a series type SPDT switch of the present invention using a pin diode, FIG.
(B) is explanatory drawing of one Embodiment of the series type SPDT switch of this invention which used FET.

6A and 6B are explanatory diagrams of an SPDT switch in which the distributed constant line in FIGS. 4A and 4B is replaced with a lumped constant line.

7A and 7B are explanatory views of an SPDT switch in which the distributed constant line in FIGS. 5A and 5B is replaced with a lumped constant line.

8A is a diagram showing an example of circuit constants of the SPDT switch having the configuration of FIG. 4A, and FIGS. 8B to 8E are electrical characteristic diagrams in this case.

FIG. 9 is an explanatory diagram of a shunt type SPDT switch having a conventional configuration.

FIG. 10 is an explanatory diagram of a series type SPDT switch having a conventional configuration.

[Explanation of symbols]

1, 2 distributed constant line 3, 13 pin diode (semiconductor switching element) 10 common terminal 11, 12 branch terminal 14 choke coil 15 bias terminal 16 FET (semiconductor switching element) 17 high resistance 18 control terminal 100, 200 lumped constant line

Claims (5)

[Claims] 1. A semiconductor switching device, comprising: one common terminal; and a pair of branch terminals connected to the common terminal via distributed constant lines, respectively, and between any one of the pair of branch terminals and a ground portion. A high-frequency single-pole double-throw switch in which an element is interposed, wherein the distributed constant line has a characteristic impedance that is a square root of 2 times the characteristic impedance of a high-frequency transmission system connected to the common terminal and a pair of branch terminals. And a transmission phase angle of 90 degrees, a high frequency single pole double throw switch. 2. A semiconductor device having one common terminal and a pair of branch terminals each connected to the common terminal via a distributed constant line, and a semiconductor is provided between any one of the pair of branch terminals and the common terminal. A high frequency single pole double throw switch in which switching elements are connected in series, wherein the distributed constant line is the fourth root of 2 with respect to the characteristic impedance of a high frequency transmission system connected to the common terminal and a pair of branch terminals. A high-frequency single-pole double-throw switch having double characteristic impedance and a transmission phase angle of 90 degrees. 3. The high frequency single pole double throw switch according to claim 1, wherein the semiconductor switching element is a pin diode. 4. The semiconductor switching element is a field effect transistor, as claimed in claim 1.
The described high frequency single pole double throw switch. 5. The high frequency single pole double throw switch according to claim 1, wherein a lumped constant line equivalent to the distributed constant line is used instead of the distributed constant line.