Low junction capacitance airborne differential signal lightning protection filtering system and lightning protection method thereof

Abstract

The invention discloses a low junction capacitance airborne differential signal lightning protection filtering system which comprises a two-stage lightning protection module, a signal filtering module and a signal processing module which are connected in sequence, the two-stage lightning protection module is connected with a signal input interface, and the signal processing module is connected with a signal output end. Through function complementation of the TSS and the ESD, separation and cooperation of energy discharge and voltage clamping are realized. The TSS serves as an energy absorber to solve the problem of large surge, and the ESD serves as a voltage limiter to solve the problems of residual voltage and fast peak. The framework successfully breaks through the performance bottleneck of a single device.

Description

TECHNICAL FIELD

[0001] The present application relates to a low junction capacitance airborne differential signal lightning protection filter system and a lightning protection method thereof. BACKGROUND

[0002] Modern aerospace vehicles, its flight safety is highly dependent on the internal complex electronic systems, especially phased array radar, electronic equipment and high-speed data link system. These systems inside through a large number of low voltage differential signal for high-speed communication, its signal edge time usually requires less than 30 nanoseconds, the signal integrity of transmission channel is extremely sensitive.

[0003] However, the aircraft in the entire mission profile, is the lightning electromagnetic environment of high-risk target. The threat of lightning to airborne equipment mainly divided into "direct effect" and "indirect effect". Direct effect (such as structure ablation, deformation) by the overall design unit of the aircraft through the discharge brush, lightning shunt strip and other external measures for protection; and "indirect effect" - lightning on the aircraft shell induced by the huge transient electromagnetic field, and then coupled to the cable in the machine to form a high voltage of thousands of surges and current, then become the airborne internal electronic equipment must be independent of the severe challenge. To meet this challenge, the industry generally use transient voltage suppression diode (TVS) or gas discharge tube (GDT) surge protection devices to build lightning protection circuit. TVS tube with its picosecond level of response speed, was the ideal choice of electronic circuit protection. However, it has a fatal defect in high-speed signal line: the inherent high junction capacitance. General type of high-power TVS tube junction capacitance is usually between several tens of picofarad to several thousand picofarad, when it is connected in parallel on high-speed differential signal line, the capacitance will be with the line impedance to form a low-pass filter, significantly prolong the rise / fall time of the signal, leading to waveform distortion, timing confusion, can not meet the edge time less than 30 ns of stringent requirements.

[0004] On the other hand, gas discharge tube (GDT) although has very low junction capacitance (usually less than 5 pF), theoretically has little effect on signal integrity, but it has two major limitations: first, its response speed is relatively slow (microsecond level), it is difficult to effectively suppress the fast lightning front; secondly, and more critical is that the breakdown voltage and performance of GDT will change significantly with the decrease of ambient pressure. For the airborne equipment in high altitude (usually corresponding to low pressure) environment for long time, the protection threshold of GDT will drift, may lead to the protection circuit misoperation or inaction at the critical moment, thus lose the reliable protection ability, therefore, the application in high altitude airborne equipment is greatly limited.

[0005] In summary, the prior art is trapped in a dilemma: the use of TVS tubes can ensure protection strength but sacrifices signal quality; the use of GDT can ensure signal quality but cannot provide stable and reliable protection in high-altitude environments. This contradiction has become a key technical bottleneck restricting the development of advanced airborne electronic systems, especially domestically produced, miniaturized, and highly reliable systems.

[0006] Therefore, there is an urgent need in the art for an innovative protection scheme that must be able to simultaneously meet the stringent requirements of high-altitude low-pressure environments, high-level lightning protection performance (such as A2J3L3 / M3) specified by RTCA / DO-160G standards, and low junction capacitance (such as less than 35 pF) of high-speed differential signals, thereby achieving the unification of protection capability and signal fidelity. SUMMARY

[0007] The purpose of the present application is to address the problem that existing lightning protection systems cannot balance signal quality and reliable protection, and to provide a low-junction-capacitance airborne differential signal lightning protection filter system that can provide high-reliability lightning surge protection for airborne equipment without degrading the integrity of high-speed signals.

[0008] The technical solution of the present application is as follows: A low-junction-capacitance airborne differential signal lightning protection filter system, comprising two-stage lightning protection modules, a signal filtering module, and a signal processing module connected in sequence, the two-stage lightning protection modules being connected to a signal input interface, and the signal processing module being connected to a signal output end: The signal input interface is a high-reliability connector for receiving external airborne wave control differential signals. The two-stage lightning protection modules, including a primary lightning protection unit and a secondary lightning protection unit, are connected to the signal input interface, the primary lightning protection unit including a semiconductor discharge tube TSS connected in parallel between the signal input line and the ground end, and the secondary lightning protection unit including multiple protection units each comprising at least two bidirectional ESD protection devices connected in parallel between the signal input line and the ground end. The signal filtering module includes a common-mode inductor and a common-mode capacitor. The signal processing module includes a level conversion circuit and a signal distribution circuit, the level conversion circuit including filter capacitors connected in parallel between the signal distribution circuit and the ground end. The signal output interface is a high-reliability connector.

[0009] The ESD device has a junction capacitance of less than 2 pF, and the total equivalent junction capacitance of the two-stage lightning protection modules is less than 35 pF.

[0010] The semiconductor discharge tube TSS is a ceramic package with a current-carrying capacity of not less than 100 A under an 8 / 20 μs waveform.

[0011] The off-state voltage of the semiconductor discharge tube TSS is greater than the maximum working voltage of the external airborne wave control differential signal, and the switching voltage is less than the maximum peak voltage of the level conversion chip in the signal processing module.

[0012] The impedance of the common mode inductor at a frequency of 100 MHz is not less than 360Ω, and the capacitance value of the common mode capacitor ranges from 100pF to 1000pF.

[0013] A lightning protection method of a low junction capacitance airborne differential signal lightning protection filter system, comprising the following steps: Step 1: receiving an external airborne wave control differential signal with an edge time less than 30ns through a signal input interface, and transmitting the signal to a two-stage lightning protection module; Step 2: the two-stage lightning protection module performs "primary energy dissipation + secondary clamping" cooperative protection on the received signal: Step 3: the signal filter module receives the lightning protection processed signal, suppresses high frequency common mode noise with high impedance characteristics through the common mode inductor, and at the same time provides a low impedance path for the common mode noise through the common mode capacitor, ensuring that the differential signal is transmitted without distortion; Step 4: the signal processing module receives the filtered clean signal, performs level conversion and signal format adaptation through the level conversion chip, and then outputs the signal through the signal distribution circuit. Step 5: the signal output interface receives the signal distributed by the signal processing module, and outputs the processed differential signal to the subsequent functional unit of the airborne.

[0014] In step 2: The specific process of the primary energy dissipation is that when the lightning surge voltage exceeds the switching voltage of the semiconductor discharge tube in the primary lightning protection unit, the semiconductor discharge tube changes from a high resistance state to a low resistance state within nanoseconds, and more than 90% of the surge energy is discharged to the ground; The specific steps of the secondary clamping are that the residual voltage spike after the primary energy dissipation enters the secondary lightning protection unit, and is accurately clamped by at least two parallel bidirectional ESD protection devices, to ensure that the voltage does not exceed the tolerance value of the rear-end circuit.

[0015] The capacitance value of the common mode capacitor in step 3 is 470pF, and the common mode inductor and the common mode capacitor cooperate to make the common mode interference suppression not less than 20dB.

[0016] The external airborne wave control differential signal in step 1 is the wave control signal of the airborne phased array radar, and the frequency is 2MHz, and the edge time of the output signal after steps 1~5 is better than 15ns.

[0017] The beneficial effects of the present application are: 1. A unique two-level collaborative surge protection architecture: By complementing the functions of TSS and ESD, it achieves the separation and synergy of "energy dissipation" and "voltage clamping". TSS acts as an "energy absorber" to solve the problem of large surges, while ESD acts as a "voltage limiter" to solve the problems of residual voltage and rapid spikes. This architecture successfully breaks through the performance bottleneck of single devices.

[0018] 2. Combining low junction capacitance and high protection level: Through a two-stage collaborative lightning protection architecture and the selection of low-capacitance components, effective protection against lightning waveforms of RTCA / DO-160G standard A2J3L3, A2J3M3 and above is achieved under the condition that the total equivalent junction capacitance is <35pF, solving the problem of "distortion after protection" in traditional TVS solutions.

[0019] 3. Excellent adaptability to high-altitude environments: The selected TSS and ESD are both solid-state semiconductor devices, whose performance is not affected by changes in ambient air pressure, overcoming the defect of performance drift of gas discharge tubes at high altitudes, and are particularly suitable for various high-altitude long-endurance aircraft.

[0020] 4. Enhanced system reliability and redundancy design: By adopting dual ESD parallel connection and other methods, not only is the discharge power of secondary protection increased (up to 800W), but circuit redundancy is also formed. When a single device fails, the system can still provide a certain degree of protection, which meets the high reliability design requirements of airborne equipment. Attached Figure Description

[0021] Figure 1 This is a block diagram illustrating the system's working principle. Figure 2 This is a schematic diagram of a lightning protection and filtering circuit. Figure 3 This is a graph showing the voltage-current characteristic curve of a traditional TVS. Figure 4 This is a graph showing the bidirectional TSS current-voltage characteristic curve. Figure 5 This is a waveform diagram for a Level A2 lightning strike test. Figure 6 This is a waveform diagram for a lightning strike test of level A3. Figure 7 The results are for a single TSS solution test. Figure 8 This is the test result for a single ESD solution. Figure 9 The results are the test results of the TSS+ESD solution of this invention.

[0022] Figure 10 This is a picture of the actual lightning protection filter test board. Detailed Implementation

[0023] like Figure 1 The system working principle block diagram shown is as follows: along the signal transmission path, this lightning protection and filtering system consists of: signal input interface → two-stage lightning protection module → signal filtering module → signal processing module → signal output interface.

[0024] 2. Component Selection and Implementation of Core Module (1) Implementation of Two-Level Lightning Protection Module The circuit principle of this module is detailed in Appendix Figure 3 .

[0025] Primary protection (TSS selection and function): A semiconductor discharge tube (TSS) is connected in parallel between the signal line and ground. The preferred model is TSS-JP0300TA. The selection criteria for this device are as follows: Off-state voltage (VDRM): greater than the maximum operating voltage of the signal line to ensure minimal leakage current during normal operation.

[0026] Switching voltage (VS): less than the maximum peak voltage that the back-end chip can withstand, ensuring reliable conduction when a surge occurs.

[0027] Current carrying capacity: Up to 100A under 8 / 20μs waveform, meeting the surge discharge requirements of A2 / A3 levels.

[0028] Junction capacitance: typically around 15pF, much lower than that of traditional TVS.

[0029] Working principle: When the surge voltage of a lightning strike exceeds its VS value, the TSS rapidly changes from a high-resistivity state to a low-resistivity state within nanoseconds, dissipating most of the surge energy to the ground.

[0030] Secondary protection (ESD selection and function): Two bidirectional ESD protection devices are connected in parallel after the TSS and immediately adjacent to the input of the signal processing module. The selection criteria are as follows: Junction capacitance: extremely low, typically less than 2pF, with negligible impact on signal edges.

[0031] Response time: picosecond level, capable of clamping the rapid voltage spikes remaining after TSS discharge.

[0032] Clamping voltage: much lower than the damage voltage of the subsequent level conversion chip.

[0033] Parallel design: The use of dual devices in parallel enables the instantaneous discharge power of this stage to reach 800W, and forms a redundant backup to improve reliability.

[0034] (2) Implementation of the signal filtering module Common-mode inductor L1: It is made of a magnetic core with an impedance of not less than 360Ω at a frequency of 100MHz, and is used to effectively suppress high-frequency common-mode interference.

[0035] Common-mode capacitors C1 and C2: The preferred capacitance value is 470pF, which is within the recommended range of 100pF to 1000pF, to provide a low impedance path to ground for common-mode noise.

[0036] (3) Implementation of signal processing and PCB layout Signal processing chip: Domestically produced chips can be used for level conversion and distribution, such as relevant models from China Zhenhua Group Yongguang Electronics Co., Ltd. (State-owned Factory No. 873), to achieve the goal of full localization.

[0037] PCB critical layout and routing rules (this is the physical core for achieving low-distortion transmission): Impedance control: Based on the PCB stack-up structure, simulation software is used to accurately calculate and control the differential trace impedance to 100Ω.

[0038] Equal length control: Differential pairs (D+, D-) must be strictly aligned internally with equal length, and the length deviation is recommended to be controlled within 5 mil (0.127 mm); different differential pairs should also be as equal in length as possible.

[0039] Reference plane: A complete and undivided reference ground plane must be maintained under the differential traces. Signal lines are strictly prohibited from crossing the split area to ensure the continuity of the signal return path.

[0040] Isolation and shielding: Signal traces in this system should be routed on different signal layers from other high-speed clocks, power supplies, and other noise sources, and proper grounding should be provided.

[0041] 3. Testing, Verification, and Performance Confirmation: To verify the effectiveness of this implementation method, the following tests were conducted: Figure 10 The test board shown.

[0042] Signal integrity test: Input a 4MHz square wave signal and use an oscilloscope to measure the edge time of the output signal. Test results (see attached table). Figure 9 The results show that, after adopting this implementation scheme, the signal edge time is much less than 15ns, which is better than the system requirement of <30ns.

[0043] Lightning protection level test: Based on the RTCA / DO-160G standard, the equipment was tested for waveform group A (pin injection) level 2, waveform group J (cable bundle single return stroke) level 3, and waveform groups L and M (cable bundle multiple pulses) level 3. See the attached diagram for detailed test waveforms. Figure 5 With appendix Figure 6 Test results show that this implementation plan successfully passed the A2J3L3 and A2J3M3 level assessments, and has a certain design margin.

[0044] In summary, this specific embodiment, through clear component selection, rigorous circuit design, and strict PCB layout and routing, fully achieves all the technical objectives of low junction capacitance, high-level lightning protection, and high signal integrity described in this invention, providing an effective solution for reliable transmission of airborne high-speed differential signals.

[0045] Example: Figure 10As shown, multiple sets of control experiments were conducted using the test board, and the core test results are compared in Table 1. This directly constitutes the basis for the specific implementation of this scheme: Table 1. Performance Comparison of Different Protection Solutions

[0046] Based on the above experimental data, the specific structure and selection criteria of this scheme are as follows: 1. Tests on the graded surge protection module have demonstrated that individual device solutions all have fatal flaws. Solution 1 (TVS) suffers from severe signal edge degradation due to excessive junction capacitance; Solution 3 (ESD), while offering good signal integrity, lacks sufficient protection capability. Therefore, this invention employs a combination of TVS and ESD, selected through testing and screening: First stage (primary coarse discharge): Parallel semiconductor discharge tube (TSS). Tests show that its current carrying capacity is sufficient to handle standard surge waveforms, and its junction capacitance (approximately 20pF) is much lower than that of traditional TVS. As shown in Scheme 2, it can significantly improve signal edges.

[0047] Secondary stage (secondary precision clamping): Parallel bidirectional ESD protection device. As shown in the test of Scheme 3, the extremely low junction capacitance of the ESD device ensures the sharpness of the signal edge. In the two-stage architecture of this invention, its function is to precisely clamp the residual voltage after the TSS discharges.

[0048] Key synergistic mechanisms: Experimental data (see...) Figure 9 (Test results of the TSS+ESD solution) demonstrate that this combination successfully controls the total equivalent junction capacitance of the system below 20pF, and the signal edge time is better than 15ns, fully meeting the requirement of less than 30ns. Meanwhile, as... Figure 5 , Figure 6 As shown, the circuit successfully passed the A2 and A3 level lightning wave waveform 4-pin injection test, achieving a balance between protection performance and signal fidelity.

[0049] 2. The common-mode rejection signal filtering module, following the verified surge protection module, incorporates a filtering network consisting of a common-mode inductor (≥360Ω / 100MHz) and a common-mode capacitor (100-1000pF). This parameter combination effectively suppressed common-mode noise in testing without causing any observable negative impact on the signal edges already protected by the surge protection module.

[0050] 3. Board-level design and signal processing to ensure integrity Our tested and verified PCB design strictly adheres to routing rules including 100Ω differential impedance, equal length between pairs, and a complete reference ground plane. Actual testing shows that boards following these rules exhibit significantly better signal integrity, larger eye diagram opening, and less jitter compared to boards with irregular routing.

[0051] Signal processing and output: The clean signal, after being protected and filtered, is conditioned by a level conversion chip and then output through a high-reliability connector.

[0052] 4. Redundancy and High Reliability Design Power redundancy: Employs a dual ESD parallel design, such as... Figure 8 and Figure 9 The test comparison shows that this design increases the secondary discharge power to over 800W and provides redundant backup, thereby improving the system's mean time between failures (MTBF).

[0053] Environmental adaptability: All core protective components (TSS, ESD) are solid-state semiconductors, and their performance is not affected by high-altitude and low-pressure environments, ensuring the stability of protection throughout the mission.

Claims

1. A low junction capacitance on-board differential signal lightning protection filter system, characterized by The application relates to a signal input interface, a signal output interface, a signal processing module, a signal filter module and a two-stage lightning protection module connected in sequence. The signal input interface is a high-reliability connector for receiving external airborne wave control differential signals. The two-stage lightning protection module is connected with the signal input interface and comprises a primary lightning protection unit and a secondary lightning protection unit. The signal filter module comprises a common-mode inductor and a common-mode capacitor. The signal processing module comprises a level conversion circuit and a signal distribution circuit. The signal output interface is a high-reliability connector.

2. The low-junction-capacitance on-board differential signal lightning protection filter system of claim 1, wherein: The ESD device has a junction capacitance of less than 2 pF, and the total equivalent junction capacitance of the two-stage lightning protection module is less than 35 pF.

3. The low-junction-capacitance on-board differential signal lightning protection filter system of claim 1, wherein: The semiconductor discharge tube TSS is a ceramic package, and the through-flow capacity under an 8 / 20 mu s waveform is not less than 100 A.

4. The low-junction-capacitance on-board differential signal lightning protection filter system of claim 1, wherein: The off-state voltage of the semiconductor discharge tube TSS is greater than the maximum working voltage of the external airborne wave control differential signal, and the switching voltage is less than the maximum peak voltage of the level conversion chip in the signal processing module.

5. The low-junction-capacitance on-board differential signal lightning protection filter system of claim 1, wherein: The common-mode inductor has an impedance of not less than 360 omega under a 100 MHz frequency, and the common-mode capacitor has a capacitance value in the range of 100 pF to 1000 pF.

6. The lightning protection method of a low-capacitance airborne differential signal lightning protection filter system according to any one of claims 1-5, characterized in that, The method comprises the following steps: Step 1: receiving external airborne wave control differential signals with an edge time of less than 30 ns through the signal input interface and transmitting the signals to the two-stage lightning protection module; Step 2: the two-stage lightning protection module performs primary energy discharge and secondary clamping on the received signals; Step 3: the signal filter module receives the lightning protection processed signals, suppresses high-frequency common-mode noise through the common-mode inductor with high impedance characteristics, and provides a low-impedance path for the common-mode noise through the common-mode capacitor, thereby ensuring the distortionless transmission of the differential signals; Step 4: the signal processing module receives the filtered clean signals, performs level conversion and signal format adaptation through the level conversion chip, and then outputs the signals through the signal distribution circuit; Step 5: the signal output interface receives the signals distributed by the signal processing module and outputs the processed differential signals to the subsequent functional units on the aircraft.

7. The method of claim 6, wherein the method further comprises: connecting the first and second low-capacitance on-board differential signal surge protection systems in series with each other. In step 2: The specific process of the primary energy discharge is that when the lightning surge voltage exceeds the switching voltage of the semiconductor discharge tube in the primary lightning protection unit, the semiconductor discharge tube is converted from a high-resistance state to a low-resistance state within nanoseconds, and more than 90% of the surge energy is discharged to the ground; The specific steps of the secondary clamping are that the residual voltage peak after the primary energy discharge enters the secondary lightning protection unit, and is accurately clamped by at least two parallel bidirectional ESD protection devices, so that the voltage is ensured to be not higher than the tolerance value of the rear-end circuit.

8. The lightning protection method for the low junction capacitance airborne differential signal lightning protection filtering system according to claim 6, characterized in that: In step 3, the capacitance value of the common-mode capacitor is 470 pF, and the common-mode inductor and the common-mode capacitor cooperate to make the common-mode interference suppression amount not less than 20 dB.

9. The method of claim 6, wherein the method further comprises: providing a low on-state capacitance (LOC) protection device between the first and second terminals of the low on-state capacitance (LOC) protection device and the first and second terminals of the low on-state capacitance (LOC) protection device, respectively. The external airborne wave control differential signal in step 1 is a wave control signal of an airborne phased array radar, the frequency is 2MHz, and the edge time of the output signal after the processing of steps 1-5 is better than 15ns.

Images