JP7625346B2 - Stabilization circuit - Google Patents

Description

This disclosure relates to a stabilization circuit for a semiconductor device that uses semiconductor elements such as FETs (field effect transistors) and HEMTs (high electron mobility transistors).

Semiconductor devices such as amplifiers and oscillators are widely used in radar equipment, communication equipment, and observation equipment. In general, the lower the frequency, the more unstable the operation of semiconductor elements such as FETs and HEMTs. For this reason, stabilization circuits are used in semiconductor devices to ensure stable operation, especially at low frequencies.
One such stabilization circuit is composed of a series resonant circuit of a capacitor and an inductor and a resistor connected in parallel to this series resonant circuit, and is connected in series to the input terminal of a semiconductor element (see, for example, Patent Document 1).

JP 2005-217753 A

However, when implementing a stabilization circuit using a microwave integrated circuit, conventional stabilization circuits have restrictions on where resistors can be placed, limiting design freedom.

The stabilization circuit disclosed herein is composed of a first series circuit of a first inductor and a first capacitor, and a second series circuit of a first resistor and a second inductor connected in parallel to the first series circuit, and the stabilization circuit is loaded in series with at least one of the input terminals or output terminals of a semiconductor element.

According to the stabilization circuit disclosed in this disclosure, by loading the second inductor in series with the first resistor, it is not necessary to load the first resistor between the main lines, and it is possible to form the first resistor at a location away from the main lines, greatly relaxing the location of the first resistor. As a result, the constraints imposed by the power handling capability and the center frequency of the semiconductor device are significantly relaxed, which has the effect of increasing the freedom of design.

1 is a diagram showing a configuration of a semiconductor device using a stabilization circuit according to a first embodiment of the present disclosure. This is an example of the stabilization circuit according to the first embodiment of this disclosure implemented using a microwave integrated circuit. 1 shows an example of an equivalent circuit of a stabilization circuit of a comparative example and a configuration example in which the stabilization circuit of the comparative example is realized using a microwave integrated circuit. FIG. 11 is a diagram showing a configuration illustrating another example of the stabilization circuit according to the first embodiment of the present disclosure. 13 is a simplified equivalent circuit of a stabilization circuit according to a second embodiment of the present disclosure. 13 is an example of a pass characteristic of a stabilization circuit according to the second embodiment of the present disclosure. 13 is an example of gain and stability factor characteristics of an amplifier to which a stabilization circuit according to a second embodiment of the present disclosure is applied. FIG. 11 is a diagram showing a configuration of a semiconductor device using a stabilization circuit according to a third embodiment of the present disclosure. FIG. 13 is a diagram showing a simplified equivalent circuit of a stabilization circuit according to a third embodiment of the present disclosure. FIG. 11 is a diagram showing the pass characteristic of a stabilization circuit according to a third embodiment of the present disclosure. FIG. 13 is a diagram showing the configuration of another embodiment of a stabilization circuit according to the third embodiment of the present disclosure. FIG. 13 is a diagram showing the configuration of yet another embodiment of a stabilization circuit according to the third embodiment of this disclosure. FIG. 13 is a diagram showing a configuration of another example of a semiconductor device using the stabilization circuit according to the first to third embodiments of this disclosure.

Embodiment 1.
Hereinafter, a first embodiment according to this disclosure will be described with reference to the drawings.
1 is a diagram showing the configuration of a semiconductor device using a stabilization circuit according to the first embodiment. Here, the semiconductor device is shown as an amplifier.
This amplifier has a configuration in which an input matching circuit 4, a semiconductor element 3 such as a FET (Field effect transistor) or a HEMT (High Electron Mobility Transistor), a stabilization circuit 12 according to the first embodiment, and an output matching circuit 5 are sequentially arranged between an input terminal 1 and an output terminal 2.
The stabilization circuit 12 is configured by connecting a first series circuit 8 consisting of a first inductor 6 and a first capacitor 7 in parallel with a second series circuit 11 consisting of a second inductor 9 and a first resistor 10, and is installed between the output terminal 3 b of the semiconductor element and the output matching circuit 5.
The stabilization circuit 12 shown in FIG. 1 is composed of only four elements: a first inductor 6, a first capacitor 7, a second inductor 9, and a first resistor 10.

An input terminal 3 a of the semiconductor element 3 is a gate terminal and is connected to an input matching circuit 4 .
The output terminal 3 b of the semiconductor element 3 is a drain terminal and is connected to a stabilization circuit 12 .
The source terminal of the semiconductor element 3 is grounded.
The input matching circuit 4 is provided to match the power supply impedance connected to the input terminal 1 with the input impedance of the semiconductor element 3. The output matching circuit 5 is provided to match the load impedance connected to the output terminal 2 with the output impedance of the semiconductor element 3. The stabilization circuit 12 minimizes the effect on the characteristics of the amplifier in the required band, and absorbs unwanted waves in the low frequency band from the semiconductor element 3 that cause unstable operation, thereby stabilizing the amplifier.
With this configuration, an amplifier is obtained in which a microwave band signal from input terminal 1 is amplified to a desired level by semiconductor element 3 and then supplied to a load via output terminal 2.

FIG. 2 shows an example of the stabilization circuit 12 of this disclosure implemented using a microwave integrated circuit.
FIG. 2(a) shows two main lines S1, S2 formed of a thin film on a ceramic substrate, arranged in a straight line so that they face each other with a gap G between them, with one end of a first resistor 10 formed of a thin film connected to the side of one of the main lines S1 and the other end connected to the side of the end of the other main line S2 via a second inductor 9 formed in an L-shape by a microstrip line, a chip-like first capacitor 7 attached to the end of the other main line S2, and the first capacitor 7 and the end of one of the main lines S1 connected by a first inductor 6 made of gold wire.
By connecting the second inductor 9 to the first resistor 10 in this way, there is more room for the position where the first resistor 10 is formed. This has the advantage of increasing the degree of freedom in designing to realize the stabilization circuit 12 without being restricted by the band center frequency of the semiconductor device and the area of the first resistor 10.

Figure 2 (b) shows a thin film formed on a ceramic substrate, with two main lines S1 and S2 arranged in a straight line with a gap G between them, a first resistor 10 of the same length as the gap G between the two main lines S1 and S2 formed on the side of the gap G between the two main lines S1 and S2, and second inductors 9a and 9b formed in a straight line from the end side of the two main lines S1 and S2 in a direction perpendicular to the direction of the main lines and in the direction in which the first resistor 10 is formed, respectively, and the first resistor 10 is loaded between these inductors 9a and 9b. By dividing the second inductor 9 into 9a and 9b, there is more room for the position of the first resistor 10 without being affected by the area of the resistor while maintaining the resonance frequency of the first inductor 6 and the first capacitor 7, which has the advantage of increasing the degree of freedom in design.

Fig. 2C shows a case where the gap G between the two main lines S1 and S2 arranged opposite to each other is narrowed, although the basic configuration is the same as Fig. 2B. Fig. 2C shows a case where a first resistor 10 longer than the gap G between the two main lines S1 and S2 is formed on the side of the gap G between the two main lines S1 and S2, a second inductor 9a is formed linearly from the side of the end of one main line S1 in the direction perpendicular to the direction of the main line where the first resistor 10 is formed, and a hook-shaped, crank-shaped or Z-shaped second inductor 9b is formed from the side of the end of the other main line S2 in the direction perpendicular to the direction of the main line where the first resistor 10 is formed, and the first resistor 10 is loaded between these inductors 9a and 9b. By using such a configuration, the gold wire length forming the first inductor 6 can be shortened.
This makes it possible to increase the resonant frequency between the first inductor 6 and the first capacitor 7 while maintaining the area of the first resistor 10. In other words, it is possible to accommodate amplifiers of a higher frequency band while maintaining the power resistance, which has the advantage of further increasing the freedom of design.
As shown in FIG. 2, the stabilization circuit 12 has two main lines S1, S2 whose ends are arranged facing each other with a gap G (or space) between them, a first resistor 10 is arranged at a position other than the gap G, and at least one or both of the two main lines S1, S2 and the first resistor 10 are connected by a second inductor 9.
In order to actually realize the stabilization circuit 12, main lines through which the microwave signal propagates are required between the output terminal 3b of the semiconductor element and the stabilization circuit 12, and between the stabilization circuit 12 and the output matching circuit 5, as shown in FIG. 2. However, these main lines are omitted in FIG. 1.

For reference, FIG. 3 shows an equivalent circuit of a stabilization circuit of the comparative example and an example of the configuration when the stabilization circuit of the comparative example is realized using a microwave integrated circuit. The stabilization circuit of the comparative example is a series resonant circuit of an inductor and a capacitor with a resistor connected in parallel as shown in FIG. 3(a). To realize such a stabilization circuit, as shown in FIG. 3(b), a thin-film resistor is loaded between the ends of two main lines S1 and S2, a chip-shaped capacitor is attached to the end of one of the main lines S1, and an inductor made of gold wire is used to connect the capacitor and the end of the other main line S2 across the resistor.

In general, the power handling capacity of a resistor depends on its area, and a large area is required to obtain high power handling capacity. On the other hand, the resonant frequency of a series resonant circuit is determined by the capacitor and inductor, and in order to fix the capacitor, it is necessary to shorten the gold wire length when the amplifier's band center frequency is high, and to lengthen the gold wire length when the band center frequency is low.
When a resistor with a large area is used to improve the power durability and the center frequency of the amplifier is high, the gold wire length across the resistor may become shorter than the resistor length, making this impossible to achieve. In addition, to use a gold wire of the desired length across the resistor, it is necessary to select a capacitor that corresponds to the series resonance frequency.
In this way, in the stabilization circuit of the comparative example, the circuit constants that can be realized are determined by the power handling capability and the resonant frequency of the series resonant circuit, restricting the freedom of design.

Fig. 4 is a configuration diagram showing another example of the stabilization circuit according to embodiment 1. The stabilization circuit 12 in Fig. 1 is configured by connecting in parallel a first series circuit 8 including a first inductor 6 and a first capacitor 7, and a second series circuit 11 including a first resistor 10 and a second inductor 9.
4A shows a case where two second series circuits 11 are connected in parallel to one first series circuit 8. With this configuration, the power resistance of the stabilization circuit can be improved without unnecessarily increasing the area of one first resistor 10.
4B shows that the first inductor 6 is divided into two inductors 6a and 6b, and these inductors 6a and 6b are connected to both sides of the first capacitor 7. This allows more room for the arrangement of the first capacitor 7, further increasing the degree of freedom in design.

***Advantages of First Embodiment***
The stabilization circuit 12 of the first embodiment is a stabilization circuit for stabilizing semiconductor devices such as amplifiers and oscillators, and is characterized in that it is connected in series to at least one or both of the input terminal 3 a or the output terminal 3 b of a semiconductor element 3 used in the semiconductor device, and comprises a first series circuit 8 of a first inductor 6 and a first capacitor 7, and a second series circuit 11 connected in parallel to the first series circuit 8 and of a first resistor 10 and a second inductor 9.
In the stabilization circuit 12 disclosed herein, a first series circuit 8 consisting of a first inductor 6 and a first capacitor 7 is connected in parallel to a second series circuit 11 consisting of a first resistor 10 and a second inductor 9, and by loading the second inductor 9 onto the first resistor 10, there is more space in the position where the first resistor 10 is formed.
Therefore, it becomes possible to design the area of the resistor which determines the power handling capability and the first series circuit 8 which determines the band of the amplifier independently, which has the advantage of significantly increasing the degree of freedom in design.

Embodiment 2.
The following mainly describes the differences from the first embodiment.
Fig. 5 is a simplified equivalent circuit diagram of a stabilization circuit according to a second embodiment of this disclosure. The configuration of the stabilization circuit according to the second embodiment is the same as that of Fig. 1, but the circuit constants are limited in order to minimize the effect on the band of the semiconductor device and to obtain a large amount of attenuation at a specific frequency in the low frequency band.
In this equivalent circuit, the values of the first inductor 6, the first capacitor 7, the second inductor 9 and the first resistor 10 are L1, C1, L0 and R, respectively, and the series resonance frequency of L1 and C1 is set to the band center frequency f0 of the semiconductor device. Also shown in Fig. 5 is a simplified equivalent circuit of the stabilization circuit of the comparative example.
The stabilization circuit 12 disclosed herein is represented as "through" at the band center frequency f0, as a parallel circuit of the equivalent capacitor C' of the first series circuit 8 and the second series circuit 11 at the band low end f1, and as a parallel circuit of the equivalent inductor L' of the first series circuit 8 and the second series circuit 11 at the band high end fh. In addition, in the low frequency band outside the band, it is represented as a parallel circuit of the equivalent capacitor C0 of the first series circuit 8 and the second series circuit 11, and in the vicinity of DC (Direct Current), it is represented as only R which is the first resistor 10.
In contrast, the stabilization circuit of the comparative example is represented as through at the band center frequency f0, as a parallel circuit of C' and resistor R at fl, and as a parallel circuit of L' and R at fh. Also, in the low frequency band outside the band, it is represented as a parallel circuit of C0 and R, and only R is present near DC.

That is, the simplified equivalent circuit at f0 and near DC is the same for the stabilization circuit 12 of the second embodiment and that of the comparative example. However, at frequencies f1 and fh at both ends of the band, the effect of the second inductor 9 connected to the first resistor 10 makes the impedance higher than that of only the resistor of the comparative example. Therefore, the attenuation of the first resistor 10 at f1 and fh is lower than that of the stabilization circuit of the comparative example. That is, by applying the stabilization circuit 12 with such circuit constants to an amplifier, it is possible to widen the bandwidth of the amplifier while maintaining the attenuation of unwanted waves near DC.
In addition, since the simplified equivalent circuit of the stabilization circuit 12 in the low frequency band of this disclosure is a parallel circuit of C0 and the second series circuit 11, by selecting a second inductor 9 that resonates in parallel with C0, it is possible to attenuate more spurious waves at a specific frequency fr in the low frequency band. The constant L0 of such a second inductor 9 can be found as follows.

Here, when C1=1/(ωo ² L1) is set so that L1 and C1 resonate in series at the center frequency ωo of the semiconductor device, the impedance Z of the stabilization circuit 12 is expressed by Equation 1, where ωo=2πf0.

Equation 1
Z={jL1(ω ² −ωo ² )(R+jωL0)}/{(jL1(ω ² −ωo ² )+ω(R+jωL0)}

Also, if R<ωL0, equation 2 can be obtained approximately from equation 1.

Equation 2
Z={-ωL1L0(ω ² -ωo ² )}/{(jL1(ω ² -ωo ² )+jω ² L0)}

From this equation, the relationship between L0 and L1 for the stabilization circuit to resonate in parallel at a certain frequency ωr in the low frequency band can be calculated using equation 3, where ωr = 2πfr.

Equation 3
L0=L1(ωo ² /ωr ² -1)

In this way, when the band center frequency ω0 of the semiconductor device, the specific frequency ωr in the low frequency band at which the attenuation is maximized, and the first inductor 6 are given, L0 of the second inductor 9 can be found from Equation 3.
For example, if f0=1.6 GHz, fr=0.8 GHz, and L1=8 nH, then L0=24 nH is obtained from equation 3. Furthermore, for C1, C1=1.25 pF is obtained from the condition for series resonance with L1 at f0.
L0=L1(ωo ² /ωr ² -1)
=L1((2πf0) ² /(2πfr) ² -1)
=L1((2π・1.6) ² /(2π・0.8) ² -1)
=8((2π・1.6) ² /(2π・0.8) ² -1)
≒8 (100/25-1)
=8 (100/25-1)
= 24 nH
C1=1/(ωo ² L1)
=1/((2πf0) ² L1)
=1/((2π・1.6) ²・8)
≒1/(100・8)
=0.00125nF
= 1.25 pF

Figure 6 shows an example of the pass characteristic of the stabilization circuit according to embodiment 2. In Figure 6(c), the solid line shows the pass characteristic of the stabilization circuit 12 of this disclosure shown in Figure 6(a), and the dotted line shows the pass characteristic of a comparative example stabilization circuit for comparison shown in Figure 6(b). The element values shown here use the values obtained above, and the element values of the comparative example stabilization circuit except for L0 are the same as those of the stabilization circuit 12 of this disclosure.
The stabilization circuit 12 of this disclosure is compared to the comparative example in that the loss at f0 of 1.6 GHz is the same for both, but the loss at the low end 1.5 GHz and the high end 1.7 GHz is lower for this disclosure. On the other hand, the frequency of the low frequency band where the loss is maximum is 0.79 GHz, and a loss of 13 dB is obtained, which is about 9 dB larger than that of the comparative example. In the vicinity of DC, the two circuits are the same.
Although the frequency at which the loss becomes maximum is 0.79 GHz, which is slightly different from 0.8 GHz obtained by Equation 3, this is based on the assumption that the effect of resistance R is very small in Equation 3. It is easy to tune to 0.8 GHz by finely adjusting L0, that is, by making L0 ≈ L1 (ωo ² /ωr ² - 1).

FIG. 7 shows an example of characteristics of the gain and stability factor of an amplifier to which the stabilization circuit according to the second embodiment is applied.
In the figure, the solid line indicates the case where the stabilization circuit 12 disclosed in this disclosure is applied, and the dotted line indicates the case where the stabilization circuit of the comparative example is applied for comparison.
The characteristic example in Figure 7 is an example of characteristics when the element values of the stabilization circuit 12 disclosed here and the stabilization circuit of the comparative example are those in Figure 6, and the stabilization circuit 12 is loaded between the semiconductor element 3 and the output matching circuit 5 as shown in (a) of Figure 7.
As shown in Fig. 7B, the stabilization circuit of this disclosure has a higher gain over the 1.5 GHz to 1.7 GHz band compared to the stabilization circuit of the comparative example, and can achieve a lower gain of about 9 dB at a specific frequency of 0.8 GHz in the low frequency band. Also, as shown in Fig. 7C, the stability factor in the vicinity of 0.8 GHz can be improved.

In the stabilization circuit of the comparative example, as the frequency decreases, the impedance of the series resonant circuit increases, and therefore the spurious waves absorbed by the resistor also gradually increase, reaching a maximum near DC (Direct Current).
However, the frequency band where the semiconductor element becomes unstable is not necessarily near DC, and there are cases where the semiconductor element operates unstably in a low frequency band near f0/2, such as half-wave oscillation. In such cases, it is necessary to absorb more unwanted waves near f0/2 with a resistor than unwanted waves near DC.
In the stabilization circuit of the comparative example, there are cases where it is not possible to sufficiently absorb unnecessary waves in a specific frequency band fr in the low frequency band, and the semiconductor element may operate unstably or oscillate in this frequency band.

In the second embodiment, the series resonant frequency of the first series circuit 8 consisting of the first inductor 6 and the first capacitor 7 of the stabilization circuit disclosed herein is set to the band center frequency f0 of the semiconductor device, and a second inductor 9 is selected which resonates in parallel with the equivalent capacitor of the first series circuit 8 at a specific frequency fr in the low frequency band of the first series circuit 8, thereby achieving a wider bandwidth for the semiconductor device than the stabilization circuit of the comparative example.
For example, by selecting fr as f0/2, it is possible to attenuate more of the unnecessary waves in the low frequency band that cause half-harmonic oscillation, and to achieve higher stability of the amplifier.
In the above embodiment, the case of absorbing unwanted waves in the frequency band f0/2 of the band has been described, but the stabilization circuit 12 disclosed here can also accommodate unwanted oscillations in other low frequency bands by arbitrarily selecting the second inductor 9.

***Advantages of the Second Embodiment***
As described above, the stabilization circuit 12 of the second embodiment can absorb more unwanted waves in a specific frequency fr band in the low frequency band while maintaining the amount of unwanted waves absorbed by the resistor near DC in the stabilization circuit of the comparative example, and can significantly suppress, for example, f0/2 oscillation. In addition, the loss of the stabilization circuit can be reduced at both ends of the band, making it possible to widen the bandwidth of the semiconductor device.

Embodiment 3.
The following mainly describes the differences from the first and second embodiments.
In the embodiment described above, the stabilization circuit 12 configured by connecting the first series circuit 8 and the second series circuit 11 in parallel is mounted in series between the output terminal 3a of the semiconductor element and the output matching circuit 5 as shown in FIG.
The stabilization circuit 12 thus loaded is significantly affected by the source impedance Zg seen from the semiconductor element 3 side or the load impedance Zl seen from the output matching circuit 5 side.
In general, the output matching circuit 5 is designed so that the output impedance of the semiconductor element 3 matches the load impedance connected to the output terminal 2 within the band of the amplifier. However, in many cases, no consideration is given to matching in the low frequency band where unstable operation is likely to occur.
For this reason, the amount of attenuation of the spurious waves absorbed by the first resistor 10 depends heavily on Zg and Zl, and depending on the impedance of these Zg and Zl, the spurious waves that should be attenuated may hardly be attenuated at all. The configuration of a stabilization circuit that solves this problem will be described below.

Figure 8 is a diagram showing the configuration of a semiconductor device using a stabilization circuit according to embodiment 3 of this disclosure. This figure also shows the case of an amplifier as the semiconductor device. The stabilization circuit 12 shown here is a parallel circuit 20 consisting of a second capacitor 13 and a third inductor 14 loaded between one end of the stabilization circuit 12 shown in embodiments 1 and 2 and ground.

The stabilization circuit 12 in FIG. 8 is configured by loading a parallel circuit 20 consisting of only two elements, a second capacitor 13 and a third inductor 14, between the terminal on the output matching circuit 5 side of a parallel-connected circuit (the stabilization circuit 12 shown in embodiments 1 and 2) formed by connecting a first series circuit 8 and a second series circuit 11 in parallel and ground, and by setting the parallel resonant frequency of the parallel circuit 20 to the band center frequency f0 of the semiconductor device.
Here, the element values of the second capacitor 13 and the third inductor 14 are C2 and L2, respectively, and these element values are selected as C2=1/(ωo ² L2) so as to resonate in parallel at the band center frequency f0 of the semiconductor device.
Also, the impedance seen from the parallel circuit 20 towards the output matching circuit 5 is designated as Zl'.

9 is a diagram showing a simplified equivalent circuit of a stabilization circuit according to a third embodiment of the present disclosure, in which the same reference numerals are used to designate the same or corresponding parts as those in FIG.
The parallel circuit 20 of the second capacitor 13 and the third inductor 14 constituting the stabilization circuit 12 of this disclosure is open near the band, and is expressed as an equivalent inductor La at fl and an equivalent capacitor Ca at fh. On the other hand, it becomes an equivalent inductor La' in the low frequency band and is short-circuited near DC.
Generally, the equivalent inductor La' in the low frequency band is very small, so the impedance Zl' including the parallel circuit 20 is not easily affected by Zl and is an almost constant low impedance.
Therefore, the first resistor 10 can sufficiently absorb the unwanted waves in the low frequency band without being affected by Zl.

Although not shown, a parallel circuit 20 consisting of a second capacitor 13 and a third inductor 14 may be loaded between the terminal on the semiconductor element 3 side of a parallel connection circuit (the stabilization circuit 12 shown in embodiments 1 and 2) formed by connecting the first series circuit 8 and the second series circuit 11 in parallel and ground.
The parallel circuit 20 of the second capacitor 13 and the third inductor 14 may be loaded between at least one or both terminals of the parallel connection circuit (the stabilization circuit 12 shown in embodiments 1 and 2) and ground.

10 is a diagram showing the pass characteristic of the stabilization circuit according to the third embodiment of this disclosure. Here, L2=4nH, C2=2.5pF, and Zl and Zg are respectively selected as 25Ω, 50Ω, and 100Ω. Even if the impedance before and after the stabilization circuit 12 changes in this way, the loss is almost 0dB over the range from fl to fh in the band, and the loss at fr in the low frequency band is about 17dB, which is hardly affected by the impedance. Therefore, even if the impedance before and after the stabilization circuit 12 changes, the loss of the stabilization circuit 12 is almost constant in the band and at low frequencies.
By applying the stabilization circuit disclosed herein to a semiconductor device, the influence of the impedance before and after the stabilization circuit 12 is small, and a wide-band, highly stable amplifier can be obtained.

11 is a diagram showing the configuration of another example of a stabilization circuit according to embodiment 3 of this disclosure. This stabilization circuit 12 is configured by loading a second resistor 15 in series to a parallel circuit 20 of the second capacitor 13 and the third inductor 14 shown in FIG.
Fig. 11(a) shows a case where a series circuit of a parallel circuit 20 and a second resistor 15 is loaded between one end of a stabilizing circuit 12 made up of a first series circuit 8 and a second series circuit 11 connected in parallel and the ground, and Fig. 11(b) shows a case where a series circuit of a parallel circuit 20 and a second resistor 15 is loaded between both ends of a stabilizing circuit made up of a first series circuit 8 and a second series circuit 11 connected in parallel and the ground, respectively. The series circuit of the parallel circuit 20 and the second resistor 15 may be loaded between at least one or both terminals of a parallel connection circuit formed by connecting the first series circuit 8 and the second series circuit 11 in parallel and the ground.

In the stabilization circuit 12 shown in Fig. 8, one end on the output matching circuit 5 side is short-circuited near DC and has a very low impedance even in the low frequency band. Therefore, the impedance seen from the output matching circuit 5 to the stabilization circuit 12 side is also very low near DC and in the low frequency band. Therefore, the impedance seen from the output terminal 2 to the stabilization circuit 12 side including the output matching circuit 5 is also low near DC and in the low frequency band.
Therefore, for example, when a subsequent amplifier is connected to the output terminal 2 of a multi-stage amplifier, the input impedance of the subsequent amplifier may become short-circuited or low impedance, causing the subsequent amplifier to operate unstably.

11, by adding the second resistor 15 to the parallel circuit 20, the series circuit of the parallel circuit 20 and the second resistor 15 in the DC vicinity and in the low frequency band can be regarded as being connected with substantially only the second resistor 15. Therefore, the impedance seen from the output terminal 2 to the output matching circuit 5 side does not become a low impedance, and unstable operation of the rear stage amplifier connected to the output terminal 2 can be avoided.
Furthermore, in the case where a series circuit consisting of a parallel circuit 20 and a second resistor 15 is loaded between both ends of the stabilization circuit consisting of the first series circuit 8 and the second series circuit 11 connected in parallel as shown in Figure 11 (b) and ground, there is an advantage that it can be applied as is between the input terminal 1 and the semiconductor element 3 without any design changes.
However, in the stabilization circuit 12 of FIG. 11, the pass characteristics near the band are the same regardless of the presence or absence of the second resistor 15, so that the in-band characteristics of the semiconductor device can be maintained while stabilizing the post-stage amplifier.

12 is a diagram showing the configuration of still another example of the stabilization circuit according to the third embodiment of this disclosure. In this example, a transmission line 16 with one end short-circuited is used instead of the parallel circuit 20 of the second capacitor 13 and the third inductor 14.
FIG. 12(a) shows a case where only a transmission line 16 is connected between one end of the stabilization circuit 12 of the first series circuit 8 and the second series circuit 11 and ground, and FIG. 12(b) shows a case where a series circuit consisting of only two elements, a second resistor 15 and a transmission line 16, is loaded.
Here, when the length of the transmission line 16 is set to 1/4 wavelength at the band center frequency of the semiconductor device, the equivalent circuit from near DC to near the band of the amplifier is approximately the same as that shown in FIG. 8 in (a) of FIG. 12, and approximately the same as that shown in FIG. 11 in (b) of FIG. 12.

Therefore, even if a transmission line 16 is used instead of the parallel circuit 20 of the second capacitor 13 and the third inductor 14, a highly stable amplifier that is less susceptible to the effects of load impedance while maintaining good characteristics can be obtained. A stabilization circuit of this configuration can be easily realized using microwave integrated circuit technology, which is particularly advantageous in realizing a stabilization circuit 12 for use in a high-frequency amplifier.

In the third embodiment, a parallel circuit 20 of a second capacitor 13 and a third inductor 14 or a series circuit of the parallel circuit 20 of the second capacitor 13 and the third inductor 14 and a second resistor 15 is loaded between at least one or both terminals of the parallel circuit formed by connecting the first series circuit 8 and the second series circuit 11 in parallel and the ground, and the parallel resonant frequency of the parallel circuit 20 is set to the band center frequency f0 of the semiconductor device.

***Advantages of Third Embodiment***
The stabilization circuit 12 of the third embodiment has the advantage of being less susceptible to the effects of the load impedance or power supply impedance seen from the stabilization circuit, while maintaining the degree of design freedom, the broadband of the semiconductor device, and stabilization at a specific frequency fr in the low-frequency band.

In the above first to third embodiments, the stabilization circuit 12 is applied between the semiconductor element 3 of the amplifier and the output matching circuit 5. The stabilization circuit 12 disclosed herein is not limited to this.
Fig. 13 is a diagram showing the configuration of another embodiment of an amplifier to which a stabilization circuit 12 is applied. The effect is the same even if the stabilization circuit 12 is connected between the input matching circuit 4 and the semiconductor device 3 as shown in Fig. 13(a) or between the input matching circuit 4 and the semiconductor device 3 and between the output matching circuit 5 and the semiconductor device 3 as shown in Fig. 13(b).
The stabilization circuit 12 may be connected to at least one or both of the input terminal 3a and the output terminal 3b of the semiconductor element.

The above describes the case of an amplifier as a semiconductor device to which a stabilization circuit is applied. This stabilization circuit can also be applied to semiconductor devices such as oscillators and multipliers.

1 Input terminal, 2 Output terminal, 3 Semiconductor element, 4 Input matching circuit, 5 Output matching circuit, 6 First inductor, 7 First capacitor, 8 First series circuit, 9 Second inductor, 10 First resistor, 11 Second series circuit, 12 Stabilization circuit, 13 Second capacitor, 14 Third inductor, 15 Second resistor, 16 Transmission line, 20 Parallel circuit, S1 Main line, S2 Main line, G Spacing.

Claims (4)

a first series circuit of a first inductor and a first capacitor;
a second series circuit including a first resistor and a second inductor, the second series circuit being connected in parallel with the first series circuit;
A stabilization circuit connected in series to at least one of an input terminal and an output terminal of a semiconductor element,
If the frequency at the center of the band of a semiconductor device in which the semiconductor element is used is taken as a band center frequency f0, the frequency at the low end of the band is taken as a band low end fl, and the frequency at the high end of the band is taken as a band high end fh, then:
The series resonant frequency of the first series circuit is set to the band center frequency f0 so that a signal passes through at the band center frequency f0;
at the band low end f1 and the band high end fh, the impedance of the second series circuit is made higher by the second inductor connected to the first resistor than the impedance in the case where the second series circuit includes only the first resistor,
An equivalent circuit at the band lower end f1 is expressed by a parallel circuit of an equivalent capacitor C′ of the first series circuit and the second series circuit,
An equivalent circuit at the high frequency band end fh is expressed by a parallel circuit of an equivalent inductor L′ of the first series circuit and the second series circuit,
an equivalent circuit in a low frequency band outside the band is represented by a parallel circuit of an equivalent capacitor C0 of the first series circuit and the second series circuit,
A stabilization circuit in which an equivalent circuit in the vicinity of DC (Direct Current) is the same as that including only the first resistor. Semiconductor device band center frequency = f0
A frequency in a low frequency band that is lower than the band of the semiconductor device and higher than the vicinity of DC=fr
Value of first inductor=L1
Value of first capacitor=C1
Value of second inductor=L0
ωo=2πf0
ωr=2πfr
In this case, the value of the first inductor and the value of the first capacitor are
C1=1/(ωo ² L1)
The relationship is as follows:
The value of the first inductor and the value of the second inductor are
L0≒L1 (ωo ² /ωr ² -1)
The relationship is as follows:
2. The stabilization circuit according to claim 1, wherein, at the frequency fr in the low frequency band, the equivalent capacitor of the first series circuit is defined as capacitor C0, and the value L0 of the second inductor is set so as to resonate in parallel with capacitor C0 . 3. The stabilization circuit according to claim 1, further comprising: a parallel circuit comprising a third inductor and a second capacitor, which is connected between at least one terminal of a parallel connection circuit formed by connecting the first series circuit and the second series circuit in parallel and ground; and a parallel resonant frequency of the parallel circuit is set to a band center frequency f0 of the semiconductor device. 3. The stabilization circuit according to claim 1 or 2, further comprising a series circuit of a parallel circuit consisting of a third inductor and a second capacitor and a second resistor, which is connected between at least one terminal of the parallel connection circuit formed by connecting the first series circuit and the second series circuit in parallel and ground.

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