A three-stage filtering circuit for a transponder locator receiver module receiver board

Abstract

A three-stage filtering circuit for a transponder locator receiver module, belonging to the field of railway communication signal technology, includes a primary circuit, a secondary circuit, and a tertiary circuit arranged in series. The primary circuit is a capacitively coupled resonator bandpass filter with a bandwidth of 256 kHz; the secondary circuit is a crystal bandstop filter targeting a frequency of 1536 kHz; and the tertiary circuit is a crystal bandstop filter targeting a frequency of 1792 kHz. This invention's circuit can both widen the receiving bandwidth and effectively suppress inherent interference signals.

Description

Technical Field

[0001] This invention belongs to the field of railway communication signal technology, and in particular relates to a three-stage filtering circuit for a transponder locator receiver module receiving board. Background Technology

[0002] The point-responder locator system is a subsystem of the wireless shunting and monitoring system (STP), mainly used to locate shunting locomotives.

[0003] The system includes a ground-based point-to-point transponder locator (hereinafter referred to as the locator), a vehicle-mounted transponder locator receiving antenna (hereinafter referred to as the antenna), and a vehicle-mounted transponder locator receiving module (hereinafter referred to as DJM).

[0004] The system uses an energy signal frequency of 256 kHz and a signal receiving frequency of 1664 kHz, employing PSK modulation. Due to the numerous onboard devices on the shunting locomotive and the complex electromagnetic environment, various interference signals coexist. In particular, the 6th and 7th harmonics (1536 kHz and 1792 kHz) of the 256 kHz energy signal frequency used by the system itself can affect signal reception. Therefore, the bandwidth design of the filter circuit is crucial for the received PSK modulated signal. A wider filter bandwidth results in more useful information being received and a better eye diagram, but also allows more interference signals to enter. Conversely, a narrower filter bandwidth reduces the input of interference signals, but results in less useful information being received and a poorer eye diagram.

[0005] The existing DJM receiver board's filter circuit design is based on narrowing the bandwidth. This design can avoid the two inherent interference frequencies of 1536 kHz and 1792 kHz, but the received useful information is less and the eye diagram deteriorates, which may have an adverse effect on the receiver board's demodulation of the PSK signal. Summary of the Invention

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a three-stage filtering circuit for the receiver board of a transponder locator receiver module. This circuit can both widen the receiving bandwidth and effectively suppress inherent interference signals.

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] A three-stage filtering circuit for a transponder locator receiver module receiving board includes a first-stage circuit, a second-stage circuit, and a third-stage circuit arranged in series. The first-stage circuit is a capacitively coupled resonator bandpass filter with a bandwidth of 256 kHz. The second-stage circuit is a crystal bandstop filter for a frequency of 1536 kHz. The third-stage circuit is a crystal bandstop filter for a frequency of 1792 kHz.

[0009] Furthermore, the first-stage circuit is a third-order Butterworth-type capacitively coupled resonator bandpass filter. The first-order circuit consists of inductor L1 and capacitor C1 connected in parallel, with one end of the parallel connection connected to one end of capacitor C12, and both connected to the signal input, while the other end is connected to ground. The second-order circuit consists of inductor L2 and capacitor C2 connected in parallel, with one end of the parallel connection connected to the other end of capacitor C12 and one end of capacitor C23, while the other end is connected to ground. The third-order circuit consists of inductor L3 and capacitor C3 connected in parallel, with one end of the parallel connection connected to the other end of capacitor C23, while the other end is connected to ground.

[0010] Furthermore, the parallel connection of inductor L1 and capacitor C1, the parallel connection of inductor L2 and capacitor C2, and the parallel connection of inductor L3 and capacitor C3 are all resonant circuits.

[0011] Furthermore, the secondary circuit consists of an inductor La1 and a capacitor Ca1 connected in parallel, with one end connected to the first-stage circuit and the other end connected to an inductor La12. One end of the capacitor Ca3 is connected to the inductor La12, and the other end is grounded. One end of the equivalent circuit Y1 of the crystal resonator is connected to the inductor La12, and the other end is connected to the capacitor C1a1, with the other end of the capacitor C1a1 grounded. The equivalent circuit Y1 of the crystal resonator is composed of a capacitor CS1, an inductor LS1, a resistor RS1, and a capacitor CP1 connected in series.

[0012] After inductor La2 and capacitor Ca2 are connected in parallel, one end is connected to inductor La12 and the other end is connected to the third stage circuit. One end of capacitor Ca4 is connected to inductor La12 and the other end is grounded. One end of the equivalent circuit Y2 of the crystal resonator is connected to inductor La12 and the other end is connected to capacitor C1b1. The other end of capacitor C1b1 is grounded. The equivalent circuit Y2 of the crystal resonator is composed of capacitor CS2, inductor LS2, resistor RS2 and capacitor CP2 connected in series.

[0013] Furthermore, the three-stage circuit consists of inductor Lb1 and capacitor Cb1 connected in parallel, with one end connected to the second-stage circuit and the other end connected to inductor Lb12. One end of capacitor Cb3 is connected to inductor Lb12, and the other end is grounded. The equivalent circuit Y3 of the crystal resonator is connected to inductor Lb12 and capacitor C1a2, with the other end of capacitor C1a2 grounded. The equivalent circuit Y3 of the crystal resonator is composed of capacitor CS3, inductor LS3, resistor RS3, and capacitor CP3 connected in series.

[0014] After inductor Lb2 and capacitor Cb2 are connected in parallel, one end is connected to inductor La12 and the other end is connected to the signal output. One end of capacitor Cb4 is connected to inductor Lb12 and the other end is grounded. One end of the equivalent circuit Y4 of the crystal resonator is connected to inductor Lb12 and the other end is connected to capacitor C1b2. The other end of capacitor C1b2 is grounded. The equivalent circuit Y4 of the crystal resonator is composed of capacitor CS4, inductor LS4, resistor RS4 and capacitor CP4 connected in series.

[0015] The beneficial effects of this invention are:

[0016] The advantages of the circuit in this invention are that it widens the bandwidth of the filter, allowing more useful information to enter, while suppressing the main interference frequencies, reducing the input of interference signals, and enabling the receiving board to better demodulate the PSK signal.

[0017] This invention is applicable not only to interference situations of the receiver board of the transponder locator receiver module, but also to other devices with the same situation. This circuit can solve interference situations that require a certain bandwidth and have major interference frequencies. Attached Figure Description

[0018] Figure 1 The present invention provides a three-stage filtering circuit for the receiver board of the transponder locator receiving module.

[0019] Figure 2 This invention relates to a first-stage third-order Butterworth capacitively coupled resonator bandpass filter;

[0020] Figure 3 The second stage of this invention is a crystal bandstop filter for the 1536 kHz frequency point;

[0021] Figure 4 The equivalent circuit of the crystal resonator of this invention;

[0022] Figure 5 The third stage of this invention is a crystal bandstop filter for the 1792 kHz frequency point;

[0023] Figure 6 Simulation diagram of the present invention. Detailed Implementation

[0024] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] This invention provides a three-stage filtering circuit for the receiver board of a transponder locator receiver module, such as... Figure 1As shown, the key technical point is the design of a three-stage filtering circuit. The first stage is a capacitively coupled resonator bandpass filter with a bandwidth of 256KHz; the second stage is a crystal bandstop filter for the 1536KHz frequency point; and the third stage is a crystal bandstop filter for the 1792KHz frequency point.

[0026] Specifically, the first stage is a third-order Butterworth-type capacitively coupled resonator bandpass filter, such as... Figure 2 As shown, the third-order resonant circuit is as follows:

[0027] The first order is that inductors L1 and C1 are connected in parallel, with one end of the parallel connection connected to the signal input and one end of capacitor C12, and the other end connected to ground;

[0028] The second order is that inductors L2 and C2 are connected in parallel, and one end of the parallel connection is connected to the other end of C12 and one end of C23, while the other end is connected to ground;

[0029] The third stage consists of inductors L3 and C3 connected in parallel, with one end of the parallel connection connected to the other end of C23 and then connected to the second stage circuit, while the other end is connected to ground.

[0030] More specifically, L1 and C1 in parallel, L2 and C2 in parallel, and L3 and C3 in parallel are all resonant circuits.

[0031] The first-order resonant circuit and the second-order resonant circuit are coupled through capacitor C12, and the second-order resonant circuit and the third-order resonant circuit are coupled through capacitor C23.

[0032] For example, such as Figure 2 As shown, the components selected in the first-stage circuit are as follows: L1 has an inductance of 5270nH, C1 has a capacitance of 1561pF, C12 has a capacitance of 189.5 pF, L2 has an inductance of 5270nH, C2 has a capacitance of 1392.4pF, C23 has a capacitance of 186 pF, L3 has an inductance of 5270nH, and C3 has a capacitance of 1595pF. The first-stage circuit forms the passband of the filter, with a bandwidth of only 256 kHz, meaning only signals in the 1536 kHz to 1792 kHz frequency range will enter the next stage circuit.

[0033] Specifically, the second stage is a crystal bandstop filter targeting the 1536 kHz frequency point, such as... Figure 3 As shown. The circuit composed of CS1, LS1, RS1, and CP1 is the equivalent circuit of a crystal resonator, as shown below. Figure 4As shown, the equivalent circuit is named Y1. Similarly, the equivalent circuit of the crystal resonator composed of CS2, LS2, RS2 and CP2 is named Y2, the equivalent circuit of the crystal resonator composed of CS3, LS3, RS3 and CP3 is named Y3, and the equivalent circuit of the crystal resonator composed of CS4, LS4, RS4 and CP4 is named Y4.

[0034] More specifically, the structure of the second-stage circuit is a symmetrical structure with the inductor La12 as the center.

[0035] More specifically, inductor La1 and capacitor Ca1 are connected in parallel, with one end connected to capacitor C23 of the first stage circuit and the other end connected to La12; capacitor Ca3 is connected to La12 at one end and grounded at the other end; crystal Y1 is connected to La12 at one end and capacitor C1a1 at the other end, with the other end of capacitor C1a1 grounded.

[0036] More specifically, inductor La2 and capacitor Ca2 are connected in parallel, with one end connected to La12 and the other end connected to the parallel circuit of Lb1 and Cb1 in the third stage circuit; capacitor Ca4 is connected to La12 with one end connected to ground; crystal Y2 is connected to La12 with one end connected to capacitor C1b1 with the other end connected to ground.

[0037] For example, such as Figure 3 As shown, the inductance of La1 is 15.15uH, the capacitance of Ca1 is 102pF, the capacitance of Ca3 is 189pF, the capacitance of CS1 is 0.016pF, the inductance of LS1 is 671.08mH, the capacitance of RS1 is 9Ω, the capacitance of CP1 is 4pF, the capacitance of C1a1 is 505pF, the inductance of La12 is 46uH, the capacitance of Ca4 is 189pF, the capacitance of CS2 is 0.016pF, the inductance of LS2 is 671.08mH, the capacitance of RS2 is 9Ω, the capacitance of CP2 is 4pF, the capacitance of C1b1 is 524.8pF, the inductance of La2 is 15.15uH, and the capacitance of Ca2 is 102pF. The second-stage circuit will generate a large notch at the 1536 kHz frequency point. Because a crystal filter is used, it can accurately notch at the 1536 kHz frequency point without affecting the passage of other frequencies. This suppresses the 1536 kHz frequency point and prevents it from entering subsequent circuits and causing interference.

[0038] Specifically, the third stage is a crystal bandstop filter targeting the 1792 kHz frequency point, such as... Figure 5 As shown.

[0039] More specifically, the third-stage circuit has the same structure as the second-stage circuit, only the parameters are different. In the third-stage circuit, inductor Lb1 and capacitor Cb1 are connected in parallel, with one end connected to the second-stage circuit and the other end connected to inductor Lb12. One end of capacitor Cb3 is connected to inductor Lb12, and the other end is grounded. The equivalent circuit Y3 of the crystal resonator is connected with one end of inductor Lb12 and the other end to capacitor C1a2, with the other end of capacitor C1a2 grounded. The equivalent circuit Y3 of the crystal resonator is composed of capacitor CS3, inductor LS3, resistor RS3, and capacitor CP3 connected in series.

[0040] After inductor Lb2 and capacitor Cb2 are connected in parallel, one end is connected to inductor La12 and the other end is connected to the signal output. One end of capacitor Cb4 is connected to inductor Lb12 and the other end is grounded. One end of the equivalent circuit Y4 of the crystal resonator is connected to inductor Lb12 and the other end is connected to capacitor C1b2. The other end of capacitor C1b2 is grounded. The equivalent circuit Y4 of the crystal resonator is composed of capacitor CS4, inductor LS4, resistor RS4 and capacitor CP4 connected in series.

[0041] For example, such as Figure 5 As shown, the inductance of Lb1 is 13uH, the capacitance of Cb1 is 87.6pF, the capacitance of Cb3 is 163pF, the capacitance of CS3 is 0.016pF, the inductance of LS3 is 493.01mH, the capacitance of RS3 is 9Ω, the capacitance of CP3 is 4pF, the capacitance of C1a2 is 505pF, the inductance of Lb12 is 39.96uH, the capacitance of Cb4 is 163pF, the capacitance of CS4 is 0.016pF, the inductance of LS4 is 493.01mH, the capacitance of RS4 is 9Ω, the capacitance of CP4 is 4pF, the capacitance of C1b2 is 524.8pF, the inductance of Lb2 is 13uH, and the capacitance of Cb2 is 87.6pF. The third-stage circuit will generate a large notch at the 1792 kHz frequency point. Because a crystal filter is used, it can accurately notch at the 1792 kHz frequency point without affecting the passage of other frequencies. This suppresses the 1792 kHz frequency point and prevents it from entering subsequent circuits and causing interference.

[0042] This invention uses ADS simulation software to simulate the circuit, where the impedances of both the input and output terminals are set to 50Ω. For impedance matching, a transformer is placed at each end of the circuit. The input transformer is TF1 with a turns ratio of 1:3. The output transformer is TF2 with a turns ratio of 3:1. The choice of transformer can be based on the specific circuit network. Figure 6The simulation results for the entire circuit show that the first-stage capacitively coupled resonator bandpass filter has a bandwidth of 256 kHz. The second-stage crystal bandstop filter circuit, targeting 1536 kHz, reduces the bandwidth by 40.853 dB at that frequency. The third-stage crystal bandstop filter circuit, targeting 1792 kHz, reduces the bandwidth by 40.968 dB at that frequency. The simulation results meet the initial design requirements.

[0043] It can be seen that the filter of the present invention enables the transponder locator receiving module to receive more useful information and effectively suppresses the main interference frequency points, thereby enabling better demodulation of PSK signals.

[0044] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any modifications, alterations, substitutions, and variations made by those skilled in the art to the above embodiments are within the scope of the present invention.

Claims

1. A three-stage filtering circuit for a receiver board of a transponder locator receiving module, characterized in that: The system includes a first-stage circuit, a second-stage circuit, and a third-stage circuit arranged in series. The first-stage circuit is a capacitively coupled resonator bandpass filter with a bandwidth of 256 kHz. The second-stage circuit is a crystal bandstop filter targeting a frequency of 1536 kHz. The third-stage circuit is a crystal bandstop filter targeting a frequency of 1792 kHz. The first-stage circuit is a third-order Butterworth capacitively coupled resonator bandpass filter. In the first stage, inductor L1 and capacitor C1 are connected in parallel, with one end of the parallel connection connected to one end of capacitor C12, and both connected to the signal input. The other end is connected to ground. In the second stage, inductor L2 and capacitor C2 are connected in parallel, with one end of the parallel connection connected to the other end of capacitor C12 and one end of capacitor C23, and the other end connected to ground. In the third stage, inductor L3 and capacitor C3... The components are connected in parallel, with one end of the parallel connection connected to the other end of capacitor C23, and the other end connected to ground; the secondary circuit consists of inductor La1 and capacitor Ca1 connected in parallel, with one end connected to the first-stage circuit and the other end connected to inductor La12; one end of capacitor Ca3 is connected to inductor La12 and the other end is grounded; one end of the equivalent circuit Y1 of the crystal resonator is connected to inductor La12 and the other end is connected to capacitor C1a1, with the other end of capacitor C1a1 grounded; the equivalent circuit Y1 of the crystal resonator is composed of capacitor CS1, inductor LS1, resistor RS1, and capacitor CP1 connected in series. One end of the parallel connection between inductor La2 and capacitor Ca2 is connected to inductor La12, and the other end is connected to the third-stage circuit. One end of capacitor Ca4 is connected to inductor La12, and the other end is grounded. One end of the equivalent circuit Y2 of the crystal resonator is connected to inductor La12, and the other end is connected to capacitor C1b1, with the other end of capacitor C1b1 grounded. The equivalent circuit Y2 of the crystal resonator is composed of capacitor CS2, inductor LS2, resistor RS2, and capacitor CP2 connected in series. The third-stage circuit consists of inductor Lb1 and capacitor Cb1 connected in parallel, one end of which is connected to the second-stage circuit, and the other end is connected to inductor Lb12. One end of capacitor Cb3 is connected to inductor Lb12, and the other end is grounded. The equivalent circuit Y3 of the crystal resonator... One end of the capacitor is connected to inductor Lb12, and the other end is connected to capacitor C1a2. The other end of capacitor C1a2 is grounded. The equivalent circuit Y3 of the crystal resonator is composed of capacitor CS3, inductor LS3, resistor RS3 and capacitor CP3 connected in series. Inductor Lb2 and capacitor Cb2 are connected in parallel, and one end is connected to inductor La12. The other end is connected to the signal output. One end of capacitor Cb4 is connected to inductor Lb12, and the other end is grounded. The equivalent circuit Y4 of the crystal resonator is composed of capacitor CS4, inductor LS4, resistor RS4 and capacitor CP4 connected in series.

2. The three-stage filtering circuit of the receiver board of the transponder locator receiver module according to claim 1, characterized in that: The parallel connection of inductor L1 and capacitor C1, inductor L2 and capacitor C2, and inductor L3 and capacitor C3 are all resonant circuits.

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