Ferrite two-path power combiner with adjustable input power proportion

Abstract

The utility model discloses a ferrite two-path power combiner with an adjustable input power proportion. The ferrite two-path power combiner comprises a first input port, a second input port, a first impedance conversion unit, a second impedance conversion unit, a power combining unit and an output port, a first power signal flows into the first impedance conversion unit through the first input port; a second power signal flows into the second impedance conversion unit through the second input port; the output of the first impedance conversion unit and the output of the second impedance conversion unit are both input into the power synthesis unit, and a synthesized power signal is output by an output port; a wiring position of a first input port and an input end of a first impedance conversion unit, a wiring position of a second input port and an input end of a second impedance conversion unit, and a wiring position of an output end of the first impedance conversion unit and a power synthesis unit are changed; and the output end of the second impedance conversion unit is connected with the wiring position of the power synthesis unit, so that the adjustment of the input power proportion and the impedance conversion proportion is realized.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of electronic information / radio frequency / broadcast television passive device, concretely relates to a ferrite two-way power combiner with adjustable input power ratio. BACKGROUND

[0002] The power combiner is an important component in radio frequency and wireless transmission system, and the power combiner combines the output power of multiple power amplifier modules together to reach the power level required by system application.

[0003] The power combiner has different structural forms, and can be classified into various types according to different technical indexes. The ferrite material has excellent insulation performance, can withstand extreme environments such as high temperature and high pressure, can stably output magnetic field and improve electrical performance, and has advantages such as greatly reducing the length of transmission line and improving the synthesis efficiency and index of transmission line. The ferrite power combiner has the advantages of both distributed parameter devices in high frequency operation and lumped parameter devices in small size and large relative bandwidth, and has the characteristics of small size, easy manufacturing, large power bearing and small loss, so the ferrite material is also widely used in the design of power combiner.

[0004] The ferrite power combiner is mainly divided into a power synthesis part and an impedance conversion part, and the two parts are independent of each other, and can form 2-way, 4-way or other multi-way synthesis through different combination cascades, but the existing ferrite combiner also has certain limitations in actual application.

[0005] (1) The existing ferrite two-way power combiner is composed of a group of magnetic rings and equal-length transmission lines wound on the group of magnetic rings, and the synthesized power signals are input from both ends of the transmission lines, and the two input signals have opposite current directions and the same power. Due to the limitation of equal-length transmission lines, this structure can only synthesize equal-division power ratio signals, and cannot realize the synthesis of non-equal-division power ratio signals.

[0006] (2) The existing ferrite power combiner has fixed length of the wound transmission line and fixed interface position of the transmission line, and the synthesis ratio of the power synthesis part and the conversion ratio of the impedance conversion part cannot be adjusted, so a single power combiner can only synthesize a single power division ratio power signal, and can only be used as a single machine, and different power combiners are required to synthesize different power division ratio signals.

[0007] (3) The existing ferrite power combiner needs to set different magnetic ring groups for different impedance conversion ratios, and one or more magnetic ring groups are required to realize each impedance conversion ratio, and multiple magnetic ring groups are required for different impedance conversion ratios. UTILITY MODEL CONTENTS

[0008] The utility model discloses a ferrite two-way power combiner with adjustable input power ratio.

[0009] Technical scheme: a ferrite two-way power combiner with adjustable input power ratio, comprising a first input port, a second input port, a first impedance conversion unit, a second impedance conversion unit, a power combination unit and an output port.

[0010] The first power signal flows into the first impedance conversion unit through the first input port.

[0011] The second power signal flows into the second impedance conversion unit through the second input port.

[0012] The output of the first impedance conversion unit and the output of the second impedance conversion unit are both input into the power combination unit, and the synthesized power signal is output through the output port.

[0013] The first impedance conversion unit is a group of magnetic rings, and a plurality of transmission lines are sequentially and serially wound on the magnetic rings.

[0014] The second impedance conversion unit is another group of magnetic rings, and a plurality of transmission lines are sequentially and serially wound on the magnetic rings.

[0015] The power combination unit is a third group of magnetic rings, and a plurality of transmission lines are sequentially and serially wound on the magnetic rings.

[0016] By changing the wiring position of the first input port and the input end of the first impedance conversion unit, the wiring position of the second input port and the input end of the second impedance conversion unit, the wiring position of the output end of the first impedance conversion unit and the power combination unit, and the wiring position of the output end of the second impedance conversion unit and the power combination unit, the input power ratio and the impedance conversion ratio can be adjusted.

[0017] Further, the first impedance conversion unit is a group of magnetic rings, and a first transmission line, a second transmission line, a third transmission line, a fourth transmission line, a fifth transmission line and a sixth transmission line are sequentially and serially wound on the magnetic rings; wherein the first end of the first transmission line is grounded, the first end of the third transmission line serves as an adjustment interface 1 of a first-end adjustment port of the first impedance conversion unit, the tail end of the third transmission line serves as an adjustment interface 1 of a tail-end adjustment port of the first impedance conversion unit, the first end of the fifth transmission line serves as an adjustment interface 2 of the first-end adjustment port of the first impedance conversion unit, the tail end of the fifth transmission line serves as an adjustment interface 2 of the tail-end adjustment port of the first impedance conversion unit, the first end of the sixth transmission line serves as an adjustment interface 3 of the first-end adjustment port of the first impedance conversion unit, and the tail end of the sixth transmission line serves as an adjustment interface 3 of the tail-end adjustment port of the first impedance conversion unit.

[0018] Further, the second impedance conversion unit is another group of magnetic rings, and a seventh transmission line, an eighth transmission line, a ninth transmission line, a tenth transmission line and an eleventh transmission line are sequentially and serially wound on the magnetic rings; wherein the first end of the seventh transmission line is grounded, the first end of the eighth transmission line is the adjusting interface 3 of the first end adjusting port of the second impedance conversion unit, the second end of the eighth transmission line is the adjusting interface 3 of the second end adjusting port of the second impedance conversion unit, the first end of the ninth transmission line is the adjusting interface 1 of the first end adjusting port of the second impedance conversion unit, the second end of the ninth transmission line is the adjusting interface 1 of the second end adjusting port of the second impedance conversion unit, the first end of the tenth transmission line is the adjusting interface 2 of the first end adjusting port of the second impedance conversion unit, and the second end of the eleventh transmission line is the adjusting interface 2 of the second end adjusting port of the second impedance conversion unit.

[0019] Further, the power synthesis unit is a third group of magnetic rings, and a twelfth transmission line, a thirteenth transmission line, a fourteenth transmission line and a fifteenth transmission line are sequentially and serially wound on the magnetic rings; wherein the second end of the twelfth transmission line is the adjusting interface 3 of the second end adjusting port of the power synthesis unit, the second end of the thirteenth transmission line is the adjusting interface 2 of the second end adjusting port of the power synthesis unit, the second end of the fourteenth transmission line is the adjusting interface 1 of the second end adjusting port of the power synthesis unit, the second end of the fifteenth transmission line is connected to the output port, and the first end of the fifteenth transmission line is connected to any one of the adjusting interfaces of the second end adjusting port of the first impedance conversion unit and any one of the adjusting interfaces of the second end adjusting port of the second impedance conversion unit is connected to the corresponding adjusting interface of the second end adjusting port of the power synthesis unit.

[0020] Further, the first end adjusting port of the first impedance conversion unit, the second end adjusting port of the first impedance conversion unit, the first end adjusting port of the second impedance conversion unit, the second end adjusting port of the second impedance conversion unit and the second end adjusting port of the power synthesis unit must select the adjusting interfaces with the same serial number.

[0021] Further, when the input power signal has a power splitting ratio of 1:1, the first end adjusting port of the first impedance conversion unit, the second end adjusting port of the first impedance conversion unit, the first end adjusting port of the second impedance conversion unit, the second end adjusting port of the second impedance conversion unit and the second end adjusting port of the power synthesis unit all select the adjusting interface 1.

[0022] When the input power signal has a power splitting ratio of 1:2, the first end adjusting port of the first impedance conversion unit, the second end adjusting port of the first impedance conversion unit, the first end adjusting port of the second impedance conversion unit, the second end adjusting port of the second impedance conversion unit and the second end adjusting port of the power synthesis unit all select the adjusting interface 2.

[0023] When the input power signal with the power division ratio of 1:3 is input, the head-end adjusting port of the first impedance conversion unit, the tail-end adjusting port of the first impedance conversion unit, the head-end adjusting port of the second impedance conversion unit, the tail-end adjusting port of the second impedance conversion unit and the tail-end adjusting port of the power synthesis unit all select the adjusting interface 3.

[0024] Further, the isolation resistor is further included, one end of the isolation resistor is connected with any one of the tail-end adjusting ports of the first impedance conversion unit, and the other end of the isolation resistor is connected with any one of the tail-end adjusting ports of the second impedance conversion unit.

[0025] Beneficial effects: Compared with the prior art, the utility model has the following advantages:

[0026] (1) Compared with the existing ferrite power synthesizer, the ferrite two-way power synthesizer can not only realize the synthesis of power signals with 1:1 equal power division ratio, but also realize the two-way power synthesis of power signals with 1:2 and 1:3 non-equal power division ratio.

[0027] (2) Compared with the existing ferrite power synthesizer, the power synthesis part and the impedance conversion part of the ferrite two-way power synthesizer are designed in multiple proportions, the synthesis ratio of the synthesizer can be adjusted, and the two-way power synthesis of power signals with multiple different power division ratios can be realized in one synthesizer.

[0028] (3) Compared with the existing ferrite power synthesizer, the power synthesis part and the impedance conversion part of the ferrite two-way power synthesizer only use one set of magnetic ring, the input power ratio and the impedance conversion ratio are adjusted by changing the wiring position of the transmission line, different input power division ratios and impedance conversion ratios do not need to be separately provided with new magnetic ring sets, the number of magnetic rings used is greatly reduced, the design size of the synthesizer is reduced, and the production cost of the synthesizer is significantly reduced.

[0029] (4) The ferrite two-way power synthesizer is designed for high power, the single-way input power is not less than 2kW, and the overall output power is not less than 4kW.

[0030] (5) The ferrite two-way power synthesizer is optimized and adjusted, has good synthesis indexes within 3MHz, the VSWR of the three different power division ratios of 1:1, 1:2 and 1:3 is ≤1.18, ≤1.27 and ≤1.27 respectively, the isolation degree is ≥26dB, ≥30dB and ≥31dB respectively, and the synthesizer can be normally used within 3MHz and can be directly used within the frequency range, without adjustment. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1This is a schematic diagram of a ferrite two-way power combiner with adjustable input power ratio proposed in this utility model.

[0032] Figure 2 This is an external view of a ferrite two-way power combiner with adjustable input power ratio proposed in this utility model;

[0033] Figure 3 This is a schematic diagram of the internal structure of a ferrite two-way power combiner with adjustable input power ratio proposed in this utility model.

[0034] Figure 4 This is a top view of the internal structure of a ferrite two-way power combiner with adjustable input power ratio proposed in this utility model. Detailed Implementation

[0035] The technical solution of this utility model will now be further described in conjunction with the accompanying drawings and embodiments.

[0036] like Figure 1 and Figure 2 As shown, this embodiment proposes a ferrite two-way power combiner with adjustable input power ratio, which mainly includes: a first input port 1, a second input port 2, a first impedance transformation unit 3, a second impedance transformation unit 4, a power combining unit 5, and an output port 6.

[0037] The first power signal flows into the first impedance transformation unit 3 through the first input port 1, and the second power signal flows into the second impedance transformation unit 4 through the second input port 2. Each impedance transformation unit has three different adjustment interfaces at both ends. Any adjustment port on the left end of the first impedance transformation unit 3 is connected to one end of the isolation resistor R, and any adjustment port on the left end of the second impedance transformation unit 4 is connected to the other end of the isolation resistor R. One end of the isolation resistor R is connected to one end of the power combining unit 5, and the other end of the isolation resistor R is connected to the other end of the power combining unit 5. In this embodiment, the other end of the power combining unit 5 also has three different adjustment interfaces. The isolation resistor R is determined by a combination of three different power division ratios.

[0038] Specifically, the first impedance conversion unit 3 is composed of a first transmission line L1, a second transmission line L2, a third transmission line L3, a fourth transmission line L4, a fifth transmission line L5 and a sixth transmission line L6; the right end of the first transmission line L1 is grounded, the left end of the first transmission line L1 is connected with the right end of the second transmission line L2, the left end of the second transmission line L2 is connected with the right end of the third transmission line L3, and the right end of the third transmission line L3 is the adjusting interface 1 of the right side adjusting port of the first impedance conversion unit 3, the left end of the third transmission line L3 is the adjusting interface 1 of the left side adjusting port of the first impedance conversion unit 3, the left end of the third transmission line L3 is connected with the right end of the fourth transmission line L4, the left end of the fourth transmission line L4 is connected with the right end of the fifth transmission line L5, the right end of the fifth transmission line L5 is the adjusting interface 2 of the right side adjusting port of the first impedance conversion unit 3, the left end of the fifth transmission line L5 is connected with the right end of the sixth transmission line L6, the left end of the fifth transmission line L5 is the adjusting interface 2 of the left side adjusting port of the first impedance conversion unit 3, the right end of the sixth transmission line L6 is the adjusting interface 3 of the right side adjusting port of the first impedance conversion unit 3, and the left end of the sixth transmission line L6 is the adjusting interface 3 of the left side adjusting port of the first impedance conversion unit 3.

[0039] Specifically, the second impedance conversion unit 4 is composed of a seventh transmission line L7, an eighth transmission line L8, a ninth transmission line L9, a tenth transmission line L10 and an eleventh transmission line L11; the right end of the seventh transmission line L7 is connected, the left end of the seventh transmission line L7 is connected with the right end of the eighth transmission line L8, and the right end of the eighth transmission line L8 is the adjusting interface 3 of the right side adjusting port of the second impedance conversion unit 4, the left end of the eighth transmission line L8 is the adjusting interface 3 of the left side adjusting port of the second impedance conversion unit 4, the left end of the eighth transmission line L8 and the right end of the ninth transmission line L9 are connected, the right end of the ninth transmission line L9 is the adjusting interface 1 of the right side adjusting port of the second impedance conversion unit 4, the left end of the ninth transmission line L9 is the adjusting interface 1 of the left side adjusting port of the second impedance conversion unit 4, the left end of the ninth transmission line L9 is connected with the right end of the tenth transmission line L10, the right end of the tenth transmission line L10 is the adjusting interface 2 of the right side adjusting port of the second impedance conversion unit 4, the left end of the tenth transmission line L10 is connected with the right end of the eleventh transmission line L11, and the left end of the eleventh transmission line L11 is the adjusting interface 2 of the left side adjusting port of the second impedance conversion unit 4.

[0040] Specifically, the power combining unit 5 is composed of a twelfth transmission line L12, a thirteenth transmission line L13, a fourteenth transmission line L14 and a fifteenth transmission line L15. The left end of the twelfth transmission line L12 is the adjusting interface 3 of the left adjusting port of the power combining unit 5, the right end of the twelfth transmission line L12 is connected with the left end of the thirteenth transmission line L13, the left end of the thirteenth transmission line L13 is the adjusting interface 2 of the left adjusting port of the power combining unit 5, the right end of the thirteenth transmission line L13 is connected with the left end of the fourteenth transmission line L14, the left end of the fourteenth transmission line L14 is the adjusting interface 1 of the left adjusting port of the power combining unit 5, the right end of the fourteenth transmission line L14 is connected with the left end of the fifteenth transmission line L15, the left end of the fifteenth transmission line L15 is the output port, and the right end of the fifteenth transmission line L15 is connected with any one of the adjusting interfaces of the left adjusting port of the first impedance conversion unit 3 and the left adjusting port of the second impedance conversion unit 4.

[0041] In actual application, the same adjusting interface is selected for the five adjusting ports. For example, when the input power division ratio is 1:1, the five adjusting ports select the adjusting interface 1, the two input power signals pass through the 1:2 impedance conversion unit, and then enter the 1:1 power combining unit, and the combined power signal is output from the output port. Similarly, when the input power division ratio is 1:2 and 1:3, the five adjusting ports select the adjusting interface 2 and the adjusting interface 3, respectively.

[0042] As shown in Figure 2 , the input power ratio adjustable ferrite two-way power combiner includes a shell 7, two input ports and two cooling fans 8 arranged at the front end of the shell, an output port 6 arranged at the rear end of the shell, and a power interface of the cooling fan 8 arranged below the cooling fan 8. In actual use, the input port with a specification of DIN 7 / 16(F) and the output port with a specification of EIA 1 5 / 8" straight port can be used.

[0043] As shown in Figure 3 and Figure 4 , three groups of magnetic rings are arranged in the shell 7, and the size of the magnetic ring is 72mmx38mmx12.7mm. Two groups of magnetic rings near the input port are impedance conversion units, and the magnetic ring near the output port is a power combining unit. According to the principle shown in Figure 1 , 1:1, 1:2 and 1:3 different input power ratios can be combined. In addition to the magnetic ring, there are five three-port coaxial switches and a group of isolation resistors.

[0044] The input port of the embodiment can input power signals with three different power division ratios of 1:1, 1:2 and 1:3 for synthesis. After the power signals enter the input port, they enter the corresponding impedance conversion units through a single large-power transmission line. Each impedance conversion unit is connected to a three-port coaxial switch 9 at both ends. The three selection ports of the coaxial switch are connected to three different interfaces of the corresponding adjustment port. By adjusting the knob on the coaxial switch, the interface is connected to the interface corresponding to the power ratio. Two groups of impedance conversion units are respectively subjected to impedance conversion. The power signals after impedance conversion are connected to both ends of the power synthesis unit through isolation resistors. One end of the interface is fixed, and the signal at the other end passes through a three-port coaxial switch. The three selection ports of the coaxial switch are connected to three interfaces corresponding to the adjustment port. The switch knob selects the corresponding input interface according to the input power ratio. The signal after synthesis by the power synthesis unit is transmitted to the output port through a large-power transmission line.

[0045] All the connecting lines and transmission lines wound on the magnetic rings used in the embodiment are single transmission lines. The transmission lines should meet the demand of large power. The single input power is not less than 2kW, and the overall output power is not less than 4kW.

[0046] The ferrite two-way power synthesizer of the embodiment can not only realize the synthesis of power signals with equal power division ratios of 1:1, but also realize the two-way power synthesis of power signals with unequal power division ratios of 1:2 and 1:3 in one synthesizer. The power synthesis part and the impedance conversion part of the ferrite two-way power synthesizer of the embodiment only use one group of magnetic rings. By changing the connection position of the transmission line, the input power ratio and the impedance conversion ratio are adjusted, which greatly reduces the number of magnetic rings used, reduces the design size of the synthesizer, and significantly reduces the production cost of the synthesizer.

[0047] The design method proposed in the embodiment can also be applied to power synthesizers of other frequencies and power synthesizers with other input numbers, such as a four-way power synthesizer, which can be composed of three two-way synthesizers in cascade. It can also be applied to power synthesizers of other power levels, such as 1kW or 10kW power synthesizers.

Claims

1. A ferrite two-way power combiner with adjustable input power ratio, characterized by: The application relates to a power combiner. The application relates to a power combiner. The first power signal flows into the first impedance transformation unit through the first input port. The second power signal flows into the second impedance transformation unit through the second input port. The output of the first impedance transformation unit and the output of the second impedance transformation unit are both input into the power combining unit, and the combined power signal is output through the output port. The first impedance transformation unit is a group of magnetic rings, and a plurality of transmission lines are sequentially and serially wound on the magnetic rings. The second impedance transformation unit is another group of magnetic rings, and a plurality of transmission lines are sequentially and serially wound on the magnetic rings. The power combining unit is a third group of magnetic rings, and a plurality of transmission lines are sequentially and serially wound on the magnetic rings. The input power ratio and the impedance transformation ratio are adjusted by changing the wiring positions of the first input port and the input end of the first impedance transformation unit, the wiring positions of the second input port and the input end of the second impedance transformation unit, the wiring positions of the output end of the first impedance transformation unit and the power combining unit, and the wiring positions of the output end of the second impedance transformation unit and the power combining unit.

2. The input power ratio adjustable ferrite two-way power combiner of claim 1, wherein: The first impedance transformation unit is a group of magnetic rings, and a first transmission line, a second transmission line, a third transmission line, a fourth transmission line, a fifth transmission line and a sixth transmission line are sequentially and serially wound on the magnetic rings; wherein the first end of the first transmission line is grounded, the first end of the third transmission line is used as an adjusting interface one of a first-end adjusting port of the first impedance transformation unit, the tail end of the third transmission line is used as an adjusting interface two of a tail-end adjusting port of the first impedance transformation unit, the first end of the fifth transmission line is used as an adjusting interface two of the first-end adjusting port of the first impedance transformation unit, the tail end of the fifth transmission line is used as an adjusting interface two of the tail-end adjusting port of the first impedance transformation unit, the first end of the sixth transmission line is used as an adjusting interface three of the first-end adjusting port of the first impedance transformation unit, and the tail end of the sixth transmission line is used as an adjusting interface three of the tail-end adjusting port of the first impedance transformation unit.

3. A ferrite two-way power combiner with adjustable input power ratio according to claim 2, characterized in that: The second impedance transformation unit is another group of magnetic rings, and a seventh transmission line, an eighth transmission line, a ninth transmission line, a tenth transmission line and an eleventh transmission line are sequentially and serially wound on the magnetic rings; wherein the first end of the seventh transmission line is grounded, the first end of the eighth transmission line is used as an adjusting interface three of a first-end adjusting port of the second impedance transformation unit, the tail end of the eighth transmission line is used as an adjusting interface three of a tail-end adjusting port of the second impedance transformation unit, the first end of the ninth transmission line is used as an adjusting interface one of the first-end adjusting port of the second impedance transformation unit, the tail end of the ninth transmission line is used as an adjusting interface one of the tail-end adjusting port of the second impedance transformation unit, the first end of the tenth transmission line is used as an adjusting interface two of the first-end adjusting port of the second impedance transformation unit, and the tail end of the eleventh transmission line is used as an adjusting interface two of the tail-end adjusting port of the second impedance transformation unit.

4. A ferrite two-way power combiner with adjustable input power ratio according to claim 3, characterized in that: The power combining unit is a third group of magnetic rings, and a twelfth transmission line, a thirteenth transmission line, a fourteenth transmission line and a fifteenth transmission line are sequentially and serially wound on the magnetic rings, wherein a tail end of the twelfth transmission line is an adjusting interface three of a tail end adjusting port of the power combining unit, a tail end of the thirteenth transmission line is an adjusting interface two of the tail end adjusting port of the power combining unit, a tail end of the fourteenth transmission line is an adjusting interface one of the tail end adjusting port of the power combining unit, and a tail end of the fifteenth transmission line is connected to an output port, and a head end of the fifteenth transmission line is connected to any one of the adjusting interfaces of the tail end adjusting port of the first impedance conversion unit, and any one of the adjusting interfaces of the tail end adjusting port of the second impedance conversion unit is connected to the corresponding adjusting interface of the tail end adjusting port of the power combining unit.

5. A ferrite two-way power combiner with adjustable input power ratio according to claim 4, characterized in that: The head end adjusting port of the first impedance conversion unit, the tail end adjusting port of the first impedance conversion unit, the head end adjusting port of the second impedance conversion unit, the tail end adjusting port of the second impedance conversion unit and the tail end adjusting port of the power combining unit must select the adjusting interfaces of the same serial number.

6. A ferrite two-way power combiner with adjustable input power ratio according to claim 5, characterized in that: When the input power signal is in a power division ratio of 1:1, the head end adjusting port of the first impedance conversion unit, the tail end adjusting port of the first impedance conversion unit, the head end adjusting port of the second impedance conversion unit, the tail end adjusting port of the second impedance conversion unit and the tail end adjusting port of the power combining unit all select the adjusting interface one; When the input power signal is in a power division ratio of 1:2, the head end adjusting port of the first impedance conversion unit, the tail end adjusting port of the first impedance conversion unit, the head end adjusting port of the second impedance conversion unit, the tail end adjusting port of the second impedance conversion unit and the tail end adjusting port of the power combining unit all select the adjusting interface two; When the input power signal is in a power division ratio of 1:3, the head end adjusting port of the first impedance conversion unit, the tail end adjusting port of the first impedance conversion unit, the head end adjusting port of the second impedance conversion unit, the tail end adjusting port of the second impedance conversion unit and the tail end adjusting port of the power combining unit all select the adjusting interface three.

7. The input power ratio adjustable ferrite two-way power combiner of claim 1, wherein: the first and second input waveguides are formed in a single ferrite rod. An isolation resistor is further included, and any one of the tail end adjusting ports of the first impedance conversion unit is connected to one end of the isolation resistor, and any one of the tail end adjusting ports of the second impedance conversion unit is connected to the other end of the isolation resistor.

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