High-frequency circuits

Abstract

To provide a high frequency circuit capable of easily predicting and controlling a cavity resonance frequency in a shield case.SOLUTION: A high-frequency circuit is provided with a printed circuit board (10) on which a circuit composed of a plurality of electronic components is arranged, a shield case (31) which is electrically connected to the ground of the printed circuit board (10) and covers the circuit, and at least one spring contact (15) which is electrically connected to the ground in a space formed by the printed circuit board (10) and the inner wall of the shield case (31), wherein the shield case (31) includes a frame (41) which is surface-mounted on the ground and is electrically connected to the ground, and a cover (51) which has a ceiling surface facing the printed circuit board (10) and is in contact with and electrically connected to the frame (41). The spring contact 15 comes into contact with a part of the ceiling surface to electrically connect the ground and the cover 51.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a high-frequency circuit, and particularly to a high-frequency circuit provided with a shield case.

Background Art

[0002] An RF (Radio Frequency) circuit is used in a state where each circuit block is covered with a shield case in order to ensure isolation between the circuit blocks. The cavity resonance frequency of a space delimited by the shield case is determined by the size and shape of the space. Since the spatial isolation becomes 0 dB at the cavity resonance frequency, this poses a problem in RF circuit design.

[0003] When the size of the space delimited by the shield case is large, there is a disadvantage that the cavity resonance frequency becomes lower; on the other hand, there is an advantage that the design of a printed circuit board is simplified because electronic components can be easily arranged. Therefore, it has been desired to increase the spatial size of the shield case while suppressing cavity resonance. Here, suppressing cavity resonance means making the cavity resonance frequency higher than the operating frequency of the circuit block.

[0004] Conventionally, as a method for suppressing cavity resonance, a method of implementing it by trial-and-error attachment of radio wave absorbers has been adopted.

[0005] Also, a technique is known that ensures isolation between a plurality of circuits by means of a radio wave absorber having grooves that individually cover the plurality of circuits formed on a circuit board (see, for example, Patent Document 1).

Prior Art Literature

Patent Literature

[0006]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0007] However, since there is no way to predict in advance how cavity resonance can be suppressed by the radio wave absorber, the technology disclosed in Patent Document 1 also had the problem that the groove shape had to be determined through trial and error.

[0008] The present invention has been made to solve these conventional problems, and aims to provide a high-frequency circuit that can easily predict and control the cavity resonance frequency within a shield case. [Means for solving the problem]

[0009] To solve the above problems, the high-frequency circuit according to the present invention comprises a printed circuit board (10) on which circuits (21-27) composed of a plurality of electronic components (11) are arranged, a shield case (31, 32, 36, 37) that is electrically connected to the ground (12, 13) of the printed circuit board and covers the circuits, and a space formed between the printed circuit board and the inner wall of the shield case that is electrically connected to the ground. multiple The shield case comprises a connecting conductor (15) and a side wall portion (41-47) surface-mounted on the ground and electrically connected to the ground, and a lid portion (51) having a top surface (52) facing the printed circuit board and in contact with the side wall portion and electrically connected, multiple The connecting conductor contacts a portion of the ceiling surface, electrically connecting the ground and the cover. Furthermore, at least two of the plurality of connecting conductors are positioned near the center of the shield case. It has that configuration. Furthermore, the high-frequency circuit according to the present invention is configured such that at least two of the plurality of connecting conductors are located near the center of the shield case, so that the cavity resonance frequency within the shield case is higher than the operating frequency.

[0010] With this configuration, the high-frequency circuit according to the present invention can achieve an effect as if the space formed between the printed circuit board and the inner wall of the shield case were narrowed, and the cavity resonance frequency can be increased without using an electromagnetic wave absorber.

[0011] Furthermore, since the arrangement of connecting conductors in which the cavity resonance frequency is higher than the operating frequency can be predicted by electromagnetic field simulation, the high-frequency circuit according to the present invention can reduce the man-hours required for performance verification.

[0012] Furthermore, the high-frequency circuit according to the present invention allows for an increase in the cavity resonance frequency by adjusting the arrangement of connecting conductors, even when the size of the space partitioned by the shielding case is increased. This facilitates the arrangement of electronic components on the printed circuit board and reduces design man-hours.

[0013] Furthermore, the high-frequency circuit according to the present invention effectively suppresses cavity resonance by positioning the connecting conductor near the center of the space within the shield case, thus not affecting the degree of freedom in the arrangement of other electronic components.

[0014] Furthermore, the high-frequency circuit according to the present invention is as described above. multiple The connecting conductor may be configured as a spring contact (15) having a contact portion (17) that elastically contacts the ceiling surface.

[0015] With this configuration, the high-frequency circuit according to the present invention can be electrically connected to the ground of the printed circuit board and the lid of the shield case reliably and easily by placing the lid of the shield case over the side walls after the multiple electronic components and the side walls of the shield case have been placed on the printed circuit board.

[0016] In order to solve the above problem, a cavity resonance suppression method according to the present invention is a cavity resonance suppression method for a high-frequency circuit (100) comprising: a printed circuit board (10) on which circuits (21 to 27) constituted by a plurality of electronic components (11) are arranged; and shield cases (31, 32, 36, 37) electrically connected to grounds (12, 13) of the printed circuit board and covering the circuits, wherein the shield case includes: side wall portions (41 to 47) surface-mounted on the ground and electrically connected to the ground; and a lid portion (51) having a ceiling surface (52) facing the printed circuit board and being in contact with and electrically connected to the side wall portions, in a space formed by the printed circuit board and an inner wall of the shield case, the multiple connection conductor (15) electrically connected to the ground is brought into contact with a part of the ceiling surface to electrically connect the ground and the lid portion Furthermore, at least two of the plurality of connecting conductors are positioned near the center of the shield case. according to the configuration. Furthermore, the cavity resonance suppression method according to the present invention is configured such that at least two of the plurality of connecting conductors are located near the center of the shield case, thereby making the cavity resonance frequency within the shield case higher than the operating frequency.

[0017] Furthermore, in the cavity resonance suppression method according to the present invention, the multiple as the connection conductor, a spring contact (15) having a contact portion (17) elastically contacting the ceiling surface may be used. [Effect of the Invention]

[0018] The present invention provides a high-frequency circuit that can facilitate prediction and control of a cavity resonance frequency in a shield case. [Brief Description of Drawings]

[0019] [Figure 1] FIG. 1 is a plan view showing a configuration of a high-frequency circuit according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing a configuration of a high-frequency circuit according to an embodiment of the present invention. [Figure 3] FIG. 3 is a side view showing an essential part of a configuration of a high-frequency circuit according to an embodiment of the present invention. [Figure 4] FIG. 4 shows a board surface of a printed circuit board in a high-frequency circuit according to an embodiment of the present invention. [Figure 5] FIG. 1 is a perspective view showing a simulation model of a high-frequency circuit according to an embodiment of the present invention, where (a) shows a model in which one spring contact is arranged near the center in a shield case, (b) shows a model in which two spring contacts are arranged in the shield case 25 mm apart from each other, and (c) shows a model in which two spring contacts are arranged near the center in the shield case 5 mm apart from each other. [Figure 6] FIG. 5 is a side view and a plan view of (a). [Figure 7] It is a graph showing transmission characteristics of the models shown in FIGS. 5(a) to (c) and transmission characteristics of a model in which no spring contact is arranged. [Figure 8] It is a graph showing transmission characteristics of a simulation model and transmission characteristics of an experimental board. [Figure 9] It is a diagram showing electric field distributions of the models shown in FIGS. 5(a) to (c) and an electric field distribution of a model in which no spring contact is arranged. DETAILED DESCRIPTION OF THE INVENTION

[0020] First, an embodiment of a high-frequency circuit according to an embodiment of the present invention will be described with reference to the drawings. Note that the dimensional ratios of respective components in the drawings do not necessarily match the actual dimensional ratios.

[0021] As shown in FIG. 1, the high-frequency circuit 100 includes circuits 21 to 27 configured by a plurality of electronic components 11, a printed circuit board 10 on which the circuits 21 to 27 are arranged, shield cases 31 to 37 that respectively cover the circuits 21 to 27, and a spring contact 15 as a connection conductor.

[0022] Each of the shield cases 31 to 37 includes frames 41 to 47 as side wall portions and covers as lid portions respectively attached to the frames 41 to 47, but FIG. 1 only illustrates the frames 41 to 47 of the respective shield cases 31 to 37.

[0023] In the example shown in Figure 1, seven circuits 21 to 27 are configured on one side 10a of the printed circuit board 10. Similarly, multiple circuits may be configured on the other side of the printed circuit board 10.

[0024] The shield cases 31-37 are metal enclosures that cover the circuits 21-27 arranged on the printed circuit board 10 to prevent noise from being input from the outside or other circuits. For example, Lairdtek's BMI-S-203, BMI-S-209, BMI-S-210, etc., can be suitably used.

[0025] The original frames 41-47 have portions that are attracted by the suction nozzle of the mounting machine, but Figure 1 shows the frames 41-47 after they have been mounted on the printed circuit board 10 and the attracted portions have been cut off. The frames 41-47 are mounted so that they are standing vertically on the substrate surface 10a of the printed circuit board 10.

[0026] Figure 2 shows the state of the shield case 31 before the cover 51 is attached to the frame 41. Note that several electronic components 11 are not shown in Figure 2. In the following, the shield case 31 will be described as a representative example, but the basic configuration of the other shield cases 32 to 37 is the same as that of shield case 31.

[0027] As shown in Figure 3, when the cover 51 is attached to the frame 41, it has a top surface 52 that is parallel to and opposite the substrate surface 10a of the printed circuit board 10. Furthermore, when the cover 51 is attached to the frame 41, the peripheral edge of the cover 51 contacts the frame 41, thereby creating an electrical connection.

[0028] The size of each shield case 31-37 should preferably correspond to the size of each circuit 21-27 and the maximum operating frequency.

[0029] For example, BMI-S-210 is used as shielding case 31, 32, 36, and 37 for circuits 21, 22, 26, and 27. The dimensions of the BMI-S-210 frame, i.e., frames 41, 42, 46, and 47, are 44.00 ± 0.10 mm for the long side, 30.50 ± 0.10 mm for the short side, and 3.00 ± 0.10 mm for the height.

[0030] Figure 4 shows a portion of the grounds 12 and 13 provided on the substrate surface 10a of the printed circuit board 10. The grounds 12 and 13 are electrically connected to a common high-frequency ground (RF ground) of the printed circuit board 10 (not shown).

[0031] The frame 41 of the shield case 31 is surface-mounted to the ground 12 by reflow soldering, so that the ground 12 and the frame 41 are electrically connected.

[0032] The spring contact 15, which will be described later, is surface-mounted on the ground 13 by reflow soldering.

[0033] The operating frequency of circuit 21 is, for example, 6 GHz. If the BMI-S-210 is mounted on the printed circuit board 10 as a shielding case 31 without using the spring contact 15, the cavity resonance frequency of the shielding case 31 will be around 5.9 GHz, which will affect the operating frequency of 6 GHz.

[0034] The high-frequency circuit 100 of this embodiment includes at least one spring contact 15 that electrically connects the ground 13 of the printed circuit board 10 and the cover 51 of the shield case 31 in the space within the shield case 31 in order to raise the cavity resonance frequency of the substantially rectangular space formed by the printed circuit board 10 and the inner wall of the shield case 31 above the operating frequency.

[0035] For example, as the spring contact 15, the SMAR-CFO275013A, which is reflowable and can be automatically mounted, manufactured by T.P.S. Creations, can be suitably used. As shown in Figure 3, the bottom 16 of the SMAR-CFO275013A is electrically connected to the ground 13 of the printed circuit board 10.

[0036] The spring contact 15 has a springy contact portion 17, and its range of motion in the height direction is 2.7 to 3.5 mm. When the cover 51 is attached to the frame 41, the height of the top surface 52 of the cover 51 of the shield case 31 is 3 mm from the board surface 10a of the printed circuit board 10. Therefore, when the cover 51 is attached to the frame 41, the contact portion 17 of the spring contact 15 elastically contacts a part of the top surface 52 of the cover 51 of the shield case 31, electrically connecting the ground 13 and the cover 51.

[0037] The following describes the results of evaluating the cavity resonance frequency within the shield case 31 in the high-frequency circuit 100 of this embodiment using electromagnetic field simulation.

[0038] Figures 5(a) to 5(c) and 5(c) and 5(c) show the simulation model. Figure 6 is a side view and a top view of Figure 5(a).

[0039] The models shown in Figures 5(a) to 5(c) simulate a situation in which a printed circuit board 10 on which spring contacts 15 are placed is covered with a BMI-S-210 (hereinafter also referred to as the "shield case 60"). In this model, the spring contacts 15 are simulated as conductive cylinders.

[0040] The printed circuit board 70 of the model has four microstrip lines L0, L1, L2, and L3 formed on it. Each end of the microstrip lines L0, L1, L2, and L3 is defined as an input port P0 and three output ports P1, P2, and P3.

[0041] Each microstrip line L0 to L3 consists of a dielectric 71, a strip conductor 72 placed on the upper surface of the dielectric 71, and a ground (not shown) placed at z < 0. Furthermore, a ground 73 is placed in the region where microstrip lines L0 to L3 are not formed at z > 0.

[0042] Microstrip lines L0 and L2 are constructed by cutting the central portion of a microstrip line that extends along the longitudinal direction of the printed circuit board 70. The same applies to microstrip lines L1 and L3.

[0043] The cut ends of each strip conductor 72 of the microstrip lines L0 to L3 are connected to ground 73 by conductive wires 74, forming four short antennas.

[0044] In other words, this simulation model intentionally makes cavity resonance more likely by increasing the radiation and spatial coupling of the four short antennas, which are microstrip lines L0 to L3.

[0045] Figure 5(a) shows a model in which one cylindrical spring contact 75 is positioned near the center of the shield case 60 (hereinafter also referred to as "Model M1"). Figure 5(b) shows a model in which two cylindrical spring contacts 75 are positioned 25 mm apart from each other in the x-direction within the shield case 60 (hereinafter also referred to as "Model M2"). Figure 5(c) shows a model in which two cylindrical spring contacts 75 are positioned 5 mm apart from each other in the x-direction near the center of the shield case 60 (hereinafter also referred to as "Model M3").

[0046] The main parameters of the simulation are as follows: Thickness of dielectric 71: 0.2 mm Strip conductor 72 thickness: 0.04mm Upper ground 73 thickness: 0.24mm Shield case 60: 44mm x 30.5mm x 3mm (Height of ceiling surface 76: 3.24mm) Length of the cut portion of the strip conductor 72: 5mm Strip conductor 72 width: 0.42mm Y-coordinate of the center line of microstrip lines L0 and L2: 2.5 mm Y-coordinate of the center line of microstrip lines L1 and L3: 15.75 mm Y-coordinate of spring contact 75: 12.75 mm

[0047] Figure 7 is a graph showing the simulation results of the transmission characteristics between input port P0 and output port P1.

[0048] The solid line shows the transmission characteristics of the model without the spring contact 75 (hereinafter also referred to as "Model M0"). In this transmission characteristic, a cavity resonance peak is observed around 5.9 GHz.

[0049] The dashed line shows the transmission characteristics of Model M1, which has one spring contact 75, as shown in Figure 5(a). In these transmission characteristics, a cavity resonance peak is observed around 6.7 GHz.

[0050] The dashed line in Figure 5(b) shows the transmission characteristics of Model M2, in which two spring contacts 75 are positioned 25 mm apart from each other. In these transmission characteristics, a cavity resonance peak is observed around 6.5 GHz.

[0051] The dotted line shows the transmission characteristics of Model M3, as shown in Figure 5(c), where two spring contacts 75 are positioned 5 mm apart from each other. In these transmission characteristics, a cavity resonance peak is observed around 7.3 GHz.

[0052] From the above simulation results, it can be seen that by placing the spring contacts 15 inside the shield case 31, the cavity resonance frequency can be shifted to a higher frequency. In particular, it is considered effective to place multiple spring contacts 15 near the center inside the shield case 31.

[0053] The following describes the results of evaluating the cavity resonance frequency within the shield case 31 in the high-frequency circuit 100 of this embodiment by measuring it on an experimental board with a configuration corresponding to the simulation model described above.

[0054] Figure 8 is a graph showing the transmission characteristics between input port P0 and output port P1 measured using a network analyzer and the simulation results.

[0055] The upper graph in Figure 8 shows the transmission characteristics of the experimental board without spring contacts as a dashed line, and the transmission characteristics of model M0 without spring contacts (same as the solid line in Figure 7) as a solid line.

[0056] In the transmission characteristics of the experimental board, a cavity resonance peak is observed at 5.73 GHz. When the cavity resonance frequency of 5.73 GHz in the transmission characteristics of the experimental board is considered the true value, the error rate of the cavity resonance frequency of 5.9 GHz in the transmission characteristics of Model M0 is 3.0%.

[0057] The lower graph in Figure 8 shows the transmission characteristics of an experimental board with two spring contacts spaced 5 mm apart using a dashed line, and the transmission characteristics of Model M3 (same as the dotted line in Figure 7) with two spring contacts spaced 5 mm apart using a dotted line.

[0058] In the transmission characteristics of the experimental board, a cavity resonance peak is observed at 7.53 GHz. When the cavity resonance frequency of 7.53 GHz in the transmission characteristics of the experimental board is considered as the true value, the error rate of the cavity resonance frequency of 7.3 GHz in the transmission characteristics of Model M3 is -3.1%.

[0059] In other words, with the configuration of the high-frequency circuit 100 of this embodiment, the cavity resonance frequency, which changes depending on the arrangement of the spring contacts 15 in the shield case 31, can be predicted with an error rate of about 3% by electromagnetic field simulation.

[0060] Generally, measuring cavity resonance is difficult, including the construction of an experimental system. However, with respect to the high-frequency circuit 100 of this embodiment, the design can be efficiently carried out using electromagnetic field simulation without the need for actual measurements.

[0061] Furthermore, in an experimental board where two spring contacts were positioned 5mm apart from each other, the isolation between input port P0 and output port P1 improved from approximately -40dB to approximately -60dB.

[0062] Figure 9 shows the electric field distribution at 6 GHz for models M0 to M3, whose transmission characteristics are shown in Figure 7. In these figures, areas with strong electric fields are shown in white, and areas with weak electric fields are shown in black.

[0063] In Model M0, a strong electric field was observed across almost the entire surface of the ground 73 (hereinafter also referred to as the "floor surface") and ceiling surface 76 of the shield case 60.

[0064] In Model M1, a relatively strong electric field was observed in the region along the microstrip line L0 on the floor and ceiling 76, but a weak electric field was observed in other regions.

[0065] In Model M2, relatively strong electric fields were observed in the areas along the microstrip line L0 on the floor and ceiling surfaces 76, as well as near the center.

[0066] In Model M3, relatively strong electric fields were observed in the region along the microstrip line L0 on the floor and ceiling 76, but weak electric fields were observed in other regions. This shows a similar trend to the electric field distribution in Model M1, but the overall electric field was weaker than in Model M1.

[0067] From the simulation results of the electric field distribution described above, it can be confirmed that cavity resonance is effectively suppressed when multiple spring contacts 15 are placed near the center of the shield case 31, compared to when the spring contacts 15 are not placed inside the shield case 31.

[0068] As described above, the high-frequency circuit 100 according to this embodiment has a configuration in which the peripheral edge of the cover 51 of the shield case 31 is electrically connected to the ground 12 of the printed circuit board 10 via the frame 41, and the area near the center of the cover 51 is electrically connected to the ground 13 of the printed circuit board 10 via the spring contact 15.

[0069] The high-frequency circuit 100 according to this embodiment, configured in this way, can achieve the effect of narrowing the space formed between the printed circuit board 10 and the inner wall of the shield case 31, thereby increasing the cavity resonance frequency without using an electromagnetic wave absorber.

[0070] Furthermore, since the arrangement of the spring contacts 15 such that the cavity resonance frequency is higher than the operating frequency can be predicted by electromagnetic field simulation, the high-frequency circuit 100 according to this embodiment can reduce the man-hours required for performance verification.

[0071] Furthermore, in this embodiment, even if the size of the space partitioned by the shield case 31 is increased, the cavity resonance frequency can be raised by the arrangement of the spring contacts 15. This makes it easier to arrange the electronic components 11 on the printed circuit board 10 and reduces design man-hours.

[0072] Furthermore, the high-frequency circuit 100 according to this embodiment effectively suppresses cavity resonance by positioning the spring contact 15 near the center of the space in the shield case 31, and therefore does not affect the degree of freedom in the arrangement of the other electronic components 11.

[0073] Furthermore, the high-frequency circuit 100 according to this embodiment uses a spring contact 15 having a contact portion 17 that elastically contacts the ceiling surface 52 of the cover 51 as a connecting conductor that electrically connects the ground 13 of the printed circuit board 10 and the cover 51 of the shield case 31.

[0074] In the high-frequency circuit 100 according to this embodiment, after the multiple electronic components 11 and the frame 41 of the shield case 31 are placed on the printed circuit board 10, the cover 51 of the shield case 31 can be placed over the frame 41 to reliably and easily electrically connect the ground 13 of the printed circuit board 10 to the cover 51 of the shield case 31.

[0075] Furthermore, in the cavity resonance suppression method according to this embodiment, at least one spring contact 15, which is electrically connected to the ground 13 in the space formed between the printed circuit board 10 and the inner wall of the shield case 31, is brought into contact with a part of the ceiling surface 52 of the cover 51, thereby electrically connecting the ground 13 and the cover 51.

[0076] Furthermore, the cavity resonance suppression method according to this embodiment uses a spring contact 15 having a contact portion 17 that elastically contacts the ceiling surface 52 of the cover 51 as a connecting conductor that electrically connects the ground 13 of the printed circuit board 10 and the cover 51 of the shield case 31. [Explanation of Symbols]

[0077] 10 Printed circuit boards 10a Substrate surface 11 Electronic Components 12, 13 Grand 15 Spring Contact 16 Bottom 17 Contact area Circuits 21-27 31-37 Shield Case 41-47 frames 51 Cover 52 Ceiling surface 100 High-Frequency Circuits

Claims

1. A printed circuit board (10) on which circuits (21-27) composed of multiple electronic components (11) are arranged, The grounds (12, 13) of the printed circuit board are electrically connected to the shield cases (31, 32, 36, 37) that cover the circuit, The space formed by the printed circuit board and the inner wall of the shield case comprises a plurality of connecting conductors (15) electrically connected to the ground, The aforementioned shield case is The side wall portions (41-47) are surface-mounted on the ground and electrically connected to the ground, It includes a lid portion (51) having a ceiling surface (52) facing the printed circuit board and contacting the side wall portion for electrical connection, The plurality of connecting conductors contact a part of the ceiling surface and electrically connect the ground and the cover. A high-frequency circuit characterized in that at least two of the plurality of connecting conductors are arranged near the center of the shield case.

2. The high-frequency circuit according to Claim 1, characterized in that at least two of the plurality of connecting conductors are located near the center of the shield case, so that the cavity resonance frequency within the shield case is higher than the operating frequency.

3. The high-frequency circuit according to claim 1, characterized in that the plurality of connecting conductors are spring contacts (15) having contact portions (17) that elastically contact the ceiling surface.

4. A printed circuit board (10) on which circuits (21-27) composed of a plurality of electronic components (11) are arranged, A method for suppressing cavity resonance in a high-frequency circuit (100) comprising a shield case (31, 32, 36, 37) electrically connected to the ground (12, 13) of the printed circuit board and covering the circuit, wherein The aforementioned shield case is The side wall portions (41-47) are surface-mounted on the ground and electrically connected to the ground, It includes a lid portion (51) having a ceiling surface (52) facing the printed circuit board and contacting the side wall portion for electrical connection, In the space formed by the printed circuit board and the inner wall of the shield case, a plurality of connecting conductors (15) electrically connected to the ground are brought into contact with a part of the ceiling surface, thereby electrically connecting the ground and the lid. A method for suppressing cavity resonance, characterized in that at least two of the plurality of connecting conductors are placed near the center of the shield case.

5. The cavity resonance suppression method according to claim 4, characterized in that at least two of the plurality of connecting conductors are arranged near the center of the shield case, thereby making the cavity resonance frequency in the shield case higher than the operating frequency.

6. The cavity resonance suppression method according to claim 4, characterized in that spring contacts (15) having contact portions (17) that elastically contact the ceiling surface are used as the plurality of connecting conductors.

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