JPH06232607A - Attenuator - Google Patents

Abstract

PURPOSE:To make the attenuator comprising a coupler and FETs and resistors connecting thereto small. CONSTITUTION:The attenuator is made up of a coupler 1, FETs 4, 6, 8, 10, 12, 14 connecting to a 90 deg. output port and a separation port of the coupler 1 and resistors 5, 7, 9, 11, 13, 15 respectively in cascade connection to the FETs. Then the circuit is made small by connecting a cascade connection pair comprising the FETs connecting to the 90 deg. output port and the separation port of the coupler and the resistors in cascade connection to the FETs in parallel with the output port and the separation port of the coupler. Moreover, the entire attenuator is made small by integrating the attenuator onto a semiconductor substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digitally controlled variable attenuator for microwave signals, which is used when finely adjusting the attenuation amount of microwave signals.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional embodiment. 1 is input,
Lange coupler having four ports of 0 ° output, 90 ° output and separation, 2 is an input terminal connected to the input port of Lange coupler 1, 3 is an output terminal connected to the 0 ° output port of Lange coupler 1, and 4 is a Lange coupler 1st FET having a drain connected to the 90 ° output port of 1, 5 is a first resistor whose one end is connected to the source of the first FET 4 and the other end is grounded, 6 is a drain to the separation port of Lange coupler 1 Is connected to the second FET, 7 is the second FET 6 at one end
Is a second resistor that is connected to the source and has the other end grounded and has the same resistance value as the first resistor.

Next, the operation will be described. First FET
4 and the second FET 6 are off at the same time, the FET
After that, the microwave signal inputted from the input terminal 2 is totally reflected by the FET and outputted from the output terminal 3 without being attenuated. Next, the first FET 4 and the second FET
When 6 is turned on at the same time, a microwave signal flows through the first resistor 5 and the second resistor 7, part of the signal is absorbed by the resistor, and the signal is attenuated and output. As mentioned above, FE
By turning T on / off, it operates as a variable attenuator capable of changing the passing amount of a signal. The amount of attenuation at this time is determined by the first resistor 5 and the second resistor 6.

[0004]

Since the conventional variable attenuator is constructed as described above, when trying to obtain many kinds of attenuation amounts, several circuits having the same configuration but different resistance values are connected in series. However, there is a problem that the circuit becomes large in size.

The present invention has been made to solve the above problems, and an object thereof is to miniaturize a variable attenuator capable of obtaining various attenuation amounts.

[0006]

SUMMARY OF THE INVENTION A variable attenuator according to the present invention comprises a FET connected to an output end of a coupler connected to a main line in parallel with a subordinate connection pair of a FET and a resistor.
It is characterized by downsizing an attenuator capable of obtaining various attenuation amounts by digital control by turning on / off.

[0007]

In the variable attenuator according to the present invention, the circuit is miniaturized by connecting the subordinate connection pair of the FET and the resistor in parallel to the output end of the coupler connected to the main line.

[0008]

EXAMPLES Example 1. FIG. 1 shows an embodiment of a variable attenuator according to the present invention. In FIG. 1, 1 is input, 0 ° output,
Lange coupler having 90 ° output and four separate ports, 2 is an input terminal connected to the input port of Lange coupler 1, 3 is an output terminal connected to the 0 ° output port of Lange coupler 1, and 4 is 0 of Lange coupler 1. ° The first FET, whose drain is connected to the output port, has one end of the first F
A first resistor connected to the source of ET4 and the other end being grounded, 6 is a second FET whose drain is connected to the separation port of Lange coupler 1, and 7 is one end connected to the source of the second FET 6 and the other end Is a grounded second resistor having the same resistance value as the first resistor 5, 8 is a third FET connected to the 90 ° output end of the Lange coupler 1, and 9 is a third FET at one end.
A third resistor connected to the source of 8 and grounded at the other end,
10 is a fourth FET having a drain connected to the separation port of the Lange coupler, 11 is a fourth FET having one end connected to the source of the fourth FET 10 and the other end grounded and having the same resistance value as the third resistor 9. 4 resistance, 12 is the fifth FET whose drain is connected to the 90 ° output port of the Lange coupler, 13
Is a fifth resistor having one end connected to the source of the fifth FET 12 and the other end grounded, 14 is a sixth FET drain-connected to the isolation port of the Lange coupler, and 15 is a sixth resistor
The sixth resistor 13 is connected to the source of the FET 14 and has the other end grounded and has the same resistance value as the fifth resistor 13.

Next, the operation of the first embodiment will be described. The first F connected to the 90 ° output port of Lange coupler 1
The second connected to the separation port of ET4 and Lange coupler 1
By simultaneously turning on the FET 6 and turning off the other FETs, a part of the microwave signal flowing from the input terminal 2 to the output terminal 3 is partially connected to the first FET 4 and the first resistor 5 and the second resistor 5 are connected. The microwave signal flowing from the input terminal 2 to the output terminal 3 is attenuated because it is absorbed by the second resistor 7 connected to the FET 6. Next, the third FET 8 and the fourth FET 10 are turned on at the same time, and the other FETs are turned off at the same time, so that the third resistor 9 and the fourth resistor 11 having a resistance value different from the above resistance are passed, and the signal A different amount of attenuation can be obtained by absorbing a different amount of a part of. Furthermore, the fifth FET 12 and the sixth FET 14
Are turned on at the same time, and the other FETs are turned off at the same time, so that the fifth resistor 13 and the sixth resistor 15 having resistance values different from those of the above resistors are passed, and signals are absorbed to obtain different attenuation amounts. it can. These first and second FE
T and resistance, 3rd and 4th FET and resistance, 5th and 6th F
By combining and turning on / off the three sets of ET and the resistor, it is possible to obtain 7 kinds (2 ³ −1 kinds) of attenuation amounts. Thus, the first, second, third, fourth, fifth and sixth
By turning on / off the FET, it is possible to pass resistances having different resistance values and change the attenuation amount.

Embodiment 2. Further, although the Lange coupler is used in the first embodiment, it is also possible to use this coupler as a distributed constant branch line coupler. In FIG. 2, 16 is a first distributed constant line having an impedance of 35Ω and a length of λ / 4 at the operating frequency, and 17 is a second distributed constant line having an impedance of 50Ω and having a length of λ / 4 at the operating frequency.
The distributed constant line is the same as that of the first embodiment.

Embodiment 3. Further, when the distributed constant type coupler is used, the size of the coupler becomes large in the low frequency band. Therefore, in order to downsize the coupler in the low frequency band, it is possible to use a lumped constant branch line coupler using a spiral inductor. In FIG. 3, 18 is the first with an inductance of L = 50 / 2πf
Inductor, 19 is a second inductor having an inductance of L = 35 / 2πf, and 20 is C = (1/50 + 1 /
35) is the first capacitor having a capacitance of / 2πf,
Others are the same as in the first embodiment.

Embodiment 4. Further, by integrating the circuit shown in the first embodiment on a semiconductor substrate such as GaAs, it is possible to reduce the size. In FIG. 4, 21 is a GaAs substrate, 22 is a first, third and fifth parallel F formed on the GaAs substrate by a semiconductor process.
ET group, 23 is second, fourth and sixth parallel FET group, 24
Is a first, a third, and a fifth resistance group connected to the respective sources of the first, third, and fifth parallel FET groups 22, 25
Is a second, fourth, and sixth resistance group connected to the respective sources of the second, fourth, and sixth parallel FET groups 23, 26
Are the first, third and fifth resistance groups 24 and the second, fourth,
It is a through hole that is electrically connected to the back surface of the GaAs substrate 21 for grounding the sixth resistor group 25.

[0013]

As described above, in the variable attenuator according to the present invention, it is possible to connect a plurality of attenuators in series by connecting the subordinate connection pairs of the FET and the resistor in parallel to the output terminal of the coupler. The same effect can be obtained, and the circuit can be miniaturized.

Further, by integrating the entire variable attenuator on the semiconductor substrate, there is an effect of downsizing the circuit.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a variable attenuator according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a variable attenuator according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of a variable attenuator according to another embodiment of the present invention.

FIG. 4 is a mounting perspective view of a variable attenuator according to an embodiment of the present invention.

FIG. 5 is a diagram showing a conventional variable attenuator.

[Explanation of symbols]

 1 Lange coupler 2 Input terminal 3 Output terminal 4 First FET 5 First resistance 6 Second FET 7 Second resistance 8 Third FET 9 Third resistance 10 Fourth FET 11 Fourth resistance 12 Second 5 FET 13 5th resistance 14 6th FET 15 6th resistance 16 1st distributed constant line 17 2nd distributed constant line 18 1st inductor 19 2nd inductor 20 1st capacitor 21 GaAs substrate 22 1st, 3rd, 5th parallel FET group 23 2nd, 4th, 6th parallel FET group 24 1st, 3rd, 5th parallel resistance group 25 2nd, 4th, 6th parallel Resistor group 26 through hole

Claims (3)

[Claims] 1. Input, 0 ° output, 90 ° output, 4 of separation
Lange coupler with two ports and first FET with drain connected to 90 ° output port of the Lange coupler
A first resistor having one end connected to the source of the first FET and the other end grounded; a second FET having a drain connected to the separation port of the Lange coupler;
A second resistor connected to the source of ET and having the other end grounded and having the same resistance value as the first resistor;
Third FET with drain connected to 0 ° output port
A third resistor having one end connected to the source of the third FET and the other end grounded, a fourth FET having a drain connected to the isolation port of the Lange coupler, and one end having a fourth F
A fourth resistor connected to the source of ET and having the other end grounded and having the same resistance value as the third resistor;
Fifth FET with drain connected to 0 ° output port
A fifth resistor having one end connected to the source of the fifth FET and the other end grounded; a sixth FET having a drain connected to the isolation port of the Lange coupler; and a sixth F end.
The sixth resistor is connected to the source of ET and the other end is grounded and has the same resistance value as the fifth resistor. These components are integrated on the semiconductor substrate and the input port of the Lange coupler is connected. Attenuator with input terminal and 0 ° output port as output terminal. 2. The attenuator according to claim 1, wherein the Lange coupler is a distributed constant branch line coupler. 3. The attenuator according to claim 1, wherein the Lange coupler is a lumped constant branch line coupler using a spiral inductor and a capacitor.