JP2005223502A - Bias circuit for microwave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a voltage drop caused by a transmission line is large, only a main second harmonic wave can be processed, and a highly efficient microwave device cannot be obtained, since the transmission line having a quarter wavelength whose one end is grounded by a capacitor in a high-frequency manner in a conventional bias circuit for a microwave device. <P>SOLUTION: The bias circuit for a microwave device is composed of a coupled line which is composed of a pair of the transmission lines and has a 1/8 wavelength at a fundamental wave, and the capacitor which grounds one end of one of the pair of transmission lines constituting the coupled line in a high-frequency manner. A bias terminal is provided between one end of the transmission line and the capacitor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bias circuit for a microwave device used in a microwave device such as an amplifier and an oscillator.

  Semiconductors such as field effect transistors (hereinafter referred to as FET) and high electron mobility transistors (hereinafter referred to as HEMT) are used in microwave devices such as radar and communication amplifiers and oscillators, and a desired bias voltage is applied to these semiconductors. Therefore, a bias circuit for a microwave device is required.

  As an example of such a bias circuit for a microwave device, there is known a prior art including a transmission line having one end grounded in a high frequency by a capacitor and having a quarter wave length of a fundamental wave (Patent Document 1). ).

Japanese Patent Laid-Open No. 2002-204133 (FIG. 14)

  However, when one end of the transmission line is grounded at a high frequency with a capacitor having a sufficiently low impedance in a desired frequency band, the impedance when the bias circuit side is viewed from the amplifier becomes infinite. Therefore, the microwave signal output from the amplifier is propagated to the output matching circuit without being affected by the bias circuit. On the other hand, the impedance of the bias circuit is almost zero Ω in the even frequency band and infinite in the odd frequency band. For this reason, of the main double and triple harmonics generated by the large signal operation of the amplifier, only the double harmonic is totally reflected to the amplifier side, but the triple harmonic is not reflected. Is propagated to the output matching circuit side. Further, a bias terminal is provided at one end of the transmission line on the capacitor side, and a bias voltage can be supplied to the amplifier via the transmission line by connecting a DC power source to this terminal.

  As described above, the conventional bias circuit has a function of suppressing only the double harmonic, which is the main harmonic, without affecting the amplification characteristic with the fundamental wave, and can supply a desired bias voltage to the amplifier. it can.

  In general, microwave devices such as amplifiers and oscillators are required to have high output and low power consumption, and high efficiency is required. In order to realize this, there is a method of performing harmonic processing in which the circuit loss is reduced as much as possible, and the main harmonics generated in the microwave device are reflected to the microwave device side and converted into the fundamental wave again.

  Since the conventional microwave device bias circuit uses a quarter-wave transmission line at the fundamental wave, when the desired frequency is low, for example, at 1 GHz, the length of the transmission line needs to be 75 mm in free space. When this transmission line is formed on an alumina substrate using microwave integrated circuit technology, a physical length of about 30 mm is required, and a DC resistance of about 0.5Ω is generated. If a current of 1 A flows through this transmission line, power consumption of 0.5 W is generated, and there is a problem that the efficiency of the microwave device is significantly reduced.

  In addition, this microwave device bias circuit can improve efficiency to some extent by reflecting only the double harmonics, which are the main harmonics, to the amplifier side, and converting them back to the fundamental wave, but it is another triple. There is a problem that the higher harmonics cannot be processed, and the efficiency improvement by the harmonic processing is insufficient.

  The present invention has been made in order to solve the above-described problems. A bias circuit for a microwave device having a low impedance and a low DC resistance in a double and triple frequency bands which are main harmonics is provided. The purpose is to get.

  A bias circuit for a microwave device according to the present invention is a bias circuit for a microwave device that applies a bias to a drain terminal of a transistor, and includes a pair of transmission lines, and one end of each transmission line is connected to the drain terminal. A coupling line and a capacitor connected to the other end of one transmission line constituting the coupling line, and a bias is applied between the other end of the transmission line and the capacitor.

  A bias circuit for a microwave device having a low impedance and a low DC resistance can be obtained in the frequency bands of double and triple which are main harmonics.

Embodiment 1 FIG.
Embodiment 1 according to the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a microwave device using the microwave device bias circuit according to the first embodiment and a characteristic example of the microwave device bias circuit. Here, a case where an amplifier is used as the microwave device will be described. In FIG. 1A, 1 is an FET, 2 is an input matching circuit, 3 is an output matching circuit, 4 is an input terminal, 5 is an output terminal, 6 and 7 are transmission lines, and 8 is a transmission line 6 and 7 respectively. Reference numeral 9 denotes a capacitor, and 10 denotes a bias terminal. The FET 1 may be a transistor such as HEMT.

  This amplifier comprises an input matching circuit 2, a FET 1 which is a semiconductor element, and a bias circuit for a microwave device for applying a desired bias voltage to the output matching circuit 3 and the drain terminal of the FET 1. An input terminal 4 to which a microwave signal is input is provided at one end of the input matching circuit 2, and an output terminal 5 for outputting the microwave signal is provided at one end of the output matching circuit 3.

  Furthermore, the microwave device bias circuit includes a coupling line 8, a capacitor 9 connected to one end of the transmission line 6 constituting the coupling line 8, and a bias applied between the transmission line 6 and the capacitor 9. The terminal 10 is provided between the drain terminal of the FET 1 and the ground. In practice, a bias circuit for applying a bias voltage to the gate terminal of the FET 1 is also necessary, but is omitted in the drawing.

  The coupling line 8 has a line width and a spacing of the transmission lines 6 and 7 selected so that a desired characteristic impedance can be obtained, and a length of 1/8 wavelength is selected as a reference. Of course, the length may be changed by about 10% depending on the design. Further, the capacitor 9 is selected to have a value with sufficiently low impedance in a desired frequency band.

  Therefore, in a desired frequency band where the coupling between the transmission lines 6 and 7 is relatively weak, it can be considered that the transmission line 6 with one end short-circuited and the transmission line 7 with an open end are connected in parallel. Therefore, these transmission lines 6 and 7 resonate in parallel, and the impedance Zi when the microwave device bias circuit side is viewed from the drain terminal of the FET 1 becomes almost infinite. Also, in the double frequency band, Zi becomes almost zero Ω due to the transmission line 7 having an open end. Further, Zi has a certain impedance in the triple frequency band where the coupling becomes strong.

  Therefore, as shown in FIG. 1B, the microwave signal from the drain terminal of the FET 1 to the output matching circuit 3 propagates without loss in the desired frequency band f0, and becomes a large loss in the double frequency band 2f0. Not propagated. In addition, the signal is propagated while being attenuated to some extent in the triple frequency band 3f0. As described above, this microwave device bias circuit can totally reflect the double harmonic to the FET 1 side without affecting the fundamental wave, and has the same function as the conventional one.

  In addition, the current is supplied to the FET 1 through the transmission line 6, but when the transmission line 6 and the transmission line 7 are formed on an alumina substrate using the microwave integrated circuit technology, the physical length may be about 15 mm. A DC resistance of about 0.25Ω is generated. If a current of 1 A flows through this transmission line, the power consumption is 0.25 W.

  Next, the operation will be described. The bias voltage applied to the bias terminal 10 is supplied to the FET 1 through the transmission line 6, and the FET 1 is in an operating state. In such a state, the weak microwave signal input to the input terminal 4 is supplied to the FET 1 via the input matching circuit 2 and amplified there. The amplified microwave signal is output from the output terminal 5 via the output matching circuit 3 without being attenuated by the microwave device bias circuit. The double harmonic generated by the large signal operation of FET 1 is totally reflected to the FET 1 side by the bias circuit for the microwave device, converted there to a fundamental wave, and output from the output terminal 5 through the output matching circuit 3. The

  As described above, in the bias circuit for a microwave device that applies a bias to the drain terminal of the transistor, the coupling line 8 includes a pair of transmission lines, and one end of each of the transmission lines 6 and 7 is connected to the drain terminal. And a capacitor 9 connected to the other end of one of the transmission lines 6 constituting the coupling line, and a bias circuit for a microwave device in which a bias is applied between the other end of the transmission line 6 and the capacitor 9 Then, the power consumption in the coupling line 8 can be reduced to about half by using the coupling line 8 that is about half the length of the transmission line used conventionally without impairing the function of the conventional bias circuit. There is an effect that the efficiency of the wave device can be increased.

Embodiment 2. FIG.
FIG. 2 is a diagram illustrating a configuration of a microwave device using the microwave device bias circuit according to the second embodiment and a characteristic example of the microwave device bias circuit. As shown in FIG. 2A, the bias circuit for the microwave device shown here is basically the same as that shown in the first embodiment in FIG. 1A, but for this microwave device. In the bias circuit, a transmission line portion 11 having a short length is provided between the transmission line 6 and the bias terminal 10. That is, the transmission line unit 11 is shorter than 1/8 wavelength of the fundamental wave.

  By providing this transmission line portion 11, it is possible to change the impedance Zi viewed from the microwave device bias circuit side. That is, in the case shown in the first embodiment, the frequency at which Zi is almost zero Ω was between 2f0, 3f0, and 4f0, but by providing this transmission line portion 11, it can be shifted to the low frequency side. it can. As a result, Zi at f0 is slightly affected, but can be ignored because of the low frequency. Further, Zi at 2f0 is not affected because it is determined by the transmission line 7 forming the coupling line 8.

  Therefore, the microwave signal from the FET 1 to the output matching circuit 3 side is propagated without being attenuated by the fundamental wave as shown in FIG. On the other hand, the double and triple major harmonics generated in the FET 1 are not totally propagated but totally reflected to the FET 1 side, converted into a fundamental wave, and then output from the output terminal 5.

  The bias circuit for a microwave device includes a pair of transmission lines, one end of each transmission line 6, 7 being connected to a drain terminal, and the other end of one transmission line 6 constituting the coupling line 8. And a capacitor 9 connected to the transmission line unit 11, and a bias is applied between the transmission line unit 11 and the capacitor 9. Thus, in the bias circuit for the microwave device, the transmission line portion 11 is provided between the transmission line 6 constituting the coupling line 8 and the bias terminal 10 so that the double and triple harmonics are simultaneously totally reflected to the FET 1 side. be able to. Further, since the bias voltage applied from the bias terminal 10 is supplied to the FET 1 through the transmission line portion 11 having a short length and the transmission line 6 having a 1/8 wavelength, the transmission line 6 and the transmission line portion 11 The voltage drop does not increase.

  Accordingly, by using this microwave device bias circuit, double and triple harmonics can be processed simultaneously, and the voltage drop due to the transmission line 6 and the transmission line unit 11 is also small. There is an effect that higher efficiency can be achieved.

Embodiment 3 FIG.
FIG. 3 is a diagram showing a configuration of a microwave device using a microwave device bias circuit according to Embodiment 3 of the present invention, in which 12 is a resistor and 13 is a capacitor.

  FIGS. 3A and 3B are obtained by connecting a series circuit of a resistor 12 and a capacitor 13 in parallel to the capacitor 9 of the bias circuit for a microwave device shown in the first and second embodiments, respectively. . The capacitor 13 is selected to have a value sufficiently larger than the value of the capacitor 9, and is selected to have a low impedance even in a very low frequency band. Therefore, since the lengths of the transmission line 6 and the transmission line portion 11 can be ignored in the low frequency band, this microwave device bias circuit can be equivalently regarded as the resistor 12.

As described above, in the third embodiment of the present invention, the voltage drop in the bias circuit for the microwave device shown in the first and second embodiments is suppressed, and the advantage of higher efficiency by harmonic processing is maintained. On the other hand, there is an effect that the unstable operation in the low frequency band can be suppressed.

It is a figure which shows the characteristic example of the structure of the microwave apparatus using the bias circuit for microwave apparatuses of Embodiment 1 by this invention, and the bias circuit for microwave apparatuses. It is a figure which shows the characteristic example of the structure of the microwave apparatus using the bias circuit for microwave apparatuses of Embodiment 2 by this invention, and the bias circuit for microwave apparatuses. It is a figure which shows the structure of the microwave apparatus using the bias circuit for microwave apparatuses of Embodiment 3 by this invention.

Explanation of symbols

1 FET
2 input matching circuit 3 output matching circuit 4 input terminal 5 output terminal 6 transmission line 7 transmission line 8 coupling line 9 capacitor 10 bias terminal 11 transmission line part 12 resistance 13 capacitor

Claims (6)

In a bias circuit for a microwave device that applies a bias to the drain terminal of a transistor,
Composed of a pair of transmission lines, one of each transmission line is connected to the drain terminal, a coupled line,
A capacitor connected to the other end of one of the transmission lines constituting the coupling line;
A bias circuit for a microwave device, wherein a bias is applied between the other end of the transmission line and the capacitor. In a bias circuit for a microwave device that applies a bias to the drain terminal of a transistor,
Composed of a pair of transmission lines, one of each transmission line is connected to the drain terminal, a coupled line,
A transmission line portion connected to the other end of one transmission line constituting the coupling line;
A capacitor connected to the transmission line section;
A bias circuit for a microwave device, wherein a bias is applied between the transmission line unit and the capacitor. The bias circuit for a microwave device according to claim 1 or 2, wherein each of the pair of transmission lines has a length of 1/8 wavelength of the fundamental wave. The bias circuit for a microwave device according to claim 2, wherein the length of the transmission line portion is shorter than 1/8 wavelength of the fundamental wave. The bias circuit for a microwave device according to any one of claims 1 to 4, wherein the transistor is a field effect transistor or a high electron mobility transistor. The bias circuit for a microwave device according to any one of claims 1 to 5, wherein a series circuit of a resistor and a capacitor is connected in parallel with the capacitor.

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