High Speed Data Transient Protection Circuit
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Solution Overview
Problem
High bandwidth data interfaces in aircraft, such as those operating in the gigahertz range, are affected by lightning transients, leading to signal attenuation due to existing transient voltage suppressors and board trace impedance.
Innovation Solution
A circuit incorporating a non-inductive resistor, a very low capacitance transient voltage suppressor, and a cable equalizer is used to remove lightning transients from high bandwidth data paths without compromising the signal, comprising a pulse tolerant non-inductive resistor to reduce surge current and an adaptive cable equalizer to recover the input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing transient voltage suppressors are used to protect against lightning transients, then protection against lightning is improved, but signal quality deteriorates due to impedance and signal attenuation
Solution Approach 1:
The patent changes the capacitance parameter of the transient voltage suppressor from high capacitance to very low capacitance (e.g., 0.5pF to 5pF range). This parameter change allows the suppressor to effectively clamp lightning transients while presenting minimal impedance to high-frequency data signals, thereby resolving the contradiction between protection effectiveness and signal quality
Solution Approach 2:
The patent introduces a cable equalizer as an intermediary component between the transient voltage suppressor and the data interface. The equalizer compensates for signal attenuation and equalizes signal levels, acting as a mediator that restores signal quality degraded by the suppressor's presence in the circuit
2Reliability
If high capacitance transient voltage suppressors are used, then transient suppression capability is improved, but bandwidth is reduced due to capacitive loading
Solution Approach 1:
The patent fundamentally changes the capacitance parameter from high values (which limit bandwidth) to very low values (maintaining gigahertz-range bandwidth). The very low capacitance suppressor can still suppress transients effectively because suppression capability depends on breakdown voltage rather than capacitance magnitude, thus resolving the contradiction between suppression capability and bandwidth
3Reliability
If transient voltage suppressors are placed in high bandwidth data paths, then protection is improved, but signal integrity deteriorates due to board trace impedance and suppressor impedance
Solution Approach 1:
By changing the suppressor capacitance to very low values, the impedance of the suppressor across the data signal frequency range is minimized. This parameter change reduces the interaction between the suppressor and board trace impedance, allowing both protection and signal integrity to be maintained
Solution Approach 2:
The cable equalizer serves as an intermediary that compensates for signal degradation caused by the combined effect of board trace impedance and suppressor impedance. It actively equalizes the signal to restore integrity while the suppressor provides protection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively removes lightning transients from high bandwidth signals, preserving data integrity and meeting DO-160 level 3 bulk cable pin injection requirements, while maintaining signal quality and integrity across high-speed video and data interfaces.
Implementation Method 1
The transient suppressor is configured to clamp the voltage transient when a reverse breakdown voltage of the transient suppressor is exceeded
Implementation Method 2
a pulse tolerant non-inductive resistor to reduce surge current
Implementation Method 3
an adaptive cable equalizer to recover the input signal
Data Source
AI summary
A high bandwidth data interface in an aircraft includes a pulse tolerant, non-inductive resistor for reducing surge current due to lightning transients, and a very low capacitance transient voltage suppressor to suppress the lightning transient voltages. A cable equalizer/redriver then recovers the original high bandwidth input signal. The high bandwidth interface is thereby able to survive DO-160 section 22 level 3 and 4 lightning transients.