Microwave Integrated Circuit Device Having Impedance Matching

The present invention relates to a microwave integrated circuit device and, more particularly, to an improved input/output matching circuit of a high frequency circuit in which an FET is employed.

A matching circuit of a prior art high frequency circuit comprises transmission lines such as a strip line, an open stub, and a short stub. FIG. 5 is a block diagram illustrating a matching circuit of a prior art microwave integrated circuit device. In FIG. 5, a high frequency input terminal 1 is connected to a first D.C. blocking capacitor 2. One end of a stub 3 is shorted connected to the junction between the first D.C. blocking capacitor 2 and a main line 4 and the other end is connected to the earth via a second D.C. blocking capacitor 2. Reference numeral 5 designates an FET having a gate connected to the main line 4, one main electrode connected to an output matching circuit 6 and the other main electrode connected to the earth. A high frequency output terminal 7 is connected to the output matching circuit 6. A gate bias terminal 8 applies a voltage to the gate of the FET 5. The elements which are provided between the input terminal 1 and the FET 5 constitute an input side matching circuit.

A description will be given of an operation.

FIG. 6 is a Smith chart showing the manner of impedance conversion by the input side matching circuit of FIG. 5. The input impedance A of the FET 5 is converted to an impedance B by the strip main line 4 and further to a desired impedance C (herein, 50.OMEGA.) by the shorted stub 3. Herein, the D.C. blocking capacitor 2 does not affect the matching. As described above, the input impedance A at the gate electrode of the FET 5 is converted to the impedance C (50.OMEGA.) at the first D.C. blocking capacitor 2 connected to the input terminal 1 and the shorted stub 3. The Smith chart used here is normalized for 50.OMEGA..

In the matching circuit of the prior art microwave integrated circuit device which is constituted as described above, the matching is carried out for a fixed impedance by the matching circuit. When the impedance A of the side to be matched such as the FET 5, varies due to a production or temperature variation, for example, to A' shown in FIG. 6, the impedance matching is carried out as shown by the dotted line of FIG. 6. Then, a desired impedance is not obtained because adjustment of matching point (length) is impossible. In addition, the matching of multiple impedances cannot be performed by the same matching circuit because the impedance to be matched is fixed, and it was necessary to provide a plurality of matching circuits for the respective impedances to be matched.

It is an object of the present invention to provide a microwave integrated circuit device for adjusting the matching length even in a case where the impedance of the element to be matched such as an FET, varies.

It is another object of the present invention to provide a microwave integrated circuit device for obtaining multiple desired matching points and matching an input impedance and output impedance independently.

Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and the scope of the invention will become apparent to those skilled in the art from this detailed description.

According to an aspect of the present invention, a phase control circuit that can change the electrical length of a strip main line is provided in a matching circuit of a microwave integrated circuit device. Therefore, when the impedance of the element to be matched such as an FET varies, it is possible to carry out an impedance conversion to a desired value.

According to another aspect of the present invention, a dual gate FET having a good isolation characteristic is employed for signal processing between an input matching circuit and an output matching circuit and phase control means for controlling the passing phase in the main line of the matching circuit is provided at both or either of the input and output side matching circuits. Therefore, it is possible to match the input and output impedances independently, thereby obtaining multiple matching points in the same matching circuit.

FIG. 1 is a circuit diagram illustrating a microwave integrated circuit device in accordance with an embodiment of the present invention;

FIG. 2 is a Smith chart illustrating an impedance conversion in the microwave integrated circuit device of FIG. 1;

FIG. 3 is a circuit diagram illustrating a microwave integrated circuit device in accordance with another embodiment of the present invention;

FIG. 4 is a Smith chart illustrating an impedance conversion in the microwave integrated circuit device of FIG. 3;

FIG. 5 is a circuit diagram illustrating a prior art microwave integrated circuit device;

FIG. 6 is a Smith chart illustrating impedance conversion in the prior art microwave integrated circuit device.

FIG. 7 is a circuit diagram illustrating a microwave integrated circuit device in accordance with an embodiment of the present invention; and

FIG. 8 is a circuit diagram illustrating a microwave integrated circuit device in accordance with an embodiment of the present invention.

An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram illustrating a circuit construction of a microwave integrated circuit device having a matching circuit in accordance with an embodiment of present invention. In FIG. 1, the same reference numerals as those of FIG. 5 designate the same or corresponding elements. Reference numeral 14 designates a phase control circuit comprising a strip line 9, a diode 10, a first D.C. blocking capacitor 2, and a bias terminal 11 of the diode 10. One end of the phase control circuit 14 is connected to the junction between the FET 5 and the main line 4 and the other end thereof is grounded.

An impedance conversion carried out by the matching circuit of the microwave integrated circuit device of this embodiment will be described with reference to the Smith chart of FIG. 2.

When the impedance of the FET 5 varies from A to A' the susceptance of the phase control circuit 14 is varied by varying the bias value of the diode 10 using the bias terminal 11, so that the passing phase of the main line 4 is controlled. Thus, the electrical length of the main line 4 is varied in accordance with the change of the input impedance of the FET 5, resulting in the impedance B matched against the input impedance A'. Then, the impedance B is converted to an impedance (50.OMEGA.) by the shorted stub 3.

In the above-described embodiment, the series circuit (phase control circuit 14) comprising the strip line 9 and the diode 10 is provided between the FET 5 and the main line 4, and the electrical length of the main line 4 is electrically varied as the bias voltage of the diode 10 is changed in accordance with the change of the input impedance of the FET 5. Therefore, even when the impedance of the FET 5 varies, the impedance can be adjusted to obtain a desired match.

Another embodiment of the present invention will be described.

FIG. 3 is a block diagram illustrating a circuit construction of a microwave integrated circuit device in accordance with another embodiment of the present invention. As shown in FIG. 3, an amplifier includes a phase control circuit 14a, provided between the input terminal 1 and the FET serving as a signal processing part for controlling the passing phase of the input main line 4a and another phase control circuit 14b for controlling the passing phase of the output side main line 4b. Further, a dual gate FET 12 having a good isolation characteristic is employed as the FET, whereby the input and output impedances can be independently controlled. A gate bias terminal 13 is connected to one of the two gate electrodes of the dual gate FET 12 and the amplification factor of the FET 12 is changed in accordance with the voltage applied to the gate bias terminal 13.

A description is given of the operation using the Smith impedance chart of FIG. 4.

In this embodiment, the phase control can be performed at input and output independently through the isolation characteristic of the dual gate FET 12. Also, impedance matching can be performed at a plurality of frequencies for any impedance of the FET because the matching length can be changed by varying the bias voltage. For example, when the impedance of the input matching circuit is A and the impedance of the output matching circuit is D, the matching at input side, which is carried out against the impedance A at the frequency f.sub.1, is carried out against the impedance A' at the frequency f.sub.2 by varying the bias applied to the diode 10 of the phase control circuit 14a. Thereafter, the impedance B is converted into a desired impedance C by the input shorted stub 3. At the output, the matching, which is to be carried out against the impedance D at the frequency f.sub.1, is carried out against the impedance D' at the frequency f.sub.2 similarly as in the input, thereby matching the impedances at a plurality of frequencies. In this operation, the phase control at the input and the output need not be carried out at the same time. Phase control may be carried out at one of the input and output first and then at the other, because the dual gate FET 12 has a good isolation characteristic and the impedance matching of the input and output matching circuit do not influence each other. The matching circuit having such construction can easily match the input and output impedances to obtain a desired impedance value with a simple circuit design.

While in the above-described embodiment, the phase control circuit 14 is provided at each of the input and output, the phase control circuit may be provided at either of input and output.

In the above-described embodiment, the phase control circuit 14 is arranged on a line between the main line 4 of the matching circuit and the FET, but the position of phase control circuit 14 is not limited to this and may be any place on a line between the FET and the input terminal 1 (output terminal 7).

Furthermore, while in the above-described embodiments the phase control circuit 14 comprises a strip line and a diode, it may comprise an FET instead of the diode as shown in FIGS. 7 and 8, with the same effects.

As is evident from the foregoing description, according to the present invention, a phase control circuit is provided at a matching circuit of a microwave integrated circuit device for changing the electrical length of a main strip line and for controlling the passing phase of the main line, thereby adjusting the matching in accordance with a change of the impedance of the element to be matched. This results in a highly precise impedance match at a desired frequency.

Furthermore, according to the present invention, a dual gate FET having a good isolation characteristic is employed for a signal processing between the input and the output matching circuits and phase control means for controlling the passing phase of the main line including the matching circuits at both or either of the input and output matching circuits, whereby the input and output impedances can be independently matched with a simple circuit design. In addition, the frequency of the impedance matching can be changed, thereby enabling precise impedance matching at multiple frequencies.