A circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter

Abstract

The utility model discloses a circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter, which comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, an inductor L1, an inductor L2, an inductor L3 and an inductor L4, wherein one end of the capacitor C1 is connected to an input end and one end of the inductor L1, the other end of the inductor L1 is connected to one end of the capacitor C2 and the capacitor C3, the other end of the capacitor C3 is connected to one end of the capacitor C4, the inductor L2 and the capacitor C5, the other end of the capacitor C5 is connected to one end of the capacitor C6, the inductor L3 and the capacitor C7, the other end of the capacitor C7 is connected to one end of the capacitor C8 and the inductor L4, the other end of the inductor L4 is connected to an output end and the capacitor C9, and the other ends of the capacitor C1, the capacitor C2, the capacitor C4, the capacitor C6, the capacitor C8, the capacitor C9, the inductor L2 and the inductor L3 are connected to a grounding end. The product size is small, 20×10×5 (±0.2) mm. By optimizing circuit parameters and reducing the number of inductors, it is smaller than the conventional 25×15×5 (±0.2) mm. There are only 4 inductors, which greatly reduces the difficulty of debugging and layout.

Description

Technical Field

[0001] The utility model relates to a circuit structure of a F0:175MHz high-inhibition low-bandwidth passive bandpass filter, belonging to the technical field of passive bandpass filters. Background Art

[0002] like Figure 7-8 The bandpass filter shown includes a shell, a coil encapsulated in the shell, and pins arranged at the bottom of the shell. The pins include left and right radio frequency input and output and a large area grounding at the bottom.

[0003] Existing bandpass filters of the same size cannot meet the requirements of insertion loss less than or equal to 7dB, F0±25MHz external suppression greater than or equal to 60dBc, and 3dB bandwidth of 4±1MHz.

[0004] Existing bandpass filters use conventional elliptical or Chebyshev models with a large number of inductors, which are not suitable for such small-package bandpass filters. In addition, the low-frequency bandpass inductors are mostly large inductors, which are very difficult to wind. Summary of the invention

[0005] The technical problem to be solved by the utility model is to provide a circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter to solve the problems existing in the above-mentioned prior art.

[0006] The technical scheme adopted by the utility model is as follows: a circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, an inductor L1, an inductor L2, an inductor L3 and an inductor L4, one end of the capacitor C1 is connected to an input end and one end of the inductor L1, the other end of the inductor L1 is connected to one end of the capacitor C2 and the capacitor C3, the other end of the capacitor C3 is connected to one end of the capacitor C4, the inductor L2 and the capacitor C5, the other end of the capacitor C5 is connected to one end of the capacitor C6, the inductor L3 and the capacitor C7, the other end of the capacitor C7 is connected to one end of the capacitor C8 and the inductor L4, the other end of the inductor L4 is connected to the output end and the capacitor C9, and the other ends of the capacitor C1, the capacitor C2, the capacitor C4, the capacitor C6, the capacitor C8, the capacitor C9, the inductor L2 and the inductor L3 are connected to the grounding end.

[0007] Furthermore, the magnetic rings of the inductor L1, the inductor L2, the inductor L3 and the inductor L4 are made of T0-0, wherein three T0-0 are wound in a stacked manner.

[0008] Beneficial effects of the utility model: Compared with the prior art, the effects of the utility model are as follows:

[0009] 1) The product size is small, 20×10×5(±0.2)mm. By optimizing the circuit and reducing the number of inductors, it is smaller than the conventional 25×15×5(±0.2)mm. There are only 4 inductors, which greatly reduces the difficulty of debugging and layout.

[0010] 2) The filter magnetic ring inductor is made of 3 T0-0 superimposed windings, which makes the number of turns smaller than the conventional ones, and the volume is greatly reduced. The Q value is higher than the conventional inductor, which has great advantages in small package bandpass filters, can reduce the loss of bandpass filters, and greatly reduce the impact of the cover on the bandpass filter indicators;

[0011] 3) The inductor is wound by stacking three T0-0 coils to increase the inductance with the same number of turns. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the top layer layout of the PCB circuit board;

[0013] Figure 2 It is a schematic diagram of the bottom layer layout of the PCB circuit board;

[0014] Figure 3 It is the patch layout diagram on the PCB circuit board;

[0015] Figure 4 It is the inductor layout diagram on the PCB circuit board;

[0016] Figure 5 It is a schematic diagram of the test fixture structure of the bandpass filter;

[0017] Figure 6 It is a schematic diagram of the left view structure of the test tooling;

[0018] Figure 7 It is a schematic diagram of the three-dimensional structure of the bandpass filter;

[0019] Figure 8 It is a schematic diagram of the structure of a bandpass filter viewed from above;

[0020] Fig. 9 It is the circuit diagram of a bandpass filter. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] Example 1: Fig. 9As shown, a circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter includes a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, an inductor L1, an inductor L2, an inductor L3 and an inductor L4, one end of the capacitor C1 is connected to the input end and one end of the inductor L1, the other end of the inductor L1 is connected to one end of the capacitor C2 and the capacitor C3, the other end of the capacitor C3 is connected to one end of the capacitor C4, the inductor L2 and the capacitor C5, the other end of the capacitor C5 is connected to one end of the capacitor C6, the inductor L3 and the capacitor C7, the other end of the capacitor C7 is connected to one end of the capacitor C8 and the inductor L4, the other end of the inductor L4 is connected to the output end and the capacitor C9, and the other ends of the capacitor C1, the capacitor C2, the capacitor C4, the capacitor C6, the capacitor C8, the capacitor C9, the inductor L2 and the inductor L3 are connected to the ground.

[0023] Furthermore, the magnetic rings of the inductor L1, the inductor L2, the inductor L3 and the inductor L4 are made of T0-0, wherein three T0-0 are wound in a stacked manner.

[0024] The circuit structure adopts a left-right symmetrical design, which can make the input and output match better and facilitate debugging.

[0025] Example 2: Figure 1-9 As shown, a circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter includes a PCB circuit board 1 and a metal shell 2. The electrical components of the bandpass filter are arranged on the PCB circuit board 1. The metal shell 2 is fixedly covered on the PCB circuit board 1. The magnetic ring in the electrical components uses a 4-T0-0 layout, of which 3 T0-0 are superimposed and wound. The layout of the filter in the PCB circuit board 1 is bilaterally symmetrical. The layout of the filter in the PCB circuit board is bilaterally symmetrical, so that the parasitic capacitance and inductance generated by the left and right pads are equal, which is convenient for the later product manufacturing; the RF input and output pins of the product are symmetrical and consistent to ensure the correct transmission and reception of RF signals; four plug-ins 3 are arranged at the bottom of the metal shell 2, and the lower end of the plug-in 3 passes through the rectangular hole 4 on the PCB circuit board 1 and is bent and attached to the bottom of the PCB circuit board 1, so that the metal shell is only locked on the PCB circuit board 1, and the middle of the two ends of the PCB circuit board 1 are respectively set as the input end 5 and the output end 6, and the input end 5 and the output end 6 are U-shaped card slot structures;

[0026] The PCB circuit board is set up with two layers. The bottom layer of the PCB circuit board is grounded over a large area, and the top layer is grounded in the space outside the component pads and traces. The grounding effect is increased by grounding over a large area.

[0027] The entire product is welded to the circuit board through a metal shell. It has a simple and compact appearance, has a certain anti-interference ability, and the metal shell is convenient for logo printing.

[0028] The filter magnetic ring inductor is made of 3 T0-0 superimposed and wound, which makes the number of turns smaller than the conventional one, and the volume is greatly reduced. The Q value is higher than the conventional inductor, which has great advantages in small package bandpass filters. It can reduce the loss of the bandpass filter and greatly reduce the influence of the cover on the bandpass filter indicators. The layout of the filter in the PCB circuit board adopts left-right symmetry, so that the parasitic capacitance and inductance generated by the left and right pads are equal, which is convenient for the later product manufacturing.

[0029] Example 3: Figure 1-9 As shown, a method for manufacturing a F0:F0:175MHz high-suppression low-bandwidth passive bandpass filter, the method comprising the following steps:

[0030] Step 1: PCB circuit board layout: The PCB circuit board is set up with two layers, and the bottom layer of the PCB circuit board is a large area grounded (such as Figure 1 ), the top layer of space outside the component pads and traces is covered with ground (such as Figure 2 ), through a large number of grounding through holes, the grounding effect is increased. The layout of the filter in the PCB circuit board adopts left-right symmetry, so that the parasitic capacitance and inductance generated by the left and right pads are equal, which is convenient for the later product manufacturing; the RF input and output pins of the product are symmetrical and consistent to ensure the correct transmission and reception of RF signals.

[0031] Step 2: The manufacturing method comprises the following steps:

[0032] 2.1) After preparing the chip capacitors, follow the circuit diagram of the bandpass filter ( Figure 3 ) patch, use lead-free solder paste S-SnAg 3.0 Cu 0.5 Perform SMT machine patching and reflow soldering to obtain patch semi-finished products;

[0033] 2.2) Prepare the corresponding inductor according to the parameter table in Table 1;

[0034]

[0035] 2.3) Use lead-free solder paste S-SnAg 3.0 Cu 0.5 , 0.5mm, solder the inductor to the corresponding position of the PCB circuit board according to the pad diagram;

[0036] 2.4) Assemble the semi-finished product to the test fixture, debug the filter inductor to achieve the best performance, and then fix it with Nanda 704 silicone;

[0037] 2.5) Use lead-free solder paste S-SnAg for metal casing 3.0 Cu 0.5 , 0.5mm for capping;

[0038] 2.6) After capping, the product is tested and the electrical performance index is tested to form a data report. Then the product is cleaned, inspected and packaged to form a finished product.

[0039] Table 2 Circuit performance parameters

[0040]

[0041] Conventional passive bandpass filters of the same size cannot meet the requirements of insertion loss less than or equal to 7dB, F0±25MHz external suppression greater than or equal to 60dBc, and 3dB bandwidth of 4±1MHz.

[0042] The filter magnetic ring inductor is made of 3 T0-0 stacked and wound, which makes the number of turns smaller than the conventional one, and the volume is greatly reduced. The Q value is higher than the conventional inductor, which has great advantages in small package bandpass filters. It can reduce the loss of the bandpass filter and greatly reduce the influence of the cover on the bandpass filter indicators.

[0043] The prepared filter has the following effects:

[0044] 1) The product size is small, 20×10×5(±0.2)mm. By optimizing the circuit parameters and reducing the number of inductors, it is smaller than the conventional 25×15×5(±0.2)mm.

[0045] 2) There are only 4 inductors, which greatly reduces the difficulty of debugging and layout.

[0046] 3) The inductor is wound by stacking three T0-0 coils to increase the inductance with the same number of turns.

[0047] 3) The test fixture can be used in conjunction with the product, so there is no need to solder the product pins during debugging and testing, avoiding secondary soldering at the customer end.

[0048] Among them, for the bandpass filter test, such as Figure 5-6The test fixture shown includes two RF probes 201, RF connector 202, door frame 1 203, door frame 204 and base 205. Base 205 is a horizontal F-type structure, that is, it includes a bottom plate and a middle vertical plate 206 and a right vertical plate 207 respectively fixedly connected to the middle and right end of the bottom plate. The middle vertical plate 206 and the right vertical plate 207 are a door-shaped structure, and four guide columns 208 are fixedly connected at the four corners. The four corners of door frame 1 203 and door frame 204 are movably sleeved on the four guide columns 208, and the four guide columns 208 on the right side of door frame 204 are sleeved with compression springs 209. The compression springs 209 can fit door frame 1 203 with door frame 204. The two RF probes 201 are respectively fixedly connected to the top of door frame 1 203 and door frame 204. They are electrically connected to two RF connectors 202, which are fixedly connected to the bottom of the top crossbeam of the door frame 1 203 and the door frame 2 204 by screws. The input and output ends of the arc-shaped U-shaped grooves at both ends of the bandpass filter can be inserted into the two RF probes 201. The door frame 1 203 and the door frame 204 are made of copper material and grounded over a large area. The two RF connectors are connected to the input cable 210 and the output cable 211 respectively. The two RF probes arranged on the left and right can firmly clamp the bandpass filter through the elastic force of the compression spring. The grounded part at the bottom of the bandpass filter is tightly fitted with the grounded door frame 1 203 and the door frame 2 204. The input RF pin and the output RF pin of the bandpass filter are connected to the network analyzer through the RF probe and the input cable and the output cable for index testing. A groove 214 is set on the left side of the base 205 to facilitate the placement of the detection device.

[0049] By using this test fixture, there is no need to solder the product pins during the bandpass filter debugging and testing process, avoiding secondary soldering at the customer end.

[0050] Both ends of each guide column 208 are fixedly connected to the middle vertical plate 206 and the right vertical plate 207 by two locking screws 212, and the connection is stable and reliable. Metal sleeves 213 are set at the places where the screws of the middle vertical plate 206 and the right vertical plate 207 pass through, which can improve the support stability.

[0051] Principle of use of test tooling:

[0052] 1. Connect two RF cables to two RF connectors, and connect the RF connectors to the "RFin" and "RFout" of the two door frames 203 and 2 respectively;

[0053] 2. Separate the door frame 1 203 and the door frame 2, align the RF input and RF output of the bandpass filter to be tested with the two RF probes of the test fixture, clamp the bandpass filter with the test fixture and make the grounding end at the bottom of the bandpass filter fit tightly with the grounded door frame 1 203 and the door frame 2 204;

[0054] 3. Connect the "RFin" RF line to the output port of the network analyzer and the "RFout" RF line to the input port of the network analyzer for measurement to test the center insertion loss, 3dB bandwidth, rectangular coefficient and standing wave ratio of the bandpass filter.

[0055] The above description is only a specific implementation method of the present utility model, but the protection scope of the present utility model is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present utility model, which should be included in the protection scope of the present utility model. Therefore, the protection scope of the present utility model should be based on the protection scope of the claims.

Claims

1. A circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter, characterized in that: It includes capacitor C1, capacitor C2, capacitor C3, capacitor C4, capacitor C5, capacitor C6, capacitor C7, capacitor C8, capacitor C9, inductor L1, inductor L2, inductor L3 and inductor L4, one end of capacitor C1 is connected to the input end and one end of inductor L1, the other end of inductor L1 is connected to capacitor C2 and one end of capacitor C3, the other end of capacitor C3 is connected to one end of capacitor C4, inductor L2 and capacitor C5, the other end of capacitor C5 is connected to one end of capacitor C6, inductor L3 and capacitor C7, the other end of capacitor C7 is connected to one end of capacitor C8 and inductor L4, the other end of inductor L4 is connected to the output end and capacitor C9, and the other ends of capacitor C1, capacitor C2, capacitor C4, capacitor C6, capacitor C8, capacitor C9, inductor L2 and inductor L3 are connected to the ground end.

2. The circuit structure of a F0:175MHz high-suppression low-bandwidth passive bandpass filter according to claim 1, characterized in that: The magnetic rings of inductors L1, L2, L3 and L4 are made of T0-0, wherein three T0-0 are wound in a stacked manner.

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