Radar Altimeter DDS Self-Test for Accurate Fault Detection
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Solution Overview
Problem
Current radar altimeters rely on expensive Bulk Acoustic Wave (BAW) devices for self-testing, which fail to accurately detect improper system operation, necessitating a cost-effective and efficient self-test method to verify proper functioning.
Innovation Solution
A radar altimeter system utilizing a Direct Digital Synthesizer (DDS) with a Digital Phase Lock Loop, generating a voltage signal by comparing a fixed reference frequency to a ramped frequency, integrating it over a predefined clock range, and providing an indication of malfunction if the comparison exceeds a threshold value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Bulk Acoustic Wave (BAW) devices are used for self-testing, then self-test capability is provided, but the system cost increases and detection accuracy is insufficient
Solution Approach 1:
The patent replaces the mechanical BAW device with an all-digital solution using a DDS (Direct Digital Synthesizer) to generate test signals and a digital phase lock loop with integrator to process and evaluate the signals. This substitution eliminates the need for expensive BAW devices while maintaining self-test capability and improving detection accuracy through digital signal processing.
Solution Approach 2:
The patent creates a digital copy of the frequency modulation process by using DDS to generate a ramped frequency signal that replicates the characteristics of the transmitted signal. This digital copy allows for accurate simulation and testing without requiring the actual BAW device or external test equipment.
2Reliability
If BAW devices are used for self-testing, then self-test function is achieved, but the system becomes expensive
Solution Approach 1:
The patent replaces expensive BAW devices with inexpensive digital components including DDS, phase lock loop, and integrator circuits. These digital components are significantly cheaper to manufacture and integrate into the radar altimeter system while providing the same self-test function.
Solution Approach 2:
The patent integrates the self-test functionality into the existing digital signal processing chain of the radar altimeter. The DDS, phase lock loop, and integrator are used both for normal signal processing and for self-testing, eliminating the need for separate dedicated test hardware and reducing overall system cost.
3Ease of operation
If conventional self-test methods are used, then basic testing is performed, but accurate detection of improper operation is not achieved
Solution Approach 1:
The patent implements a feedback mechanism where the integrator continuously monitors the phase difference between the transmitted signal and the local oscillator signal. When the accumulated phase error exceeds a threshold, the system generates a fault indication. This feedback loop enables accurate detection of improper operation while maintaining simple operation.
Solution Approach 2:
The patent performs preliminary calibration by integrating the voltage signal over a predefined range of clock ticks to establish a baseline. This preliminary action allows the system to detect deviations from normal operation by comparing subsequent measurements against the calibrated reference, improving detection accuracy without complicating operation.
Data Source
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AI summary
Systems and methods for testing a signal generated by a Direct Digital Synthesizer (DDS) 100 in a radar altimeter 20. In an embodiment of the method, a voltage signal derived by comparing a fixed reference frequency to a ramped frequency signal generated by the DDS based on a clock-based reference signal is generated. The generated voltage signal is integrated over a predefined range of clock signals. The integration is sampled at a previously defined clock tick. The sample is compared to a desired value and an indication that the radar altimeter is malfunctioning is provided if the comparison exceeds a predefined threshold value. The radar altimeter system is deactivate if an indication that the radar altimeter is malfunctioning has been provided.