JPH04282908A - High pass filter and multi-stage amplifier using the filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave circuit used in a high frequency band and a multistage amplifier using the same.

0002

2. Description of the Related Art Generally, in a high frequency band of several GHz or higher, a transmission line is widened to form a capacitor, and the width of the line is narrowed to form an inductor, and these are combined to form a filter. Therefore, when this is applied to an actual microwave circuit, the problem is that the area becomes large. Furthermore, with this configuration, when used in a circuit using an amplification element, which will be described later, the circuit can be easily designed to a preset value, but when the value of the amplification element varies, adjustment becomes very difficult. It becomes difficult. That is, when used in an amplifier circuit, there is a drawback that it is difficult to improve the characteristics of the filter after mounting the amplifier element. Further, FETs (field effect transistors) are generally used as amplification elements, but as is well known in FETs, the unidirectional gain simply decreases by -6 dB/octave as the frequency increases. That is,
It has relatively high gain below the desired frequency. For example, maximum oscillation frequency fmax
When a FET whose frequency is 30 GHz is used at 15 GHz, the gain at this time is 8 dB, and the gain at 3 GHz is about 21 dB. In other words, when such amplification elements are connected in multiple stages, there is a concern that there is a very high possibility of oscillation in a band lower than a desired frequency. Therefore, a high-pass filter is formed and used by widening or narrowing the line, but in this case, the above-mentioned problem exists.

0003

[Problems to be Solved by the Invention] As described above, in the conventional high-pass filter and the multistage amplifier using the same,
Oscillation in the low frequency range is likely to occur due to the frequency characteristics of the amplification element, so if a high-pass filter is used, the area of the filter becomes large, and the adjustment of the filter characteristics after the amplification element is mounted is difficult. There were problems such as difficulty. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a high-pass filter and a multi-stage amplifier using the same, which can achieve miniaturization of components, high performance, and ease of manufacture.

0004

[Means for Solving the Problems] To achieve this object, the present invention provides an inductor consisting of a capacitor formed on a microstrip line and bonding wires connected in parallel to the line on both input and output sides of the capacitor. and a capacitor connected in series to the inductor, forming a high-pass filter, or a capacitor formed in a microstrip line, and bonding wires connected in parallel to the line on both input and output sides thereof. This constitutes a multi-stage amplifier using at least one stage of a high-pass filter consisting of an inductor and a capacitor connected in series to the inductor.

[0005]

[Operation] In the high-pass filter according to the present invention and the multistage amplifier using the same, the high-pass filter is first designed according to the high frequency characteristics of the FET, which is an amplifying element, and then the FET is
After mounting, the connection position and size of the inductor can be easily adjusted appropriately depending on the variations in the characteristics of each FET. This makes it easy to adjust the filter characteristics, which was difficult in the past, and also makes it possible to miniaturize and improve the performance of the entire component, making it easier to manufacture a multi-stage amplifier.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view showing the structure of an embodiment of a high-pass filter according to the present invention. In this case, the capacitor is a ceramic chip capacitor,
Of course, a thin film capacitor may also be used. Dielectric substrate 1
Microstrip line 2 formed on top, this line 2
A direct current blocking capacitor 3 formed on the line, a bonding wire 4 for line connection, and inductors 5 and 6 each consisting of bonding wires connected in parallel to the line 2 on both input and output sides thereof and in series with the inductors 5 and 6, respectively. A high-pass filter is constructed from the connected capacitors 7 and 8. According to this configuration, first, the DC blocking capacitor constituting the microwave circuit can also be used as a component part of the high-pass filter, making it possible to downsize the circuit and reduce the number of parts. Next, when this high-pass filter is used in an amplifier, amplification elements are placed before and after the high-pass filter, but the input and output impedance of the amplification elements used in high frequency bands is low, especially for high power output. The more it goes, the lower it becomes. That is, the characteristic impedance is only a few ohms compared to 50 ohms of a commonly used high frequency circuit. Furthermore, the input/output impedance values vary due to variations in the characteristics of the amplification elements. Therefore, the values of the components of the high-pass filter also need to be changed accordingly. According to the present invention, since a bonding wire is used for the inductor which is a component of the high-pass filter, the length thereof can be easily changed and the inductance value can be changed. Furthermore, since the capacitors 7 and 8 used as capacitors are not mounted on the dielectric substrate 1, they can be easily replaced, and the values of the capacitors constituting the high-pass filter can be easily changed.

FIG. 2 shows an equivalent circuit of a high-pass filter in one embodiment of the present invention. The values actually used when designing a high-pass filter are as follows:
Based on data obtained by measuring the high frequency characteristics of a semiconductor element used in an amplifier, the characteristic impedances 16 and 17 on the input side and output side of the high-pass filter are each 10Ω. The values of the elements constituting the high-pass filter are determined so that impedance matching can be achieved well with this value. The DC blocking capacitor 11 formed on the microstrip line is 1.5 pF,
Inductor 1 connected in parallel to the line on both sides
2 and 13 are each 0.2nH, and inductors 12 and 13
Capacitors 14 and 15 each connected in series with
00 pF.

FIG. 3 shows the high frequency characteristics of the filter obtained from the equivalent circuit shown in FIG. 2 above. In this figure, looking at the filter characteristics at a frequency of 15 GHz, the reflection coefficient S11 on the input side is 20 dB or less, indicating that matching with the input side is well achieved. (Although S22 is omitted here, characteristics similar to S11 are obtained.) Further, the forward gain S21 is approximately 0 dB, which indicates that there is almost no loss. That is, good characteristics as a high-pass filter are obtained.

FIG. 4 is a perspective view showing the structure of an embodiment in which a high-pass filter according to the present invention is used in a multistage amplifier. In this case, a ceramic chip capacitor is used as the capacitor, but of course a thin film capacitor may also be used. A microstrip line 2 formed on a dielectric substrate 1, a DC blocking capacitor 3 formed on this line 2, a bonding wire 4 for connecting the line, and connected in parallel to the line 2 on both input and output sides thereof. Inductors 5 and 6 made of bonding wires, capacitors 7 and 8 connected in series to the inductors 5 and 6, a bias circuit 21 for the semiconductor element in the previous stage, a bias circuit 22 for the semiconductor element in the latter stage, a semiconductor element 23 in the former stage, and a semiconductor element 23 in the latter stage. The semiconductor device 24 includes a bonding wire 25 that connects the semiconductor device and the line. By introducing a high-pass filter into the multi-stage amplifier in this way, we can suppress the oscillation of the semiconductor element in the low frequency range as described above, and also insert some high-pass filter in the necessary frequency band. The filter is not affected by the filter, and the dimensions are not larger than before the filter was inserted. That is, Figure 4
As is clear from the figure, the capacitors 7 and 8 are connected to the semiconductor element 23.
, 24, it does not affect the design of the microwave circuit on the dielectric substrate. Further, since the inductors 5 and 6 are bonding wires, a configuration can be adopted that does not affect the dimensions at all. Furthermore, the DC blocking capacitor required to configure the amplifier circuit can also be used as a component part of the high-pass filter, making it possible to downsize the circuit and reduce the number of components.

0010

As described above, the present invention has a capacitor formed on a microstrip line, an inductor made of bonding wires connected in parallel to the line on both input and output sides, and a bonding wire connected in series with the inductor. By configuring a high-pass filter consisting of a capacitor, or by using this high-pass filter in at least one or more stages of a multi-stage amplifier, the high-frequency characteristics are not affected in any way in the required frequency band, and the dimensions can be reduced. It is an object of the present invention to provide a high-pass filter and a multi-stage amplifier that can suppress oscillation in a low frequency range in a multi-stage amplifier without increasing the size and can easily cope with variations in characteristics of amplifying elements.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of an embodiment of a high-pass filter according to the present invention.

FIG. 2 is an equivalent circuit diagram of a high-pass filter in an embodiment of the present invention.

FIG. 3 is a high-frequency characteristic diagram of a high-pass filter obtained by the equivalent circuit shown in FIG. 2;

FIG. 4 is a perspective view showing the configuration of an embodiment in which a high-pass filter according to the present invention is used in a multistage amplifier.

[Explanation of symbols]

1 Dielectric substrate 2 Microstrip line 3 DC blocking capacitor 4 Bonding wire for line connection 5 Inductor 6 Inductor 7 Capacitor 8 Capacitor 11 DC blocking capacitor 12 Inductor 13 Inductor 14 Capacitor 15 Capacitor 16 Input side characteristic impedance 17 Output side Characteristic impedance 21 Pre-stage semiconductor element bias circuit 22 Rear-stage semiconductor element bias circuit 23 Previous-stage semiconductor element 24 Rear-stage semiconductor element

Claims (4)

[Claims] 1. A high-frequency device comprising a capacitor formed on a microstrip line, an inductor made of a bonding wire connected in parallel to the line on both input and output sides, and a capacitor connected in series to the inductor. pass filter. 2. The high-pass filter according to claim 1, wherein at least one of the capacitor formed on the microstrip line and the capacitor connected in series with the inductor is a ceramic chip capacitor. 3. The high-pass filter according to claim 1, wherein at least one of the capacitor formed in the microstrip line and the capacitor connected in series with the inductor is a thin film capacitor. 4. A high-frequency device comprising a capacitor formed on a microstrip line, an inductor made of a bonding wire connected in parallel to the line on both input and output sides, and a capacitor connected in series to the inductor. A multistage amplifier that uses at least one stage of pass filters.