JPH0795007A - Band pass filter - Google Patents

Abstract

PURPOSE:To realize the miniaturization, and also, to vary a passing frequency by varying a gate voltage, and to vary a passing band by varying a drain voltage by constituting this filter of a gallium arsenide field effect transistor and a phase shifter, with regard to the band pass filter of a microwave circuit. CONSTITUTION:This filter is provided with a gallium arsenide field effect transistor 1 whose input signal is connected to a drain 21, and a phase shifter 2 which is connected between the drain 21 and a gate 23 of this transistor 1, delays a phase of the input signal about 360 degrees, and synchronizes a gate signal and a drain signal. In such a state, a signal of a frequency for synchronizing the gate signal and the drain signal is outputted to a source 22 of this transistor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band pass filter for a microwave circuit, and more particularly to a band pass filter which can be downsized and whose pass frequency and pass band can be easily changed.

[0002]

2. Description of the Related Art Bandpass filters, like other microwave circuit components, are required to be miniaturized, but conventionally, miniaturization is not easy due to the length of the strip line and the size of the dielectric. There wasn't. Further, it is difficult to change the pass frequency, and the filter had to be replaced when changing. Therefore, there is a need for a filter which is small and whose pass frequency and pass band can be easily changed.

The construction of a conventional bandpass filter is shown in FIGS. FIG. 7 shows a stripline type filter, and FIGS. 8 and 9 show a dielectric filter. 3 in the figure
Reference numerals 1 and 36 are strip lines, 32 and 37 are dielectric substrates, 33 is a dielectric resonator, 34 is a support for the dielectric resonator, and 35 is a ground conductor. As shown in the figure, the stripline filter has a line length of λ / 2 (λ is a wavelength), and three lines or more are required.

Further, the dielectric filter has a structure having a dielectric resonator mounted on a support near the strip line. To reduce the size of the stripline filter, it is sufficient to use a dielectric substrate having a high dielectric constant, but the current technology cannot be expected to reduce the size very much. In the dielectric filter as well, the dielectric resonator may be a dielectric resonator having a high Q, but this cannot be expected to be downsized by the current technology.

As described above, the conventional bandpass filter is difficult to miniaturize because the size of the filter is determined by the size of the strip line having a length of λ / 2 of the pass frequency and the size of the dielectric resonator. Further, since the strip line and the dielectric resonator are fixed circuits, the pass frequency and pass band cannot be changed.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to realize the miniaturization of a bandpass filter by constructing the bandpass filter with a gallium arsenide field effect transistor (GaAs FET) and a phase shifter. It is in. Further, the pass frequency can be changed by changing the gate voltage of the GaAs FET, and the pass band can be changed by changing the drain voltage.

[0007]

In the present invention, FIG.
As illustrated in FIG.
GaAs FET1 and GaAs FET connected to
1. A phase shifter 2 connected between the drain 21 and the gate 23 of 1 for delaying the phase of the input signal by approximately 360 degrees and synchronizing the gate signal and the drain signal is provided. The signal of the synchronizing frequency is Ga
It is configured to be output to the source 22 of As FET1.

[0008]

When the present invention is used, the size of the stripline bandpass filter is about half that of the stripline bandpass filter, and the size reduction is achieved. Also, by changing the gate voltage, GaA
The gate-drain capacitance (C _gd ), the gate-source capacitance (C _gs ), and the drain-source capacitance (C _ds ) of the sFET1 change to change the passing frequency. The conductance changes and the pass band changes.

[0009]

1 is a circuit diagram of a bandpass filter according to a first embodiment of the present invention. The bandpass filter 10 of this embodiment includes a GaAs FET 1 and a phase shifter 25 as main elements, and the phase shifter 25 is composed of a strip line. The input terminal 5 of the bandpass filter 10 is connected via a capacitor to the drain of the GaAs FET 1, and this drain is connected via an inductance to the drain voltage terminal 7. Further, the drain is connected to one terminal of the phase shifter 25 via the capacitor 13. The other terminal of the phase shifter 25 is GaAs FET1.
Is connected to the gate voltage terminal 8 via the gate and another inductance. The gate voltage terminal 8 is grounded via another capacitor. The source of the GaAs FET 1 is connected to the output terminal 6 of the bandpass filter 10, and the output terminal 6 is further grounded via another series circuit of an inductance and a resistance.

The phase shifter 25 is composed of a linear strip line or a plurality of U-shaped strip lines.
It is possible to obtain the phase shifter 25 which can be separated by cutting the respective central portions, and which provides the required delay time. By adjusting the delay time of the phase shifter 25, the frequency of the bandpass filter 10 can be roughly adjusted. Further, by changing the voltage applied to the gate voltage terminal 8, the bandwidth of the bandpass filter can be changed as shown in FIG. Furthermore, by varying the voltage applied to the drain voltage terminal 7, the frequency of the bandpass filter can be finely adjusted as shown in FIG.

By changing the gate voltage, GaAs FE
T1 of C _gd, C _gs, by varying the pass frequency C _ds is changed, the band pass while varying the drain-source conductance of GaAs FET1 is varied by varying the drain voltage. The phase shifter 25 delays the phase by about 360 degrees, synchronizes the signal input to the drain with the signal applied to the gate, outputs the signal of that frequency to the terminal 6, and forms a bandpass filter. . Frequencies that are out of sync cannot pass through this filter.

A circuit diagram of a bandpass filter as a second embodiment of the present invention is shown in FIG. The bandpass filter 11 of this embodiment includes a GaAs FET 1 and a phase shifter 26 as main components, and the phase shifter 26 is composed of a diode phase shifter. The diode phase shifter is one in which a diode is connected to one of two coupled coils (H: hybrid), and a voltage is applied to two terminals indicated by 14 in FIG. The frequency of can be roughly adjusted. Since the other points are the same as those in the first embodiment, description thereof will be omitted.

A circuit diagram of a bandpass filter according to a third embodiment of the present invention is shown in FIG. The band pass filter 12 of this embodiment has a GaAs FET1 as a main element.
And a phase shifter 27, which is composed of a field effect transistor (FET) 28. The FET 28 has a drain connected to one terminal of the phase shifter 27 and a source connected to the other terminal. The gate of the FET 28 is connected to the bias terminal 14 of the phase shifter. By varying the voltage applied to the bias terminal 14, the delay amount between the drain and source of the FET is changed and the frequency of the band pass filter 12 can be roughly adjusted. Since the other points are the same as those in the first embodiment, description thereof will be omitted.

[0014]

According to the present invention, the band pass filter is
Miniaturization can be realized by using the aAs FET and the phase shifter. And further GaAs
Pass frequency can be changed by changing the gate power supply
The pass band can be changed by changing the drain voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of the present invention.

FIG. 2 is a circuit diagram of a bandpass filter according to a first embodiment of the present invention.

FIG. 3 is a circuit diagram of a bandpass filter according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a bandpass filter according to a third embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a change in frequency of insertion loss due to variable gate voltage in the example.

FIG. 6 is a characteristic diagram showing a change in frequency band of insertion loss due to variable drain voltage in the example.

FIG. 7 is a plan view of a conventional stripline filter.

FIG. 8 is a plan view of a conventional dielectric filter.

FIG. 9 is a side view of the conventional dielectric filter in the direction A in FIG.

[Explanation of symbols]

 1 ... GaAs FET 2 ... Phase shifter 5 ... Signal input terminal 6 ... Signal output terminal 7 ... Drain voltage terminal 8 ... Gate voltage terminal 10, 11, 12 ... Bandpass filter 13 ... Capacitor 14 ... Phase shifter bias terminal 21 ... Drain 22 ... Source 23 ... Gate 25, 26, 27 ... Phase shifter 28 ... FET 31 ... Micro strip line 32 ... Dielectric substrate 33 ... Dielectric resonator 34 ... Support stand 35 ... Ground conductor 36 ... Micro strip line 37 … Dielectric substrate

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shin Watanabe 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (8)

[Claims] 1. A gallium arsenide field effect transistor (1) having an input signal connected to a drain (21) and a drain (2) of the gallium arsenide field effect transistor (1).
1) and the gate (23) are provided, and the phase shifter (2) for delaying the phase of the input signal by approximately 360 degrees and synchronizing the gate signal and the drain signal is provided, and the gate signal and the drain signal are A band pass filter, wherein a signal having a synchronized frequency is output to a source (22) of the gallium arsenide field effect transistor (1). 2. The band pass filter according to claim 1, wherein the pass frequency is varied by changing the gate voltage of the gallium arsenide field effect transistor (1). 3. The band pass filter according to claim 1, wherein the pass band is varied by changing the drain voltage of the gallium arsenide field effect transistor (1). 4. The phase shifter (2) is composed of a strip line, and the passing frequency is variable by changing the shape of the strip line.
Band pass filter. 5. The band pass according to claim 1, wherein the phase shifter (2) is composed of a diode phase shifter, and a pass frequency is varied by changing a bias voltage of the diode phase shifter. filter. 6. The phase shifter (2) is composed of another field effect transistor (28), and the pass frequency is variable by changing the gate voltage of the field effect transistor (28). The bandpass filter according to claim 1. 7. An integrated circuit band-pass filter comprising the band-pass filter according to claim 1 as an integrated circuit. 8. A method of using a band pass filter, wherein the band pass filters according to claim 1 are connected in multiple stages to narrow a pass band.