FMCW Source Nonlinearity Compensation Using Etalon Sampling
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Solution Overview
Problem
Existing FMCW-based systems face degradation in range resolution due to non-linearity in linearly swept sources, which is range-dependent and worsens at long distances, and current methods for non-linearity correction require additional hardware resources, increasing system cost.
Innovation Solution
A cost-effective FMCW-based system that uses a frequency filter, such as an etalon, to sparsely sample the modulated signal, transforming it into the frequency domain to estimate and compensate for non-linearity by approximating the difference between linear and non-linear frequency components using basis function coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated reference arm is used to correct non-linearity, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential function of non-linearity measurement from the traditional reference arm configuration. Instead of implementing a complete reference arm with mixer and ADC, the invention uses a simplified frequency filter (etalon) that directly samples the laser output to capture non-linearity information, eliminating unnecessary hardware components while maintaining correction capability
Solution Approach 2:
The patent creates a simplified copy of the reference measurement function using a frequency filter that mimics the non-linearity sampling capability of a full reference arm. The etalon provides a spectral copy of the laser frequency information, allowing non-linearity estimation without requiring a complete duplicate of the signal path
2Measurement precision
If high-frequency signals are sampled directly, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary frequency filtering to the high-frequency laser signal before sampling. The etalon pre-processes the signal by creating discrete spectral copies at lower effective frequencies, allowing the ADC to sample at a reduced rate while still capturing the essential non-linearity information that would otherwise require direct high-frequency sampling
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
This approach reduces hardware complexity and cost while maintaining accurate range estimation by compensating for non-linearity without a dedicated reference arm, ensuring precise distance determination.
Implementation Method 1
a frequency filter configured to pass signals at predetermined frequencies, the frequency filter operatively connected to the emitter passing the modulated signal transmitted by the emitter at different time instances at the predetermined frequencies to generate measurements of the modulated signal in a time-domain
Data Source
AI summary
A frequency modulation continuous wave (FMCW)-based system configured to convert measurements of a linearly modulated wave from a time-domain into a frequency-domain to produce a non-linear frequency signal, where the non-linear frequency signal comprises a known linear component representing the desired linear modulation and an unknown non-linear component representing the non-linearity of the modulation. The FMCW-based system is further configured to determine coefficients of a basis function approximating a difference between the non-linear frequency signal and the linear frequency component in the frequency domain. The FMCW-based system is further configured to detect one or multiple spectrum peaks in the distorted beat signal with the distortion compensated according to the basis function with the determined coefficients to determine one or multiple distances to the one or multiple objects in the scene.