A BTM receiving plate third-order band-pass filter circuit

Abstract

The application is suitable for the field of communication, and provides a BTM receiving board third-order band-pass filter circuit, which comprises a first-order circuit, a second-order circuit and a third-order circuit, and the first-order circuit, the second-order circuit and the third-order circuit are connected in series; wherein the first-order circuit is used for filtering out interference signals outside the specified passband, the second-order circuit is used for increasing the stopband suppression degree and the passband flatness of the filter circuit, and the third-order circuit is consistent with the first-order circuit and can increase the stopband suppression degree of the filter circuit again. After the filter circuit, the frequency range of the output signal relative to the input signal is 3.9MHz as the center frequency and 0.34MHz as the bandwidth, and 4.5MHz as the center frequency and 0.35MHz as the bandwidth. Since the filter circuit is a double-passband relative to a single-passband, the bandwidth is narrower, and more interference signals are filtered out. The filter circuit can be used for a BTM host receiving board, filters out the interference components of the BTM device uplink signal, and makes the receiving board better demodulate the FSK signal.

Description

Technical Field

[0001] This invention belongs to the field of communication-related technology, and specifically relates to a third-order bandpass filter circuit for a BTM receiver board. Background Technology

[0002] With the rapid development of China's railways, transponders, as train transmission equipment, require increasingly higher levels of safety and reliability. The BTM (balise transmission module) consists of two parts: the BTM main unit and the antenna unit. The BTM main unit includes a power board, a transmitter board, a receiver board, a decoder board, a communication board, and a recording board. The transmitter board is connected to the antenna unit via a D-cable and to the receiver board via a pull-up cable. The receiver board receives the FSK modulated information transmitted from the transmitter board and amplifies and demodulates it. The center frequency of the BTM's uplink signal is 4.234MHz ± 175kHz, with a frequency deviation of ± 282kHz. When a "0" is received, a modulated signal with a carrier frequency of 3.948MHz is transmitted; when a "1" is received, a modulated signal with a carrier frequency of 4.512MHz is transmitted to modulate the FSK. Higher-performance filters are needed to ensure normal transponder communication.

[0003] Existing filter circuits have a wide passband bandwidth, low stopband rejection, and high insertion loss. They can introduce electromagnetic interference during use, which can adversely affect the demodulation of FSK signals on the receiving board. Summary of the Invention

[0004] To address the aforementioned problems, this invention discloses a third-order bandpass filter circuit for a BTM receiver board, the filter circuit comprising:

[0005] A first-order circuit, a second-order circuit, and a third-order circuit, wherein the first-order circuit, the second-order circuit, and the third-order circuit are connected in series.

[0006] The first-order circuit is used to filter out interference signals outside the specified passband, the second-order circuit is used to increase the stopband suppression and passband flatness of the filter circuit, and the third-order circuit has the same function as the first-order circuit, which can further increase the stopband suppression of the filter circuit in the circuit. One end of the first-order circuit and one end of the third-order circuit are respectively connected to the two ends of the second-order circuit, and the other ends of the first-order circuit and the third-order circuit are both grounded.

[0007] Furthermore, the first-order circuit includes a first-order first branch, a first-order second branch, a first-order third branch, and a first-order fourth branch, and the four branches of the first-order circuit are connected in parallel with each other in sequence.

[0008] The first branch of the first order includes capacitor C7; the second branch of the first order includes capacitor C1.

[0009] The first-order third branch comprises a plurality of inductors.

[0010] The first-order fourth branch comprises a first series inductor component and a first parallel capacitor component, and the first series inductor component and the first parallel capacitor component are connected in series with each other.

[0011] Further, the first-order third branch comprises inductors L1, L9 and L10 connected in series, and the inductor L9 is arranged between the inductor L1 and the inductor L10.

[0012] Further, the first series inductor component in the first-order fourth branch comprises inductors L8 and L9 connected in series with each other.

[0013] The first parallel capacitor component in the first-order fourth branch comprises capacitors C2 and C8 connected in parallel with each other.

[0014] The inductor L2 is arranged between the inductor L8 and the first parallel capacitor component.

[0015] Further, one end of the capacitor C7 in the first-order first branch, one end of the capacitor C1 in the first-order second branch, one end of the inductor L10 in the first-order third branch and one end of the inductor L8 in the first-order fourth branch are connected at a common point, and the common point is connected to one end of a second-order circuit.

[0016] The other end of the capacitor C7 in the first-order first branch, the other end of the capacitor C1 in the first-order second branch, one end of the inductor L1 in the first-order third branch and one end of the first parallel capacitor component in the first-order fourth branch are connected at a common point, and the common point is connected to ground.

[0017] Further, the second-order circuit comprises inductors L7, L3, a second parallel capacitor component and a second-order branch connected in series.

[0018] The second-order branch comprises a second-order first branch and a second-order second branch connected in parallel with each other, the second-order first branch comprises a plurality of inductors connected in series with each other, the second-order second branch comprises a plurality of capacitors connected in parallel with each other, and one end of the inductor L7 is connected to the first-order circuit.

[0019] Further, the second parallel capacitor component comprises capacitors C3 and C9 connected in parallel, one end of the second parallel capacitor component is connected to one end of the inductor L3, and the other end of the second parallel capacitor component is connected to one end of the second-order branch.

[0020] Further, the second-order first branch comprises inductors L4, L11 and L12 connected in series.

[0021] The second-order second branch comprises capacitors C4 and C10 connected in parallel.

[0022] One end of the inductor L4 is connected with one end of the second branch of the second order and the other end of the second parallel capacitor component, and one end of the inductor L12 is connected with the other end of the second branch of the second order and one end of the third circuit.

[0023] Further, the third circuit comprises a first branch of the third order, a second branch of the third order, a third branch of the third order and a fourth branch of the third order, and the four branches of the third circuit are connected with each other in parallel.

[0024] The first branch of the third order comprises a capacitor C11, and the second branch of the third order comprises a capacitor C5.

[0025] The third branch of the third order comprises a plurality of inductors.

[0026] The fourth branch of the third order comprises a second series inductor component and a third parallel capacitor component, and the second series inductor component and the third parallel capacitor component are connected with each other in series.

[0027] Further, the third branch of the third order comprises an inductor L15, an inductor L14 and an inductor L5 connected in series, and the inductor L14 is arranged between the inductor L15 and the inductor L5.

[0028] Further, the second series inductor component in the fourth branch of the third order comprises an inductor L13 and an inductor L6 connected in series.

[0029] The third parallel capacitor component in the fourth branch of the third order comprises a capacitor C6 and a capacitor C12 connected in parallel, and the inductor L6 is arranged between the inductor L13 and the third parallel capacitor component.

[0030] Further, one end of the capacitor C11 in the first branch of the third order, one end of the capacitor C5 in the second branch of the third order, one end of the inductor L15 in the third branch of the third order and one end of the inductor L13 in the fourth branch of the third order are connected at the same point, and the same point is connected with the other end of the second circuit.

[0031] The other end of the capacitor C11 in the first branch of the third order, the other end of the capacitor C5 in the second branch of the third order, one end of the inductor L5 in the third branch of the third order and one end of the third parallel capacitor component in the fourth branch of the third order are connected at the same point, and the same point is connected with the ground.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] The application provides a three-order band-pass filter circuit of a BTM receiving board, after the filter circuit, the frequency range of an output signal relative to an input signal is 3.9MHz as a center frequency and 0.34MHz as a bandwidth, and 4.5MHz as a center frequency and 0.35MHz as a bandwidth, and almost no interference signal is output in other frequency ranges, since the filter circuit is a double-passband relative to a single-passband, the bandwidth is narrower, and more interference signals are filtered out. The filter circuit can be used in a BTM host receiving board, interference components of a BTM device uplink signal are filtered out, and the receiving board can better demodulate a FSK signal.

[0034] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and attained by the structure particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0036] Figure 1 A three-order band-pass filter circuit principle diagram of the embodiment of the present application is shown;

[0037] Figure 2 A three-order band-pass filter circuit principle diagram of the embodiment of the present application is shown; DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0039] The present application does not solve the above background technical problems, and a three-order band-pass filter circuit is designed, in an embodiment of the present application, as shown in Figure 1 A three-order band-pass filter circuit principle diagram, combined with Figure 2The diagram illustrates the circuit division of a third-order bandpass filter circuit. The filter circuit includes a first-order circuit, a second-order circuit, and a third-order circuit, which are connected in series. The first-order circuit filters out interference signals outside the specified passband. The second-order circuit increases the stopband rejection and passband flatness of the filter circuit. The third-order circuit further increases the stopband rejection. One end of the first-order circuit and one end of the third-order circuit are connected to the two ends of the second-order circuit, respectively. The other ends of the first-order circuit and the third-order circuit are both grounded.

[0040] This bandpass filter circuit has two passbands: one with a center frequency of 3.9MHz and a bandwidth of 0.34MHz, and the other with a center frequency of 4.5MHz and a bandwidth of 0.35MHz. Compared to the original filter circuit on the receiver board, it has a narrower passband bandwidth, a stopband attenuation of less than -50dB, and better suppression performance. After receiving the signal, this filter circuit removes interference signals other than the two passbands. The narrower the passband bandwidth, the more interference signals are filtered out, facilitating better demodulation of the FSK signal by the receiver board.

[0041] In one embodiment of the present invention, such as Figure 1 and Figure 2 The first-order circuit includes a first-order first branch, a second-order first branch, a third-order first branch, and a fourth-order first branch, with the four branches connected in parallel sequentially. The first-order first branch includes a capacitor C7; the second-order first branch includes a capacitor C1; the third-order first branch includes multiple inductors; and the fourth-order first branch includes a first series inductor assembly and a first parallel capacitor assembly, which are connected in series.

[0042] In one embodiment, the first-order third branch includes inductors L1, L9, and L10 connected in series, with inductor L9 disposed between inductors L1 and L10.

[0043] In one embodiment, the first series inductor component in the first-order fourth branch includes inductors L8 and L9 connected in series; the first parallel capacitor component in the first-order fourth branch includes capacitors C2 and C8 connected in parallel; and the inductor L2 is disposed between inductor L8 and the first parallel capacitor component.

[0044] In one case of the embodiment, one end of the capacitor C7 in the first branch, one end of the capacitor C1 in the second branch, one end of the inductor L10 in the third branch, and one end of the inductor L8 in the fourth branch are connected at a common point, and the common point is connected to one end of the second-order circuit; the other end of the capacitor C7 in the first branch, the other end of the capacitor C1 in the second branch, one end of the inductor L1 in the third branch, and one end of the first parallel capacitor assembly in the fourth branch are connected at a common point, and the common point is grounded.

[0045] As shown in the example, Figure 1 In the first-order circuit, the selection of each component is as follows: the capacitance of C7 is 3.3 nF, the capacitance of C1 is 1 nF, the inductance of L10 is 270 nH, the inductance of L9 is 56 nH, the inductance of L1 is 1.8 nH, the inductance of L8 is 18 μH, the inductance of L2 is 2.7 μH, the capacitance of C2 is 62 pF, and the capacitance of C8 is 4.7 pF. The capacitors and inductors in the first-order circuit form two passbands of a filter through series and parallel connection. In a complex electromagnetic environment, many noise signals are received by the BTM antenna. The correct signals mixed with the noise signals pass through the first-order circuit, and the filtered signals in the frequency bands of 3.914 MHz to 4.073 MHz and 4.476 MHz to 4.627 MHz enter the second-order circuit.

[0046] In one embodiment of the application, Figure 1 and Figure 2 The second-order circuit comprises, in sequence, an inductor L7, an inductor L3, a second parallel capacitor assembly, and a second-order branch, the second-order branch comprises a second-order first branch and a second-order second branch in parallel with each other, the second-order first branch comprises a plurality of inductors connected in series with each other, the second-order second branch comprises a plurality of capacitors connected in parallel with each other, and one end of the inductor L7 is connected to the first-order circuit.

[0047] In one case of the embodiment, the second parallel capacitor assembly comprises a capacitor C3 and a capacitor C9 connected in parallel, one end of the second parallel capacitor assembly is connected to one end of the inductor L3, and the other end of the second parallel capacitor assembly is connected to one end of the second-order branch.

[0048] In one case of the embodiment, the second-order first branch comprises, in sequence, an inductor L4, an inductor L11, and an inductor L12; the second-order second branch comprises a capacitor C4 and a capacitor C10 connected in parallel; one end of the inductor L4 is connected to one end of the second-order second branch and the other end of the second parallel capacitor assembly at a common point, and one end of the inductor L12 is connected to the other end of the second-order second branch and one end of the third-order circuit at a common point.

[0049] For example, such as Figure 1 As shown, in the second-order circuit, the selected components are as follows: L7 has an inductance of 12μH, L3 has an inductance of 1.5μH, C9 has a capacitance of 100pF, C3 has a capacitance of 3.6pF, L4 has an inductance of 120nH, L11 has an inductance of 82nH, L12 has an inductance of 8.2nH, C4 has a capacitance of 3.3nF, and C10 has a capacitance of 3.3nF. The series and parallel connection between the inductors and capacitors in the second-order circuit ensures that the filter has dual passbands while achieving a stopband rejection ratio of -80dB from -60dB. The ground signal filtered out from the first-order circuit is further filtered out by the second-order circuit to remove irrelevant signals.

[0050] In one embodiment of the present invention, such as Figure 1 and Figure 2 The third-order circuit includes a third-order first branch, a third-order second branch, a third-order third branch, and a third-order fourth branch, with the four branches connected in parallel sequentially. The third-order first branch includes a capacitor C11; the third-order second branch includes a capacitor C5; the third-order third branch includes multiple inductors; and the third-order fourth branch includes a second series inductor assembly and a third parallel capacitor assembly, which are connected in series.

[0051] In one embodiment, the third branch of the third order includes inductors L15, L14 and L5 connected in series, with inductor L14 disposed between inductors L15 and L5.

[0052] In one embodiment, the second series inductor assembly in the third-order fourth branch includes inductors L13 and L6 connected in series; the third parallel capacitor assembly in the third-order fourth branch includes capacitors C6 and C12 connected in parallel; and the inductor L6 is disposed between inductor L13 and the third parallel capacitor assembly.

[0053] In one embodiment, one end of capacitor C11 in the third-order first branch, one end of capacitor C5 in the third-order second branch, one end of inductor L15 in the third-order third branch, and one end of inductor L13 in the third-order fourth branch are connected at a common point, and this common connection point is connected to the other end of the second-order circuit; the other end of capacitor C11 in the third-order first branch, the other end of capacitor C5 in the third-order second branch, one end of inductor L5 in the third-order third branch, and one end of the third parallel capacitor assembly in the third-order fourth branch are connected at a common point, and this common connection point is grounded.

[0054] For example, such as Figure 1As shown, in the three-stage circuit, the selection of each component is as follows: the capacitance of C11 is 3.3nF, the capacitance of C5 is 1nF, the inductance of L15 is 270nH, the inductance of L14 is 56nH, the inductance of L5 is 1.8nH, the inductance of L13 is 18μH, the inductance of L6 is 2.7μH, the capacitance of C6 is 62pF, and the capacitance of C12 is 4.7pF. The component types of the three-stage circuit are consistent with those of the first-stage circuit, and the components have the same functions.

[0055] In general, the first-stage, second-stage and third-stage circuits are connected in series and interact with each other, and two passband bandwidths, i.e., a center frequency of 3.9MHz and a bandwidth of 0.34MHz, and a center frequency of 4.5MHz and a bandwidth of 0.35MHz, are obtained, and the stopband suppression degree at both ends of the passband can reach -55dB, and the stopband suppression degree in the middle of the passband can reach -140dB.

[0056] With respect to the input signal, the frequency range of the output signal is a center frequency of 3.9MHz and a bandwidth of 0.34MHz, and a center frequency of 4.5MHz and a bandwidth of 0.35MHz, and almost no interference signal is output in other frequency ranges. Since the filter circuit is a double-passband with respect to a single-passband, the bandwidth is narrower, and more interference signals are filtered out. The filter circuit can be used in a BTM host receiving board to filter out interference components of the BTM device uplink signal, so that the receiving board can better demodulate the FSK signal.

[0057] Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent features, and these modifications or replacements do not change the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A BTM receive board third order band pass filter circuit, characterized by, The filter circuit comprises: A first-order circuit, a second-order circuit and a third-order circuit are connected in series; one end of the first-order circuit and one end of the third-order circuit are connected to two ends of the second-order circuit, and the other end of the first-order circuit and the other end of the third-order circuit are grounded; wherein the first-order circuit comprises a first-order first branch, a first-order second branch, a first-order third branch and a first-order fourth branch, and the four branches of the first-order circuit are connected in parallel; the first-order first branch comprises a capacitor C7; the first-order second branch comprises a capacitor C1; the first-order third branch comprises a plurality of inductors; the first-order fourth branch comprises a first series inductor component and a first parallel capacitor component, and the first series inductor component and the first parallel capacitor component are connected in series; wherein the second-order circuit comprises an inductor L7, an inductor L3, a second parallel capacitor component and a second-order branch connected in series; the second-order branch comprises a second-order first branch and a second-order second branch connected in parallel, the second-order first branch comprises a plurality of inductors connected in series, and the second-order second branch comprises a plurality of capacitors connected in parallel, and one end of the inductor L7 is connected to the first-order circuit. The first-order circuit is used to filter out interference signals outside the specified passband, the second-order circuit is used to increase the stopband suppression degree and passband flatness of the filter circuit, and the third-order circuit has the same effect as the first-order circuit and can further increase the stopband suppression degree of the filter circuit.

2. The BTM receive board third-order bandpass filter circuit of claim 1, wherein, The first-order third branch comprises an inductor L1, an inductor L9 and an inductor L10 connected in series, and the inductor L9 is arranged between the inductor L1 and the inductor L10.

3. The BTM receive board third-order bandpass filter circuit of claim 1, wherein, The first series inductor component in the first-order fourth branch comprises an inductor L8 and an inductor L2 connected in series. The first parallel capacitor component in the first-order fourth branch comprises a capacitor C2 and a capacitor C8 connected in parallel. The inductor L2 is arranged between the inductor L8 and the first parallel capacitor component.

4. The BTM receive board third-order bandpass filter circuit of any of claims 1-3, wherein, One end of the capacitor C7 in the first-order first branch, one end of the capacitor C1 in the first-order second branch, one end of the inductor L10 in the first-order third branch and one end of the inductor L8 in the first-order fourth branch are connected to a common point, and the common point is connected to one end of the second-order circuit. The other end of the capacitor C7 in the first-order first branch, the other end of the capacitor C1 in the first-order second branch, one end of the inductor L1 in the first-order third branch and one end of the first parallel capacitor component in the first-order fourth branch are connected to a common point, and the common point is grounded.

5. The BTM receive board third-order bandpass filter circuit of claim 1, wherein, The second parallel capacitor component comprises a capacitor C3 and a capacitor C9 connected in parallel, one end of the second parallel capacitor component is connected to one end of the inductor L3, and the other end of the second parallel capacitor component is connected to one end of the second-order branch.

6. The BTM receive board third-order bandpass filter circuit of claim 1, wherein, The second-order first branch comprises an inductor L4, an inductor L11 and an inductor L12 connected in series. The second-order second branch comprises a capacitor C4 and a capacitor C10 connected in parallel. One end of the inductor L4 is connected to one end of the second-order second branch and the other end of the second parallel capacitor component, and one end of the inductor L12 is connected to the other end of the second-order second branch and one end of the third-order circuit.

7. The BTM receive board third-order bandpass filter circuit of claim 1, wherein, The third-order circuit comprises a third-order first branch, a third-order second branch, a third-order third branch and a third-order fourth branch, and the third-order circuit comprises four branches which are connected in parallel with each other; The third-order first branch comprises a capacitor C11; The third-order second branch comprises a capacitor C5; The third-order third branch comprises a plurality of inductors; The third-order fourth branch comprises a second series inductor assembly and a third parallel capacitor assembly, and the second series inductor assembly and the third parallel capacitor assembly are connected in series with each other.

8. The BTM receive board third-order bandpass filter circuit of claim 7, wherein, The third-order third branch comprises an inductor L15, an inductor L14 and an inductor L5 which are connected in series, and the inductor L14 is arranged between the inductor L15 and the inductor L5.

9. The BTM receive board third-order bandpass filter circuit of claim 8, wherein, The second series inductor assembly in the third-order fourth branch comprises an inductor L13 and an inductor L6 which are connected in series with each other; The third parallel capacitor assembly in the third-order fourth branch comprises a capacitor C6 and a capacitor C12 which are connected in parallel with each other, and the inductor L6 is arranged between the inductor L13 and the third parallel capacitor assembly.

10. The BTM receive board third order bandpass filter circuit of any of claims 7-9, wherein, One end of the capacitor C11 in the third-order first branch, one end of the capacitor C5 in the third-order second branch, one end of the inductor L15 in the third-order third branch and one end of the inductor L13 in the third-order fourth branch are connected to a common point, and the common point is connected to the other end of the second-order circuit; The other end of the capacitor C11 in the third-order first branch, the other end of the capacitor C5 in the third-order second branch, one end of the inductor L5 in the third-order third branch and one end of the third parallel capacitor assembly in the third-order fourth branch are connected to a common point, and the common point is connected to the ground.

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