A duplexer based on LTCC technology with low-frequency transmission zeros

Abstract

The present invention relates to a duplexer with low-frequency transmission zeros based on LTCC technology, belonging to the technical field of duplexers. The present invention includes an LTCC substrate layer, and a duplexer circuit structure is formed on the LTCC substrate layer. The duplexer circuit structure is composed of a low-pass filter circuit and a band-pass filter circuit. The low-pass filter circuit includes a first inductor and a first parallel resonator connected in series between a common input port and a low-frequency output port. A first capacitor grounded is connected between the first inductor and the first parallel resonator. The band-pass filter circuit includes a first series resonator and a second series resonator connected in series between the common input port and a high-frequency output port. A third series resonator is connected between the first series resonator and the second series resonator. The third series resonator is connected with a second parallel resonator grounded. By introducing a parallel resonator into the low-pass filter circuit, the present invention introduces an out-of-band zero in the out-of-band region, increasing the out-of-band suppression of the low-pass branch.

Description

Technical Field

[0001] The present invention relates to a duplexer with a low-frequency transmission zero based on LTCC technology, belonging to the technical field of duplexers. Background Art

[0002] A duplexer is a microwave device widely used in radio receivers, which can combine two signals with different frequencies or split a single broadband signal into two frequency-band signals. Its function is to isolate the transmitted and received signals to ensure that both transmission and reception can work properly simultaneously. Duplexers are widely used in fields such as mobile communication and electronic countermeasures. The main technical indicators of a duplexer include: operating frequency band, in-band insertion loss, in-band return loss, out-of-band rejection, output port isolation, etc. In addition, the temperature stability, volume, weight, etc. of the duplexer are also important indicators for measuring its performance.

[0003] With the rapid development of wireless communication technology, communication systems are developing towards high performance, high reliability, and miniaturization, requiring the duplexer to be small in size and light in weight, and requiring the filters in the duplexer to have a wide operating frequency band, good filter characteristics, and high common-mode suppression ratio. However, in the prior art, the volume of the duplexer can no longer meet the requirements of wireless communication for volume; according to different operating frequency bands, duplexers mainly include low-pass and high-pass duplexers, low-pass and band-pass duplexers, and band-pass and band-pass duplexers. In the design of traditional duplexers, there are parasitic passbands in the low-frequency part, and the out-of-band rejection ability in the high-frequency part is poor, so that the isolation degree and out-of-band rejection degree between the output ports cannot meet the requirements of microwave and millimeter-wave circuits when the size is small. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects existing in the existing duplexers, and provide a duplexer with a low-frequency transmission zero based on LTCC technology. By introducing a parallel resonator into the low-pass filter circuit, an out-of-band zero is introduced outside the band to increase the out-of-band rejection of the low-pass branch.

[0005] The present invention is implemented by adopting the following technical solutions:

[0006] A duplexer with a low-frequency transmission zero based on LTCC technology includes an LTCC substrate layer. The LTCC substrate layer forms a duplexer circuit structure. The duplexer circuit structure is composed of a low-pass filter circuit and a band-pass filter circuit. The low-pass filter circuit includes a first inductor and a first parallel resonator connected in series between a common input port and a low-frequency output port. A first capacitor grounded is connected between the first inductor and the first parallel resonator. The band-pass filter circuit includes a first series resonator and a second series resonator connected in series between the common input port and a high-frequency output port. A third series resonator is connected between the first series resonator and the second series resonator. The third series resonator is connected with a second parallel resonator grounded.

[0007] Furthermore, the inductors of the low-pass filter circuit and the band-pass filter circuit are stacked inductors, and the metal conductors on different circuit layers are connected through vias. The inductance value is adjusted by adjusting the line length and line width of each layer of the stacked inductor wire.

[0008] Furthermore, the capacitors of the low-pass filter circuit and the band-pass filter circuit utilize MIM capacitors formed between the upper and lower layers of the board.

[0009] Furthermore, there are eleven circuit layers in the LTCC substrate layer. The first, second, and third layers form the first inductor of the low-pass filter circuit and the inductor of the first parallel resonator. The fifth and sixth layers form the first capacitor. The fourth and fifth layers form the capacitor of the first parallel resonator. The seventh and eighth layers form the third series resonator and the first parallel resonator of the band-pass filter circuit. The ninth, tenth, and eleventh layers form the first series resonator and the second series resonator of the band-pass filter circuit.

[0010] Furthermore, the first inductor is connected to the common input port through the inductor wire on the third layer. The inductor of the first parallel resonator is connected to the low-frequency output port through the inductor wire on the third layer. The capacitor of the first parallel resonator is connected to the low-frequency output port on the fourth layer. The first capacitor is connected to the ground port. The first series resonator is connected to the common input port through the inductor wire on the ninth layer. The second series resonator is connected to the high-frequency output port through the inductor wire on the ninth layer. The first series resonator, the second series resonator, the third series resonator, and the first parallel resonator are connected through connection vias. The second parallel resonator is connected to the ground port through the connection wire on the sixth layer.

[0011] The beneficial effects of the present invention are as follows:

[0012] Through reasonable three-dimensional layout and utilization of the parasitic parameters of each component, the present invention realizes the suppression of the parasitic passband on the low-pass duplexer and the optimization of the out-of-band rejection of the high-pass duplexer, achieving a balance between the volume and performance of the duplexer. At the same time, by introducing the first parallel resonator into the low-pass filter circuit, a band-out zero point is introduced in the out-of-band region, increasing the out-of-band rejection of the low-pass branch. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The equivalent circuit diagram of the present invention;

[0014] Figure 2 The structural schematic diagram of the present invention;

[0015] Figure 3 The circuit separation schematic diagram of the present invention;

[0016] Figure 4 The S-parameter simulation results of the present invention;

[0017] Markings in the figure: 1. LTCC substrate layer; 2. Low-pass filter circuit; 3. Band-pass filter circuit. Specific embodiments

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] As Figure 1 shown, the equivalent circuit diagram of the present invention, the duplexer circuit structure is composed of a low-pass filter circuit and a band-pass filter circuit. The low-pass filter circuit includes a first inductor and a first parallel resonator connected in series between a common input port and a low-frequency output port. A first capacitor grounded is connected between the first inductor and the first parallel resonator. The band-pass filter circuit includes a first series resonator and a second series resonator connected in series between the common input port and the high-frequency output port. A third series resonator is connected between the first series resonator and the second series resonator. The third series resonator is connected with a second parallel resonator grounded. By introducing the first parallel resonator into the low-pass filter circuit, an out-of-band zero point is introduced outside the band, increasing the out-of-band suppression of the low-pass branch.

[0020] As Figure 2 shown, the present invention includes an LTCC substrate layer 1 sintered by a stacked low-temperature co-fired ceramic process, a first grounding end G1, a common input end P1, a second grounding end G2, a low-frequency signal output end P2, a third grounding end G3, and a high-frequency signal output end P3 on the outer wall of the LTCC substrate layer 1, a low-pass filter circuit 2 and a band-pass filter circuit 3 inside the ceramic substrate; the typical size of the present invention is 2.0×1.25×0.59 mm.

[0021] As Figure 3As shown, the LTCC substrate layer 1 contains eleven circuit layers, where: The first layer, inductors (1-L1) and (1-L2) are printed on the ceramic dielectric. Inductors (1-L1) and (1-L2) are connected by a connecting wire. A via hole (1-V3) is connected between inductors (1-L1) and (1-L2). The other end of inductor (1-L1) is connected to (1-V1), and the other end of inductor (1-L2) is connected to (1-V2); The second layer, inductors (2-L1) and (2-L2) are printed on the ceramic dielectric. One end of inductor (2-L1) is connected to via hole (1-V1), and the other end is connected to via hole (2-V1). One end of inductor (2-L2) is connected to via hole (1-V2), and the other end is connected to via hole (2-V2). Via hole (1-V3) is connected to via hole (2-V3); The third layer, inductors (3-L1) and (3-L2) are printed on the ceramic dielectric. One end of inductor (3-L1) is connected to via hole (2-V1), and the other end is connected to the common input terminal P1. One end of inductor (3-L2) is connected to via hole (2-V2), and the other end is connected to the low-frequency signal output terminal P2. Via hole (2-V3) is connected to via hole (3-V3); The fourth layer, capacitor (4-C2) is printed on the ceramic dielectric. One end of capacitor (4-C2) is connected to the low-frequency signal output port P2. Via hole (3-V3) is connected to via hole (4-V3); The fifth layer, capacitors (5-C1) and (5-C2) are printed on the ceramic dielectric. Capacitor (5-C1) is connected to via hole (4-V3), and capacitor (5-C1) is connected to capacitor (5-C2) by a connecting wire; The sixth layer, capacitor (6-C1) is printed on the ceramic dielectric, serving as the isolation ground plane for the low-pass filter circuit and the band-pass filter circuit. Capacitor (6-C1) is connected to ports G1, G2, and G3; The seventh layer, inductors 7-L5, 7-L6, capacitors 7-C5, 7-C6 are printed on the ceramic dielectric. One end of inductor 7-L5 is connected to capacitor 7-C5, and the other end is connected to via hole 7-V5. One end of inductor 7L6 is connected to capacitor 7-C6, and the other end is connected to via hole 7-V6. A connecting wire is used to connect inductor 7-L6 and capacitor 7-C6 to the ground port G3; The eighth layer, inductors 8-L5, 8-L6, capacitors 8-C5, 8-C6 are printed on the ceramic dielectric. Capacitor 8-C5 is connected to via hole 8-V4. One end of inductor 8-L5 is connected to via hole 7-V5, and the other end is connected to capacitor 8-C6. Capacitor 8-C6 is connected to inductor 8-L6, and the other end of inductor 8-L6 is connected to via hole 7-V6; The ninth layer, inductors 9-L3 and 9-L4 are printed on the ceramic dielectric. One end of inductor 9-L3 is connected to 9-V7, and the other end is connected to the high-frequency output port P3. One end of inductor 9-L4 is connected to 9-V8, and the other end is connected to the common input port P1. Via hole 9-V4 is connected to via hole 8-V4;The tenth layer prints inductors 10-L3, 10-L4, capacitors 10-C3, 10-C4 on the ceramic medium. One end of inductor 10-L3 is connected to via hole 9-V7, and the other end is connected to via hole 10-V7. One end of inductor 10-L3 is connected to via hole 9-V8, and the other end is connected to via hole 10-V8. One end of capacitor 10-C3 and capacitor 10-C4 are connected to each other, and via hole 9-V4 is connected between capacitor 10-C3 and capacitor 10-C4. The eleventh layer prints inductors 11-L3, 11-L4, capacitors 11-C3, 11-C4 on the ceramic medium. One end of inductor 11-L3 is connected to via hole 10-V7, and the other end is connected to capacitor 11-C3. One end of inductor 11-L4 is connected to via hole 10-V8, and the other end is connected to capacitor 11-C5.;

[0022] As Figure 4 shown, for the duplexer of the present invention, the low-frequency operating frequency is DC~3.0 GHz, and the high-frequency operating frequency is 5.2 GHz~6.0 GHz. The insertion loss of this duplexer is better than 0.8 dB at low frequencies, and the insertion loss is better than 1.2 dB in the two frequency bands of 5.2 GHz~6.0 GHz. The return loss in both bands is better than 15 dB, the isolation between the two output ports is better than 20 dB, the out-of-band rejection of the low-pass branch in the range of 4.6 GHz~15 GHz is better than 25 dB, the out-of-band rejection of the band-pass branch in the range of DC~3.5 GHz is better than 20 dB, and the out-of-band rejection in the range of 8.0 GHz~15 GHz is better than 20 dB.

[0023] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A duplexer with low-frequency transmission zeros based on LTCC technology, characterized in that, it includes an LTCC substrate layer, a duplexer circuit structure is formed on the LTCC substrate layer, the duplexer circuit structure is composed of a low-pass filter circuit and a band-pass filter circuit, the low-pass filter circuit includes a first inductor and a first parallel resonator connected in series between a common input port and a low-frequency output port, a first capacitor grounded is connected between the first inductor and the first parallel resonator, the band-pass filter circuit includes a first series resonator and a second series resonator connected in series between the common input port and a high-frequency output port, a third series resonator is connected between the first series resonator and the second series resonator, and the third series resonator is connected with a second parallel resonator grounded.

2. The duplexer with low-frequency transmission zeros based on LTCC technology according to claim 1, characterized in that: The inductors of the low-pass filter circuit and the band-pass filter circuit adopt stacked inductors, and the metal conductors on different circuit layers are connected through vias. The inductance value is adjusted by adjusting the line length and line width of each layer of the stacked inductor wire.

3. The duplexer with low-frequency transmission zeros based on LTCC technology according to claim 1, characterized in that: The capacitors of the low-pass filter circuit and the band-pass filter circuit adopt MIM capacitors formed between the upper and lower layer boards.

4. The duplexer with low-frequency transmission zeros based on LTCC technology according to claim 1, characterized in that: There are eleven circuit layers in the LTCC substrate layer. The first, second, and third layers form the first inductor of the low-pass filter circuit and the inductor of the first parallel resonator. The fifth and sixth layers form the first capacitor. The fourth and fifth layers form the capacitor of the first parallel resonator. The seventh and eighth layers form the third series resonator and the first parallel resonator of the band-pass filter circuit. The ninth, tenth, and eleventh layers form the first series resonator and the second series resonator of the band-pass filter circuit.

5. The duplexer with low-frequency transmission zeros based on LTCC technology according to claim 4, characterized in that: The first inductor is connected to the common input port through the inductor wire on the third layer. The inductor of the first parallel resonator is connected to the low-frequency output port through the inductor wire on the third layer. The capacitor of the first parallel resonator is connected to the low-frequency output port on the fourth layer. The first capacitor is connected to the ground port. The first series resonator is connected to the common input port through the inductor wire on the ninth layer. The second series resonator is connected to the high-frequency output port through the inductor wire on the ninth layer. The first series resonator, the second series resonator, the third series resonator, and the first parallel resonator are connected through connection vias. The second parallel resonator is connected to the ground port through the connecting wire on the sixth layer.

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