Signal transmission circuit and electronic equipment

Abstract

The invention provides a signal transmission circuit and an electronic device. The signal transmission circuit includes: a common mode filter including a first inductor and a second inductor; a first circuit including a first capacitor; the second circuit comprises a second capacitor, and the circuit structure is the same as that of the first circuit; a third circuit having a circuit configuration different from that of the second circuit, reflecting a predetermined amount of a signal of a predetermined frequency band including the frequency of the transmission signal among the input signals, and passing other components therethrough, the third circuit having an input terminal and an output terminal; a first transmission line connected to one end of the first inductor via a first circuit from a communication circuit that outputs a differential signal; a second transmission line connected from the communication circuit to one end of the second inductor via the second circuit, the second transmission line having a characteristic impedance different from the impedance of the third circuit; a third transmission line connected to the other end of the first inductor and the output terminal; a fourth transmission line connected to the other end of the second inductor and the input end; and the fifth transmission line is connected with the output end and the ground.

Description

Technical Field

[0001] The present disclosure relates to a signal transmission circuit and an electronic device. Background Art

[0002] A transmission circuit is disclosed in Patent Document 1. The transmission circuit includes a common mode filter (common mode choke) having two input connection portions and two output connection portions, and transmits signals via a coaxial cable. Moreover, one of the two output connection portions is connected to the coaxial cable, and the other is connected to the chassis via a series connection of a resistor and a capacitor.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-536300 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] It is desired to increase the strength of the transmitted signal.

[0008] Solutions to the Problems

[0009] The signal transmission circuit according to the embodiment includes: a common mode filter including a first inductor and a second inductor; a first circuit including a first capacitor; a second circuit including a second capacitor and having the same circuit structure as the first circuit; a third circuit having an input terminal and an output terminal, having a circuit structure different from that of the second circuit, reflecting a signal in a specified frequency band including the transmission signal frequency among the input signals, and passing other components of the input signals; a first transmission line having one end connected to a communication circuit that outputs a differential signal and the other end connected to one end of the first inductor via the first circuit; a second transmission line having one end connected to the communication circuit and the other end connected to one end of the second inductor via the second circuit, having a characteristic impedance different from that of the third circuit; a third transmission line connected to the other end of the first inductor and the output terminal; a fourth transmission line connected to the other end of the second inductor and the input terminal; and a fifth transmission line connected to the output terminal and the ground.

[0010] Effects of the Invention

[0011] According to the present invention, the strength of the transmitted signal can be increased. Brief Description of the Drawings

[0012] Figure 1 It is a schematic diagram of the structure of the electronic device according to the first embodiment.

[0013] Figure 2 This is a diagram showing an example of the simulation result of the impedance of the third circuit of the signal transmission circuit according to the first embodiment.

[0014] Figure 3 This is a reference example of the structure of an electronic device in which the invention of the present disclosure is not implemented.

[0015] Figure 4 This is a diagram showing an example of the simulation result of the eye diagram of the signal passing through the coaxial cable in Figure 3

[0016] Figure 5 This is a diagram showing an example of the simulation result of the eye diagram of the signal passing through the coaxial cable in Figure 1

[0017] Figure 6 This is a schematic diagram of the structure of the electronic device according to the second embodiment.

[0018] Figure 7 This is a diagram showing an example of the simulation result of the impedance of the fifth circuit of the signal transmission circuit according to the second embodiment.

[0019] Figure 8 This is a diagram showing an example of the simulation result of the eye diagram of the signal passing through the coaxial cable in Figure 6 Detailed Embodiments

[0020] The signal transmission circuit according to the present disclosure is configured as follows. Hereinafter, the same or equivalent components, members, or processes shown in the respective drawings are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. In addition, for ease of understanding, the dimensions of the respective members in the respective drawings are appropriately enlarged or reduced.

[0021] In addition, in this specification, the expression "equal" also includes cases where two elements are not exactly equal but can be regarded as substantially equal. That is, the expression "equal" also includes cases where two elements can be regarded as substantially equal, for example, cases where the difference is about a few percent.

[0022] (First Embodiment)

[0023] Figure 1 This is a schematic diagram of the structure of the electronic device according to the first embodiment.

[0024] In addition, in Figure 1 , for ease of understanding, in addition to showing the electronic device 1000, the electronic device 2000 as the signal transmission object and the coaxial cable 3000 are also shown.

[0025] As shown in Figure 1As shown, the electronic device 1000 is connected to the electronic device 2000 via the coaxial cable 3000. The electronic device 1000 and the electronic device 2000 are, for example, in-vehicle devices. The electronic device 1000 as an in-vehicle device is, for example, an in-vehicle camera that captures the surroundings of the vehicle.

[0026] In addition, the electronic device 2000 as an in-vehicle device is, for example, a display device. The electronic device 2000 is, for example, a display device mounted on a vehicle such as a car navigation system, a Display audio system, a monitor, etc. The electronic device 2000 can also be a display device that displays the image captured by the in-vehicle camera.

[0027] The electronic device 1000 includes a signal transmission circuit 1.

[0028] The signal transmission circuit 1 transmits the signal generated by the electronic device 1000 to the electronic device 2000 via the coaxial cable 3000. For example, when the electronic device 1000 is an in-vehicle camera, the signal transmission circuit 1 transmits the signal of the image captured by the electronic device 1000 to the electronic device 2000 via the coaxial cable 3000.

[0029] The signal transmission circuit 1 includes a common-mode filter 12, a first transmission line 13, a second transmission line 14, a third transmission line 15, a fourth transmission line 16, a fifth transmission line 17, a first circuit 18, a second circuit 19, and a third circuit 20. The common-mode filter 12 includes a first inductor 121 and a second inductor 122.

[0030] In addition, the signal transmission circuit 1 may also include a communication circuit 11 and an output terminal 21. By including the communication circuit 11 in the signal transmission circuit 1, the lengths of the first transmission line 13 and the second transmission line 14 can be shortened compared to the case where the communication circuit 11 is provided outside the signal transmission circuit 1. Therefore, the attenuation amount of the energy of the signal flowing through the transmission line can be reduced. In addition, the possibility of generating noise in the signal flowing through the first transmission line 13 and the second transmission line 14 can be reduced.

[0031] Moreover, when the electronic device 1000 is an in-vehicle device, the electronic device 1000 may include a housing, and the signal transmission circuit 1 may include a vehicle body ground potential 22 and a housing ground potential 23. The vehicle body ground potential 22 is the connection point between the vehicle body and the signal transmission circuit 1. In addition, the housing ground potential 23 is the connection point between the housing of the electronic device 1000 and the signal transmission circuit 1. Furthermore, since the electronic device 1000 is housed in a non-conductive housing, such as a resin housing, there may be a case where the signal transmission circuit 1 cannot be connected to the vehicle body. In this case, the signal transmission circuit 1 may not include the vehicle body ground potential 22.

[0032] In the following description, the case where the signal transmission circuit 1 includes a communication circuit 11, an output terminal 21, a vehicle body ground potential 22, and a housing ground potential 23 will be described as an example.

[0033] The communication circuit 11 has a first output node 111 and a second output node 112, and the communication circuit 11 outputs a differential signal via the first output node 111 and the second output node 112.

[0034] One end of a first transmission line 13 is connected to the first output node 111 of the communication circuit 11. Thus, the communication circuit 11 outputs a first signal, which is a differential signal, from the output node 111 to the first transmission line 13.

[0035] In addition, one end of a second transmission line 14 is connected to the second output node 112 of the communication circuit 11. Thus, the communication circuit 11 outputs a second signal, which is a differential signal, from the second output node 112 to the second transmission line 14.

[0036] Here, the first signal and the second signal are high-frequency signals with opposite phases to each other. As an example, the signal transmission circuit 1 of the present embodiment transmits a high-frequency signal of 100 MHz or more.

[0037] The other end of the first transmission line 13 is connected to one end of a first inductor 121 via a first circuit 18. The first signal output from the first output node 111 is input to the first inductor 121 via the first transmission line 13. The first circuit 18 includes a first capacitor 181. The first circuit 18 may also include only the first capacitor 181. The first capacitor 181 shields the DC component in the DC component and the AC component included in the first signal. As an example, in the present embodiment, the capacitance of the first capacitor 181 is 100 nF.

[0038] The other end of the second transmission line 14 is connected to one end of a second inductor 122 via a second circuit 19. The second signal output from the second output node 112 is input to the second inductor 122 via the second transmission line 14. The first circuit 18 and the second circuit 19 have the same circuit structure. The second circuit 19 includes a second capacitor 191. The second circuit 19 may also include only the second capacitor 191. The second capacitor 191 shields the DC component in the DC component and the AC component included in the second signal. As an example, in the present embodiment, the capacitance of the second capacitor 191 is 100 nF.

[0039] In the present embodiment, the first transmission line 13 and the second transmission line 14 are formed of, for example, copper wires. The characteristic impedance of the first transmission line 13 and the second transmission line 14 is determined by, for example, the thickness of the copper wires.

[0040] In addition, when the characteristic impedance of the first transmission line 13 is different from that of the second transmission line 14, the waveforms of the first signal and the second signal change during the process of passing through the first transmission line 13 and the second transmission line 14, and the first signal and the second signal may not be in opposite phases to each other. As a result, common-mode noise may be generated in the first signal and the second signal.

[0041] However, in the present embodiment, the characteristic impedances of the first transmission line 13 and the second transmission line 14 are both 50 Ω, for example. That is, the characteristic impedance of the first transmission line 13 is equal to the characteristic impedance of the second transmission line 14. Thus, the signal transmission circuit 1 in the present embodiment can reduce the possibility of generating common-mode noise in the first signal and the second signal.

[0042] The common-mode filter 12 includes a first inductor 121 and a second inductor 122.

[0043] One end of the first inductor 121 is connected to the first transmission line 13, and the other end is connected to the third transmission line 15. The first signal is input from the first transmission line 13 to the first inductor 121. In addition, the first inductor 121 outputs a signal based on the first signal, that is, a third signal, to the third transmission line 15.

[0044] One end of the second inductor 122 is connected to the second transmission line 14, and the other end is connected to the fourth transmission line 16. The second signal is input from the second transmission line 14 to the second inductor 122. In addition, the second inductor 122 outputs a signal based on the second signal, that is, a fourth signal, to the fourth transmission line 16.

[0045] The common-mode filter 12 is a filter that attenuates the common-mode noise included in the input first signal and second signal and allows the components that are not common-mode noise to pass through. That is, by including the common-mode filter 12, the signal transmission circuit 1 can reduce the common-mode noise when common-mode noise is generated in the first signal and the second signal. When common-mode noise is generated in the first signal and the second signal, the third signal is a signal obtained by attenuating the common-mode noise included in the first signal, and the fourth signal is a signal obtained by attenuating the common-mode noise included in the second signal.

[0046] Therefore, when no common-mode noise is generated in the first signal and the second signal, the first signal and the third signal are signals with the same waveform, and the second signal and the fourth signal are signals with the same waveform.

[0047] The third transmission line 15 is connected to the other end of the first inductor 121 and the output terminal 21. In addition, a coaxial cable 3000 is connected to the output terminal 21. The third signal input from the first inductor 121 to the third transmission line 15 is output to the coaxial cable 3000 via the output terminal 21.

[0048] The third circuit 20 has an input terminal 201 and an output terminal 202. The third circuit 20 has a circuit structure different from that of the first circuit 18 and the second circuit 19. Specifically, the third circuit 20 may also include a first resistor 203 and a third capacitor 204 connected in parallel with the first resistor 203. As an example, in the present embodiment, the resistance value of the first resistor 203 is 50 Ω, and the capacitance of the third capacitor 204 is 10 pF. In the present embodiment, the characteristic impedance of the second transmission line 14 is different from the impedance of the third circuit 20. The impedance of the third circuit 20 may be smaller than the characteristic impedance of the second transmission line 14 or may be larger than the characteristic impedance of the second transmission line 14. In the present embodiment, the impedance of the third circuit 20 is smaller than the characteristic impedance of the second transmission line 14. The details of the impedance of the third circuit 20 will be described later.

[0049] The fourth transmission line 16 is connected to the other end of the second inductor 122 and the input terminal 201. The fourth transmission line 16 is preferably as short as possible. By shortening the fourth transmission line 16, it is possible to reduce the phase deviation between the signal flowing from the other end of the second inductor 122 to the input terminal 201 and the signal reflected by the third circuit 20 described later. In addition, when the second inductor 122 can be directly connected to the third circuit 20, the fourth transmission line 16 can be omitted. The case where the second inductor 122 can be directly connected to the third circuit 20 is, for example, a case where the second inductor 122 and the surface mounting pads of the third circuit 20 can be directly connected.

[0050] The fifth transmission line 17 is connected to the output terminal 202 and ground. In the present embodiment, the fifth transmission line 17 is connected to the output terminal 202 and ground. Here, the ground is the vehicle body ground potential 22 and the housing ground potential 23. In addition, as described above, there is a case where the signal transmission circuit 1 does not have the vehicle body ground potential 22. In this case, the ground is the housing ground potential 23.

[0051] Generally, when transmitting a signal, a part of the energy of the signal is converted into other energy such as heat, and thus signal attenuation may occur. In addition, the higher the frequency of the signal, the greater the amount of signal attenuation. Therefore, for example, when transmitting a high-frequency signal from the electronic device 1000 to the electronic device 2000 via the coaxial cable 3000, the energy of the third signal output from the electronic device 1000 may attenuate before being input to the electronic device 2000. Depending on the amount of attenuation of the energy of the third signal, the intensity of the third signal input to the electronic device 2000 may be lower than the threshold of the intensity of the signal that can be detected in the electronic device 2000. As a result, it may not be possible to detect the signal in the electronic device 2000.

[0052] In the signal transmission circuit 1 of the present embodiment, the third circuit 20 reflects a part of the input signal. Then, the signal reflected by the third circuit 20 is output from the electronic device 1000 via the third transmission line 15. Thus, the energy of the signal reflected by the third circuit 20 can be superimposed on the third signal. As a result, the intensity of the signal output from the electronic device 1000 can be increased. Hereinafter, the principle by which the third circuit 20 reflects a part of the input signal will be described.

[0053] First, the impedance of the third circuit 20 will be described.

[0054] The impedance of the third circuit 20 is determined by the resistance value of the first resistor 203, the capacitance of the third capacitor 204, and the frequency of the signal input to the third circuit 20. Here, the signal input to the third circuit 20 is the fourth signal.

[0055] Figure 2 is a simulation result showing the relationship between the frequency of the signal input to the third circuit 20 in the present embodiment and the impedance of the third circuit 20.

[0056] In Figure 2 the horizontal axis represents the frequency of the signal input to the third circuit 20, and the vertical axis represents the impedance of the third circuit 20.

[0057] According to Figure 2 it is known that as the frequency of the signal input to the third circuit 20 increases, the impedance of the third circuit 20 decreases.

[0058] In addition, according to Figure 2 it is known that if the frequency of the signal input to the third circuit 20 is greater than about several tens of MHz, a decrease in the impedance of the third circuit 20 will occur.

[0059] Here, the frequency of the signal input to the third circuit 20 when the decrease in the impedance of the third circuit 20 starts to occur is referred to as the start frequency of the decrease. And, when a signal having a frequency lower than the start frequency of the decrease is input, the impedance of the third circuit 20 coincides with the resistance value of the first resistor 203. Therefore, as also shown in Figure 2 the impedance of the third circuit 20 in the case where a signal having a frequency lower than the start frequency of the decrease is input is 50 Ω, which coincides with the characteristic impedance of the second transmission line 14.

[0060] In addition, the reduction start frequency is determined by the resistance value of the first resistor 203 and the capacitance of the third capacitor 204. Here, in the present embodiment, the resistance value of the first resistor 203 is fixed at 50 Ω so that the impedance of the third circuit 20 when a signal having a frequency lower than the reduction start frequency is input is made to match the characteristic impedance of the second transmission line 14. Therefore, when changing the reduction start frequency, the capacitance of the third capacitor 204 is changed. That is, the larger the capacitance of the third capacitor 204 in the present embodiment is than 10 pF, the smaller the reduction start frequency is. In addition, the smaller the capacitance of the third capacitor 204 is than 10 pF, the larger the reduction start frequency is.

[0061] According to the above, in the present embodiment in which high-frequency signals of 100 MHz or more are transmitted, the characteristic impedance of the second transmission line 14 is made different from the impedance of the third circuit 20. As a result, signals are reflected by the third circuit 20. Specifically, the third circuit 20 reflects a part of the input signal and passes the other part of the input signal. Here, the signal input to the third circuit 20 refers to the fourth signal. That is, the third circuit 20 reflects a part of the fourth signal, i.e., the fifth signal, toward the second inductor 122 and passes the signal other than the fifth signal in the fourth signal, i.e., the sixth signal. The fifth signal is an example of a signal of a specified frequency band including the frequency of the transmission signal in a specified amount. The sixth signal that has passed through the third circuit 20 flows toward the vehicle body ground potential 22 and the housing ground potential 23.

[0062] The fifth signal reflected by the third circuit 20 is input to the second inductor 122. When the fifth signal is input to the second inductor 122, due to the mutual induction between the first inductor 121 and the second inductor 122, the energy of the fifth signal is transferred from the second inductor 122 to the first inductor 121, and thus a seventh signal is generated in the first inductor 121. The seventh signal is output from the first inductor 121 to the coaxial cable 3000 via the third transmission line 15 and the output terminal 21.

[0063] According to the above, in addition to the third signal, the seventh signal is also input to the third transmission line 15 and the coaxial cable 3000. As a result, the energy of the seventh signal can be superimposed on the third signal whose energy has attenuated during transmission at high frequencies. Therefore, the intensity of the signal output from the electronic device 1000 can be increased.

[0064] In addition, the reflection coefficient Γ representing the ratio of the signal reflected by the third circuit 20 is expressed by the following equation using Z1 as the characteristic impedance of the second transmission line 14 and Z2 as the impedance of the third circuit 20.

[0065] Γ = (Z1 - Z2) / (Z1 + Z2)

[0066] Therefore, in the present embodiment, the greater the difference between the characteristic impedance of the second transmission line 14 and the impedance of the third circuit 20, the greater the reflection coefficient, and thus the greater the amount of the signal reflected by the third circuit 20. Additionally, as Figure 2 shown, as the frequency of the signal input to the third circuit 20 increases, the impedance of the third circuit 20 decreases significantly, and thus the difference from the characteristic impedance of the second transmission line 14 also increases. Based on the above, in the present embodiment, as the frequency of the transmitted signal increases, the third circuit 20 can reflect a greater amount of the signal. Therefore, as the frequency of the transmitted signal increases, a greater amount of energy (the energy of the seventh signal) can be superimposed on the third signal.

[0067] Figure 3 is a schematic diagram of a reference example of the electronic device 1100 that does not implement the invention of the present disclosure.

[0068] Figure 3 The signal transmission circuit 2 of the reference example includes a resistor 100 instead of Figure 1 the third circuit 20 in the signal transmission circuit 1. Other structures are the same as those of the electronic device 1000 of the first embodiment. Therefore, the same reference numerals are assigned to the same components as those of the electronic device 1000 of the first embodiment, and their descriptions are omitted. The resistance value of the resistor 100 is 50 Ω. That is, in the reference example, the characteristic impedance of the second transmission line 14 is equal to the resistance value of the resistor 100. Thus, in the reference example, no signal is reflected by the resistor 100, and all the signals input to the fourth transmission line 16 flow to the vehicle body ground potential 22 and the housing ground potential 23.

[0069] Figure 4 is in Figure 3 the simulation result of the eye diagram of the signal passing through the coaxial cable 3000 of the reference example shown.

[0070] Additionally, Figure 5 is in Figure 1 the simulation result of the eye diagram of the signal passing through the coaxial cable 3000 of the present embodiment shown.

[0071] In Figure 4 and Figure 5 , the horizontal axis represents time, and the vertical axis represents the amplitude (relative value).

[0072] Figure 4 The amplitude A of

[0073] represents the magnitude of the amplitude of the eye diagram at 200 psec. Figure 5 Additionally,

[0074] In the eye diagram, a case where the greater the amplitude, the higher the signal strength is shown. When comparing amplitude A with amplitude B, it is found that: compared with the reference example where no signal is reflected by resistor 100, in the present embodiment where the signal is reflected by the third circuit 20, the amplitude is larger and the signal strength is higher. Therefore, compared with the reference example, in the present embodiment, the signal passing through the coaxial cable 3000, that is, the signal output from the electronic device 1000, has a higher strength, so the possibility that the signal cannot be detected in the electronic device 2000 can be reduced.

[0075] As described above, the signal transmission circuit 1 of the present embodiment includes: a common-mode filter 12 including a first inductor 121 and a second inductor 122; a first circuit 18 including a first capacitor 181; a second circuit 19 including a second capacitor 191 and having the same circuit structure as the first circuit 18; a third circuit 20 having an input terminal 201 and an output terminal 202, having a circuit structure different from that of the second circuit 19, reflecting a signal in a specified frequency band including the transmission signal in a specified amount of the input signal, and passing other components of the input signal; a first transmission line 13 having one end connected to the communication circuit 11 that outputs a differential signal and the other end connected to one end of the first inductor 121 via the first circuit 18; a second transmission line 14 having one end connected to the communication circuit 11 and the other end connected to one end of the second inductor 122 via the second circuit 19 and having a characteristic impedance different from that of the third circuit 20; a third transmission line 15 connected to the other end of the first inductor 121 and the output terminal 21; a fourth transmission line 16 connected to the other end of the second inductor 122 and the input terminal 201; and a fifth transmission line 17 connected to the output terminal and the ground.

[0076] By being configured in this way, the signal transmission circuit 1 of the present embodiment can increase the strength of the transmitted signal.

[0077] (Second Embodiment)

[0078] Next, a second embodiment of the electronic device according to the present disclosure will be described with reference to the drawings.

[0079] The electronic device 1200 of the present embodiment further includes a fourth circuit 24 between the fourth transmission line 16 and the fifth transmission line 17 in addition to the third circuit 20 of the first embodiment. In addition, in the present embodiment, the resistance value of the first resistor 203 and the capacitance of the third capacitor 204 are different from those of the first embodiment. The other structures are the same as those of the electronic device 1000 of the first embodiment, so the same reference numerals are assigned to the same constituent elements as those of the electronic device 1000 of the first embodiment and their descriptions are omitted.

[0080] Figure 6 is a schematic diagram of the structure of the electronic device 1200. As Figure 6 shown, the electronic device 1200 includes a signal transmission circuit 3. The signal transmission circuit 3 includes a fourth circuit 24 connected in series between the output terminal 202 and the fifth transmission line 17.

[0081] The third circuit 20 includes a first resistor 203 and a third capacitor 204 connected in parallel with the first resistor 203.

[0082] The fourth circuit 24 includes a second resistor 241 and a fourth capacitor 242 connected in parallel with the second resistor 241. The fourth circuit 24 may also have the following structure: it further includes a third resistor 243, a fifth capacitor 244 connected in parallel with the third resistor 243, a fourth resistor 245, and a sixth capacitor 246 connected in parallel with the fourth resistor 245. The parallel connection of the second resistor 241 and the fourth capacitor 242, the parallel connection of the third resistor 243 and the fifth capacitor 244, and the parallel connection of the fourth resistor 245 and the sixth capacitor 246 are connected in series in this order. Hereinafter, an example of its structure will be described.

[0083] In the present embodiment, the capacitances of the third capacitor 204, the fourth capacitor 242, the fifth capacitor 244, and the sixth capacitor 246 are different from each other. As an example, in the present embodiment, the capacitance of the third capacitor 204 is 100 pF, the capacitance of the fourth capacitor 242 is 10 pF, the capacitance of the fifth capacitor 244 is 1 pF, and the capacitance of the sixth capacitor 246 is 0.1 pF. Additionally, as an example, in the present embodiment, the resistance values of the first resistor 203, the second resistor 241, the third resistor 243, and the fourth resistor 245 are all 12.5 Ω.

[0084] Hereinafter, the third circuit 20 and the fourth circuit 24 are collectively regarded as one circuit, which is called the fifth circuit. In the present embodiment, the impedance of the fifth circuit is determined by the resistance values of the first resistor 203, the second resistor 241, the third resistor 243, the fourth resistor 245, the capacitances of the third capacitor 204, the fourth capacitor 242, the fifth capacitor 244, the sixth capacitor 246, and the frequency of the signal input to the fifth circuit.

[0085] Figure 7 is the simulation result showing the relationship between the frequency of the signal input to the fifth circuit in the present embodiment and the impedance of the fifth circuit.

[0086] In Figure 7 it, the horizontal axis represents the frequency of the signal input to the fifth circuit, and the vertical axis represents the impedance of the fifth circuit.

[0087] When a signal having a frequency lower than the reduction start frequency is input, the impedance of the fifth circuit matches the sum of the resistance values of the first resistor 203, the second resistor 241, the third resistor 243, and the fourth resistor 245. Thus, as also shown in Figure 7 , the impedance of the fifth circuit when a signal having a frequency lower than the reduction start frequency is input is 50 Ω. The resistance values of the respective resistors can be appropriately set so that the characteristic impedance of the second transmission line 14 is equal to the impedance of the fifth circuit when a signal having a frequency lower than the reduction start frequency is input.

[0088] In addition, according to Figure 7 , it is known that as the frequency of the signal input to the fifth circuit increases, the impedance of the fifth circuit decreases.

[0089] In the present embodiment, the reduction start frequency is determined by the resistance values of the first resistor 203, the second resistor 241, the third resistor 243, the fourth resistor 245, the capacitance of the third capacitor 204, the capacitance of the fourth capacitor 242, the capacitance of the fifth capacitor 244, and the capacitance of the sixth capacitor 246. Here, in the present embodiment, the sum of the resistance values of the respective resistors is fixed at 50 Ω so that the impedance of the fifth circuit when a signal having a frequency lower than the reduction start frequency is input matches the characteristic impedance of the second transmission line 14. Therefore, when changing the reduction start frequency, the capacitance of at least one of the capacitors is changed. If the capacitance of at least one of the capacitors is increased, the reduction start frequency becomes smaller. In addition, if the capacitance of at least one of the capacitors is decreased, the reduction start frequency becomes larger.

[0090] As an example, by increasing the capacitances of the respective capacitors at the same ratio, the reduction start frequency can be decreased in such a way that the change amount of the impedance of the fifth circuit with respect to the change amount of the frequency of the signal input to the fifth circuit when a signal having a frequency higher than the reduction start frequency is input is not changed. Similarly, by decreasing the capacitances of the respective capacitors at the same ratio, the reduction start frequency can be increased in such a way that the change amount of the impedance of the fifth circuit with respect to the change amount of the frequency of the signal input to the fifth circuit when a signal having a frequency higher than the reduction start frequency is input is not changed. The capacitances of the respective capacitors can be appropriately set to obtain a desired reduction start frequency.

[0091] In the present embodiment where high-frequency signals of 100 MHz or more are transmitted in the same manner as in the first embodiment, the characteristic impedance of the second transmission line 14 is also different from the impedance of the fifth circuit. As a result, the fifth circuit can reflect a part of the signals in the fourth signal, that is, the fifth signal. Thereby, a seventh signal is generated in the second inductor 122, and thus the energy of the seventh signal can be superimposed on the third signal. Therefore, the intensity of the signal output from the electronic device 1000 can be increased.

[0092] In addition, when Figure 2 is compared with Figure 7 , it is found that: in Figure 7 , the change amount of the impedance of the fifth circuit with respect to the change amount of the frequency of the signal input to the fifth circuit is small. Depending on the performance of the coaxial cable 3000, there is a case where: since the attenuation amount of the energy of the third signal is small, the amount of the signal reflected by the third circuit 20 and the fourth circuit 24 can be small. In such a case, as in the present embodiment, the number of parallel connections of the resistor and the capacitor provided between the fourth transmission line 16 and the fifth transmission line 17 is set to be plural, and the electrostatic capacitances of the respective capacitors are made different from each other. Thus, even when a high-frequency signal is input, a large reduction in impedance can be prevented. Thereby, the amount of the signal reflected by the fifth circuit can be reduced. Further, as the number of parallel connections of the resistor and the capacitor provided between the fourth transmission line 16 and the fifth transmission line 17 increases, the change amount of the impedance of the fifth circuit with respect to the change amount of the frequency of the signal input to the fifth circuit can become smaller. Therefore, the number of parallel connections of the resistor and the capacitor can be determined according to the performance of the coaxial cable 3000. In the present embodiment, the number of parallel connections of the resistor and the capacitor is four, but depending on the performance of the coaxial cable 3000, the number of parallel connections of the resistor and the capacitor can also be two or three, or can be five or more.

[0093] Figure 8 is the simulation result of the eye diagram of the signal passing through the coaxial cable 3000 showing the schematic structure of the present embodiment. Figure 1 The horizontal axis of Figure 8 represents time, and the vertical axis represents the amplitude (relative value).

[0094] Figure 8 The amplitude C of

[0095] represents the magnitude of the amplitude of the eye diagram at 200 psec. Figure 4When comparing the amplitude A, it is known that: compared with the reference example where no signal is reflected by the resistor 100, the amplitude of the eye diagram of the present embodiment where the signal is reflected by the fifth circuit is larger, and the signal intensity is higher. Therefore, compared with the reference example, in the present embodiment, the intensity of the signal passing through the coaxial cable 3000, that is, the intensity of the signal output from the electronic device 1000 is high, so the possibility that the signal cannot be detected in the electronic device 2000 can be reduced.

[0096] In addition, when Figure 8 is compared with the Figure 5 simulation result showing the eye diagram in the first embodiment, in Figure 8 , since the amount of the signal reflecting a frequency other than the desired frequency is small, the upper end of the amplitude of the eye diagram at 200 psec is closer to 1.0 and the lower end is closer to 0.0. That is, in the present embodiment, compared with the first embodiment, the EMC (ElectroMagnetic Compatibility) performance is excellent, and the possibility of emitting noise to the outside can be reduced.

[0097] The above has described the embodiments of the present disclosure, but the above embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These new embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope. And, the constituent elements related to different embodiments and modification examples can be appropriately combined.

[0098] In addition, the effects of the embodiments described in this specification are always illustrative and not restrictive, and there may be other effects.

[0099] (Supplementary Note)

[0100] One aspect of the present disclosure is as follows.

[0101] [First Aspect]

[0102] A signal transmission circuit includes:

[0103] A common mode filter including a first inductor and a second inductor;

[0104] A first circuit including a first capacitor;

[0105] A second circuit including a second capacitor and having the same circuit structure as the first circuit;

[0106] A third circuit, having an input terminal and an output terminal, having a circuit structure different from that of the second circuit, reflecting a signal in a specified frequency band including the frequency of the transmission signal among a specified amount of the input signal, and passing other components of the input signal;

[0107] A first transmission line, one end of which is connected to a communication circuit that outputs a differential signal, and the other end of which is connected to one end of the first inductor via the first circuit;

[0108] A second transmission line, one end of which is connected to the communication circuit, and the other end of which is connected to one end of the second inductor via the second circuit, having a characteristic impedance different from the impedance of the third circuit;

[0109] A third transmission line, connected to the other end of the first inductor and an output terminal;

[0110] A fourth transmission line, connected to the other end of the second inductor and the input terminal; and

[0111] A fifth transmission line, connected to the output terminal and ground.

[0112] According to this method, it is possible to superimpose the energy of the signal reflected by the third circuit on the signal whose energy has attenuated and flows to the coaxial cable via the third transmission line. Thereby, the intensity of the transmitted signal can be increased.

[0113] [Second method]

[0114] The signal transmission circuit according to the first method, wherein

[0115] The impedance of the third circuit is smaller than the characteristic impedance of the second transmission line.

[0116] According to this method, it is possible to reflect a part of the signal input to the third circuit to the second inductor.

[0117] [Third method]

[0118] The signal transmission circuit according to the first method or the second method, wherein

[0119] The third circuit includes a first resistor and a third capacitor connected in parallel with the first resistor.

[0120] According to this method, it is possible to reflect a part of the signal input to the third circuit to the second inductor.

[0121] [Fourth method]

[0122] The signal transmission circuit according to the third method, wherein

[0123] It also has a fourth circuit connected in series between the output terminal and the fifth transmission line.

[0124] The fourth circuit includes a second resistor and a fourth capacitor connected in parallel with the second resistor.

[0125] According to this method, it is possible to reduce the change amount of the impedance of the third circuit and the fourth circuit with respect to the change amount of the frequency of the signal input to the third circuit and the fourth circuit. Thus, it is possible to reduce the possibility of reflecting a signal that is larger than necessary.

[0126] [Fifth Method]

[0127] In the signal transmission circuit according to the fourth method,

[0128] The capacitance of the third capacitor is different from the capacitance of the fourth capacitor.

[0129] According to this method, it is possible to reduce the change amount of the impedance of the third circuit and the fourth circuit with respect to the change amount of the frequency of the signal input to the third circuit and the fourth circuit. Thus, it is possible to reduce the possibility of reflecting a signal that is larger than necessary.

[0130] [Sixth Method]

[0131] In the signal transmission circuit according to any one of the first method to the fifth method,

[0132] The characteristic impedance of the first transmission line is equal to the characteristic impedance of the second transmission line.

[0133] According to this method, it is not easy to generate common mode noise in each signal passing through the first transmission line and the second transmission line.

[0134] [Seventh Method]

[0135] In the signal transmission circuit according to any one of the first method to the sixth method,

[0136] The first circuit only includes the first capacitor,

[0137] The second circuit only includes the second capacitor,

[0138] The capacitance of the first capacitor is equal to the capacitance of the second capacitor.

[0139] According to this method, it is not easy to generate common mode noise in each signal passing through the first transmission line and the second transmission line.

[0140] [Eighth Method]

[0141] The signal transmission circuit according to any one of the first to seventh modes, wherein,

[0142] comprises the communication circuit.

[0143] According to this mode, compared with the case where the communication circuit is provided outside the signal transmission circuit, the length of the transmission line can be shortened, so that the attenuation amount of the energy of the signal flowing through the transmission line can be reduced. In addition, the possibility of generating noise in the signal flowing through the transmission line can be reduced.

[0144] [Ninth mode]

[0145] An electronic device comprising the signal transmission circuit according to any one of the first to eighth modes.

[0146] According to this mode, it is possible to superimpose the energy of the signal reflected by the third circuit on the signal whose energy has been attenuated and flows through the third transmission line to the coaxial cable. Thereby, the intensity of the transmitted signal can be increased.

Claims

1. A signal transmission circuit, comprising: A common mode filter comprising a first inductor and a second inductor; a first circuit comprising a first capacitor; A second circuit, comprising a second capacitor, having the same circuit structure as the first circuit; a third circuit having an input terminal and an output terminal, having a circuit structure different from that of the second circuit, reflecting a predetermined amount of a signal of a predetermined frequency band including a frequency of a transmission signal in the input signal, and passing other components of the input signal; a first transmission line, one end of which is connected to a communication circuit that outputs a differential signal, and the other end of which is connected to one end of the first inductor via the first circuit; a second transmission line, one end of which is connected to the communication circuit, the other end of which is connected to one end of the second inductor via the second circuit, and has a characteristic impedance different from the impedance of the third circuit; a third transmission line connected to the other end of the first inductor and an output terminal of the signal transmission circuit; a fourth transmission line connected to the other end of the second inductor and an input end; as well as A fifth transmission line is connected to the output terminal and ground.

2. The signal transmission circuit according to claim 1, wherein: The impedance of the third circuit is smaller than the characteristic impedance of the second transmission line.

3. The signal transmission circuit according to claim 1 or 2, wherein: The third circuit includes a first resistor and a third capacitor connected in parallel with the first resistor.

4. The signal transmission circuit according to claim 3, wherein: further comprising a fourth circuit connected in series between the output terminal and the ground, The fourth circuit includes a second resistor and a fourth capacitor connected in parallel with the second resistor.

5. The signal transmission circuit according to claim 4, wherein: The electrostatic capacitance of the third capacitor is different from the electrostatic capacitance of the fourth capacitor.

6. The signal transmission circuit according to claim 1, wherein: The characteristic impedance of the first transmission line is equal to the characteristic impedance of the second transmission line.

7. The signal transmission circuit according to claim 1, wherein: the first circuit only includes the first capacitor, the second circuit comprises only the second capacitor, The electrostatic capacitance of the first capacitor is equal to the electrostatic capacitance of the second capacitor.

8. The signal transmission circuit according to claim 1, wherein: The communication circuit is provided.

9. An electronic device, A signal transmission circuit according to claim 1 is provided.

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