A 225MHz~678MHz high-inhibition low-loss electronically tunable filter

Abstract

The utility model discloses a 225MHz~678MHz high-suppression low-loss electrically tunable filter, including a PCB circuit board and a metal shell covering the PCB circuit board, the PCB circuit board is arranged with electrical components of the electrically tunable filter, and the layout of the electrically tunable filter in the PCB circuit board is bilaterally symmetrical; the RF input and output pins of the electrically tunable filter are built-in with DC blocking capacitors, and the inductance of the electrically tunable filter adopts an enameled wire of a hollow coil. The hollow coil is made of enameled wire to replace the conventional inductor, and the Q value can reach 250~300, and it has adjustability, while ensuring the insertion loss of the filter, it also improves the suppression of the center frequency plus or minus 10% and the far-end double frequency.

Description

Technical Field

[0001] The utility model relates to a 225MHz-678MHz high-suppression low-loss electrically adjustable filter, belonging to the technical field of electrically adjustable filters. Background Art

[0002] like Figure 6-8 The electronically tunable filter shown includes a housing, a coil encapsulated in the housing, and pins arranged at the bottom of the housing. The pin definitions are shown in Table 1 below.

[0003] Table 1

[0004] Serial number 1 2 3 4 5 6 7 definition GND RF GND VT GND RF GND

[0005] The existing electronically tunable filter cannot achieve a significant increase in inductance by using conventional enameled wire. Summary of the invention

[0006] The technical problem to be solved by the utility model is to provide a 225MHz-678MHz high-suppression low-loss electrically tunable filter to solve the problems existing in the above-mentioned prior art.

[0007] The technical solution adopted by the utility model is: a 225MHz-678MHz high-suppression low-loss electrically tunable filter, comprising a PCB circuit board and a metal shell covering the PCB circuit board, the PCB circuit board is arranged with electrical components of the electrically tunable filter, and the layout of the electrically tunable filter in the PCB circuit board adopts bilateral symmetry; the radio frequency input and output pins of the electrically tunable filter are both built-in DC blocking capacitors, and the inductance of the electrically tunable filter adopts an enameled wire of a hollow coil.

[0008] Further, for the above 225-678MHz channel: Magnetic ring name: main magnetic ring, magnetic ring specification 2.3mm winding rod, copper wire diameter 0.45mm, number of turns 10, tap position 2, quantity 1, winding direction counterclockwise;

[0009] Input / output channel: magnetic ring specification T10-0, copper wire diameter 0.17mm, number of turns 2, quantity 2, winding direction counterclockwise;

[0010] The IN / OUT magnetic ring lead wire length of the electronically tunable filter is: IN: 6mm, 17mm; OUT: 6mm, 17mm, with a tolerance of ±0.1mm.

[0011] The circuit of the electronically tunable filter includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C1 and a capacitor C2, including an inductor L5, an inductor L3, an inductor L1, an inductor L2, an inductor L4, an inductor L6, a capacitor C1 and a capacitor C2, wherein the inductor L5, the inductor L1, the inductor L2 and the inductor L6 are connected in series in sequence, the other ends of the inductor L5 and the inductor L6 are respectively connected to the RF switch U1 and the RF switch U2, one end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, the other end of the inductor L3 is connected to one end of the capacitor C1, one end of the inductor L2 and the inductor L6 connected in series is connected to one end of the inductor L4, the other end of the inductor L4 is connected to one end of the capacitor C2, and the other ends of the capacitors C1 and C2 are grounded.

[0012] Furthermore, the inductor L4, the inductor L1, the inductor L2 and the inductor L3 are made of an enameled wire of an air-core coil, which are respectively welded to different positions on the welding pads to obtain four inductors.

[0013] Beneficial effects of the utility model: Compared with the prior art, the effects of the utility model are as follows:

[0014] 1) Use enameled wire to make hollow coils to replace conventional inductors, with a Q value of 250-300 and adjustable. While ensuring the insertion loss of the filter, it also improves the suppression of the center frequency plus or minus 10% and the double frequency at the far end; the PCB circuit board uses a large amount of grounding to increase the grounding effect. The layout of the filter in the PCB circuit board is symmetrical on the left and right, 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 filter are built-in DC blocking capacitors to ensure the correct transmission and reception of RF signals;

[0015] 2) By reducing the number of inductors, the size of the electrically tunable filter becomes smaller, which is 17×12×6 (±0.2) mm, while the conventional size is 20*15*7.5 mm; conventional electrically tunable filters of the same size cannot meet the requirement that the insertion loss is less than or equal to 4dB, and the positive and negative 10% suppression of any center frequency from 225MHz to 678MHz is greater than or equal to 13dBc, and the far-end suppression at twice the center frequency is greater than or equal to 40dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the top layer layout of the PCB circuit board;

[0017] Figure 2 It is a schematic diagram of the bottom layer layout of the PCB circuit board;

[0018] Figure 3 It is the patch layout diagram on the PCB circuit board;

[0019] Figure 4 It is the inductor layout diagram on the PCB circuit board;

[0020] Figure 5 It is a top view structural diagram of the electronically tunable filter test fixture;

[0021] Figure 6 Schematic diagram of the top view of the electrically tunable filter;

[0022] Figure 7 It is a left-view structural diagram of the electronically tunable filter;

[0023] Figure 8 It is a schematic diagram of the structure of the electronically tunable filter viewed from above;

[0024] Fig. 9 This is the circuit diagram of the electronically tunable filter. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] Example 1: Figure 1-9 As shown, a 225MHz-678MHz high-suppression low-loss electrically tunable filter comprises a PCB circuit board 1 and a metal housing 2 covering the PCB circuit board 1. The PCB circuit board 1 is arranged with electrical components of the electrically tunable filter. The layout of the electrically tunable filter in the PCB circuit board 1 is bilaterally symmetrical. Both the RF input and output pins of the electrically tunable filter 1 have built-in DC blocking capacitors, and the inductance of the electrically tunable filter 1 adopts an enameled wire of an air-core coil.

[0027] Further, for the above 225-678MHz channel: Magnetic ring name: main magnetic ring, magnetic ring specification 2.3mm winding rod, copper wire diameter 0.45mm, number of turns 10, tap position 2, quantity 1, winding direction counterclockwise;

[0028] Input / output channel: magnetic ring specification T10-0, copper wire diameter 0.17mm, number of turns 2, quantity 2, winding direction counterclockwise;

[0029] The IN / OUT magnetic ring lead wire length of the electronically tunable filter is: IN: 6mm, 17mm; OUT: 6mm, 17mm, with a tolerance of ±0.1mm.

[0030] The circuit of the electronically tunable filter includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C1 and a capacitor C2, including an inductor L5, an inductor L3, an inductor L1, an inductor L2, an inductor L4, an inductor L6, a capacitor C1 and a capacitor C2, wherein the inductor L5, the inductor L1, the inductor L2 and the inductor L6 are connected in series in sequence, the other ends of the inductor L5 and the inductor L6 are respectively connected to the RF switch U1 and the RF switch U2, one end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, the other end of the inductor L3 is connected to one end of the capacitor C1, one end of the inductor L2 and the inductor L6 connected in series is connected to one end of the inductor L4, the other end of the inductor L4 is connected to one end of the capacitor C2, and the other ends of the capacitors C1 and C2 are grounded.

[0031] Furthermore, the inductor L4, the inductor L2, the inductor L1 and the inductor L3 are made of an enameled wire of an air-core coil, which are respectively welded to different positions on the welding pads to obtain four inductors.

[0032] Example 2: Figure 1-9 As shown, a method for manufacturing a 225MHz to 678MHz high-suppression low-loss electrically tunable filter comprises the following steps:

[0033] Step 1: PCB layout: The PCB is provided with two layers, and each layer of the PCB is grounded through a large area (such as Figure 1 , Figure 2 ), the space outside the component pads and traces on the PCB is covered with ground, the bottom layer of the PCB is a complete ground, and the PCB uses a large number of grounding vias to increase the grounding effect. The layout of the filter in the PCB 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 filter are built-in DC blocking capacitors to ensure the correct transmission and reception of RF signals;

[0034] Step 2: The manufacturing method comprises the following steps:

[0035] 2.1) After preparing the chip inductors and capacitors, patch them according to the circuit diagram of the electronically tuned filter, use lead solder paste Sn40Pb60 for SMT machine patching and reflow soldering to obtain the chip semi-finished products. The reflow soldering adopts the following temperature, time, heating rate, cooling rate and heating range to control;

[0036] Table 2

[0037] Reflux temperature above 183°C Duration 60-90 seconds Peak temperature above 210℃ Time 40-60 seconds Peak maximum temperature 235℃ Time < 10 seconds Preheating rate 1-3℃ / sec Cooling zone temperature drop rate Cooling rate <4℃ Heating zone 130-170℃ time 70-120 seconds, heating rate <2℃ / second

[0038] 2.2) Prepare the corresponding inductor according to the following channel requirements;

[0039] 225-678MHz channel: Magnetic ring name: main magnetic ring, magnetic ring specification 2.3mm winding rod, copper wire diameter 0.45mm, number of turns 10, tap position 2, quantity 1, winding direction counterclockwise;

[0040] Input / output channel, magnetic ring specification T10-0, copper wire diameter 0.17mm, number of turns 2, quantity 2, winding direction counterclockwise;

[0041] The length of the IN / OUT magnetic ring lead wire of the electronically tunable filter is: IN: 6mm, 17mm; OUT: 6mm, 17mm, with a tolerance of ±0.1mm;

[0042] 2.3) Use lead tin wire Sn40 / Pb60, 0.5mm to solder the inductor to the corresponding position of the PCB circuit board according to the pad diagram;

[0043] 2.4) Assemble the semi-finished product to the test fixture, debug the filter inductor to achieve the set performance index of the optimal performance, and then fix it with Nanda 704 silicone;

[0044] 2.5) Use lead tin wire Sn40 / Pb60, 0.5mm to seal the metal shell;

[0045] 2.6) After capping, the product is tested and the electrical performance index is tested to form a data report. Then the product is removed from the test tooling, cleaned, inspected, and packaged to form a finished product.

[0046] Furthermore, the circuit of the 225MHz-678MHz high-suppression, low-loss electrically tunable filter prepared above includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C1 and a capacitor C2, including an inductor L5, an inductor L3, an inductor L1, an inductor L2, an inductor L4, an inductor L6, a capacitor C1 and a capacitor C2, wherein the inductor L5, the inductor L1, the inductor L2 and the inductor L6 are connected in series in sequence, and the other ends of the inductor L5 and the inductor L6 are respectively connected to the RF switch U1 and the RF switch U2, one end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, the other end of the inductor L3 is connected to one end of the capacitor C1, one end of the inductor L2 and the inductor L6 connected in series is connected to one end of the inductor L4, the other end of the inductor L4 is connected to one end of the capacitor C2, and the other ends of the capacitor C1 and the capacitor C2 are grounded.

[0047] Furthermore, the inductor L4, the inductor L1, the inductor L2 and the inductor L3 are made of an enameled wire of an air-core coil, which are respectively welded to different positions on the welding pads to obtain four inductors.

[0048] Table 3 Circuit performance parameters

[0049]

[0050] 225MHz~678MHz high suppression low insertion loss electronically tunable filter circuit Fig. 9 As shown, conventional electrically tunable filters of the same size cannot meet the requirement that the insertion loss is less than or equal to 4dB, while the positive and negative 10% suppression of any center frequency from 225MHz to 678MHz is greater than or equal to 13dBc, and the far-end suppression at twice the center frequency is greater than or equal to 40dB.

[0051] The main magnetic ring inductor of the filter in the utility model uses an air-core coil wound by enameled wire, so that the Q value is higher than that of a conventional inductor, and while ensuring the insertion loss of the filter, the suppression of the center frequency plus or minus 10% and the double frequency at the far end is improved.

[0052] like Figure 5 As shown, the test fixture includes a PCB board, on which seven welding pads are arranged, and the seven welding pads correspond to a total of seven terminals on the left side, top and right side of the electronically tunable filter.

[0053] The test fixture welds the ETC filter to the pad of the PCB board, and can perform reliable and stable tests on the newly customized ETC filter. The data test is accurate, and the pins are fixed by welding. After the test is completed, the welding points are loosened by a welding gun or other methods, which will not damage the pins. The test fixture is used to directly weld the ground pin to the pad, without using the bottom of the product, thereby avoiding affecting the product's bottom due to welding and grounding during the ground pin test. The following problems exist in the prior art of using a connecting cable to connect the power supply end and the RF end for testing:

[0054] 1) Too many wires are connected, which can easily lead to errors and poor test accuracy;

[0055] 2) There is a risk of tearing off the product pins;

[0056] 3) The RF line connecting RFin and RFout needs to be grounded. If the test tooling is not used, the bottom of the product will be grounded, which will affect the product appearance and most of the tin left, affecting the customer's use function.

[0057] In order to quickly position the electronically tunable filter, a limit indication frame is drawn on the PCB board. The limit indication frame is larger than the electronically tunable filter. Seven welding pads are arranged on the left, top and right sides of the limit indication frame. The electronically tunable filter can be quickly limited through the limit indication frame, and then the terminals can be quickly welded, thereby improving welding efficiency and testing efficiency.

[0058] In order to avoid shaking during the welding process of the electronically tunable filter, two rows of limit rolling pins (tangent to the outer side of the limit indicator frame) are symmetrically arranged on the front and back sides of the upper surface of the above-mentioned PCB board. There are four limit rolling pins in total in the two rows, which are symmetrical front, back, left and right. The two rows of limit rolling pins can limit the front and rear ends of the electronically tunable filter. When in use, the electronically tunable filter is quickly placed in the two rows of limit rolling pins and moved left and right to the corresponding welding pads of the terminals. Before welding, it plays a role in quick positioning, and during welding, shaking is avoided, making welding more stable and reliable.

[0059] Principle of use of test tooling:

[0060] 1. Solder and fix the two RF wires separately. Figure 5 At the "RFin (serial number 2)" and "RFout (serial number 6)" pins in the PCB;

[0061] 2. Align pins 1 to 7 of the tested ESC filter with the soldering pads on the test fixture, and then fix pins 1 to 7 with lead tin wire Sn40 / Pb60, 0.5mm;

[0062] 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;

[0063] 4. Yes Figure 5 The 23V power supply terminal connected to the "VT" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured.

[0064] 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 225MHz~678MHz high-inhibition low-loss electronically tunable filter, characterized by: It includes a PCB circuit board and a metal shell covering the PCB circuit board. The PCB circuit board is arranged with electrical components of the electronically tunable filter. The layout of the electronically tunable filter in the PCB circuit board adopts left-right symmetry; the RF input and output pins of the electronically tunable filter are both built-in DC blocking capacitors, and the inductance of the electronically tunable filter adopts hollow coil enameled wire.

2. A 225MHz~678MHz high suppression low loss electronically tunable filter according to claim 1, characterized in that: 225-678 MHz channel: Magnetic ring name: main magnetic ring, magnetic ring specification 2.3mm winding rod, copper wire diameter 0.45mm, number of turns 10, tap position 2, quantity 1, winding direction counterclockwise; Input / output channel: magnetic ring specification T10-0, copper wire diameter 0.17mm, number of turns 2, quantity 2, winding direction counterclockwise; The IN / OUT magnetic ring lead wire length of the electronically tunable filter is: IN: 6mm, 17mm; OUT: 6mm, 17mm, with a tolerance of ±0.1mm.

3. A 225MHz~678MHz high suppression low loss electronically tunable filter according to claim 1, characterized in that: The circuit of the electronically tunable filter includes an inductor L1, an inductor L2, an inductor L3, an inductor L4, an inductor L5, an inductor L6, a capacitor C1 and a capacitor C2, including an inductor L5, an inductor L3, an inductor L1, an inductor L2, an inductor L4, an inductor L6, a capacitor C1 and a capacitor C2, wherein the inductor L5, the inductor L1, the inductor L2 and the inductor L6 are connected in series in sequence, the other ends of the inductor L5 and the inductor L6 are respectively connected to the RF switch U1 and the RF switch U2, one end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, the other end of the inductor L3 is connected to one end of the capacitor C1, one end of the inductor L2 and the inductor L6 connected in series is connected to one end of the inductor L4, the other end of the inductor L4 is connected to one end of the capacitor C2, and the other ends of the capacitors C1 and C2 are grounded.

4. A 225MHz~678MHz high suppression low loss electronically tunable filter according to claim 3, characterized in that: Inductor L4, inductor L1, inductor L2 and inductor L3 use an enameled wire of a hollow coil, which is welded to different positions on the welding pad to obtain four inductors.

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