CN102394325B - L frequency band LTCC band pass filter - Google Patents

Abstract

An L-band LTCC bandpass filter consists of five layers of dielectric substrates and six layers of metal layers, the bottom layer of which is the ground metal layer, the top layer is the input and output layer, and the second and third layers of high-impedance strip lines form inductors L2 and L3 are connected to the input and output layers of the first layer through the metal vias of the third layer; the metal discs of the fourth layer and the metal discs of the fifth layer form capacitors C2 and C3, which are connected through the metal vias of the second layer The hole is connected to the inductance of the second and third layers to form a series relationship; the metal disc on the fifth layer and the ground metal layer form a capacitor C1, and at the same time, the two high-impedance lines on the fourth and fifth layers are connected through metal vias to form a capacitor C1. The inductor L1 is connected to the ground through a metal via to form a grounding inductance. The invention reduces the parameter sensitivity of the filter, lowers the requirement on the processing technology, and effectively improves the yield of the product.

Description

A kind of L-band LTCC bandpass filter

technical field

The invention relates to a band-pass filter, in particular to an L-band LTCC (low temperature co-fired ceramic) band-pass filter.

Background technique

Microwave bandpass filter is a key component of microwave radio system. With the development of microwave circuit design simulation technology and process in recent years, the demand for miniaturization of radio frequency system is getting higher and higher, and the miniaturization of filter is even more important. Bearing the brunt, how to reduce the size of the filter as much as possible while ensuring a certain performance index has become an important problem to be solved in the miniaturized radio frequency system. LTCC technology is a multi-layer ceramic technology developed in recent years. Using this technology, three-dimensional structures that cannot be realized by traditional ceramic substrate technology can be realized. Designing microwave passive devices using LTCC technology has great flexibility. How to make full use of the advantages of the LTCC process and determine the structure of the filter through a reasonable layout. And making the design have a certain stability, and ensuring the success rate of the product within the necessary processing error range is a key issue in the design of the LTCC filter.

At present, there is no public literature reporting this technology at home and abroad.

Contents of the invention

Technical solution problem of the present invention: overcome the deficiencies in the prior art, provide a kind of L-band LTCC (low temperature co-fired ceramics) band-pass filter, this L-band LTCC band-pass filter, structure is very compact, reduces the parameter of filter Sensitivity, thereby reducing the requirements for processing technology and effectively improving the yield of products.

Technical solution of the present invention: an L-band LTCC bandpass filter, characterized in that: the bandpass filter is an LTCC multilayer structure consisting of five layers of dielectric substrates (1-5) and six layers of metal layers (11 -16) composition, wherein the bottom layer is a ground metal layer (16), the first layer of dielectric substrate (1) is the top layer, printed with a 50 ohm impedance microstrip line metal layer as the input and output layer; the second layer of dielectric substrate (2) ) and the high-impedance stripline (28) printed on the third-layer dielectric substrate (3) pass through the metal vias (2) on the second-layer dielectric substrate (2) respectively 21) and the metal vias (23) on the third-layer dielectric substrate (3) constitute inductors L2 and L3, while L2 is connected to the first through the side metal vias (22) on the second-layer dielectric substrate (2). The input 50 ohm impedance microstrip line (32) of the layer dielectric substrate (1), L3 passes through the other side metal via (34) symmetrical to the side metal via (22) on the second layer of dielectric substrate (2). ) is connected to the output 50 ohm impedance microstrip line (33) of the first layer of dielectric substrate (1); the metal disc (29) printed on the fourth layer of dielectric substrate (4) and the fifth layer of dielectric substrate (5) The metal discs (31) printed on the top form capacitors C2 and C3 respectively, and the capacitors C2 and C3 are connected to the inductors L2 and L3 through the metal vias (21) on the second layer dielectric substrate (2), forming a series relationship; The metal disc (31) and the ground metal layer (16) on the five-layer dielectric substrate (5) form a capacitor C1; meanwhile, the high-impedance strip line (30) printed on the fourth layer dielectric substrate (4) and the fifth layer The high-impedance striplines (25) printed on the dielectric substrate (5) are respectively connected through metal vias (24, 26) to form an inductance L1, and L1 passes through the metal vias (26) on the fifth-layer dielectric substrate (5) Connect to the ground metal layer (16), forming a ground inductance.

The advantage of the present invention compared with prior art is:

(1) The present invention makes the structure of the filter very compact through the ingenious layout mode of the structure, reduces the parameter sensitivity of the filter at the same time, thereby reduces the requirement to the processing technology, effectively improves the yield of the product, the present invention It can be widely applied to radio frequency wireless communication systems.

(2) In the present invention, C1 and C2 share a capacitor plate, so that the three parallel plates form a grounded parallel capacitor and a series capacitor, making the structure more compact.

(3) The capacitors C2 and C3 in the present invention have no grounding path, which solves the problem of stray capacitance to the ground of the series capacitors.

(4) The two transmission zero points of the present invention can be independently controlled, and applying this property in the design process can greatly improve efficiency. The design idea of this product can be easily extended to LTCC filters in other frequency bands, and provides a new design template for the design of LTCC filters.

Description of drawings

Fig. 1 is a schematic circuit diagram of the present invention;

Fig. 2 is the simulation curve of principle circuit of the present invention;

Fig. 3 is the principle circuit equivalent circuit 1 of the present invention;

Fig. 4 is the principle circuit equivalent circuit 2 of the present invention;

Fig. 5 is a comparison curve of the principle circuit of the present invention, field simulation results, and actual measurement results.

Detailed ways

As shown in Figure 1, the present invention is a third-order bandpass filter with a pair of transmission zeros, including two LC parallel resonators connected in parallel to the ground, and two series-connected LC parallel resonators separately control a transmission zero, in the design Using this feature in the process can improve work efficiency.

The input terminals of the filter are connected to the input terminals of the capacitors C1 and C2 and the inductors L1 and L2, the output terminals of C1 and L1 are grounded, the output terminals of C2 and L2 are connected to the input terminals of C3 and L3, and the output terminals of C3 and L3 are connected to the other The input terminals of a pair of C1 and L1 are connected with the output terminals of the filter. Due to the parallel loop on the series branch, the transmission admittance of the whole circuit is 0 at parallel resonance, so the two loops form two independently controllable transmission zeros.

Figure 2 shows the simulation curve of the principle circuit, in which S11 is the return loss curve, and S21 is the transmission coefficient curve. It can be seen from the figure that under the premise of satisfying the same passband, the existence of out-of-band transmission zeros can effectively improve the steepness of out-of-band attenuation within a given frequency range.

As shown in Fig. 3, 4, the structure that the present invention realizes Fig. 1 circuit principle is that LTCC multilayer structure is made of five-layer dielectric substrate 1-5 and grounding metal layer 11-16, a kind of L frequency band LTCC bandpass filter, its It is characterized in that: the bandpass filter is an LTCC multilayer structure consisting of five layers of dielectric substrates 1, 2, 3, 4, 5 and six layers of metal layers 11, 12, 13, 14, 15, 16, wherein the bottom layer It is the ground metal layer 16 . The first layer of dielectric substrate 1 is the top layer. As the input and output layer, the metal layer of the input and output 50-ohm impedance microstrip line is printed, which includes the input 50-ohm impedance microstrip line 32 and the output 50-ohm impedance microstrip line 33 . The high-impedance stripline metal layer 27 printed on the second dielectric substrate 2 and the high-impedance stripline 28 printed on the third dielectric substrate 3 respectively pass through the metal via hole 21 on the second dielectric substrate 2 and the third via. The metal vias 23 on the dielectric substrate 3 form inductors L2 and L3, and L2 passes through the side metal vias 22 on the second layer of dielectric substrate 2 (the metal vias in the figure penetrate to the bottom, but in fact they may not penetrate Bottom) connected to the input 50 ohm impedance microstrip line 32 of the first layer of dielectric substrate 1, L3 is connected to the first layer through a metal via 34 symmetrical to the metal via 22 on the other side of the second layer of dielectric substrate 2 The output 50 ohm impedance microstrip line 33 of the dielectric substrate 1; the metal disk 29 printed on the fourth layer of dielectric substrate 4 and the metal disk 31 printed on the fifth layer of dielectric substrate 5 form capacitors C2 and C3 respectively, and the capacitors C2 and C3 are connected to the inductors L2 and L3 through the metal vias 21 on the second dielectric substrate 2 to form a series relationship; the metal disc 31 on the fifth dielectric substrate 5 and the ground metal layer 16 form a capacitor C1; The high-impedance stripline 30 printed on the four-layer dielectric substrate 4 and the high-impedance stripline 25 printed on the fifth-layer dielectric substrate 5 are respectively connected through metal vias 24 and 26 to form an inductor L1, which passes through the fifth-layer dielectric The metal vias 26 on the substrate 5 are connected to the ground metal layer 16 to form a ground inductance.

C1 and C2 of the present invention share a metal disc, so that the three metal discs form a grounded parallel capacitor and a series capacitor, so that the structure is more compact. Capacitors C2 and C3 have no ground path, which solves the problem of stray capacitance to ground of series capacitors. Such a layout can reduce the stray capacitance of the two series capacitors to ground and the parasitic capacitance between different capacitor plates. The arrangement of the inductors is misplaced with each other, and there is no overlapping area, which reduces the mutual inductance effect between the inductors.

The material of each dielectric substrate layer in the present invention uses Ferro A6 type LTCC ceramic substrate material, the relative dielectric constant is 6.1, and the conduction band thickness after sintering is 0.096mm. The material used for all metal layers is silver with a thickness of 8 microns. High impedance striplines have an impedance of 100 ohms. The size of the whole filter is 6mm*9mm*1mm.

The center frequency of the filter is 1.3GHz, the bandwidth is 240MHz, and there are a pair of transmission zeros above and below the passband to improve the selectivity of the filter. In a given frequency range, the stopband attenuation is greater than 20dB. Through the test of 300 products obtained by using the design of the invention, the yield rate of the products is 100%.

Figure 5 shows the comparison curves of the principle circuit, field simulation results, and actual measurement results. Among them, the thin solid line is the simulation curve of the principle circuit, the dotted line is the simulation curve of the HFSS full-wave electromagnetic field, and the thick solid line is the measured curve. S11 is the return loss curve, and S21 is the transmission coefficient curve. It can be seen from the figure that the out-of-band attenuation of the filter is greater than 25dB within a given stopband, and the return loss of the filter is greater than 18dB within a given passband range, and the three simulation results are in good agreement, fully illustrating The effectiveness of the layout of the present invention has been confirmed.

In summary, the present invention has the advantages of small size, good performance, compact structure, high yield, and convenient mass production, and can be widely used in radio frequency wireless systems.

Claims (2)

1. a kind of L frequency band LTCC band-pass filter, it is characterized in that: described band-pass filter is LTCC multilayer structure, by the first layer dielectric substrate (1), the second layer dielectric substrate (2), the third layer Dielectric substrate (3), fourth dielectric substrate (4), fifth dielectric substrate (5), first metal layer (11), second metal layer (12), third metal layer (13) , the fourth metal layer (14), the fifth metal layer (15) and the ground metal layer (16), wherein the bottom layer is the ground metal layer (16), and the first layer of dielectric substrate (1) is the top layer, as The input and output layer is printed with a 50-ohm impedance microstrip line metal layer; the high-impedance strip line metal layer (27) printed on the second layer of dielectric substrate (2) and the first printed on the third layer of dielectric substrate (3) Two high-impedance striplines (28) respectively pass through the first metal via hole (21) on the second layer dielectric substrate (2) and the third metal via hole (23) on the third layer dielectric substrate (3) to form an inductor L2 and inductance L3, while inductance L2 is connected to the input 50 ohm impedance microstrip line (32) of the first layer of dielectric substrate (1) through the side second metal via hole (22) on the second layer of dielectric substrate (2), The inductance L3 is connected to the output of the first layer dielectric substrate (1) through the sixth metal via hole (34) on the other side which is symmetrical to the second metal via hole (22) on the second layer dielectric substrate (2). 50 ohm impedance microstrip line (33); the first metal disc (29) printed on the fourth layer dielectric substrate (4) and the second metal disc (31) printed on the fifth layer dielectric substrate (5) ) form capacitor C2 and capacitor C3 respectively, through the first metal via hole (21) on the second layer dielectric substrate (2), the capacitor C2 is connected in parallel with the inductor L2, the capacitor C3 is connected in parallel with the inductor L3, and passes through the first metal via hole (21). Metal vias (21) realize the series connection of the two parallel units; the second metal disc (31) on the fifth-layer dielectric substrate (5) and the ground metal layer (16) form a capacitor C1; at the same time, the fifth-layer dielectric One end of the first high-impedance stripline (25) printed on the substrate (5) passes through the fourth metal via hole (24) and the second high-impedance stripline (30) printed on the fourth-layer dielectric substrate (4) The inductance L1 is formed by being connected with each other, and the other end is connected to the ground metal layer (16) through the fifth metal via hole (26), so that the inductance L1 forms a ground inductance. 2. The L-band LTCC bandpass filter according to claim 1, characterized in that: the impedance of all high-impedance striplines is 100 ohms.