Preparation method of low rectangular coefficient band-pass filter with center frequency of 275MHz

Abstract

The invention discloses a preparation method of a low-rectangular-coefficient band-pass filter with the center frequency of 275 MHz. The method comprises the steps that a PCB is arranged, a chip capacitor and an inductor are welded to the PCB after being wound, the filter in the PCB is arranged in a bilateral symmetry mode, and the filter is assembled to a test tool to be tested. The layout of the filter in the PCB adopts bilateral symmetry, so that parasitic capacitance and inductance generated by the left and right bonding pads are equal, and later product manufacturing is facilitated; radio frequency input and output pins of the product are symmetrical and consistent, so that correct transmission and reception of radio frequency signals are ensured; the size of the product is small and is 20 * 10 * 5 (+ / -0.2) mm, and the size is smaller than that of the conventional 25 * 15 * 5 (+ / -0.2) mm by optimizing circuit parameters and reducing the number of inductors.

Description

Technical Field

[0001] The invention relates to a method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275 MHz, and belongs to the technical field of bandpass filters. Background Art

[0002] like Figure 7-8 The bandpass filter shown includes a housing, a coil encapsulated in the housing, and pins arranged at the bottom of the housing. The pins include left and right RF input and output and a large area ground at the bottom. Main technical indicators: insertion loss ≤4.5dB; rectangular coefficient K60 / K3 ≤3.5; 3dB bandwidth: 20MHz±1.5MH.

[0003] The existing bandpass filters with the same size and the same index design have complex topological structures, are difficult to debug, have low reliability and low efficiency. The 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. Moreover, for low-frequency bandpass inductors, most of them are large inductors, which are very difficult to wind. Summary of the invention

[0004] The technical problem to be solved by the present invention is: a method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275 MHz, so as to solve the problems existing in the above-mentioned prior art.

[0005] The technical solution adopted by the present invention is: a method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275MHz, the method comprising the following steps:

[0006] Step 1: PCB circuit board layout: The PCB circuit board is set up with two layers. The bottom layer of the PCB circuit board is grounded in a large area, and the top layer is paved with the ground in the space outside the component pads and traces. 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; the RF input and output pins of the product are symmetrical and consistent;

[0007] Step 2: The manufacturing method comprises the following steps:

[0008] 2.1) After preparing the chip capacitors, patch them according to the circuit diagram of the bandpass filter, using lead-free solder paste S-SnAg 3.0 Cu 0.5 Perform SMT machine patching and reflow soldering to obtain patch semi-finished products;

[0009] 2.2) Prepare the inductor, where:

[0010] Magnetic ring L1, specification T10-0, copper wire diameter 0.2mm, 5 turns, clockwise winding, magnetic ring lead wire length 10mm;

[0011] Magnetic ring L2, specifications of air-core coil: winding diameter 3.5mm, copper wire diameter 0.5mm, number of turns 6, clockwise winding, magnetic ring lead wire length 1mm;

[0012] Magnetic ring L3, specification T10-0, copper wire diameter 0.2mm, 3 magnetic rings are wound in a superimposed manner, 5 turns, clockwise winding, and the lead wire length of the magnetic ring is 5mm;

[0013] Magnetic ring L4, specification T10-0, copper wire diameter 0.2mm, 5 turns, clockwise winding, magnetic ring lead wire length 5mm;

[0014] Magnetic ring L5, specification air core coil: winding diameter 3.5mm, copper wire diameter 0.5mm, number of turns 6, clockwise winding, magnetic ring lead wire length 1mm;

[0015] Magnetic ring L6, specification air core coil: winding diameter 3.5mm, 3 magnetic rings superimposed winding, copper wire diameter 0.5mm, 6 turns, clockwise winding, magnetic ring lead wire length 1mm;

[0016] 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;

[0017] 2.4) Assemble the semi-finished product input and output to the input and output terminals of the test fixture, loosen or clamp the inductor coil to debug the indicators to achieve the set indicators of the optimal performance, and then fix it with Nanda 704 silicone;

[0018] 2.5) Use lead-free solder paste S-SnAg for metal casing 3.0 Cu 0.5 , 0.5mm for capping;

[0019] 2.6) After capping, use the test tooling to conduct tests and electrical performance index tests to generate data reports, and then clean, inspect, and package the products to form finished products.

[0020] Beneficial effects of the present invention: Compared with the prior art, the effects of the present invention are as follows:

[0021] 1) The layout of the filter in the PCB circuit board is 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; the product size is small, 20×10×5(±0.2)mm, and by optimizing the circuit parameters and reducing the number of inductors, it is smaller than the conventional 25×15×5(±0.2)mm;

[0022] 2) There are only 6 inductors, which greatly reduces the difficulty of debugging and layout;

[0023] 3) Inductors L3 and L6 are wound with three magnetic rings stacked together to increase the inductance with the same number of turns;

[0024] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the top layer layout of the PCB circuit board;

[0026] Figure 2 It is a schematic diagram of the bottom layer layout of the PCB circuit board;

[0027] Figure 3 It is the patch layout diagram on the PCB circuit board;

[0028] Figure 4 It is the inductor layout diagram on the PCB circuit board;

[0029] Figure 5 It is a schematic diagram of the test fixture structure of the bandpass filter;

[0030] Figure 6 It is a schematic diagram of the left view structure of the test tooling;

[0031] Figure 7 It is a schematic diagram of the three-dimensional structure of the bandpass filter; Figure 8 It is a schematic diagram of the structure of a bandpass filter viewed from above; Fig. 9 It is the circuit diagram of a bandpass filter. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0033] Example 1: Figure 1-9 As shown, a method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275 MHz, the method comprising the following steps:

[0034] 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.

[0035] Step 2: The manufacturing method comprises the following steps:

[0036] 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;

[0037] 2.2) Prepare the corresponding inductor according to the parameter table in Table 1;

[0038]

[0039] 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;

[0040] 2.4) Assemble the semi-finished product to the test fixture, debug the filter inductor to achieve the optimal performance setting indicators, and then fix it with Nanda 704 silicone;

[0041] 2.5) Use lead-free solder paste S-SnAg for metal casing 3.0 Cu 0.5 , 0.5mm for capping;

[0042] 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.

[0043] The prepared bandpass filter has the following advantages:

[0044] 1) Adopting new topology circuit structure, reducing the number of capacitors and inductors, facilitating debugging and reducing costs. 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.

[0045] 2) There are only 6 inductors, which greatly reduces the difficulty of debugging and layout;

[0046] 3) Inductors L3 and L6 are wound with three magnetic rings stacked together to increase the inductance with the same number of turns;

[0047] 4) The layout of the filter in the PCB circuit board is 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;

[0048] 5) The circuit structure adopts a left-right symmetrical design, which can make the input and output match better and facilitate debugging.

[0049] Table 2 Circuit performance parameters

[0050] Theoretical frequency Measured frequency Center Insertion Loss 3dB bandwidth Rectangular coefficient VSWR (MHz) (MHz) ≤4.5dB 20.5±1MHz K60 / 3≤3 @275MHz±8MHz≤1.5 275 275.10 4.32 20.63 2.89 1.37

[0051] Conventional bandpass filters of the same size cannot meet the requirement of insertion loss less than or equal to 4.5dB, and the rectangular coefficient K60 / K3≤3.5. The filter adopts a new topology to reduce the number of capacitors and inductors, facilitate debugging, and reduce costs.

[0052] A preparation method for a low rectangular coefficient bandpass filter with a center frequency of 275MHz is provided. The main inductor coil is wound with 3.5 winding diameter and 0.5mm enameled wire. During assembly, the middle position of the main coil is grounded, so that the winding speed is smaller than usual, the volume is also greatly reduced, and the Q value is higher than that of conventional inductors. It has great advantages in small package bandpass filters, can reduce the loss of the bandpass filter, and greatly reduce the influence of the cover on the bandpass filter indicators.

[0053] Among them, for the bandpass filter test, such as Figure 5-6 The 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.

[0054] 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.

[0055] 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.

[0056] Principle of use of test tooling:

[0057] 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;

[0058] 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;

[0059] 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.

[0060] like Fig. 9As shown, the circuit structure of the prepared low rectangular coefficient bandpass filter with a center frequency of 275MHz includes capacitor C1, capacitor C2, inductor L1, inductor L2, inductor L3, inductor L4, inductor L5 and inductor L6. Capacitor C1, inductor L1, inductor L2, inductor L4, inductor L5 and capacitor C2 are connected in series in sequence, the other end of capacitor C1 and capacitor C2 is grounded, one end of inductor L3 is connected to one end connected in series between inductor L1 and inductor L2, the other end of inductor L3 is connected to the input end, one end of inductor L6 is connected to one end connected in series between inductor L4 and inductor L5, the other end of inductor L6 is connected to the output end, and one end of inductor L2 and inductor L4 is grounded. The layout of the filter in the circuit structure in the PCB circuit board adopts left-right symmetry. Inductor L3 and inductor L6 are wound by superposition of 3 magnetic rings. The circuit structure is arranged on the PCB circuit board 1, and the PCB circuit board 1 is covered with a metal shell 2. Four plug-ins 3 are arranged at the bottom of the metal shell. 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. The whole product is welded to the circuit board through the metal shell. The appearance is simple and compact, with a certain anti-interference ability, and the metal shell is convenient for label printing. The middle part of the two ends of the PCB circuit board 1 is 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.

[0061] The circuit structure adopts a left-right symmetrical design, which can make the input and output match better and facilitate debugging.

[0062] 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.

[0063] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention 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 invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275MHz, characterized in that: The method comprises the following steps: Step 1: PCB circuit board layout: The PCB circuit board is set up with two layers. The bottom layer of the PCB circuit board is grounded in a large area, and the top layer is paved with the ground in the space outside the component pads and traces. The layout of the filter in the PCB circuit board is bilaterally symmetrical; the RF input and output pins of the product are symmetrical and consistent; Step 2: The manufacturing method comprises the following steps: 2.1) After preparing the chip capacitors, patch them according to the circuit diagram of the bandpass filter, using lead-free solder paste S-SnAg 3.0 Cu 0.5 Perform SMT machine patching and reflow soldering to obtain patch semi-finished products; 2.2) Prepare the inductor, where: Magnetic ring L1, specification T10-0, copper wire diameter 0.2mm, 5 turns, clockwise winding, magnetic ring lead wire length 10mm; Magnetic ring L2, specifications of air-core coil: winding diameter 3.5mm, copper wire diameter 0.5mm, number of turns 6, clockwise winding, magnetic ring lead wire length 1mm; Magnetic ring L3, specification T10-0, copper wire diameter 0.2mm, 3 magnetic rings are wound in a superimposed manner, 5 turns, clockwise winding, and the lead wire length of the magnetic ring is 5mm; Magnetic ring L4, specification T10-0, copper wire diameter 0.2mm, 5 turns, clockwise winding, magnetic ring lead wire length 5mm; Magnetic ring L5, specification air core coil: winding diameter 3.5mm, copper wire diameter 0.5mm, number of turns 6, clockwise winding, magnetic ring lead wire length 1mm; Magnetic ring L6, specification air-core coil: winding diameter 3.5mm, 3 magnetic rings superimposed winding, copper wire diameter 0.5mm, 6 turns, clockwise winding, magnetic ring lead wire length 1mm; 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; 2.4) Assemble the semi-finished product input and output to the input and output terminals of the corresponding test fixture, loosen or clamp the inductor coil to debug the indicators, reach the set indicators, and then fix it with Nanda 704 silicone; 2.5) Use lead-free solder paste S-SnAg for metal casing 3.0 Cu 0.5 , 0.5mm for capping; 2.6) After capping, use the test tooling to conduct tests and electrical performance index tests to generate data reports. Then, the products are cleaned, inspected, and packaged to form finished products.

2. The method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275 MHz according to claim 1, characterized in that: The circuit structure of the prepared low rectangular coefficient bandpass filter with a center frequency of 275MHz includes a capacitor C1, a capacitor C2, an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5 and an inductor L6. The capacitor C1, the inductor L1, the inductor L2, the inductor L4, the inductor L5 and the capacitor C2 are connected in series in sequence, the other ends of the capacitor C1 and the capacitor C2 are grounded, one end of the inductor L3 is connected to an end connected in series between the inductor L1 and the inductor L2, the other end of the inductor L3 is connected to the input end, one end of the inductor L6 is connected to an end connected in series between the inductor L4 and the inductor L5, the other end of the inductor L6 is connected to the output end, and one end of the inductor L2 connected in series with the inductor L4 is grounded; The layout of the filter in the PCB circuit board is bilaterally symmetrical; Inductor L3 and inductor L6 are wound by stacking three magnetic rings.

3. The method for preparing a low rectangular coefficient bandpass filter with a center frequency of 275 MHz according to claim 1, characterized in that: The test fixture in step 2.4) includes two RF probes, an RF connector, a door frame 1, a door frame 2 and a base. The base is a horizontal F-type structure, that is, it includes a bottom plate and a middle vertical plate and a right end vertical plate respectively fixedly connected to the middle and right end of the bottom plate. The middle vertical plate and the right end vertical plate are a door-shaped structure. Four guide columns are fixedly connected to the four corners. The four corners of the door frame 1 and the door frame 2 are movably sleeved on the four guide columns, and the four guide columns on the right side of the door frame 2 are sleeved with compression springs. The compression springs can fit the door frame 1 with the door frame 2. The two RF probes are respectively fixedly connected to the top of the door frame 1 and the door frame 2 and are respectively electrically connected to the two RF connectors. The two RF connectors are respectively fixedly connected to the bottom of the top crossbeams of the door frame 1 and the door frame 2. The two RF probes can be inserted into the input and output ends of the arc-shaped U-shaped grooves at both ends of the bandpass filter.

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