Radio frequency signal multistage lightning protection circuit

Abstract

The invention, which belongs to the technical field of the electromagnetic environment effect, provides a radio-frequency signal multistage lightning protection circuit comprising a front-stage clamping sub-circuit and a rear-stage filtering sub-circuit connected in series with the front-stage clamping sub-circuit. The front-stage clamping sub-circuit comprises a first-stage gas discharge tube connected in parallel to the ground, a second-stage transient voltage suppressor connected in parallel to the ground and a transient blocking unit connected in series between the gas discharge tube and the transient voltage suppressor, and the rear-stage filtering sub-circuit is a T-shaped filtering circuit. The T-shaped filter circuit comprises a first capacitor C1, an inductor L and a second capacitor C2. The number of devices used by the protection circuit can be reduced to 6, the design and the manufacturing are simple, and high-grade lightning protection can be met. The protection circuit is suitable for lightning indirect effect protection of radio frequency signals of avionics equipment, and is also suitable for lightning indirect effect protection of other electronic equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic environmental effects, and in particular relates to a multi-level lightning protection circuit for radio frequency signals. Background Art

[0002] Lightning is an important natural factor that affects the flight safety of aircraft. When an aircraft is struck by lightning, a large current flows through the fuselage. Due to the large current, the interconnection cables of the internal equipment of the fuselage will be coupled to voltage and current surge signals (called lightning indirect effects). Therefore, cables need to be designed for lightning indirect effects protection, including RF cables. Chapter 22 of the airworthiness standard RTCA / DO-160G "Environmental Test Conditions for Airborne Equipment" is the main source of requirements for lightning indirect protection of avionics products. Chapter 22 of the standard specifies different lightning indirect effects protection waveforms and levels to match the lightning indirect effects protection requirements of avionics equipment in different compartments of the aircraft.

[0003] According to the airworthiness standard RTCA / DO-160G, the lightning indirect effect waveforms include waveform 1 (half-peak pulse width 69μs), waveform 2 (half-peak pulse width 6.4μs), waveform 3 (half-peak pulse width 5μs), waveform 4 (half-peak pulse width 69μs), waveform 5A (half-peak pulse width 120μs), and waveform 6 (half-peak pulse width 4μs), and their energy is mainly distributed below 10MHz. The above waveforms are divided into pin injection (waveform 3, waveform 4, waveform 5A) and cable bundle waveform 1, waveform 2, waveform 3, waveform 4, waveform 5A, and waveform 6 requirements. Since pin injection is a destructive test, its requirements are higher than those of the cable bundle coupling test. Therefore, when performing lightning indirect effect protection, the pin injection requirements shall prevail.

[0004] The requirements for lightning indirect effect pin injection include waveform 3, waveform 4 and waveform 5A, and level 1 to level 5 requirements. The limit of waveform 5A level 5 is 1600V / 1600A, which is the most stringent waveform (with the widest pulse width) required by the airworthiness standard, that is, the highest level requirement. The lightning indirect effect design is designed with this maximum value. Since the pulse width of waveform 3 is 5us, which is much smaller than the pulse width of waveform 4, which is 69us, and the pulse width of waveform 5A, which is 120us, and its source impedance internal resistance of 25Ω is greater than the internal resistance of waveform 4, which is 4Ω, and the internal resistance of waveform 5A, which is 1Ω, the energy coupled to the device end by waveform 3 is smaller. Therefore, when designing lightning indirect effect protection, it meets the requirements of waveform 4 or waveform 5A, and it is considered to meet the requirements of waveform 3.

[0005] The protection against indirect effects of lightning focuses on two aspects of design: first, whether the protection circuit itself will be damaged under high voltage and high current conditions; second, the impact of the protection circuit and its clamping voltage on the signal transmission quality and back-end chips.

[0006] The protection of avionics equipment against indirect effects of lightning mainly sets up a special protection circuit for indirect effects of lightning at the RF port of the equipment. The protection circuit adopts different protection devices according to the protection waveform and level to build a multi-level protection circuit. Commonly used protection devices include GDT (gas discharge tube), TSS (semiconductor discharge tube), TVS (transient voltage suppressor), ESD (TVS for electrostatic discharge protection), MOV (varistor), TBU (transient blocking unit), etc. The following is an introduction to the protection devices GDT, TBU, and ESD used in this patent. D is a voltage-triggered device with a minimum response time of ns. When the surge voltage across the ESD exceeds its breakdown voltage VBR-ESD, the ESD clamps its voltage to its clamping voltage VC. GDT is a voltage-triggered device with a response time of us. When the surge voltage across the GDT exceeds its breakdown voltage VBR-GDT, the GDT clamps its voltage to the arc voltage VA. TBU is a current-triggered device with a response time of <100ns. When the current flowing through the TBU exceeds its trigger current IT, the TBU will present a high impedance state (disconnected), thereby interrupting its current. Patent 202010495181.5 is one of the RF multi-level protection circuits.

[0007] Patent 202010495181.5 discloses a multi-level bidirectional protection device for radio frequency signal lightning electromagnetic pulses, and introduces a multi-level protection circuit composed of multiple GDTs, multiple TVSs, multiple filter capacitors C, and multiple inductors L. The input and output of the protection circuit constitute two paths, the composition is relatively complex, the production is cumbersome, and the size is large; and when protecting against the highest level (such as 1600V / 1600A) of lightning indirect effects, each of its filter capacitors, inductors, and TVS needs to select high-voltage (thousands of volts) and large-current (thousands of amperes) specification parameter devices, so that their size becomes larger as the protection level becomes higher.

[0008] Therefore, it is necessary to provide a protection circuit that can solve the problems of complex protection circuits for the indirect effects of lightning on radio frequency signals, complicated manufacturing, and large size of the protection device. Summary of the invention

[0009] In order to solve the above problems, the purpose of the present invention is to provide a multi-level lightning protection circuit for radio frequency signals, so as to solve the problems that the protection circuit for the indirect effect of lightning of radio frequency signals is complex, the production is cumbersome, and the size of the protection device is large. The protection circuit is composed of 6 devices in series, the protection link is simple, the design is convenient, the size is small, and it can meet all the requirements of RTCA / DO-160G Chapter 22 for applied waveform levels 1-5. At the same time, the patent provides its clamping circuit compliance algorithm.

[0010] In order to achieve the above object, the present invention provides the following technical solution: a multi-stage lightning protection circuit for radio frequency signals, the circuit comprising a front-stage clamping subcircuit and a rear-stage filtering subcircuit connected in series with the front-stage clamping subcircuit,

[0011] The front-stage clamping subcircuit comprises a first-stage gas discharge tube connected in parallel to the ground, a second-stage transient voltage suppressor connected in parallel to the ground, and a transient blocking unit connected in series between the gas discharge tube and the transient voltage suppressor.

[0012] The post-stage filtering subcircuit is a T-shaped filtering circuit, and the T-shaped filtering circuit includes a first capacitor C1, an inductor L, and a second capacitor C2.

[0013] The radio frequency signal multi-stage lightning protection circuit provided by the present invention also has the following characteristics: the maximum surge current I 0-GDT Greater than the maximum transient current I of the gas discharge tube in the protection circuit MAX-GDT , the maximum pulse power P of the transient voltage suppressor 0-ESD Greater than the maximum transient power P of the transient voltage suppressor in the protection circuit MAX-ESD .

[0014] The radio frequency signal multi-stage lightning protection circuit provided by the present invention also has the following characteristics: the maximum transient current I MAX-GDT for:

[0015] I MAX-GDT =I GDT-8×20 ×(e -120000×0.000008 -e -140000×0.000008 ),

[0016] Among them, I GDT-8×20 It is a 8 / 20us double exponential current waveform coefficient.

[0017] The radio frequency signal multi-stage lightning protection circuit provided by the present invention also has the following characteristics: the maximum transient power P of the transient voltage suppressor in the protection circuit is MAX-ESD for:

[0018] P MAX-ESD =MAX{I ESD (8μs)×V BR-ESD},

[0019] Among them, V BR-ESD is the clamping voltage of the transient voltage suppressor.

[0020] The radio frequency signal multi-stage lightning protection circuit provided by the present invention also has the following characteristics: the transient blocking unit is a switch type device, and the withstand voltage value V TBUGreater than the breakdown voltage of the gas discharge tube at 100V / μs.

[0021] The radio frequency signal multi-stage lightning protection circuit provided by the present invention also has the following characteristics: the post-stage filter subcircuit is an LC circuit, and the LC device withstand voltage value of the LC circuit is greater than the clamping voltage V BR-ESD And the arc voltage V A , the insertion loss IL of the LC circuit at 10MHz S21-simulation , insertion loss IL S21-simulation Greater than the design value IL S21 .

[0022] Beneficial Effects

[0023] The number of components used in the multi-level lightning protection circuit for radio frequency signals provided by the present invention can be reduced to 6, the design and manufacture are relatively simple, and it can meet the requirements of high-level lightning protection. The protection circuit is suitable for lightning indirect effect protection of radio frequency signals of avionics equipment, and is also suitable for lightning indirect effect protection of other electronic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A circuit diagram of a protection circuit provided by an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the electromagnetic insertion loss of the filter mentioned in the embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the 5A voltage waveform mentioned in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and examples, but it should be noted that these implementation modes are not limitations of the present invention, and any equivalent transformations or substitutions in functions, methods, or structures made by ordinary technicians in the field based on these implementation modes are all within the scope of protection of the present invention.

[0029] In the description of the embodiments of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the invention.

[0030] In addition, the terms "first", "second", "third", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0031] The terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0032] like Figure 1-Figure 3 As shown, an embodiment of the present invention provides a multi-stage lightning protection circuit for radio frequency signals, the circuit comprising a front-stage clamping subcircuit and a rear-stage filtering subcircuit connected in series with the front-stage clamping subcircuit.

[0033] The front-stage clamping subcircuit comprises a first-stage gas discharge tube GDT connected in parallel to the ground, a second-stage transient voltage suppressor ESD connected in parallel to the ground, and a transient blocking unit TBU connected in series between the gas discharge tube GDT and the transient voltage suppressor ESD.

[0034] The post-stage filtering subcircuit is a T-shaped filtering circuit, and the T-shaped filtering circuit includes a first capacitor C1, an inductor L, and a second capacitor C2.

[0035] The protection circuit provided in the above embodiment can be applied to 100MHz~1GHz radio frequency signal protection. In the 100MHz~1GHz frequency band, its insertion loss is <0.6dB and the standing wave ratio is <1.4.

[0036] In the clamping subcircuit in the above embodiment, when the lightning waveform is applied to the input port SMA1, the ESD response time is short and the breakdown voltage is low, so the lightning surge voltage is clamped to V BR-ESDAt this time, the lightning surge energy will pass through the TBU and ESD and enter the chassis ground. When the surge current exceeds the trigger current I of the TBU T When the surge duration is greater than 100ns, the TBU is triggered to a high impedance state, and the ESD stops working. As the lightning surge duration continues, the lightning surge voltage increases until the GDT breaks down, and the GDT clamps its lightning surge voltage to the arc voltage V A ; Under the action of lightning surge, the GDT, TBU, and ESD form the front-stage clamping circuit, and the maximum output residual voltage is V BR-ESD or V A , select appropriate GDT and ESD, residual voltage (V BR-ESD or V A ) will be less than 10V. To reduce the impact of the clamp circuit on the RF signal, the GDT and ESD junction capacitance in the clamp circuit should be as low as possible.

[0037] In some embodiments, the maximum surge current I 0-GDT Greater than the maximum transient current I of the gas discharge tube in the protection circuit MAX-GDT , the maximum pulse power P of the transient voltage suppressor 0-ESD Greater than the maximum transient power P of the transient voltage suppressor in the protection circuit MAX-ESD .

[0038] In some embodiments, the GDT and ESD junction capacitance algorithms in the clamp subcircuit are as follows:

[0039] Step 1: Based on the lightning indirect effect waveform 4 or 5A open circuit voltage V OC , short circuit current I SC , where the transient signal source internal resistance R of waveform 4 and waveform 5A S =V OC / I SC , its waveform 4 and waveform 5A function expression V WF4 (t) and V WF5A (t) See formula (1) for details;

[0040]

[0041]

[0042] Step 2: Calculate the ESD conduction time T1. The calculation formula is shown in formula (2).

[0043] V WF4 (T1) = V BR-ESD or V WF5A (T1) = V BR-ESD (2)

[0044] Step 3: When the ESD is turned on, a current will flow through the TBU, and the TBU trigger current is I T , the current I(t) in TBU can be expressed by the following formula, where t>T1;

[0045]

[0046] Step 4: Calculate TBU conduction time T2 (ESD cut-off). Since t>T1, plus TBU response time 100ns, TBU conduction current is greater than I T ; That is, T2 = T1 + 100ns;

[0047] Step 5: Equivalent ESD energy to the 8 / 20us double exponential current waveform function (I ESD The maximum transient power value P under (t) MAX-ESD :Where I in formula (4) ESD-8×20 is the 8 / 20us double exponential current waveform coefficient. The ESD withstand energy and test energy are equal, which can be expressed by formula (5) and formula (6). WF4 (t)orV WF5A (t) is the function expression V of waveform 4 or waveform 5A WF4 (t) or V WF5A (t), V BR-ESD is the clamping voltage of the ESD device, RS is the internal resistance of the lightning generator, and formula (5) and formula (6) can be used to obtain its I ESD-8×20 Then, the maximum transient power value P is obtained by formula (7): MAX-ESD ;

[0048] I ESD (t) = I ESD-8×20 ×(e -120000t -e -140000t ) (4)

[0049] Waveform 4:

[0050] Waveform 5A:

[0051] P MAX-ESD =MAX{I ESD (8μs)×V BR-ESD} (7)

[0052] Step 6: Equivalent the energy borne by the GDT to the maximum current I of the GDT under the 8 / 20us double exponential waveform MAX-GDT ; GDT's 8 / 20us double exponential current waveform function I GDT (t) can be expressed by formula (8); I GDT-8×20is the 8 / 20us double exponential current waveform coefficient. The GDT withstand energy is equal to the test energy, which can be expressed by formula (9) and formula (10). A is the arc voltage of GDT, where V WF4 (t)orV WF5A (t) is the function expression V of waveform 4 or waveform 5A WF4 (t) or V WF5A (t), RS is the internal resistance of the lightning generator, and then the maximum transient current I is obtained from formula (11): MAX-GDT ;

[0053] I GDT (t) = I GDT-8×20 ×(e -120000t -e -140000t ) (8)

[0054] Waveform 4:

[0055] Waveform 5A:

[0056] I MAX-GDT =I GDT-8×20 ×(e -120000×0.000008 -e -140000×0.000008 ) (11)

[0057] Step 7: Check the maximum pulse power P under 8 / 20μs conditions according to the ESD manual 0-ESD , according to the GDT manual, check the maximum surge current I under 8 / 20μs conditions 0-GDT , P 0-ESD >P MAX-ESD ,I 0-GDT >I MAX-GDT , and leave a certain margin, at this time the selected ESD and GDT meet the requirements;

[0058] Step 8: TBU is a switch type device, so it is sensitive to voltage. In order to ensure the normal opening and recovery of TBU, its withstand voltage value V TBU It should be greater than the breakdown voltage of GDT under 100V / μs.

[0059] In some embodiments, in the filter subcircuit, since the pulse energy of the lightning indirect effect is mainly concentrated within 10MHz, the filter circuit adopts an LC circuit to build a high-pass filter circuit, so that its insertion loss at 10MHz is greater than the design value IL S21 Since the maximum output voltage of the clamp circuit is less than 10V, if it is 10V, the residual voltage of the RF signal is often less than 500mV, so the insertion loss design value IL of the post-stage filter circuit at 10MHz S21The insertion loss IL of the LC filter circuit at 10MHz is 20log(10 / 0.5)=26dB. S21-simulation , which is inserted into IL S21-simulation Greater than IL S21 ; Since the subsequent circuit will not be subjected to large voltage shocks, the withstand voltage value of the LC device is selected to be greater than V BR-ESD and V A Design with the larger value in .

[0060] In some embodiments, the transient blocking unit is a switch type device, and the withstand voltage value V TBU Greater than the breakdown voltage of the gas discharge tube at 100V / μs.

[0061] In some embodiments, the post-stage filtering subcircuit may use other types of filters, such as π-type and L-type. The filter order is not limited to 3rd order and can be expanded to other orders.

[0062] In some embodiments, the front-end clamp circuit is composed of a HM091M model GDT, a SOD32LC03V1B model ESD, and a HTBU-CA085A-200-WH model TBU, and the compliance algorithm steps are as follows:

[0063] Step 1: According to the B5K5M5 level of indirect lightning effects, select waveform 5A (the most stringent requirement) for calculation. The waveform of waveform 5A is as follows: Figure 3 As shown, the open circuit voltage V OC =1600V, short circuit current I SC =1600A, where the internal resistance of the waveform 5A transient signal source is R S =V OC / I SC =1Ω, waveform 5A function expression V WF5A (t) See formula (1) for details;

[0064]

[0065] Step 2: Calculate the ESD conduction time T1. The calculation formula is shown in formula (2). The calculated value is T1 = 0.074 μS.

[0066] V WF5A (T1) = V BR-ESD =8.5V (2)

[0067] Step 3: When TVS is turned on, current will flow through TBU. The trigger current of TBU is IT = 200mA. The current I(t) in TBU can be expressed by the following formula, where t>T1;

[0068]

[0069] Step 4: Calculate TBU conduction time T2 (TVS cut-off). Since t>T1, plus TBU response time 100ns, TBU conduction current is greater than I T ; That is, T2 = T1 + 100ns = 0.174μs;

[0070] Step 5: Equivalent ESD energy to the 8 / 20us double exponential current waveform function (I ESD The maximum transient power value P under (t) MAX-ESD :Where I in formula (4) ESD-8×20 is the 8 / 20us double exponential current waveform coefficient. The ESD withstand energy and the test energy are equal, which can be expressed by formula (5). Formula (5) can be used to obtain its I ESD-8×20 Then, the maximum transient power value P is obtained by formula (6): MAX-ESD =99.36W;

[0071] I ESD (t) = I ESD-8×20 ×(e -120000t -e -140000t ) (4)

[0072]

[0073] P MAX-ESD =MAX{I ESD (8μs)×V BR-ESD} (6)

[0074] Step 6: Equivalent the energy borne by the GDT to the maximum current I under the GDT 8 / 20us double exponential waveform MAX-GDT ; GDT's 8 / 20us double exponential current waveform function I GDT (t) can be expressed by formula (7); I GDT-8×20 The current waveform coefficient is 8 / 20us double exponential. The GDT withstand energy is equal to the test energy, which can be expressed by formula (8). Then, the maximum transient current I is obtained by formula (9). MAX-GDT =9734.1A;

[0075] I GDT (t) = I GDT-8×20 ×(e -120000t -e -140000t ) (7)

[0076]

[0077] I MAX-GDT =I GDT-8×20 ×(e -120000×0.000008 -e -140000×0.000008 ) (9)

[0078] Step 7: Check the maximum pulse power P under 8 / 20μs conditions according to the ESD manual 0-ESD =280W, according to the GDT manual, check the maximum surge current I under 8 / 20μs condition 0-GDT =10000A, that is, P 0-ESD >P MAX-ESD ,I 0-GDT >I MAX-GDT , and there is a certain margin. At this time, the selected HM091M model GDT and SOD32LC03V1B model ESD meet the requirements;

[0079] Step 8: TBU is a switch type device, so it is sensitive to voltage. In order to ensure that TBU is normally turned on and restored, its withstand voltage VTBU = 850V is greater than the breakdown voltage ≤500Ω corresponding to GDT@100V / μs. HTBU-CA085A-200-WH model TBU meets the requirements.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A multi-level lightning protection circuit for radio frequency signals, characterized in that: The circuit comprises a front-stage clamping subcircuit and a rear-stage filtering subcircuit connected in series with the front-stage clamping subcircuit. The front-stage clamping subcircuit comprises a first-stage gas discharge tube connected in parallel to the ground, a second-stage transient voltage suppressor connected in parallel to the ground, and a transient blocking unit connected in series between the gas discharge tube and the transient voltage suppressor. The post-stage filtering subcircuit is a T-shaped filtering circuit, and the T-shaped filtering circuit includes a first capacitor C1, an inductor L, and a second capacitor C2.

2. The radio frequency signal multi-level lightning protection circuit according to claim 1, characterized in that: The maximum surge current I of the gas discharge tube 0-GDT Greater than the maximum transient current I of the gas discharge tube in the protection circuit MAX-GDT , the maximum pulse power P of the transient voltage suppressor 0-ESD Greater than the maximum transient power P of the transient voltage suppressor in the protection circuit MAX-ESD .

3. The radio frequency signal multi-stage lightning protection circuit according to claim 2, characterized in that: The maximum transient current I of the gas discharge tube in the protection circuit MAX-GDT for: I MAX-GDT =I GDT-8×20 ×(e -120000×0.000008 -e -140000×0.000008 ), Among them, I GDT-8×20 It is a 8 / 20us double exponential current waveform coefficient.

4. The radio frequency signal multi-stage lightning protection circuit according to claim 2, characterized in that: The maximum transient power P of the transient voltage suppressor in the protection circuit MAX-ESD for: P MAX-ESD =MAX{I ESD (8μs)×V BR-ESD }, Among them, V BR-ESD is the clamping voltage of the transient voltage suppressor.

5. The radio frequency signal multi-stage lightning protection circuit according to claim 1, characterized in that: The transient blocking unit is a switch type device, and the withstand voltage value of the transient blocking unit is V TBU Greater than the breakdown voltage of the gas discharge tube at 100V / μs.

6. The radio frequency signal multi-stage lightning protection circuit according to claim 1, characterized in that: The post-stage filter subcircuit is an LC circuit, and the withstand voltage of the LC device of the LC circuit is greater than the clamping voltage V BR-ESD And the arc voltage V A , the insertion loss IL of the LC circuit at 10MHz S21-simulation Greater than the design value IL S21 .

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