US 20020084867 A1 Abstract Microwave semiconductor variable attenuation circuit includes a coupler, two series circuits of inductors and a plurality of means having controllable resistance. Each Inductor of the series circuits has a defined inductance, where one end of the series circuit is connected to a terminal of the coupler. Each of means having controllable resistance respectively being connected to a junction point between two respective inductors of the series circuit. All of means having controllable resistance are controlled on the basis of a common signal is provided at a single terminal.
By the above features provided that inductors of defined inductance between the coupler and the means having controllable resistance (e.g. a transistor or diode), the total impedance of the attenuation circuit can be properly set and a performance degradation at high frequency can be avoided.
Claims(33) 1. A circuit for the variable attenuation of microwave signals, comprising;
(a) at least a first coupler, (b) a first series circuit of inductors, each inductor having a defined inductance, where one end of said first series circuit is connected to a first terminal of said first coupler, (c) a second series circuit of inductors, each inductor having a defined inductance, where one end of said second series circuit is connected to a second terminal of said first coupler, and (d) a plurality of means having controllable resistance, each of said means respectively being connected to a junction point between two respective inductors of said first or second series circuit. 2. A circuit according to 3. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 4. A circuit according to claims 2, characterized in that each series circuit contains two inductors of equal inductance represented as L. 5. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 6. A circuit according to 7. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 8. A circuit according to claims 6, characterized in that each series circuit contains two inductors of equal inductance represented as L. 9. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 10. A circuit according to 11. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 12. A circuit according to claims 10, characterized in that each series circuit contains two inductors of equal inductance represented as L. 13. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 14. A circuit according to 15. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 16. A circuit according to claims 14, characterized in that each series circuit contains two inductors of equal inductance represented as L. 17. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}. and the capacity of said means having controllable resistance is represented as C. 18. A circuit according to 19. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 20. A circuit according to claims 18, characterized in that each series circuit contains two inductors of equal inductance represented as L. 21. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 22. A circuit according to 23. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 24. A circuit according to claims 22, characterized in that each series circuit contains two inductors of equal inductance represented as L. 25. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 26. A circuit according to 27. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 28. A circuit according to claims 26, characterized in that each series circuit contains two inductors of equal inductance represented as L. 29. A circuit according to _{0} ^{2}=2L/C, where the characteristic impedance of said first coupler is represented as Z_{0}, and the capacity of said means having controllable resistance is represented as C. 30. A circuit according to 31. A circuit according to 32. A circuit according to 33. A circuit according to Description [0001] This invention relates to the variable attenuation circuit used for microwave communication device, for example. Microwave communication device is controlling high frequency characteristics, such as a power gain of apparatus and an output power level by using the variable attenuation circuit. As an attenuation circuit, a variable resistor network linked to the T type or I type is constituted, and a diode or a field effect transistor is used as a variable resistor. [0002] However, it is necessary for realizing desired attenuation and desired impedance to decide each resistance of the variable resistor connected in series in parallel as any resistance according to attenuation. when above attenuation circuit is used, and the control circuit setting up resistor of a variable resistance becomes complicated. [0003] Therefore, a circuit using the directivity coupler shown in FIG. 1 or FIG. 2 is used much as a circuit of microwave. Referring now to the attenuation circuit shown in FIG. 1, a passage terminal [0004] Moreover, Since the reflective power produced by the mismatching with the impedance of FET and the characteristic impedance of a directional coupler is absorbed by the terminus resistance [0005] Next referring now to the attenuation circuit shown in FIG. 2, this circuit uses the mismatching with impedance of the directional coupler [0006] However, since reactance component of the impedance by influence of the parasitic capacity of FET or a parasitic inductance becomes large According frequency becomes high, even if gate bias changes, it is not able to change enough in the impedance of FET. Referring now to FIG. 3, FIG. 3 is a passage characteristic diagram of the variable attenuator in consideration of parasitic capacity of FET. FIG. 3 shows the passage characteristic of the case, for example, in the composition of FIG. 1, used High-Electron-Mobility-Transistor (HEMT) that gate length is 0.3 micrometers and gate width is 300 micrometers. Moreover, it uses four fingers Lange couplers of main frequency 25 GHz as directional coupler. There is a problem that the variable range becomes small remarkably, in high frequency domain, as passage loss becomes large. [0007] Accordingly, it is an object of the present invention to provide a microwave variable attenuation circuit, in the variable attenuation circuit using a coupler, preventing increase of the passage loss and decrease of the variable attenuation by the parasitic capacity of a variable resistor, and having good transmission characteristic. [0008]FIG. 1 is a circuit diagram of a variable attenuator according to the prior art: [0009]FIG. 2 is a circuit diagram of a variable attenuator according to the prior art; and [0010]FIG. 3 is a passage characteristic diagram of a variable attenuator according to the prior art. [0011]FIG. 4 is a circuit diagram of first embodiment of a variable attenuator according to the present invention; [0012]FIG. 5 is an equivalent circuit diagram of a Field-Effect-Transistor; [0013]FIG. 6 is a passage characteristic diagram of variable attenuator according to the present invention; [0014]FIG. 7 is a circuit diagram of second embodiment of a variable attenuator according to the present invention; [0015]FIG. 8 is a circuit diagram of third embodiment of a variable attenuator according to the present invention; [0016]FIG. 9 is a circuit diagram of fourth embodiment of a variable attenuator according to the present invention; [0017]FIG. 10 is a circuit diagram of fifth embodiment of a variable attenuator according to the present invention; [0018]FIG. 11 is a monolithic microwave integrated circuit diagram of fifth embodiment of a variable attenuator according to the present invention; [0019]FIG. 12 is a circuit diagram of sixth embodiment of a variable attenuator according to the present invention; [0020]FIG. 13 is a circuit diagram of seventh embodiment of a variable attenuator according to the present invention; [0021]FIG. 14 is a circuit diagram of eighth embodiment of a variable attenuator according to the present invention; [0022] This invention will be described in further detail with reference to the accompanying drawings. [0023] (First Embodiment) [0024] Referring now to FIG. 4, there is shown a variable attenuator circuit using Field-Effect-Transistors (referred to as FET below). Inductors [0025] By the way, an equivalent circuit of FET Z [0026] A signal inputted from the signal input (the input terminal [0027] Accordingly, since inductance L of the inductors [0028] Referring now to FIG. 6, there is shown a passage characteristic drawing of variable attenuator. Compared with FIG. 6 of the prior art, the passage loss is small, the variable range is large, and the frequency band which can be used as an attenuator becomes large. [0029] (Second Embodiment) [0030] Referring now to second embodiment of the present invention shown in FIG. 7, the same part as FIG. 7 is shown in the same mark. [0031] A coupling terminal [0032] In above variable attenuation circuit, there is the same effect as description of first embodiment. Since inductors [0033] (Third and Fourth Embodiments) [0034] The present invention is embodied the variable attenuation circuit used the diode instead of FET, but the attenuation variable circuit used FET as a variable resistor is explained in above first and second embodiments. [0035] Referring now to FIG. 8 and FIG. 9 of third and fourth embodiments, diodes [0036] Accordingly, since inductance L of inductor Z [0037] (Fifth Embodiment) [0038] Referring now to FIG. 10 of fifth embodiment, ends of first and second ladder type circuits are connected to a coupling terminal [0039] Accordingly, in above variable attenuation circuit, the passage loss of a reflective signal decreases in a high frequency domain, the variable range of attenuation can be enlarged, and the frequency ranges which can use as an attenuator becomes large. Since number of components of MMIC can be reduced by communalizing through holes [0040] Moreover, since each FET can be set up small by using two or more FET, parasitic capacity and inductance of inductors become small. Therefore as the whole circuit, the variable range of attenuation can be enlarged according as the minimum insertion loss can become smaller. [0041] (Sixth Embodiment) [0042] Referring now to sixth embodiment of the present invention shown in FIG. 12, ends of first and second ladder type circuits are connected to a coupling terminal [0043] In above variable attenuation circuit, reflected signals are outputted from a isolation terminal [0044] Moreover, when the circuit of this embodiment forms as MMIC as shown in FIG. 11, the common through hole is not connected to only the gate terminal of FET but also the termination resistor. In this embodiment, FET and through holes of MMIC are also symmetrical with a passing line through the through holes. [0045] Accordingly, since number of components of MMIC can be reduced by communalizing through holes, the size of MMIC can become small. And since the FET of the MMIC is set up symmetry, characteristic of the whole attenuator is improved. [0046] Moreover, since each FET can be set up small by using two or more FET, parasitic capacity and inductance of inductors become small. Therefore for the whole circuit, the minimum insertion loss can become smaller, and the variable range of attenuation can be enlarged. [0047] (Seventh and Eighth Embodiments) [0048] Referring now to FIG. 13 and FIG. 14, seventh and eighth embodiments of the present invention use diodes [0049] In above embodiments like the fifth and sixth embodiments, the passage loss of a reflective signal decreases in a high frequency domain, the variable range of attenuation can be enlarged, and the frequency range that can use as an attenuator becomes large. When these embodiments form MMIC like FIG. 11, the size of MMIC can reduce by using common through holes. Since diodes of MMIC are set up symmetry, characteristic of the whole attenuator is improved. [0050] Accordingly, since each diode can be set up small by using two or more diodes, connection capacity of the diode and inductance of the inductor become small. Therefore as the whole circuit, the minimum insertion loss can be reduce, and the variable range of attenuation can be enlarged. Referenced by
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