An LC bandpass filter

Abstract

The application discloses a kind of LC band-pass filter in the field of signal filtering processing, including band-pass filter network, input end and / or output end of band-pass filter network is connected with attenuation network;The band-pass filter network includes inductance L1, capacitor C4, capacitor C7, inductance L3, capacitor C11, inductance L4, capacitor C14, inductance L5 connected in series in turn;The first end of the inductance L1 and the second end of the inductance L5 are respectively as the input end and the output end of the band-pass filter network;The second end of the inductance L1, L3, L4, L5 and the second end of capacitor C7, C11, C14 are all connected with capacitor to ground;The second end of capacitor C4 is also connected with inductance L2 and capacitor C6 in series to ground;Between the second end of inductance L3 and the first end of inductance L5, there is capacitor C10.The application can effectively improve the input end / output end return loss through attenuation network, reduce the dependence on component accuracy, circuit debugging is simple, low in cost, with good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of signal filtering processing, and particularly relates to an LC band-pass filter. BACKGROUND

[0002] With the deepening of the scientific and technological revolution, wireless communication technology has developed rapidly, and the signal transmission distance is required to be higher and higher, and the signal interference is enhanced, and the requirements for the rectangle ratio and transmission rate of the filter are higher and higher. The high-frequency ultra-wideband filter has great market value and development prospect in the military fields such as positioning, detection and weapon guidance and the civil fields such as high-speed wireless local area network due to its high speed, low power consumption and anti-interference characteristics. The LC filter has a wide application in the fields of wireless communication and electronic countermeasure due to its simple structure, high equipment investment, high reliability and low operation cost. Since the capacitance and inductance elements used in the LC filter at high frequency have small values and higher precision requirements, the process manufacturing difficulty and cost are increased, and the high rectangle ratio requirement needs to increase the circuit order, which will increase the size of the filter and further increase the process manufacturing difficulty and cost. How to realize the high-frequency ultra-wideband high-rectangle-ratio LC band-pass filter while simplifying the circuit model, reducing the dependence on element precision and reducing the process manufacturing difficulty and cost is a problem to be solved at present. SUMMARY

[0003] The present application relates to the field of signal filtering processing, and particularly relates to an LC band-pass filter.

[0004] To achieve the above object, the present application provides the following technical scheme.

[0005] An LC band-pass filter comprises a band-pass filter network, and an attenuation network connected to the input end and / or the output end of the band-pass filter network.

[0006] As an improved scheme of the present application, the band-pass filter network comprises inductance L1, capacitance C4, capacitance C7, inductance L3, capacitance C11, inductance L4, capacitance C14 and inductance L5 connected in series; the first end of the inductance L1 and the second end of the inductance L5 are respectively used as the input end and the output end of the band-pass filter network; the second end of the inductance L1, L3, L4 and L5 and the second end of the capacitance C7, C11 and C14 are connected to the ground through a capacitance; the second end of the capacitance C4 is connected to the ground through the inductance L2 and the capacitance C6 in series; and the capacitance C10 is connected between the second end of the inductance L3 and the first end of the inductance L5.

[0007] As an improved scheme of the present application, the first end of the inductance L1 is connected to the ground through the capacitance C2.

[0008] As an improved scheme of the present application, the second end of the capacitance C4 is connected to the ground through the capacitance C5.

[0009] As an improved scheme of the present application, the input end and the output end of the band-pass filter network are connected with the first attenuation network and the second attenuation network respectively, and the first attenuation network and the second attenuation network are symmetrical in structure.

[0010] As an improved scheme of the present application, the input end of the band-pass filter network is connected with the first attenuation network, and the first attenuation network comprises a capacitor C1 and resistors R1, R2 and R3; the first end of the capacitor C1 is the input end of the first attenuation network, and the second end is connected with the first end of the resistor R1 and the resistor R2; the second end of the resistor R2 is the output end of the first attenuation network, and is connected with the first end of the resistor R3 and the input end of the band-pass filter network; the second ends of the resistors R1 and R3 are grounded.

[0011] As an improved scheme of the present application, the output end of the band-pass filter network is connected with the second attenuation network, and the second attenuation network comprises a capacitor C17 and resistors R4, R5 and R6; the second end of the capacitor C17 is the output end of the second attenuation network, and the first end is connected with the second end of the resistor R5 and the first end of the resistor R6; the first end of the resistor R5 is the input end of the second attenuation network, and is connected with the first end of the resistor R4 and the output end of the band-pass filter network; the second ends of the resistors R4 and R6 are grounded.

[0012] Beneficial effects: the input end and / or the output end of the LC band-pass filter are connected with the attenuation network, which can effectively improve the return loss of the input end / output end, reduce the dependence on the accuracy of components, is simple in circuit debugging, low in cost, and has a good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The circuit schematic diagram of the present application. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0015] An LC band-pass filter comprises a band-pass filter network and an attenuation network, wherein the band-pass filter network is 5-order, and the attenuation network comprises a first attenuation network and a second attenuation network.

[0016] In some embodiments, to improve the reliability of the process, the first end of the inductor L1 is further connected to ground through a capacitor C2, and the second end of the capacitor C4 is connected to ground through a capacitor C5.

[0017] The 5th order band-pass filter network is based on the Chebyshev prototype. First, the suspended nodes are eliminated by the Norden transformation. Grounded capacitors C3, C8, C12 and C15 are added to the suspended nodes to absorb stray capacitance. Then, the element parameters are optimized by the inversion transformation, and the DC-900MHz and 7600MHz-13000MHz stop-band suppressions are balanced. Finally, capacitors C6 and C10 are added by network transformation. The capacitor C6 and the inductor L2 form a series resonance loop, which can form a transmission zero point at the low frequency end of the passband. At the resonance frequency point, the impedance is infinitesimal, forming an attenuation pole, which greatly improves the stop-band suppression at DC-900MHz. The capacitor C10 and the loop in parallel with it form cross-coupling, which forms a transmission zero point at the high frequency end of the passband, thereby generating another attenuation pole, which greatly improves the stop-band suppression at 7600MHz-13000MHz.

[0018] In the 5th order band-pass filter network, the capacitors are realized by LTCC thick film process, which can accurately adjust the capacitor parameters and achieve high precision and miniaturization. Since the inductors and capacitors are fixed, the filter indicators are poor due to the influence of distributed parameters and shrinkage rate, such as large passband standing wave and large passband fluctuation. Therefore, the first end of the inductor L1 is connected to the input end of the 5th order band-pass filter network as a first attenuation network. The first attenuation network introduces attenuation in the specified frequency range, which plays the role of input amplitude modulation, and can effectively improve the input return loss and passband fluctuation.

[0019] As an embodiment, the first attenuation network comprises a capacitor C1 and resistors R1, R2, R3; a first end of the capacitor C1 is the input end of the first attenuation network, and a second end thereof is connected with a first end of the resistor R1 and a first end of the resistor R2; a second end of the resistor R2 is the output end of the first attenuation network, and is connected with a first end of the resistor R3 and an input end of the band-pass filter network; and second ends of the resistors R1 and R3 are grounded. Since the filter has a high frequency, the capacitor and the inductor used have small values, and a slight error can multiply the difficulty of debugging the filter. Improving the return loss can effectively reduce the dependence on the accuracy of the values of the components, reduce the difficulty of debugging, and improve the production efficiency. Therefore, the values of the components of the resistors R1, R2 and R3 can be adjusted by laser, so as to effectively absorb the echo, reduce the standing wave and the passband fluctuation, increase the effective bandwidth, realize impedance matching, and change the attenuation at the same time.

[0020] In the embodiment 2, the structure of the 5-order band-pass filter network is the same as that in the embodiment 1, and the difference from the embodiment 1 is that the embodiment 2 only comprises the second attenuation network, and a second end of the inductor L5 is the output end of the 5-order band-pass filter network and is connected with the second attenuation network.

[0021] As an embodiment, the second attenuation network comprises a capacitor C17 and resistors R4, R5, R6; a second end of the capacitor C17 is the output end of the second attenuation network, and a first end thereof is connected with a second end of the resistor R5 and a first end of the resistor R6; a first end of the resistor R5 is the input end of the second attenuation network, and is connected with a first end of the resistor R4 and an output end of the band-pass filter network; and second ends of the resistors R4 and R6 are grounded.

[0022] Corresponding to the principle of the first attenuation network for improving the return loss at the input end, the second attenuation network can improve the return loss at the output end, and the description is not repeated.

[0023] In the embodiment 3, the structure of the 5-order band-pass filter network is the same as that in the embodiment 1, and in actual use, the filter generally adopts a symmetrical design to reduce the difficulty of debugging the matching components. Therefore, in the embodiment 3, the first attenuation network and the second attenuation network also adopt a symmetrical structure design, and are connected at the input end and the output end of the 5-order band-pass filter network respectively. Therefore, the first attenuation network and the second attenuation network can improve the waveform consistency of the input return loss and the output return loss.

[0024] It should be noted that the first attenuation network and the second attenuation network in the above embodiments can be applied to band-pass filter networks of different mathematical models (Butterworth, Chebyshev, elliptical, etc.) and different orders, and are not limited to the 5-order band-pass filter network in the embodiments, and can also play a good role in improving the input return loss and / or the output return loss.

[0025] The LC band-pass filter provided by the application comprises a 5-order band-pass filter network, has high out-of-band suppression, and can effectively resist signal interference. The LC band-pass filter has a relatively wide relative bandwidth, so the time delay is small and flat, which is beneficial to receiving pulse signals. The input end and / or the output end of the LC band-pass filter is connected with an attenuation network, so that the input end / output end return loss can be effectively improved, the dependence on the accuracy of components is reduced, the circuit debugging is simple, the cost is low, and the LC band-pass filter has a good application prospect.

[0026] Although the specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

[0027] Therefore, the above description is only a preferred embodiment of the application, and is not intended to limit the scope of the application; that is, various equivalent transformations made within the scope of the claims of the application are within the protection scope of the claims of the application.

Claims

1. An LC bandpass filter, characterized in that, The system includes a bandpass filter network, with an attenuation network connected to its input and / or output terminals. The bandpass filter network comprises an inductor L1, a capacitor C4, a capacitor C7, an inductor L3, a capacitor C11, an inductor L4, a capacitor C14, and an inductor L5 connected in series. The first terminal of inductor L1 and the second terminal of inductor L5 serve as the input and output terminals of the bandpass filter network, respectively. The second terminals of inductors L1, L3, L4, and L5, as well as the second terminals of capacitors C7, C11, and C14, are all connected to ground. The second terminal of inductor L1 is connected to the first terminal of capacitor C4, and capacitor C3 is connected to ground at the connection point; capacitor C8 is connected to ground at the connection point of capacitor C7 and inductor L3; capacitor C9 is connected to ground at the connection point of inductor L3 and capacitor C11; capacitor C12 is connected to ground at the connection point of capacitor C11 and inductor L4; capacitor C13 is connected to ground at the connection point of inductor L4 and capacitor C14; the second terminal of capacitor C14 is connected to the first terminal of inductor L5, and capacitor C15 is connected to ground at this connection point; capacitor C16 is connected to ground at the second terminal of inductor L5; inductor L2 and capacitor C6 are connected in series with the second terminal of capacitor C4 to ground; capacitor C10 is connected between the second terminal of inductor L3 and the first terminal of inductor L5. The input of the bandpass filter network is connected to the first attenuation network, which includes a capacitor C1 and resistors R1, R2, and R3 whose resistance can be adjusted by laser. The first terminal of capacitor C1 serves as the input of the first attenuation network, and the second terminal is connected to the first terminals of resistors R1 and R2. The second terminal of resistor R2 serves as the output of the first attenuation network and is connected to the first terminal of resistor R3 and the input of the bandpass filter network. The second terminals of resistors R1 and R3 are both grounded. The output of the bandpass filter network is connected to the second attenuation network, which includes capacitor C17 and resistors R4, R5, and R6 whose resistance can be adjusted by laser. The second terminal of capacitor C17 serves as the output of the second attenuation network, and its first terminal is connected to the second terminal of resistor R5 and the first terminal of resistor R6. The first terminal of resistor R5 serves as the input of the second attenuation network and is connected to the first terminal of resistor R4 and the output of the bandpass filter network. The second terminals of resistors R4 and R6 are both grounded. The capacitors C3, C8, C12, and C15 are used to absorb stray capacitance at the floating node; the capacitor C6 and the inductor L2 form a series resonant circuit, which is used to form a transmission zero at the low-frequency end outside the passband, and the impedance is infinitely small at the resonant frequency point, forming an attenuation pole; the capacitor C10, capacitor C11, inductor L4, and capacitor C14 form a cross-coupled circuit, forming a transmission zero at the high-frequency end outside the passband, generating another attenuation pole.

2. An LC bandpass filter according to claim 1, characterized in that, The first terminal of the inductor L1 is connected to ground by a capacitor C2.

3. An LC bandpass filter according to claim 1, characterized in that, The second terminal of capacitor C4 is connected to ground by capacitor C5.

4. An LC bandpass filter according to claim 1, characterized in that, When the input and output of the bandpass filter network are connected to the first attenuation network and the second attenuation network respectively, the first attenuation network and the second attenuation network have symmetrical structures.

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