Electrically tunable filter with low insertion loss

Abstract

The utility model discloses an electrically tunable filter with low insertion loss, which belongs to the technical field of electrically tunable filters, and comprises a PCB (printed circuit board) and a metal shell, the PCB is provided with electrical components of the electrically tunable filter, the PCB is provided with six layers, each layer of the PCB is grounded in a large area, and the ground is paved in the space outside component pads and wires of the PCB. The first layer, the third layer and the fifth layer of the PCB are wired, the second layer, the fourth layer and the bottom layer are all completely grounded, and radio frequency pin outgoing lines of a radio frequency switch U1 and a radio frequency switch U2 arranged on the PCB adopt 50-ohm impedance wiring on the first layer and the third layer; the filters arranged on the PCB are arranged in a bilateral symmetry mode. The product size is small, the first layer and the third layer are provided with 50-ohm impedance wiring, and the loss of a connecting line between a radio frequency port of the radio frequency switch and the input / output of the filter is reduced, especially the high-frequency part (1000-2500MHz).

Description

Technical Field

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

[0002] like Figure 11-13 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 the following table.

[0003] Pinout definition 1 GND 2 VT 3～10 GND 11 RFIN 12 RFOUT 13～18 GND 19 +3.3V 20 A0 21 A1 22 A2

[0004] The insertion loss of conventional electronically tunable filters cannot meet the requirement of “less than or equal to 4.5dB” in the 1650-2500MHz range. If they were made using a cavity, the size would be about 10 times the current size, which would have no advantage. Summary of the invention

[0005] The technical problem to be solved by the utility model is to provide a low insertion loss electrically tunable filter to solve the problems existing in the above-mentioned prior art.

[0006] The technical scheme adopted by the utility model is: a low insertion loss electrically tunable filter, including a PCB circuit board and a metal shell, the PCB circuit board is arranged with electrical components of the electrically tunable filter, the PCB circuit board is provided with six layers, each layer of the PCB circuit board is grounded through a large area, the space outside the component pads and wiring of the PCB circuit board is paved with the ground, the first layer, the third layer and the fifth layer of the PCB circuit board are wiring, the second layer, the fourth layer and the bottom layer are all complete grounds, the RF pin lead-out lines of the RF switch U1 and the RF switch U2 arranged on the PCB circuit board are wired with 50 ohm impedance on the first layer and the third layer; the filter arranged on the PCB circuit board adopts a left-right symmetrical layout.

[0007] Furthermore, the circuit of the above-mentioned low insertion loss electrically tunable filter includes a first filter circuit, a second filter circuit, a third filter circuit, a RF switch U1 and a RF switch U2. The two ends of the first filter circuit, the second filter circuit and the third filter circuit are respectively connected to the RF switch U1 and the RF switch U2. The first filter circuit is a circuit of 30-90MHz and 90-225MHz models, the second filter circuit is a circuit of 225-650MHz, 650-1200MHz, 1200-1650MHz and 1650-2100MHz models, and the third filter circuit is a circuit of 2100-2500MHz model. Hollow coils are used to make inductors in the high frequency bands of 225-650MHz, 650-1200MHz, 1200-1650MHz, 1650-2100MHz and 2100-2500MHz.

[0008] Furthermore, the first filter circuit includes an inductor LIN, an inductor L19, an inductor L18, an inductor L17, an inductor L16, an inductor L15, an inductor L10, an inductor L11, an inductor LIN1, a capacitor C5 and a capacitor C3, wherein the inductor LIN, the inductor L18, the inductor L17, the inductor L15, the inductor L16, the inductor L10 and the inductor LIN1 are connected in series in sequence, and one end of the inductor LIN and the inductor L18 is connected in series to the inductor L11. 9, one end of the series connection between inductor L17 and inductor L15 is connected to one end of inductor L11, one end of the series connection between inductor L18 and inductor L17 is connected to one end of capacitor C5, one end of the series connection between inductor L16 and inductor L10 is connected to one end of capacitor C3, the other ends of inductor L19, inductor L11, capacitor C5 and capacitor C3 are grounded, and the other ends of inductor LIN and inductor LIN1 are respectively connected to RF switch U1 and RF switch U2.

[0009] Furthermore, the second filter circuit includes 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. 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 connected to the RF switch U1 and the RF switch U2 respectively. 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. The other ends of the capacitors C1 and C2 are grounded.

[0010] Further, the third filter circuit includes an inductor L5', an inductor L3', an inductor L1', an inductor L2', an inductor L4', an inductor L6', an inductor L7, an inductor L8, a capacitor C1' and a capacitor C2'. 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 connected to the RF switch U1 and the RF switch U2 respectively. One end of the inductor L5' and the inductor L1' are connected in series to one end of the inductor L3'. The other end of L3' is connected to one end of capacitor C1', one end of the series connection between inductor L2' and inductor L6' is connected to one end of inductor L4', the other end of inductor L4' is connected to one end of capacitor C2', the other ends of capacitor C1' and capacitor C2' are grounded, one end of inductor L7 is connected to one end connected between inductor L3' and capacitor C1', the other end of inductor L7 is connected to one end of inductor L8 and ground, and the other end of inductor L8 is connected to one end connected between inductor L4' and capacitor C2'.

[0011] Beneficial effects of the utility model: Compared with the prior art, the PCB circuit board of the utility model adopts a large number of grounding through holes to increase the grounding effect, and the filter arranged on the PCB circuit board adopts a left-right symmetrical layout, 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 other specific effects are as follows:

[0012] 1. Divide the 30-2500MHz frequency band into 7 filters (30-90MHz, 90-225MHz, 225-650MHz, 650-1200MHz, 1200-1650MHz, 1650-2100MHz, 2100-2500MHz);

[0013] 2. Use hollow coils to make inductors in the high frequency bands of 225-650MHz, 650-1200MHz, 1200-1650MHz, 1650-2100MHz, and 2100-2500MHz to improve the Q value of the product. The larger the Q value, the better the product indicators; at the same time, it saves size and cost;

[0014] 3. 30~90MHz, 90~225MHz need to remove a large amount of inductance, which requires the use of a magnetic core;

[0015] 4. The product is small in size, with 6 layers. The first layer uses 50 ohm microstrip line and the third layer uses 50 ohm strip line to reduce the connection loss between the RF port of the RF switch and the filter input / output. Especially for the high frequency part (1000-2500MHz), 50 ohm RF line must be used for connection, otherwise it will have a great impact on various product indicators and will not be able to achieve the indicators.

[0016] 5. For filters in the frequency bands of 1650-2100MHz and 2100-2500MHz, hollow coil inductors are connected in parallel to reduce the inductance, so that the filter frequency reaches 2100MHz and 2500MHz;

[0017] 6. The PCB base is connected to the metal shell to shield external interference and reduce the size of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the first layer layout of the PCB circuit board;

[0019] Figure 2 This is a schematic diagram of the second layer layout of the PCB circuit board;

[0020] Figure 3 This is the schematic diagram of the third layer layout of the PCB circuit board;

[0021] Figure 4 This is the schematic diagram of the fourth layer layout of the PCB circuit board;

[0022] Figure 5 This is the schematic diagram of the fifth layer layout of the PCB circuit board;

[0023] Figure 6 This is a schematic diagram of the circuit principle of the electronically tunable filter;

[0024] Figure 7 is a schematic diagram of the first filter circuit structure of the electronically tunable filter;

[0025] Figure 8 is a schematic diagram of the circuit structure of a second filter of the electronically tunable filter;

[0026] Fig. 9 It is a schematic diagram of the circuit structure of the third filter of the electronically tunable filter;

[0027] Fig.10 It is the layout diagram of the test tooling PCB;

[0028] Fig.11 Schematic diagram of the top view of the electrically tunable filter;

[0029] Fig.12 1 is a schematic diagram of the side view structure of the electronically tunable filter;

[0030] Fig.13 This is a schematic diagram of the structure of the electronically tunable filter from an upward perspective. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0032] Example 1: Figure 1-13 As shown, a low insertion loss electrically tunable filter comprises a PCB circuit board 1 and a metal shell 2. The PCB circuit board 1 is arranged with electrical components of the electrically tunable filter. The PCB circuit board is provided with six layers. Each layer of the PCB circuit board is grounded through a large area. The space outside the component pads and wiring of the PCB circuit board is paved with the ground. The first, third and fifth layers of the PCB circuit board are wiring, and the second, fourth and bottom layers are all complete grounds. The RF pin lead wires of the RF switch U1 and the RF switch U2 arranged on the PCB circuit board are wired with 50 ohm impedance on the first and third layers; the filter arranged on the PCB circuit board adopts a left-right symmetrical layout.

[0033] Furthermore, if Figure 6As shown, the circuit of the above-mentioned low insertion loss electrically tunable filter includes a first filter circuit, a second filter circuit, a third filter circuit, a RF switch U1 and a RF switch U2, and the two ends of the first filter circuit, the second filter circuit and the third filter circuit are respectively connected to the RF switch U1 and the RF switch U2, the first filter circuit is a circuit of 30-90MHz and 90-225MHz models, the second filter circuit is a circuit of 225-650MHz, 650-1200MHz, 1200-1650MHz and 1650-2100MHz models, and the third filter circuit is a circuit of 2100-2500MHz model.

[0034] Furthermore, if Figure 7 As shown, the first filter circuit includes an inductor LIN, an inductor L19, an inductor L18, an inductor L17, an inductor L16, an inductor L15, an inductor L10, an inductor L11, an inductor LIN1, a capacitor C5 and a capacitor C3. The inductor LIN, the inductor L18, the inductor L17, the inductor L15, the inductor L16, the inductor L10 and the inductor LIN1 are connected in series in sequence, and one end of the inductor LIN and the inductor L18 is connected to the inductor L19. One end of the inductor L17 and the inductor L15 connected in series is connected to one end of the inductor L11, one end of the inductor L18 and the inductor L17 connected in series is connected to one end of the capacitor C5, one end of the inductor L16 and the inductor L10 connected in series is connected to one end of the capacitor C3, the other ends of the inductor L19, the inductor L11, the capacitor C5 and the capacitor C3 are grounded, and the other ends of the inductor LIN and the inductor LIN1 are respectively connected to the RF switch U1 and the RF switch U2.

[0035] Furthermore, if Figure 8 As shown, the second filter circuit includes 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. 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 connected to the RF switch U1 and the RF switch U2 respectively. One end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, and 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, and the other end of the inductor L4 is connected to one end of the capacitor C2. The other ends of the capacitors C1 and C2 are grounded.

[0036] Furthermore, if Fig. 9As shown, the third filter circuit includes an inductor L5', an inductor L3', an inductor L1', an inductor L2', an inductor L4', an inductor L6', an inductor L7, an inductor L8, a capacitor C1' and a capacitor C2'. 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 connected to the RF switch U1 and the RF switch U2 respectively. One end of the inductor L5' and the inductor L1' are connected in series to one end of the inductor L3'. The other end of inductor L3' is connected to one end of capacitor C1', one end of inductor L2' and inductor L6' in series is connected to one end of inductor L4', the other end of inductor L4' is connected to one end of capacitor C2', the other ends of capacitor C1' and capacitor C2' are grounded, one end of inductor L7 is connected to one end connected between inductor L3' and capacitor C1', the other end of inductor L7 is connected to one end of inductor L8 and ground, and the other end of inductor L8 is connected to one end connected between inductor L4' and capacitor C2'.

[0037] Example 2: Figure 1-13 As shown, a method for manufacturing a 30MHz to 2500MHz low insertion loss electrically tunable filter comprises the following steps:

[0038] Step 1: PCB layout: The PCB has six layers, and each layer is grounded over a large area (such as Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 ), the space outside the component pads and traces is paved with the ground, the first, third and fifth layers of the PCB are traced, and the second, fourth and bottom layers are all complete grounds. The PCB uses a large number of grounding vias to increase the grounding effect. The 2500MHz high frequency has very strict grounding requirements. In addition, the RF pin lead wires of the RF switch U1 and RF switch U2 arranged on the PCB are wired with 50 ohm impedance on the first and third layers; the filter arranged on the PCB adopts a left-right symmetrical layout, so that the parasitic capacitance and inductance generated by the left and right pads are equal, which is convenient for the later product manufacturing;

[0039] Step 2: The manufacturing method comprises the following steps:

[0040] 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;

[0041] 2.2) Prepare the corresponding inductor according to the parameter table in Table 1;

[0042]

[0043]

[0044] In the high frequency bands of 225~650MHz, 650~1200MHz, 1200~1650MHz, 1650~2100MHz, 2100~2500MHz, hollow coils are used to make inductors;

[0045] 2.3) Use lead tin wire Sn40 / Pb60, 0.5mm to solder the inductor prepared in step 2.2) to the corresponding position of the PCB circuit board according to the pad diagram;

[0046] 2.4) Assemble the semi-finished products to the test fixture to test the insertion loss, 3dB relative bandwidth, out-of-band suppression and standing wave ratio, and debug the filter inductance (by adjusting the size of the inductance, the position of the magnetic ring, and the formation of LC matching to optimize the filter indicators) until the optimal performance setting conditions are met (insertion loss ≤4.5dB, 3dB relative bandwidth ≥5%, out-of-band suppression: center frequency ±10% ≥8dBc, standing wave ratio ≤1.8), and then use Nanda 704 silicone to fix it;

[0047] 2.5) The semi-finished products that have passed the test are sealed with metal shells, and lead tin wire Sn40 / Pb60, 0.5mm is used for sealing;

[0048] 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.

[0049] Furthermore, if Figure 6 As shown, the circuit of the 30MHz~2500MHz low insertion loss electrically tunable filter prepared above includes a first filter circuit, a second filter circuit, a third filter circuit, a RF switch U1 and a RF switch U2, and the two ends of the first filter circuit, the second filter circuit and the third filter circuit are respectively connected to the RF switch U1 and the RF switch U2, the first filter circuit is a circuit of 30~90MHz and 90~225MHz models, the second filter circuit is a circuit of 225-650MHz, 650~1200MHz, 1200~1650MHz and 1650~2100MHz models, and the third filter circuit is a circuit of 2100~2500MHz model.

[0050] Furthermore, if Figure 7As shown, the first filter circuit includes an inductor LIN, an inductor L19, an inductor L18, an inductor L17, an inductor L16, an inductor L15, an inductor L10, an inductor L11, an inductor LIN1, a capacitor C5 and a capacitor C3. The inductor LIN, the inductor L18, the inductor L17, the inductor L15, the inductor L16, the inductor L10 and the inductor LIN1 are connected in series in sequence, and one end of the inductor LIN and the inductor L18 is connected to the inductor L19. One end of the inductor L17 and the inductor L15 connected in series is connected to one end of the inductor L11, one end of the inductor L18 and the inductor L17 connected in series is connected to one end of the capacitor C5, one end of the inductor L16 and the inductor L10 connected in series is connected to one end of the capacitor C3, the other ends of the inductor L19, the inductor L11, the capacitor C5 and the capacitor C3 are grounded, and the other ends of the inductor LIN and the inductor LIN1 are respectively connected to the RF switch U1 and the RF switch U2.

[0051] Furthermore, if Figure 8 As shown, the second filter circuit includes 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. 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 connected to the RF switch U1 and the RF switch U2 respectively. One end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, and 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, and the other end of the inductor L4 is connected to one end of the capacitor C2. The other ends of the capacitors C1 and C2 are grounded.

[0052] Furthermore, if Fig. 9 As shown, the third filter circuit includes an inductor L5', an inductor L3', an inductor L1', an inductor L2', an inductor L4', an inductor L6', an inductor L7, an inductor L8, a capacitor C1' and a capacitor C2'. 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 connected to the RF switch U1 and the RF switch U2 respectively. One end of the inductor L5' and the inductor L1' are connected in series to one end of the inductor L3'. The other end of inductor L3' is connected to one end of capacitor C1', one end of inductor L2' and inductor L6' in series is connected to one end of inductor L4', the other end of inductor L4' is connected to one end of capacitor C2', the other ends of capacitor C1' and capacitor C2' are grounded, one end of inductor L7 is connected to one end connected between inductor L3' and capacitor C1', the other end of inductor L7 is connected to one end of inductor L8 and ground, and the other end of inductor L8 is connected to one end connected between inductor L4' and capacitor C2'.

[0053] The circuit performance parameters are shown in Table 2:

[0054] Table 2 Circuit performance parameters

[0055]

[0056] The existing circuit of 30MHz~2500MHz low insertion loss electronically tunable filter is as follows Figure 7 As shown, the insertion loss of the conventional 30MHz~2500MHz electronically tunable filter cannot be less than or equal to 5dB at 1GHz~2.5GHz, which greatly reduces the sensitivity of the filter.

[0057] The circuit in the utility model connects two inductors in parallel (such as Fig. 9 ), while ensuring the filter performance, the filter conversion frequency is extended to 2.5GHz, and the entire section of 30MH~2500MHz maintains low insertion loss.

[0058] The prepared electrically tunable filter has the following effects:

[0059] The PCB circuit board uses a large number of grounding through holes to increase the grounding effect, and the filter arranged on the PCB circuit board adopts a left-right symmetrical layout, 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 other specific effects are as follows:

[0060] 1. Divide the 30-2500MHz frequency band into 7 filters (30-90MHz, 90-225MHz, 225-650MHz, 650-1200MHz, 1200-1650MHz, 1650-2100MHz, 2100-2500MHz);

[0061] 2. Use hollow coils to make inductors in the high frequency bands of 225-650MHz, 650-1200MHz, 1200-1650MHz, 1650-2100MHz, and 2100-2500MHz to improve the Q value of the product. The larger the Q value, the better the product indicators; at the same time, it saves size and cost;

[0062] 3. 30~90MHz, 90~225MHz need to remove a large amount of inductance, which requires the use of a magnetic core;

[0063] 4. The product is small in size, with 6 layers. The first layer uses 50 ohm microstrip line and the third layer uses 50 ohm strip line to reduce the connection loss between the RF port of the RF switch and the filter input / output. Especially for the high frequency part (1000-2500MHz), 50 ohm RF line must be used for connection, otherwise it will have a great impact on various product indicators and will not be able to achieve the indicators.

[0064] 5. For filters in the frequency bands of 1650-2100MHz and 2100-2500MHz, hollow coil inductors are connected in parallel to reduce the inductance, so that the filter frequency reaches 2100MHz and 2500MHz;

[0065] 6. High Q varactor diode (Q value 4500) is used for 1650~2100MHz and 2100~2500MHz;

[0066] 7. Use low-loss RF switches, with an average loss of 0.4dB, an average isolation of 31dB, and an average standing wave ratio of 1.1. This indicator has little effect on the filter and can improve the overall performance;

[0067] 8. The PCB base is connected to the metal shell to shield external interference and reduce the size of the product.

[0068] like Fig.10 As shown, the test fixture welds the ETC filter on the pad, which 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, the welding points are loosened by a welding gun or other methods without damaging the pins. The test fixture is used to directly weld the ground pins 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 in the prior art of using a connecting cable to connect the power supply end and the RF end for testing are effectively solved:

[0069] 1) Too many wires are connected, which can easily lead to errors and poor test accuracy;

[0070] 2) There is a risk of tearing off the product pins;

[0071] 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.

[0072] In order to quickly position the electronically tunable filter, a limit indication frame is drawn in the middle of the PCB board. The limit indication frame is larger than the electronically tunable filter. Multiple welding pads corresponding to the pins of the electronically tunable filter are arranged on the left and right sides of the limit indication frame (11 on each side, 22 in total). 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.

[0073] In order to avoid shaking during the welding process of the electronically tunable filter, two rows of limit rolling pins are symmetrically arranged on the front and back sides of the upper surface of the above-mentioned PCB board (the limit indication frame and the limit rolling pins are tangent to the outside). There are four limit rolling pins in the two rows, which are symmetrical front and back and 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.

[0074] Principle of use of test tooling:

[0075] 1. Solder and fix the two RF wires separately. Fig. 9 At the "RFin" and "RFout" pins in the PCB;

[0076] 2. Align the pins 1 to 22 of the tested ESC filter with the soldering pads on the test fixture, and then fix the pins 1 to 22 with lead tin wire Sn40 / Pb60, 0.5mm;

[0077] 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;

[0078] 4. Fig.13 The 3.3V power terminal plug row connected to the "+3.3V" pin normally supplies +3.3V.

[0079] (1) When the "A0" pin is connected to a high level (1.3-2.7V), the "A1" pin is connected to a low level (0-0.45V), and the "A2" pin is connected to a low level (0-0.45V), the ETC filter under test is switched to the 30-90MHz frequency band, and then Fig. 9 The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0080] (2) When the "A0" pin is connected to a low level (0-0.45V), the "A1" pin is connected to a high level (1.3-2.7V), and the "A2" pin is connected to a low level (0-0.45V), the ETC filter under test is switched to the 90-225MHz frequency band, and then Fig. 9 The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0081] (3) When the "A0" pin is connected to a high level (1.3-2.7V), the "A1" pin is connected to a high level (1.3-2.7V), and the "A2" pin is connected to a low level (0-0.45V), the ETC filter under test is switched to the 225-650MHz frequency band, and then Fig. 9The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0082] (4) When the "A0" pin is connected to a low level (0-0.45V), the "A1" pin is connected to a low level (0-0.45V), and the "A2" pin is connected to a high level (1.3-2.7V), the ETC filter under test is switched to the 2100-2500MHz frequency band, and then Fig. 9 The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0083] (5) When the "A0" pin is connected to a high level (1.3-2.7V), the "A1" pin is connected to a low level (0-0.45V), and the "A2" pin is connected to a high level (1.3-2.7V), the ETC filter under test is switched to the 1650-2100MHz frequency band, and then Fig. 9 The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0084] (6) When the "A0" pin is connected to a low level (0-0.45V), the "A1" pin is connected to a high level (1.3-2.7V), and the "A2" pin is connected to a high level (1.3-2.7V), the ETC filter under test is switched to the 650-1200MHz frequency band, and then Fig. 9 The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0085] (7) When the "A0" pin is connected to a high level (1.3-2.7V), the "A1" pin is connected to a high level (1.3-2.7V), and the "A2" pin is connected to a high level (1.3-2.7V), the ETC filter under test is switched to the 1200-1650MHz frequency band, and then Fig. 9 The 23V power supply terminal plug row 3 connected to the "+23V" pin in the middle is used to tune the voltage from 1 to 23V to reach the frequency to be measured;

[0086] (8) When the "A0" pin is connected to a low level (0-0.45V), the "A1" pin is connected to a low level (0-0.45V), and the "A2" pin is connected to a low level (0-0.45V), the ETC filter under test is switched to the through state.

[0087] 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 low insertion loss electrically tunable filter, characterized in that: It includes a PCB circuit board and a metal shell. The PCB circuit board is arranged with electrical components of the electrically tunable filter. The PCB circuit board is provided with six layers. Each layer of the PCB circuit board is grounded through a large area. The space outside the component pads and wiring of the PCB circuit board is paved with the ground. The first, third and fifth layers of the PCB circuit board are used for wiring, and the second, fourth and bottom layers are all complete grounds. The RF pin lead-out lines of the RF switch U1 and the RF switch U2 arranged on the PCB circuit board are wired with 50 ohm impedance on the first and third layers; the filter arranged on the PCB circuit board adopts a left-right symmetrical layout.

2. A low insertion loss electrically tunable filter according to claim 1, characterized in that: The circuit of the electronically tunable filter includes a first filter circuit, a second filter circuit, a third filter circuit, a radio frequency switch U1 and a radio frequency switch U2. The two ends of the first filter circuit, the second filter circuit and the third filter circuit are respectively connected to the radio frequency switch U1 and the radio frequency switch U2. The first filter circuit is a circuit of 30-90MHz and 90-225MHz models, the second filter circuit is a circuit of 225-650MHz, 650-1200MHz, 1200-1650MHz and 1650-2100MHz models, and the third filter circuit is a circuit of 2100-2500MHz model. Hollow coils are used to make inductors in the high frequency bands of 225-650MHz, 650-1200MHz, 1200-1650MHz, 1650-2100MHz and 2100-2500MHz.

3. A low insertion loss electrically tunable filter according to claim 2, characterized in that: The first filter circuit includes an inductor LIN, an inductor L19, an inductor L18, an inductor L17, an inductor L16, an inductor L15, an inductor L10, an inductor L11, an inductor LIN1, a capacitor C5 and a capacitor C3. The inductor LIN, the inductor L18, the inductor L17, the inductor L15, the inductor L16, the inductor L10 and the inductor LIN1 are connected in series in sequence, one end of the series connection between the inductor LIN and the inductor L18 is connected to one end of the inductor L19, one end of the series connection between the inductor L17 and the inductor L15 is connected to one end of the inductor L11, one end of the series connection between the inductor L18 and the inductor L17 is connected to one end of the capacitor C5, one end of the series connection between the inductor L16 and the inductor L10 is connected to one end of the capacitor C3, the other ends of the inductor L19, the inductor L11, the capacitor C5 and the capacitor C3 are grounded, and the other ends of the inductor LIN and the inductor LIN1 are connected to the RF switch U1 and the RF switch U2 respectively.

4. The low insertion loss electrically tunable filter according to claim 2, characterized in that: The second filter circuit includes 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. 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 connected to the RF switch U1 and the RF switch U2 respectively. One end of the inductor L5 connected in series with the inductor L1 is connected to one end of the inductor L3, and 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, and the other end of the inductor L4 is connected to one end of the capacitor C2. The other ends of the capacitors C1 and C2 are grounded.

5. The low insertion loss electrically tunable filter according to claim 2, characterized in that: The third filter circuit includes an inductor L5', an inductor L3', an inductor L1', an inductor L2', an inductor L4', an inductor L6', an inductor L7, Inductor L8, capacitor C1' and capacitor C2', inductor L5', inductor L1', inductor L2' and inductor L6' are connected in series in sequence, the other ends of inductor L5' and inductor L6' are connected to RF switch U1 and RF switch U2 respectively, one end of inductor L5' and inductor L1' connected in series is connected to one end of inductor L3', the other end of inductor L3' is connected to one end of capacitor C1', one end of inductor L2' and inductor L6' connected in series is connected to one end of inductor L4', the other end of inductor L4' is connected to one end of capacitor C2', the other ends of capacitor C1' and capacitor C2' are grounded, one end of inductor L7 is connected to one end connected between inductor L3' and capacitor C1', the other end of inductor L7 is connected to one end of inductor L8 and ground, and the other end of inductor L8 is connected to one end connected between inductor L4' and capacitor C2'.

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