High frequency circuit

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 more particularly to a high-frequency circuit equipped with a shield case. [Background technology]

[0002] In order to ensure isolation between circuit blocks, RF (Radio Frequency) circuits are used with each circuit block covered by a shielding case. The size and shape of the space separated by the shielding case determine the cavity resonance frequency of that space. At the cavity resonance frequency, the spatial isolation becomes 0 dB, which poses a problem in RF circuit design.

[0003] While a large space partitioned by a shielding case has the disadvantage of lowering the cavity resonance frequency, it has the advantage of simplifying the design of printed circuit boards because it makes it easier to arrange electronic components. Therefore, it is desirable to suppress cavity resonance and increase the spatial size of the shielding case. Here, suppressing cavity resonance means making the cavity resonance frequency higher than the operating frequency of the circuit block.

[0004] Conventionally, a method of suppressing cavity resonance has been adopted in which a radio wave absorber is attached by trial and error.

[0005] There is also known a technique for ensuring isolation between a plurality of circuits by using a radio wave absorber having grooves for individually covering the plurality of circuits formed on a circuit board (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-199417 Summary of the Invention [Problem to be solved by the invention]

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

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

[0009] In order to solve the above problem, the high-frequency circuit of the present invention comprises a printed circuit board (10) on which a circuit (21-27) composed of a plurality of electronic components (11) is arranged, a shielding case (31, 32, 36, 37) electrically connected to a ground (12, 13) of the printed circuit board and covering the circuit, and at least one connecting conductor (15) electrically connected to the ground in a space formed by the printed circuit board and an inner wall of the shielding case, the shielding case including side wall portions (41-47) 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 in contact with the side wall portions and electrically connected, the connecting conductor contacting a portion of the ceiling surface and electrically connecting the ground and the lid portion.

[0010] With this configuration, the high-frequency circuit according to the present invention can obtain the effect of narrowing the space formed by the printed circuit board and the inner wall of the shielding case, and can increase the cavity resonance frequency without using a radio wave absorber.

[0011] Furthermore, since the arrangement of the connecting conductors that will cause the cavity resonance frequency to be higher than the operating frequency can be predicted by electromagnetic field simulation, the high-frequency circuit according to the present invention can reduce the number of steps required for performance verification.

[0012] Furthermore, the high-frequency circuit according to the present invention can increase the cavity resonance frequency by arranging the connecting conductors even if the size of the space partitioned by the shielding case is increased, which makes it easier to arrange electronic components on the printed circuit board and reduces the number of design steps.

[0013] Furthermore, the high-frequency circuit according to the present invention can effectively suppress cavity resonance by arranging the connecting conductor near the center of the space in the shielding case, so that the degree of freedom in arranging multiple other electronic components is not affected.

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

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

[0016] In order to solve the above problem, the cavity resonance suppression method of the present invention is a method for suppressing cavity resonance in a high-frequency circuit (100) including a printed circuit board (10) on which a circuit (21-27) composed of a plurality of electronic components (11) is arranged, and a shielding case (31, 32, 36, 37) electrically connected to a ground (12, 13) of the printed circuit board and covering the circuit, wherein the shielding case includes side wall portions (41-47) surface-mounted on the ground and electrically connected to the ground, and a ceiling surface (52) facing the printed circuit board, and a lid portion (51) in contact with and electrically connected to the side wall portions, and in the space formed by the printed circuit board and the inner wall of the shielding case, at least one connecting conductor (15) electrically connected to the ground is brought into contact with a part of the ceiling surface, thereby electrically connecting the ground and the lid portion.

[0017] Furthermore, the cavity resonance suppression method according to the present invention may be configured such that the connecting conductor is a spring contact (15) having a contact portion (17) that elastically contacts the ceiling surface. [Effects of the Invention]

[0018] The present invention provides a high-frequency circuit that can easily predict and control the cavity resonance frequency within a shield case. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a plan view showing a configuration of a high-frequency circuit according to an embodiment of the present invention. [Figure 2] 1 is a perspective view showing a configuration of a high-frequency circuit according to an embodiment of the present invention; [Figure 3] 1 is a side view showing a main part of a configuration of a high-frequency circuit according to an embodiment of the present invention. [Figure 4] 2 shows a board surface of a printed circuit board in a high-frequency circuit according to an embodiment of the present invention. [Figure 5] 1A and 1B are perspective views showing simulation models of a high-frequency circuit according to an embodiment of the present invention, in which (a) shows a model in which one spring contact is arranged near the center of a shielding case, (b) shows a model in which two spring contacts are arranged 25 mm apart from each other in a shielding case, and (c) shows a model in which two spring contacts are arranged 5 mm apart from each other near the center of a shielding case. [Figure 6] 5(a) is a side view and a plan view. [Figure 7] 6 is a graph showing the transmission characteristics of the model shown in FIGS. 5(a) to 5(c) and the transmission characteristics of a model in which no spring contacts are arranged. [Figure 8] 10 is a graph showing the transmission characteristics of a simulation model and the transmission characteristics of an experimental board. [Figure 9] FIG. 6 is a diagram showing the electric field distribution of the model shown in FIGS. 5(a) to 5(c) and the electric field distribution of a model in which no spring contacts are arranged. DETAILED DESCRIPTION OF THE INVENTION

[0020] First, high-frequency circuits according to embodiments of the present invention will be described with reference to the drawings. Note that the dimensional ratios of the 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 with a plurality of electronic components 11, a printed circuit board 10 on which the circuits 21 to 27 are arranged, shielding cases 31 to 37 that cover the circuits 21 to 27, and spring contacts 15 as connecting conductors.

[0022] Each of the shielding cases 31 to 37 includes a frame 41 to 47 as a side wall portion and a cover as a lid portion attached to each of the frames 41 to 47, but FIG. 1 shows only the frame 41 to 47 of each of the shielding cases 31 to 37.

[0023] 1, seven circuits 21 to 27 are configured on one board surface 10a of the printed circuit board 10. Similarly, a plurality of circuits may be configured on the other board surface of the printed circuit board 10.

[0024] The shielding cases 31 to 37 are metal housings that cover the circuits 21 to 27 arranged on the printed circuit board 10 to prevent noise from being input from the outside or from other circuits, and for example, BMI-S-203, BMI-S-209, BMI-S-210 manufactured by Laird Tech, Inc. can be suitably used.

[0025] The original frames 41 to 47 have portions that are sucked by the suction nozzle of the mounting machine, but Fig. 1 shows the state in which the sucked portions have been cut away after the frames 41 to 47 have been mounted on the printed circuit board 10. The frames 41 to 47 are mounted so as to stand perpendicular to the board surface 10a of the printed circuit board 10.

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

[0027] 3, when cover 51 is attached to frame 41, cover 51 has a ceiling surface 52 that faces parallel to board surface 10a of printed circuit board 10. When cover 51 is attached to frame 41, the peripheral edge of cover 51 comes into contact with frame 41 and is electrically connected thereto.

[0028] The size of each of the shield cases 31 to 37 is preferably determined according to the size of each of the circuits 21 to 27 and the maximum frequency used.

[0029] For example, BMI-S-210 is used as shielding cases 31, 32, 36, and 37 for circuits 21, 22, 26, and 27. The size of the frame of BMI-S-210, i.e., frames 41, 42, 46, and 47, is 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] 4 shows a part of the grounds 12 and 13 provided on the board 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 on the ground 12 by reflow soldering, so that the ground 12 and the frame 41 are electrically connected.

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

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

[0034] The high-frequency circuit 100 of this embodiment is provided with at least one spring contact 15 that electrically connects the ground 13 of the printed circuit board 10 to 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 approximately rectangular parallelepiped space formed by the printed circuit board 10 and the inner wall of the shield case 31 above the operating frequency.

[0035] For example, the SMAR-CFO275013A, manufactured by T·P·S·Creations and capable of automatic reflow mounting, can be suitably used as the spring contact 15. As shown in FIG. 3, the bottom 16 of the SMAR-CFO275013A is electrically connected to the ground 13 of the printed circuit board 10.

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

[0037] The results of evaluating the cavity resonance frequency inside the shield case 31 in the high-frequency circuit 100 of this embodiment by electromagnetic field simulation will be described below.

[0038] Figures 5(a) to 5(c) and Figure 6 are diagrams showing a simulation model, and Figure 6 is a side view and a plan view of Figure 5(a).

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

[0040] Four microstrip lines L0, L1, L2, and L3 are formed on the model printed circuit board 70. 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 of the microstrip lines L0 to L3 is made up of a dielectric 71, a strip conductor 72 arranged on the upper surface of the dielectric 71, and a ground (not shown) arranged at z<0. In addition, a ground 73 is arranged in an area where the microstrip lines L0 to L3 are not formed at z>0.

[0042] The microstrip lines L0 and L2 are configured by cutting the center of the strip conductor of a microstrip line having a length in the longitudinal direction of the printed circuit board 70. The same applies to the microstrip lines L1 and L3.

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

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

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

[0046] The main parameters of the simulation are as follows: Dielectric 71 thickness: 0.2 mm Strip conductor 72 thickness: 0.04 mm Thickness of upper gland 73: 0.24mm Shield case 60: 44mm x 30.5mm x 3mm (height of ceiling surface 76: 3.24mm) Length of cut portion of strip conductor 72: 5 mm Strip conductor 72 width: 0.42 mm 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] FIG. 7 is a graph showing the simulation results of the transmission characteristics between the input port P0 and the output port P1.

[0048] The solid line shows the transmission characteristics of a model (hereinafter also referred to as "model M0") that does not have the spring contact 75. 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 shown in Fig. 5(a) which is provided with one spring contact 75. In this transmission characteristic, a cavity resonance peak is observed around 6.7 GHz.

[0050] The dashed line shows the transmission characteristics of model M2, which has two spring contacts 75 spaced 25 mm apart, as shown in Figure 5(b). In this transmission characteristic, a cavity resonance peak is observed around 6.5 GHz.

[0051] The dotted line shows the transmission characteristics of model M3, which has two spring contacts 75 spaced 5 mm apart, as shown in Figure 5(c). In this transmission characteristic, a cavity resonance peak is observed around 7.3 GHz.

[0052] The above simulation results show that the cavity resonance frequency can be shifted to a higher frequency by arranging the spring contacts 15 inside the shielding case 31. It is considered particularly effective to arrange multiple spring contacts 15 near the center inside the shielding case 31.

[0053] Hereinafter, the results of evaluating the cavity resonance frequency inside the shield case 31 in the high-frequency circuit 100 of this embodiment by measuring an experimental board having a configuration corresponding to the above simulation model will be described.

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

[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 (the 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 to be 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 bottom graph in Figure 8 shows the transmission characteristics of the experimental board with two spring contacts spaced 5 mm apart (dashed line), and the transmission characteristics of model M3 with two spring contacts spaced 5 mm apart (the same as the dotted line in Figure 7).

[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 to be 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] That is, 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 inside the shield case 31, can be predicted by electromagnetic field simulation with an error rate of about 3%.

[0060] Generally, it is difficult to actually measure cavity resonance, including the construction of an experimental system. However, for the high-frequency circuit 100 of this embodiment, the design can be efficiently advanced using electromagnetic field simulations without actually measuring.

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

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

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

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

[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 and near the center.

[0066] In model M3, a relatively strong electric field was observed in the area along the microstrip line L0 on the floor and ceiling surfaces 76, but a weak electric field was observed in other areas. This shows a similar tendency to the electric field distribution in model M1, but overall the electric field was weaker than that in model M1.

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

[0068] As described above, the high-frequency circuit 100 according to this embodiment is configured such that the peripheral portion of the cover 51 of the shielding case 31 is electrically connected to the ground 12 of the printed circuit board 10 via the frame 41, and 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 manner can obtain the effect of narrowing the space formed between the printed circuit board 10 and the inner wall of the shielding case 31, and can increase the cavity resonance frequency without using a radio wave absorber.

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

[0071] Furthermore, in the high-frequency circuit 100 according to this embodiment, even if the size of the space partitioned by the shielding case 31 is increased, the cavity resonance frequency can be increased by arranging the spring contacts 15, which makes it easier to arrange the electronic components 11 on the printed circuit board 10 and reduces the design man-hours.

[0072] Furthermore, in the high-frequency circuit 100 according to this embodiment, cavity resonance can be effectively suppressed by arranging the spring contact 15 near the center of the space in the shielding case 31, so that the degree of freedom in arranging the other electronic components 11 is not affected.

[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 shielding case 31.

[0074] In the high-frequency circuit 100 of this embodiment configured as described above, after 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 is placed over the frame 41, thereby enabling a reliable and easy electrical connection between the ground 13 of the printed circuit board 10 and the cover 51 of the shield case 31.

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

[0076] In addition, 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 shielding case 31. [Explanation of symbols]

[0077] 10 Printed circuit board 10a Board 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 Circuit

Claims

1. a printed circuit board (10) on which a circuit (21-27) composed of a plurality of electronic components (11) is arranged; a shield case (31, 32, 36, 37) electrically connected to the ground (12, 13) of the printed circuit board and covering the circuit; and at least one connection conductor (15) electrically connected to the ground in a space formed by the printed circuit board and the inner wall of the shielding case, The shield case is a sidewall portion (41 to 47) surface-mounted on the ground and electrically connected to the ground; a cover portion (51) having a ceiling surface (52) facing the printed circuit board and contacting and electrically connected to the side wall portion, The high-frequency circuit is characterized in that the connecting conductor contacts a part of the ceiling surface and electrically connects the ground and the lid portion.

2. 2. The high frequency circuit according to claim 1, wherein the connecting conductor is a spring contact (15) having a contact portion (17) that elastically contacts the ceiling surface.

3. a printed circuit board (10) on which a circuit (21-27) composed of a plurality of electronic components (11) is arranged; A method for suppressing cavity resonance in a high-frequency circuit (100) including a shield case (31, 32, 36, 37) electrically connected to the ground (12, 13) of the printed circuit board and covering the circuit, The shield case is a sidewall portion (41 to 47) surface-mounted on the ground and electrically connected to the ground; a cover portion (51) having a ceiling surface (52) facing the printed circuit board and contacting and electrically connected to the side wall portion, A cavity resonance suppression method, characterized in that in a space formed by the printed circuit board and the inner wall of the shielding case, at least one connecting conductor (15) electrically connected to the ground is brought into contact with a part of the ceiling surface, thereby electrically connecting the ground and the lid portion.

4. 4. The cavity resonance suppression method according to claim 3, wherein a spring contact (15) having a contact portion (17) that elastically contacts the ceiling surface is used as the connecting conductor.

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