Filter circuits and semiconductor devices

Abstract

The filter circuit according to this disclosure comprises a first inductor and a second inductor connected in series with respect to each other and magnetically coupled to each other, and a capacitor connected between the connection point of the first inductor and the second inductor and a grounding terminal, wherein the second inductor is a variable inductor.

Description

[Technical Field]

[0001] This disclosure relates to filter circuits and semiconductor devices. [Background technology]

[0002] Patent Document 1 discloses a filter module having good attenuation characteristics over a wide bandwidth on the higher frequency side than the passband. The filter module consists of a circuit board on which a ground electrode is formed and a low-pass filter mounted on this circuit board. The low-pass filter includes a first inductor, a second inductor, and a capacitor. The first inductor and the second inductor are connected in additively. When the inductance of the path between the connection point between the first inductor and the second inductor and the ground terminal is represented by Lp, the inductance of the path between the ground terminal and the ground electrode is represented by Lg, and the mutual inductance between the first inductor and the second inductor is represented by M, the relationships Lp + Lg - M ≥ 0 and Lp - M < 0 hold. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-144683 [Overview of the project] [Problems that the invention aims to solve]

[0004] In filter circuits, a capacitor is sometimes shunt-connected at the connection point of a first and second inductor connected in series. In this case, there was a problem in that the filter performance of the filter circuit deteriorated due to the effect of the equivalent series inductance (ESL). Patent document 1 reduces the effect of ESL by utilizing the negative mutual inductance between the first and second inductors. However, when connecting capacitors by wire bonding, for example, the ESL value may vary. Therefore, it may be difficult to set an ideal mutual inductance.

[0005] This disclosure aims to provide a filter circuit and a semiconductor device that can improve filter performance. [Means for solving the problem]

[0006] The filter circuit according to this disclosure comprises a first inductor and a second inductor connected in series with respect to each other and magnetically coupled to each other, and a capacitor connected between the connection point of the first inductor and the second inductor and a grounding terminal, wherein the second inductor is a variable inductor. Furthermore, the inductance of the second inductor is set such that the mutual inductance of the first inductor and the second inductor cancels out the parasitic inductance associated with the connection of the capacitor. ru. [Effects of the Invention]

[0007] The filter circuit according to this disclosure allows the mutual inductance between the first inductor and the second inductor to be set to an appropriate value by using a variable inductor. Therefore, the filter performance can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the configuration of the filter circuit according to Embodiment 1. [Figure 2] This diagram illustrates the function of the variable inductor according to Embodiment 1. [Figure 3] This is a diagram illustrating the configuration of a semiconductor device according to Embodiment 1. [Figure 4] This figure shows the calculation results for impedance. [Figure 5] This figure shows the actual measurement results for IM3. [Figure 6] This figure shows the calculation results of impedance when multiple capacitors are used. [Figure 7] This is a diagram illustrating the inductance of a variable inductor according to Embodiment 1. [Figure 8] This diagram illustrates the mutual inductance between the first inductor and the second inductor according to Embodiment 1. [Figure 9A] This figure shows the equivalent circuit relating to the first comparative example. [Figure 9B] FIG. showing an equivalent circuit according to a second comparative example. [Figure 9C] FIG. showing an equivalent circuit corresponding to the present embodiment [Figure 10] FIG. explaining the insertion loss of the second comparative example. [Figure 11] FIG. explaining the insertion loss of the present embodiment. [Figure 12] FIG. explaining the configuration of the filter circuit according to Embodiment 2. [Figure 13] FIG. explaining the function of the variable inductor according to Embodiment 2. [Figure 14] FIG. explaining the inductance of the variable inductor according to Embodiment 2. [Figure 15] FIG. explaining the mutual inductance between the first inductor and the second inductor according to Embodiment 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] The filter circuits and semiconductor devices according to the respective embodiments will be described with reference to the drawings. The same or corresponding components may be denoted by the same reference numerals, and the description thereof may be omitted.

[0010] Embodiment 1. FIG. 1 is a diagram for explaining the configuration of a filter circuit 10 according to Embodiment 1. The filter circuit 10 includes a first inductor L1 and a second inductor 20 connected in series between a first terminal 11 and a second terminal 12. The first inductor L1 and the second inductor 20 are magnetically coupled to each other. The coupling coefficient between the first inductor L1 and the second inductor 20 is k1. The second inductor 20 is a variable inductor.

[0011] The second inductor 20 constitutes a transformer. The second inductor 20 includes a primary inductor L2 connected in series with the first inductor L1. The secondary inductor L3 is magnetically coupled to the primary inductor L2. The coupling coefficient between the secondary inductor L3 and the primary inductor L2 is k2. A capacitive load, a variable capacitance element Ca, is connected to the secondary inductor L3. The variable capacitance element Ca is composed of, for example, a diode. The inductance of the second inductor 20 is configured to be changeable by the voltage applied to the variable capacitance element Ca. Here, the inductance of the second inductor 20 refers to the inductance of the primary inductor L2.

[0012] Here, the changeable inductance L2a of the second inductor 20 is expressed by the following equation, where ω is the frequency.

[0013]

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[0014] A capacitor 16 is connected between the connection point 13 between the first inductor L1 and the second inductor 20 and the grounding terminal. The capacitor 16 is, for example, a wire bonding capacitor, and is connected to the connection point 13 by a wire 14. The capacitor 16 can be represented by its capacitance C and equivalent series inductance Ls. The equivalent series inductance Ls is the parasitic inductance associated with the connection of the capacitor 16. The inductance L of the wire 14 is... wire The combined value of Ls can be called parasitic inductance.

[0015] The first terminal 11 is connected to an amplifier, for example, and the second terminal 12 is connected to a bias circuit that supplies bias to the amplifier, for example. In other words, the first inductor L1 is connected to the amplifier side than the second inductor 20.

[0016] Figure 2 is a diagram illustrating the function of a variable inductor according to Embodiment 1. In Figure 2, M represents the mutual inductance between the first inductor L1 and the second inductor 20. The mutual inductance M is expressed by the following formula.

[0017]

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[0018] The inductance L2a of the variable inductor, the second inductor 20, is equal to the mutual inductance M plus the parasitic inductance Ls + L due to the connection of the capacitor 16. wire It is set to cancel each other out. In other words, Ls+L wire L2a is set so that =M.

[0019] Figure 3 is a diagram illustrating the configuration of a semiconductor device 100 according to Embodiment 1. The semiconductor device 100 includes an amplifier 30 and a filter circuit 10 connected between the amplifier 30 and a bias circuit 40. The amplifier 30 amplifies the signal input from the input terminal 31 and outputs it from the output terminal 32. The filter circuit 10 is connected, for example, to the drain terminal of a transistor constituting the amplifier 30. In other words, the bias circuit 40 is a drain bias circuit. The filter circuit 10 may also be connected to the gate terminal of a transistor. In this case, the bias circuit 40 is a gate bias circuit.

[0020] Next, the effects of this embodiment will be explained. Figure 4 shows the calculation results of impedance. Figure 5 shows the measured results of IM3. As shown in Figures 4 and 5, there is a correlation between low-frequency impedance and IM3 (third-order intermodulation distortion). Therefore, IM3 can be suppressed by reducing impedance. To achieve low impedance, multiple wire-bonded type capacitors are sometimes connected to the amplifier. This makes it possible to achieve wide detuning.

[0021] Figure 6 shows the calculation results of impedance when multiple capacitors are used. Figure 6 shows the calculation results of the impedance of the output matching circuit when a 1000pF capacitor is connected to the input-side differential frequency short circuit of the amplifier, and a 1000pF capacitor and a 6800pF capacitor are connected to the output-side differential frequency short circuit of the amplifier. It can be seen that the impedance is reduced at the frequencies corresponding to 1000pF and 6800pF.

[0022] When a capacitor is shunt-connected to a filter circuit, there is a problem in that the filter performance of the filter circuit deteriorates due to the effect of the equivalent series inductance Ls associated with the capacitor connection. In contrast, the effect of Ls can be reduced by utilizing the negative mutual inductance of the two inductors in the filter circuit.

[0023] However, when connecting capacitors using wire bonding, for example, the inductance (Ls) can vary. This could make it difficult to set an ideal mutual inductance.

[0024] In contrast, this embodiment employs a variable inductor as the second inductor 20. By changing the inductance of the second inductor 20, the mutual inductance M between the first inductor L1 and the second inductor 20 can be set to an appropriate value. The optimal value for the mutual inductance M is M = Ls. The inductance L of the wire 14 is a factor in the variation of Ls. wire When considering this, the optimal value of mutual inductance is M = Ls + L wire It can also be said that, therefore, in this embodiment, ideal filter performance can be achieved even when there are manufacturing variations or when it is difficult to predict the ESL in advance.

[0025] Here, we will explain the expected variation in Ls when capacitor 16 is connected by wire 14. The inductance of wire 14 can be calculated using the following formula.

[0026]

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[0027] Here, l is the length of wire 14 and r is the radius of wire 14. Assume l >> r. The mounting position of capacitor 16 and the height variation of wire 14 are generally about 100 μm. In this case, using the above formula, the amount of inductance variation due to wire 14 is about 50 pH. In other words, if the mutual inductance M can be changed by about 50 pH, the mutual inductance can be set to the optimal value even when the inductance varies due to wire 14.

[0028] Figure 7 is a diagram illustrating the inductance L2a of the variable inductor according to Embodiment 1. Figure 8 is a diagram illustrating the mutual inductance M of the first inductor L1 and the second inductor 20 according to Embodiment 1. Figure 8 shows the mutual inductance M corresponding to the inductance L2a in Figure 7. In calculating the values ​​shown in Figures 7 and 8, L1=300pH, L2=300pH, L3=300pH, and k1=k2=0.6 were used.

[0029] In Figure 7, the solid line 70 represents the inductance L2a of the second inductor 20 in this embodiment. The dashed line 71 shows the case where the inductance of the second inductor is fixed at L2. By changing the capacitance of the variable capacitance element Ca, the inductance L2a can be changed by about 100 pH. In Figure 8, the solid line 80 represents the mutual inductance M in this embodiment. The dashed line 81 shows the case where the inductance of the second inductor is fixed at L2. It can be seen that by changing the inductance L2a, the mutual inductance M can be changed by about 50 pH.

[0030] From the above, by employing a variable inductor, the inductance L of wire 14 can be adjusted. wire Even considering the 50 pH variation that can be assumed, the optimal value for mutual inductance M is M=L s +L wire This can be set to [a certain value]. Therefore, a filter circuit 10 with strong tolerance to variations can be obtained.

[0031] Next, in order to explain the impedance reduction effect by the filter circuit 10 of the present embodiment, calculation results using an equivalent circuit are shown. FIG. 9A is a diagram showing an equivalent circuit according to the first comparative example. The first comparative example shows a case where there is no mutual inductance M that cancels the equivalent series inductance Ls. For the calculation, Ls = 200 pH, C = 6800 pF, and Rs = 0.1 Ω were used.

[0032] FIG. 9B is a diagram showing an equivalent circuit according to the second comparative example. The second comparative example shows a case where a mutual inductance M = 150 pH is provided as the mutual inductance that cancels the equivalent series inductance Ls. However, the mutual inductance M is set to a value 50 pH smaller than Ls = 200 pH in consideration of the variation of Ls. FIG. 9C is a diagram showing an equivalent circuit corresponding to the present embodiment. In the example of FIG. 9C, a mutual inductance M equal to Ls, which is 200 pH, is set as the mutual inductance that cancels the equivalent series inductance Ls.

[0033] FIG. 10 is a diagram for explaining the insertion loss of the second comparative example. The solid line 9A shows the calculation result using the first comparative example, and the broken line 9B shows the calculation result using the second comparative example. FIG. 11 is a diagram for explaining the insertion loss of the present embodiment. The solid line 9A shows the calculation result using the first comparative example, and the broken line 9C shows the calculation result using the equivalent circuit corresponding to the present embodiment. It can be seen that in the present embodiment, a lower impedance can be obtained in a wider frequency band than in the second comparative example.

[0034] Also, in the present embodiment, a variable capacitance element Ca is used for the variable inductor. By increasing the capacitance of the variable capacitance element Ca, the self-resonance frequency of the filter circuit 10 can be shifted to a lower frequency range.

[0035] In the present embodiment, it is assumed that the mutual inductance M is set so as to cancel the parasitic inductance associated with the connection of the capacitor 16. Here, canceling the parasitic inductance does not mean that Ls + L wire = M is necessary, but Ls + L wireIt would be ideal if the effect could be reduced by mutual inductance M.

[0036] In this embodiment, variations in wire 14 were assumed to be a factor in the variation of Ls. However, variations in Ls are not limited to this; variations in the structure of the capacitor 16, mounting factors, and variations in the distance to ground also affect Ls. Variations in the structure of the capacitor 16 include, for example, variations in electrode dimensions or layer thickness. Mounting factors include, for example, variations in the amount of solder or mounting position misalignment. Variations in the distance to ground include, for example, misalignment of via holes and variations in substrate thickness. Thus, even when there are variations in Ls due to various factors, according to this embodiment, the parasitic inductance associated with the connection of the capacitor 16 can be canceled out by the mutual inductance M. Furthermore, this embodiment may also be applied, for example, when the capacitor 16 is not connected by wire.

[0037] In this embodiment, the mutual inductance M was adjusted by changing the capacitance of the variable capacitance element Ca. In addition, the mutual inductance M can also be adjusted by changing the coupling coefficient k2 of L2 and L3, or by changing the inductance of the secondary inductor L3.

[0038] Furthermore, in this embodiment, the inductor on the bias circuit 40 side of the first inductor L1 and the second inductor 20 is made a variable inductor. This eliminates the need to change the inductance of the first inductor L1 on the transistor side used for impedance matching. It is also possible to make the first inductor L1 a variable inductor instead of the second inductor 20.

[0039] The modifications described above can be appropriately applied to the filter circuit and semiconductor device according to the following embodiments. Since the filter circuit and semiconductor device according to the following embodiments have many similarities with Embodiment 1, the explanation will focus on the differences from Embodiment 1.

[0040] Embodiment 2. Figure 12 is a diagram illustrating the configuration of the filter circuit 210 according to Embodiment 2. In this embodiment, the first inductor 221 and the second inductor 20 are both variable inductors, which is different from Embodiment 1. The other configurations are the same as in Embodiment 1.

[0041] The first inductor 221 includes a primary inductor L1 connected in series with the second inductor 20. The secondary inductor L4 is magnetically coupled to the primary inductor L1. The coupling coefficient between the secondary inductor L4 and the primary inductor L1 is k3. A capacitive load, a variable capacitance element Cb, is connected to the secondary inductor L4. The variable capacitance element Cb is composed of, for example, a diode. The inductance of the first inductor 221 is configured to be changeable by the voltage applied to the variable capacitance element Cb. Here, the inductance of the first inductor 221 refers to the inductance of the primary inductor L1.

[0042] Figure 13 is a diagram illustrating the function of a variable inductor according to Embodiment 2. Let L1a be the changeable inductance of the first inductor 221, and L2a be the changeable inductance of the second inductor 20. M represents the mutual inductance of the first inductor 221 and the second inductor 20.

[0043] The inductance L1a of the first inductor 221 and the inductance L2a of the second inductor 20 have a mutual inductance M equal to the parasitic inductance Ls + L due to the connection of capacitor 16. wire It is set to cancel each other out. In other words, Ls+L wire L1a and L2a are set so that =M.

[0044] Figure 14 is a diagram illustrating the inductances L1a and L2a of the variable inductor according to Embodiment 2. Figure 15 is a diagram illustrating the mutual inductance M of the first inductor 221 and the second inductor 20 according to Embodiment 2. Figure 15 shows the mutual inductance M corresponding to the inductances L1a and L2a in Figure 14.

[0045] As shown by the solid line 70 in Figure 14, the inductances L1a and L2a of each variable inductor change in the same way as the inductance L2a in Embodiment 1. In Figure 15, the solid line 80 shows the mutual inductance M in this embodiment. By changing the inductances L1a and L2a, it is possible to change the mutual inductance M more significantly than in Embodiment 1.

[0046] Thus, in this embodiment, by providing two variable inductors, a larger mutual inductance M can be obtained compared to Embodiment 1. Therefore, even when there is a large variation in equivalent series inductance, the mutual inductance M can be set to an optimal value.

[0047] The technical features described in each embodiment may be used in combination as appropriate. [Explanation of Symbols]

[0048] 10 Filter circuit, 11 First terminal, 12 Second terminal, 13 Connection point, 14 Wire, 16 Capacitor, 20 Second inductor, 30 Amplifier, 31 Input terminal, 32 Output terminal, 40 Bias circuit, 100 Semiconductor device, 210 Filter circuit, 221 L1 First inductor, C Capacitor, Ca, Cb Variable capacitance element

Claims

1. A first inductor and a second inductor are connected in series with each other and are magnetically coupled to each other, A capacitor is connected between the connection point of the first inductor and the second inductor and the grounding terminal, Equipped with, The second inductor is a variable inductor, The filter circuit is characterized in that the inductance of the second inductor is set such that the mutual inductance of the first inductor and the second inductor cancels out the parasitic inductance associated with the connection of the capacitor.

2. The filter circuit according to claim 1, further comprising a wire connecting the connection point and the capacitor.

3. The filter circuit according to claim 1 or 2, characterized in that the first inductor is connected to the amplifier side than the second inductor.

4. The filter circuit according to claim 1 or 2, characterized in that the first inductor is a variable inductor.

5. The filter circuit according to claim 1 or 2, characterized in that the second inductor has a variable capacitance element and is configured so that its inductance can be changed by a voltage applied to the variable capacitance element.

6. Amplifier and A filter circuit according to claim 1 or 2 is connected between the amplifier and the bias circuit, A semiconductor device characterized by comprising the following features.

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